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Effect of H 2 S on metal dusting of iron
Author(s) -
Schneider A.,
Grabke H. J.
Publication year - 2003
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200303735
Subject(s) - cementite , carbide , carburizing , materials science , metal , carbon fibers , adsorption , graphite , metallurgy , nucleation , inorganic chemistry , chemistry , austenite , microstructure , organic chemistry , composite number , composite material
A review is given on the effect of H 2 S on metal dusting of iron which has been studied by gas carburisation in CO‐H 2 ‐H 2 O‐H 2 S and CH 4 ‐H 2 ‐H 2 S mixtures at 500 and 700°C. The presence of H 2 S in carburising gas atmospheres leads to sulphur adsorption on the iron surface, which retards carbon transfer. Segregation experiments and surface analyses have shown that sulphur segregates (and thus adsorbs) on cementite surfaces as well as on iron surfaces. The adsorbed sulphur also suppresses graphite nucleation and thus can stop the reaction sequence of metal dusting. Experiments by thermogravimetric analysis (TGA) have shown that the extent of retardation of metal dusting depends on temperature, carbon activity and H 2 S content. The higher the carbon activity, the higher is the H 2 S content required for suppression of metal dusting. At carbon activities a C > a C (Fe/Fe 3 C) the metastable iron carbide, cementite (Fe 3 C), occurs as an intermediate phase during metal dusting. Carburisation experiments in CO‐H 2 ‐H 2 O‐H 2 S mixtures at 500°C and X‐ray diffraction analysis (XRD) of carburised samples have revealed that at very high carbon activities a second iron carbide, Hägg carbide (Fe 5 C 2 ), forms on the cementite surface. Microstructural investigations have shown that both metastable carbides decompose during metal dusting. Metal dusting experiments on iron at 700°C have been performed in CH 4 ‐H 2 ‐H 2 S gas mixtures. By adding 15 ppm H 2 S to the CH 4 ‐H 2 atmosphere the onset of metal dusting can be retarded for more than 350 hours. By means of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDX) it was shown that coke contains graphite, cementite and iron particles with adsorbed sulphur.