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Filler influence on microstructure of Fe/resin composites. M . Stre čková, R. Bureš, M. Fáberová, T. Sopčák. Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, Košice, Slovak Republic. Acknowledgement - PowerPoint PPT Presentation
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Filler influence on microstructure of Fe/resin compositesFiller influence on microstructure of Fe/resin composites
M. Strečková, R. Bureš, M. Fáberová, T. Sopčák
Institute of Materials Research, Slovak Academy of
Sciences, Watsonova 47, Košice,
Slovak Republic
AcknowledgementThis work was financially supported by Slovak Research and Development Agency under the contract no APVV 0222/10
Outline of my presentation is as follows
Theoretical background and motivation
Aim of the present work
Experimental procedure
Results and discussions
Conclusions
Theoretical background
The phenol-formaldehyde resin (PFR) belong to the oldest thermosetting polymers
with a wide range of usage, because of their low cost, aging endurance,
undemanding preparation and grate modification with regard for further use.
The appropriate design of composite powder materials with desirable
mechanical and physical-chemical properties is a very difficult task, because
their chemical modification should simultaneously improve various properties
such as dimensional and shape stability, hardness and flexural strength,
electric and magnetic properties.
Soft magnetic composites (SMC), which are used in electromagnetic
applications, can be produced from ferromagnetic powder particles
coated by an electrical insulating film.
Theoretical background
PFR is a possible insulating organic coating for preparation of SMC, but conservation of
dimensional stability after curing is a limiting factor of overall sample preparation.
The evolution of water and other volatile by-products is a undesirable part of crosslinking
process during curing and causes formation of micro- and macrovoids in the sample
(foaming of resin at the surface as shown in both figures below).
Aim of the present work
Preparation of resol type phenol – formaldehyde resin suitable as a organic coating on
Fe powder particle.
Modification of PFR by two different inorganic additives SiO2 and ZnSO4, with the aim
to prepare Fe-PFR, Fe-PFR-SiO2 and Fe-PFR-ZnSO4 microcomposite materials.
The analysis of thermal degradation process of pure and modified PFR by TG and DSC
analysis.
The observation of morphology and microstructure with respect to the additives.
The study of mechanical hardness, flexural strength, electric resistivity and magnetic
properties.
Experimental
Preparation of PFR
The reaction molar ratio of phenol/formaldehyde/ammonia – 1.0/1.5/0.35
phenol
formaldehyde37%Water solution
catalyst26% NH3
heating 85°C
Reflux 45 min
Experimental
Preparation of PFR
After removal water under vacuum PREPOLYMER with
honey – like viscosity
The structure was identified by IR and 13C-NMR spectroscopy.
Experimental
Preparation of modified PFR
The two type of modified resins were prepared PFR-SiO2
PFR-ZnSO4
The dried additives SiO2 and ZnSO4 were added to PFR in the fortieth minute of water
removing under vacuum.
Coating
The pure and modified resins were dissolved in acetone, the Fe particles were added
to those solutions and mechanically mixed after a complete evaporation of acetone
was achieved from the suspension.
In order to prepare the microcomposites Fe-PFR-SiO2 and Fe-PFR-ZnSO4,
the coated powder was pressed into required shape for mechanical testing at 800 MPa.
Experimental
Curing
Curing schedule applied for each sample.
Temperature [°C] 50 60 80 90 100 120 160 180
Time [h] 3 3 15 2 1 2 1 1
Thermal analysis
Simultaneous DSC and TG analysis were performed by difference scanning calorimeter,
samples were heated up to 700°C at heating rate of 10°C/min in air.
SEM, mechanical testing
The microstructure and morphology were analyzed by scanning electron microscopy
equipped with EDX analysis.
Vickers hardness and flexural strength were measured according to standards.
