Internal oxidation: does the classical model contradict local equilibrium conditions?

Abstract

Previously, Morral and Li have published an anomalous behaviour of the classical model of internal oxidation with respect to their local-equilibrium conditions/rules. The local-equilibrium conditions were interpreted from the local-equilibrium expression derived from the flux balance at the inter-region boundary – the boundary between a two-phase region and a single-phase region – under the local-equilibrium assumption. These local-equilibrium conditions predict a continuous average composition profile for the system where the two-phase region is growing at the expense of the single-phase region. In contrast, the classical model of internal oxidation shows a composition jump at the boundary of the growing two-phase region and the shrinking single-phase region.Here, a complete interpretation of the local-equilibrium expression is delineated including the case of zero solubility-product. The relative behaviour of two of the composition-vectors in the local-equilibrium expression undergoes an abrupt change at zero solubility-product. This change in behaviour predicts a composition jump at the inter-region boundary for the growing two-phase region. Consequently, the classical model of internal oxidation is shown to follow the local equilibrium on all counts and thereby eliminating all contradictions.