Fabrication of high-performance FeSiCr-based soft magnetic composites using thermal decomposition of salt compounds

Optimising solid-phase reactions at the interface between an iron-based soft magnetic powder matrix and an inorganic oxide ceramic insulating layer in soft magnetic composites is an effective method to overcome the inverse relationship between magnetic conductivity and energy losses in these materials. However, solid-phase reactions at the interface are currently based on using highly reactive aluminium within iron-based soft magnetic powders. Herein, an interface reaction between ZnSO4 and FeSiCr was successfully conducted to afford formation of FeSiCr-based soft magnetic composites, which are characterised by a three-layer structure comprising FeSiCr, a Si and Cr-rich layer and a ZnO·SiO2·Cr2O3 composite insulating layer. Thermal decomposition of ZnSO4 releases O2, which induces the migration of Cr and Si atoms from the FeSi3.7Cr4.5 soft magnetic powder matrix towards the interface and their subsequent reaction; this increases the magnetic phase content and enhances the crystalline structure order of the powder matrix. Furthermore, the ZnO·SiO2·Cr2O3 composite insulating layer effectively insulated the FeSiCr soft magnetic powder matrix. The resulting FeSiCr-based soft magnetic composite materials with the ZnO·SiO2·Cr2O3 composite insulating layer exhibit low core losses (58.5 kW/m3), high magnetic permeability (39.1) and high saturation magnetisation (166.5 emu/g), indicating they are an ideal choice for high-performance electromagnetic components. The proposed innovative strategy of oxygen release through the thermal decomposition of salt compounds affords an insulating coating on soft magnetic composite materials fabricated based on interfacial solid-phase reactions.