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