Kinetics of dielectric coating formation on iron powders to obtain soft magnetic composite materials

The paper justifies the significance and  effectiveness of silicate-containing inorganic coating usage as an electric insulator in the production of soft magnetic composite materials (SMCM) from iron powders. The study demonstrates the effect of sodium silicate (Na₂O–SiO₂) concentration in the water solution on the kinetics of dielectric coating formation on different iron powder grades, as well as on  their weight gain, average coating thickness, as well as physical and  process characteristics. It is experimentally established that  the influence of iron powder particle morphology and  surface tension coefficient at solid-liquid interface on the coating thickness can be assessed indirectly by the wettability indicators, in particular, by the contact angle. The features of SMCM interlayer boundary structure formation are described. Elemental mapping using the energy dispersive X-ray spectrometer shows that after sample pressing at 600 MPa and their subsequent heating within 400–600°C, the coating thickness changes and silicon is partially redistributed in the dielectric layer. This is determined by the fact that silicon featuring higher oxophilicity than  iron actively reacts with oxygen adsorbed on the iron particle surface and/or reduces iron oxides forming SiO₂ in the form of a dense film, which on the one hand protects iron particles from  oxidation, and  on the other hand forms a dielectric layer in the zone of iron particle contact that  affects specific magnetic losses. It is determined that  the distinctive feature of coated iron powder compaction is the structural deformation predominance during pressing since the coating reduces the internal friction coefficient. It is shown that according to its magnetic characteristics, the developed SMCM meets essential contemporary requirements for soft magnetic composite materials.

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