Anodic Oxidization of Aluminum at High Current Densities and Mechanism of Film Formation

Galvanostatic anodization of aluminum at high current densities (100, 150, 200 mA cm -2 ) was studied. The growth rates of the synthesized anodic aluminum films were 1-3 μm/min. Films with ordered pores or with a fractal surface were also prepared. Consequently, nonlinear anodization and hypothesis for film formation are proposed and applied to elucidate experimental results. Transmission electron microscopy (TEM) and scanning Auger electron microscopy (SAM) were applied to acquire supplementary experimental results to support the proposed hypothesis. TEM shows that initial oxygen bubbles were collected on the boundary of neighboring hexagonal cells, channels for bubble liberation were located in the center of hexagonal cells. By profiling on SAM, depth profiles of Al and O atoms in the film were obtained, and the assumption that oxygen evolution plays positive roles in ion transfer during anodizing was supported indirectly. Although the validity of the hypothesis needs further testing, some points of the assumption are supported.