Model for a Spinel Oxide Film on an AN Fe-Cr-Ni Alloy, SS304

A spinel point defect model for an iron-chromium-nickel alloy, 304 stainless steel, has been developed on the basis of previously-developed point defect models. Post-processing according to the mixed conduction model has been incorporated. With the spinel point defect model one can calculate the evolution of film thickness and current density with time, the ionic species and vacancy profiles across the oxide film and the electrochemical impedance for alloys that grow a spinel anodic oxide film. The spinel with chemical formulation AB2O4 is modelled assuming bivalent iron and nickel compete in the bivalent ionic group (A) and trivalent iron and chromium in the trivalent ionic group (B). Competition is modelled by modifying the diffusion term in the Nernst-Planck equation by a multicomponent diffusion equation.