Soft Magnetic Properties of Gas-Atomized FeSiAl Microparticles with a Triple Phosphoric Acid-Sodium Silicate-Silicone Resin Insulation Treatment

In order to optimize the porous, fragile and high-temperature decomposition of phosphate and strengthen the molding ability of gas-atomized FeSiAl powder, triple insulating layers including phosphoric acid, sodium silicate and silicone resin have been fabricated in this work. Phosphoric acid can form a phosphate insulating layer on the surface of FeSiAl powder. Compared with the common silicon source properties and molding ability of silicone resin, sodium silicate can further improve the thermal stability of magnetic core. Because of the multiple insulating layers composed by phosphate, sodium silicate and silicon dioxide, for five soft magnetic composite (SMC) core samples (outer diameter× inner diameter× height: 33.02× 19.94 × 10.67 mm), total core loss is as low as 133.98 mW/cm 3 at 100 kHz and 50 mT and 53.45 mW/cm 3 at 50 kHz and 50 mT. Among five cores, the samples with 3 wt.% phosphoric acid possess the highest averaged effective permeability of 50.91. However, with further increase of phosphoric acid concentration, the effective permeability decreased markedly, ascribed to the decreasing density caused by the insulating layer falling off. According to scanning electron microscopy, elemental distribution, x-ray photoelectron spectroscopy analysis results and metallography images of the cross section, it can be inferred that sodium phosphate produced by excessive phosphoric acid and sodium silicate can promote the rupture of insulating layer and reduce permeability, density and crush strengthen.