3VPI Fe+0.4%SiO2 (as nano powder) / shellac

4VPI Fe+2% SiO2(sol-gel coating) / shellac

Margita Kabátová 1, Eva Dudrová 1, Ján. Füzer 2, Jana Füzerová 3, Peter Kollár 2

1 Institute of Materials Research SAS, Watsonova 47, 040 01 Košice, SR 2 Institute of Physics, P. J. Šafárik University, Park Angelinum 9, 041 54 Košice, SR

3 Technical University Košice, Letná 9, 040 01 Košice, SR

Fe/(0.4-2 wt.%)SiO2/polymer composite materials on the basis of irregularly and spherically shaped iron powder particles coated with sol-gel SiO2 layer or with an addition of SiO2 nanopowder were prepared in two ways - using the vacuum/pressure impregnation of low-temperature sintered Fe/SiO2 compacts with shellac and/or with thermoplast SL450 and by mixing Fe/SiO2 powder with shellac. The impact of the iron particles shape, the way of addition of SiO2 and the type of polymer used on the thickness and continuity of electro-insulating layer was microscopically evaluated and analyzed in relation to the electrical resistivity and magnetic coercivity. It was found that these are controlled by the shape of iron particles. The insulation with shellac is more advantageous when compared with thermoset SL450. At the application of the VPI procedure, the bumpy-irregular surface of iron particles may cause discontinuities of the insulating layer, while the insulation of spherical iron particles with smooth surface is excellent with positive impact on the electrical and magnetic properties.

• Spherical shape and smooth surface of iron particles have resulted to an even distribution of SiO2 nanoparticles creating that create effective “spacers” between adjacent iron particles and thus effective “barriers” preventing the metallic connections formation and allow excellent filling the space between ferromagnetic iron particles. • The use of the irregularly shaped particles with protrusions on the surface resulted in metallic connections formation and consequently to a breach of the continuity insulating layer. In this case, the more appropriate method is the preparation of the Fe+SiO2 nano-powder mixtures with shellac, but the disadvantage are higher values of the coercivity.• In terms of the thickness and continuity of insulating layer, the application of shellac is more preferable for the VPI than the thermoset SL450. • Creating the continuous insulating SiO2/shellac layer, with well isolation of iron particles, leads to the acceptable values of electrical resistivity and coercivity, 776 µΩ.m and 178 A/m; it can be expected that they will result in good ac soft magnetic properties at frequencies above 1 kHz. This work was realized within the frame of the project „Advanced technology of preparing of micro-composite materials for electrotechnics“, which is supported by The Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic for the Structural Funds of EU, the Operational Program “Research and Development” financed through European Regional Development Fund ITMS:26220220105. This work was also supported by the Slovak Research and Development Agency through project APVV-0222-10.

EXPERIMENTALEXPERIMENTAL

RESULTS RESULTS

CONCLUSIONCONCLUSIONSS

SMCs Fe/(0.4-2.0 wt.%)SiO2/polymer prepared by vacuum/pressure impregnation

ABSTRACTABSTRACT

Sign. Formulation Shape and size of Fe particles

Preparation

1M Fe powder+shellac irregular30-160 µm mixed with 1wt.%shellac

compacted, cured at 100°C/20min/air 2M Fe+0.4%SiO2+shellac*

3M Fe+1% SiO2+shellac**

1VPI Fe powder/shellac Fe or Fe/SiO2 powder compaction,

low-temperature sintering, VPI using shellac

cured at 100°C/20min/air

2VPI Fe+0.4%SiO2/shellac*

3VPI Fe+0.4%SiO2/shellac* spherical100-160 µm4VPI Fe+2%SiO2/shellac**

5VPI Fe+0.4%SiO2/SL450* as for 3VPI - using SL450 cured at 350°C/1h/air6VPI Fe+2%SiO2/SL450**

*SiO2 added as nano-powder, **SiO2 sol-gel coating

1M Fe powder+ shellac

2M Fe+0.4%SiO2 (as nano powder)+shellac

3M Fe+1% SiO2(sol-gel coating)+shellac

Si distribution

Shellacor

SL450

Fe/SiO2

coating ormixing

MixingFe/SiO2/shellac

compaction

curing

sintering850°C/15 min

vacuum pump

curing

samples

XX

Vacuum/Pressure Impregnation (VPI)

10-2 kPa; 500 kPa

Electrical resistivity(Van der Pauw method)

Magnetic coercivity(Koerzimat HCJ 1.097)

1VPI Fe powder/ shellac

2VPI Fe+0.4%SiO2 (as nano powder) / shellac

5VPI Fe+0.4%SiO2 (as nano powder) / SL450

6VPI Fe+2% SiO2(sol-gel coating) / SL450

Material Density g.cm-3

Electrical resistivityµΩ.m

CoercivityA/m

1M 7.02 176090 4085

2M 6.90 4010200 4255

3M 6.73 3697190 8899

Material Densityg.cm-3

Electrical resistivity µΩ.m

CoercivityA/m

1VPI 7.20 0.1190.010 1332

2VPI 7.10 0.3650.018 1692

Material Density g.cm-3

Electrical resistivity µΩ.m

CoercivityA/m

3VPI 7.03 77640 1782

4VPI 6.70 112060 2883

Material Densityg.cm-3

Electrical resistivity µΩ.m

CoercivityA/m

5VPI 6.93 2000100 1612

6VPI 6.65 56230 2333