Research on the Morphologies and Corrosion Resistance of Anodic Alumina Films Influenced by Additives in Sulfuric Electrolyte

Abstract

The surface morphologies, chemical composition, phase composition, compactness, thickness and the corrosion resistance of porous anodic films prepared in the sulfuric electrolyte with different additives at 35°C were investigated by XRD, FESEM, EDS, drop method in this paper. The additives are including organic acids, polyhydric alcohols and rare earth (REE) salts. It is indicated that a porously anodic film with about 20 nm holes in diameter can be obtained by additives into the sulfuric electrolyte. The main chemical compositions of the anodic films are Al, O elements, and a small amount of S. The film after boiling water sealing is composed of boehmite phase (Al2O3·H2O) and alumina (Al2O3). The corrosion resistance of the anodic film can be improved by the coupling effect of the additives. The mechanism is discussed.