STUDY OF ALUMINUM ANODIZATION IN SULFURIC AND CHROMIC-ACID SOLUTIONS .2. OXIDE MORPHOLOGY AND STRUCTURE

The morphology and structure of the anodic oxides, formed on aluminium in chromic and/or sulfuric acid aqueous solutions have been studied by the methods of high-resolution transmission electron microscopy, X-ray crystallography, ultrasoft X-ray spectroscopy and thermal derivatography. It has been shown, that the porous structure of oxides grown in the chromium acid solutions is less-ordered as compared with that for oxides formed in sulfuric acid. All the anodic oxides are amorphous and contain a mixture of AlO4 tetrahedra and AlO6 octahedra. The derivatography data indicate lower hydration of the anodic oxides grown in chromium acid but also their enhanced ability to absorb the water during the oxide sealing. The possible reasons of weak chromate incorporation into the anodic aluminium oxide are discussed. The decrease of cation transport number within the layer of incorporated anions is suggested to be the main reason. © 1990.