· PDF fileEDITORIAL BOARD EDITOR-IN-CHIEF Prof. Marian BORDEI - ˇ ˇDunarea de Jos ˇ ˇ University of Galati, Romania EXECUTIVE EDITOR Lecturer Marius BODOR-

MINISTRY OF NATIONAL EDUCATION

THE ANNALS OF“DUNAREA DE JOS” UNIVERSITY

OF GALATI

Fascicle IXMETALLURGY AND MATERIALS SCIENCE

YEAR XXXIII (XXXVIII)June 2015, no. 2

ISSN 1453-083X

2015GALATI UNIVERSITY PRESS

EDITORIAL BOARD

EDITOR-IN-CHIEFProf. Marian BORDEI - ’’Dunarea de Jos’’ University of Galati, Romania

EXECUTIVE EDITORLecturer Marius BODOR- ’’Dunarea de Jos’’ University of Galati, Romania

PRESIDENT OF HONOURProf. Nicolae CANANAU - ’’Dunarea de Jos’’ University of Galati, Romania

SCIENTIFIC ADVISORY COMMITTEELecturer Stefan BALTA - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Lidia BENEA - ’’Dunarea de Jos’’ University of Galati, RomaniaAcad. Prof. Ion BOSTAN - Technical University of Moldova, Moldova RepublicProf. Bart Van der BRUGGEN - Katholieke Universiteit Leuven, BelgiumProf. Francisco Manuel BRAZ FERNANDES - New University of Lisbon Caparica, PortugalAcad. Prof. Valeriu CANTSER - Academy of Moldova Republic, Moldova RepublicProf. Anisoara CIOCAN - ’’Dunarea de Jos’’ University of Galati, RomaniaLecturer Alina CIUBOTARIU - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Alexandru CHIRIAC - ’’Dunarea de Jos’’ University of Galati, RomaniaAssoc. Prof. Stela CONSTANTINESCU - ’’Dunarea de Jos’’ University of Galati, RomaniaAssoc. Prof. Viorel DRAGAN - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Valeriu DULGHERU - Technical University of Moldova, Moldova RepublicProf. Jean Bernard GUILLOT - École Centrale Paris, FranceAssoc. Prof. Gheorghe GURAU - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Iulian IONITA - ’’Gheorghe Asachi’’ Technical University Iasi, RomaniaProf. Philippe MARCUS - École Nationale Supérieure de Chimie de Paris, FranceProf. Vasile MARINA - Technical University of Moldova, Moldova RepublicProf. Rodrigo MARTINS - NOVA University of Lisbon, PortugalProf. Strul MOISA - Ben Gurion University of the Negev, IsraelProf. Daniel MUNTEANU - Transilvania University of Brasov, RomaniaProf. Viorica MUSAT - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Maria NICOLAE - Politehnica University Bucuresti, RomaniaProf. Petre Stelian NITA - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Florentina POTECASU - ’’Dunarea de Jos’’ University of Galati, RomaniaAssoc. Prof. Octavian POTECASU - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Cristian PREDESCU - Politehnica University Bucuresti, RomaniaProf. Iulian RIPOSAN - Politehnica University Bucuresti, RomaniaProf. Antonio de SAJA - University of Valladolid, SpainProf. Wolfgang SAND - Duisburg-Essen University Duisburg GermanyProf. Ion SANDU - ’’Al. I. Cuza’’ University of Iasi, RomaniaProf. Georgios SAVAIDIS - Aristotle University of Thessaloniki, GreeceProf. Elisabeta VASILESCU - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. Ioan VIDA-SIMITI - Technical University of Cluj Napoca, RomaniaProf. Mircea Horia TIEREAN - Transilvania University of Brasov, RomaniaAssoc. Prof. Petrica VIZUREANU - ’’Gheorghe Asachi’’ Technical University Iasi, RomaniaProf. Maria VLAD - ’’Dunarea de Jos’’ University of Galati, RomaniaProf. François WENGER - École Centrale Paris, France

EDITING SECRETARYProf. Marian BORDEI - ’’Dunarea de Jos’’ University of Galati, RomaniaLecturer Marius BODOR - ’’Dunarea de Jos’’ University of Galati, Romania

THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI.FASCICLE IX. METALLURGY AND MATERIALS SCIENCE

N0. 2 – 2015, ISSN 1453 – 083X

Table of Content

1. Jiří ERHART and Sebastian TUTU - Effective Electromechanical Coupling for the PartiallyElectroded Ceramic Resonators of Different Geometries.……………............................................... 7

2. Maria-Iuliana MĂRCUȘ, Maria VLAD, Ileana MÎȚIU, Mihaela Andreea MÎȚIU -Selective Recovery by Solubilization of Metals Ions of Chromium, Iron and Zinc fromElectroplating Sludge to Develop Pigments for Ceramics Industry...................................................... 17

3. A. ALEXA, A. PIMENTEL, T. CALMEIRO, A. ISTRATE, E. FORTUNATO, V. MUȘAT- Conductive-Atomic Force Microscopy Investigation of the Electrical Properties of LowTemperature Deposed ZnO Transparent Thin Films............................................................................ 22

4. I. G. BÎRSAN, Marina BUNEA, G. MIHU, A. CÎRCIUMARU - The ElectromagneticProprieties of Hybrid Composites........................................................................................................ 27

5. M. BASTIUREA, M.S. BASTIUREA, G. ANDREI, M. MURARESCU, D. DUMITRU-Determination of Glass Transition Temperature for Polyester/Graphene Oxide andPolyester/Graphite Composite by TMA and DSC................................................................................. 32

6. Ovidiu-Magdin ȚANȚA, Mihaela POIENAR, Ilie NIȚAN, Mihai CENUȘĂ, Adrian-Neculai ROMANESCU - Applications Based on Variable Frequency Rotating Magnetic Field.Electromechanical Agitator with Dual Direction.................................................................................. 37

7. Georgel CHIRITA, Gabriel ANDREI, Iulian Gabriel BIRSAN, Dima DUMITRU, AlinaCANTARAGIU - Electrical Properties Characterization of Vinyl Ester Resin Filled with CarbonNanotubes.............................................................................................................................................. 41

8. Nicoleta MATEI, Dan SCARPETE - The Use of Ultrasound in Treatment Process ofWastewater. A Review.......................................................................................................................... 45

9. Ovidiu-Magdin ȚANȚA, Adrian-Neculai ROMANESCU, Mihai CENUȘĂ, Ilie NIȚAN,Mihaela POIENAR- Solutions for Diagnosing Faults in Asynchronous Motor Stator Through anFerrofluid Installation............................................................................................................................ 51

10. Adrian PRESURA, Ionel CHIRICA, Elena-Felicia BEZNEA - The Structural DesignImprovement of a Twin-Hull Ship........................................................................................................ 57

11. Adrian-Neculai ROMANESCU, Ovidiu-Magdin ȚANȚA, Mihai CENUȘĂ, Ilie NIȚAN,Mihaela POIENAR - Contributions Regarding Development of New Types of Solar Actuators….. 62

12. Lucian ANDRIEȘ, Vasile Gheorghiță GĂITAN - Dual Priority Scheduling Algorithm Usedin the nMPRA Microcontrollers – Dynamic Scheduler..…………………………………………….. 66

13. Vlad VRABIE, Dan SCARPETE, Bianca Elena CHIOSA - Water-in-Diesel Emulsions as anAlternative Fuel for Diesel Engines. Part II: Performance of Diesel Engines Fueled with Water-in-Diesel Emulsions. A Literature Review.……………………………………………………………... 72

14. Florentina ROTARU, Ionel CHIRICA, Elena Felicia BEZNEA - Strength Analysis of aComposite Joint Used in Ship Structure................................................................................................ 79

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15. Iulia GRAUR, Georgel MIHU, Vasile BRIA, Adrian CÎRCIUMARU, Iulian-GabrielBÎRSAN - Compressive Behaviour of Ultra-Sonicated Starch/Carbon Black/Epoxy Composites...... 84

16. Marina BUNEA, V. BRIA, A. CÎRCIUMARU, I. G. BÎRSAN - The UnusualElectromagnetic Proprieties of Fabric Reinforced Epoxy Composites.................................... 90

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Fascicle IXMetallurgy and Materials Science

ISSN 1453 - 083X

1978

THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATIFASCICLE IX. METALLURGY AND MATERIALS SCIENCE

No. 2 – 2015, ISSN 1453 – 083X

EFFECTIVE ELECTROMECHANICAL COUPLING FOR THEPARTIALLY ELECTRODED CERAMIC RESONATORS OF

DIFFERENT GEOMETRIES

Jiří ERHART* and Sebastian TUTUDepartment of Physics and Piezoelectricity Research Laboratory, Technical University of Liberec,

Studentská 2, 461 17 Liberec 1, Czech Republic*Corresponding author

e-mail: [email protected]

ABSTRACT

Effective electromechanical coupling factor (ECF) was studied on bar, discand ring ceramic resonators partially covered by the electrodes. ECF’s werecalculated theoretically and verified experimentally. Bar resonators (k31-mode)show maximum value of ECF keff = 0.26 at the electrode aspect ratio equal 0.75with calculated values fitting the experimental data for all aspect ratios.Calculations for bar resonators with embedded electrodes (k33-mode) show similarbehavior like for k31-mode, but at higher ECF’s. Maximum value of ECF for suchmode reaches keff = 0.67 for the electrode aspect ratio 0.75. Partially electrodeddisc resonators (kp-mode) are well described analytically by one-dimensional modelonly for the electrode aspect ratios up to 0.5. Maximum value keff = 0.58 for discresonators was measured at the electrode aspect ratio equal 0.80. Partiallyelectroded ring resonators (kp-mode) show the same trend as discs withoutsaturation of ECF values. Maximum ECF keff = 0.34 was measured for ringresonators with full electrode. Presented analytical formulae may serve as a guidefor the optimum electrode pattern design for the partially electroded resonators.

KEYWORDS: piezoelectric ceramics, PZT, resonator, vibration modes,electromechanical coupling factor

1. Introduction

Electromechanical coupling factor (ECF)describes the energy transfer between its mechanicaland electrical form.

Static electromechanical coupling might bedifferent from the dynamic coupling factor specificfor certain vibration mode [1]. ECF links together“free” and “clamped” material properties for thedifferent resonators shapes. Also ECF’s for thedifferent vibration modes are cross-linked by variousrelations [2].

ECF’s are practically measured using theanalysis of impedance spectrum in terms of resonance(fr) and antiresonance (fa) frequencies [1, 3] with aneffective dynamic coupling factor

2

222

a

raeff f

ffk (1)

This formula is universal for any vibrationmodes of resonator, but there are also specificformulae for the different vibration modes ofresonators (e.g. k31, k33, kp, kt, k15 modes) in the shapeof bar, thin disc or plate [3]. Resonators for ECFmeasurement are designed as fully electrodedpiezoelectric ceramic bodies. Such resonators are notnecessarily optimized with respect to ECF value.

It is basically anticipated that piezoelectricresonator with full electrode has its maximumelectromechanical coupling. However, sometimes it isnot possible to deposit full electrode on thepiezoelectric resonator faces due to the mechanicalclamping or electrical insulation of the resonator.Small facet at the piezoelectric ceramic ring or discedges is one of the examples of such electrodedeposition deficiency. There is also possibility ofECF enhancement by the electrode patternoptimization.

Experimental visualization of modal shapes waspublished for fully electroded ceramic disc resonatorsfor the radial and flexural vibration modes and

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verified by the laser holography [4]. Similarvisualization was also performed by the sametechnique on the partially electroded discs in twogeometries [5] – disc with central circular electrode orwith annular electrode arrangement. The optimumelectromechanical coupling k = 0.605 for the discplanar mode was theoretically calculated for theelectrode size ratio r0 = 0.83a for PIC-151 PZTceramics (r0, a are the radii of electrode and disc).

Theoretical calculations on partially electrodeddisc ceramic resonators were published by Ivina [6].Ceramic disc was partially electroded inside thecentral circular area or at the outer annular electrode.The optimum ECF k = 0.51 was calculated for thecentral circular electrode size ratio r0 = 0.9a forTsTBS-3 PZT type. Enhancement of ECF for thepartially electroded disc (k = 0.51) with respect tofully electroded one (k = 0.50) was calculated.Ceramic resonator operates more efficiently withoptimum electrode size than with the full electrode.

Other theoretical calculations on the partiallycovered ceramic resonators were published byRogacheva [7]. She calculated ECF’s for severalelectrode geometries – disc plate with central circularor ring electrode and cylindrical ceramic shell withfully or partially electroded circumference. Allnumerical data were presented for PZT-5piezoelectric ceramics under “free” and “clamped”mechanical conditions. ECF reaches maximum k =0.55 for the electrode size of r0 = 0.85a for centralcircular electrode arrangement and k = 0.413 for ringelectrode covering the radii range 0.6a ≤ r0 ≤ 0.9a.Maximum ECF calculated for the cylindrical ceramicshell was k = 0.57 for the electrode covering the shelllength L0 = 0.7L (for the shell aspect ratio 2L = 2a,where L and a are shell’s total length and radius).Enhancement of ECF for partially electrodedresonator with respect to full electrode was alsopredicted.

Presented paper addresses the issues of partiallyelectroded and longitudinally vibrating bar, radiallyvibrating disc with central circular electrode andradially vibrating ring resonator with partial annularelectrode. ECF’s are theoretically calculated andexperimentally verified by the resonance /antiresonance frequency measurement [3].

Presented work confirms experimentallypreviously published theoretical results on thepartially electroded disc resonators. ECF’s for bar andring resonators with partial electrodes aretheoretically calculated and experimentally measured.Optimum electrode size and corresponding ECF’swere found. Choice of bar and ring resonators withpartial electrodes was motivated by the use of suchstructures in piezoelectric ceramic transformersdesign – e.g. ring transformer with axisymmetricallydivided electrodes or bar transformer with

symmetrical or asymmetrical electrode pattern.Ceramic resonators in the shape of ring made fromhard PZT’s are also typically used for the ultrasoundgeneration in ultrasonic welding and cleaningtechnology – e.g. in Langevin transducer design.Partially electroded bar and ring resonators were notreported previously neither theoretically, norexperimentally. One type of soft PZT (APC850) andone type of hard PZT (APC841) was selected forexperiments in order not to limit our results only forone specific PZT type.

2. Theory

For the calculation of resonator’s electricalimpedance/admittance we adopted one-dimensionalvibration modes for thin bar, thin disc and thin ring.Equation of motion:

3,2,1,, iuT ijij (2)

and Maxwell’s equation for non-conducting medium:

,0, iiD (3)

will be solved for the piezoelectric ceramics medium.Piezoelectric equations of state:

iiE EdTsS (4)

jTijii ETdD (5)

are defined by the crystallographic symmetry ofceramics material. Electrode’s material and itsthickness are not taken into account. Elastic straintensor is defined by the derivatives of displacementcomponents:

ijjiij uuS ,,21

(6)

and electric field by the electric potential derivative:

iiE , (7

Electrical impedance of the resonator is calculatedfrom the displacement current:

)(

3S

dSDt

I (8)

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where electric displacement is integrated over theelectrode surface. Electrical admittance is a ratio ofthe displacement current and input voltage:

tjUeIY (9)

2.1. Partially electroded thin bar –transverse longitudinal mode

Mechanical stress/strain system for thethickness-poled and longitudinally vibrating thin baris given by only one non-zero stress component (T1 ≠0) and one electrical field/displacement (E3 ≠ 0, D3 ≠0) – for coordinate system see Fig. 1.

l0

l

w

b

ceramics electrode

x1

x2

x3

Fig. 1. Partially electroded bar resonator – thickness poled

Boundary conditions include mechanically freeends of bar (i.e. T1 = 0) and continuity of mechanicalstress/displacement at the electrode edges. After the

calculations described above, we can derive formulafor the electrical admittance:

)cos(

))1cos(()sin(1

0

00231

231

033

ll

ll

ll

kkb

wljY T (10)

where

Esfkkl 112,21

In a limiting case of fully electroded resonator(i.e. l0 → l), formula is reduced to the admittance ofbar resonator [3].

)tan(1 2

3123133 kk

bwljY T (11)

Resonance condition for partially electrodedresonator is the same as for fully electroded one:

,...2

5,2

3,2

r (12)

but antiresonance condition includes the dimension ofelectroded resonator’s part in a transcendentalequation:

0)cos(

))1cos(()sin(1

0

00231

231

aa

aa

ll

ll

ll

kk

(13)

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2.2. Thin bar with embedded electrodes –longitudinal mode

Mechanical stress/strain system for thelongitudinally-poled and longitudinally vibrating thinbar is given by only one non-zero stress component

( 03 T ) and one electrical field/displacement

( 0,0 33 DE ) – for coordinate system see Fig.2.

Fig. 2. Bar resonator with embedded electrodes – longitudinally poled

Boundary conditions include mechanically freeends of bar (i.e. 03 T ) and continuity ofmechanical stress/displacement at the electrode edges.

After the calculations described above, we can deriveformula for the electrical impedance:

)cos(

))1cos(()sin(1

1

10

00233

233

033

ll

ll

ll

kk

lSj

ZT

(14)

where Dsfkkl 332,21 and S is the

electrode area. In a limiting case of fully electrodedresonator (i.e. ll 0 ), formula is reduced to theimpedance of bar resonator [3].

)tan(11

1 233

233

033

kk

lSj

ZT

(15)

Antiresonance condition is the same as for fullyelectroded resonator

,...2

5,2

3,2

a (16)

but the resonance condition depends on the dimensionof electroded part

0)cos(

))1cos(()sin(1

0

00233

rr

rr

ll

ll

ll

k

(17)

2.3. Partially electroded thin disc – planarmode

Mechanical stress/strain system for thethickness-poled and radially vibrating thin disc isgiven by non-zero radial and thickness displacementcomponents ( 0,0 zr uu ) and one electric

field/displacement component ( 0,0 33 DE ) –for coordinate system see Fig. 3.

ceramics electrode

x1

x2

x3

ll0

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2r0

2a

b

ceramics electrode

x1

x2

x3

Fig. 3. Partially electroded disc resonator – thickness poled

Boundary conditions include mechanically freeouter disc circumference (i.e. 0rT ) and continuityof mechanical stress/displacement at the electrode

edges. We use the calculation method published in [8]for homogeneously poled thin ceramic disc.Resonator’s admittance could be calculated as:

)()()()(

)()()()(

)(

)(

1

)1(1

01

02

01

01

012

011

1

00

2

220

33

arJ

arK

arY

arK

arJK

arYK

KarJ

k

kbrjY

p

EpP (18)

where )()1()()( 101 JJK E ;

)()1()()( 102 YYK E ;

Pcfa 112 ; E is Poisson’s ratio,

ESP

ce

33

233

3333 ;

E

EEP

cccc

33

213

1111 ; kp is planar

electromechanical coupling factor and 10, JJ ;

10 ,YY are zero- and first-order Bessel’s functions ofthe first and second kind. In a limiting case of fullyelectroded disc (i.e. ar 0 ), admittance reduces tothe known formula for disc resonator [3]:

)()(

1

)1(1

1

02

2233

KJ

k

kbajY

p

EpP (19)

Resonance condition for the homogeneous discresonator is identical with the zero value fordenominator in Eq. (18).

0)()()()()( 01

02

01

011

rrrrr a

rJarK

arY

arKK (20)

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Antiresonance condition is:

0)()()()(

)()()()(

)(

)(

1

)1(1

01

02

01

01

012

011

1

00

2

2

aaaa

aaaa

a

a

p

Ep

arJ

arK

arY

arK

arJK

arYK

KarJ

k

k

(21)

2.4. Partially electroded thin ring – planarmode

Similar calculation method like for thin disc,stress/strain system and boundary conditions(including free ring’s inner diameter circumference)

were adopted also for thin partially electroded ringvibrating radially – for geometry see Fig. 4.

Admittance of such resonator is

( Pcfa 1122 ).

)()()()()(

)()()()()()(

1

)1(

)()()()()(

)()()()(

)()()()()(

)()()()(

)()()()()(

)()()()(

)()()()()(

)()()()(

1

)1(1)(

2

11

2

12

2

11

2

11

2

12

2

11

2

11

2

12

2

11

2

11

2

1

2

21

2

2

2

1

2

2

2

21

2

22

2

21

2

212

2

212

2

211

2

2

2

11

2

12

2

11

2

11

2

12

2

11

2

11

2

11

2

12

2

1

2

1212

2

112

2

21

22

222

2

11

2

1

2

21

2

2

2

112

2

1212

2

112

2

21

22

222

2

11

2

1

2

21

2

2

2

122

2

221

22

33

arJ

arK

arY

arK

aaK

aaK

arY

aaK

arJ

arY

ar

arY

ar

ar

k

k

arJ

arK

arY

arKK

arJK

arYK

ar

arJ

arK

arY

arK

aaK

arY

aaK

arJ

aaK

ar

aaKKK

aaK

ar

ar

arY

ar

arY

ar

aaKK

aaKKK

aaK

ar

ar

arJ

ar

arJ

ar

aaKK

k

kb

rrjY

p

Ep

p

EpP

(22)

Resonance and antiresonance follow the sameconditions ( Y for resonance and 0Y for

antiresonance), but the formulae are not listed herebecause of long expressions.

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ceramics electrode

x1

x2

x3

2a2

2a1

2r1

2r2

Fig. 4. Partially electroded ring resonator – thickness poled

3. Experiment and numerical calculations

Resonance and antiresonance wave numbers ηrand ηa were calculated as solutions of Eqs. (12) and(13) for thin bar in transverse longitudinal vibrationmode, Eqs. (16) and (17) for thin bar in longitudinalmode, Eqs. (20) and (21) for thin disc vibrating inradial mode and from Eq.(22) for thin ring.Resonance and antiresonance frequencies are simplyrelated to the wave numbers for each vibration mode.Therefore ECF’s definition - Eq.(1) - could be writtenas:

2

222

a

raeffk

(23)

For the numerical values of material propertycoefficients used in calculations see Table 1.

Table 1. Material properties of PZT ceramicsused in calculations

Ceramicstype

k31[-]

k33[-]

kp[-]

σE

[-]APC841

Hard PZT 0.27 0.63 0.60 0.30

APC850Soft PZT - - 0.63 0.35

Partially electroded resonators were realized forbar, disc and ring resonators from soft and hard PZTceramics (APC International Ltd., Mackeyville, PA,USA). Electrodes were deposited by air-dry Ag-paste(Agar Scientific, Silver paint type G302). Impedancespectra were measured by Agilent 4294A Impedanceanalyzer.

Samples of partially electroded disc resonatorswere prepared from soft PZT ceramics, type APC850.Disc dimensions were 20 mm diameter and 1.78 mmthickness and 26.25 mm diameter and 2 mmthickness. Set of samples with electrode aspect ratiosranging from 0.1 to 1.0 was prepared for bothdimensions.

Samples of partially electroded bar resonatorswere made from hard PZT, type APC841. Sampledimensions were 49.6 mm length, 6 mm width and0.5 mm thickness. Set of samples with electrodeaspect ratios from 0.1 to 1.0 was prepared. Samplesof partially electroded ring resonators were madefrom hard PZT, type APC841.

Ring inner diameter was 20 mm, outer diameter50 mm and thickness 6 mm. While there are too manycombinations of dimensions only three sets ofsamples were prepared. First set was from sampleswith outer electrode diameter equal to the ring outerdiameter. Second set of samples included sampleswith electrode inner diameter equal to the ring innerdiameter.

Samples in the third set had electrodesdistributed symmetrically with respect to the centerdiameter (35 mm diameter) – for details ondimensions see Table 2.

Table 2. Dimensions of partially electroded ringresonators (total diameter 20 mm/50

mm/thickness 6 mm)SetNo.

Inner electrode diameter/outerelectrode diameter [mm]

1 24/50 28/50 32/50 36/50 40/502 20/30 20/34 20/38 20/42 20/463 32/38 29/41 26/44 23/47 -

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4. Results and discussion

ECF for partially electroded bar resonators (k31-mode) shows dependence on the electroded partaspect ratio (i.e. l0/l) with saturated value starting atthe aspect ratio l0/l = 0.6 – see Fig. 5. Calculated datafits experimental data for all aspect ratios. MaximumECF keff = 0.26 was measured for the electrode sizeaspect ratio equal l0/l = 0.75 for k31-mode for the barresonator.

Calculations for the bar resonator vibrating ink33-mode (Fig. 6) show similar aspect ratiodependence as the bar resonator working in k31-mode,but with higher values of ECF due to the higherelectromechanical coupling factor k33 of used PZT.Maximum ECF keff = 0.67 was calculated for theelectrode size aspect ratio equal l0/l = 0.75 for k33-mode for the bar resonator with embedded electrodes.

Fig. 5. Effective coupling factor for partially electroded bar resonators (k31-mode, APC841, 49.6 mmx 6 mm x 0.5 mm)

Fig. 6. Effective coupling factor for the bar resonators with embedded electrodes (k33-mode, APC841,20 mm x 3 mm x 1 mm)

ECFs for partially electroded disc resonators (kp-mode) shows saturation at the aspect ratio (i.e.electrode’s diameter/total diameter) equal to aboutr0/a = 0.7 – see Fig. 7. Calculated data fitexperimental values only for the aspect ratios below

r0/a = 0.5. Approximation employed in calculations isnot valid for higher values of aspect ratios, becausenot electroded outer ring segment can be no moreapproximated by the shape of thin ring. Samples withdifferent disc diameters exhibit the same behavior in

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ECF as it is seen from Eq. (18) and in Fig. 7. ECFdepends on the values of electromechanical couplingfactor kp, Poisson’s ratio σE, but not on the discdiameter like the resonance and antiresonancefrequencies themselves. Maximum ECF keff = 0.58was measured for the electrode size aspect ratio equal

r0/a = 0.80 for kp-mode for the disc resonator. Thisvalue agrees well with the previously published [7]theoretical value keff = 0.55 for the electrode sizeaspect ratio equal r0/a = 0.83 calculated for differentPZT type.

Fig. 7. Effective coupling factor for partially electroded disc resonators (kp-mode, APC850, diameter20 mm/thickness 1.78 mm and 26.25 mm/thickness 2 mm)

Fig. 8. Effective coupling factor for partially electroded ring resonators (kp-mode, APC841, diameter20 mm/50 mm/thickness 6 mm) as a function of ring electrode relative width

All three sets of partially electroded ringsexhibit the same trend in ECF with the highest valuekeff = 0.34 for ring resonator with full electrode – seeFig. 8. Set No. 1 and 3 fit theoretical calculations upto the electrode width aspect ratio equal 0.7.Calculations for set No. 2 (inner electrode diameter isequal to disc inner diameter) show higher values thanit was measured, on the contrary. Some differences inthe calculated values are due to the approximationsemployed for one-dimensional calculations of ringadmittance. Data shows the same trend in calculatedas well as in measured values of ECF.

5. Conclusions

Effective ECF reaches its top value at anoptimum electrode size for all studied resonator cases(bar, disc and ring). Values of effective ECF’s werepredicted in analytical one-dimensional models forthin bar (k31-mode), thin disc (kp-mode) and thin ring(kp-mode) with partial electrodes and thin bar withembedded electrodes (k33-mode). Numericallycalculated effective ECF’s were measured on thesamples of bar, disc and ring resonators with partial

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electrodes. Maximum effective ECF’s weremeasured:

keff = 0.26 for thin bar (k31-mode) for theaspect ratio l0/l = 0.75

keff = 0.58 for thin disc (kp-mode) for theaspect ratio r0/a = 0.80

keff = 0.34 for thin ring (kp-mode) for theresonator with full electrode (outer/inner ringdiameters are 50 mm/20 mm).

Maximum ECF for bar resonator with embeddedelectrodes (k33-mode) was calculated as keff = 0.67 forthe electrode aspect ratio l0/l = 0.75. ECF saturates atthe aspect ratio of r0/a = 0.7 for thin disc with partialelectrode. Ring resonators show the same trend asdiscs without saturation of ECF. Presented resultsmay serve as a guide for the optimum electrodepattern design for resonators with partial electrodes.

Acknowledgements

This work was supported by ESF operationalprogram “Education for competitiveness” in theCzech Republic in the framework of project “Supportof engineering of excellent research and developmentteams at the Technical University of Liberec” No.CZ.1.07/2.3.00/30.0065.

References[1]. Chang S. H., Rogacheva N. N., Chou C. C., Analysis ofmethods for determining of electromechanical coupling coefficientsof piezoelectric elements, IEEE Transactions on UltrasonicsFerroelectrics and Frequency Control, 42(4), p. 630-640, 1995.[2]. Mezheritskiy A. V., Invariants of electromechanical couplingcoefficients in piezoceramics, IEEE Transactions on UltrasonicsFerroelectrics and Frequency Control, 50(12), p. 1742-1751, 2003.[3]. IRE Standards on Piezoelectric Crystals, Measurement ofPiezoelectric Ceramics, Proceedings of the IRE, 49(7), p. 1161-1169, 1961.[4]. Huang C. H., Lin Y. C., Ma C. C., Theoretical Analysis andExperimental Measurement for Resonant Vibration ofPiezoceramic Circular Plates, IEEE Transactions on UltrasonicsFerroelectrics and Frequency Control, 51(1), p. 12-24, 2004.[5]. Huang C. H., Theoretical and experimental vibration analysisfor a piezoceramic disk partially covered with electrodes, TheJournal of the Acoustical Society of America, 118(2), p. 751-761,2005.[6]. Ivina N. F., Analysis of the Natural Vibrations of CircularPiezoceramic Plates with Partial Electrodes, Acoustical Physics47(6), p. 714-720, 2001.[7]. Rogacheva N. N., The dependence of the electromechanicalcoupling coefficient of piezoelectric elements on the position andsize of the electrodes, Journal of Applield Mathematics andMechanics, 65(2) p. 317-326, 2001.[8]. Meitzler A. H., O’Bryan Jr. H. M., Tiersten H. F.,Definition and measurement of radial mode coupling factors inpiezoelectric ceramic materials with large variations in Poisson’sratio, IEEE Transactions on Sonics and Ultrasonics, SU-20(3), p.233-239, 1973.

