Innovative Method for the Mass Preparation of α-Fe16N2 Powders via Gas Atomization

The iron nitride materials, especially alpha ''-Fe16N2, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of alpha ''-Fe16N2 powders as a raw material for permanent magnets is still challenging. In this work, starting from iron lumps as a raw material, we have managed to prepare the alpha ''-Fe16N2 powders via the gas atomization method, followed by subsequent nitriding in an ammonia-hydrogen gas mixture stream. The particle size was controlled by changing the gas atomization preparation conditions. X-ray diffractograms (XRD) analyses show that the prepared powders are composed of alpha ''-Fe(16)N(2 )and alpha-Fe phases. The alpha ''-Fe16N2 volume ratio increases with decreasing powder size and increasing nitriding time, reaching a maximum of 57% alpha ''-Fe16N2 phase in powders with size below 32 +/- 3 mu m after 96 h nitridation. The saturation magnetization reaches the value of 237 emu/g and a reasonable coercivity value of 884 Oe. Compared to the saturation magnetization values of alpha-Fe powders, the alpha ''-Fe16N2 powders prepared through our proposed approach show an increase of up to 10% in saturation and demonstrate the possibility of mass production of alpha ''-Fe16N2 powders as precursors of permanent magnets without rare earths.

Automated summary

In this work, alpha ''-Fe16N2 powders were successfully prepared from iron lumps using the gas atomization method, followed by subsequent nitriding in an ammonia-hydrogen gas mixture stream. The particle size of the powders can be controlled by changing the preparation conditions. The prepared powders demonstrated a high saturation magnetization and showed the potential for mass production of rare-earth-free precursors for permanent magnets.