Surface protection of copper by azoles in borate buffers-voltammetric and impedance analysis

The inhibitory action of five azoles namely benzotriazole (BTA), mercaptobenzothiazole (MBT), benzimidazole (BIMD), mercaptobenzimidazole (MBIMD) and thiadiazole (TDA) on copper was examined in sodium borate solution of pH 6.4, 8.4 and 10.4 using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A considerable drop off in the corrosion rate of copper was detected in the presence of the investigated compounds. CV showed that the inhibitors were of mixed type that they affect both the anodic and cathodic currents. Impedance spectra were characterized in terms of the charge transfer resistance and transport of copper ions through the oxide layer. The results indicate that the surface layer is of dielectric nature, and its protection increases with increasing inhibitor concentration and solution pH. On the basis of calculated adsorption data the process was concluded as chemisorption. Some quantum chemical parameters were also calculated using ab initio Hartree–Fock 6-31G*basis set and were used to complement the experimental results. The relative inhibition efficiencies of the azoles in controlling the copper corrosion was found to be in order of MBT > TDA > MBIMD≈BIMD > BTA.