Results
0 50 100 150 200 250 300 350 400 450 500 550 600 650 7000
20
40
60
80
100
PFR-SiO2
PFR-ZnSO4
PFR
m w
t
T 0C50 100 150 200 250 300 350 400 450 500 550 600 650 700
4,5
5,0
5,5
6,0
6,5
PFR PFR-SiO
2
PFR-ZnSO4
endo
exo
T 0C
0 50 100 150 200 250 300 350 400 450 5000,0
0,5
1,0
1,5
2,0
2,5
3,0
Fe-PFR-ZnSO4
Fe-PFR-SiO2
Fe-PFR
-m
/ w
t%
T oC
The rapid evolution of water at 175°C from PFR
The higher mass loss, slow and easier evolution in the PFR-SiO2
Small mass loss corresponds to release of chemically weakly bonded water in Fe microcomposite powder
The opposite situation in the case of Fe microcomposite powder in comparison with resins without Fe can be observedThe highest mass loss in the Fe-PFR-ZnSO4 because of different structure of PFR-ZnSO4 after coating process.
Two significant regions in DSC traces. First 125 °C-225 °C Second 400 °C - 600 °C
Results – SEM characterisation
The negative effect of evolution of water
– foaming of PFR on the surface
– destabilization of dimensional shape
– formation of micro- and macrovoids
The positive effect of additives
– act against surface deformation
– act against separation of PFR from bulk
Results
The morphology of modified PFR-SiO2
coating on Fe powder before curing.
– uniform
– smooth
– adhesive
– the native agglomerates of SiO2
The zoom of SiO2 agglomerates
sticked on Fe particles
– the size of SiO2 is around 1 μm
– SiO2 agglomerates are composed of fine 100nm
nanoparticles and they did not disaggregated
during the composite preparation
Results
The morphology of modified PFR-ZnSO4
coating on Fe powder before curing.
– addition of ZnSO4 causes a significant change
in the polymer structure, which is constituted
by nano-fibers linking Fe particles
– formation of fibrillar structure
The zoom on fibrillar structure
– fiber is around 10 μm long, 100 nm thick
– very small ZnSO4 particles are located on their
surface
– incorporation of ZnSO4 to the PFR structure
was confirmed by EDX analysis
Results
The morphology of modified PFR-ZnSO4
coating on Fe powder after curing.
– more rough but still compact coating
– the different morphology arises because of
the breakdown of PFR fibers during
polymer melting at the curing temperature
The morphology of modified PFR-SiO2
coating on Fe powder after curing.
– homogeneous
– smooth
– adhesive
– incorporated SiO2 particles in the coating
Results
Detail on the coating
– the resin coating is uniform without any
visible exfoliation
SEM image on microstructure
– PFR creates macroscopically continuous
phase around Fe particles
– uniform network
– resin clusters are occasionally evident
– overall microstructure exhibits insignificant porosity
Results
Samples notation
PFR[wt %]
Fe[wt %]
SiO2
[wt %]
ZnSO4
[wt %]HV10
TRS[MPa]
Specific resistivityρ (μΩ m)
Coercitive
field
Hc (kA/m)
Saturation
induction
Bmax (T)
Höganäs Fe - 100 - - 115 - 1.62 x 10-1 0.12-0.2 [48] 1.0/1.3 [48]
A 100 - - - - - - - -
B 3 97 - - 93 74,32 3,16 x 103 0.19 1.2-1.3
C 5 95 - - 83,63 86,34 4,58 x 104 0.26 1.1-1.25
D 90 - 10 - - - - - -
E 90 - - 10 - - - - -
F 3,5 95 1,5 119,85 55,67 2,42 x 105 0.34 1.1-1.25
G 4,5 95 - 0,5 178,17 39,87 1,03 x 104 0.29 1.15-1.25
Composition of microcomposites, Vickers hardness and flexural strength
– the hardness of sintered Fe at 1100 °C is 115 HV/10
– the microcomposite material Fe-PFR-ZnSO4, shows much higher hardness than
the pure sintered Fe at the expense of smaller flexural strength
– the growth in resistivity comes from the higher amount of electroinsulating component
– the highest resistivity in the sample F can be attributed to incorporation of chemically
inert SiO2 fine particles into the PFR coating.
