Surface charge at the oxide-covered aluminium-electrolyte interface

Abstract

The streaming potential was measured on aluminium samples anodized in sulphuric, oxalic and boric acid on samples which were boehmitized in boiling water after they had been anodized and on samples of boehmitized aluminium. During the measurements the samples were in contact with KCl solutions of various pH values. The contact angle between the oxidized aluminium and KCl solutions of various pH values was estimated for several samples. The results of direct measurements of the streaming potential as a function of pH show that this relation is linear. The results, which depend on the method of preparation of the layer, differ in the value of the streaming potential and in the value of the isoelectric point. In the analysis of the results the ζ potentials are calculated and the surface charge is also estimated for the same systems. The results of the contact angle measurements for two selected systems correlate very well with those obtained from the streaming potential experiments. The results are finally analysed and discussed in terms of incorporation of the electrolyte anion in the oxide layers.