Factors affecting the corrosion behaviour of aluminium in acid solutions. II. Inorganic additives as corrosion inhibitors for Al in HCl solutions

CrO42−, WO42− and HPO42− ions affect on the corrosion behaviour of Al in 2 M HCl. The inhibition efficiencies of the additives depend on their type and increase with increasing concentration. Oxide film destruction and/or repair follow a direct logarithmic law. The inhibitive action of these anions is discussed in terms of competitive adsorption with Cl− ions on the electrode surface followed by a reduction mechanism to form metal oxides. The calculated values of ΔG°ads of the inhibition process reveal a physical adsorption of the inhibitors. The inhibition efficiency is found to decrease in the order: CrO42− > WO42− > HPO42−.

► CrO42−, WO42−, HPO42− decrease the rate of oxide film destruction of Al in HCl solution. ► The rate of destruction follows a direct logarithmic law. ► Metal oxides formed by reduction process are incorporated in the Al2O3 film. ► The suggested inhibitive action is attributed to competitive adsorption mechanism.