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SELECTIVE RECOVERY BY SOLUBILIZATION OF METALS IONSOF CHROMIUM, IRON AND ZINC FROM ELECTROPLATING

SLUDGE TO DEVELOP PIGMENTS FOR CERAMICS INDUSTRY

Maria-Iuliana MĂRCUȘ1,*, Maria VLAD2, Ileana MÎȚIU1,Mihaela Andreea MÎȚIU1

1 National Institute for Research and Development in Environmental Protection – INCDPM, 294,Spl. Independentei, District 6th, Bucharest, Postal Code 060031, Romania

2”Dunărea de Jos” University of Galati, Faculty of Engineering,Domnească Street, 47, RO-800008, Galati, Romania

*Corresponding author: [email protected]

ABSTRACT

Electroplating industries discharge large amounts of heavy metals, includingchromium (Cr), iron (Fe) and zinc (Zn) ions in wastewater resulted fromtechnological processes, including in sludge from wastewater treatment.

In this paper are reported the results of the scientific activity on laboratory torecovery Cr(VI,III), Fe(III), and Zn(II) from the galvanic sludge by selectivesolubilization and obtaining metal salts which can then be used as pigments inceramics industry.

Chromium recovery from the sludge was performed by alkaline sludgeoxidation to obtain salts of Cr(VI). It was aimed to obtain two types of pigmentsbased on chromium: chromium yellow pigments by precipitation of Cr(VI) in theform of lead chromate (PbCrO4) and chromium green pigments by reducing Cr(VI)and its precipitation in the form of Cr(III).

Red pigment based on Fe(III) was obtained by solubilizing the resultingsludge after the recovery of chromium and iron precipitation at a pH correspondingto complete precipitation.

From the remaining solution by recovering Cr and Fe, Zn was recovered aszinc hydroxide [Zn(OH)2] that can be used as raw material in the ceramics industry.

In the experiments performed at laboratory scale, optimal technologicalparameters were set for the selective recovery of sludge metal ions tested.

KEYWORDS: electroplating sludge, chromium, iron, zinc, selective recovery

1. Introduction

Treatment and metal surfaces coating processesrequire the use of hazardous chemical substanceswhich are further discharged as process wastesolutions and washing wastewater. The process wastesolutions that are regularly discharged come from themetal surfaces preparing operations (degreasing,pickling passivating, polishing, etching) and from thedischarge of active washing wastewater (copperplating, nickel plating, chrome plating, zinc plating,cadmium plating). The technological solutions aredischarged when they cannot fit in the technologicalwork parameters through corrections or when thework technology is changed [1].

Given the high concentrations of metallic ions,the main source of wastewater with such content isrepresented by the process waste solutions whichactually have a share of 90 – 95 % from the amountof discharged salts together with wastewaters frommetal plating workshops.

Waters and concentrated solutions fromchemical and electrochemical processing operationsof metal surfaces are treated through two technologies[2]:- Treatment technologies to result sludge (metal ionsprecipitation / solid ion exchange prehension / recyclechemical washing, etc.).- Recovery treatment technologies in order to avoidsludge formation and to recover useful compounds.

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Collecting and treatment of waste water(washing water and wastewater concentrates) withheavy metals content (copper, trivalent chromium,cadmium, nickel, zinc, iron, etc.), cyanide andhexavalent chromium are jointly performed, resultingin a precipitation sludge with complex chemicalcomposition, classified as a hazardous waste/eco-toxic. Removing it by landfilling impliesenvironmental risks, due to the risk of rainwaterleaching (pH = 5.0 – 5.5) of heavy metals content,which leads to soil pollution and surface and groundwater pollution. These treatment processes wereoriginally designed only for retaining toxicsubstances from water, but they were later adapted tothe possibility to recover metal compounds.

The recovery of industrial waste is one of themain national and international research themesconcerning the reuse technologies in variousindustries, correlated with the environmental impact.The reuse potential represents the essential criteria inwaste management approach. From this point ofview, the equivalence of waste concept with theconcept of secondary raw material is increasing [3, 4].

In the following, is presented a process for theselective recovery of metal ions such as chromium(Cr), iron (Fe), zinc (Zn) from solid sludge resulted

from wastewater treatment from a company withactivities in the chemical and electrochemicaltreatment of metal surfaces, namely: galvanizingmetal surfaces.

2. Experimental results

The scientific experiments at laboratory scalehave been performed in order to recover Cr(VI,III),Fe(III), and Zn(II) ions from the galvanic sludge byselective solubilization and obtain metal salts. Thegalvanic sludge employed in this research wascollected from a local plant, after the waste solutionsand washing wastewater treatment. The sludge to betested was milled in a porcelain jar to obtain particles<1 μm for increase the reaction surface and dried at105 oC for 24 h (water content of the sludge 68 wt%).The waste was characterized by atomic absorptionspectrometry in order to estimate the chromium, ironand zinc content.

The physico-chemical analyzes performed onthe galvanic sludge revealed the following chemicalcomposition, expressed in percentage (%) towardsdry substance are presented in Table 1:

Table 1. Physicochemical composition of analyzed galvanic sludge

Ions % towards drysubstance

The total amount of the metalsin 150 g of sample

(g)Cr 0.27 0.4050Fe 9.10 13.6500Zn 18.10 27.1500Ni 0.05 0.0750Cu 0.009 0.0135Cd 0.004 0.0060

2.1. Chromium recovery

Experiments conducted in the laboratory led tothe establishment of a procedure for recoveringchromium from galvanic sludge resulting from thegalvanic wastewater treatment. Technology ofwastewater neutralization is based on detoxificationof waste by reducing chromium(VI) to chromium(III)and then using an hydroxide to precipitate insolublechromium(III) hydroxide. Other metal hydroxides arealso precipitated in the resulting sludge [5, 6].

The chromium recovery procedure includes the

alkaline oxidation of Cr(III) to Cr(VI) and Cr(VI)recovery by precipitation.

The phases of chromium recovery procedure arepresented in Fig. 1.

PHASE 1: Solubilization of Cr(III) throughalkaline oxidation

Solubilization of Cr(III) has been performedfrom 150 g of the galvanic sludge sample throughalkaline oxidation at pH = 12.0-12.5, with sodiumhypoclorite (NaOCl) 12% and sodium hydroxide(NaOH) 30%; reaction temperature = 80 oC, reactiontime = 30 minutes; stirring throughout the reactiontime.

2Cr(OH)3 + 3NaOCl + 4NaOH = 2Na2CrO4 + 3NaCl + 5H2O (1)

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Simultaneously with chromium oxidation alsooccurred a partial oxidation reaction of Fe(II) toFe(VI) in the form of sodium perferrate (Na2FeO4),

insoluble compound at this stage which will remain insludge cake after solution filtering:

Fe(OH)2 + 2 NaOCl + 2 NaOH = Na2FeO4 + 2 NaCl + 2 H2O (2)

Fig. 1. Scheme of chromium recovery procedure from galvanic sludge

PHASE 2: Filtering the chromium solutionFiltering the chromium solution was performed

using a vacuum pump, yielding a wet cake containingmainly zinc and iron and a solution of sodiumchromate (Na2CrO4) which will be subject toprocessing in order to obtain chrome pigments.

PHASE 3: Washing wet cake from filtrationWashing the wet cake resulting from filtration

with vacuum pump was performed for full recoveryof chromium absorbed by the cake.

In the experiments it was intended to obtain twodifferent types of pigments based on chromium:

- Chromium yellow pigment by precipitation ofhexavalent chromium in the form of lead chromate;

- Chromium green pigment by reduction ofhexavalent chromium to trivalent chromium and itsprecipitation in the form of chromium hydroxide.

PHASE 4: Precipitation Cr(VI) with leadacetate [Pb(CH3COO)23H2O] in the form of leadchromate (PbCrO4) – resulting chromium yellowpigment (Fig. 2).

Na2CrO4 + Pb(CH3COO)2 = PbCrO4 + 2NaCH3COO (3)

Fig. 2. Chromium yellow pigment (PbCrO4)

PHASE 5: Reducing Cr(VI) to Cr(III), in acidmedium (H2SO4 20%) with sodium sulfite (Na2HSO3)and its precipitation with sodium hydroxide

(NaOH)30% in the form of chromium hydroxide[Cr(OH)3] - chromium green pigment (Fig. 3).

2 Na2CrO4 + 3 Na2SO3 + 5 H2O = 2 Cr(OH)3 + 3 Na2SO4 + 4 NaOH (4)

Fig. 3. Chromium green pigment Cr(OH)3

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Fig. 4. Scheme of iron recovery procedure

2.2. Iron recovery

Iron is present in the cake obtained afterchromium recovery, in the form of compound ofFe(II), Fe(III) and Fe(VI). Fe (VI) was obtained in thefirst phase of a chrome recovery process by partialoxidation of Fe(II) to Fe(VI) in the form of sodiumperferrate (Na2FeO4).

The phases of iron recovery procedure arepresented in Fig. 4.

PHASE 1: Solubilization of the sludge cakeremaining after chromium recovery

Solubilization of the sludge cake has beenperformed with sulfuric acid (H2SO4) 20% at pH =1.0–1.5; reaction temperature = 90 oC; reaction time =30 minutes; stirring throughout the reaction time.Iron compounds solubilizing reactions are thefollowing:

Na2FeO4 + 16 H2SO4 +3Fe3O4 = 5Fe2(SO4)3 + Na2SO4 + 16H2O (5)

2Fe(OH)3 + 3H2SO4 = Fe2(SO4)3 + 6H2O (6)

Fe(OH)2 + H2SO4 = FeSO4 + 2H2O (7)

Simultaneously with iron solubilization alsooccurred the solubilization of Zn(II), according to thefollowing chemical reaction:

Zn(OH)2 + H2SO4 = ZnSO4 + 2H2O (8)

PHASE 2: Filtering the solutionAfter the solubilization of the sludge cake, the

resulting solution was filtered with vacuum pump,resulting a solution containing Fe(II), Fe(III) andZn(II) and the wet cake with small traces of metalions.

PHASE 3: Oxidation of Fe(II) to Fe(III)Oxidation reaction has been performed in two

stages: in the first stage with sodium hypochlorite(NaOCl) and sodium hydroxide (NaOH) along withCr(III) (as mentioned above) and the secondoxidation step with hydrogen peroxide (H2O2),reaction temperature = 90 oC, reaction time = 30minutes; stirring throughout the reaction time.

The chemical reaction was:2FeSO4 + H2SO4 + H2O2 = Fe2(SO4)3 + 2H2O (9)

PHASE 4: Complete precipitation of Fe(III)Ferric sulphate [Fe2(SO4)3] formed in the

previous steps was precipitated at pH = 3.5- 4 withsodium hydroxide (NaOH) 30%; temperature reaction- ambient, reaction time = 15 minutes, stirringthroughout the reaction time, to obtain a suspensionof iron hydroxide. The chemical reaction was:

Fe2(SO4)3 + 6 NaOH = 3 Na2SO4 + 2 Fe(OH)3 (10)

PHASE 5: Filtering the suspension obtainedafter precipitation of Fe (III) with vacuum pump andwashing wet cake from filtration for full recovery ofred iron pigment (Fig. 5).

The zinc recovery has been performed from theremaining solution after iron recovery.

The phases of zinc recovery procedure arepresented in Fig. 6.

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Fig. 5. Wet cake of iron Red iron pigment Fe(OH)3

Fig. 6. Scheme of zinc recovery procedure

PHASE 1: Precipitation of ZnThe precipitation has been performed with

sodium hydroxide (NaOH) 30% by raising the pH of4 to 9-9.5; reaction temperature - ambient, reactiontime = 15 minutes.

The pH was raised from 4 to 9-9.5 to ensurecomplete precipitation of the zinc.

ZnSO4 + 2NaOH = Zn(OH)2 + Na2SO4 (11)

PHASE 2: Filtering the solution with vacuumpump and washing wet cake from filtration for fullrecovery of zinc as zinc hydroxide [Zn(OH)2] (Fig. 7).

Fig. 7. Zinc hydroxide [Zn(OH)2]

This scientific activity at laboratory scale has ledto selective recovery efficiency for studied metal ionsof: 84.20 % for chromium; 99.93 % for iron; 85.74 %for zinc (Table 2).

Table 2. Metal ions recovery efficiency

IonsThe initial amount of themetals in sludge sample

(g)

The total recovered amountof metals in solution

(g)

Recovery efficiency(%)

Cr 0.4050 0.3410 84.20Fe 13.6500 13.6410 99.93Zn 27.1500 23.2771 85.74

4. Conclusions

The main conclusions of these experimentalresearches are:

Recovery efficiencies for the 3 metals ions areconsidered quite satisfactory but future research willcontinue to improve them by establishing optimaltechnical parameters and to obtain an inert sludgecake behaved as an inert in terms of recovery ofuseful compounds which are the subject of thisresearch.

Experiments conducted in the laboratory led tothe obtaining of: Chromium yellow pigment(PbCrO4), Chromium green pigment Cr(OH)3, Rediron pigment Fe(OH)3; zinc hydroxide [Zn(OH)2] asraw material.

Future research will focus on analyzing thepossibilities for capitalization of metal ions recoveredas pigments in glazes for ceramic products industry.

References[1]. L Oniciu, E. Grunwald, Galvanotehnica, Scientific andEncyclopedic Publishing, Bucharest, 1980.[2]. Tonni Agustiono Kurniawana, Gilbert Y. S. Chana, Wai-Hung Loa, Sandhya Babelb, Physico–chemical treatmenttechniques for wastewater laden with heavy metals, ChemicalEngineering Journal, Volume 118, Issues 1–2, 1 May 2006, Pages83–98.[3]. BREF, Waste Treatments, august 2006.[4]. INCDPM Bucharest, The hazardous waste neutralizationtechnologies, capitalizing them in vitreous and ceramic materials,Project 2008-2011, Bucharest.[5]. I. Bojanowska, Recovery of Chromium from Sludge Formedafter Neutralization of Chromic Wastewater, Polish J. Environ.Stud., 11(2), 117, 2002.[6]. I. Bojanowska, Recovery of Chromium from GalvanicWastewater Sludge, Polish J. Environ. Stud., 11(3), 225, 2002.

drying /grinding

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CONDUCTIVE-ATOMIC FORCE MICROSCOPY INVESTIGATIONOF THE ELECTRICAL PROPERTIES OF LOW TEMPERATURE

DEPOSED ZnO TRANSPARENT THIN FILMS

A. ALEXA1, A. PIMENTEL2, T. CALMEIRO2, A. ISTRATE3,E. FORTUNATO2, V. MUȘAT1*

1 Center of Nanostructures and Functional Materials- CNFM, Faculty of Engineering, "Dunarea de Jos"University of Galati, Galati, Romania

2 CENIMAT/I3N, Departamento de Ciencia dos Materiais, Faculdade de Ciencias e Tecnologia, FCT,Universidade Nova de Lisboa (UNL), and CEMOP/UNINOVA, Caparica, Portugal

3 National Institute for R & D in Microtechnologies (IMT), Erou Iancu Nicolae Str. 126A,Bucharest 077190, Romania

*Corresponding authore-mail: [email protected]

ABSTRACT

The paper presents the investigation by conductive-atomic force microscopy(C-AFM) of the variation of the local conductivity and topography of thetransparent ZnO thin films deposed onto soda lima glass substrates by spin-coatingof pre-prepared ZnO nanoparticles. With conductivity measurements at thenanometer level, the chemical and crystalline structure of the thin films obtained attemperature below 200 °C were investigated by Fourier transform infrared (FTIR)spectroscopy and X-ray diffraction, respectively, as a function of the number of thedeposed layers and conditions of their deposition, as deposition rate and thetemperature of post-deposition annealing. The increase of the thermal treatmenttemperature, from 120 to 180 °C, leads to increased values of all thin films, mostnotably for the thickest sample with three layers deposed at 500 rpm that shows thehighest decrease of thickness indicating the highest compaction. The samples withthree layers post-treated at 180 oC show grain growth associated with increasedroughness.

KEYWORDS: ZnO nanoparticles, transparent thin films, spin-coating,microstructure, conductive atomic force microscopy

1. Introduction

Due to the recent development of transparentand flexible electronics, there is a growing interest indepositing transparent thin-film metal-oxidesemiconductors at low temperature that can offerflexibility, lighter weight, and potentially lead tocheaper manufacturing processing.

Zinc oxide, which is an II-VI groupsemiconductor with a broad energy band (3.37 eV),high thermal and mechanical stability even at roomtemperature, is a very attractive material for potentialapplications in electronics, optoelectronics and lasertechnology [1].

When using polymer flexible substrate, thedevice processing temperatures should not exceed 80ºC, 150 ºC, 300 ºC for polyethylene terephthalate

(PET), polyethylene naphtalate (PEN) and Polyimide(PI) substrates in order to avoid their degradation [2].For these low temperatures processing, one potentialroute is represented by deposition of pre-preparedoxide nanoparticles dispersions.

There are more methods for the preparation ofZnO-based thin films, as sol–gel, supercriticalprecipitation, colloidal synthesis, vapor-phaseoxidation, thermal vapor transport and condensation,chemical vapor deposition, micro-emulsion, spraypyrolysis, combustion method and organometallicsynthesis [3-7].

Efficient use of transparent thin films in flexibleelectronics applications require advanced knowledgeof their electrical properties at micro/ nano level.Conventionally, the study of electrical proprieties isdone by four-point probe method that measures the

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average value of the electrical resistivity of the thinfilm at the macroscopic level. In contrast, conductive-atomic force microscopy (C-AFM) technique allowsobtaining a mapping of the local variations in theconductivity of the thin films surface at high spatialresolution of variations in height and current responsesimultaneously, giving information about the localelectronic structure for a local morphology. Thismethod allows to quantitatively investigate theelectron transport at the nanometer-scale (nm-scale)[8].

In the present paper, we have used C-AFM tomap the local conductivity variations of transparentZnO thin films deposed onto soda lima glasssubstrates by spin coating using an alcohol dispersionof ZnO nanoparticles pre-prepared from solution. Thechemical and crystalline structure of the thin filmsobtained at temperature below 200 oC wereinvestigated by Fourier transform infrared (FTIR)spectroscopy and X-ray diffraction, respectively, as afunction of the number of the deposed layers andconditions of their deposition, i.e. deposition rate andthe temperature of post-deposition annealing.

2. Experimental details

2.1. Materials and synthesis of ZnOnanoparticles

Zinc acetate dehydrate (purity >98%), potassiumhydroxide and methanol (purity ≥99%) werepurchased from Sigma Aldrich and were used withoutfurther purification.

For the synthesis of ZnO nanoparticles, twomethanol solutions, A (KOH) and B (zinc acetatedehydrate) were prepared by dissolving in methanolunder reflux at 60 °C. Over the solution A, solution Bwas added and the mixture was heated under refluxand magnetic stirring to precipitate ZnO NPs.

High-speed centrifugation (9000 rpm) was usedfor the separation of ZnO NPs from the mothersolution, and for each centrifugation step, a washingwith ethanol was applied. The obtained powder wasfinally dried in air at 100 °C.

2.2. Thin film preparation

The prepared ZnO NPs were re-dispersed inmethanol and deposed on soda lima glass substratesas thin films by spin-coating using Spin-Coater WS-650SZ-8NPP AS, Laurell. Single-layered (labeledwith F1 to F4 in Table 1) and three-layered thin filmssamples (labeled with F5 to F8 in Table 1) weredeposed at 500 and 1000 rpm and annealed at 120and 180 °C.

2.3. Nanoparticles and thin filmscharacterization

The thickness of the deposed thin film wasmeasured with NanoCalc-XR type refractometer.

The crystalline structure of the investigatedfilms was evaluated by X-ray diffraction on grazingincidence geometry using a PANalytical's X’PertPRO MRD X-ray diffractometer in the 2θ scanningrange of 20° - 70° using a monochromatic CuKαradiation source (wavelength 1.540598 Å). Theaverage crystallite size (L) of ZnO thin films wascalculated based on Debye-Scherrer’s equation:

B(2θ) = (K·λ)/(L·cosθ) (1)

where B is the full width at half of the maximumintensity (FWHM) of the peak, λ is the X-raywavelength, θ is the diffraction angle and K is theScherrer’s constant whose value for sphericalparticles is 0.89 [10].

The active functional groups inside the filmswere identified by Fourier Transform Infrared (FT-IR) measurements, in the spectral region of 500–4500cm−1, using a Nicolet 6700 FTIR spectrometer.

Table 1. Experimental deposition parametersand thickness of the investigated films

Samplesymbol

No. oflayers

Depositionrate

(rpm)

Annealingtemperatur

e (°C)

Filmthickness

(nm)F1 120 271F2 500 180 216F3 120 173F4

11000 180 126

F5 120 894F6 500 180 558F7 120 713F8

31000 180 561

Simultaneous local current and topographymeasurements were made on the surface of ZnO thinfilms by conductive-atomic force microscopy (C-AFM) in ambient conditions with Asylum ResearchMFP-3D Standalone atomic force microscopeoperating in contact mode with a 2.504 μm/s scanningspeed; samples scanning was performed with acommercial Pt probes (Nanoworld ContPt) having acurrent sensitivity of 2 nA/V and 10 mV bias. Thesamples were contacted using a silver paint applied tothe back side and margins of the samples. The imageresolution is 256 x 256 and the roughness (RMS) wasevaluated with Gwyddion software. Conductivechannel measurements are overlaid on the AFMimage by color mapping.

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3. Results and discussions

3.1. Fourier Transform Infraredinvestigation

Figure 1 shows the FT-IR spectra of the deposedZnO thin films with different thickness, consisting ofone and three layers. All the spectra contain intensetransmittance peaks at 550 cm-1 attributed to bendingand stretching vibrations of Zn–O bond. The increaseof their intensity is related to the increase of filmthickness (Table 1). Two intense peaks at 1583 and1414 cm-1 in the ZnO spectrum are assigned to theasymmetric and symmetric stretching modes of COO-

acetate groups, not totally removed by the washingprocedure. Also a broad band is presented in therange of 3500-3000 cm-1 which can be assigned to thestretching modes of OH groups exposed on theparticle surface and to the presence of residual watercondensed on the surface of thin films.

5000 4000 3000 2000 1000 050

60

70

80

90

100

110

120

s(Z

nO)

s(C

OO

)a

s(CO

O)

-1

F1 F2 F3 F4

Tran

smitt

ance

(%)

Wavenumbers (cm )

(O

H)

5000 4000 3000 2000 1000 050

60

70

80

90

100

110

120

(Zn

O)s

(CO

O)

as(

COO

)

T5T6T7T8

Tran

smitt

ance

(%)

Wavenumbers (cm )-1

(O

H)

Fig. 1. The FTIR spectra of thin film sampleswith one (a) and three layers (b).

3.2. Microstructural characterization

The XRD pattern of the deposed thin filmspresented in Figure 2 confirm the polycrystallinewurtzite type zinc oxide phase. The three maindiffraction peaks located at 2θ values of 31.7°, 36.2°and 56.6° are assigned to (100), (110) and (101)crystallographic planes, respectively.

The average crystallite size (L) of the obtainedthin films, calculated with Debye-Scherrer’s fordifferent diffraction peaks shows different values, asfollows: 10-13 nm estimated for (100) and (110)peaks, and 70-120 nm estimated for (101) peak,indicating an anisotropic crystal growth.

The three-layered thin films show an increase ofintensity of the diffraction peaks in respect to onelayer thin films related to the increase of filmthickness (Table 1) and crystallinity.

10 20 30 40 50 60 70 80500

1000

1500

2000

2500

3000

(110

)

(002

)(1

00) F1

F2 F3 F4

Inte

nsity

(Cou

nts)

Angle (°2 theta)

20 30 40 50 60 70

500

1000

1500

2000

2500

3000

3500

4000

(110

)

(101

)(100

)

F5 F6 F7 F8

Inte

nsity

(Cou

nts)

Angle (°2 theta)

Fig. 2. X-Ray diffraction patterns of the onelayer (a) and three-layer (b) thin films

a)

b)

a)

b)

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3.3. Conductive atomic force microscopymeasurements

Figure 3 shows the superposition of current andtopography C-AFM mapping of thin film samples, in2D and 3D presentations. According to the C-AFMtopography images, the thin films consist of relativelycompact and homogeneous by size and shaperoundish grains with diameters between 20 and 60nm.

Generally, the C-AFM measurements revealedelectrically resistive undoped ZnO thin films. In allsamples, darker spots between the grains can beobserved, indicating no-conductive pore spaces.Based on color tones, different gradients in current,can be observed. The highest current gradient, from -11 to 122 pA, was obtained for the most compactsample (F8 in Fig.3).

F6

F7

F8

F5

Fig. 3. C-AFM mapping of three-layer thin filmsamples, in 2D and 3D presentations

The influence of the post-deposition temperatureon the films thickness, Rms roughness and highestgrain conductivity are quantified in Figure 4. Theincrease of thermal treatment temperature from 120°C to 180 °C induced changes in thicknesses,roughness, porosity and conductivity for all theinvestigated films. Considering the thickness of thinfilms (Fig 4a), one can observe a shrinkage of allsamples, about 20% for samples deposed at 1000 rpm

with one (sample F4) and three layers (sample F8).Higher shrinkage of about 27% (sample F2) and 37%(sample F6) can be observed for samples with oneand three layers, respectively, deposed at 500 rpm(Fig. 4a).

The increase of the annealing temperature hasinduced an opposite effect to the surface roughness,depending on the number of layers and depositionrate (Fig 4b). For the films with one layer, the Rmsvalues decrease with 12% and 20% for 1000 and 500rpm, respectively, while for the samples with threelayers the Rms values increased with 9.1 and 8.4%when the deposition rate was 1000 and 500 rpm,respectively (Fig. 4b).

120 180

120

180

240

540600660720780840900960

3.0

3.5

4.0

4.5

5.0

5.5

120 180-45

-40

-35

-30

-25

-20

-15

-10

204060

(1000rpm)

(500rpm)

(500rpm)

(1000rpm)(1000rpm)

(500rpm)1 layer

3 layers

F4

F2

F1

F3

F8F6

F7

F5

Thick

ness

(nm

)

(1000rpm)

(1000rpm)

(1000rpm)

(1000rpm)

(1000rpm)

(1000rpm)

(500rpm)

(500rpm)

(500rpm)

(500rpm)

(500rpm)

F8

3 layers

1 layerF4

F2

F3F1

F8F6

F7F5

Rms (

nm)

(500rpm)(1000rpm)

(1000rpm)

(1000rpm)

(500rpm)

(500rpm)

(500rpm)

Temperature (C)

3 layers

1 layer

F4

F2F1F3F5

F6

F7

grain

max

Cur

rent

(pA)

Temperature (C)

Fig. 4. Variation of the thin films thickness (a),Rms roughness (b) and maximum peak grainconductivity (c) versus the temperature of the

post deposition treatment

The increase of thermal treatment from 120 °Cto 180 °C led to higher conductivity values of allsamples, most notably for the thin film sample with

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three layers deposed at 500 rpm (Fig. 4c). One canobserve an increase of overall surface currentresponse with the increase of thickness for allsamples, the thermal treatment have lowered thevalue response of grain maximum peak for one-layersamples, which is in accordance with decreasedvalues of roughness. Best conductivity is achieved bysample F8 as a result of better compaction; lowergrain boundary scattering, higher conductivity [11].

4. Conclusions

ZnO thin films were obtained by spin-coatingusing pre-prepared oxide nanoparticles, at depositionrate of 500 and 1000 rpm and subsequent thermaltreatment at 120 and 180 oC.

The increase of thermal treatment from 120 °Cto 180 °C led to increased values of conductivity ofall thin films, most notably for the thickest samplewith three layers deposed at 500 rpm that shows thehighest decrease of thickness indicating the highestcompaction. The samples with three layers post-treated at 180 oC show a simultaneously grain growth,associated with an increase of sample roughness.

AcknowledgementThe work of Alexandru Alexa has been funded

by the Sectoral Operational Programme HumanResources Development 2007-2013 of the Ministry ofEuropean Funds through the Financial AgreementPOSDRU/159/1.5/S/132397.

