The temperature of alumina barrier layer during a high electric field anodization of aluminum (the current density more than 50[Formula: see text]mA/cm[Formula: see text] has been studied by analyzing the aluminum film resistance. In the case of Joule heat power density to be larger than 20[Formula: see text]W/cm2, the temperature inside the barrier layer can exceed [Formula: see text]C, which leads to the local melting of aluminum. Scanning electron microscopy has shown the location of molten aluminum droplets and their movement during the anodization process.

We have shown that the surface potential of anodic alumina films changes in time: immediately after the anodization process it was positively followed by the substantial decrease to negative values. Such variations of the surface potential can be associated with the negative built-in electric charge in alumina. The highest negative charge density occurs in the films formed in citric and phosphoric electrolytes.

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