High-temperature sulfidation of Mo-50 Wt.% Re

Abstract

Mo-50Re was sulfidized over the range of 1000–1100°C in sulfur vapor at pressures of 10⁻⁴ and 10⁻² atm. The reaction kinetics followed the parabolic rate law with an activation energy of 55.4 kcal/mole for$p_{S_2 } = 10^{ - 4}$ and 48.2 kcal/mole for$p_{S_2 } = 10^{ - 2}$ atm. The pressure dependence varied between +1/4 to +1/6 for the slope of a plot of log K_p vs log$p_{S_2 }$.

Analysis of the diffusional processes occurring in both the scale and the alloy substrate gave an expression for the ratio of the thickness of the scale and of the χ-phase as a function of the corresponding rate constants for the growth of each layer. Finally, the conditions required for the formation of the χ-phase layer between the outer scale and the alloy substrate were obtained in terms of the ratio between the diffusion coefficients of the two metals in the intermetallic compound.