Non-equilibrium Gas-phase Nitrogenation

Non-equi l ibr ium ni trogenat ion of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of S m 2 F e l 7 using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition S m 2 F e 1 7 N x with x = 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, a s an intermediate step. For overloaded S m ~ F e 1 7 N x with xz-3 the net reaction energy U, = 5 f 10 kJlmole indicates a nearly temperature-independent occupation of the non-9e s i t e s .