Abstract
Aluminum specimens were covered with SiO2 film by a sol-gel coating and then anodized galvanostatically in a boric acid solution. Time variations in the anode potential during anodizing were monitored, and the structure and dielectric properties of anodic oxide films were examined by TEM-EDX, and electrochemical impedance measurements. It was found that anodizing of aluminum coated with SiO2 films leads to the formation of anodic oxide films that consist of an outer Al-Si composite oxide layer and an inner Al2O3 layer at the interface between the SiO2 film and the metal substrate. The breakdown potential of anodic oxide films formed on specimens with SiO2-coating was about 100 V higher than that without SiO2 coating. The capacitance of specimens after sol-gel coating and anodizing was slightly higher than that without sol-gel coating. In the film formation mechanism, the conversion of Al2O3 into Al-Si composite oxide at the interface between the inner and outer layers is discussed in terms of inward transport of Si-bearing anions across the outer layer.
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