References[1]. Radzimska A. K., Jesionowski T., Zinc Oxide - FromSynthesis to Application: A Review, Materials, 7, 2833, 2014.[2]. Facchetti A., Marks T. J., Transparent electronics: Fromsynthesis to Applications, Wiley, 2010, ISBN 978-0-99077-3.[3]. Pasquarelli R. M., Ginley D. S., O’Hayre R., Solutionprocessing of transparent conductors: from flask to film, Chem.Soc. Rev. 2011, 40, p. 5406-5441[4]. Fortunato E., Barquinha P., Martins R., Oxidesemiconductor thin-film transistors: a review of recent advances,Advanced materials, 24, p. 2945-86, 2012.[5]. Fan J. C., Sreekanth K. M., Xie Z., Chang S. L., Rao K. V.,p-Type ZnO materials: Theory, growth, properties and devices,Progress in Materials Science, 58, 874, 2013.[6]. Kang Y. H., Jeong S., Min Ko J., Ji-Yo, Lee, Choi Y., LeeC., Cho S. Y., Two-component solution processing of oxidesemiconductors for thin-film transistors via self-combustionreaction, Journal of Materials Chemistry C, 2, p. 42-47, 2014.[7]. Schneller T., Waser R., Kosec M., Payne D., ChemicalSolution Deposition of Functional Oxide Thin Films, Springer,New York, 2013, ISBN 978-3-211-99311-8.[8]. Vasu K., Ghanashyam Krishna M., K. Padmanabhan A.,Conductive-atomic force microscopy study of local electrontransport in nanostructured titanium nitride thin films, Thin SolidFilms, 519, p. 7702-7706, 2011.[9]. Sun B., Sirringhaus H., Solution-Processed Zinc Oxide Field-Effect Transistors Based on Self-Assembly of Colloidal Nanorods,Nano Letters, 2005, Vol. 5, No. 12, p. 2408-2413.[10]. Costenaro D., Carniato F., Gatti G., Marchesea L., BisioC., Preparation of Luminescent ZnO Nanoparticles Modified withAminopropyltriethoxy Silane for Optoelectronic Applications, NewJ. Chem. 2013, 37, 2103.[11]. Vinodkumar R. et. al., Structural, spectroscopic andelectrical studies of nanostructured porous ZnO thin filmsprepared by pulsed laser deposition, Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy, 118, p. 724-732, 2014.

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THE ELECTROMAGNETIC PROPRIETIESOF HYBRID COMPOSITES

I. G. BÎRSAN1, Marina BUNEA2, G. MIHU, A. CÎRCIUMARU1,*1”Dunărea de Jos” University of Galati, Border Faculty of Humanities, Economics and Engineering,

Domnească Street, 47, RO-800008, Galati, Romania2”Dunărea de Jos” University of Galati, Faculty of Mechanical Engineering,

Domnească Street, 47, RO-800008, Galati, Romania*Corresponding author


ABSTRACT

In this research, the electromagnetic behaviour of hybrid composites withheterogeneous epoxy matrix was investigated. The hybrid composites were formedby wet lay-up method and were made of three types of simple plain fabrics assheets. In order to improve the electrical and magnetic properties of hybridmaterials and to modify the basic properties of epoxy resin had been used the fillerslike carbon black and ferrite. Analysing the electromagnetic properties of formedhybrid composites it was observed that the composites with outer layers made ofcarbon fabric sheets exhibit higher dielectric permittivity and electricalconductivity in comparison with other materials. The magnetic permeability ofstudied composites showed negative values under whole range of frequencies, butthe materials with aramid fabric in outer layers exhibit more negative values ofmagnetic constants.

KEYWORDS: electrical conductivity, magnetic permeability, hybridcomposites, filled matrix

1. Introduction

The advance of fibres reinforced compositesleads to achievement of materials with unusualelectromagnetic behaviour. As, many studies haveshown that the polymeric composites are electricalnon- conductive, but electrical properties can beimproved by use of fillers like carbon nanotubes(CNT), carbon black, graphite, graphene, short carbonfibres and magnetic properties by using of bariumferrite (BaFe). It is necessary to know that the use ofthe fillers in structure of composites may improve theelectrical and magnetic properties, but they can affectthe mechanical properties, that is why it must beconsidered the weight fraction of used fillers, becauseit should not exceed 30-40% of the matrix, due to itsdifferent directions arrangement and multiplegeometric patterns forming [1].

Short fibres are used not only to improve themechanical properties, but also to improve theelectrical properties [2]. Carbon nano-fibres (CNFs)can effectively improve the electrical conductivity ofCNFs/epoxy nano-composites, which can form theconductive path at a low content, and the threshold of

CNFs/epoxy nano-composites ranges between 0.1%to 0.2% weight ratios [3].

Markov et al. [4] had studied the influence ofcarbon black and short carbon fibres on electrical andmechanical properties of unidirectional glass fibrereinforced polyethylene. It had been determined ananisotropic electrical conductivity in the range ofpercolation threshold. Also, Wong et al. [5]investigated the influence of recycled carbon fibreson development of electromagnetic shielding.

Witchman et al. [6] had studied the influence ofcarbon nanotubes, fumed silica and carbon black onmechanical and electrical properties of glass fibrereinforced epoxy composite. They obtained that theelectrical conductivity could be implied into the FRPsby using only very small amounts (0.3%) of carbonnanotubes without any decreasing of the mechanicalproperties. The nanoparticles (fumed silica andcarbon black) had improved the mechanicalproperties and had exhibited an adjustable electricalconductivity.

In this paper the electrical and magneticproperties of six fabric reinforced composites withheterogeneous epoxy matrix were analysed. The type

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of fabric sheets in outer layers of hybrid compositeshad affected the electromagnetic parameters. Thenegative magnetic permeability values of studiedhybrid composites were obtained. The negativemagnetic permeability is found by many scientists incase of meta-materials, which are artificial materialswith simultaneously negative dielectric permittivityand negative magnetic permeability at the samefrequency leading to negative refraction index, or oneof these parameters can have negative value and otherpositive value. When these parameters have differentsigns, the electromagnetic wave cannot spread [7-10].

2. Materials

For this research six different hybrid reinforcedcomposite materials with heterogeneous epoxy matrixwere formed. The reinforcement is made of threetypes of fibre fabrics namely: carbon fibre fabricdenoted by C, aramid fibre fabric denoted by K andglass fibre fabric denoted by G. The orientation oflayers is different as it may be noticed in table 1. Eachcomposite is reinforced with 17 layers of abovementioned fabrics excepting the medial layer that ismade of a hybrid fabric.

The hybrid fabric was obtained by replacingeach second yarn of aramid fibres on the fill of amixed simple type fabric with 2:1 (carbon:aramid)yarns on warp and 1:2 (carbon:aramid) yarns on thefill with a glass fibres yarn of 200 tex in which atinned cooper wire of 0.2 mm diameter had beeninserted.

The three types of fabrics were symmetricallydistributed relative to the medial layer but based ontheir orientation they are realising an anti-symmetrical balanced structure.

The matrix of materials is realized from epoxysystem EPIPHEN RE 4020 - DE 4020 (Bostik).Epoxy resins exhibit superior mechanical andelectrical properties in comparison with other resins[11].

The heterogeneous epoxy matrix was formed bymodifying the epoxy system with 10% wr of starch,10% wr of aramid powder and, 10% wr of carbonblack (MF1) and 10% wr starch, 10% wr carbonblack and, 10% wr ferrite (MF2). The MF1 filledmatrix was used for reinforcement layers 1 to 5 and13 to 17 while MF2 filled matrix was used forreinforcement layers 6 to 12.

These fillers were used to improveelectromagnetic properties of studied materials.

So, the ferrite was used improve the magneticproperties, but the particle size, the fillerconcentration and the mutual orientation of the ferriteparticles in the matrix affect the value of these

properties [12], that is why the potato starch wasused, to prevent the sedimentation of the other fillers.

The carbon black was used for improving theelectrical properties and aramid powder was used forimproving the impact properties that will be discussedin other paper.

All the hybrid composite materials were formedby wet lay-up method with each sheet of fabricimbued with correspondent pre-polymer mixture andthen placed into a mould. The microscopical imagesof transversal surfaces of materials are presented inFig. 1.

Table 1. The layers configuration of hybridreinforced composite materials with

heterogeneous matrix

MaterialsLa

yers

M1F M2F M3F M4F M5F M6F

01 30K 15K 30K 30G 45C 0C02 -30K 30K 15K -30C -30C -30C03 45C -15C 0C 0K 15G 45C04 0C -30C 45G 45G 30G 0K05 45C 45G -30G 30C -30C -30K06 0C 15C -15C 15K 0C 45K07 15K 30K 30K -30K 30G 30G08 30K 45K 45K 30G 45G 45G09 90M 90M 90M 90M 90M 90M10 -30K 45K 45K 30G 45G 45G11 -15K -30K -30K 45K -30G -30G12 0C -15C 15C -15K 0C 45K13 45C 45G 30G -30C 30C 30K14 0C 30C 45G 45G -30G 0K15 45C 15C 0C 0K -15G 45C16 30K -30K -15K 30C 30C -30C17 -30K -15K -30K 30G 45C 0C

Carbon fabric: 4×4 plain weave, 160 g/m2.Aramid fabric: 6.7×6.7 plain weave, 173 g/m2.Glass fabric: 12×12 plain weave, 163 g/m2.

3. Experimental method

To determine the electromagnetic properties, asdielectric permittivity, electrical conductivity and,magnetic permeability of hybrid composites a digitalLCR-meter Protek 9216A, was used together with themeasurement cell, according [13]. Both bulk andsurface measurements were performed at the fivebuilt-in frequencies of LCR-meter in five points oneach formed material.

The calculation of dielectric permittivity,electrical conductivity, electrical resistivity andmagnetic permeability of hybrid composites weremade by application of the formulas given in [14].

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Fig. 1. The microscopical images of hybrid laminates transversal surfaces


Generally, the electrical properties of the fibrereinforced composite materials depend on themoisture content, crystalline or amorphouscomponent present, presence of impurities, etc. [15,16].

In Fig. 2 are plotted the values of surface andbulk dielectric permittivity constants of the materials.The hybrid composite materials with outer layersmade of carbon fabric sheets exhibit higher dielectricpermittivity values than other hybrid compositematerials, which outer layers are made of aramid andglass fabrics sheets, but these values decrease withincreasing of frequencies.

The glass fabric reinforced composites andaramid fabric reinforced composites are used asinsulators. In this regard M5F hybrid compositematerial exhibits the highest value of bulk dielectricpermittivity and M6F hybrid composite materialexhibits a similar value of bulk dielectric permittivity

with those of other hybrid materials, which valuesdoes not vary with frequency.

In Fig. 3 are plotted the values of electricalconductivity of hybrid composite materials. As it canbe seen, the electrical conductivity of materials hadincreased with increasing of frequency till thefrequency rise to 1 kHz, the hybrid materials withouter layers made of carbon fabric sheets exhibithigher values of electrical conductivity, but at 10 kHzand 100 kHz these values become almost equal withvalues of other studied hybrid materials.

The surface and bulk magnetic permeabilityconstants of all hybrid composites had showednegative values on the entire frequency domain (Fig.4).

All the magnetic values become less negativewith increasing of frequency. The magneticpermeability of hybrid composites with outer layersmade of aramid fabric sheets showed more negativevalues and the glass fabric outer layers compositeexhibits intermediate values of magnetic constants.

M1F

M4F

M2F

M3F

M5F M6F

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Fig. 2. The dielectric permittivity of the hybrid composite materials

Fig. 3. The electrical conductivity of the hybrid composite materials

Fig. 4. The magnetic permeability of the hybrid composite materials

5. Conclusions

The electrical and magnetic parameters ofhybrid composites were measured by standardelectrical method applied for plates in electric andelectronic engineering and the electrical and magneticconstants were calculated. Analysing theelectromagnetic behaviour of studied hybridcomposites, it can be made the following conclusions:

● The hybrid composites with outer layers madeof carbon fabric sheets exhibit highest dielectricpermittivity, which decreases with increasing offrequency.

● The highest surface electrical conductivity at0.1-1 kHz range of frequencies was exhibited by M5Fhybrid composite due to its outer layers made of morecarbon fabric sheets. The highest bulk electricalconductivity at the same range of frequencies wasexhibited by M5F hybrid composite because itsstructure does not contain the aramid fabric sheets.However, at 10 kHz and 100 kHz frequencies thevalues of electrical conductivity of these hybridmaterials become similar with the values of otherhybrid materials studied in this research.

● All the hybrid composites exhibit negativemagnetic parameters under whole range offrequencies.

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● The values of magnetic permeability of hybridcomposites with outer layers made of aramid fabricsheets were more negative than those of other hybridcomposites.

Acknowledgements

The work has been funded by the SectoralOperational Programme Human ResourcesDevelopment 2007-2013 of the Ministry of EuropeanFunds through the Financial AgreementPOSDRU/159/1.5/S/132397.

References[1]. Xanthos M., Functional Fillers for Plastics: Second, updatedand enlarged edition, WILEY-VCH Verlag GmbH & Co. KGaA,ISBN: 978-3-527-32361-6, Weinheim, Germany, 2010.[2]. Van der Vegt A. K., From polymers to plastics, DUP BluePrint, The Netherlands, 2002.[3]. Qilin M., Jihui W., Fuling W., Zhixiong H., Xiaolin Y., TaoW., Conductive Behaviors of Carbon Nanofibers Reinforced EpoxyComposites, Journal of Wuhan University of Technology-Mater.Sci. Ed., Vol. 23, No. 1, p. 139-142, 2008.[4]. Markov Al., Fiedler B., Schulte K., Electrical conductivity ofcarbon black/fibers filled glass-fibre-reinforced thermoplasticcomposites, Composites: Part A 37, p. 1390-1395, 2006.[5]. Wong K. H., Pickering S. J., Rudd C. D., Recycled carbonfibre reinforced polymer composite for electromagneticinterference shielding, Composites: Part A 41, p. 693-702, 2010.

[6]. Wichmann M. H. G., Sumfleth J., Gojny Fl. H.,Quaresimin M., Fiedler B., Schulte K., Glass-fibre-reinforcedcomposites with enhanced mechanical and electrical properties –Benefits and limitations of a nanoparticle modified matrix,Engineering Fracture Mechanics 73, p. 2346-2359, 2006.[7]. Solymar L., Shamonina E., Waves in Metamaterials, OxfordUniversity Press, ISBN 978-0-19-921533-1, 2009.[8]. Ramakrishna S. A., Physics of negative refractive indexmaterials, IOP Publishing Ltd, Rep. Prog. Phys. 68, p. 449-521,2005.[9]. Liu Y., Zhang X., Metamaterials: a new frontier of scienceand technology, Chem. Soc. Rev., 40, p. 2494-2507, 2011.[10]. Wartak M. S., Tsakmakidis K. L., Hess O., Introduction toMetamaterials, Physics in Canada, Vol. 67, No. 1, p. 30-34, Jan.-Mar. 2011.[11]. Ellis B., Chemistry and Technology of Epoxy Resin, 1st

edition, ISBN 0-7514-0092-5, Chapman & Hall, 1993.[12]. Valko L., Bucek P., Dosoudil R., Usakova M., Magneticproperties of ferrite-polymer composites, Journal of ElectricalEngineering, Vol. 54, No. 3-4, p. 100-103, 2003.[13]. Misra D. K., Permittivity measurement, Webster, J. G. (ed.),Measurements, Instrumentations, and Sensors, CRC Press, 46,1999.[14]. Cîrciumaru A., Proiectarea, formarea și caracterizareamaterialelor compozite cu matrice polimerică, Editura Europlus,Galați, ISBN 978-606-628-060-0, 2013.[15]. Abd Alradha R. M., Electrical Resistivity Study forUnsaturated Polyester Reinforcement Glass Fiber, InternationalJournal of Current Engineering and Technology Vol. 4, No. 2, p.890-892, 2004.[16]. Patania D., Singh D., A review on electrical properties offiber reinforced polymer composites, International Journal ofTheoretical & Applied Sciences, 1 (2), p. 34-37, 2009.

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DETERMINATION OF GLASS TRANSITION TEMPERATURE FORPOLYESTER/GRAPHENE OXIDE AND POLYESTER/GRAPHITE

COMPOSITE BY TMA AND DSC

M. BASTIUREA1, M.S. BASTIUREA1, G. ANDREI1,M. MURARESCU2, D. DUMITRU2

1Faculty of Engineering, “Dunarea de Jos” University of Galati, Romania2Faculty of Sciences and Environment, “Dunarea de Jos” University of Galati, Romania


ABSTRACT

The influences of graphene oxide and graphite in thermosetting polymercomposites are complex and they very much depend on the chemical bonds formedbetween the fillers and the polymer matrix. This study has used polyester aspolymeric matrix and graphene oxide and graphite as fillers. Determination ofglass transition temperature (Tg) is important for practical uses of polyestercomposites due to the changes of characteristics which glass transition imply, thusthe polymer changes from elastic to plastic state. In order to determine the Tg weused TMA, DSC tests. The differences in determined Tg values for the samecomposite are due to different measurements as resulted from each test.

KEYWORDS: polyester, graphene oxide, graphite, Tg, TMA, DSC, DMA

1. Introduction

The glass transition temperature (Tg), ofamorphous polyester is one of the most importantparameters for industrial applications. Attemperatures above Tg, polyester behaves rubbery,below the Tg, polyester is described as a glass state.The rubbery state of polyester may be described asthe situation in which the entanglements restricted themotion of polyester chains, will be resolved andpolyester will behave like viscous fluid. Polyester isone of the most used rigid polymer raisins; it ismainly used as matrix for composites used in almostall industries due to excellent mechanical properties,improved processability, good thermal, electrical,chemical and dimensional stabilities.

Polymer matrix composites with graphene oxideor graphite will improve mechanic and thermalcharacteristics of polyester [1-5].

Graphite is a allotropic form of carbon, which isnaturally abundant. In graphite, carbon atoms arecovalently bonded in hexagonal network, formingindividual graphene sheets, and these sheets arebound together by Van der Waals forces. Graphitehas been used in many industrial applications such aslubricant and additives in composite. It has receivedattention lately due to its superior in-plane properties.There are two types of graphene structures mainly

used as additives in composites namely, the grapheneoxide and reduced graphene. Graphene oxide consistof oxygen based groups such as carbonyl, hydroxileor oxygen, these being bonded to the graphenes[6] inorder to make graphene oxide more functional, aswell as their better dispersion into the polymers, moremethods have been discovered [7-9]. The difficulty intreating the glass transition is caused by almostundettectable changes in the structure despite ofqualitative changes in characteristic and extremelylarge change in the time scale [10]. For that reason itused to determining Tg, different test and physicsparameters. The values of Tg depends on functionalgroups of the polymer, as carbonyl, carboxyl [11].

2. Methods and materials

2.1. Thermomechanical analysis (TMA)

Thermomechanical analysis (TMA) is a methodused in order to determine the size changes of thematerial, according to the temperature. This changecan be used to determine the coefficient of linearthermal expansion and temperature of glass transition.For testing we used TMA/SDTA 840 tester fromMETTLER TOLEDO. The samples were measuredbefore testing. A 0.02 N load has been applied on thesample, which was necessary in order to keep the

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sample still during heating. The thickness of thesample was 4mm. There have been tested fivesamples for each concentration. The TMA test onlydetermines the beginning the glass transitiontemperature, which takes place during a temperaturerange. The test was made according to ASTM E831standard. The testing process consists of thefollowing steps: 3 min maintaining at 30 oC, heatingwith heating rates 10 oC/min up to 190 oC,maintaining for 3 min at 190 oC, cooling with coolingrates 10 oC/min down to 30 oC.

2.2. Differential Scanning Calorimetry(DSC)

Differential Scanning Calorimetry (DSC) is amethod used in order to determine heat quantityneeded by the tested material in order to change itstemperature with 1 oC. Measurements are madeaccording to a reference material. Thus, the specificheat and the glass transition temperature of thematerial can be determined. Tester DSC1 MettlerToledo was used for testing.

The sample mass was measured by weighingthem on the analytic scales Mettler Toledo AB204-S/FACT with 0.1 mg precision. The testing processconsists of the following steps: 3 min maintaining at30 oC, heating with heating rates 10 oC/min up to 190oC, maintaining for 3 min at 190 oC, cooling withcooling rates 10 oC/min down to 30 oC, maintainingfor 3 min at 30 oC. For each concentration there havebeen tested five samples. DSC test determines boththe temperature beginning of the glass transition onthe curve temperature or “midpoint”. In order tocompare them, only the beginning of the glasstransition temperature will be used. The tests havebeen made according to ASTM E 1269 standard.

2.3. Materials

The analysis have been made on non-saturatedpolyester raisin samples added at five concentrations:0.02 wt%; 0.04 wt%; 0.06 wt%; 0.08 wt%; 0.10 wt%by using two additives: graphene oxide and graphite.In a 500 ml beaker was placed graphite (GraphiteCrystalline PMM 11/99.9 KOH-I-NOOR GRAFIs.r.o Netolice, CZ). Then it was added perchloric acid70%, purchased from Merck and the obtained mixturewas homogenized using a magnetic stirring for 20minutes (1500 rpm). Then the mixture was cooled inan ice bath before the addition of potassiumpermanganate (achieved from Fluka). The additionreaction is highly exothermic, so that thepermanganate was added in four steps. Thetemperature during the reaction process increasedfrom 25 oC to 35 oC. In order to keep the temperaturebelow 35 oC, it was made a cooling procedure of the

entire reaction mass using an ice bath. The globalreaction time was 24 hours. Then, at this mixture wasadded the hydrogen peroxide 30% in ten steps. Thetotal reaction time was 3 h. After the reaction isfinished (CO2 emission ceased), the resultingsuspension was centrifuged at 18,000 rpm. The clearphase was separated, washed with distilled water in 5stages; the total distilled water was 1500 ml. Finallythe solution achieved the pH value of 6.5 (identicalwith distilled water one). At the end the solution waswashed for two times using absolute ethanol in a totalvolume of 500 ml and then it was centrifuged. Theresulting residue was placed into a crystallizer vesselas a thin film and dried in an oven at 105 oC for 8 h.

In order to obtain polyester/graphite andpolyester/graphene oxide nanocomposite respectively,it was introduced the determined quantities ofgraphite, graphene oxide into resin mass, achievingfinally a total amount of 100 g of nanocomposite.According to the concentrations established for theexperiment, it was weighed at the analytical balance% grams of graphite and graphene oxide respectivelyand it was placed in a mortar. A dry grinding stagewas performed for 30 minutes. Then it was added 1-2g of polyester resin and followed a "wet grinding"stage for another 30 minutes. The mixture wassampled by a "washing" procedure, using newquantities of resin till the final amount of 100 g. Theentire mixture was sloped in a 200 ml stirred tank andit was stirred for 1h using a magnetic stirrer (1500rpm). After this step, it was continued the dispersionof the particles into the matrix by sonication in twostages of 5 minutes. In order to keep the temperatureunder control during the reaction process at 50 oC, themixture was cooled in an ice bath. The reaction masswas then degassed under vacuum (1-2 torr) for 1minute. After that, the catalyst (2% PMEK) wasadded under continuously stirring. This stage wasfollowed by a mechanical homogenization for another1 minute. Then, the reaction mixture was poured intorubber molds. The gelling time was 17 minutes. Afteran hour the nanocomposite was draw out from themold and placed in the oven to complete the reactionat 60 oC for 4 h.

3. Results

3.1. Glass transitions temperaturedetermined by TMA

Determination of Tg by using TMA method ismade on the samples heating curve as can be seen inFigure 1.

Figure 1 shows the variation of samplesdimension versus the temperature for the polyester +0.02 wt% graphene oxide composite. It has beennoticed an increase of Tg for all the concentrations

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tested. The biggest values have been obtained forpolyester + 0.1 wt% graphene oxide composite andpolyester + 0.1 wt% graphite. The values obtained are

showed in Table 1. For all the concentrations studiedthe maximum values have been obtained for polyesterwith graphene oxide composites.

Fig. 1. Change length vs. temperature for polyester + 0.02 wt% graphene oxide

3.2. Glass transitions temperaturedetermined by DSC

The DSC test can determine Tg both on theheating and the cooling stage. In order to compare thevalues obtained by this test with the values obtainedby the TMA tests, only the value determined on theheating stage of heat flow or specific heat will beused. The best Tg values have been obtained forpolyester + 0.1 wt% graphene oxide composites andpolyester + 0.1 wt% graphite composites. For all theconcentrations studied, the maximum values have

been obtained in polyester/graphene oxidecomposites. Fig. 2 shows the thermal curve fluxaccording to the temperature for the polyester + 0.02wt% graphene oxide composites on which the glasstransition temperature has been determined both inthe heating and cooling process.

The differences between Tg determined onheating stage and cooling stage could be determine bythe generates gases such as CO, CO2, H2O in heatingstage [12, 13].

Table 1 shows us a small difference between Tgdetermined by DSC and TMA test.

Fig. 2. Tg for polyester + 0.02 wt% graphene oxide determined by DSC

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Table 1. Glass transition temperature determined by DSC and TMA test

DSC TMA[0C] [0C]

polyester 55.27 54.14polyester+0.02%wt graphene oxide 60.45 59.32polyester+0.04%wt graphene oxide 63.45 61.86polyester+0.06%wt graphene oxide 65.98 63.25polyester+0.08%wt graphene oxide 68.41 65polyester+0.1%wt graphene oxide 68.98 65.8polyester+0.02%wt graphite 58.02 56.92polyester+0.04%wt graphite 59.95 57.9polyester+0.06%wt graphite 61.83 59.26polyester+0.08%wt graphite 63.05 60.45polyester+0.1%wt graphite 65.06 63.45

Tg

Each test use different physics parameters todetermine glass transition temperature. In DSC test itused heat flow or specific heat curves and in TMAtest it used change length curve. In the literature havebeen reports differences of values up to 13 oC. In bothtest the glass transition temperatures determined ison-set temperatures for glass transition, glasstransitions extended over a range of temperature.

4. Conclusions

For all the composites studied, there has beenobserved a rise in glass transition temperatureaccording to the rise of the additives concentration.The biggest increase in temperature has beenobserved for polyester/graphene oxide composites.This can be the result of both the nature and thenumber of the chemical bonds formed between thegraphene oxide and the polyester matrix. Inpolyester/graphite composites only Van der Waalsbonds appear while in polyester/graphen oxidecomposites there also appear hydrogen bonds whichare much stronger than Van der Waals bonds. Theseare formed between ester groups from the polyestermatrix with carbonyl and carboxyl groups which areformed during the process of obtaining the grapheneoxide. The number of hydrogen bonds is smaller thanVan der Waals bonds but much stronger than that.For the same concentration of additives, the numberof chemical bonds formed between graphene layerand the polyester matrix is much bigger than forpolyester with graphite composites due to the graphiteexfoliations into graphene layers, which have aspecific surface much bigger comparing it with that ofgraphite they come from. Graphene oxide blockmolecular movement of the polyester chains duringheating, thus the process of glass transition will startat a higher temperature comparing it with that of purepolyester. The differences obtained for the same

concentrations, is due to different physical parametersused in DMA and TMA test.

Acknowledgement

The work has been funded by the SectorialOperational Programme Human ResourcesDevelopment 2007-2013 of the Ministry of EuropeanFunds through the Financial AgreementPOSDRU/159/1.5/S/132397 ExcelDOC.

References[1]. M. A. Rafiee, J. Rafiee, I. Srivastava, Z. Wang, H. Song, Z.-Z. Yu, N. Koratkar, Fracture and fatigue in graphenenanocomposites, Small Vol. 6(2), p. 179-183, 2010.[2]. Y. F, M. A. Rafiee, J. Rafiee, Z. Z. Yu, N. Koratkar,Dramatic increase in fatigue life in hierarchical graphenecomposites, ACS Applied Materials Interfaces, Vol. 2(10), p. 2738-2743, 2010.[3]. L. He, S. C. Tjong, Low percolation threshold ofgraphene/polymer composites prepared by solvothermal reductionof graphene oxide in the polymer solution, Nanoscale ResearchLetters, Vol. 8(1), p.132-139, 2013.[4]. M. Monti, M. Rallini, D. Puglia, L. Peponi, L. Torre, J. M.Kenny, Morphology and electrical properties of graphene–epoxynanocomposites obtained by different solvent assisted processingmethods, Composites, Part A, Vol. 46, p.166-172, 2013.[5]. S. Chandrasekaran, G. Faiella, L. A. S. A. Prado, F. Tölle,R. Mülhaupt, K. Schulte, Thermally reduced graphene oxideacting as a trap for multiwall carbon nanotubes in bi-filler epoxycomposites, Composites, Part A, Vol. 49, p. 51-57, 2013.[6]. D. R. Bortz, E. G. Heras, I. Martin-Gullon, Impressivefatigue life and fracture toughness improvements in grapheneoxide/epoxy composites, Macromolecules, Vol. 45(1), p. 238-245,2012.[7]. M. Fang, Z. Zhang, J. Li, H. Zhang, H. Lu, Y. Yang,Constructing hierarchically structured interphases for strong andtough epoxy nanocomposites by aminerich graphene surfaces,Journal of Material Chemistry, Vol. 20(43), p. 9635-43, 2010.[8]. C. Bao, Y. Guo, L. Song, Y. Kan, X. Qian, Y. Hu, In situpreparation of functionalized graphene oxide/epoxynanocomposites with effective reinforcements, Journal of MaterialChemistry, Vol. 21(35), p. 13290–13298, 2011.[9]. M. Cano, U. Khan, T. Sainsbury, A. O’Neill, Z. Wang, I. T.McGovern, K. M. Wolfgang, Improving the mechanical

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properties of graphene oxide based materials by covalentattachment of polymer chains, Carbon, Vol. 52, p. 363-371, 2013.[10]. M. I. Ojovan, Configurons: Thermodynamics parametersand symmetry changes at glass transition, Entropy, Vol. 10, p 334-364, 2008.[11]. M. Erber, A. Khalyavina, K.-J. Eichhorn, B. I. VoitLeibniz, Variations in the glass transition temperature of polyesterwith special architectures confined in thin film, Polymer, Vol. 51,p. 129-135, 2010.

