No abstract

Air-formed and anodized barrier-type aluminum oxides were studied in neutral borate electrolyte as a preliminary investigation into the possibility of using this environment for nondestructive evaluation of aluminum/polymer laminates. Polarization scans on air-formed oxides determined a potential range where the faradaic current was minimized and samples appeared unaffected after several days of exposure. X-ray photoelectron spectroscopy determined that borate exposure, under the prescribed testing conditions, does not permanently change the oxide thickness, and that borate ions are not incorporated into the oxide film. Analysis of the electrochemical impedance spectra of air-formed oxides and different thicknesses of anodized barrier-type oxide films established that the impedance response for all thicknesses could be described by a single-circuit model whose components correspond to a parallel-plate dielectric-filled capacitor.