Aluminum specimens were covered with zirconium oxide film by a sol-gel coating and galvanostatically anodized in a neutral borate solution. The time variation in anode potential during anodizing was monitored, and the structure and dielectric properties of the anodic oxide film were studied by TEM, EDX, RBS, and impedance measurement.
We found that the anode potential increases with time, and that the slope of the potential-time curve increases with increasing the numbers of sol-gel dip coatings. During anodizing, an anodic oxide film, which consisted of an inner Al2
layer and an outer Al-Zr composite oxide layer, formed at the interface between Zr-oxide and the substrate. The thickness of the inner layer increased with anodizing time, and the thickness of the outer layer peaked before decreasing with time. The capacitance of the specimen after sol-gel coating and anodizing was 20% higher than that without sol-gel coating. The dielectric property of anodic oxide films was correlated with film structure.
The mechanism of anodic oxide films growth on the spceimen covered with Zr-oxide is discussed in terms of the porosity distribution in the Zr-oxide layer and the outward transport of Zr4+
ions across the composite oxide layer during anodizing.