Department of Interstitial Nitrogen Rare-Earth Magnet Material Through Nitriding under Atmospheric-pressure Plasma

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The aim of this research is first development of new atmospheric pressure hybrid plasma nitriding apparatus by which a number of advantages are expected to be introduced into synthesis of new nitrides and surface modification. Secondly the aim is development of recently found Sm_2Fe_<17>N_X magnetic materials with high quality and excellent property. Moreover, in order to ensure the effects of the newly developed atmospheric pressure hybrid plasma nitriding apparatus, synthesis of Mo nitrides was first tried at lower temperatures using the newly developed apparatus.In 1994, we studied the formation process of Sm_2Fe_<17>N_X through usual nitriding under 1 atm N_2 gas flow and made clear the precipitation process of a-Fe which degraded the magnetic properties of Sm_2Fe_<17>N_X materials. Furthermore, we developed, first in the world the atmospheric pressure hybrid plasma nitriding apparatus which was enable to increase the degree of ionization due to high presure (atmospheric) plasma and to supply much larger amount of nitrogen than thermal equilibrium one due to hybrid of DC and RF glow charge plasma. The conditions of stable hybrid plasma were discussed.In 1995, the preparation of high quality Sm_2Fe_<17>N_X materials was studied using newly developed atmospheric pressure hybrid plasma nitriding apparatus. As a result we succeeded synthesis of the materials at markedly lower temperatures in comparison with usual N_2 gas nitriding. We also found high quality materials due to suppression of formation of a-Fe.Furthermore, synthesis of Mo nitrides was studied using atmospheric pressure high hybrid plasma nitriding apparatus. We first found that the formation temperature of the Mo nitrides were remarkably lower in hybrid plasma nitriding than in the usual N_2 gas nitriding. In addition, MoN which did not formed at low temperature in the usual N_2 gas nitriding, was found to form at 500ﾟC in hybrid plasma nitriding.