ELECTROCHEMICAL AND PHOTOELECTROCHEMICAL CHARACTERIZATION OF NATURALLY GROWN OXIDE LAYERS ON COPPER IN SODIUM-ACETATE SOLUTIONS WITH AND WITHOUT BENZOTRIAZOLE

The aim of this work is the characterization of as-grown oxide layers of copper in aerated sodium acetate solutions, in relation to the understanding of the mechanism of protection in the presence of benzotriazole, which is a well known inhibitor of corrosion. The growth and the characteristics of the film at rest potential are studied using cathodic stripping analysis in a deaerated solution. Its properties are determined by using the photoelectrochemical technique. It is shown that in BTA solution, the photoactive layer is the same as without BTA, giving the same optical indirect transitions at 2.6 and 1.9 eV, its thickness being in the range of a few nm. Both cathodic and anodic photocurrents are generated and the particular dependence of the spectral response as a function of potential is evidenced and explained. At the rest potential both photocurrents are superimposed. The layer is attributed to cuprous oxide, weakly modified with BTA. In the presence of BTA, changes in the reduction curves are observed and special attention is paid to a cathodic wave in excess, specific to BTA-aerated solutions. The formation of a polymeric copper(I)-BTA outer film is suggested for the formation of a Cu(II)-superoxide complex related to the uptake of molecular dioxygen.