Anodizing as a Corrosion Process

Abstract

This chapter describes how the various parts of the fundamental model for corrosion are linked to anodizing. From the oxidation potential to the anodic dissolution of aluminum, the equilibrium and nonequilibrium conditions that produce a stable oxide on the substrate surface at the interface with the electrolyte are considered as it relates to electrochemical circuits. The basis for anodic oxide formation under atmospheric conditions is explained from first principles for unalloyed isotropic aluminum, beginning with the formation of the passive oxide layer in terms of the thermodynamic concept of work function, and continues with the establishment of the anodizing process as nonequilibrium, accounting for the dynamic conditions that enable the formation of stable anodic aluminum oxide. The effects of anodizing process parameters on oxide formation: polarization, the imposition of an electrical bias electrolyte concentration, temperature, and current density are discussed with respect to reaction kinetics and resistance effects that utilize the concept of work function for the total anodizing circuit, known as the Tafel equation.