Adsorption and corrosion inhibitive properties of gemini surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide) on aluminium in hydrochloric acid solution

Four new quaternary ammonium gemini surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide), referred as CmC6Cm(Et)·2Br (m = 10, 12, 14, 16), were synthesized and tested as corrosion inhibitors of aluminium in 1 mol/L HCl solution at 25 °C using gravimetric, gasometric measurements and SEM techniques. Results obtained show that the surfactants studied are efficient corrosion inhibitors for aluminium in hydrochloric acid solution. The inhibition efficiencies of CmC6Cm(Et)·2Br increase with the surfactant concentrations, and the good inhibiton efficiencies are reached near their critical micelle concentrations. In addition, the inhibition efficiency for aluminium slightly increases with increasing surfactant chain length (m) at the same concentration since the adsorption capacity of CmC6Cm(Et)·2Br is increased with m. These gemini surfactant inhibitors adsorb at the aluminium/solution interface according the Langmuir adsorption isotherm. Thermodynamic parameters of adsorption (b, ΔGads) of CmC6Cm(Et)·2Br were determined and the inhibition mechanism has been discussed. The adsorption of gemini surfactants CmC6Cm(Et)·2Br at the aluminium/solution interface can be considered as a cooperative adsorption and the high absolute values of ΔGads could be attributed to the high adsorption ability of the gemini surfactant molecules on the aluminium surface, forming a strong protective film by the synergistic effect between bromide anions and positive quaternary ammonium ions. On the basis of the variation of surface coverage rates (θ) with the surfactant concentrations, the adsorption modes of the gemini surfactants CmC6Cm(Et)·2Br at the aluminium/solution interface were proposed.