Iron nitrides phase diagram

Nitrogen dissolves in iron to form a solid solution and several nitride phases the phase diagram is complex. Specific nitrides are best obtained via reaction of iron with ammonia. At 400 500 °C, gray orthorhombic Fc2N is obtained, which when heated at abont 500 °C in vacuo, loses nitrogen to give face-centered cubic Fc4N. 

Nitrogen also plays a role in steel, not only as a component of solid solutions in carbides, but especially in the form of hard surface coatings. The crystal structures of the respective hard materials are not all well known. In the present section we discuss some representative structures that were determined reliably. The nomenclature of the iron nitrides derives from the phase diagram of the binary system iron-nitrogen. Thus, the a- and y-phases are soUd solutions of nitrogen in the a-and y-modifications of iron. 

Dar] Darken, L.S., Smith, RP., Filer, E.W., Solubility of Gaseous Nitrogen in y Iron and the Effect of Alloying Constituents - Aluminium Nitride Precipitation , Trans. Metall. Soc. AIME, 191, 1174-1179 (1951) (Phase Diagram, Phase Relations, Experimental,, 12)... 

Isa] Isaev, V.F., Danilovich, Yu.A., Morozov, A.N., SolubiUty of Nitrogen for the Formation of Nitrides in Molten Alloys Based on Iron and Nickel (in Russian), Fiz-Khim. Osn. Pro. Stall Publ. Nauka, Samarin, A.M. (Ed.), Nauka, Moscow, 296-301 (1968) (Phase Diagram, Phase Relations, Thermodyn., Experimental, 11)... 

Wad] Wada, H., Pehike, R.D., Nitrogen Solubility and Aluminium Nitride Precipitation in Liquid Iron Alloys containing Nickel and Aluminum , Metall Trans. B, lOB, 409-412 (1979) (Phase Diagram, Phase Relations, Thermodyn., Experimental,, 4)... 

Figure 6 pvra the mole fractions at equilibrium for the system 1 C, 4 H, 3 O, 2 Fe. This mixture (CH + FejOj) has been studied to provide data on the equilibrium vapour phase composition in a plasma furnace used for the reduction of iron oxide. A priori this diagram shows that the reduction of iron oxide to iron attains 1(K)% in the vapour phase. As we have shown previously for the nitrides the problem of condensation remains tmresolved, however, experimental results indicate that the cooling rate has little effect on the overall yield in that particular case. Figure 7 shows the reducing powers of hydrogen and carbon. 

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