INHIBITION OF THE HYDROGEN EVOLUTION REACTION ON ALUMINUM COVERED BY SPONTANEOUS OXIDE

The electrochemical behaviour of aluminium covered by a thin 'spontane ous' oxide film was studied as a function of temperature and electroly te composition at pH 1.3 The rectification mechanism of the charge tra nsfer reactions is discussed on the basis of E/I characteristics. Tafe l plots for the hydrogen evolution reaction showed anomalous slopes be tween 2.3 x 3 RT/F and 2.3 x 4RT/F, depending on temperature. The inhi biting effects of 1 and 2-naphthylamines on the corrosion kinetics of aluminium in acid media (HClO4 and NaCl + HCl) were determined using e lectrochemical methods. Consideration of the protonation of amines and the effects of the positively charged surface suggest that the observ ed excellent inhibition is due to the planar orientation (with pi-elec tron bonds) of the adsorbed inhibitor molecules and the existence of s ynergetic effects. The degree of surface coverage was found to increas e with temperature up to 40-degrees-C. At approximately 40-degrees-C t he adsorbed molecules probably change their orientation becoming verti cally adsorbed on the surface with strong lateral repulsion.