Fabrication of cold sintered soft magnetic composites using oxalate coated iron powders

The advancement of electric vehicles to replace gas-powered cars requires more efficient designs for electric motors. Three-dimensional flux motors, employing high-strength soft magnetic composites made from powdered metals, are considered a promising alternative to current state-of-the-art motors. In this study, we demonstrate that utilizing cold sintering of iron particles coated with hydrated oxalate leads to the creation of a soft magnetic composite with approximately 55 MPa of transverse rupture strength when compacted at 100 °C. Upon subsequent heat treatment up to 700 °C, the strength significantly rose to almost 219 MPa. During the heat treatment process, the oxalate undergoes transformation into iron/copper oxides. We systematically examined this chemical transformation using diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron dispersive x-ray spectroscopy. Our findings from AC and DC magnetic measurements of the cold-sintered toroid, in relation to heat treatment temperature, demonstrate an increase in DC permeability with rising heat treatment temperatures. Additionally, our analysis of AC core loss data revealed that hysteresis power losses dominate the performance at lower heat treatment temperatures (<300 °C), beyond which dynamic core losses show significant escalation.