A Theory of the Corrosion of Substrates with Protective Metallic Coatings

A theory of corrosion of substrate materials with protective coatings is presented and applied to uranium. This theory assumes that the coating is adherent and acts as a barrier to the corrodent and that galvanic interactions between the coating and substrate are neglected. Corrosion of the substrate is assumed to be uniform and isotropic. Under these conditions, corrosion occurs at defects present in the coating. Based on the theory of phase transformation kinetics, an equation is derived that predicts the extent of substrate corrosion, given the number of defects per unit area and knowledge of the corrosion kinetics of the bare substrate material. This equation is used to predict the behavior of coated substrate materials that exhibit linear and parabolic corrosion kinetics. Accelerated corrosion tests of uranium with protective metallic coatings are shown to be in good agreement with this model of substrate corrosion.