Benzimidazole-2-tione and benzoxazole-2-tione derivatives as corrosion inhibitors for aluminium in hydrochloric acid

The effect of benzimidazole-2-tione and benzoxazole-2-tione derivatives on the corrosion of aluminium in 0.1 M HCl has been investigated by a potentiostatic polarisation technique. Inhibition efficiencies were found to follow the order: benzimidazole-2-tione > 5-methyl benzimidazole-2-tione > 5-chioro benzimidazole-2-tione, while that of benzoxazole-2-tione derivatives were found to follow the order: 5-methyl benzoxazole-2-tione > benzoxazole-2-tione > 5-chloro benzoxazole-2-tione > 5-nitro benzoxazole-2-tione. The inhibitive action of these heterocyclic compounds was mainly due to adsorption on the metal surfaces, which show parallelism with the calculated total negative charge of each of the molecules. Thermodynamic parameters, such as values of free energies of adsorption DeltaG(ads) and values of equilibrium constants K-ads, were determined. Activation energies E-a, activation enthalpies DeltaH* and activation entropies DeltaS* were determined from the corrosion currents measured at different temperatures.