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Characterization of a variety of electrochemical parameters associated with the corrosion of aluminum, Al-Cu, and Al-Si alloy thin films (∼1-μm-thickness) in dilute hydrofluoric acid (HF) has been accomplished using electrochemical impedance spectros-copy (EIS). Phenomena characterized include the transition from passive to active dissolution with increasing HF concentration, determination of diffusional impedances associated with ionic transport through the passive oxide, detection of the initiation and repassivation of a population of metastable pits, changes in aluminum oxide resistivity and state of hydration at open circuit potential (OCP), and establishment of trends in oxide film growth with anodic potential. Impedance studies on model intermetallic phases and artificial pits were also conducted in order to aid in the interpretation of these phenomena. A survey of the analyses and interpretation methods utilized to obtain such information from impedance spectra is presented.
aluminum oxide film, electrochemical impedance, diffusional impedance, hydrofluoric acid, metastable pitting, oxide capacitance, oxide resistance, passivity, pit capacitance, repassivation, theta phase precipitates
Assistant professor, University of Virginia, Center for Electrochemical Sciences and Engineering, Charlottesville, VA