Characterization of anodized and sealed aluminium by EIS

Anodized and sealed aluminium samples exposed to different atmospheres for up to three years have been studied by means of electrochemical impedance spectroscopy (EIS). EIS was used to obtain detailed information concerning the electrochemical properties of the porous and barrier layer of anodized aluminium. An equivalent circuit that reproduces the a.c. impedance results of porous aluminium oxide films is proposed. The results reveal that the EIS technique is a good tool for obtaining detailed information on the influence of autosealing and the ageing process on anodized aluminium. This research shows that porous layer sealing quality increases over months and years (especially in the first 24 months) as the ageing proceeds when exposed to the natural atmospheric conditions. The analysis was completed with the aid of the SEM technique. (C) 2002 Elsevier Science Ltd. All rights reserved.