Electrical properties of growing porous anodic aluminum oxide films

Electrochemical oxidation of aluminum and aluminum alloys in acid electrolytes results in a coating with ordered structure on the nano-scale. Although this highly functional nano-material is available commercially for a diverse range of applications, the driving forces responsible for structure development are not well understood. Two electrical properties, the resistance and capacitance, contain information about the current, space charge and electric field distribution during structure development. The electrical properties of porous oxide films were extracted in situ during growth on three base materials at varying temperatures and current densities. In this work, a single frequency electrochemical impedance spectroscopy technique and an experimental apparatus designed for in situ measurement of cell potential and current were used. The electrical properties calculated during structure development in sulfuric acid at current densities between 5 and 35 mA·cm--2 support the hypothesis that structure originates from competition between electrostatic forces and viscous dissipation