Non-equilibrium gas-phase nitrogenation

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of Sm/sub 2/Fe/sub 17/ using ammonia yields volume expansions up to 8.3 vol.%, which correspond to a composition Sm/sub 2/Fe/sub 17/N/sub x/ with x/spl ap/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, as an intermediate step. For overloaded Sm/sub 2/Fe/sub 17/N/sub x/ with x>3 the net reaction energy U/sub 0/=5/spl plusmn/10 kJ/mole indicates a nearly temperature-independent occupation of the non-9e sites.<
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