Sulfidation of an iron-nickel-chromium-cobalt- Phosphorus alloy in1% H ₂S-H ₂ gas mixtures at 400-1000°C

The sulfidation of an Fe-based alloy containing 4.75 wt.% Ni, 0.99 wt.% Co, 0.89 wt.% Cr, and 0.66 wt.% P in 1.1% H ₂S-H ₂ gas mixtures was studied at 400-1000°C. Reaction kinetics were determined by monitoring the abundance of S-gas species continuously throughout each experiment. This approach allows for determination of both linear rate constants associated with adsorption and decomposition of S-gas molecules and parabolic rate constants associated with cation diffusion. The activation energy for these processes are 12 ± 4 kJ/mole and 50 ± 12 kJ/mole, respectively. In all experiments, P is excluded from the sulfide phase and precipitates as the mineral schreibersite [(Fe, Ni, Co) ₃P]. In addition a monosulfide solid solution formed containing variable abundances of Ni, Cr, and Co. Analyses of the compositional profiles allows for the determination of activity coefficients for NiS, CrS, and CoS in FeS as well as the self-diffusivities for Ni, Cr, and Co in the sulfide scale, relative to Fe.