ALKALINE CORROSION-RESISTANCE OF ALUMINUM ANODIC OXIDE FILM-COATED WITH ZIRCONIUM-OXIDE BY A SOL-GEL PROCESS

A zirconium oxide has been coated on aluminum anodic oxide with micro pores by a sol-gel process using zirconium alkoxide, and the alkaline corrosion resistance of its composite film has been examined by an electromotive force measurement method. The main results obtained are summarized as follows: (1) Micro pores of the aluminum anodic oxide film were charged by the zirconium oxide with an increase in dip-coating number of sol-gel solution, and a thin coating layer of the zirconium oxide was finally formed on aluminum anodic oxide film. The coating layer consisted of fine amorphous zirconium oxide particles. Defects and bubbles could not be observed in the coating layer by scanning electron microscopy. (2) Alkaline duration time of the coating composite film evaluated by the electromotive force measurement method increased with increasing dip coating number. The alkaline corrosion resistance of the coating composite film was extremely improved when the thin coating layer was formed on aluminum anodic oxide film. Since the vibration behavior of voltage was observed in the duration time curve of the electromotive force mesurement, it was found that the composite film had a self-repairing action for alkaline corrosion. (3) The composite film dried in air had alkaline corrosion resistance superior to that in nitrogen. In addition, the composite film formed by a heating treatment in oxygen had alkaline corrosion resistance superior to those in air and argon.