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 Sm₂Fe₁₇ using ammonia yields volume expansions up to 8.3 vol.%, which correspond to a composition Sm₂Fe₁₇ 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, as an intermediate step. For overloaded Sm₂Fe ₁₇N_x with x>3 the net reaction energy U₀ =5±10 kJ/mole indicates a nearly temperature-independent occupation of the non-9e sites