Effects of a pre-existed anodic alumina on successive anodization behavior of aluminum and structure of its oxide film

The effects of pre-existed anodic alumina on successive anodization behavior of aluminum and the structure characteristic of the successive AAO (anodic aluminum oxide) film were studied by sequential anodization of aluminum substrate in H2SO4 solution and H2C2O4 solution respectively. The pre-existed SAAO (anodic aluminum oxide formed in sulfuric acid) film not only affects the film growth rate in oxalic acid, but also widens anodization potential range. The new prepared film undergoes a continuous change in the morphology from SAAO-like, to transient state, then to OAAO (anodic aluminum oxide formed in oxalic acid)-like, accompanying a process from disorder to order. In the series of changing processes, approximately two thirds of channels of SAAO film successively stop growing.