Preparation of ultrafine Sm2Fe17N3 magnetic powders without ball milling

Abstract

Ultrafine Sm2Fe17N3 powders obtained via ball or airflow milling usually exhibit defects and localized demagnetization owing to their irregular morphologies. Therefore, this study employs the ultrasonic spray pyrolysis–reduction diffusion method in conjunction with CaO coating to control the precursor size of the oxides and obtain a size-controllable nearly spherical micronano-sized pure-phase Sm2Fe17N3 magnetic powder. The investigation involved testing and analyzing the microstructure, phase composition, and magnetic properties of the magnetic powder. The results indicate that the influence of hydrogen reduction after calcium oxide coating is crucial for achieving morphology control, and the amount of calcium oxide coating can regulate the size and morphology of the powder; excessive coating can hinder the subsequent calcium reduction and nitriding processes. By using 40 wt% Ca(NO3)2 to coat the composite oxide obtained via ultrasonic spray pyrolysis and by adjusting the reduction diffusion time, further particle refinement can be achieved, ultimately resulting in a nearly spherical strontium iron nitride magnetic powder with a D50 of 0.52 μm. The coercivity of this magnetic powder reaches 9.13 kOe, and the maximum energy product is 27.83 MGOe. This study provides new methods and avenues to address the issues of magnetic powder sintering growth and improve magnetic performance. It also lays the foundation for the further enhancement of the performance of Sm2Fe17N3 magnets.