Industrial-scale fabrication of FeSiCr magnetic powder cores with high magnetic permeability and low loss

FeSiCr magnetic powders is the key raw material for inductive components such as molding choke and power factor correction (PFC) inductors. In this paper, the industrial-scale insulation coating process of high-performance FeSiCr soft magnetic powder cores (SMPCs) were studied by using mature and environmentally friendly silica sol (SiO2), aluminum dihydrogen phosphate solution (AHP), glass powders (GP), and phosphoric acid (PA) as insulators and water-soluble sodium silicate (NSO) as an inorganic binder, respectively. A comprehensive analysis of the SEM, EDS, and XPS results showed that the surface insulation layer uniformity of the four coating powders is poor due to the irregular morphology of the FeSiCr powder, with the glass powder having the worst coating uniformity due to partial agglomeration occurring in mechanical mixing. The four coated powders all had high saturation magnetization (173.1–176.5 emu∙g−1), in which the chemical reaction of FeSiCr in the phosphoric acid coating process consumed Fe atoms, resulting in the lowest Ms of the powders in the several coating processes. At the corresponding optimum heat treatment temperature, the FeSiCr@SiO2 @NSO SMPCs had the highest permeability of 96.1, while the FeSiCr@PA@NSO SMPCs had the lowest at 75.5, due to the phosphoric acid consuming part of the ferromagnetic material and the loose porous structure of the phosphate layer further reducing the density of SMPCs. The total losses of the four powder cores are low (228.9–259.2 mW·cm−3, 100 Gs, 1000 kHz), while loss separation and experiments with different pressing tonnages showed that the eddy current losses of SMPCs was higher than the hysteresis losses, which was caused by the irregular morphology of FeSiCr powders. The FeSiCr@SiO2 @NSO SMPCs exhibit optimum corrosion resistance due to the uniform coating of the SiO2 nano-insulating layer on the powders surface as a result of the strong bonding of the silica sol with FeSiCr. As can be seen, FeSiCr@SiO2 @NSO SMPCs prepared using silica sols have very high saturation magnetization, very high permeability, low core loss, and good corrosion resistance compared to the other three insulation processes and can be industrially produced on a large scale, offering great application prospects in the field of high current and high frequency.