Temperature resistance of soft magnetic composites based on carbonyl iron powder for molding inductor

Abstract

The temperature resistance of carbonyl iron powder (CIP) based soft magnetic composites (SMCs) for molding inductor was investigated. The magnetic powder with median particle size D50 = 6.5 μm was fabricated into SMCs and molding inductors. The morphology, composition, and magnetic properties of SMC rings and the inductors before and after thermal aging at 155 °C and 180 °C under still and flowing air atmosphere were investigated. The results indicate that CIP is easily oxidized under atmosphere at high temperatures. The oxides formed on the powder surface are confirmed to be Fe3O4 and Fe2O3. Higher temperature or higher oxygen content results in more severe oxidation. The oxidation of the powder leads to the reduced saturation magnetization and magnetic permeability. It also increases the coercivity of the SMCs, leading to higher hysteresis loss and total core loss. The decreased permeability and increased core loss result in a reduction of quality factor, which reduces the energy storage capacity of the inductor. In the SMCs, the phosphate layer and resin cannot effectively prevent the oxidation of CIP. Electromagnetic simulations on the oxidation effects of the magnetic ring and the molding inductor also show that the more serious oxidation leads to the lower magnetic performance, but the ring inductor and molding inductor may exhibit different behaviors. This thermal aging mechanism of CIP revealed in this work provides a reference for industrial applications and an effective guide for the subsequent improvement of the temperature resistance of CIP-based molding inductor.