Effect of solvents on the corrosion inhibition of copper by 1,2,3-benzotriazole

Electromotive force (E) measurements have been made at 303.15 K on the cell, Cu_x Hg/CuCl₂ (m) in solvent S′ [S′=W or FD or DMF each containing 15 ppm of 1,2,3-benzotriazole (BTA)] /AgCl/Ag (where W, FD and DMF represent the solvents water, formamide and N,N-dimethylformamide, respectively). The Emf data have been compared with the corresponding data under the same conditions in pure W, FD and DMF; the Emf values change from negative to very positive in the presence of BTA in these solutions and suggest the possibility that the presence of BTA in W, FD and DMF helps to bind copper ions with solvent molecules through formation of new complex structures of the film formed on the metal surface. We have suggested the probable mechanism of formation of a protective film through complex formation. The higher Emf values in the presence of BTA indicate strong ion-solvent interactions and the order of interactions was found to be as: FD≥DMF>W. Further iterative procedures were employed to evaluate K₁,K₂ (dissociation constants), α₁,α₂ (degrees of dissociation), γ_± (mean activity coefficient) and E^o (standard cell potential) making use of the measured E values. The standard molar Gibbs energy of transfer, ΔG_tr ^o , of CuCl₂ from the pure S to S′ were calculated using the computed standard cell potentials. The calculated ΔG_tr^o values were found to be negative which was indicative of strong ion-solvent interactions and reasonably supported the trend of ion-solvent interactions. From these studies we concluded that BTA acts as a better corrosion inhibitor towards copper in FD and DMF than water.