Microstructure and properties of amorphous FeSiCrBC soft magnetic composites prepared by using HNO3 solution

FeSiCrBC amorphous powder was treated by nitric acid HNO₃ solution and the soft magnetic composites (SMCs) was prepared through compacting and annealing. The microstructure, magnetic and electrical properties of coated powder and SMCs were examined by modern analytical techniques including to X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimeter (DSC), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and M-H magnetization curve. The effects of HNO₃ concentration and annealing temperature on the microstructure and magnetic properties of amorphous FeSiCrBC powders and SMCs were investigated, respectively. A thin layer was formed on the surface of powder particles after HNO₃ solution treatments, and the thickness of surface layer were 240 nm and 260 nm when the concentration of HNO₃ were 2wt% and 4wt%, respectively. HNO₃ treatments decreased the saturation magnetization (M_s) of the powder. The trend is more obvious with the increase of HNO₃ concentration. The formation mechanism of insulating layer on the surface of amorphous powder particle treated by HNO₃ solution was discussed. The insulation layers were mainly consist of iron complex oxides. The sample annealed at 450 °C has best values effective permeability μ_e (19.6) and magnetic loss P_cv (520 kW/m³) at 2% HNO₃, and and μ_e (18.1) and P_cv (509 kW/m³) at 4% HNO₃ under 50 kHz and 100mT.