Measurements of the parabolic sulfidation kinetics were carried out at sulfur pressures ranging from i0 -Iz to 10 -2 arm and at temperatures in the range 600~176The effect of sulfur activity on these kinetics is most pronounced at low sulfur pressures. Temperature exhibits the largest influence on these kinetics at high sulfur pressures. An expression is derived for the parabolic rational rate constant in terms of the chemical diffusivity and nonstoichiometry of iron sulfide using the Wagner equation for scaling by iron diffusion and the Libowitz point defect model involving a strong repulsive interaction between iron vacancies to relate nonstoichiometry to sulfur pressure. The predicted values for these rate constants were in good agreement with those found experimentally. A comparison of available results on the parabolic scaling rates at sulfur pressures ranging up to 1 atm suggests that a transition in scale texture with sulfur pressure influences the sulfidation rates since iron diffusion is more rapid in the "c" than in the "a" crystallographic direction of iron sulfide.

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The sulfidation kinetics of Ni‐Al alloys containing 3–13 atomic percent Al were investigated at 700°C in H2S‐H2 atmospheres at sulfur pressures 10−8 ≤PS2≤10−2 normalatm . The reaction product was comprised of three regions: an external normalNiS or Ni3S2 layer, an Al2S3‐Ni3S2 lamellar layer, and an innermost Al‐Ni‐S liquid layer. Sigmoidal shaped reaction curves before onset of linear kinetics resulted from the temporally partial protective nature of the oxide films on the metallographically polished specimens. The magnitudes of the linear rate constant for growth of the reaction product layers were predominantly determined by interfacial processes for transfer of reactants at the gas/ scale and scale/subscale interfaces.

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