Carbonitrides of iron

The first detailed studies of carbonitrides of iron were published by-Jack (17) in 1948. The nitrogen-rich carbonitride phases are isomorphous with y -, e-, and ("-nitrides, i.e., nitrogen has simply been replaced partially by carbon. The compositions of phases in the Fe-N-C system as given by Jack (17) are shown in Fig. 2. 

Bril] Bridelle, R., Michel, A., Physicochemical Characteristics of Carbonitrides of Iron (in French), Compt. Rend. Acad. Sci. Paris, 239, 274-275 (1954) (Experimental, Crys. Structure, 8)... 

The complex iron carbonitride is the hard component in steels that have been annealed with ammonia (nitrided steels). Complex carbonitrides with iron metals are also present in superaHoys in the form of precipitates. 

Nitrides, carbides, and borides of iron (as well as carbonitrides and other possible mixed compounds such as borocarbides or boronitrides) are... 

Hall, Dieter, Hofer, and Anderson (19) studied reactions of nitrides and carbonitrides in a reduced, fused iron catalyst (Bureau of Mines number D3001). The results of these experiments were in general similar to those of Jack, and most of the differences may be explained by the differences in the type of iron employed. The major discrepancy was that in the catalyst of large surface area and small crystallite size, the <-carbonitride phase was found under conditions under which massive iron is converted to the f-phase. Since the transformation of the - to the f-phase involves only slight changes in the lattice positions of iron atoms and small changes in the x-ray pattern, it is possible either that this transformation did not occur in the catalyst or that the pattern of the f-phase could not be distinguished from that of the e-phase in the diffuse diffraction patterns. 

The reduction of nitrides of iron in pure hydrogen was very rapid, and at 200°C. nitrogen was virtually completely removed from fused iron catalysts in three hours. The hydrogenation of carbonitrides was considerably slower than that of nitrides, and the rate varied inversely with the carbon content of the carbonitride (Table III and reference 19). In... 

Fig. 9. Composition changes of catalyst D3001 with days of synthesis with IH2 + ICO gas at 7.8 atmosphere in test X218. Part A presents atom ratios of nitrogen, total carbon, elemental carbon, and oxygen to iron. Part B shows the distribution of iron as carbonitride and magnetite. Part C presents the temperatures of synthesis. Reprinted by permission of the American Chemical Society.

Developments in the Fischer-Tropsch synthesiis at the Bureau of Mines from 19 5 to I960 include a simple mechanism for chain growth and the use of iron nitrides as catalysts. The chain-growth schene can predict the carbon-number and isomer distributions for products from most catalysts with reasonable accuracy using only 2 adjustable parameters. Iron nitrides are active, durable catalysts that produce high yields of alcohols and no wax. During the synthesis, the nitrides are converted to carbonitrides. 

Table 3 Reaction Sequences for Nitrides, Carbonitrides and Carbides of Iron.

Pop] Popov, V.V., Diffusion Interaction of Carbides, Nitrides and Carbonitrides With Iron and Steels , Metallofizika Nov. Tekhnol, 21(2), 99-103 (1999) (Phase Relations, Experimental, Transport Phenomena, 11)... 

Som] Somers, M.A.J., Colijin, P.F., Sloof, W.G., Mittemeijer, E.J., Microstructural and Compositional Evolution of Iron Carbonitride Compound Layers During Salt Bath Nitrocarburizing , Z. Metallkd., 81(1), 33-43 (1990) (Experimental, Morphology, 28)... 

Pop] Popov, VV, Diffusion Interaction of Carbides, Nitrides and Carbonitrides with Iron and... 

UFPs of the Fe-N system can be synthesized from iron pentacarbonyl Fe(CO)s] and NH3 as reactants by a IOOO-W continuous wave C02 laser irradiation. The NH, gas is the absorbent of the laser beam in this case. At the lower synthesis temperature, below 650°C, UFPs of y -Fe4N with particle size of 10-25 nm grew dominantly. Above 1150°C, however, the growth of y-Fe UFPs with larger particle size of 30-100 nm was predominant (73). Iron carbonitride (lCN) UFPs were also synthesized from the ternary reactants of Fe(CO)s, NH3, and C2H i. The structure oflCN UFPs was hexagonal with e-Fe3(N,C) phase. A large saturation magnetization up to 142 emu/g was obtained and was ascribed to the carbon layer on 1CN UFPs (74). 

Phases listed in order of decreasing intensity of diffraction pattern, e = c-phase (nitride or car bonitride). f f-phase (carbonitride), x M Hftgg carbide, a — a-iron, and M magnetite. 

Nitrided iron catalysts are remarkably stable toward oxidation and deposition of elemental carbon in the synthesis at both 7.8 and 21.4 atm. Shultz, Seligman, Lecky, and Anderson (23) described composition changes in nitrided fused, sintered, and precipitated catalysts in the synthesis. In a test (X218) with 1H2 + ICO synthesis gas at 7.8 atm., the catalyst was sampled frequently for analysis. X-ray diffraction patterns showed only the e-nitride or carbonitride phase, except for weak... 

Phases in order of decreasing amounts, a = a-iron, = e-nitride or carbonitride, and M — magnetite. 

In considering the effect of the electronic structure of catalysts on activity, Dowden (33) suggested that carbides, and similarly nitrides and carbonitrides, should be less active for synthesis than the corresponding metal since the interstitial atoms may contribute electrons to the unfilled d-shells of the metal, which are believed to be essential for the catalytic activity of transition metals in hydrogenation reactions. This hypothesis is supported by the low activity of cobalt carbide compared with that of reduced cobalt (28,29). For iron catalysts the hypothesis... 

Various iron nitrides and carbonitrides are formed during case hardening of steels and alloyed steels. " These iron nitrides are hard, highly wear resistant and usually do not lead to dimensional changes in the case-hardened items. 

Altounian, Z., Chan, X., Liao, L. X., Ryan, D. H. Strom-Olsen, J. O. (1993). Structure and magnetic properties of rare earth iron nitrides, carbides and carbonitrides. Journal of Applied Physics, 73, 6017-22. 

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