Carburization and metal dusting on iron

Fundamental studies have been conducted on the kinetics and mechanisms of r eactions of iron in CH4-H-2 and CO-H-2-H2O mixtures, also in the presence o f H2S, to understand carburization, iron carbide formation, metal dusting a nd carbon deposition. The rate equations and mechanisms of the surface reac tion in carburization of iron are presented, the carburization in CH4-H-2 i s much slower than in CO-H-2. Both reactions are retarded by adsorbed sulfu r, the carburization rate becomes inversely proportional to the sulfur acti vity a(s) similar to pH(2)S/pH(2) with increasing as. At carbon activities a(c) > 1 cementite growth can be started in both gas mixtures on iron, howe ver, the decomposition of this unstable carbide gives rise to a corrosion p rocess 'metal dusting', i.e. the material disintegrates to a dust of metal particles and graphitic carbon. This disintegration can be prevented by ads orbed sulfur which hinders the nucleation of graphite. The stabilizing effe ct of sulfur on cementite and higher carbides such as Hagg carbide, allows fundamental studies about their thermodynamics, non-stoichiometry and diffu sional growth mechanisms, on the other hand the presence of sulfur will all ow iron carbide production in the reduction of iron ores in carburizing gas mixtures.