The Migration of Metal and Oxygen during Anodic Film Formation

Abstract

Beta-ray spectroscopy and radiotracer techniques have been used to study the transport of metal and oxygen during anodic oxidation. Both species are mobile during oxide film growth on A], Nb, Ta, and W, but in Zr and Hf only oxygen transport is observed. Radiotracer measurements showed that the amount of metal dissolving in the electrolyte was usually less than 1 % of the total oxidized, but that for A1 it could be as high as 40%, depending on the current density and electrolyte used. Although the anodic oxidation of metals has been studied extensively in recent years, the nature of the mobile species within the growing oxide film has not been clearly established. Experimental evidence has been presented in A1, for example, to suggest that anodic oxidation proceeds by metal ion migration (1, 2), by oxygen ion migration (3), or by a combina-