Aluminum Anodization in a Basic Ambient Temperature Molten Salt

Aluminum anodization has been studied in the basic ambient temperature molten salt . The anodization process was studied as a function of chloride anion concentration. Two different anodization processes are observed with onset potentials of approximately −1.1 and 0 V. The more cathodic anodization involves formation of the tetrachloroaluminate anion and exhibits a limiting current controlled by diffusion of chloride to the electrode surface. The number of chlorides required for each Al anodized was determined to be . The more anodic anodization shows no diffusion control. A value for the diffusion coefficient of chloride was obtained which is lower than previously reported; the difference involves using an n value of 1, rather than . No reduction of the tetrachloroaluminate anion was observed even at elevated temperatures.