NITROGEN ABSORPTION AND DESORPTION OF SM2FE17 HYDROGEN ATMOSPHERES

Sm2Fe17 was nitrided in ammonia and then denitrided in a hydrogen atmo sphere at temperatures between 563 and 715 K. The amounts of absorbed and desorbed nitrogen, and the kinetics of the reaction were measured gravimetrically in situ. In flowing ammonia, Sm2Fe17 can quickly absor b nitrogen up to about [N]/[Sm2Fe17]=10. The high uptake and high abso rption rate in ammonia, compared with the uptake in nitrogen, can be e xplained with thermodynamic arguments. At these high concentrations, t he lattice is highly distorted. The rate-limiting step of the absorpti on is diffusion of nitrogen atoms in the lattice. For desorption in hy drogen, the nitrogen content can be quickly reduced to [N]/[Sm2Fe17]=3 -3.5. The desorption rate in hydrogen is much faster than that in argo n. The magnetic properties were measured for compounds produced in thi s way.