Characterization of porous aluminium oxide films from ac impedance measurements

An equivalent circuit (EC) that reproduces the a.c. impedance of porous alu minium oxide films in a highly approximate manner is proposed. The results reveal that electrochemical impedance spectroscopy (EIS) is a powerful tool for obtaining detailed information on the electrochemical properties of bo th the porous and barrier layer on which the corrosion resistance of alumin ium depends. The impedance at a given frequency can be used for accurate ca lculation of the electrochemical parameter for the oxide film represented b y each element of the EC. In this way, the effects of any factor on sealing and ageing of anodized aluminium oxide films can be precisely analysed. Th e EIS technique provides an effective, advantageous alternative to existing seal quality control tests.