Behavior of interfacial micro-defects in aluminum and its oxide film

In this dissertation, numerical simulation was used to calculate the equilibrium solution composition of cylindrical nanopores in surface oxide films as a step to evaluate their possible roles in the breakdown of protective oxide films. The solution composition of such nanopores is of interest from a corrosion perspective, since they play prominent roles in several mechanisms for the breakdown of passive films leading to pitting corrosion. The chemical composition of the pore solution would determine whether rapid dissolution at the pore could initiate. The effects of nanoscale pore dimensions, solution pH and adsorbing ion borate concentration on the solution composition in the pore were examined. Additionally, the behavior of interfacial voids in aluminum and voids in aluminum oxide films, of interest as corrosion initiation sites, was investigated using Atomic Force Microscopy (AFM), Transmission Electron Microscopy, and Positron Annihilation Spectroscopy (PAS). TEM successfully detected circular voids with size of ∼50 nm in anodic films. The depth profiles of voids in the oxide film were also obtained from AFM images after different extents of oxide stripping. The result demonstrated that oxide voids are formed at the metal-film interface during anodic oxide growth, likely as a result of the oxidation of metal atoms. The result also suggested that metallic voids are formed repeatedly at certain sites on the metal surface.