Regulation of Interface Compatibility and Performance in Soft Magnetic Composites with Inorganic Insulation Layers by FePO4 Intermediate Transition Layer

In the fabrication of soft magnetic composites, the lattice mismatch between the inorganic insulation layer and the iron matrix often leads to the formation of cracks during the molding process, which significantly impairs the operational performance of the materials. Consequently, it is imperative to develop novel strategies for inorganic insulation coatings that offer high electrical resistivity and thermal stability and are less susceptible to cracking during formation. This paper presents a new structure for soft magnetic composites that incorporates FePO₄ as an intermediate transition layer between the iron-based soft magnetic particles and the inorganic ceramic insulation layer. This configuration is designed to provide insulation coatings with superior voltage and thermal resistance, as well as high electrical resistivity. The research details the processes forming the FePO₄ intermediate transition layer and the SiO₂ insulation layer on the iron powder surface, along with their interaction mechanisms. An analysis comparing the scenarios with and without the FePO₄ intermediate transition layer shows its beneficial impact on the magnetic properties and mechanical strength of the soft magnetic composites. Further investigations reveal that at a phosphoric acid concentration of 1 wt.%, the FePO₄ layer significantly enhances the interface compatibility between the Fe powder matrix and the SiO₂ insulation layer. Under these conditions, the Fe@ FePO₄/SiO₂ soft magnetic composites demonstrate outstanding overall performance: the saturation magnetization stands at 215.60 emu/g, effective permeability at 83.2, resistivity at 57.42 Ω·m, power loss at 375.0 kW/m³ under 30 mT/100 kHz, and radial compressive strength at 15.95 Kgf. These findings offer novel insights and practical approaches for advancing inorganic insulation coating strategies and provide vital scientific support for further enhancing the magnetic and mechanical properties of soft magnetic composites.