Fabrication of carbonyl iron powder/SiO2–reduced iron powder/SiO2 soft magnetic composites with a high resistivity and low core loss

Abstract

Carbonyl iron powder (CIP) and reduced iron powder (RIP) were homogeneously coated with an SiO2 insulating layer by a controlled in-suit chemical deposition procedure and used as raw materials to fabricate CIP/SiO2-RIP/SiO2 (C-R) soft magnetic composites (SMCs) by powder metallurgy techniques. Compared with RIP/SiO2 powders, CIP/SiO2 powders possess a higher SiO2 content and more stable Si-O covalent network. The addition of CIP/SiO2 to the C-R SMCs leads to a significantly increase in the resistivity due to the full electrical isolation of the RIP/SiO2 particles. Transmission electron microscopy analysis confirms that a SiO2 amorphous layer approximately 100–400 nm in thickness grows with a high packing density and adheres tightly to the iron grains, resulting in the effective constraint of electron transfer between the Si and O atoms. Annealed C-R SMCs containing 15–20 wt% CIP/SiO2 have optimum properties with a high resistivity of 4980–6383 μΩ·m and a low core loss of 19.08–23.66 W/kg (50 mT, 100 kHz). The results of this present study provide a significant method to improve resistivity and reduce core loss.