Magnetic properties of iron-based soft magnetic composites prepared by utilizing polyimide insulating layer

Polyimide (PI) with excellent insulating property and enhanced thermal stability was used as insulating coating material for the preparation of iron-based soft magnetic composites (SMCs), and the effect of insulating coating content and curing temperature on the magnetic properties of iron-polyimide SMCs was investigated. The results demonstrate that the insulating layer of PI shows satisfactory adhesion property on the surface of iron particles, and uniform insulating layer of PI was obtained by imidization of polyamic acid (PAA) at 200 degrees C. With the increase of PI content, the thickness of insulating layer increases gradually, accompanied by the increase of resistivity and the reduction of core loss. PI shows enhanced heat resistance, the SMCs can be cured at the temperature up to 400 degrees C, leading to the effectively release of residual internal stress generated during the compaction process. At the optimized PI content of 1.5 wt% and curing temperature of 400 degrees C, low core loss of 780 W/Kg (measured at 50 mT and 100 kHz) and higher maximum permeability of 305 were achieved.