Effect of azole compounds on corrosion of copper in acid medium

The corrosion behaviour of a copper electrode in 0.1 M H2SO4 solution has been studied potentiodynamically at different temperatures ranging from 30 to 65 degrees C. The inhibition efficiencies of benzotriazole (BTA), tolytriazole (TTA) and imidazole (IA) are then studied for four concentrations in the range 8 X 10(-2) to 10(-1) M. Benzotriazole and imidazole, in the presence of H2SO4 solution, cause a shift, mainly in the anodic direction, of the corrosion potential at low current densities as well as in the line part of the cathodic Tafel line, but tolytriazole shifts the corrosion potential to the cathodic direction of the corrosion potential. The protection efficiency of each compound has been calculated for different temperatures and concentrations. The three tested azole compounds act as corrosion inhibitors in 0.1 M H2SO4 solution through adsorption on the copper electrode surface. The similar values of the activation energy E-a suggest that the azole compounds used have similar mechanisms of action. The higher values of E-a in inhibited acid indicate that the azole compounds act as catalysts on the copper surface. The inhibition efficiencies of the azole compounds used follow the sequence benzotriazole > tolytriazole > imidazole; this sequence agrees with the activation-energy results. The azole compounds used are classified as toxic substances and can inhibit the catalytic activity of a copper surface owing to the presence of lone pairs of electrons on the nitrogen atoms. The results reported in this research elucidate the effects of temperature and; molecular structure on the inhibition efficiency. Benzotriazole is the most efficient of the three azole compounds for inhibiting the corrosion of copper in sulphuric acid solution. The thermodynamic parameters for adsorption of azole compounds are calculated. (C) 1998 Elsevier Science S.A. All rights reserved.