Abstract
The objective of this study was to form a crystalline oxide film on a titanium substrate using the micro-arc oxidation (MAO) method. The study demonstrated that this was possible by controlling the type of electrolytic aqueous solution and pH value. Phosphoric acid radical in the electrolytic aqueous solution was indispensable. In principle, the crystalline oxide film was anatase, but the film made from electrolytic aqueous solution having a pH exceeding 12 or including poly-phosphoric acid was rutile. Below pH 12, the film was unstable and dissolved in the electrolytic aqueous solution considerably. The crystalline oxide film had a double-layer structure, and anions in the electrolytic aqueous solution entered the side layer of the electrolytic aqueous solution. As a result, the O2- concentration rose and much more rutile was formed. Anatase contained little holes and the surface was smooth, whereas rutile contained columnar grains at the hole edges and the grains were oriented.
