熱酸化皮膜で覆われたＡｌ表面上に形成されるバリヤー皮膜内におけるγ′‐アルミナ結晶の成長に及ぼす化成電解液の効果

Abstract

The development, during anodizing, of γ'-alumina within the barrier oxide layer formed on aluminum covered with a thin thermal oxide layer is strongly influenced by the nature of anion species of the electrolytes. The development of γ'-alumina is strongly inhibited when the thermally oxidized aluminum specimens were anodized in such solutions as aqueous ammonium dihydrogen phosphate, ammonium tartrate and ammonium citrate, where anion species of the respective electrolytes are known to exhibit inward movement after they have been incorporated into the growing barrier oxide layer. In such cases, the fine crystals of γ-alumina, which are thought to act as nuclei for the amorphous to crystalline transformation, are likely present surrounded by the amorphous film material doped with anion species of the electrolytes. The strong inhibition for the development of γ'-alumina can be explained as being due to the presence of the incorporated anions which are known to hinder the structural rearrangement at the amorphous/crystalline boundary.