[12]. Y. Wan, L. Gong, L. Tang, L. Wu, J. Jiang, Mechanicalproperties of epoxy composites filled with silane-functionalizedgraphene oxide, Composites A, Vol. 64, p. 79-89, 2014.[13]. Bindu S. T. K., A. B. Nair, B. T. Abraham, P. M. S.Beegum, E. T. Thachil, Mechanical properties of epoxycomposites filled with silane-functionalized graphene oxide,Polymer Vol. 55, p. 3614-3627, 2014.

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APPLICATIONS BASED ON VARIABLE FREQUENCY ROTATINGMAGNETIC FIELD. ELECTROMECHANICAL AGITATOR WITH

DUAL DIRECTION

Ovidiu-Magdin ȚANȚA1,2,*, Mihaela POIENAR1, Ilie NIȚAN1,Mihai CENUȘĂ1, Adrian-Neculai ROMANESCU1

1”Ștefan cel Mare” University of Suceava, Faculty of Electrical Engineering and Computer Science,str. Universităţii, nr. 13, 720229, Suceava, Romania

2 E.ON Distribuție România, str. Piaţa Trandafirilor, nr. 21, cod 540049, Târgu Mureş, România*Corresponding author


ABSTRACT

This paper presents a series of experimental results obtained by studying thespecific effects and phenomena of the rotating magnetic field. During the researchit was observed an interesting phenomenon specific to variable frequency rotatingmagnetic field. Thus, a ferromagnetic metal ball placed in rotating magnetic field,rotates in field direction until it reaches a critical speed. If the speed of themagnetic field continues to increase, the ball reverses its rotation direction, even ifthe magnetic field direction remains the same. This has led to development of standsand experimental installations including dual direction electromechanical agitatordescribed in this paper.

KEYWORDS: rotating magnetic field, fluid agitator, feromagnetic balls

1. Introduction

Research on the behavior of magnetic liquidsand ferromagnetic objects placed in rotating magneticfield, were based on Kagan effect study. Based on themagnetic liquid experiments carried by R. Moscowitzand R. E. Rosensweig in 1967, it was shown that in aconstantly rotating magnetic field, the magnetic liquiddrive is given by the dipolar torque applied to eachparticle from the suspension composition. Later, in1973, Kagan made studies on the phenomenon offerrofluid spinning when it is exposed on the rotatingmagnetic field action. This reflects the magneticliquid behavior which develop a rotative motionopposite to the magnetic field, in the context whereelectrically conductive liquid are spinning in the samedirection as the field. Also it was observed that allcylindrical dielectric bodies immersed in ferrofluidrotates in reverse direction as the rotating magneticfield [4].

Continuing research in this area, the EMAD(Research Center in Electrical Engines, Apparatusand Driving) researchers started a series ofexperiments based on the characteristic phenomenaand the magnetic field applications.

2. Variable frequency rotating magneticfields specific phenomena

In 2001, in a series of experiments, ProfessorDorel Cernomazu notes the action of a steel magnetoactive particle spread in water. The solution describedhad been submitted to a rotating magnetic fieldgenerated by the stator of a three-phase asynchronousmotor. Initially, the spread analyzed tended to revolvein the same direction as the rotating magnetic field,whereupon, suddenly, has started a reverse rotaryflow [1].

In subsequent experiments we used a ball fromferromagnetic material placed in a rotary magneticfield with rotational frequency varying between 0 and6000 rot/min. It was observed that the ferromagneticball, under the rotating magnetic field action isspinning initially in the same direction with the field,and subsequently, increasing rotational frequency, theball direction is reversing.

The reversal moment is dependent on the ballposition related to rotary magnetic field, balldimensions and composition, the medium where isplaced and the field rotational speed. Experimentalstand is shown in Figure 1.

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a)

b)

Fig. 1. Stand for generation of variablefrequency rotating magnetic field: a) side view;

b) top view – insulating vessel detail

Reproducing the stand presented in the patentapplication [3], and the experiments described in thethesis [4], were seen a number of interesting physicalphenomena.

The device for variable frequency rotatingmagnetic field generation is actuated by a motor M2,supplied by an autotransformer AT, through anisolating transformer. Continuous adjustment of M2motor supply voltage is achieved through the fact thatthe autotransformer potentiometer is actuated by aDC motor M1, supplied by a source AC/DC as it isshown in Figure 2.

During the first experiments, it was found adifferent behavior of the ball placed in the rotatingmagnetic field, results being influenced by manyfactors:

- the rotation speed of the shaft which drivesthe permanent magnets;

- physical (size, weight) and magneticproperties of the ball;

- position of the container, and position of theball in the magnetic field lines;

- viscosity of the environment in which isplaced the ball (air, water, oil, glycerin).

230 V~

c.a.

c.c.M1

M2

K1TAT

230 V~

Fig. 2. Feeding electrical diagram for the stand

To obtain conclusive results have been reducedthe variables influencing the test results and, theywere made several sets of measurements with thefollowing constants:

Fe – 97.5%; Cr – 1.6%diameter: 11,1 mmThe ball used

weight: 5.6 gThe environment where is

placed the ball air

Growth rate of speed formotor M2

constant

Ball placement in the center of thepermanent magnets

In order to verify results obtained it wasperformed three sets of measurements for fivedifferent motor (M1) supply voltages, thus identifyingfour critical points of the rotating magnetic fieldspeed:

v1 – the speed of the first reversal in direction ofrotation - to the left;v2 – the maximum speed;v3 – the speed at which the ball remains inbalance (at decreasing speed);v4 – the speed of the second reversal in directionof rotation (at decreasing speed) – to the right.To illustrate the behavior of the ferromagnetic

ball in time, we draw the graph shown in Figure 3, onthe first group of values, for 14 volts supply voltageof the engine M1.

UM1 = 14 VccGroup I Group II Group IIIv1 = 596 [RPM] v1 = 614 [RPM] v1 = 622 [RPM]v2 = 3380 [RPM] v2 = 3392 [RPM] v2 = 3387 [RPM]v3 = 339 [RPM] v3 = 341 [RPM] v3 = 323 [RPM]v4 = 206 [RPM] v4 = 204 [RPM] v4 = 217 [RPM]

Analyzing the chart above, can be observed, inthe diagram, five areas in which the ferromagneticball has different behaviors:

At increasing speed

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0 – v1 the ferromagnetic ball rotates clockwise(right), and when the speed reaches 595 RPMsuddenly changes its direction of rotation to left;

v1 – v2 the ball continues to rotate to left up tothe maximum speed of 3380 RPM;

At lowering speedv2 – v3 the direction of rotation is kept to the left

until it reaches a speed of 339 RPM;v3 – v4 in this range, the ferromagnetic the ball

remains in balance;v4 – 0 at the speed of 206 RPM appears the

second reversal in direction of rotation (to the right),direction of motion kept up to speed of 0 RPM.

Fig. 3. The rotational speed of the ball in time

Based on the results obtained with one ball, withdifferent diameters, materials and weights, placed inagents with different viscosities, had been conceived,developed and tested a double-actingelectromechanical stirrer, described in the nextchapter.

3. Double-acting electromechanical stirrer

The double-acting electrochemical stirrer offersa number of advantages over the appliance describedabove, in that two stirring systems made by twoferromagnetic balls, with different diameters, isolated,placed under the same rotating magnetic field action,and that are moving on different tracks with differentmovement directions. In this manner was obtained anincreased stirring effect, which reduces the timeadequate for stirring and increases the deviceefficiency.

The double-acting electrochemical stirrer ismade up of an electrically insulating vessel 1 fitted inan electrically insulating support 2, inside which isplaced a rotating assembly. The rotating assembly iscomprised of a ferromagnetic vessel as a glass 3,which has disposed on the inner surface twopermanent magnets 4, fixed in diametrically oppositepositions. The ferromagnetic vessel driven in rotaryflow by means of an arbor 5, of a DC motor 6supplied from an auto-transformer with slidingcontact. Inside the electrically insulating vessel 1there are placed two electrically insulating

ferromagnetic balls 7 and 8, one of which is placed onthe bottom of the vessel, and the other on an annularchamfer 9 made by an insulating material, bonded onthe inner side of the vessel, under the fluid level.

The ferromagnetic balls 7 and 8, of differentsizes, placed in different areas of the same variablefrequency rotating magnetic field, are moving oneclockwise and other counterclockwise, within thevessel containing dielectric fluid. The balls directionof rotation is depending on the relative positionwithin the magnetic field and of the critical frequencyat which is breaking the magnetic synchronous torquefor one of the balls [1].

SSN N

1 2

3

4

5

6

8

7

9

Fig. 4. Double-acting electromechanical stirrer[1]: 1 - insulating vessel; 2 - insulating support;

3 - ferromagnetic support; 4 - permanentmagnets; 5 – axle; 6 - DC motor; 7, 8 -

ferromagnetic balls; 9 - annular chamfer

4. Conclusions

The phenomenon studied, of changing the balldirection of rotation on the frequency increasing, wascalled by the researchers CEUS effect(Electrotechnical Department of the University ofSuceava).

CEUS effect was the basis for practicalrealization of fluids stirrer designed in a first variant

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with a single ferromagnetic ball with reversibledirection of rotation at the rotating magnetic fieldfrequency increasing.

An improved version of the stirrer is the onepresented in the paper, characterized in that thestirring effect is carried out by two balls placed indifferent planes, under the action of the same rotatingmagnetic field, which rotate in opposite directions.

The studied CEUS effect can be applied toachieve an electric motor with reversible direction ofrotation at the change of frequency.

Another research direction detached fromexperiments is the study of a possible breaking torquegenerated by the flow of leaking over the ball bearing.

References

[1]. Graur A., Milici, M. R., Milici L. D., Raţă M., Țanța O. M.,Nițan I., Romaniuc I., Negru M. B., Cernomazu D., Agitatorelectromecanic cu acțiune dublă, Cerere de Brevet de Invenție nr.A/00330 din 29.04.2013, OSIM București.[2]. Luca E., Călugăru Gh., Bădescu R., Cotae C., Bădescu V.,Ferofluidele şi aplicaţiile lor în industrie, Bucureşti, EdituraTehnică, 1978.[3]. Negru M. B., Cernomazu D., Mandici L., Minescu D.,Ungureanu C., Savu E., Prodan C., Agitator pentru fluidedielectrice. Cerere de brevet de invenţie nr. a 2002 00412 A2. ÎnB.O.P.I. nr. 2/2004, OSIM Bucureşti, pag. 19.[4]. Negru M. B., Contribuţii privind extinderea aplicaţiilorferofluidelor şi a pulberilor feromagnetice în electrotehnică. Tezăde doctorat. Suceava: Universitatea „Ştefan cel Mare”, Facultateade Inginerie Electrică şi Ştiinţa Calculatoarelor, 2012.

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ELECTRICAL PROPERTIES CHARACTERIZATION OF VINYLESTER RESIN FILLED WITH CARBON NANOTUBES

Georgel CHIRITA1, Gabriel ANDREI1, Iulian Gabriel BIRSAN1,Dima DUMITRU2, Alina CANTARAGIU1

1 Faculty of Engineering, „Dunarea de Jos” University of Galati, Romania2 Faculty of Science and Environment, Department of Chemistry, Physics and Environment,

„Dunarea de Jos” University of Galati, Romaniae-mail: [email protected]

ABSTRACT

In this paper has been done a characterization of electrical properties of vinylester based nanocomposites containing different percentages of carbonnanomaterials.

The carbon fillers used in this study were single wall carbon nanotubes(SWCNTs) and multiwall carbon nanotubes (MWCNTs). Three weight percentage(0.10, 0.15 and 0.20) of each type of carbon nanotubes used as filler were addedinto the thermoset polymer matrix of vinyl-ester resulting six nanocompositematerials.

The electrical properties were measured with TeraOhm 5 kV tester for all sixcomposite materials along with neat vinyl ester resin. The experimental resultsshow that by the addition of multi wall carbon nanotubes filler to the vinyl-estermatrix was improved significantly the electrical properties of the nanocompositematerial thus obtained. The electrical percolation threshold concentration for multiwall carbon nanotubes based vinyl ester nanocomposite was 0.20 wt.%.

KEYWORDS: electrical properties, vinyl-ester resin, conductivity, single wallcarbon nanotubes, multiwall carbon nanotubes

1. Introduction

Due to their superior overall properties suchthermal, electrical and mechanical properties, carbonnanotubes filled polymer composites have been ofgreat interest for industrial and research communityin the last years [1, 2]. Most polymers arecharacterized as insulator regarding the electricalproperties. This became a challenge to researchcommunity which are studying the way of improvingthe electrical properties of polymers by addingdifferent materials as reinforcement [3, 4].

Carbon nanotubes are the one of common fillerused in polymer composites that alreadydemonstrated the capability of enhancement ofelectrical conductivity, by several orders ofmagnitude at low percolation threshold [5-7]. Evenwith very low concentrations, carbon nanotubes areable to form conductive networks mainly due to theircapability of high conductivity [8-10].

The principal factors that are influencing theelectrical conductivity are close related of type ofpolymer matrix. Enhancement of electrical

conductivity of the polymer matrix can be achievedby proper choice of filler type and amount, along witha good dispersion of the filler in the matrix [9, 11].

2. Experimental

Vinyl ester resin type Polimal VE-11 M wasused as polymer matrix. Two type of carbonnanotubes: single wall carbon nanotubes (SWCNTs)and multi-wall carbon nanotubes (MWCNTs)provided by Cheap Tubes Inc. Company has beenadded to vinyl ester thermoset polymer. The mainproperties of the carbon nanotubes used in this studyare presented in Table 1.

For each type of nanocomposite were used threeweight percentage of nanomaterials (0.10 wt.%, 0.15wt.% and 0.20 wt.%) obtaining six nanocompositematerials. The procedure of obtaining thenanocomposite materials using the vinyl ester resin asmatrix and carbon nanotubes as reinforcement was bymechanical stirring. After the addition of carbonnanotubes into polymer matrix has been done thehomogenization of the mixture by magnetic stirring at

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600 rpm for one hour. After the mixture has beendegassed using a vacuum pump, has been added themethyl ethyl ketone peroxide as catalyst, to start thepolymerization process. The mixture was then

homogenized at 600 rpm for 5 minutes and degassedagain. The materials thus obtained has been moldedand placed into an oven for 8 hours at 80 oC tocomplete the polymerization process.

Table 1. Properties of carbon nanotubes

Carbonnanotubes type

Purity

[daN/mm2]

Density

[daN/mm2]

Outerdiameter

[nm]

Innerdiameter

[nm]

Length

[µm]

Specificsurface[m2/g]

SWCNTs >90 2.1 1-2 0.8-1.6 5-30 407MWCNTs >95 2.1 8-15 3-5 10-50 233

Three specimens with round cross-section shapewith diameter of 5 mm and length of 150 mm hasbeen obtained by this method for all of the compositematerials studied. All the nanocomposite materialsalong with the neat vinyl ester resin were tested withTeraOhm 5 kV tester (Fig. 1). In Figure 2 is presenteda picture with the position of the tester electrodesduring the measurement.

Fig. 1. TeraOhm 5 kV tester

Fig. 2. The position of electrodes during tests


The electrical conductivity results for materialstested in this study are synthesized in the followinggraphs. The graphs show the calculated mean valuesof conductivity for the vinyl ester / CNTs composites.

Fig. 3. Electrical conductivity of vinyl ester/CNTs composites

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In Figure 3 are represented together the resultsof electrical conductivity for the two type of carbonfiller based vinyl ester nanocomposite. For the 0.10weight percentage of filler content, the conductivity isalmost the same for the single and multi-wall carbonnanotubes/vinyl ester composite. In the case of 0.15

wt.% filler content, the value of the conductivityincrease of about 200% for the multi wallnanocomposite compared with single wall / vinylester composite. The difference became of severalorders of magnitude for 0.20 wt.% filler content.

a) b)

Fig. 4. The tendency of electrical conductivity of nanocomposite of vinyl ester filled with differentweight percentage (0 wt.%, 0.10 wt.%, 0.15 wt.% and 0.20 wt.%) of : a) single wall carbon nanotubes

and b) multi wall carbon nanotubes

The filler content influence over the electricalproperties for vinyl ester polymer matrix isrepresented in figure 4. It is observed almost nodifference between 0.10 wt. % SWCNTs fillercontent nanocomposite and the neat vinyl ester (0wt.% filler) electrical conductivity results. Theaddition of 0.15wt% and 0.20 wt.% of single wallcarbon nanotube increase the electrical conductivitywith approximately 14% and 27 % respectively. Theincreasing of electrical conductivity for addition ofSWCNTs till the 0.20 wt.% content brings almost nochanges in the insulating characters of the vinyl esterpolymer matrix. In the case of multi wall carbonnanotubes, an increase of 18% of electricalconductivity has been achieved for 0.10 wt.%content, compared with 0 wt.% of filler. Theenhancement of several orders of magnitude ofelectrical conductivity has been obtained for above0.15% weight percentage level content of multi wallcarbon nanotubes /vinyl ester composite.

4. Conclusions

Carbon nanotubes have already demonstratedtheir capability as fillers in multiples multifunctionalnanocomposites. For electrical properties animportant factor is the percolation threshold linkedclosely by the dispersion of the nanoparticle in vinylester matrix.

By the experimentally results, multi wall carbonnanotubes can be successfully used as filler alongwith vinyl ester polymer as matrix. The observationof an improvement of electrical conductivity byseveral orders of magnitude at very low percolationthreshold could be observed mainly on multiwallcarbon nanotubes for more than 0.15 wt.%. For singlewall carbon nanotubes fillers the results show a slightincreasing for 0.15 wt.% and 0.20 wt.%, concludingthat the percolation threshold for this case was notachieved. The electrical percolation thresholdconcentration were obtained for MWCNTs/vinyl esterfor 0.20 wt. % content of carbon nanotubes.

Acknowledgement

The work of Georgel Chirita was supported byProject SOP HRD /159/1.5/S/138963 – PERFORM.

The work of Alina Cantaragiu has been fundedby the Sectoral Operational Programme HumanResources Development 2007-2013 of the Ministry ofEuropean Funds through the Financial AgreementPOSDRU/159/1.5/S/132397.

References[1]. Gojny K. S., Wuchmann F. H. H. G., Fiedler B., Influence ofdifferent carbon nanotubes on the mechanical properties of epoxymatrix composites, Composites Science and Technology, p. 256-270, 2005.

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[2]. Wernik J. M., Meguid S. A., Recent Developments inMultifunctional Nanocomposites Using Carbon Nanotubes, Appl.Mech. Rev., vol. 63, no. 5, 2010.[3]. Choudhary V., Gupta A., Polymer / Carbon NanotubeNanocomposites, 2001.[4]. Paul D. R., Robeson L. M., Polymer nanotechnology:Nanocomposites, Polymer (Guildf), vol. 49, no. 15, p. 3187-3204,2008.[5]. Battisti A., Skordos A. A., Partridge I. K., Percolationthreshold of carbon nanotubes filled unsaturated polyesters,Compos. Sci. Technol., vol. 70, no. 4, p. 633-637, Apr. 2010.[6]. Spitalsky Z., Tasis D., Papagelis K., Galiotis C., Carbonnanotube-polymer composites: Chemistry, processing, mechanicaland electrical properties, Prog. Polym. Sci., vol. 35, no. 3, p. 357-401, 2010.[7]. Murarescu A. C. M., Dumitru D., Andrei G., Influence ofmwcnt dispersion on electric properties of nanocomposites with

polyester matrix, Ann. DAAM 2011, Proceeding 122 Int. DAAMSymp., vol. 22, no. 1, p. 925-926.[8]. Tjong S. C., Electrical and dielectric behavior of carbonnanotube-filled polymer composites, Woodhead PublishingLimited, 2010.[9]. Thostenson E. T., Ziaee S., Chou T. W., Processing andelectrical properties of carbon nanotube/vinyl esternanocomposites, Compos. Sci. Technol., vol. 69, no. 6, p. 801-804,2009.[10]. Ayatollahi M. R., Shadlou S., Shokrieh M. M.,Chitsazzadeh M., Effect of multi-walled carbon nanotube aspectratio on mechanical and electrical properties of epoxy-basednanocomposites, Polym. Test., vol. 30, no. 5, p. 548-556, 2011.[11]. Yurdakul H., Seyhan A. T., Turan S., Tanoğlu M.,Bauhofer W., Schulte K., Electric field effects on CNTs/vinyl estersuspensions and the resulting electrical and thermal compositeproperties, Compos. Sci. Technol., vol. 70, no. 14, p. 2102-2110,Nov. 2010.

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THE USE OF ULTRASOUND IN TREATMENT PROCESS OFWASTEWATER. A REVIEW

Nicoleta MATEI*, Dan SCARPETE”Dunarea de Jos” University of Galati, Romania


ABSTRACT

In this paper, different types of ultrasound devices for treatment process ofwastewater are presented. The use of ultrasound in treatment processes is a methodof perspective, an alternative to conventional methods. This technique is based oncavitation phenomenon that occurs in liquids at ultrasonic irradiation and it is usedto enhance or ensure the processes of heat and mass transfer. Some of the mainadvantages of using ultrasound, namely low consumption of additional material orenergy, are presented in this paper. The categories of the ultrasonic transmittersdistinguished on the basis of the principle underlying the generation of acousticwaves are described.

KEYWORDS: ultrasound, ultrasonic frequency, cavitation, wastewatertreatment

1. Introduction

Ultrasound has proved to be effective in manyprocesses common in the chemical industry toimprove dewatering and drying materials, enhancefiltration, to assist heat transfer, to degas liquids, toaccelerate extraction processes, to degrade chemicalcontaminants in water and to enhance processeswhere diffusion takes place [1]. The reason whyultrasound power can produce chemical and physicaleffects is due to the phenomenon of acousticcavitation [2]. In most liquids, cavitation is initiatedby excitation of preexisting microbubbles or otherinhomogeneities in the fluid such as suspendedparticles or gas bubble nuclei [3]. Acoustic cavitation,involves the formation and subsequent collapse ofmicro-bubbles from the acoustical wave inducedcompression/ rarefaction [4].

The main driving mechanism in the degradationof pollutants using cavitation is the generation andsubsequent attack of the free radicals though some ofthe reactions have been explained more suitably onthe basis of hot-spot theory (localized generation ofextreme conditions of temperature and pressure) [5].

Upon collapsing, each of the bubble would actas a hotspot, generating an unusual mechanism forhigh-energy chemical reactions to increase thetemperature and pressure up to 5000 K and 500 atm,respectively, and cooling rate as fast as 109 K/s(Figure 1) [7, 8]. There are three potential reactionzones in sonochemistry [9, 10] i.e. inside of thecavitation bubble, interfacial liquid region betweencavitation bubbles and bulk liquid, and in the bulksolution.

bubbleforms

bubble growsin successive cycles

reachesunstable size

5000 K

undergoescollapse

Fig. 1. Cavitation bubble formation, growth and collapse [6]

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A representation of the pilot-scale equipmentsbased on acoustic cavitations is shown in Figure 2[11]. According to Gogate et al. (2004) theequipments with higher dissipation area give largerenergy efficiency at similar levels of the supplied

input energy. Also, use of equipments based onmultiple frequencies (multiple transducers) has beenreported to be more beneficial as compared to theequipments based on a single frequency [11].

Generator

Reaction mixture

Ultrasonic horn

Cooling water-inCooling water-out

Thermocouple

Transducers

Cooling pipe

25 kHz 40 kHz

Dual frequency flow cell

Ultrasonic bath

Pollutant

Ultrasonic bath

Transducers

Quartz tube

Effluent

T1 T2T6

T5T4

T3

UltrasoundtransducersQuartz tube

Triple frequency flow cell

Fig. 2. Schematic representation of the equipments based on acoustic cavitations [11]

Nowadays, there are numerous constructivetypes of acoustic emitters, used in the treatmentprocess of wastewater. The most often used are theelectromechanical ultrasound generators, relying onpiezoelectricity [12-15] and magnetostriction phenol-mena [16-19]. There are also several applications ofsonic mechanical generators [20-26]. Therefore, inthis brief review some experimental achievementsover the use of different ultrasonic generators fortreatment process of wastewater are presented.

2. Wastewater treatment by piezoelectricgenerators

The basis for the present-day generation ofultrasound was established as far back as 1880 withthe discovery of the piezoelectric effect by the Curies[27, 28].

Certain materials will generate an electriccharge when subjected to a mechanical stress, andchange its dimensions when an electric field isapplied across the material. These are known respecti-vely as the direct and the inverse piezoelectric effect[29]. The effect is observed in a variety of materials,

such as quartz, dry bone, polyvinylindene fluoride[30].

The ultrasonic transducers based on the inversepiezoelectric effect, are relying on some materialsresponse to the application of an electrical potentialacross opposite faces, with a small change indimensions [28]. Operation of the piezoelectricgenerator is based on the property usually of a quartzcrystal to deform in the electric field.

The transducer, typically an assembly comprisedof a series of aluminum blocks or discs andelectrically active piezoelectric elements in a“sandwich” configuration, acts as a mechanicaltransformer and “rings” much like a bell at itsresonant frequency when suitably excited by thedriving piezoelectric element [31]. The schematicrepresentation of this type of transducer is shown inFigure 3, where: 1-screw or pin settings (gripping) totransmitter; 2, 5-blocks of metal (eg. aluminum, iron,brass); 3, 4-piezoelectric ceramic plates (cylindrical,annular).

Considering that sonochemistry occurs in closevicinity to the ultrasonic transducer, where theacoustic cavitation activity is relatively high [33], themost applications of ultrasound are performed

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laboratory-scale [34] by the use of ultrasonictransducers based on the invers of piezoelectric effect.From the reverse piezoelectric effect, the conversionof electrical to mechanical energy is carried out bythe ultrasonic transducer, enabling the formation,growth and collapse of transitory cavitation bubblesin the sonified liquid [8, 35]. Important physicalproperties for a piezoelectric ceramic used as a driverfor high amplitude oscillations are (1) A high Curietemperature, (2) a low dissipation factor, and (3) ahigh ‘‘d’’ constant. Low losses result in less heatingof the ceramic, thus prolonging its lifetime ofoperation. The ‘‘d’’ constant is the ratio of themechanical strain produced from an appliedelectromagnetic field [36].

1

2

3

4

5

~

Fig. 3. Construction of sandwich typepiezoelectric ceramic transducer [32]

Spreading area of cavitational influence (thezone of developed cavitation) is limited by dampingof spread vibrations in viscous liquids or change ofwave resistance in cavitating liquid (practically up towave resistance in gas media) it limits the output ofultrasonic vibration energy from irradiator [14].

Some of the numerous experimentalachievements using piezoelectric transducers areshown below. It should be noted that the majority ofthe work using this type of transducers is on alaboratory scale. Wenjun et al. [4] proposed a facilitywith ultrasonic transducer based on the piezoelectriceffect. Experiments have allowed the removal ofammonia nitrogen and of two other organic pollutants(hydrazine and urea) from the simulated ammoniawastewater, up to 90%. The treatment conditionsvaried depending on the treatment type (intermittentor continuous), the pH variation and the treatmenttime. Matouq et al. used a piezoelectric transducer toremove pesticides from simulated wastewater. Theexperiment succeeded to remove the contaminant in a70% ratio [37]. In paper [38], ultrasonic irradiationwas carried out with a high-intensity ultrasonic probesystem to remove chlorpyrifos and diazinon inaqueous solution. The two pesticides were removedfor up to 55%. Young K. studied the decompositionof monochlorphenols in paper [39] by sonication of550 W output power and 20 kHz frequency. After 6

hours of reaction time, more than 80% ofmonochlorophenols were decomposed forexperiments conducted in aqueous solution of pH 3[39]. There should also be noted the promising resultsobtained for the formic acid degradation processusing ultrasound proposed by [40]. The optimaloperating volume was set at 300 ml, at differentinitial concentrations and by the use of additionalmechanical agitation, with a 40 W constant suppliedpower and 590 kHz constant frequency of irradiation.

3. Wastewater treatment bymagnetostrictive generators

Operation of the magnetostrictive generator isbased on the fact that some ferromagnetic substanceschange size at magnetization. If these substances aredisposed in an alternating magnetic field, they willstart to oscillate, in which case they can becomesources of ultrasound. Such as piezoelectricgenerator, oscillating plates sizes need to be chosenso that their own frequency coincides with thefrequency of the excitation (electric or magneticfrequency field), since they work in resonant mode.Magnetostriction occurs in the most ferromagneticmaterials, but among them the rare-earth alloyTerfenol–D (Tb0.3Dy0.7Fe1.9) presents, at roomtemperature, the best compromise between a largemagnetostrain and a low magnetic field [41]. Figure 4shows the cross section of a prototypical Terfenol-Dmagnetostrictive transducer, in which the generatedstrains and forces are sufficiently large to proveadvantageous in transducer design [42].

For magnetostrictive materials, due to themagnetomechanical effect, the change inmagnetization along the stress direction can beproduced by the stress, leading to the conversion ofthe mechanical energy into electric energy [17, 43].

