1305. HÄGG, G. X-Ray Studies on the “Nitrides” of Iron. Nature, vol. 121, 1928, pp. 826-827; Chem. Abs., vol. 22, 1928, p. 4056.

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Literature Abstracts

X-Ray examinations by the powder method have been made of Fe nitrides prepared by passing NH₃ over pure Fe, which was prepared by reducing Fe oxides with H₂. The structure is dependent only on the N content and not on the method or conditions of preparation. The maximum N content is 11.3%. The nitrides are really solid solutions of N in Fe. At 0.2% N, faint lines of a face-centered cubic lattice begin to appear; all a-Fe lines have disappeared at 5.7% N. The new lines remain fixed as N increases and indicate a unit cube of edge 3.789 Å. U. somewhat larger than that of γ-Fe. However this is called γ-phase and is considered to be a solid solution of N in γ-Fe. The Fe atoms are in a close-packed cubic array, with N atoms in the interstices. No evidence that the N atoms are regularly arranged appears. A new phase, ε, appears at 5.7-6.1% N. It is hexagonal and close-packed, the unit cell remaining fixed in size at first, but beginning to increase at 7.3-8.6% N. The phase is estimated to become homogeneous at 7.5-8% N. The ε parameters are the a=2.695 Å. U., c=4.362 Å. U. Increase in N increases the parameters, c increasing relatively less than a. The ε phase is a solid solution of N in hexagonal close-packed Fe. A thin Fe sheet nitrided at 450° for 4 hr. showed strong γ and week ε lines.