Novel Method for Making Surface Insulation Layer on Fe-Based Amorphous Alloy Powder by Surface-Modification Using Two-Step Acid Solution Processing

By introducing the SiC/GaN power devices, the high-frequency switching dc-dc converters are expected to have higher efficiency and lightweight. This paper focuses on the Fe-based amorphous alloy powder (Fe-Si-B-Cr-C based) used in the metal composite bulk magnetic core for high-frequency power inductor and transformer. In terms of eddy-current loss at MHz band or beyond, iron-based metal composites are required to have fine magnetic particles with surface insulation layer. In this paper, the finest amorphous powder with a median diameter of 2.57 μm made by water atomization process was used. In order to fabricate the amorphous powder with surface insulation layer, a surface-modification scheme through the two-step acid solution processing using phosphoric acid and hydrochloric acid was introduced. As a result, the surface-modification scheme enabled to make a single-phase silica thin layer on the surface of the amorphous powder, and the silica thin layer was considered to be derivable from the silicon element in the amorphous (Fe-Si-B-Cr-C based) powder.