Magnetostrictive transducers are inherentlymore rugged [44] and better suited for industrial use[19].

The highest reasonable frequency achievable ina magnetostrictive transducer is around 30 kHz. [45].Magnetostrictive systems rely on the doubleconversion of electrical to magnetic energy and thenfrom magnetic to mechanical to produce the soundwave. Magnetic systems are usually less than 50%efficient due to the energy lost in heating of the coilsand the effects of magnetic hysteresis. Additionally,the generators, even if well tuned, are generally nomore than 70% efficient [46].

Thoma et al. used a magnetostrictive system todegrade both benzene and toluene in a continuousstirred tank reactor [19]. They obtained gooddecontamination results by the use of 22 litersreaction vessel consisting of opposing diaphragmplates operating at 16 kHz and 20 kHz [19].

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Permanent Magnet

CompressionBolt

Wound Wire Solenoid

Terfenol-D Rod

SpringWasher

EndMass

Direction ofRod Motion

Fig. 4. Cross section of a prototypical Terfenol-D magnetostrictive transducer [42]

4. Wastewater treatment by mechanicalgenerators

Mechanical transducers can be both gas drivenand liquid driven [6]. The mechanical air-jetgenerator was proposed by Hartmann in order to treatliquids both by means of ultrasonic and bubbling[47]. The air-jet generators are mechanical deviceswith no moving parts that generate ultrasonic pressurewaves with low frequency (10÷30 kHz), based on thenonstationary phenomena [48] occurring in the flowof high-speed jets of gas. The technological processof aeration/bubbling serves to enhance the diffusionof oxygen into the water. Figure 5 shows one of themany constructive schemes of this type of generators,where: 1-nozzle; 2-resonator; 3-stem; 4-the jet firstcavitational nucleus; 5-acoustic oscillations of thegenerator; φa-nozzle edge angle; ψR - resonator edgeangle.

air

1

5

5

4

3

aR

3 2

Fig. 5. Oscillations occurrence in the sonicgenerator [49]

The sonic gasodynamic generator proved to be asolution in water purification technology arising fromaquaculture [50, 51], and also in some applications of

liquids from food industry [52, 53].In paper [54] the used sonic air-jet axial

revealed a complete turbidity reduction fromwastewater, after 40 seconds of treatment, with 40NTU initial concentration. Paper [55] shows thereduction of ammonia concentration from industrialammonia water, using the air-jet generator calculatedby the method [56].

Conclusions

Sonochemical degradation seems to be apromising technology for degradation of severalorganic compounds.

The present study shows the operationalpossibilities of the two types of existing ultrasonictransducers, namely mechanical andelectromechanical (piezoelectric andmagnetostrictive). Piezoelectric transducers utilize thepiezoelectric property of a material to convertelectrical energy directly into mechanical energy.Magnetostrictive transducers utilize themagnetostrictive property of a material to convert theenergy in a magnetic field into mechanical energy.Mechanical transducers utilize mainly the air asworking agent to produce both low frequencyultrasound and bubbling. All constructive types ofultrasonic transducers have promising results, but dueto the large range of frequencies and power supply,the piezoelectric based ones are the most commonlyused. It should be noted that the ultrasonictechnology, regardless the type of transducer, is gene-rally used on laboratory scale, the magnetostrictivebased being the best suited for industrial use.

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Acknowledgements

The work has been funded by the SectoralOperational Programme Human ResourcesDevelopment 2007-2013 of the Ministry of EuropeanFunds through the Financial AgreementPOSDRU/159/1.5/S/132397.

References[1]. Gerardo L. et al., Increasing stability and transport efficiencyof supported liquid membranes through a novel ultrasound-assistedpreparation method. Its application to cobalt(II) removal,Ultrasonics Sonochemistry, 20, 2013 p. 650-654.[2]. Naddeo V. et al., Wastewater disinfection by combination ofultrasound and ultraviolet irradiation, Journal of HazardousMaterials, 168, 2009, p. 925-929.[3]. H. Hung et al., Kinetics and mechanism of the sonolyticdegradation of chlorinated hydrocarbons: frequency effects, J.Phys. Chem., A. 103(15), 1999, p. 2734-2739.[4]. L. Wenjun et al., Removal of Organic Matter and AmmoniaNitrogen in Azodicarbonamide Wastewater by a Combination ofPower Ultrasound Radiation and Hydrogen Peroxide, ChineseJournal of Chem., 20, 2012, p. 754-759.[5]. Parag R. Gogate, Treatment of wastewater streams containingphenolic compounds using hybrid techniques based on cavitation:A review of the current status and the way forward, UltrasonicsSonochemistry, 15, 2008, p. 1–15.[6]. P. Chowdhury et al., Sonochemical degradation ofchlorinated organic compounds, phenolic compounds and organicdyes–A review, Science of total environ., 407, 2009, p. 2474-2492.[7]. Suslick K.S., Sonochemistry, Science, 247, 1990, p. 1438-1445.[8]. Wu T. et al., Advances in Ultrasound Technology forEnvironmental Remediation, ISBN 978-94-007-5532-1, 2013.[9]. Y. G. Adewuyi, Sonochemistry: environmental science andengineering applications, Ind. Eng. Chem. Res., 40(22), 2001, p.4681-4715.[10]. Pang Y. L. et al., Review on sonochemical methods in thepresence of catalysts and chemical additives for treatment oforganic pollutants in wastewater, Desalination, 277, 2011, p. 1-14.[11]. P. R. Gogate et al., A review of imperative technologies forwastewater treatment I: oxidation technologies at ambientconditions, Advances in Environmental Research, 8, 2004, p. 501-551.[12]. Songlin Wang et al., Removal of organic matter andammonia nitrogen from landfill leachate by ultrasound, UltrasonicsSonochemistry, 15, 2008, p. 933-937.[13]. Matouq M. A.-D., Al-Anber Z. A., The application of highfrequency ultrasound waves to remove ammonia from simulatedindustrial wastewater, Ultrasonics Sonochemistry, 14, 2007, p.393-397.[14]. Vladimir N. Khmelev et al., Development and Application ofPiezoelectric Transducer with the Enlarged Radiation Surface forWastewater Treatment, 10th International Conference And SeminarEdm'2009, Section Iv, July 1-6, Erlagol.[15]. Nygren M. W., Finite Element Modeling of PiezoelectricUltrasonic Transducers, Master of Science in Electronics, 2011.[16]. Cavill S. A. et al., Electrical control of magnetic reversalprocesses in magnetostrictive structures, Applied Physics Letters,102, 2013.[17]. Zhang H., Power generation transducer frommagnetostrictive materials, Applied Physics Letters, 98, 2011.[18]. Albach T. S. et al., Sound Generation Using aMagnetostrictive Microactuator, Journal of Applied Physics, 109,2011.[19]. G. Thoma, M. Gleason, Sonochemical Treatment ofBenzene/Toluene Contaminated Wastewater, EnvironmentalProgress, 17, 1998, p. 154-160.

[20]. Hartmann J. et al., New Investigation on the Air JetGenerator for Acoustic Waves, Kongelige Danske VidenskabernesSelskab Matematisk-Fysiske Meddelelser, 7, 1926.[21]. Hartmann J. et al., A New Acoustic Generator. The Air-Jet-Generator, Journal of Scientific Instruments, 4, 1927, p. 101-111.[22]. Hartmann J., Construction, Performance, and Design of theAcoustic Air-Jet Generator, Journal of Scientific Instruments, 16,1939, p. 140-149.[23]. Hartmann J. et al., Synchronization of Air-Jet Generatorswith an Appendix on the Stem Generator, Kongelige DanskeVidenskabernes Selskab Matematisk-Fysiske Meddelelser, 26,1951.[24]. Balan G. et al., The sonic technologies, Quatrieme EditionDu Colloque Francophone en Energie, Environnement, Economieet Thermo-dynamique COFRET’08, Nantes, France, 2008, p. 20-29.[25]. Stefan A., The research of the physico-chemical parametersof water treated with sonic technology, Journal of science and arts,Targoviste, 12, 2010, p. 79-82.[26]. Matei N., Sonic treatment effect on industrial ammonia waterdecontamination, The Annals of "Dunarea de Jos” University ofGalati, ISSN 1221-4558, 2013, p. 62-67.[27]. Gelate P, Hodnett M, Zeqiri B., Supporting infrastructureand early measurements, National Physical Laboratory Report.Teddington. Middlesex, UK, 2000, p. 2-11.[28]. ***, Application of Ultrasonic Technology for Water andWastewater Treatment.[29]. R. S. C. Cobbold, Foundations of biomedical ultrasound,Oxford University Press, 2006.[30]. Nygren M., Finite Element Modeling of PiezoelectricUltrasonic Transducers, Master of Science in Electronics,Norwegian University of Science and Technology, 2011.[31]. F. J. Fuchs et al., Application of Multiple FrequencyUltrasonics, Blackstone ultrasonics, 716, 2005, p. 665-2340.[32]. Fabijanski P. et al., Modeling and Identification ofParameters the Piezoelectric Transducers in Ultrasonic Systems,Advances in Ceramics - Electric and Magnetic Ceramics,Bioceramics, Ceramics and Environment, ISBN 978-953-307-350-7, InTech, 2011.[33]. Gogate P. R. et al., Mapping of sonochemical reactors:review, analysis, and experimental verification, AIChE J. 48, 2002,p. 1542-1560.[34]. Sostaric J. Z. et al., Advancement of high power ultrasoundtechnology for the destruction of surface active waterbornecontaminants, Ultrasonics Sonochemistry, 17, 2010, p. 1021-1026.[35]. Rochebrochard S. et al., Sonochemical efficiencydependence on liquid height and frequency in an improvedsonochemical reactor, Ultrasonics Sonochemistry, 19, 2012, p.280-285.[36]. ***, Design and calibration of a single-transducer variable-frequency sonication system.[37]. Matouq M. A. et al., Degradation of dissolved diazinonpesticide in water using the high frequency of ultrasound wave,Ultrasonics Sonochemistry, 15, 2008, p. 869-874.[38]. Zhang Y. et al., The degradation of chlorpyrifos anddiazinon in aqueous solution by ultrasonic irradiation: Effect ofparameters and degradation pathway, Chemosphere, 82, 2011, p.1109-1115.[39]. Young K. et al., Decomposition of monochlorophenols bysonolysis in aqueous solution, Journal of EnvironmentalEngineering and Management, Vol. 16, No. 4, 2006, p. 259-265.[40]. Gogate P. R. et al., Destruction of formic acid using highfrequency cup horn reactor, Water research, 40, 2006, p. 1697-1705.[41]. Claeyssen F. et al., Actuators, transducers and motors basedon giant magnetostrictive materials, Journal of Alloys andCompouns, 258, 1997, p. 61-73.[42]. Dapino M. et al., A structural-magnetic strain model formagnetostrictive transducers, J of Magnetics, Vol. 36, Issue 3, p.545-556, ISSN 0018-9464.[43]. Cullity B.D. et al., Introduction to Magnetic Materials,Wiley, New Jersey, 2009, p. 258.

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[44]. Petrier C. et al., Characteristics of PentachlorophenateDegradation in Aqueous Solution by Means of Ultrasound,Environ. Sci. Technol., 26(8), 1992, p. 1639-1642.[45]. Pedeflous F., Ultrasonic Transducers: Piezoelectric vs.Magnetostrictive, http://blog.omegasonics.com/archives, 2014.[46]. ***, Magnetostrictive Versus Piezoelectric Transducers ForPower Ultrasonic Applications, www.ctgclean.com.[47]. Serban A., Utilizarea generatoarelor sonice gazodinamice inprocesele tehnologice de epurare a apelor uzate, Ed. Zigotto,Galati, ISBN 978-606-8303-57-4, 2009.[48]. Magheţi I., Savu M., Teoria şi practica vibraţiilor mecanice,Ed. Didactică şi Pedagogică, Bucureşti, ISBN 978-973-30-1969-9,2007.[49]. Bălan G., Principii de elaborare a sistemelor tehnice cuinjectoare sonice, Teza de doctor Habilitat, U.T.M., Chişinău,2001.[50]. Bălan G. et al., Acoustical research of the sonic air-jet radialgenerator, Analele Universităţii Maritime, Anul IX, Vol. 11, p.293-298, ISSN 1582-3601, Constanţa, 2008.[51]. Graur I. et al., Sonic activation of water derived fromaquaculture and microbiological effect, Poss. Conf. Int. „Moderntechnologies in the food industry - 2012”, Chisinau, 2012.

[52]. Graur I. et al., Effects of Air-Jet Stem Generator andUP400S Treatment on Vitamin C, Colour and pH of GrapefruitJuice, International Journal of Engineering Science and InnovativeTechnology (IJESIT), Vol. 2, Issue 5, 2013, p. 180-184.[53]. Bălan V., Balan G., The sonic technology in the beerindustry, The Annual Symposium of the Institute of SolidMechanics SISOM 2012 and Session of the Commission ofAcoustics, ISSN: 0035-4074, Bucharest, 2012.[55]. Stefan A. et al., The physical and chemical indicators at theultrasound treatment of water with poly aluminium chloride,Annals of Dunarea de Jos University of Galati, Fascicle II, ISSN2067-2071, 2011, p. 164-170.[55]. Matei N., Sonic treatment effect on industrial ammonia waterdecontamination, Annals of Dunarea de Jos University of Galati,Fascicle IV, ISSN 1221-4558, 2013, p. 62-67.[56]. Bălan G. et al., The sonic technologies, Quatrieme EditionDu Colloque Francophone en Energie, Environnement, Economieet Thermo-dynamique COFRET’08, Nantes, France, 2008, p. 20-29.

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SOLUTIONS FOR DIAGNOSING FAULTS IN ASYNCHRONOUSMOTOR STATOR THROUGH AN FERROFLUID INSTALLATION

Ovidiu-Magdin ȚANȚA1,2,*, Adrian-Neculai ROMANESCU1,Mihai CENUȘĂ1, Ilie NIȚAN1, Mihaela POIENAR1

1”Ștefan cel Mare” University of Suceava, Faculty of Electrical Engineering and Computer Science,str. Universităţii, nr. 13, 720229, Suceava, Romania

2 E.ON Distribuție România, str. Piaţa Trandafirilor, nr. 21, cod 540049, Târgu Mureş, România*Corresponding author


ABSTRACT

Due to reliability, robustness and multitude of variants of motors, they arecommonly used electric machines in industrial drives. However, although they arerelatively simple equipment, asynchronous motors can sometimes malfunction dueto various causes. Whether it is a problem in the supply network (lack of a phase,wrong phase sequence, different phase voltages etc.) or about an internal fault ofstator winding (winding interrupted, reversing the winding beginning with the end,shorted coils, etc.) motors diagnosis was a constant concern in the art. Although anumber of classic solutions are known, generally dedicated to type of defectassumed, this paper proposes a completely new approach applicable to all types ofanomalies that may occur in the functioning of these engines.

KEYWORDS: ferrofluid, rotating magnetic field, asynchronous motor

1. Introduction

The magnetic fields study and the opportunitiesto highlight the load line were constant concerns forthe EMAD research team from the Ștefan cel MareUniversity of Suceava. During the experiments wereobtained a series of images by exposing the content ofa cylindrical container on a continuous magnetic fieldaction. These images were named “CEUS figures”(Electrotechnical Department of the University ofSuceava), the acronym being suggested byacademician Emanuel Diaconescu in a scientificsession.

Using CEUS figures, were made a series ofdevices to diagnose defects that may appear at themachines. Because of the multitude of causes thatlead to machine malfunction, it has been tried toidentify some types of defects. For example, thedefects in the driven magnetic circuits have asimmediate effect strong local heating, which leads topremature aging of insulation. However, the mostoften defects are located in the stator winding, andmanifests as: strong heating, stiff starting, anomalousnoise, absorbed currents unequal on phases,inappropriate rotational frequency and insufficientpower.

2. Apparatus for asynchronous motorsdefects diagnosis

The experimental model used to obtain theCEUS figures is constituted, mainly, through thestator of a three-phase asynchronous motor whoserotor has been replaced by a sample container madeof an insulating material, partially filled withferrofluid. To highlight the ferrofluid movement andfor the CEUS figures caption, on the fluid surfacewas interspersed with bronze ultrafine powder, thathas indicator role.

The unfolded arrangement type of theexperimental apparatus stator winding is shownbelow in Figure 1 and Figure 2.

The CEUS figures having the form shown inFigure 2 were obtained by applying the continuousmagnetic field produced by the stator of theasynchronous motor over the ferrofluid from theinsulating cylindrical container.

To correlate the images with the direction of thefield lines was used a pointer located in the center ofthe stator, which deviate or rotates in the direction ofthe rotating magnetic fields when the stand issupplied.

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U1 V2 V1 W2 W1 U2

Fig. 1 Stator winding schema used in the arrangement

0

315

270

225

180

135

90

45

124

23

22

21

2019

18

17

16

15

14 1312

11

10

9

87

6

5

4

3

2

U2 V2 W2

U1 V1 W1

R S T

Fig. 2 The windings disposal on the three phases unto the ferrofluid container

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The entire experimental study comprises 31distinct abnormal operating situations of theasynchronous motor for: defects in supply network,flawed terminal connection or stator windingsinternal defects. Due to limited space, this paperpresents only a small part of the result, respectivelythe typical images of the following situations:

- engine supplied in delta connection with aphase missing in the electric-power-supply-network;

- engine supplied in Y connection with a phasemissing in the electric-power-supply-network;

- engine supplied in delta connection with ainterrupted winding in the stator coil;

- engine supplied in Y connection whereat wasreversed the winding beginning with the end ;

- engine supplied in “V” connection.

3. The diagnosis of asynchronous motorsmalfunctioning

The CEUS figures for various abnormal motiontypes of the asynchronous motor are shown in theimages presented below:

Fig. 3 Engine supplied in delta connection with a phase missing in the electric-power-supply-network

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Fig. 4 Engine supplied in Y connection with a phase missing in the electric-power-supply-network

Fig. 5 Engine supplied in delta connection with a interrupted winding in the stator coil

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Fig. 6 Engine supplied in Y connection whereat was reversed the winding beginning with the end

Fig. 7 Engine supplied in “V” connection

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4. Conclusion

The rotating magnetic field sense of rotationproduced by the analyzed stator is given by the phasesequence. The ferrofluid sense of rotation is inverselyas the rotating magnetic field.

During the research has been developed amethod to highlight the movement, by sprinkling onthe ferrofluid surface with a powder that has indicatorrole.

To obtain the ferrofluid motion pictures atlow rotational speed, it was used a high performancecamera with a high exposure time.

The CEUS figures obtained are true stampsthat can provide information for malfunctiondiagnosis of an asynchronous motor stator. Whether itis a problem in the supply network, a flawed terminalconnection or stator windings internal defects, theimages may indicate the defect character.

References[1]. Bălă C., Fetița A., Lefter V., Cartea bobinatorului de mașinielectrice, București: Editura Tehnică, 1967.[2]. Bogatu V., Probe și verificări ale mașinilor electrice,Bucureşti: Editura Tehnică, 1968.[3]. Buzduga C., Contribuţii la extinderea aplicaţiilorferofluidelor şi pulberilor feromagnetice în electrotehnică, Teză dedoctorat. Suceava: Universitatea „Ştefan cel Mare”, Facultatea deInginerie Electrică şi Ştiinţa Calculatoarelor, 2012.[4]. Luca E., Călugăru Gh., Bădescu R., Cotae C., Bădescu V.,Ferofluidele şi aplicaţiile lor în industrie, Bucureşti: EdituraTehnică, 1978.[5]. Negru M. B., Contribuţii privind extinderea aplicaţiilorferofluidelor şi a pulberilor feromagnetice în electrotehnică, Tezăde doctorat. Suceava: Universitatea „Ştefan cel Mare”, Facultateade Inginerie Electrică şi Ştiinţa Calculatoarelor, 2012.[6]. Răduți C., Nicolescu E., Mașini electrice rotative fabricate înRomânia, Bucureşti: Editura Tehnică, 1981.[7]. Vrînceanu Gh., Schnell Fl., Stabilirea defectelor îninstalațiile electrice de joasă tensiune, Bucureşti: Editura Tehnică,1976.

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THE STRUCTURAL DESIGN IMPROVEMENTOF A TWIN-HULL SHIP

Adrian PRESURA, Ionel CHIRICA, Elena-Felicia BEZNEA“Dunarea de Jos” University of Galati, Faculty of Engineering,

Domneasca Street, No. 47, 800008, Galati, Romaniae-mails: [email protected], [email protected], [email protected]

ABSTRACT

The paper is focused on the strength analysis of the structure of twin-hullships, particularly a passenger catamaran. The catamarans have some advantagesagainst conventional monohulls: the larger deck area and cargo volume, bettertransverse stability and in general improved behavior in waves. But due to need oflarge open spaces, for passenger/car ferry ships and having as major restriction thestructure weight, one of the problems raised during designing of the catamaranstructure is the determination of the effectiveness of deck structure. The FiniteElement Method was used for examining the behavior of different deck structuredesigns in order determine the solution which accomplish better designing criteriaregarding allowable stress and deformations and total weight . The results of thisanalysis shows that, making a proper structural analysis and using lightweightmaterials, important gains for ship owners and for environment protections can beachieved.

KEYWORDS: catamarans, deck structures, FEM analysis, lightweightmaterials

1. Introduction

This study is based on a new concept of inlandnavigation catamaran for 150 passengers, having 28.5m length, 7.8 m beam, 1 m maximum hull draft and amaximum speed of 25 km/h. Considering the smalldraft and relatively high speed the total light shipweight must remain as low as possible so the materialused for construction of hulls, main deck andsuperstructure deck is aluminium or glass reinforcedplastics (GRP).

The craft has a closed salon for passengers onmain deck and an open salon on upper deck, whichadds significant load on upper deck structure.

In addition this particular design involves theowner request for availability of different deckarrangements without any hull structuremodifications.

Consequently the number of pillars or othersimilar supporting structures was reduced tominimum or even none, in order to ensure maximumflexibility in deck arrangements, thus increasing thespan of primary supporting members.

In this research were analyzed different structuresolutions for upper deck, in order to fulfill, as far as

practicable, with the above designing restriction andother criteria, presented later.

Fig. 1. Ship transverse section

2. Designing criteria and restrictions

In order to make an qualitative assessment ofdifferent structure designs, several designing criteriaand also some objective restrictions were considered.

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Designing criteria:

i) Permissible stress was considered forAluminium Alloy 6005A-T6 as follows:

- primary stiffenersσlocam τlocam σVM76[N/mm2] 54[N/mm2] 86[N/mm2]

- ordinay stiffenersσlocam τlocam70[N/mm2] 49[N/mm2]

σlocam – local permissible bending stressτlocam – local permissible shear stress σVM – allowable equivalent stress

In order to reduce the weight, one aim was toavoid oversizing of structure elements. Therefore thegeometric characteristics of primary and ordinarystiffeners were varied so to achieve stresses as closeas possible to the permissible values, consideringnevertheless a safety margin of 80% from the abovementioned values.

ii) Maximum allowable deflection of deckstructure = 8 mm, was considered L/500, where Lwas taken as spacing between the transverse primarysupporting members (maximum distance of 4 m).This limit of deflection is related to on board personscomfort and is usually meet in civil constructionregulations.

iii) Maximum deflection of windows framing =5mm, was considered not to exceed 1/175 of theglass smaller edge length (windows dimensions 2 m x1 m), considered according to United States buildingregulations (IBC 2006 Section 2403.3) as to ensurethe integrity of the windows.

Designing restrictions:

i) Weight of the structure was optimized, as ageneral desideratum in ship building and especiallyfor this catamaran with relatively small displacement(abt. 60 t) and shallow draft (abt. 1 m). In this sense,taking as example 1 t of weight reduction, severaladvantages can be gained for the project:

- more passengers on board 1 t = 10 averagepersons with their luggage;

- more fuel oil and/or other stores on board,meaning greater flexibility in operation;

- less hull resistance because of draft reduction.

ii) Ventilation ducts required for 150 personssalon needed a minimum height of 0.1 m clearance inorder to ensure a good distribution of air and a

reduced level of noise. In consequence the upper deckstiffeners had either to permit such large cutouts forpassage of ventilation or to have minimum over allheight so as to permit the installation of ventilationduct underneath (Figure 2).

Fig. 2. Installation of ventilation ducts

iii) Structure arrangement was anotherrestriction, considering the owner request to haveminimum/none intermediate supporting members, atthe level of main and upper decks. In this way it willbe possible to rearrange the spaces, for example froma hidrobus/economy type for 100/150 passengers to apleasure/business type for 60 passengers (Figure 3).

Fig. 3. Deck arrangement

3. Assumptions and methods

In the structural analysis developed further thefollowing simplifying assumption was considered: themain deck (strength deck) of catamaran is rigid andthe transverse bulkheads enclosing the aft and foreends of upper deck structure are also rigid.

Boundary condition (Figure 4):- fixed displacement and fixed rotation

constraints at the level of main deck (Ux, Uy,Uz, Rx, Ry, Rz);

- fixed displacement and fixed rotationconstraints at transverse sections limiting demodel in longitudinal direction (Ux, Uy, Uz,Rx, Rz).

Design loads:- lateral pressure on sides of superstructure ps =

2.3 kN/m2, according to “NR217-Rules forInland Navigation Vessels – PartB – Ch. 6,Sec 4”;

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- pressure due to load carried on deck pd = 5kN/m2, according to “NR217-Rules for InlandNavigation Vessels – PartB – Ch. 6, Sec 4”;

- weight of structure above upper deck abt. 1 kNforce at every supporting pillar.

Fig. 4. Boundary conditions

The structural analysis was performed withFinite Element Method, using SHELL 3T elements,average size 0.05 m, COSMOS software and beamelements, NAUTICUS 3D-Beam software.

4. Analysis of different structure designs

The research started from an typical structuredesign, having primary supporting members disposedtransversely at every 2 m and ordinary stiffenersspaced transversely and longitudinally at every 0.5 m.Based on “BV Rules for the Classification of InlandNavigation Vessels” some minimum net thicknesswere calculated for deck plating, web plating ofordinary and primary stiffeners.

Further this typical structure was optimized,considering the equal strength girger principle,looking to lighten those elements with low stressand/or deflection.

Finally a transverse arch structure wasinvestigated aiming to reduce even more the totalweight of the structure.

4.1. Typical structure

In Figure 5 below are shown the elements thatform the structure:

- shell plates 5 mm;- primary supporting members web 220 x 8 mm

and flange 100 x 8 mm;- ordinary stiffeners web 100 x 6 mm and flange

100 x 8 mm;- side bulkheads ordinary stiffeners face plate 70

x 6 mm;- pillars ϕ 130 x 10 mm.The results showed the following situation:- the maximum von Mises stress of 38 N/mm2

(well below the limit of 86 N/mm2) wasreached in primary supporting members asshown in Figure 6;

- deck deflection of 4 mm, in the areas as shownin Figure 7.

Fig. 5. Typical structure details

Totalweight

Max. vonMises stress

Max.displacement

[t] [N/mm2] [mm]4.187 37.7 4.2

Fig. 6. Typical structure-von Mises stress

Fig. 7. Typical structure - displacement

4.2. Typical structure optimized

Based on the above results, some improvementsare possible:

i) reducing and even eliminating the ordinarystiffener flanges 100 x 8 mm, due to low stress level.

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The weight reduction resulted about 0.6 t (14% frominitial weight).

Fig. 8. Typical structure – ordinary stiffenerflange stress

Fig. 9. Typical structure optimized – ordinarystiffener flange stress

ii) reducing the section area of vertical primarysupporting members, due to low stress level. Theweight reduction obtained about 0.175 t (4% frominitial weight).

Fig. 10. Typical structure – von Misses stress inprimary vertical members

Fig. 11. Typical structure optimized– von Missesstress in primary vertical members

Totalweight

Max. vonMises stress

Max.displacement

[t] [N/mm2] [mm]3.412 ≈40 ≈4

Conclusion: The total weight of the initialstructure was reduced with 18%.

4.3. Transverse arch structure

Aiming to reduce the number of pillars and inthe same time keep deck deflection under limits,further below a beam model was used to evaluate theefficiency of a transverse arch frame solution.

Fig. 12. 3D Beam model – arch structure

In Figure 12 below are shown the elements thatform the structure:

- arch transverse beam web 200 x 10 mm;- central longitudinal stiffeners web 300 x 8 mm

and flange 100 x 8 mm;- longitudinal ordinary stiffeners flat plate 50 x 5

mm;- side stiffeners web 200x6mm and flange 50 x 5

mm;- only one line of pillars ϕ 130 x 10 mm.

The results showed the following situation:Total

weightMax. von

Mises stressMax.

displacement[t] [N/mm2] [mm]

3.820 45 5.6

Conclusion: The total weight increased with12% than the typical structure optimized presentedabove but the deflection was similar.

By comparison the same structure, but havingstraight transverse stiffeners, showed significantlyhigher deflection:

- the maximum von Mises stress of 69 N/mm2;- the maximum deck deflection of 8.2 mm.

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Fig. 13. 3D Beam model – straight transversestructure

5. Conclusions

This research underlined two aspects:

i) the weight of a ship structure can beconsiderable decreased, from initial design based on“Rules” dimensioning, using a FEM calculation;

ii) a classical structure solution, like arch design,can be integrated in a ship structure in order to reducethe number of intermediate supporting members.

