Electric insulation of a FeSiBC soft magnetic amorphous powder by a wet chemical method: Identification of the oxide layer and its thickness control

An electrical insulating layer formed on the surface of an Fe79.3Si5.7B13.3C1.7 soft magnetic amorphous powder was characterized and its layer thickness was evaluated. The insulating layer was prepared by chemical oxidation of the powder in 10% nitric acid-ethanol solution. The insulating layer mainly consisted of magnetite and/or maghemite. Moreover, the insulating layer avoided further oxidation up to T ≈ 940 K, which is above the crystallization temperature of the amorphous powder. A correlation of the layer thickness with density and saturation magnetization is presented and discussed. Layer thicknesses calculated either from density or saturation magnetization of either magnetite or maghemite were in good agreement with each other.