Inhibition of copper corrosion by coatings of alkyl esters of carboxybenzotriazole

The inhibitive effect of coatings formed dipping copper in solutions of alkyl esters (methyl, butyl, hexyl and octyl) of carboxybenzotriazole was studied by potentiodynamic polarisation, electrical impedance spectroscopy, coulometry and surface enhanced Raman scattering (SERS) spectroscopy. The inhibition efficiency of the dry film depends on type of solvent used in the coating solution, temperature and period of immersion. Pretreatment by immersing copper in hot (70 °C) aqueous solution (1×10⁻⁴ M) for approximately 2-3 h gave a film with the highest degree of corrosion protection. Higher temperatures or longer time of immersion reduce the protectiveness of the film. Copper coated using either alcohol or acetone as solvent was less well protected than when dipped in aqueous solution. Impedance spectra showed that the film formed by pretreatment in aqueous solution of inhibitors can be stable in acidic sulphate corrodent (pH∼0) for up to 3 days before breaking down. In near-neutral sulphate solution (pH∼8) the film can be stable for up to 10 days. In both acidic and neutral sulphate solution, the inhibition efficiencies of the protective film increased with the length of the alkyl ester chain in the order: methyl < butyl < hexyl < octyl. This is different to the behaviour of copper in a near-neutral aqueous corrodent containing dissolved inhibitor. The ester films also exhibit anti-tarnishing properties in a sulphidising environment with inhibition efficiencies increasing as the alkyl chain is made longer. Again the films formed by pretreatment in aqueous solution have superior anti-corrosion properties compared to those formed by pretreatment in either alcohol or acetone solution. SERS measurements indicate that the azole ring is close to the copper surface with chemisorption through azole nitrogen. It is also suggested that the hydrocarbon chain of the ester is physically adsorbed on the copper.