EFFECTS OF SULFUR PRESSURE ON THE SULFIDATION BEHAVIOR OF FE-MO ALLOYS AT 700-900-DEGREES-C

High-temperature sulfidation behavior of Fe-Mo alloys (containing 10 a nd 20 at.% Mo) was studied over the temperature range of 700-900 degre es C above a pure sulfur pool with the sulfur-vapor of 10(2)-10(5) Pa. The sulfidation kinetics followed the parabolic rate law in all cases . The corrosion rates increased with increasing temperature and sulfur pressure but decreased with increasing Mo content. The scales formed on the alloys were complex and bilayered, consisting of an outer layer of iron sulfide (FeS/Fe1-xS) and an inner heterophasic layer of mostl y FeMo4S6, FeMo2S4, Fe1-xS, MoS2 (only detected at P-S2 = 10(5) Pa) an d uncorroded Fe3Mo2. Platinum markers were located at the interface be tween the inner and outer scales, suggesting that the outer scale grew by the outward transport of an Fe ion and the inner scale grew by the inward S diffusion, as similar to the results in the literature. (C) 1998 Elsevier Science S.A. All rights reserved.