CORROSION PROTECTION OF ALUMINUM 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 p resence of substituted N-aryl pyrroles was studied using electrochemic al impedance spectroscopy and quasi steady-state polarization. Measure ments were performed on a rotating disc electrode in an argon-deaerate d solution in the temperature range 20 to 50 degrees C. The addition o f 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 ac tion occurs by pi-bonding between the adsorbed inhibitor molecules and the electrode surface. The electrode coverage follows the Langmuir ad sorption isotherm with an adsorption equilibrium constant K = 1.1-2.64 x 10(5) dm(3) mol(-1). The adsorption of organic compound prevents th e adsorption of chloride ions and slow down the rate of corrosion.