Improved magnetic properties of iron-based soft magnetic composites with a double phosphate-SiO2 shells structure

Abstract

Herein a double shells structure was proposed to overcome the drawbacks such as poor heat resistance, incomplete insulation and high core loss coating of ironbased soft magnetic composites (SMCs) with single shell structure. The surface of the iron powder was coated with a double shells structure composed of an inner phosphate coating and an outer SiO 2 coating through phosphating and hydrolysis successively. Subsequently, the effects of different SiO 2 addition amount on the microstructure of iron powder and magnetic properties of SMCs were studied. The introduction of SiO 2 in the double shells structure inhibited the decomposition and failure of phosphating layer after being annealed at a high temperature. The iron powder coated with the phosphate-SiO 2 insulating layer was still effective after annealing in a N 2 atmosphere at 570 °C, achieving the purpose of eliminating residual stress and improving magnetic properties. The optimal process parameters were set at 0.2 wt% phosphoric acid and 0.5 wt% tetraethyl orthosilicate to fabricate the phosphate-SiO 2 double shells. The iron-based SMCs presented excellent magnetic properties with B s of 1.29 T and P s of 169.2 W/kg (measured at 1 T and 1 kHz). In addition, the core loss of SMCs introduced with SiO 2 is 83% lower than that of SMCs produced by the phosphating process. This paper provides a feasible method for improving the magnetic properties of SMCs.

Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems

“…Choi et al [17] prepared Al 2 O 3 insulating layers of varying thicknesses on the surface of Fe-Si-Cr alloy powders using the sol-gel method, thereby fabricating a composite with an effective permeability of 33.9 and a loss of 252 mW/cm 3 at 50 mT and 100 kHz. Although previous studies [18][19][20][21] have demonstrated that metal oxides are promising candidates for use as insulating layers in the production of Fe-based SMCs, recent studies have predominantly focused on developing new metal oxide insulating layers and improving the properties of Fe-based SMCs [22,23].…”