An amendment to the classical model of internal oxidation: Model-inherent transition characteristics

An analytical method based on the flux balance at the inter-region boundary is explored for the evolution of a binary alloy in the corresponding Rhines pack atmosphere where the solute forms only one type of oxide. This alloy may undergo an exclusive external oxidation, an exclusive internal oxidation or a mixed oxidation. The assumption of zero solubility-product is very restrictive for a complete analysis of the mixed oxidation. Nevertheless, an analysis of the exclusive internal oxidation, improved upon the classical theory, gives the transition characteristics and hence a domain of the existence of this possibility.

► The classical model of internal oxidation assumes negligible precipitate in IO zone.
► The extended model eliminates the assumption of negligible precipitate in IO zone.
► The characteristic equation from the extended model gives an invariant sigmoidal plot.
► The invariant sigmoidal plot divides the reaction landscape into two regions.
► These two regions correspond to external oxidation and exclusive internal oxidation.