The internal oxidation of ternary alloys I: The single oxidation of the most-reactive component under low oxidant pressures

The internal oxidation of the most-reactive component C of ternary A-B-C alloys by a single oxidant is examined assuming a gas-phase oxidant pressure below the stability of the oxides of the other two components. The precipitation of the most-stable oxide leaves behind a matrix composed of a binary alloy of the two less-reactive components, whose composition affects the solubility and diffusivity of the oxidant within the region of internal oxidation, with an effect on the reaction kinetics. Approximate relations between these properties are proposed and used to predict the kinetics of internal oxidation of C under the assumption of parabolic rate law. The results obtained for the ternary alloys are compared with the behavior of binary A-C and B-C alloys with the same C content. A new important factor in establishing the difference between the internal oxidation in ternary A-B-C alloys and in binary A-C and B-C alloys under a fixed gas-phase oxygen pressure and C content is the ratio between the concentrations of A and B in the bulk ternary alloy.