Acknowledgement

The present research has been supported by ShipDesign Group Galati.

References

[1]. ***, NR217 - Rules for Inland Navigation Vessels, NovemberEdition 2014.[2]. ***, 2008 New York City Building Code, (IBC 2006 Section2403.3).[3]. ***, COSMOS software.[4]. ***, 3D-Beam software.

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CONTRIBUTIONS REGARDING DEVELOPMENT OF NEW TYPESOF SOLAR ACTUATORS

Adrian-Neculai ROMANESCU, Ovidiu-Magdin ȚANȚA, Mihai CENUȘĂ,Ilie NIȚAN, Mihaela POIENAR*

”Ștefan cel Mare” University of Suceava, Faculty of Electrical Engineering and Computer Science,str. Universităţii, nr. 13, 720229, Suceava, Romania


ABSTRACT

The paper presents the authors contributions on the development of solaractuators with bimetallic band and Bourdon tube in the EMAD Research Centre ofUniversity ”Ștefan cel Mare” of Suceava. The solutions and the experimentaldevices are described with their peculiarities and advantages. The paper ends withmain conclusions about testing and practical implementation.

KEYWORDS: bimetallic band, Bourdon tube, actuator

1. General considerations

Within the EMAD Research Center of the USVhave been developed since 1996 a number ofsolutions in heliothermic actuators and motors areamade on the basis of solid heating medium [3].

The solutions relates to rotary actuators andmotors as well as linear actuators with limitedmovement.

Are presented the primary constructive solutionswith the peculiarities and finally, the generalconclusion regarding the experimentation andpractical implementation.

By solid heating medium is meant athermobimetal or a shape memory material after theaction of temperature.

In technical applications the thermobimetals arewidely used because at temperature variation canproduce:

- movement due to deformation;- force due to internal stresses that occur if

external forces oppose producing strain.Both of these effects can be achieved with

thermo bimetals of different forms, such as: hoggingthin bands, U shaped work where the angular aperturevary, twisting contrivance or helical spiral, discswhose bend vary, as it is shown in Figure 1.

Overall technical applications using thecombined effect of force and motion production by aheated thermo bimetal. The two effects are applied insequence or simultaneously. For example, abimetallic band embedded at one termination canoperate as a pawl. By heating the band hogs at the

free point and its moving, proportional to thetemperature, to pawl until comes in contact with itand then the movement ceases in practice. By raisingthe temperature further, appear the internal stressesthat increase in proportion to temperature untilachieve the value necessary to operate the pawl. Thenthe bimetallic piece can close or disclose a contact[3].

a)

b)

c)Fig. 1. Thermobimetallic modules

a) bimetallic arc modeled after a cylindrical helicalpath; b) bimetallic arc modeled after a conical

helical path; c) bimetallic arc curved – preformed in“U” shape [3]

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In that manner numerous constructions, used inelectrotechnics, operate to actuate when limittemperature is reached, as: overload protection relayand temperature controller (thermostat for warmingpad or chamber, flatting mill with regulator, warmers,baking machine, etc.).

Another is the operation of a helical band in theform of an arc, from thermobimetal, that mustovercome the elastic force of an spring. The thermobimetal member through heating, deforms and actswith a force over the spring, compressing it.Increasing the resistance force of the spring, as it iscompressed, proportionally with the extent ofdeformation prevents the thermobimetal movement.The thermobimetal will continuously shift onincreasingly smaller distance, as the spring elasticforce increase, not in proportion with temperaturevariation.

2. Heliothermic mixed actuator withparabolic concentrator

One of the solutions achieved in the EMADResearch Center is the heliothermic mixed actuatorconstituted by a mechanical converter withthermobimetallic band associated with a thermo-mechanical converter with paraffin, both placed in thesolar concentrator focusing point as it is presented inFigures 2 and 3.

The solution is made of a bimetallic band 1,modeled after a spiral arc with several coils,embedded in a paraffin based thermoconductor agent2, contained in a flat cylindrical container 3 sealedand placed through a cannular fastening piece 4 in theparabolic concentrator focusing point 5 fixed in turnby a adjusting bolster with toggle joint 6 on asupporting surface 7. The bimetallic band 1 isanchored to the inner wall of the container 3, and theinner end of the axle with pap which is supported insliding bearing sealed through an insertion. The axlestub is connected through a mechanical thimble 8 to aflexible axle, positioned within the tubular support 4,that actuate the associated mechanism.

To compensate the volume variations, of theagent 2 at the transition from the solid to the liquidphase, under the solar radiation action, it is used anassembly consisting two Bourdon tubes 10 and 10’positioned coaxial and coplanar. Through thecollecting channels 11 and 11’, the Bourdon tubes areclamped to the cylindrical surface of the container 3and are connected, on the same time to thethermoconductor agent 2.

The molten paraffin discharged to the 10 and10’ Bourdon tubes determines, through the pressurecreated, their outwards deformation. In the mannerdescribed the deformation is converted, through a bar

with spool and spring 12 and 12’, in linear drive,transmitted to another two mechanisms.

Fig. 2. Longitudinal section through theheliothermic mixed actuator with parabolic

concentrator [1]

Fig. 3. Transverse section through theheliothermic mixed actuator with parabolic

concentrator [1]

The advantages of the solution are:- increase the number of operable elements;- educed size;- constructive simplicity.

3. Heliothermic mixed actuator with acylindrical – parabolic concentrator

Another solution is shown in figure 4 and ismade through a thermobimetallic converter associatedwith a thermomechanical converter with paraffin andpiston together with a thermomechanical convertorwith paraffin and Bourdon tube.

The heliothermic mixed actuator is constitutedthrough a bimetallic band 1, shaped as a coiled layoutand placed within a tubular container 2 made of brassand closed by a bonnet 2’ sealed through an insertion2”. Inside the tubular container 2, it is placedcoaxially with the bimetallic band 1 athermomechanical converter with paraffin and piston3, fixed to the mentioned bonnet and sealed withanother insertion 3’.

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The container 2 interior is filled with athermoconductor agent 4 constituted from paraffin,which facilitate the heat transmission from thecontainer metallic wall to the two converter elementsrepresented by the thermobimetallic band and thethermomechanical convertor with paraffin andBourdon tube. At the container free tip it is placedanother thermomechanical actuator, with bilateralaction, that is constituted from two Bourdon tube 5and 5’, connected with the container by means of thecollecting canals 6 and 6’.

Fig. 4. Longitudinal section through theheliothermic mixed actuator with cylindrical-

parabolic concentrator [2]

Fig. 5. Transverse section through theheliothermic mixed actuator with cylindrical-

parabolic concentrator [2]

The cylindrical container is exposed to directand reflected solar radiation through a cylindrical-parabolic concentrator 7.

As previously mentioned, within the containerare placed, the thermobimetallic converter and thethermomechanical converter with paraffin and piston.One of the thermobimetallic band tips is fixed to theinner wall of the container 2 by means of a screwsupport 11. The other tip is fixed of a pap 12, whichis integral with a rigid axle 12’ provided in itsextension with a flexible axle 14 which connect thethermobimetallic converter with the driven element,that is not represented in the figure.

The pap 12 is fixed in regard to the container 2through a ball bearing 15, and in relation to thethermomechanical converter trough the ball bearing16 and a pap 17. The Bourdon tube deformation istransmitted to a bar with spool and spring 18 and 18’mounted in a support frame 19.

The system has the advantage of completecapitalization of the effects generated by changing theparaffin state of aggregation: using as heat-transferagent to a complete and fast excitation of thethermobimetallic converter and the thermomechanicalconverter placed coacially within the first; the agentvolume compensation and production of power anddrive through the thermomechanical converter withBourdon tubes.

4. Conclusions

1. The paper presents the authors contributionson the development of solar actuators with bimetallicband and Bourdon tube in the EMAD ResearchCentre of University ”Ștefan cel Mare” of Suceava.

2. One of the solutions achieved in the EMADResearch Center is the heliothermic mixed actuatorconstituted by a mechanical converter withthermobimetallic band associated with a thermo-mechanical converter with paraffin, both placed in asolar concentrator focusing point.

3. Another solution is the heliothermic mixedactuator with cylindrical-parabolic concentrator thatis made through a thermobimetallic converterassociated with a thermomechanical converter withparaffin and piston together with a thermomechanicalconvertor with paraffin and Bourdon tube.

4. The solutions present a series of advantages,as: an increased number of operable elements,constructive simplicity, a reduced gauge.

References

[1]. Cernomazu D., Poienar M., Romanescu A. N., Ţanţa O. M.,Prodan C., Georgescu D. Ş., Niţan I., Olariu E. D., UngureanuC., Raţă M., Actuator heliotermic mixt, Cerere de brevet deinvenție nr A/00619 din 13.08.2014.

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[2]. Cernomazu D., Poienar M., Romanescu A. N., Ţanţa O. M.,Prodan C., Georgescu D. Ş., Niţan I., Olariu E. D., UngureanuC., Raţă M., Actuator heliotermic mixt cu concentrator parabolic,Cerere de brevet de invenție nr A/00620 din 13.08.2014.[3]. Romanescu A. N, Ţanţa O. M, Poienar M., Niţan I.,Ungureanu C., Mandici L., Cernomazu D., Current state of

research at the EMAD Research Center from „Ştefan cel Mare”University in connection with actuators and solar motors with solidheating medium, In: Analele Universităţii „Eftimie Murgu” Reşiţa,Fascicula de Inginerie, anul XXI, nr. 2, 2014, p. 123 – 134, ISSN:1453-7397.

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DUAL PRIORITY SCHEDULING ALGORITHM USED IN THE nMPRAMICROCONTROLLERS – DYNAMIC SCHEDULER

Lucian ANDRIEȘ, Vasile Gheorghiță GĂITANFaculty of Electrical Engineering and Computer Science

Ștefan cel Mare University of SuceavaSuceava, Romania

e-mails: [email protected], [email protected]

ABSTRACT

This paper is a follow up of an already published paper, that described thestatic scheduler, which is presenting a true dynamic scheduling algorithm that isgoing to maximize the CPU utilization. The dual priority algorithm is composed oftwo different scheduling algorithms, earliest deadline first (EDF) and round robin(RR). We choose EDF, because is a dynamic scheduling algorithm, used in realtime operating systems, that can be easily implemented in hardware, by improvingthe nHSE architecture. The new dynamic scheduler algorithm provides a muchbetter CPU utilization, very good switching time for tasks and events within 5 to 8machine cycles and guaranties that no task will suffer from starvation.

KEYWORDS: real time system, dynamic hardware scheduler,microcontroller, pipeline processor

1. Introduction

In article [1], the author provided a review aboutfundamental results of two important schedulingalgorithms:

Fixed priority (FP - Fixed priorityscheduling assures that the processor will execute thehighest priority task among others).

Earliest deadline first (EDF - Earliestdeadline first scheduler is a real time operatingsystem that place processed in a priority queue inorder to be scheduled for execution).

The FP algorithm will assigned a fixed prioritythat cannot be modified at run time or in normaloperation to each task, while the EDF algorithm is theopposite. Each priority of a task is computedcontinuously based on the earliest absolute deadline.

Other scheduling algorithms such as ShortestRemaining Processing timer First (SRPT) [2] andLeast Laxity first (LLF) [3] are very powerful andefficient in software, but are difficult to implement inhardware because of the logical ports cost. Because ofthis reason we are going to detail only the EDFalgorithm.

The scheduling algorithms based on FP andEDF, to a certain extent, are good algorithms that canbe used in real time operating systems. But in themajority of the commercial real time operating

systems, the FP algorithm is implemented due to thesimplicity and lower overhead of resources.

The overheads are more visible in software,because EDF can be implemented in different waysthat can deal more or less resources. Each softwareimplementation can lead to less or more CPUutilization.

The hardware resources that are going to beused are not going to increase drastically by EDF,because Scheduler described in [4] will not bechanged at all and the nHSE architecture, described in[6-9], will suffer minor improvements.

The nHSE architecture, described in [8], cansupport two types of schedulers, static or dynamic.Until this moment only the static scheduler wasdescribed and implemented in paper [4], while thedynamic scheduler was postponed for futureimplementations.

This paper will present only the theoretical partbehind the actual hardware implementation [4]. Basedon our experience with the static scheduler we areconvinced that the scheduler will work as intendedand the resource utilization will not be much higher.

This paper is organized as follows. Theimprovements of the nHSE architecture is presentedin Section III, the proposed dynamic dual priorityalgorithm is presented in Section III, followed by theresults in Section IV. In the end in Section V someconclusions are listed.

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Fig. 1. The nMPRA architecture

2. nMPRA architecture overview

In order to understand this paper an overview ofthe nMPRA architecture must be performed. InFigure 1 is described the initial nMPRA architecture[8], while the representations colored in red are theimprovements described in [4].

To the current nMPRA architecture [8], wasadded a slow bus with a Buss Controller and aperipheral (Scheduler) which contains the schedulingalgorithm (Figure 1).

This new approach optimizes the switching ofthe hardware tasks in terms of silicon costs andsystem complexity. During this process we encountersome synchronization issue, caused by the currentarchitecture of the processor, MIPS with 5 pipelinestages. In order to stop a working task the ProgramCounter (PC) must be stopped. The switch process ofa task is really simple and is done in two steps.

Stop the PC of current task. Select the appropriate task to share theresources.From this description we can think that the

switching of a task can be done in 1 machine cycle,because the stopping of the PC and the selection ofthe appropriate input / output of the multiplexer /demultiplexer can be done simultaneously.

It could be true if there were no depencies withthe RAM and ALU that are shared. So when theSelectTask[2..0] bus (Figure 2) will have a differentvalue, in order to select the new task, the ROM, ALUand ALU will no longer be available for the currenttask.

Fig. 2. Simplified nMPRA architecture

We’ve choose to wait 3 machine cycles to solvethe synchronization issue. The other 2 machine cyclesare used to synchronize the next task program counteraddress with the ROM memory and the instructionfetch pipeline register because the Scheduler and theprogram counter are using 3 quadrature clock signals.

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The whole architecture was design using VHDLhardware description language (VHDL 93). AltiumDesigner 2014 was used, only as a text editor, toinclude the individual VHDL module and create thearchitecture. The design created was simulated usingModelSim Altera Started Edition 10.1d. The onlystimulus applied to the microcontroller was 3quadrature clock signals, while the ROM memorywas already initialized with the machine code for all 5tasks.

The following results were observed, in normaloperation, at key points. In the following lines we aregoing to detail the steps required to do a task switch:

a) var_process0ready ((1) from Figure 3)signal represents the event occurring after activationof the first task. Because no jump instruction isperformed all of the active task will be stopped withthe help of processXstall (X will have values from 0to 4) signal. The process1ready will remain active asa sign that the task is still active. At this momenttask1 will be in the ITQ.

b) Wait one clock cycle.c) Processactiv signal selects thread 0 as the

active one (3) from Figure 3).Process0resetstall and process0startagain

signals are activated ((4) from Figure 3).

Fig. 3. Time for a task switch

Fig. 4. Local nHSE registers

As we can see from Figure 3 the response timeof the scheduler is one machine cycle (between (2)and (5)), the time spent after the task with higherpriority became active and the starting of executingcode (between (2) and (5) from Figure 3) is done in 5machine cycles in an interval of 75 ns, where theperiod of the clock is 15 ns.

3. nHSE Arhitecture Improvements

The architecture of the microcontroller thatincludes the nMPRA and nHSE architecture firstlydescribed in [8] and then improved in [4] will beimproved again in order for the nHSE architecture tomake use of the dynamic scheduler.

nMRA architecture stands for n Multi PipelineRegister architecture which means that the mostimportant resources, ROM, RAM, ALU were sharedbetween multiple hardware tasks.

nHSE architecture stands for “n HardwareScheduler Engine” and can be used for real timepreemptive capabilities of the static of dynamicscheduler.

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Also provides support for: Logic events:

o Interruptso Events generated by watchdog timers.o Events generated by timer.o Events generated by the deadline1 timer.o Events generated by the deadline2 timer.o Events generated by mutexes.o Events generated by synchronization

events. Static Scheduler: The priorities of n tasks

cannot be changed during execution. Dynamic Scheduler: The priorities of n tasks

can be changed during execution. Global and local nHSE registers.

In order to support dynamic scheduling, thenHSE architecture was updated with a new registermrCntAvgRuni, added to the local nHSE registers(Figure 4) for all hardware tasks.

The registers will always be equal with theaverage of the current task execution time. Theregister mrCntRuni will start to count each machinecycle only after the task has started again. At the endof the task execution the nHSE_lr will add the currentvalue from mrCntRuni to mrCntAvgRun register andshift to the right the result, in order to achieve adivision by two. The final result will be stored inmrCntAvgRun.

In the following example we are going to detailthe operation performed by nHSE_lr in Table 1:

Table 1. Average task computation for EDF algorithmStep mrCntRuni Operation mrCntAvgRuni

1mrCntAvgRuni =

(mrCntRuni + rCntAvgRuni);mrCntAvgRuni =>> 1;

0

2 500 (500 + 0) >>1 2503 700 (700 + 250) >>1 4754 450 (450 + 475) >>1 4625 900 (900 + 462) >>1 6816 1000 (1000 + 681) >>1 8407 1200 (1200 + 840) >>1 10208 300 (300 + 1020) >>1 660

As can be easily seen the average algorithm hasstarted with the value of the register mrCntAvgRuniequal with 0. If we are going to compute again thesame task execution, but this time with floating point,the result will be approximately the same: anarithmetic average will be performed on the numberof the processor cycle of the register mrCntAvgRunifrom Table 1. The result is (500 + 700 + 450 + 900 +1000 + 1200 + 200) / 7 = 721.4285714285714machine cycles.

The difference between the unsigned averageand the floating point average is just 61 machinecycles, which can be equal with 12 R type assemblerinstructions if we consider that an R type instructionis executed in 5 machine cycles.

From the examples above we can say that thecomputation error for the unsigned average algorithmis 8.46% witch is deducted with the followingequation: 100% - (660 * 100) / 721 = 100% -91.539% = 8.46%

The result 8.46 % means the maximumpercentage that the unsigned average algorithm canhave. The value of the error will decrease as thenumber of task recurrence will increase.

The cost of hardware resources, per hardwaretask, for a true dynamic dual priority algorithm is:

One register of 32 bits.

A add module; A shift to right by one module.

4. The proposed dynamic dual priorityalgorithm

This paper is a follow up of the article [4], thathas an overview in chapter II, where the presenteddual priority scheduling algorithm was not a truedynamic scheduler because, the dynamic execution ofthe algorithm was that the priority of the tasks werechanged only when one or several tasks did not metthe Round Robin timer (RRB) time constraints.

The algorithm will behave like a true staticscheduler only when the following requirements willbe met:

The RRB time constrains are met. The sum of all concrete task execution is less

than the lowest task recurrence. No task is going to be promoted to long

execution tasks class (LTQ).The main difference between scheduling

algorithm from the article [4] and the algorithmpresented in this paper is the use of a true dynamicscheduling algorithm, earliest deadline firstscheduling (EDF).

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In this paper the switching time has not beenimproved, since the last article [4], because we arepresenting the other half of the Scheduler. In order tohave a better understanding of the algorithm we aregoing to reuse and detail some of the informationfrom [4].

Dispacher

Round Robin SchedulingTsk 1

...

Tsk 2 Tsk n

EDF Scheduling

Tsk 1 Tsk 2 Tsk 1

LTQ notempty

Tasks promoted to long tasks

Idle State

If another Taskbecame active

ITQ

Tsk 1Tsk 2

...Tsk n

No

LTQ

Tsk 1Tsk 2

...Tsk n

Running State

If Task x is running


If the Task has aleast CPUutilization

Yes

Move Task xinto ITQ

Yes


No

If TBR elapsed

No

Move Task xinto LTQ

YesNo

If Task finishsuccessfully

Move Task xinto ATQ

Yes

Yes

No

No

No

Yes

ITQ notempty

Tasks promoted to Interrupted state

Yes

Yes

No

No

Yes

Start

Initialization stage of:- Timer (TRB) used for the Round Robin time stamp

- Active tasks queue(ATQ) a- Interrupt tasks queue(ITQ) a- Long time task queue(LTQ) a

EMTQ

Tsk 1Tsk 2

...Tsk n

Extract task with theleast CPU

utilization(fromEMTQ)

Extract task with theleast CPU

utilization(from EMTQ)

Registers

...mrCntMedRuni

Registers

...mrCntMedRuni

Registers

...mrCntMedRuni

Registers

...mrCntMedRuni

nHSE_lr

Registers

...mrCntMedRuni

40...

Fig. 5. The flowchart of a scheduler with adynamic dual priority algorithm (Figure 3 from

[4])

In the following lines, the classes that each taskcan belong are presented:

The class of execution medium time queue,which has the higher priority (the tasks willbe inserted by the medium execution time(EMTQ)): will schedule the tasks, based onmedium execution time, only in the RunningState (RS) of the Scheduler.

The class of interrupted tasks, which has thesecond priority (the tasks will be insertedonly in the interrupted task queue (ITQ)):will schedule the tasks, based on priorities,only in the Idle State (IS) of the Scheduler.

The long execution tasks class (significantlyexceed the base period T corresponding to

the priority task), which as the least priorities(the tasks will be inserted only in the longtask queue (LTQ)): will schedule the tasks,based on ROUND ROBIN (RR) algorithm,only in the Idle State (IS) of the Scheduler.

A global timer, Round Robin timer (TRB), isused to verify if the active time of the current task isnot taking too long. If the TRB expires, the currenttask will be promoted to LTQ and will be scheduledbased by RR algorithm.

The TRB must be initialized with the occurrenceof the slowest task from the system or less. In Figure5 is presented the operational flowchart of thedynamic Scheduler (event driven), which is driven bythe main clock signal of the processor.

The operation of the Scheduler is exactly thesame as in the paper [4] that has an overview inchapter II, with the main difference that the EDFalgorithm will guarantee a better control process unit(CPU) utilization.

5. Conclusions

The current paper presented the true dynamicdual priority algorithm which is the other part of thenHSE architecture, which uses the EDF algorithm forbetter CPU utilization.

The EDF algorithm will not be efficient in thefollowing cases:

The execution time of each task is greaterthan the TRB. In this particularly case onlythe RR algorithm will be used.

The execution time of all taks is less than thetime recurrence of the fastest task. Thisprecondition must be achieved in a systemwhere the CPU load is normal.

The EDF algorithm will be efficient, byscheduling the tasks that have the higher probabilityto finish the execution before another task becomeactive, only when the CPU load will rise abovenormal utilization.

The algorithm, shown in the Figure 5 will ensurea constant 5 machine cycles for each switch task andthe guaranties that the tasks will be scheduled nomatter how difficult were the requirements of thesystem.

Acknowledgement

This paper was supported by the project"Sustainable performance in doctoral and post-doctoral research PERFORM - Contract no.POSDRU/159/1.5/S/138963", project co-funded fromEuropean Social Fund through Sectorial OperationalProgram Human Resources 2007-2013.

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References[1]. Robert I. Davis, A review of fixed priority and EDFscheduling for hard real-time uniprocessor systems, Real-TimeSystems Research Group, Department of Compuyter Science,University of York, York, UK.[2]. Davis R. I., Burns A., Walker W., Guaranteeing TimingConstraints Under Shortest Remaining Processing TimeScheduling. In proceedings of the Euromicro Workshop on Real -Time Systems, p. 88-93, 1997.[3]. Shaohua Teng, Wei Zhang, Haibin Zhu, Xiufen Fu, JiangyiSu, Baoliang Cui, A Least-Laxity-First Scheduling Algorithm ofVariable Time Slice for Periodic Tasks, International Journal ofSoftware Science and Computational Intelligence, Vol. 2, Issue 2,April 2010, ISSN: 1942-9045 EISSN: 1942-9037.[4]. Lucian Andries, Vasile Gheorghita Gaitan, Dual PriorityScheduling algorithm used in the nMPRA Microcontrollers, 18th

International Conference on System Theory, Control andComputing, Sinaia, Romania, October 17-19, 2015.[5]. Lucian Andries, Vasile Gheorghita Gaitan, DetailedMicrocontroller Architecture based on a Hardware Scheduler

Engine and Independent Pipeline Registers, 19th InternationalConference on System Theory, Control and Computing, Sinaia,Romania, October 17-19, 2014, ISBN 978-1-4799-4602-0, 2014.[6]. Dodiu E., Gaitan V. G., Custom designed CPU architecturebased on a hardware scheduler and independent pipeline registers– concept and theory of operation, IEEE EIT InternationalConference on Electro-Information Technology, Indianapolis, IN,USA, 6-8 May 2012, ISBN: 978-1-4673-0818-2.[7]. Dodiu E., Gaitan V. G., Graur A., Custom designed CPUarchitecture based on a hardware scheduler and independentpipeline registers – architecture description, IEEE 35th JubileeInternational Convention on Information and CommunicationTechnology, Electronics and Microelectronics, Croatia, May 2012.[8]. Gaitan V. G., Gaitan N. C., Ungurean I., CPU Arhitecturebased on a Hardware Scheduler and Independent PipelineRegisters, IEEE Transactions on VLSI System, 2014, ISSN :1063-8210.[9]. Gaitan N., Lucian A., Using Dual Priority Scheduling toImprove the Resource Utilization in the nMPRA Microcontrollers,IEEE 12th International Conference on Development andApplication Systems, Suceava, Romania, May 15-17, 2014.

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WATER-IN-DIESEL EMULSIONS AS AN ALTERNATIVE FUEL FORDIESEL ENGINES. PART II: PERFORMANCE OF DIESEL ENGINES

FUELED WITH WATER-IN-DIESEL EMULSIONS.A LITERATURE REVIEW

Vlad VRABIE*, Dan SCARPETE, Bianca Elena CHIOSA„Dunărea de Jos” University of Galati, Faculty of Engineering,

Domnească Street, 47, RO-800008, Galati, Romania* Corresponding author


ABSTRACT

This paper presents the recent advance of water-in-diesel emulsion fuelstudies especially the impact of using this emulsions fuel to the performance andemissions of diesel engine. Studies revealed that the onset and the strength ofmicro-explosion process give strong effect with regards to the combustion efficiencyinside the combustion chamber.

Most of the researchers tested emulsions with 5-40% of water in diesel fuel.Some studies concluded that 20% of water in the emulsion fuel gives the optimumengine performance. Many researchers and experts agree that the reason why thereis a slight drop in brake power and torque is due to the fact that water-in-dieselemulsion fuel has a lower heating value than a neat diesel fuel, thus less energy isreleased during combustion.

In general, the results suggest that the water emulsification has a potential toslightly improve the brake efficiency and to significantly reduce the formation ofNOx, soot, hydrocarbons and PM in the diesel engine.

Some factors may affect the experimental results that need to be considered,such as the effect of volatility of the base fuel, the water content of the emulsion,emulsion stability, ambient temperature, pressure, type of surfactant and engine testconditions: engine load, speed, injection timing and compression ratio.

KEYWORDS: water-in-diesel emulsion, performance, emissions, dieselengine, combustion

1. Introduction

Diesel engines have been used in heavy dutyapplications for a long time [1] and, nowadays, dieselengines are obtaining more and more attention intransportation, industrial and agricultural applicationsdue to their high efficiency and reliability [2].

A good fuel for diesel engine should holdcharacteristic features like short ignition lag,sufficiently high cetane rating in order to avoidknocking, suitably volatile in the operating rangetemperatures for good mixing and combustion, easystartup characteristics, limited smoke and odor,suitable viscosity for the fueling system, free fromcorrosion and wear, and ease of handling [3].

Higher fuel efficiency in the diesel engine isachieved due to the high compression ratios along

with relatively high oxygen concentration in thecombustion chamber [4].

The introduction of water prolongs the ignitiondelay, increases the amount of fuel burned and therate of heat release in the kinetic burning period. Inthe diffusive burning period the temperature isgenerally lower in the cylinder when water is added.The change in maximum cylinder pressure isinsignificant [5].

Primary pollutants emitted from diesel enginesare particulate matters (PM), black smoke, nitrogenoxides (NOx), sulphur oxides (SOx), unburnedhydrocarbon (HC), carbonmonoxide (CO), andcarbon dioxide (CO2) [6].

Water-in-diesel emulsions are fuels for regulardiesel engines. The advantages of an emulsion fuelare reductions in the emissions of nitrogen oxides and

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particulate matters, which are both health hazardous,and reduction in fuel consumption due to betterburning efficiency. An important aspect is that dieselemulsions can be used without engine modifications[7]. Most emulsions are not thermodynamicallystable, but as a practical matter, quite stableemulsions can occur that resist demulsificationtreatments and may be stable for weeks/months/years.Most meta-stable emulsions that will be encounteredin practice contain oil, water and an emulsifyingagent (or stabilizer) which is usually a surfactant, amacro-molecule, or finely divided solids [8].

This review presents the influence of water-in-diesel emulsion on the diesel engine performance andthe effects of water-in-diesel emulsion fuel oncombustion process and emissions.

2. Combustion process

Combustion process is generally characterizedby factors such as injection characteristics, spraypenetration, evaporation, chemical and physicalatomization and mixture ignition, engine cylinderpressure and temperature, and heat releasecharacteristics. Figure 2 presents the primary andsecondary atomization in spray flame of emulsifiedfuel [6].

