Abstract: | Effects of silicon and of carbon on the sulfidation of iron The corrosive attack of steels by H2S under FeS formation is impeding the use of heat exchangers in processes in which sulfidizing gases occur at low oxygen pressures – the project was aimed at finding ways and means to retard or suppress the FeS growth. Thermogravimetric investigations in H2? H2S at 400 °C showed that during the first 100 h of sulfidation a transition takes place from the linear kinetics controlled by the phase boundary reaction H2S ? S (in FeS) + H2 to the parabolic kinetics controlled by solid state diffusion in the corrosion products. During this transition the linear constant decreases with time and increasing sulfur activity as at the FeS surface (k1 ? 1/as). Upon sulfidation of Fe-6%Si an internal Fe3Si layer is formed te sulfidation is retarded since for long time ( 100 h) the slow surface reaction at high as is rate determining. Carbon deposits formed in carburizing atmospheres (ac 1) on the iron surface, have a negligible effect on the sulfidation. Only graphitization of the iron surface at 700 °C after preceding carbon saturation at 1000 °C in CH4? H2 has an initially retarding effect. This study demonstrated possibilities of retarding the H2S corrosion by Si or C which, however, are rather limited. |