Corrosion protection of aluminium in acidic chloride solutions with nontoxic inhibitors

Corrosion kinetics of 99.6% aluminium covered by a thin spontaneously formed oxide film in hydrochloric acid solution with and without the presence of substituted N-aryl pyrroles was studied using electrochemical impedance spectroscopy and quasi steady-state polarization. Measurements were performed on a rotating disc electrode in an argon-deaerated solution in the temperature range 20 to 50 degrees C. The addition of inhibitor considerably increases overvoltage of the cathodic process (HER) and shifts E-corr to negative potential values. The activation energy of the hydrogen evolution reaction was E-a = 50 +/- 5 kJ mol(-1) and was not affected by the presence of inhibitor. The inhibitory action occurs by pi-bonding between the adsorbed inhibitor molecules and the electrode surface. The electrode coverage follows the Langmuir adsorption isotherm with an adsorption equilibrium constant K = 1.1-2.64 x 10(5) dm(3) mol(-1). The adsorption of organic compound prevents the adsorption of chloride ions and slow down the rate of corrosion.