Formation Kinetics of the Dielectric Coatings on Iron Powders for the Fabrication of Soft Magnetic Composite Materials

The topicality and efficiency of applying a silicate-containing inorganic coating as an electric insulator when producing soft magnetic composite materials (SMCMs) from iron powders are substantiated. The influence of the sodium silicate (Na 2 O–SiO 2 ) concentration in an aqueous solution on the formation kinetics of the dielectric coating on iron powders of various brands is shown as well as on their weight increment, average coating thickness, and physical and manufacturing characteristics. It is established experimentally that the influence of particle morphology of iron powders and surface-tension coefficient at the liquid–solid interface on the coating thickness can be indirectly evaluated by wettability characteristics, in particular, by the contact angle. The peculiarities of formation of interlayer SMCM boundaries are considered. Elemental mapping using an energy-dispersive microanalyzer shows that the coating thickness changes after sample compaction under a pressure of 600 MPa and subsequent heating in a range of 400–600°C, and silicon partially redistributes in the dielectric layer. This is caused by the fact that silicon, having a higher oxygen affinity when compared with iron, actively reacts with oxygen arranged on the surface of iron particles and/or reduces iron oxides, forming SiO 2 dioxide in the form of a dense film, which, on the one hand, protects iron particles against oxidation, and on the other hand, the dielectric layer affecting specific magnetic losses is formed in the contact zone of iron particles. It is established that the distinctive feature of densification of iron powders with the coating is the prevalence of the structural deformation under compacting, because the coating reduces the internal friction coefficient. It is shown that the developed SMCM corresponds to modern requirements demanded of soft magnetic composite materials in regards to its magnetic characteristics.