Formation of Al–Zr composite oxide films on aluminum by sol–gel coating and anodizing

Abstract

Al specimens were covered with zirconium oxide film by sol–gel coating using zirconium alkoxide, and then anodized galvanostatically in a neutral borate solution. The time-variation in anode potential during anodizing was followed, and the structure and dielectric properties of the anodic oxide film were examined by TEM, EDX, RBS, and impedance measurements. It was found that the anode potential increases during anodizing, and that the slope of the potential–time curve becomes steeper with increasing number of dippings in sol–gel solution. An anodic oxide film was formed at the interface between zirconium oxide and the aluminum substrate during anodizing. This anodic oxide film was composed of an inner Al2O3 layer and an outer Al–Zr composite oxide layer. The capacitance of anodic oxide films formed after sol–gel Zr-oxide coating and anodizing was about 20% higher than without Zr-oxide coating.