# Iron nitride

Iron nitrides are inorganic chemical compounds of iron from the group of nitrides . With diiron nitride Fe 2 N, triiron nitride Fe 3 N (more precisely Fe 3 N 1 + x ), tetrairon nitride Fe 4 N and nitrogen martensite α´´-Fe 16 N 2 as well as FeN several iron nitrides are known.

## Occurrence

Tetrairon nitride occurs naturally as the mineral roaldite , triiron nitride as the mineral siderazot .

## Extraction and presentation

Iron nitrides can be obtained by reacting iron with ammonia at 350 to 550 ° C. The resulting product corresponds in its composition to the formula Fe 2 N and represents the orthorhombic γ´-modification, which has a very narrow homogeneity range.

${\ displaystyle \ mathrm {4 \ Fe + 2 \ NH_ {3} \ longrightarrow 2 \ Fe_ {2} N + 3 \ H_ {2}}}$

However, with similar production, the occurrence of a hexagonal ε-phase with a lower nitrogen content, roughly equivalent to Fe 3 N, is often observed. When heated in vacuo at around 500 ° C., the product initially changes to the ε phase and then to Fe 4 N , releasing nitrogen .

## properties

Iron nitrides are gray to black powders with a metallic character. ζ-Fe 2 N (CAS number: 12023-20-0) has a density of 6.35 gcm −3 and has an orthorhombic crystal structure with the space group Pbcn (space group no. 60) (a = 444 pm, b = 554 pm, c = 484 pm). The ε-modification Fe 3 N (CAS number: 12053-51-7) has a density of 7.36 g · cm −3 and has a hexagonal crystal structure with the space group P 6 3 22 (No. 182) (a = 270 pm, c = 437 pm). Fe 4 N (CAS number: 12023-64-0) has a density of 6.57 g cm −3 and has a crystal structure with a cubic closest packing of the iron atoms and the space group P 4 3 m (No. 215) (a = 379.5 pm).

## use

Iron nitrides are formed during the surface treatment (hardening) of steel . The corresponding process is called nitriding (chemically correct: nitriding).

## Individual evidence

1. ^ ST Oyama: Chemistry of Transition Metal Carbides and Nitrides . Springer, 1996, ISBN 0-7514-0365-2 , pp. 186 ( limited preview in Google Book search).
2. Wolfgang Bergmann: Material technology 2: Material production - Material processing ... Hanser Verlag, 2009, ISBN 3-446-41711-7 , p. 268 ( limited preview in Google Book search).
3. Georg Brauer (ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1649.
4. D. Rechenbach, H. Jacobs: Structure determination of ζ-Fe 2 N by neutron and synchrotron powder diffraction . In: Journal of Alloys and Compounds , 1996, 235 (1), pp. 15-22, doi : 10.1016 / 0925-8388 (95) 02097-7 .
5. ^ Jean d'Ans, Ellen Lax, Roger Blachnik: Pocket book for chemists and physicists . Springer DE, 1998, ISBN 3-642-58842-5 , pp. 454 f . ( limited preview in Google Book search).