-40 -30 -20 -10 0 10 20 30 40
-1,0
-0,5
0,0
0,5
1,0
B [
T]
H [kA.m-1]
sample C
11a
-40 -30 -20 -10 0 10 20 30 40-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
B [
T]
H [kA.m-1]
sample G
11b
DC hysteresis loop of Fe-PFR
(95% Fe - 5% PFR)
DC hysteresis loop of Fe-PFR-ZnSO4
(95% - 4,5% PFR - 0,5%ZnSO4)
Concluding remarks
The iron powder coated by PFR as a thin electrical insulating layer was prepared with aim to
design a new class of prospective soft magnetic composite.
The elimination of undesirable foaming and destabilization of the sample was achieved by
modification of PFR coating by two inorganic additives SiO2 and ZnSO4 and proposed curing
schedule.
The results of TG and DSC analysis showed that both additives are suitable water absorbents.
The addition of ZnSO4 caused a significant change in the polymer structure, which consist of
nano-fibers linking Fe particle in final composite.
The mechanical hardness test has confirmed that the fibrillar structure of Fe-PFR-ZnSO4
microcomposite results in a more stable material with significantly higher hardness
The pure and modified PFR coating form an excellent insulating spacer in between Fe
microparticles, which consequently leads to enormous increase of the specific resistivity.
Syntéza PFR-SiO2 (s teosom) pre prípravu mikrokompozitného materiálu Fe-PFR-SiO2
Možné výhody: - samotná syntéza SiO2 priamo v PFR by mohla spevniť PFR a zvýšiť mechanickú pevnosť materiálu. - príprava nano SiO2 sol-gel procesom in-situ je jednoduchšia a rýchlejšia - dôkaz o veľkosti takto pripravených SiO2 bol robený TEM-kou, syntetizujú sa častice s veľkosťou 180nm a 50nm - IR analýzy potvrdzujú prítomnosť Si v polymérnej matrici-TG a DSC analýzy (ešte vyhodnotím)
Mólový pomer fenol-formaldehyd-amoniak-teos (ďalej Ph:F:NH3:TEOS)
Ph:F:NH3:TEOS 1 : 1,5 : 0,35 : (0,17 0,085 0,064)
Príprava PFR-SiO2 podľa postupu zaužívanom pri príprave samotnej PFR.
Postuptné znižovanie SiO2 v PFR (podľa potreby a výsledkov mechanickej
tvrddosti).Stanovenie SiO2 v PFR spektrofotometricky.
Povlakovanie (snaha znižovať hmotnostné percento PFR na Fe časticach)Vytvrdzovanie (vytvrdzovací cyklus).LisovanieMechanické skúškyElektrický odpor a Magnetické merania
Syntéza PFR-B (s H3BO3) pre prípravu mikrokompozitného materiálu Fe-PFR-B
Možné výhody: - priame naviazanie bóru do štruktúry PFR, fenolové jadrá sa premosťujú O-B-O mostíkmy čo by malo viesť k výraznej mechanickej tvrddosti a termálnej stabilite pripravejej modifikovanej živice. - analýzy ktoré mám urobené sú: IR spektrofotometria PFR-B, kde mám dôkaz priameho naviazania B do polymérnej štruktúry. - TG a DSC analýza PFR-B (ešte musím vyhodnotiť)
O OO
OH
B
B
OH
C6H5OO
CH2O
B
OH OH
. Mólový pomer Ph:F:NH3:B3BO3 1:1,5:0,35:0,3
Príprava PFR-H3BO3 podľa postupu zaužívanom pri príprave samotnej PFR.Stanovenie B v pripravenej PFR-B spektrofotometricky s chinalizarínomDaná PFR-B sa rozúšťa v etanolePovlakovanieVytvrdzovanie Lisovanie Mechanické skúšky.SEM,TEM, elektrický odpor, magnetické merania.
4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000
50
55
60
65
70
75
80
85
2000 1800 1600 1400 1200 1000 800 600
wavenumer cm-1
Tra
nsm
itta
nce
3365
1677
1600
1500
1470
1370
1248
750
1126 11
16
950
816
685
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