EFFECT OF COPPER CATION ON ELECTROCHEMICAL-BEHAVIOR OF STEEL IN PRESENCE OF IMIDAZOLE IN ACID-MEDIUM

The influence of different concentrations of imidazole in the presence of 1 M sulphuric acid on electrochemical and corrosion behaviour of s teel both with and without different concentrations of copper cation C u++ was studied potentiokinetically. It was found that imidazole reduc es the corrosion current, corrosion rate and increases the polarizatio n resistance to a gnat extent. For each additive, the protective catio n was incorporated into the protective layer formed on the electrode s urface 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(2)SO(4) is appreciably reduc ed by imidazole in combination with metallic copper cation, as a resul t 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 t o metal The increase in the corrosion rate is a result of cationic red uction, and the potential is shifted towards electropositive direction , indicating a new anodic and cathodic polarization curve formation re sulting from the deposition of the metal. In the presence of imidazole and lower metallic copper cation concentrations (10(-5) M), the poten tials shift in the electronegative direction, indicating suppression o f the cathodic reaction by conjoint adsorption of the inhibitor and me tallic cation. The corrosion potential, corrosion current, corrosion r ate, polarization resistance, as well as activation energy and thermod ynamic parameters were calculated at different temperatures. The tempe rature 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 dir ectly.