Passivation layer for the magnetic property enhancement of Fe72.8Si11.2B10.8Cr2.3C2.9 amorphous powder

This paper reports the preparation of insulated soft magnetic powders by HNO3 passivation process with SWAP Fe72.8Si11.2B10.8Cr2.3C2.9 amorphous powder. The toroid-shaped cores were fabricated by pressing the mixture of the insulated magnetic powder and silicone resin under a pressure of 1.31 GPa (density = 5.15 g/cm3). The results showed that amorphous magnetic powder produced by 8 vol.% nitric acid insulating process had good frequency characteristics and high quality factor at higher frequency (1 MHz). The value of initial permeability (μi) was 29.03, and the value of quality factor (Q) was 68.2. The value of saturation magnetization (Ms) was 0.93 T, and the coercive force (Hc) was 89.6 A/m. Furthermore, the amorphous powder was mixed with the Fe-Si-Cr alloy powder by the powder metallurgy process and formed into toroid-shaped cores. The maximum permeability of the toroid-shaped cores with 10 wt.% alloy powder annealed for 10 min at 773 K increased by about 69.8%. The cores were annealed to improve the soft magnetic properties and decrease the stress. The mixed powders also indicated excellent soft magnetic properties; the Ms increased from 0.93 T to 0.97 T, and the Hc decreased from 89.6 A/m to 68.6 A/m.