The interest in water-in-diesel emulsions derivesfrom the fact that water in the form of micrometer-sized droplets exerts some positive effects on thecombustion of fuels. When an emulsion fuel isheated, the water droplets are vaporized first becausewater is more volatile than diesel under the superheatconditions.

The vaporization of water will cause thecontinuous hydrocarbon phase to „explode”.

This phenomenon, known as micro-explosion,helps in the atomization of fuel, accelerating fuelevaporation rate and enhancing fuel-air mixingprocess, thereby improving [1].

Micro-explosion is an important phenomenon inthe secondary atomization process of water-in-dieselemulsion fuels. Generally, this phenomenon isaffected by volatility of base fuel, type of emulsion,water content, diameter of the dispersed liquid,location of the dispersed liquid and ambientconditions like pressure and temperature [6].

Sheng, Zhang and Wu [9] observed that thewater dots of 0.001 mm in emulsion droplets can berecognized, a no-water layer is found near surface ofthe droplet (Figure 1).

The micro-explosion can hardly be observedbelow 733 K. At 823 K, the explosion takes placeearly and is slightly weaker. In lower gas pressurecases, the velocity of torn fragments of droplets afterexplosion is much higher than that in higher gaspressure due to lower gas density.

Fig. 1. Micro-structure of the vaporing emulsiondroplet [9]

Fig. 2. Primary and secondary atomization in spray flame of emulsified fuel [6]

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Study of the combustion process was difficultsince there has not been any optical access to thecombustion chamber. As a result, more focus wasgiven to the cylinder and thermocouple readings forthe engine wall and inlet and exhaust temperatures tostudy the performance of combustion [6].

The temperature in the combustion chamber isthe key factor of the utilization of emulsion, micro-emulsion will take place in a certain temperaturerange and become stronger at a proper temperature.Higher pressure in the combustion chamber has littleeffect on the occurrence of the explosion, but thepenetration of fragments of torn droplet will be muchlower due to denser gas in the combustion chamber, ifmay weaken the effect of micro-explosion on theimprovement of air-fuel mixing. The explosion willtake place more easily for larger initial dropletdiameters. The energy of explosion is strong enoughto emit fragments of torn droplets to a distanceseveral millimeters away from the spray boundary, ifthe gas temperature is suitable [9].

3. Performance of diesel engine fueledwith water-in-diesel emulsions

Fahd et al. [10] investigated the effect of 10%water emulsion diesel (ED10) on engine performanceand emission characteristics and the results werecompared with base diesel fuel (Euro 4). Theexperiments were performed in a four cylinder 2.5 LDI turbocharged Toyota diesel engine at fourdifferent engine loading conditions (25%, 50%, 75%and 100% load) in order to analyze the effect ofemulsion diesel over the entire engine load condition.For each load the engine speed was varied from 800rpm to 3600 rpm in steps of 400 rpm. The water-in-diesel emulsion (ED10) produces less output powerand engine efficiency as compared to neat diesel fuel(Figure 3). Besides these, W/D E10% shows higherbrake specific fuel consumption (BSFC) for allengine operating conditions (Figure 4).

Fig. 3. Thermal efficiencies for diesel and ED10fuel vs. engine speed and load [10]

Reduction in exhaust gas temperature isobserved for ED10 fuel and at higher engine loadconditions. In addition, ED10 demonstrates lower NOemission at all load conditions and higher COemission at low load and low speed condition whicheventually reduces significantly at higher enginespeed.

Fig. 4. Brake specific fuel consumption fordiesel and ED10 fuels vs. engine speed and load

[10]

Armas et al. [11] investigated the effect ofwater–oil emulsions on the engine performance andon the main pollutant emissions, NOx, totalhydrocarbons (THC), soot, particulate matter (PM)and its composition. Renault F8Q turbochargedintercooler IDI Diesel engine was tested under fivedifferent steady state operating conditions, selectedfrom the transient cycle for light duty vehiclesestablished in the European Emission Directive70/220. Tests were performed using a commercialfuel as a reference and an emulsified fuel (water-in-diesel emulsion with 10% water percentage and withthe surfactants recommended by Repsol-YPFcompany – polyethylene glycolemonoleate andsorbitol-esesquioleate) for each operating condition.

Results reported here suggest that the wateremulsification has a potential to slightly improve thefuel consumption, the brake efficiency and tosignificantly reduce the formation of thermal NO,soot, hydrocarbons and PM in the diesel engine [11].

Suresh et al. [12] investigated the emissions andperformance characteristics of a four stroke dieselengine operating on water in diesel emulsified fuelsand its CFD (Computational Fluid Dynamics)analysis of NOx emission. Emulsion fuels withvarying contents of water in diesel (5%, 10%, 15%and 20%) are prepared and stabilized by sorbitan-monooleate surfactant. The experimental resultsreveal that 20% water-in-diesel reduces 45% of NOxemission.

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Figure 5 presents the brake power versus NOxand it’s observed that water-in-diesel fuel with 20%water records the lowest values of NOx.

The exhaust gas temperature and smokeemissions are drastically reduced for the emulsionfuels compared to the pure diesel. When water isadded to diesel fuel, brake thermal efficiency isslightly reduced. It is acceptable by considering theNOx emissions characteristics.

Fig. 5. NOx emission vs. brake power [12]

According to a report by Sadler [13], anapplication of 13% water content (not mentionedwhether by volume or mass percentage) in theemulsified fuel in UK has brought 13% and 25%reduction of NOx and PM, respectively.

Ahmad et al. [14] investigated the effect ofwater-in-diesel emulsion fuel (W/D) originating fromlow-grade diesel fuel (D2) on the combustionperformance and emission characteristics of a directinjection diesel engine under varying engine loads(25–100%) and constant engine speed (3000 rpm).Four types of W/D are tested, which consist ofdifferent water percentages (5%, 10%, 15% and20%), with constant 2% of surfactant and labeled asE5, E10, E15 and E20, respectively. It is observedthat NOx (Figure 6) and PM (Figure 7) are found tobe reduced for all types of W/D.

The carbon monoxide (CO) and carbon dioxide(CO2) emissions increase compared to D2 at lowloadand high load, respectively. E20 is reported to bethe best in reducing NOx and PM with an averagereduction of 41% and 35%, respectively, in everyload condition.

Attia and Kulchitskiy[15] studied the effect ofthe structure of water-in-diesel fuel emulsion (WFE)on a three cylinder diesel engine performance. Basedon membrane emulsification, two differentmembranes of pore sizes of 0.2 µm and 0.45 µm hasbeen individually used to change the emulsionstructure while keeping the same WFE volumetriccontent (at 17% water volumetric content and 0.5%mixing emulsifier content). The results showed that

emulsions with large size of water droplets resulted ingreater reduction in NOx emissions up to 25%. While,emulsions with finer droplets not only gavereductions in engine smoke and unburnedhydrocarbons of values greater than 80% and 35%respectively, but also resulted in an increase of theengine effective efficiency up to 20%.

Fig. 6. Formation of PM for D2 and W/D (E5,E10, E15 and E 20) under varied loads (25%,

50%, 75% and 100%) [14]

Fig. 7. Formation of NOx for D2 and W/D (E5,E10, E15 and E 20) under varied loads (25%,

50%, 75% and 100%) [14]

Alahmer [16] investigated the effect ofemulsified diesel fuel on the engine performance andon the main pollutant emissions for a water-cooled,four stroke, four cylinders, and direct injection dieselengine. Emulsified diesel fuels with water content ofrange 0-30% by volume were used. The experimentswere conducted in the speed range from 1000 to 3000rpm. While the brake specific fuel consumption(BSFC) has a minimum value at 5% water contentand 2000 rpm, the torque, the break mean effectivepressure and thermal efficiency (Figure 8) are foundto have maximum values under these conditions. Theemission CO2 was found to increase with enginespeed and to decrease with water content. NOxproduced from emulsified fuel is significantly lessthan that produced from pure diesel under the same

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conditions (Figure 9), and as the percentage of watercontent in the emulsion increases, the emitted amountof oxygen also increases.

Fig.8. Thermal efficiencies for pure diesel, 5%,10%, 15%, 20%, 25% and 30% water addition

[16]

Fig. 9. NOx emission for pure diesel, 5%, 10%,15%, 20%, 25% and 30% water addition [16]

It was found that, in general, the usingemulsified fuel improves the engine performance andreduces emissions [16].

Canfield [17] examined the effects ofcombusting a mixture of diesel fuel, water, andsurfactant on the nitrogen oxides (NOx) emissionsfrom a compression ignition diesel engine.The datashows significant NOx emission reduction with up to45% water, by volume, in the fuel. These results arecorrelated with thermodynamic first law andequilibrium combustion products analyses to estimatethe adiabatic flame temperature of the standard fueland fuel-water emulsion cases. Results indicate thatthermal NOx is indeed reduced by quenching andflame temperature suppression, confirming reports inthe literature. Recommendations are given for furtherstudies, including improving the fuel-water emulsionand considerations for long-term testing.

Ghojel and coworkers [18] have reported 29-37% reduction of NOx emissions when operating ondiesel oil emulsion of 13% water content by volume.

Samec et al. reported a reduction of 20% and18% NOx emission compared to pure diesel fuel with10% and 15% water content in the emulsion,respectively [19, 20].

Barnes et al. [21] investigated the effect of waterblended fuel on the performance and emissions of acity bus engine considering 10% water content byvolume. They showed a decrease of NOx with 9% incomparison with the use of neat diesel fuel.

Fig. 10. NOx emission (left) and HC emission (right) vs. brake power [22]

Kanaan and Udayakumar [22] studied the effectof water emulsified diesel fuel combustion on brakethermal efficiency, brake specific fuel consumption

and NOx and hydrocarbon emissions in a dieselengine. The experiments were conducted on a singlecylinder Kirloskar with direct injection and four

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stroke cycle diesel engine at constant speed of 1500rpm with a fuel injection pressure of 200 bars. Theaim of the experimental study was to investigate theeffect of diesel (DSL), diesel with10% water (D10)and diesel with 20% water (D20) on performance andemission in a light duty single cylinder diesel engine.

The water emulsified diesel fuel was preparedby mixing 10% and 20% of distilled water with 90%and 80% of diesel by volume, respectively. Sodiumlauryl sulphate was used as surfactant to prepareemulsion. Sodium lauryl sulphate (0.1%) is addedwith 100 ml and 200 ml distilled water and mixedwith 900 ml and 800 ml diesel to prepare D10 andD20 emulsified diesel fuels, respectively. The mixerwas stirred for 2-3 minutes in an electrically operatedagitator. As the amount of water in the emulsionincreases, the brake thermal efficiency increases. Thepresence of water in the emulsion increases theexpansion work and reduces the compression workresulting increased net work done during the cycle[22]. The NOx (Figure 12, left) and hydrocarbon(Figure 12, right) emissions were found to decrease

with increase in water percentage (until 20%) in theemulsified diesel [22].

Nadeem et al. [23] have studied water-in-dieselemulsion with conventional (sorbitanmonooleate) andgemini surfactants for main pollutant emissions byfuelling it in a four stroke and four cylinder enginetest bed and concluded that for 15% water content,there is 71% reduction in PM emission with Geminisurfactant water in diesel emulsion fuel.

Emulsified fuels containing 5-15% watercontents were prepared using conventional andgemini surfactants and studied in an engine bed XLD418 (Ford, four strokes, four cylinders, water-cooled,compression ratio: 21.50, total displacement volume:1753 cc and a maximum output brake horsepower:60.0 at 4800 rpm) to clarify the changes in the mainpollutant emissions (NOx, CO and PM). The emissionof NOx, CO and PM was reduced using the emulsifiedfuels instead of neat diesel.

The emulsified fuels containing geminisurfactant were most prominent in the reduction ofPM.

Fig. 11. NOx emission (left) and articulate matter emission (right) from neat diesel and emulsifiedfuels [23]

In addition, emulsion fuels have higher specificfuel consumption and produced less torque, powerand brake mean effective pressure but the differenceis insignificant. Water emulsification has a potentialto significantly reduce the formation of thermal NOx(Figure 11, left), CO, SOx, soot, hydrocarbons andPM (Figure 11, right) in the diesel engines [23].

4. Conclusion

Diesel engines have been used in heavy dutyapplications for a long time and, nowadays, dieselengines are obtaining more and more attention intransportation, industrial and agricultural applicationsdue to their high efficiency and reliability.

Primary pollutants emitted from diesel enginesare particulate matters (PM), black smoke, nitrogenoxides (NOx), sulphur oxides (SOx), unburnedhydrocarbon (HC), carbon monoxide (CO), andcarbon dioxide (CO2).

Combustion process is generally characterizedby factors such as injection characteristics, spraypenetration, evaporation, chemical and physicalatomization and mixture ignition, engine cylinderpressure and temperature, and heat releasecharacteristics. Water-in-diesel emulsions are fuelsfor regular diesel engines. The researches weremainly focused in specific engine operation variablesand due to this, the results has become very difficultto draw a general conclusion.

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The results reported by different researchers areoften conflicting, sometimes generating results thatare even worse than pure diesel.

Many researchers have concluded that a W/Demulsion fuel with water content of up to 20% canreduce:

- NOx emissions by up to 45% (in Suresh'sexperiment), and in most cases up to 20%, comparedwith standard diesel fuel;

- Emissions of PM, HC and soot with significantpercentages compared to standard diesel.

Some characteristics, such as the waterpercentage, dispersed droplet size and viscositydepending on the engine working conditions, such asengine load and speed would be an interestingresearch area that can be explored fundamentally andpractically in the near future.

The proven benefit of the water emulsifieddiesel is that the heat absorption by watervaporization causes a decrease of local adiabaticflame temperature and therefore reduces the chemicalreaction in gas phase to produce thermal NO. Fuelwith a larger emulsion ratio results in a longerignition delay and a longer premixed combustionphase. A higher content of water weakens luminousflames and reduces the peak temperature in thediffusion controlled combustion phase and leads to alower peak pressure and a lower level of NOxemission.

With the advantage of the energy saving andless environmental pollution for W/D emulsion,together with the newly developed emulsion fuelmaking device, it will provide a great contribution tothe industries, and, at the same time, reduce theconsumption of energy and ensure less pollution tothe environment.

Further, it requires a lot of studies andexperimental works about the optimization of watercontent in the emulsion for best engine performanceand low emissions so these can give the bestrecommendations for the commercialization of water-in-diesel emulsion as an alternative source of energyfor the future diesel engines.

Acknowledgement

The authors would like to acknowledge to theProject POSDRU/159/1.5/S/132397 for supportingthis research and the paper publishing.

References[1]. Yang W. M. et al., Impact of emulsion fuel with nano-organicadditives on the performance of diesel engine, Applied Energy,112, 2013, p. 1206-1212.[2]. Heywood J. B., Internal combustion engine fundamentals,McGraw-Hill, 1988.

[3]. Ganesan V., Internal Combustion Engines, Tata McGraw-Hill,NewDelhi, India, 1994.[4]. Kannan K., Udayakumar M., NOx and HC emission controlusing water emulsified diesel in single cylinder diesel engine,ARPN Journal of Engineering and Applied Sciences, Vol. 4, No. 8,October 2009, ISSN 1819-6608.[5]. Hsu B. D., Combustion of water-in-diesel emulsion in anexperiment medium speed diesel engine, SAE, 860300. p. 2285-2295.[6]. Khan M. Y. et al., Current trends in water-in-diesel emulsionas a fuel, Hindawi Publishing Corporation The Scientific WorldJournal, Volume 2014, Article ID 527472, 15 pages.[7]. Lif A., Holmberg K., Water-in-diesel emulsions and relatedsystems, Advances in Colloid and Interface Science, 123-126,2006, p. 231-239.[8]. Laurier L., Schramm L., Emulsions, Foams and Suspensions:Fundamentals and Applications, Copyright@2005 Wiley-vchVerlag GmbH & Co, KGaA, Weinheim, ISBN: 3-527-30743.[9]. Sheng H.-Z., Zhang Z.-P., Wu C.-K., Study of atomizationand micro-explosion of water-in-diesel fuel emulsion droplets inspray within a high temperature, high pressure bomb, InternationalSymposium COMODIA 90, p. 275-280, 1990.[10]. Ebna M., Fahd A., Experimental investigation of theperformance and emission characteristics of direct injection dieselengine by water emulsion diesel under varying engine loadcondition, Applied Energy, 102, 2013, p. 1042-1049.[11]. Armas O. et al., Characterization of light duty Diesel enginepollutant emissions using water-emulsified fuel, Fuel, 84, 2005, p.1011-1018.[12]. Suresh V. et al., Emission Characteristics of Diesel Engineusing Water-in-Diesel Emulsified Fuel and its CFD Analysis,International Journal of Applied Environmental Sciences, ISSN0973-6077, Vol. 9, Number 5, 2014, p. 2739-2749.[13]. Sadler L., The airquality impact of water-diesel emulsion fuel(WDE) and selective catalytic reduction (SCR) technologies,Mayor of London, London, UK, 2003.[14]. Ithnin A. M. et al., Combustion performance and emissionanalysis of diesel engine fuelled with water-in-diesel emulsion fuelmade from low-grade diesel fuel, Energy Conversion andManagement, 90, 2015, p. 375-382.[15]. Attia A. M. A., Kulchitskiy A. R., Influence of the structureof water-in-fuel emulsion on diesel engine performance, Fuel, 116,2014, p. 703-708.[16]. Alahmer A., Influence of using emulsified diesel fuel on theperformance and pollutants emitted from diesel engine, EnergyConversion and Management, 73, 2013, p. 361-369.[17]. Canfield C. A., Effects of diesel-water emulsion combustionon diesel engine NOx emissions [M.S. thesis], MechanicalEngineering, University of Florida, Gainesville, Fla, USA, 1999.[18]. Ghojel J., Honnery D., Al-Khaleefi K., Performance,emissions and heat release characteristics of direct injection dieselengine operating on diesel oil emulsion, Applied ThermalEngineering, vol. 26, no. 17-18, p. 2132-2141, 2006.[19]. Samec N., Kegl B., R. Dibble W., Numerical andexperiment-tal study of water/oil emulsified fuel combustion in adiesel engine, Fuel, vol. 81, no. 16, p. 2035-2044, 2002.[20]. Samec N., Dobovisek Z., Hribernik A., The effect of wateremulsified in diesel fuel on diesel fuel on exhaust emission, Gorivai Maziva, vol. 39, p. 377-392, 2000.[21]. Barnes A. et al., Evaluation of water-blend fuels in a city busand an assessment of performance with emission control devices,Proceedings of the Better air Quality Motor Vehicle Control&Technology, Workshop 2000.[22]. Ithnin A. M. et al., An overview of utilizing water-in-dieselemulsion fuel in diesel engine and its potential research study,Journal of the Energy Institute, 87, 2014, p. 273-288.[23]. Nadeem M. et al., Diesel engine performance and emissionevaluation using emulsified fuels stabilized by conventional andgemini surfactants, Fuel, 85, 2006, p. 2111-2119.

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STRENGTH ANALYSIS OF A COMPOSITE JOINT USEDIN SHIP STRUCTURE

Florentina ROTARU*, Ionel CHIRICA, Elena Felicia BEZNEA“Dunarea de Jos” University of Galati, Romania

e-mails: [email protected], [email protected], [email protected]

ABSTRACT

Low weight and high strength panels is always a design consideration.Sandwich panel technology offers an efficient solution for this problem. Differenttypes of sandwich panels are currently being used depending on the applications.Honeycomb sandwich panels are a better solution in structural design problem. Thework presented in the paper is focused on the study on the behaviour of a compositejoint used in ship structure, loaded by transversal force. The components of thejoint are sandwich plates, made out of core polypropylene honeycomb andpolystyrene extruded and face sheets of the resin polymer. A typical sandwich panelis made of three layers, in which two thin sheets (faces) of a stiff and strongmaterial are separated by a thick core of low-density materials (Allen, 1961).Considering the very varied use of these materials in numerous fields, it is essentialto know their mechanical properties so that to predict and calculate their behaviourin specific and diverse environments.

KEYWORDS: Joint ship, sandwich composite, Ansys FEM, modeling

1. Introduction

Year by year the interests in using composites invarious structure building have grown. Nowadays, theidea of using sandwich construction has become moreand more popular due to the new materials such ascellular materials can be used as core for sandwich.The idea of separation of the skins by the core isderived from the beam theory (sectional moment ofinertia) [10].

The maritime and aerospace industry has provedthe using of composite materials in reducing the totalweight and low fuel consumption. In the maritimefield the use of composites started since 1950 due tothe low costs of GFRP (Glass fiber reinforced plastic)structures. The first applications include lifeboats,pleasure crafts and small yachts [11].

The merits of the sandwich composite structuresare the high strength/weight ratio, heat resistance,sound / vibration insulation and easy assembly. In thelast decades sandwich structures have been widelyused in various fields: aerospace, automotive, shipbuilding and construction industries (Yu andCleghorn, 2005; Wang and Yang, 2000; Kim andHwang, 2000). In maritime industry, sandwichcomposites are ideally suited for the special structures[1, 2]. Foam cores meet the critical requirements ofstrength, buoyancy and low water absorption. The

most applications include the construction ofbulkheads, hulls, decks, transoms and furniture, butalso, which is the most important, the strengthstructural elements. Considering the very varied useof these materials in many fields, it is very importantto know their mechanical properties in order topredict and calculate the structural behavior inspecific and various environments.

One of the most used core materials ishoneycomb because it has good properties such as:very high strength to weight ratio, electrically andthermally insulating, chemically stable, goodnonflammable (being self-extinguishing) and non-corrosion properties, shock and fatigue resistant. Innearly all sandwich constructions certain types ofjoints have to be used for assembly, but little isknown about their failure behavior. This paper dealswith the investigation of joints used in shipbuildingand beyond.

2. Literature review

Peter Huson [7] (2012) analyzed a joint (joint)similar to the combination of this work but thematerials used to sandwich the core were balsa woodand foam (General Plastics FR3707 structural foamcore), skins used sheets CRFP (Carbon FibreReinforced Plastic (polymer)) and for the carrier

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(triangle) using balsa wood. FR-3707 foams arechosen for applications in nuclear and hazardouswaste transportation extreme. When used as a linerfor IMPACT- as fire insulation in transportcontainers, FR-3707 can be designed to deliver theultimate in protection against fire and collision fordangerous, surpassing wood and other polymericmaterials. 3707-FR formulation is specificallydesigned to enable predictable performance impact-absorption under dynamic loading. At the same timeit provides intumescent char layer that insulates andprotects hazardous materials, even when exposed tofire conditions. In the work of Peter Huson weremade more complex tests of experimental andsimulation using LS-Dyna program. Since thiscomposite were performed impact tests quasi-staticand dynamic strain and pursuing the compositedelamination.

Ch.Naresh [8] comparing of response of Squareand Hexagonal honeycomb sandwich panels in paperentitled “Numerical Investigation into Effect of CellShape on the Behavior of Honeycomb SandwichPanel”. Numerical simulations using FE techniquesare used for simulating the behavior of the sandwichpanels under uniformly distributed loads. Duringsimulation, two different combinations of materials(face material – core material) are considered. Basedon the response, it is found that though Al-Alsandwich panel with square honeycomb structurethough has lower stress values, showed greaterdeflection than SS-Cu panel.

Modal analysis is also executed to extract thenatural frequencies. It is found that squarehoneycomb panel has higher natural frequencies thanthat of hexagonal honeycomb panel. This paperanalyzes the natural frequency and displacement forthese sandwiches.

3. Problem definition

The purpose of this paper is to make acomparison between two matters that used in heartpolypropylene honeycomb sandwich and extrudedpolystyrene, following the behaviour of mechanically.The main steps in this study are:

1. Calculations using classical and finiteelements methods for simple constructionswith FEM package Ansys[9];

2. Understanding of properties of various faceand core materials;

3. This is an analysis to stiffness during statictest of sandwich panels and theircomponents;

4. Analysis the joint deflection behaviour;5. Studying the behaviour of the more cases the

application of different forces on joint.The materials used for sandwich are: for two

skins Epoxy E Glass-Wet; for a core usepolypropylene honeycomb and polystyrene extruded.The geometry of these structures can be seen below inFigure 1.

a) Composite joint with polypropylene honeycomb core b) Joint Composite San Foam core 81

Fig. 1 Geometry Composite Joints and blunts are considered for review

4. Meshing and boundary conditions

Geometric nonlinear static analysis has beendone for the panels’ models using ANSYSWorkbench to determine the effect of the previously-mentioned parameters on the deflection as well asstresses. The skins were modeled using SHELL with

orthotropic properties, while SHELL was used formodeling the cores with isotropic properties. Thismodel was able to accommodate both isotropic andorthotropic material properties, but isotropic materialproperties were initially applied to the model asreported in the present section. The loading andboundary conditions were adapted.

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a) Case1, Joint with core Honeycomb b) Case 2, Joint with San Foam 81

Fig. 2. Meshed models

The materials used for the analysis of the twocases are presented in the tables below:

Table 1. Honeycomb polypropylene [Source:From ANSYS library]

Honeycomb property Value Unit

Density 80 Kg/m3

Orthotropic elasticity

Young’s Modulus Ex 1 MPa

Young’s Modulus Ey 1 MPa

Young’s Modulus Ez 255 MPa

Poisson’s Ratio xy 0.49

Poisson’s Ratio yz 0.001

Poisson’s Ratio xz 0.001

Shear Modulus Gxy 10-6 MPa

Shear Modulus Gyz 37 MPa

Shear Modulus Gxz 70 MPa

For skin using Mechanical Properties of theEpoxy-E Glass-Wet [Source: From ANSYS library]Density =1850 Kgm3

Young’s Modulus x = 3500 MpaYoung’s Modulus y = 9000 MpaYoung’s Modulus y = 9000 MpaPoisson’s Ratio xy= 0.28Poisson’s Ratio xy= 0.4Poisson’s Ratio xz= 0.2

Table 2. SAN_Foam_81 [Source: From ANSYSlibrary]

SAN_Foam_81kgm3 Isotropic Elasticity

Young’s Modulus 60 MPa

Poisson’s Ratio 0.3

Bulk Modulus 50 MPaShear Modulus 22.077 MPa

Density 81 Kg/m3

5. Results and discussions

As mentioned earlier, static analysis with thepanels subjected uniformly distributed load from 2KN – 27 KN are executed on models of the twostructures.

Fig. 3. Total Deformation of structure

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Fig. 4. Maximum Principal Elastic StrainFig. 5. The geometry of three layers

Fig. 6. The arrangement of layers

Table 3. Analysis of several strengths in terms ofterms deflection for honeycomb core

HoneycombNr.crt. KN Displacement [mm]

1 2 0.262442 4 0.524883 6 0.787314 8 1.04985 10 1.31226 12 1.57467 14 1.83718 15 1.96839 16 2.0995

10 17 2.230711 18 2.361912 19 2.493213 20 2.624414 21 2.755615 22 2.886816 23 3.01817 24 3.149318 25 3.280519 26 3.411720 27 3.5429

Table 4. Analysis of several strengths in ofdeflection for SANFoam 81

SanFoam81Nr.crt KN Displacement [mm]

1 2 0.496592 4 0.993183 6 1.48984 8 1.98645 10 2.4836 12 2.97967 14 3.47618 15 3.72449 16 3.9727

10 17 4.22111 18 4.469312 19 4.717613 20 4.965914 21 5.214215 22 5.462516 23 5.710817 24 5.959118 25 6.207419 26 6.455720 27 6.704

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Forty cases were analysed in Ansys Workbench,but these cases were divided into two mean matteredmore displacement behaviour for two different cores:honeycomb polypropylene and extruded polystyrene(San Foam 81). Each case has a different force eachstarting from 2 kN to 27 kN. It followed thedisplacement of the biggest forces application andthen made a comparison to the two cores. In Figures 3and 4 are shown some images of some the forty casesto reveal total displacement and maximum principalstrain. Figure 5 and 6 showed how layers were builtto model the structure.

Results of local modelling are included in moredetail, because they can help explain specificphenomena related to the experimental investigation.

In Figure 7 compares the two cases importantchart displacements to different cores; Observe thatthe displacement for polypropylene honeycomb wassmaller than San Foam 81.

Fig. 7. Comparing the results of two differentcores Joints and blunts

6. Conclusions

Static analysis was performed to study theresponse honeycomb core and expanded polystyrenesandwich for different strengths. Static analysis wasperformed with the back edge encased T's. Staticanalysis was performed to check whether the nodecan support some typical naval forces. Based on theresults it is found that the typical naval node withhoneycomb core has a smaller displacement than

polystyrene. And core figure (Honeycomb) providesbetter rigidity than the core of extruded polystyrene(foam breast 81). For better results in typical nodenaval reinforcement core to use all extrudedpolystyrene (san foam81) because of honeycombboards cannot sit tight but should remain a space freewhen using the foam will fill the air gap.

Acknowledgement

The work has been funded by the SectoralOperational Program Human Resources Development2007-2013 of the Ministry of European Fundsthrough the Financial AgreementPOSDRU/159/1.5/S/132397.

