Copper corrosion at various pH values with and without the inhibitor

The inhibitory action of BTAH on copper was investigated in 1 M sodium acetate solution in the pH range 4-10, using cyclic voltammetry and impedance spectroscopy. Cyclic voltammetry showed that the rearrangement of the surface oxide layer in the presence of BTAH is very fast in slightly alkaline solutions, while it is time- and concentration-dependent in neutral and slightly acidic solutions. The adsorption behaviour of BTAH on the electrode surface at c(BTAH) less than or equal to 0.5 mM followed a Flory-Huggins adsorption isotherm with Delta G degrees ranging from -30.0 to -39.0 kJ mol(-1), depending on the pH. Impedance spectra were characterized by two time constants relating to the charge transfer and transport of copper ions through the oxide layer, the latter being the rate determining step. These enabled the determination of important properties of the adsorbed layer and the passivated film. The results indicate that the surface layer is of dielectric nature, and its protection increases with increasing inhibitor concentration and solution pH. The finite diffusion impedance was analysed using a diffusion factor B, and the values of the diffusion coefficient and concentration of copper species in the film were estimated.