An ESCA Study of Sulfidation of Fe-25 Wt% Cr Alloy in H2S at 50 to 400 C

Abstract The surface reaction of polycrystalline Fe-25 Wt% Cr alloy with H2S was studied in situ with ESCA in the temperature range of 50 to 400 C at pressures of 0.005 to 5 torr of H2S, with and without preexposure to oxygen. On the oxidized surface, Cr2O3 is stable at 200 C, but is converted to Cr2S3 at PH2S=5 torr at 300 C and sulfidized at a lower PH2S at 400 C. Chromium sulfides are more readily formed on clean alloy surface, whereas iron sulfides are more readily formed on the oxidized surface. The surface iron content is gradually increased as sulfidation proceeds. During annealing in vacuum, the surface chromium content increases more rapidly and at lower temperatures in the presence of surface oxygen than in the presence of surface sulfur.