INVESTIGATION OF ANODIC ALUMINUM-OXIDE LAYERS BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

The effects of a.c.-electrochemical graining and anodizing of an aluminium substrate on the layer properties of both barrier and porous alumina layers are examined using electrochemical impedance spectroscopy (EIS). In order to show the capabilities of the technique for a quantitative determination, results based on impedance data are compared with complementary information from surface analytical techniques. Though the results for the determination of barrier layer thickness and dielectric constant look promising, calculations are troubled by non-trivial dispersion phenomena. This problem is treated using a fractal description of surface roughness of the substrate and of the layer thicknesses. Information on pore structure of porous oxide films could not be obtained from the approach considered in this study. © 1990 Chapman and Hall Ltd.