Sulfidation properties of Fe-6.1 at.% Mo alloy at 973–1273 K

Sulfidation of an Fe-6.1 at% Mo alloy was investigated in H₂S-H₂ atmospheres, 10^?4 ? P_s2 ? 10²Pa, at 973-1273 K. The reaction kinetics are parabolic except at 1273 K as liquid sulfide formation leads to catastrophic corrosion. This solid-liquid transformation between Fe₂Mo₂S₄ and Mo₂S₃ occurs at 1214 ± 9 K. At 1073 K and P_s2 = 10^?4Pa, growth of a duplex Mo₂S₃/FeMo₂S₄ scale offers high resistance to sulfidation. At 973, 1073 and 1173 K, 10^?2 ? P_s2 ? 10²Pa, parabolic sulfidation kinetics of the same magnitude as for pure iron describe growth of a duplex scale composed of an inner (FeMo₂S₄ + Mo₂S₃) layer and at an outer FeS layer. Marker measurements indicated that growth of the inner two-phase layer was supported by inward migration of sulfur and that growth of the outer FeS layer resulted from outward migration of iron.