High-field anodization of aluminum in concentrated acid solutions and at higher temperatures

Previous studies suggested that high-field anodization of aluminum could be realized only in relatively dilute acid at a low temperature to avoid the occurrence of undesired breakdown during anodization process. According to the model of avalanche breakdown, we proposed that the key to preventing the breakdown is to reduce the barrier-layer thickness of porous anodic alumina (PAA). Since the barrier-layer thickness of PAA decreases with increasing the acid concentration and temperature, the breakdown phenomenon during high-field anodization should not be occurred in concentrated acid solutions and at higher temperatures. Anodization behaviors of aluminum in concentrated oxalic acid solutions and at higher temperature were studied in detail. The results indicated that in the oxalic acid solutions of higher concentrations (>0.3 M) and at higher temperatures (16–40 °C), stable high-field anodization can be realized without the occurrence of breakdown and well-ordered PAA films can be available. Moreover, the well-ordered PAA film can be obtained even without stirring of the electrolyte. Our findings offer not only a simple and fast fabrication process of PAA templates but also an opportunity to fully understand the breakdown and the self-ordering mechanism during the growth of PAA.