Effects of sulfur pressure on the sulfidation behavior of Fe-Mo alloys at 700-900°C

Institute of Materials Engineering, National Taiwan Ocean University, Keelung 202, Taiwan High-temperature sulfidation behavior of Fe-Mo alloys (containing 10 and 20 at.% Mo) was studied over the temperature range of 700-900°C above a pure sulfur pool with the sulfur-vapor of 10²-10⁵ 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/Fe_1-xS) and an inner heterophasic layer of mostly FeMo₄S₆, FeMo₂S₄, Fe_1-xS, MoS₂ (only detected at P_S2 = 10⁵ Pa) and uncorroded Fe₃Mo₂. Platinum markers were located at the interface between 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. © 1998 Elsevier Science S.A. All rights reserved.