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 1986.    ----------------.  [KRICHEVSKII, I. R., AND KHAZANOVA, N. E.]  [Nitriding of Iron.]  Doklady Akad. Nauk. S.S.S.R., vol. 71, 1950, pp. 481-484; Chem. Abs., vol. 44, 1950, p. 10,631.

        Specimens of Fe were nitrided at 375°, 400°, 450°, and 500° at atmospheric pressure in NH₃-H₂ mixtures, the NH₃ content ranging 35-65%.  The nitriding reaction stopped almost completely as a limiting N₂ content in the Fe was approached, the final N₂ content increasing with increase in temperature or NH₃ concentration.  Nitriding is the result of 2 opposing reactions:  (1) 2 NH₃+2xFe→2 FexN+3 H₂, and (2) 2 FexN→2xFe+N₂.  Reaction (1) is limited by rate of diffusion of N₂ through Fe and Fe nitrides, and because of the low rate of diffusion through Fe nitrides, the reaction slows down as the nitrides increase until equilibrium between the 2 reactions is attained.

                  KRIEG, A.  See abs. 43a, 44, 46, 48, 49.