Sulfidation Properties of a Nickel-20 w/o Chromium Alloy at 700°C and Low Sulfur Pressures

Abstract

The sulfidation kinetics and the morphological development of the reaction product for a Ni‐20 weight per cent Cr alloy have been determined at 700°C and sulfur pressures below . The kinetics were observed to be parabolic; the parabolic sulfidation rate constant was found to vary as a semilogarithmic function of the sulfur pressure. The reaction product consisted of an external scale identified mainly as with dissolved nickel up to 5 atomic per cent, and a chromium sulfide subscale with morphological breakdown of the alloy/external scale interface. Approximate determinations for the diffusion rates of chromium in the scale and sulfur in the alloy were made. Tentative mechanisms are proposed to explain the diffusion‐controlled reaction and the stabilization of the external scale by dissolved nickel.