Surface analytical studies of metal dusting of iron in CH4-H2-H2S mixtures

Abstract

The metastable iron carbide, cementite (Fe 3 C), occurs as an intermediate phase during the high temperature corrosion process called metal dusting. The kinetics and thermodynamics of metal dusting of iron have been studied by Grabke et al. [1-5] using CO-H 2 -H 2 O and CH 4 -H 2 gas mixtures. H 2 S additions to carburising atmospheres impede the carbon transfer and retard the onset of metal dusting [6-14], thus allowing to study the early stages of the process. In this work the metal dusting process was studied in CH 4 -H 2 -H 2 S atmospheres at 700°C. Segregation experiments and surface analyses showed that S segregates on iron surfaces as well as on cementite surfaces. By means of Auger electron spectroscopy (AES), scanning Auger electron microscopy (SAM) and energy dispersive X-ray analysis (EDX) it was shown that coke contains graphite, cementite and iron particles with adsorbed sulphur.