Sulfidation properties of nickel-20 wt.% molybdenum alloy in hydrogen-hydrogen sulfide atmospheres at 700°C

Abstract

The sulfidation kinetics and morphological development of the reaction products for a Ni-20wt.% Mo alloy exposed at 700° C to H₂-H₂S atm at sulfur pressures in the range 1×10⁻¹¹ to 2×10⁻² atm are reported. At Ps₂≤5×10⁻¹¹ atm, the reaction product was Mo₂S₃ which grew as an external scale by parabolic kinetics. For 1×10⁻¹⁰<pS₂≤4×10⁻¹⁰ atm, simultaneous internal precipitation and external growth of MoS₂ occurred by linear kinetics. An external duplex scale was formed at sulfur pressures 2×10⁻⁸<Ps₂≤2×10⁻² atm in which the inner layer was a two-phase mixture of MoS₂ and nickel sulfide, and the outer layer contained solid nickel sulfides and a liquid Ni-Mo sulfide phase. Catastrophic linear kinetics occurred under these latter condition.