Structure Evolution and Performance of Fe-Si Core Used in Power Inductors of Smart Meters

Fe-Si cores with a CoO-SiO_x-Co composite coating layer were prepared by sintering Fe-6.5wt.%Si/Co₃O₄ composite powders. The effects of Co₃O₄ coating content and structural evolution mechanism on magnetic properties of the Fe-Si cores were systematically studied. The results indicate that the high temperature during hot pressing sintering promotes solid-state interface reactions between Co₃O₄ coating and Si atoms from the Fe-6.5wt.%Si magnetic powder, resulting in the formation of electrical insulation phase SiO_x and ferromagnetic phase Co. The formed CoO-SiO_x-Co composite coating layer can effectively weaken the eddy current effect and magnetic dilution effect. When the Co₃O₄ coating content increases, the saturation magnetization of Fe-Si core decreases but still maintains a high value. And the magnetic loss shows a trend of first decreasing and then increasing. When the Co₃O₄ coating content is 5.0 wt.%, the Fe-Si core exhibits relatively superior magnetic properties, such as high saturation magnetization (192.9 emu/g), high permeability (98), and low magnetic loss (343.3 kW/m³, 0.02 T/50 kHz).