Effect of copper cation on electrochemical behaviour of steel in presence of imidazole in acid medium

Abstract

The influence of different concentrations of imidazole in the presence of 1 M sulphuric acid on electrochemical and corrosion behaviour of steel both with and without different concentrations of copper cation Cu ++ was studied potentiokinetically. It was found that imidazole reduces the corrosion current, corrosion rate and increases the polarization resistance to a great extent. For each additive, the protective cation was incorporated into the protective layer formed on the electrode surface during exposure to the tested solution. It was found that at a concentration of 10 −4 M, Cu cation strongly inhibited the corrosion rate. The corrosion of the steel in 1 M M 2SO 4 is appreciably reduced by imidazole in combination with metallic copper cation, as a result of coadsorption. At a higher concentration of the copper cation (10 −3 M) in association with the inhibitor, the dissolution of the steel is increased owing to the cathodic reduction of the metallic cation to metal. The increase in the corrosion rate is a result of cationic reduction, and the potential is shifted towards electropositive direction, indicating a new anodic and cathodic polarization curve formation resulting from the deposition of the metal. In the presence of imidazole and lower metallic copper cation concentrations (10 −5 M), the potentials shift in the electronegative direction, indicating suppression of the cathodic reaction by conjoint adsorption of the inhibitor and metallic cation. The corrosion potential, corrosion current, corrosion rate, polarization resistance, as well as activation energy and thermodynamic parameters were calculated at different temperatures. The temperature coefficient for corrosion inhibition has a negative value which may be explained by assuming that the corrosion reaction is no longer the simple metal/acid reaction, but involves the adsorbed species directly.