References

[1]. Araboui J., Schmitt Y., Pierrot J. L., Royer F. X.,Numerical Simulation and experimental bending behaviour ofmulti-layer sandwich structures, Laboratory de Physique desMilieux Denses, France 2014.[2]. Akour S., Maatah H., Finite element Analysis of LoadingArea Effect on Sandwich Panel Behaviour Beyond theyeld Limit,Chapter 16.[3]. Craig A. Steeves, Norman A. Fleck, Collapse mechanisms ofsandwich beams with composite faces and a foam core, loaded inthree-point bending. Part II: experimental investigation andnumerical modelling, Cambridge University EngineeringDepartment, 26 November 2003.[4]. Kantha K. R., Jayathirtha K. R., Sarwade A. G., ChandraS. M., Strength Analysis on Honeycomb Sandwich Panels ofdifferent Materials, Hyderabad May-Jun 2012.[5]. ***, Ansys theory, http://www.ansys.com/staticassets/ANSYS/staticassets/resourcelibrary/presentation/2014-sd-mechanical-contact-best-practices.pdf.[6]. ***, http://www.ansys.com/staticassets/ANSYS%20UK/staticassets/Presentations/2014%20Convergence%20Presentations/CONF2014_John_Lin_MechanicalContactBestPractices.pdf.[7]. Huson P. N., Experimental and numerical simulations ofexplosive loading on structural components: composite sandwichconnections, UC San Diego, 2012.[8]. Naresh Ch., Numerical Investigation into Effect of Cell Shapeon the Behavior of Honeycomb Sandwich Panel, InternationalJournal of Innovative Research in Science, Engineering andTechnologyDecember 2013.[9]. ANSYS Inc., ANSYS 12.0 reference manual, 2009.[10]. Bianchi G., Thesis Structural Performance of SpacecraftHoneycomb Panels, University of Southampton, April 2011.[11]. Taylor E. M., Thesis Two-Way Behavior and FatiguePerformance of 3-D GFRP Sandwich Panels, Faculty of NorthCarolina State University, 2009.

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COMPRESSIVE BEHAVIOUR OF ULTRA-SONICATEDSTARCH/CARBON BLACK/EPOXY COMPOSITES

Iulia GRAUR1,2, Georgel MIHU3, Vasile BRIA1,Adrian CÎRCIUMARU1,2*, Iulian-Gabriel BÎRSAN11”Dunărea de Jos” University of Galati, Cross Border Faculty of Humanities,

Economics and Engineering Sciences2 Diagnose and Measurement Group, Galati

3”Dunărea de Jos” University of Galati, Engineering Faculty*Corresponding author


ABSTRACT

Generally the fillers are used in order to change some basic properties ofpolymer matrix but often the filler’s particles tends to aggregate with consequencesin mechanical properties of final composite. In order to avoid the aggregation manysolution have been purposed and one of them is to use the ultra-sounds in variousstages of composites formation. In this study the compressive behaviour of filledepoxy were analysed. As filler, at a 10% volume ratio, a mixture of three parts ofstarch and one part carbon black had been used. The aim of the analysis was toidentify the effect of ultra-sonication at different frequencies and for differentperiods of time on the compressive properties of composites.

KEYWORDS: compressive behaviour, polymer, ultra-sonic treatment, epoxyresin

1. Introduction

Among the thermoset materials, epoxy resinsshows special chemical characteristics such asabsence of secondary products or volatiles duringcuring reactions, low shrinkage up on curing, curingover a wide temperature range and the control ofdegree of cross-linking. Depending on the chemicalstructure of the curing agents and curing conditions,the properties of cured epoxy resins will vary [1].Ultra-sonication during polymerization is a veryefficient method to increase the dispersion of fillerparticles in the pre-polymer mixture, in the case ofthermoset polymers. The effect of ultra-sonication isalso observable through some changes which occur inhomogeneity, viscosity, relaxation time andhardening of pre-polymer gel [2]. To get superiorproperties of polymers one usual way is to modify itby placing another phase, for instance a nano-sizedone, into the polymer volume [3]. Such materialsshould provide unique mechanical and thermalproperties combined with low specific weight andhigh wear resistance in order to ensure the safety andeconomic efficiency [4]. Among the most commonlyused fillers are: carbon nanotubes, carbon black [5,6], nano-metals, talc, clays, starch [7, 8] and nano-

ceramics. Carbon black [9] and starch are used toenhance the properties of epoxy composites comparedwith unfilled ones – especially regarding tribological[10] and electrical behaviour [11].

The technique of modifying the polymer byadding certain powders is not new at all but ischallenged by some difficulties when the usedparticles are smaller and smaller [12]. Such amodified polymer properties are depending not onlyon powders properties but also on dispersion ofparticles into the polymer volume.

The main goal is to obtain uniform dispersionavoiding clusters formation as the clusters areconstituting structural defects from the polymernetwork point of view [13]. The use of ultra-soundsexposure of pre-polymer mixture might solve theuniform distribution problem. Under the action ofultra-sounds there is a change in homogenization,viscosity, relaxation time of pre-polymer mixture andstrengthening of formed polymer [14].

Ultra-sound has found numerous uses in widelydifferent fields of application. Recently, attention hasturned to multiphase systems where attempts havebeen made to relate the ultra-sonic velocity with theconcentration and the degree of dispersion of two-phase systems [15]. In this paper the effect of ultra-

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sonication over the compressive properties of carbonblack and starch filled epoxy resin composites wasinvestigated, as the starch is meant to avoid theaggregation of carbon-black particles.


For this study compressive test were performedon modified epoxy composites. The matrix consistsof EPIPHEN RE4020 – DE4020 epoxy system thatwas modified with a mixture of three parts of starchand one part of carbon black. A composite material isgenerally composed of two or more materials withdistinct properties but through their bond can providea single composite material with unique properties[16]. This is true, however, if both constituents arepresent in a reasonable proportion of at least 5% andvarious properties [17]. The powder mixture was usedto obtain a 10% volume ratio of modifying agent inthe epoxy matrix - based on other studies [18]. Thepowder was mechanically dispersed into the requiredquantity of resin and mixture was exposed from oneto five minutes to the ultra-sonic flux generated by an

air-generator at different frequencies. After this stepthe required quantity of hardener was added and themixture was mechanically mixed at 45 oC for 15minutes - in order to maintain the low viscosity ofmixture during the gel phase and, than poured intomoulds. The 15 minutes time of mixing wasestablished after trial and error tests that confirm thefact that during this step the viscosity of mixtureremains low such as it may be easily poured into themoulds and allowing the elimination of gaseousproducts. After this step all the samples were exposedto ultra-sonic influence at a distance of 1 m from theultra-sound air-generator. Samples extraction wasperformed after 24 hours and was followed bythermal recommended treatment. Compressive testswere carried out at room temperature with M350-5ATtesting machine from Testometric (Fig. 1). Thecompression tests were performed at a speed of 5mm/min. The compressive specimens were 5mmheight and 10 mm diameter. Five specimens of eachmaterial were tested. Testing method, sampledimensions and test parameters were set according toASTM-D-3410-87 [19, 20].

I. II.

Fig. 1. I - M350-5AT compressive testing machine from Testometric; II - compressive specimens fortesting: a) before compression test; b) after the compression test

3. Results

Compression Young Modulus and Strain atYield of epoxy resin are plotted as a function of ultra-sonic exposure time (0 to 5 minutes).

Regarding compression Young modulus itseems (Fig. 2-5) – but this assumption has to beverified – that the exposure at 24 kHz and 42 kHzleads to an improvement in compression elasticity of

polymer – on the x-axis the time of epoxy resin ultra-sound exposure. The results are strongly influencedby the local conditions at the time of forming andultra-sonication.

However the results in the case of 26 kHzfrequency seem that ultra-sonic exposure has noeffect on compressive elastic modulus excepting theuse of four minutes ultra-sound exposure when theeffect is destructive.

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Fig. 2. Compression Young Modulus of 24 kHz ultra-sonicated epoxy




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At the two higher frequencies it seems that theultra-sound exposure time is important since the threeminutes ultra-sound exposure time (30 kHz) and,respectively, two minutes ultra-sound exposure time(42 kHz) leads to better results regarding thematerials elasticity.

Marking a change in polymer mechanicalresponse (from elastic to plastic) the strain at yield is

an important parameter used to describe polymersbehaviour. The values of this parameter are notshowing dramatic changes excepting the cases of oneminute ultra-sound exposure time at 30 kHz and threeminutes ultra-sound exposure time at 42 kHz but,once again, these results might be influenced by theenvironmental conditions.

Fig. 6. Strain at Yield of 24 kHz ultra-sonicated epoxy



Because of the interaction between ultra-soundsand polymer matrix it was expected a decrease ofcompressive parameters values but, analysing thegraphs above the behaviour is far from expectation.The strain at yield (Fig. 6-9) is practically unchangedrelative to standard probe (sample of epoxy resinwithout any ultra-sound exposure) taking into account

the unavoidable gaseous intrusions inside of thesamples. The strain at yield is independent both fromthe ultra-sound frequency and from ultra-soundenergy. Fact is that the use of ultra-sound exposurehad leaded to better dispersions of powders that hadbeen used to modify the basic properties of the epoxyresin.

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4. Conclusions

These experimental results provided a databaseon the compressive behaviour of ultra-sonicatedstarch/carbon black/epoxy composites. Acomprehensive and reproducible set of data has beenobtained to characterise the mechanical behaviour ofthe ultra-sonicated starch/carbon black/epoxycomposites. These results are particularly significantfrom the compression point of view, because it seemsthat the ultra-sonication does not induce severmodifications but tensile and bending tests arenecessary in order to complete the picture of theinfluence of this type of treatment over themechanical properties of epoxy resin. One issue thathas to be followed during the further studies isidentification of a method to avoid the gaseousintrusions tacking into account the fact that they areresponsible for non-linear responses at externalloadings.

Acknowledgement

The work of Vasile Bria was supported byContract nr. 138963/2014, Project code:POSDRU/159/1.5/S/138963.

The work of Georgel Mihu has been funded bythe Sectorial Operational Programme HumanResources Development 2007-2013 of the Ministry ofEuropean Funds through the Financial AgreementPOSDRU/159/1.5/S/132397.

The work of Iulia Graur and Adrian Cîrciumaruhad been supported by the Project 12 P01 024 21(C11) /31.08.2012 (code SMIS 50414).

References[1]. Asif Abdul Azeez, Kyong Yop Rhee, Soo Jin Park, DavidHui, Epoxy clay nanocomposites – processing, properties andapplications: A review, Composites Part B: Engineering, Vol. 45,Issue 1, 2013.[2]. Horun S., Aditivi pentru prelucrarea polimerilor, Ed.Tehnică,București, 1978.

[3]. Bart J. C. J., Additives in Polymers.Industrial Analysis andApplications, John Wiley & Sons, ISBN 0-470-85062-0, 2005.[4]. Amit C., Muhammad S. I., Fabrication and characterizationof TiO2 – epoxy nanocomposite, Materials Science and EngineeringA 487, p.574 – 585, 2008.[5]. Balberg I., A comprehensive picture of the electricalphenomena in carbon black–polymer composites, Carbon 40, p.139 – 143, 2002.[6]. Gubbels F., Blacher S., Vanlathem E., Jerome R., DeltourR., Brouers F., Design of Electrical Conductive Composites: KeyRole of the Morphology on the Electrical Properties of CarbonBlack Filled Polymer Blends, Macromolecules, 28, p. 1559 – 1566,1996.[7]. Vargha Viktoria, Truter Patricia, Biodegradable polymersby reactive blending trans-esterification of thermoplastic starchwith poly(vinyl acetate) and poly(vinyl acetate-co-butyl acrylate),European Polymer Journal, 41, p. 715 – 726, 2005.[8]. Rodriguez-Gonzalez F. J., Ramsay B., Favis B. D.,Rheological and thermal properties of thermoplastic starch withhigh glycerol content, Carbohydrate Polymers, 58, p. 139 – 147,2004.[9]. Fiedler B., Gojny F. H., Wichmann M. H. G., Nolte M. C.M., Schulte K., Fundamental Aspects of Nano-ReinforcedComposites, Composites Science and Technology, Vol. 66, Issue16, p. 3115 – 3125, ISSN 0266-3538, 2006.[10]. Birsan I. G., Andrei G., Bria V., Postolache I., CirciumaruA., Tribological Behavior of Clay/Epoxy Composites, Proceedingsof the 5th International Scientific Conference BALTRIB’2009,Kaunas, Lithuania, Vol. 5, p. 164 – 169, ISSN 1822-8801.[11]. Claudia Ungureanu, Marius Bodor, Iulia Graur, AdrianCîrciumaru, Vasile Bria, Carbon filled polymers, UGALINVENT, Research and Innovation Exhibition, “Dunarea de Jos”University of Galati, Romania, 7 – 9 October 2015.[12]. Colbert D. T., Single-wall nanotubes: a new option forconductive plastics and engineering polymers, Plastics AdditivesCompd, p. 18 – 25, 2003.[13]. Rocco A. M., Pereora R. P., Felisberti M. I., Polymer, Vol.42, p. 199 – 205, 2007.[14]. Kolosov A. E., Sakharov A. S., Sivetskii V. I., Sidorov D.E., Sokolskii A. L., Substantiation of the efficiency of usingultrasonic modification as a basis of a production cycle forpreparing reinforced objects of epoxy polymer composition,Chemical and Petroleum Engineering, Vol. 48, Nos. 5 – 6, Sept.,2012 (Russian Original Nos. 5 – 6, May – June, 2012).[15]. R. Gendron, J. Tatibouet, J. Guevremont, M. M.Dumouliu, L. Piche, Ultrasonic behavior of polymer blends,Polymer Engineering and Science, Vol. 35, no. 1, 1995.[16]. Calienciug A., Cercetări privind bara paraşoc pentruautovehicule, confecţionată din materiale compozite noi, (PhDthesis), 2012.[17]. Matthews F. L., Rawlings R. D., Composite Materials:Engineering and Science, Woodhead Publishing Limited, ISBN978-1-85573-473-9, 2008.

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[18]. Roman I., Ungureanu V., Bria V., Circiumaru A., BirsanI. G., Strach Epoxy Composites a Study of Starch AmountInfluence, Proceedings of the 12th International Conference onTribology – SERBIATRIB’11, Kragujevac, Serbia, p. 181 – 184,ISBN 978-86-86663-74-0.

[19]. Cîrciumaru A., Caracterizarea si testarea materialelorcomposite cu matrice polimerice, Ed. Europlus, Galati, 2013.[20]. Cîrciumaru A., Caracterizarea si testarea materialelorpolimerice, Ed. Europlus, Galati, 2013.

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THE UNUSUAL ELECTROMAGNETIC PROPRIETIES OF FABRICREINFORCED EPOXY COMPOSITES

Marina BUNEA1, V. BRIA2, A. CÎRCIUMARU2,*, I. G. BÎRSAN21”Dunărea de Jos” University of Galati, Faculty of Mechanical Engineering,

Domnească Street, 47, RO-800008, Galati, Romania2”Dunărea de Jos” University of Galati, Border Faculty of Humanities, Economics and Engineering,

Domnească Street, 47, RO-800008, Galati, Romaniae-mail: [email protected]

ABSTRACT

In this research, the electromagnetic behaviour of four composite materialswas investigated as an important issue of composite researchers is to control theelectrical properties of polymer matrix composites. The four materials are epoxymatrix fabric reinforced composites. Each of reinforcements is realized from 17layers of fibres fabric of each type excepting the medial layer which is made of ahybrid fabric meant to solve two issues – one is about gathering information aboutmaterials loading state while the second is to increase the electromagneticshielding properties of formed materials. The four used fabrics are of simple typeplain fabrics made of yarns of carbon fibres, aramid fibres and, respectively, twotypes of glass fibres. All the reinforcement layers, excepting the medial one, havethe yarns of warp and fill, respectively parallel while the medial layer has warpyarns perpendicular on warp yarns of the other layers. The matrix of wet lay-uptechnique formed materials is made of epoxy system Epiphen RE 4020 – DE 4020.

KEYWORDS: dielectric permittivity, electrical conductivity, magneticpermeability, epoxy matrix

1. Introduction

The composite materials with unusualelectromagnetic properties, which exhibit negativevalue of electrical and magnetic properties, are ofparticular interest.

The materials with negative values of dielectricpermittivity and magnetic permeability are known asthe meta-materials. Meta-materials which exhibitsimultaneously negative dielectric permittivity andnegative magnetic permeability are called left-handedmaterials, which have the negative index ofrefraction, so as these materials have the similarfunction of a lens [1-5], it meaning that phase andgroup velocity of an electromagnetic wave canpropagate in opposite direction [6, 7], leading todisappearance of the object in the radar field. Whenthese parameters have different signs, these materialsare called right-handed materials [8]. In this case, theelectromagnetic wave cannot spread [9].

For a negative ε, the force between twoelectrons will be attractive, leading to electron-pairingif other electron instabilities can be arrested. Electron-pairing has been demonstrated to be responsible for

superconductivity in the conventional lowtemperature superconductors as well as in the newlydiscovered high temperature superconductors [10].

In spacecraft construction the meta-materials areimportant due to their electromagnetic shielding,which can protect the spacecraft against radiation andoverheating.

The constitutive elements of a meta-material aremeta-atoms or meta-molecules. Through the meta-atoms we can identify wire meshes, splitter ringresonators, conical Swiss rolls, Swiss rolls, furtherdevelopment of this fascinating domain allowingother types of constitutive elements [11].

Other structures were also suggested to instigatemeta-material behavior, including multi-layerscomposed of alternately overlapped negativepermittivity and negative permeability layers. In theexploration of meta-materials, polymers have beenapplied only as an insulating host, but the specificcontributions of the polymer layer were rarelymentioned, which may be due to the weakelectromagnetic responses to outer electric or/andmagnetic field with respect to ferromagnetic materials[4].

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Also, the composite materials with specialelectromagnetic properties are studied formanufacturing of smart composites, which theimportant characteristic is the auto-repairing ofdamage area. By measuring of the electricalconductivity of object, it can be determined themechanical damage area and then applying a strongelectric pulse for partially melt the polymer matrix inthe area of damage, which would eliminate the defect[12, 13]. Carbon fiber reinforced polymer compositesare multifunctional materials in which the damage iscoupled with the material electrical resistance,providing the possibility of real-time informationabout the damage state through monitoring ofresistance [14]. The heterogeneous smart materialsmight exhibit new properties not existing in any ofthe constituents due to the coupling of different fields[15].

2. Materials

Four fabric reinforced epoxy matrix compositeshad been formed for this study. They are denoted asHCH – carbon fiber fabric reinforced epoxycomposite, HKH aramid fiber fabric reinforced epoxycomposite, H1SH and H2SH glass fiber fabricreinforced epoxy composites. The fabrics are simpleplain fabrics: 4×4 plain weave carbon fabric with 160g/m2 density denoted C, 6.7×6.7 plain weave aramidfabric with 173 g/m2 density denoted K, 12×12 plainweave glass fabric with 163 g/m2 density denoted 1Sand 6×6 plain weave glass fabric with 390 g/m2

density denoted 2S. All the materials have 17 layersreinforcements symmetrically distributed relatively tothe medial layer. The medial layer only is made of aspecial hybrid fabric that had been obtained byreplacing each second yarn of aramid fibers in the fillof a mixed carbon-aramid fabric.

The mixed fabric has a structure of 2:1carbon:aramid yarns on warp and 1:2 carbon:aramidyarns on the fill. Each second yarn of aramid fibers inthe fill was manually replaced with a glass fibers yarnof 200 tex in which a tinned cooper wire 0.2 mmdiameter was inserted. (Fig. 1).

Fig. 1. The special modified fabric M

Each material has 16 layers of reinforcement ofsame fabric while the medial layer consists of abovedescribed fabric. For all the 16 identical layers thedirections of warp yarns and fill yarns arerespectively parallel while the fill yarns of mediallayer are perpendicular on others layers fill yarns.

The materials were formed using the wet lay-upmethod placing each pre-polymer imbued sheet offabric into a glass mold. After polymerization all thematerials were thermally cured according to epoxysystem producer to reach the best properties ofpolymer.


The measurement of electromagnetic parametersof composite materials was performed with a LCR-meter Protek 9216A at five frequencies (100 Hz, 120Hz, 1 kHz, 10 kHz and 100 kHz) in the four modesthat the LCR meter is build: R+Q (resistance andquality factor), L+Q (inductance and quality factor),C+D (capacitance and dielectric loss and C+R(capacitance and resistance). For measurements wasused 1V drive voltage. The dimensions of testedspecimens were 281×194 mm. For each sample fivecomplete sets of measurements were realized – withthe measuring cell in different points on the surface ofsample – according to standard electriccharacterization of plates used in electric andelectronic applications.


The evaluations of dielectric permittivity,electrical conductivity and, magnetic permeabilitywere made based on the 200 measured values of eachC, R and L parameters and were calculated by theformulas given in [16]. In Fig. 2-5 are plotted thevalues of surface and bulk dielectric permittivity ofthe composite materials. The higher values ofdielectric constants were determined at 100 Hzfrequency and then these values were decreased withincreasing of frequency with exception of aramidfabric reinforced epoxy composite. How it can beseen in fig. 3 and 5, the carbon fabric reinforcedepoxy composite exhibits negative values of surfaceand bulk dielectric permittivity in 0.1-10 kHz. Thedielectric values were calculated based on recordedvalues of electrical capacitance.

Negative capacitance had been observed in solidstate device structures and explained by reference toimpact ionization, injection of minority carriers, or animaginary component in the carrier mobility [17] andthe dielectric constant of conducting polymercomposites becomes negative after the forming of a

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continuous conducting pathway because the chargedelocalized in a macroscopic scale [6].

Fig. 2. The surface dielectric permittivity of thefabric reinforced epoxy composite materials

Fig. 3. The surface dielectric permittivity ofcarbon fabric reinforced epoxy composite

material

Fig. 4. The bulk dielectric permittivity of thefabric reinforced epoxy composite materials

As would be expected higher surface electricalconductivity exhibits the carbon fabric reinforcedepoxy composite in comparison with other studiedcomposites (Fig. 6). The lower electrical conductivityof aramid and glass fabric reinforced epoxy materialswere determined at 0.1 kHz and then the electricalconductivity of these composites decrease with

increasing of frequency, while the electricalconductivity of HCH composite remained unchanged.The similar values of electrical conductivity of thecomposites were determined for bulk measurements(Fig. 7), with exception of H1SH composite whichexhibits the negative electrical conductivity at 0.1kHz frequency, but from 0.12 kHz frequency upwardsthe electrical conductivity of this composite is similarto that of HKH and H2SH composites (Fig. 8).

Fig. 5. The bulk dielectric permittivity of carbonfabric reinforced epoxy composite material

Fig. 6. The surface electrical conductivity offabric reinforced epoxy composite materials

It is possible that the appearance of negativeconductivity in a non-equilibrium electron system,i.e., a situation in which the current flows opposite tothe electric field [18]. The values of electricalconductivity of composites were calculated onrecorded electrical resistance by LCR-meter.Negative resistance means that the more positive isthe voltage, the more negative is the current, i. e. thecurrent–voltage characteristic is a straight line ofnegative slope through the origin. Although thenegative resistance is apparent, its mechanismresembles that of true negative resistance, i.e. theelectrons traveling in the unexpected directionrelative to the applied voltage gradient [19].

In Fig. 9-12 are plotted the unusual values ofmagnetic permeability of the composites.

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Fig. 7. The bulk electrical conductivity of fabricreinforced epoxy composite materials

Fig. 8. The bulk electrical conductivity of 1Sglass fabric reinforced epoxy composite material

Fig. 9. The surface magnetic permeability offabric reinforced epoxy composite materials

Fig. 10. The bulk magnetic permeability offabric reinforced epoxy composite material

Fig. 11. The magnetic permeability of carbon fabric reinforced epoxy composite material

It can be observed that the HKH and H1SHcomposites exhibit negative values of both surfaceand bulk magnetic permeability constants at allfrequencies in decreasing mode. The compositeH2SH exhibits negative magnetic permeability at allfrequencies, with exception of 0.1 kHz where the bulkmagnetic constant is positive. Regarding the magneticbehavior of HCH composite, this material exhibitspositive values of surface magnetic permeability in0.1 – 10 kHz frequency range and at 100 kHz thevalue magnetic constant is negative. But the bulkmagnetic constants exhibited by HCH composite arepositive in 0.1 – 1 kHz frequency range and negativeat 10 and 100 kHz frequencies.

Fig. 12. The bulk magnetic permeability of 2Sglass fabric reinforced epoxy composite

materials

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5. Conclusions

The measurements of electrical and magneticparameters of fabric reinforced epoxy compositeswere performed. The electric, dielectric and, magneticconstants were evaluated and the electromagneticbehaviour of materials was investigated. Theconclusions are as follows:

● The carbon fabric reinforced epoxy compositeexhibits negative values of dielectric permittivity in0.1-10 kHz frequency range. The electric conductivityof this material is higher in comparison with othercomposites and invariable. It exhibits negativesurface magnetic permeability value at 100 kHz andnegative bulk magnetic permeability values at 10 and100 kHz.

● HCH composite exhibits simultaneouslynegative bulk dielectric permittivity and negativebulk magnetic permeability at the same 10 kHzmeasurement frequency.

● The magnetic permeability of HKH, H1SHand H2SH composites showed negative values onentire range of frequencies, but only bulk magneticconstant H2SH of these materials showed positivevalue.

● The bulk electrical conductivity and resistivityof H1SH composite showed negative values at 0.1kHz.

References[1]. Veselago V. G., The electrodynamics of substances withsimultaneously negative values of ε and μ, Sov. Phys. Uspekhi,Vol. 10, No. 4, p. 509-514, Jan-Feb. 1966.[2]. Ramakrishna S. A., Physics of negative refractive indexmaterials, IOP Publishing Ltd, Rep. Prog. Phys., 68, p. 449-521,2005.[3]. Bayindir M., Aydin K., Ozbay I., Marcos P., Soukoulis C.M., Transmission properties of composite metamaterials in freespace, Applied Physics Letters, Vol. 81, No. 1, 2002.[4]. Caglayan H., Ozbay E., Observation of cavity structures incomposite metamaterials, Journal of Nanophotonics, Vol. 4, 29July 2010.

[5]. Li M., Yang H., Wen D., Transmission and reflection ofcomposite metamaterials in free space: experiments andsimulations, Microwave and Optical Technology Letters, Vol. 51,No. 8, August 2009.[6]. Sui G., Li B., Bratzel Gr., Baker L., Zhong W. H., Yang X.P., Carbon nanofiber/polyetherimide composite membranes withspecial dielectric properties, Soft Matter, 5, p. 3593-3598, 2009.[7]. Solymar L., Shamonina E., Waves in Metamaterials, OxfordUniversity Press, ISBN 978-0-19-921533-1, 2009.[8]. Si L. M., Jiang T., Chang K., Chen T. Ch., Lv X., Ran L.,Xin H., Active Microwaves Metamaterials Incorporating IdealGain Devices, Materials, 4, p. 73-83, 2011.[9]. Liu Y., Zhang X., Metamaterials: a new frontier of scienceand technology, Chem. Soc. Rev., 40, p. 2494-2507, 2011.[10]. Chu C. W., Chen F., Shulman J., Tsui S., Xue Y. Y., WenW., Sheng P., A negative dielectric constant in nano-particlematerials under an electric field at very low frequencies, StronglyCorrelated Electron Materials: Physics and Nanoengineering, Vol.5932, 2005.[11]. Grimberg R., Electromagnetic metamaterials, MaterialsScience and Engineering, B, 178, p. 1285-1295, 2013.[12]. Makunin A. V., Chechenin N. G., Nanocarbon-polymercomposites for space technologies, Part 1: Synthesis and propertiesof nano-carbon structures, "University Book", ISBN 978-5-91304-249-1, 2011.[13]. ***, Intelligent air construction materials and microsystemtechnology, Moscow Institute of Physics and Technology (StateUniversity), Conference Series "The Future of the Industry», SkyShell, Russia, 2012.[14]. Wen J., Xia Zh., Choy Fr., Damage detection of carbonfiber reinforced polymer composites via electrical resistancemeasurement, Composites: Part B 42, p. 77-86, 2011.[15]. Qilin M., Jihui W., Fuling W., Zhixiong H., Xiaolin Y.,Tao W., Conductive Behaviors of Carbon Nanofibers ReinforcedEpoxy Composites, Journal of Wuhan University of Technology-Mater. Sci. Ed., Vol. 23, No.1, p. 139-142, 2008.[16]. Cîrciumaru A., Proiectarea, formarea și caracterizareamaterialelor compozite cu matrice polimerică, Editura Europlus,Galați, ISBN 978-606-628-060-0, 2013.[17]. Bakueva L., Konstantatos G., Musikhin S., Ruda H. E.,Shik A., Negative capacitance in polymer-nanocrystal composites,Applied Physics Letters, Vol. 85, No. 16, 2004.[18]. Belonenko M. B., Lebedev N. G., Yanyushkina N. N.,Sharkizyanov M. M., Absolute Negative Conductivity ofGraphene with Impurities in Magnetic Field, Semiconductors, Vol.45, No. 5, p. 628-632, 2011.[19]. Wang Sh., Chung D. D. L., Apparent negative electricalresistance in carbon fiber composites, Composites: Part B 30, p.579-590, 1999.

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· PDF fileEDITORIAL BOARD EDITOR-IN-CHIEF Prof. Marian BORDEI - ˇ ˇDunarea de Jos ˇ ˇ University of Galati, Romania EXECUTIVE EDITOR Lecturer Marius BODOR-