HIGH COERCIVITY ANISOTROPIC SM2FE17N3 POWDERS

Anisotropic Sm2Fe17N3 powders can be prepared by introduction of nitrogen into Sm2Fe17 single-grain powders produced by interstitial hydrogen absorption desorption. Nitrogenation can be performed with direct reaction with N-2 gas or alternatively by reaction with mixtures of N-2-H2 or NH3 and subsequent preferential dehydrogenation. The use of NH3 was found to be particularly advantageous because particles can be completely nitrogenated at lower temperatures and in shorter times, in that way minimizing the decomposition of Sm2Fe17N3 into undesirable SmN, FeNx and alpha-Fe. The expected high nitrogen activity (from the dissociation of NH3) on the surface of the particles together with the severe microstructural changes (cracks) are believed to be responsible for the observed high Sm2Fe17N3 growth rate. With the use of NH3 high intrinsic coercivities (8 kOe or greater) can be achieved in a wide range of temperatures (375-500 degrees C).