The effect of electrochemical reactions on the surface film composition and corrosion resistance of aluminum in acid solutions

athodic polarization was found to reduce the hydrogen transport resistance of the surface oxide film on aluminum, at potentials around ;The cathodic product detected by ex-situ infrared spectroscopy is an aluminum oxide or hydroxide which contains water. The peak areas for three major bands increased linearly with cathodic charge suggesting that the film maintains an approximately uniform composition as it become thicker. The spectra for the cathodic products compare most favorably to that of the porous, amorphous oxide films formed by anodizing in acid solution. Aluminum ions in the film are highly coordinated to hydroxyl groups. The OH groups or H;Cathodic charging of aluminum in acid solution induced an anodic current transient in the passive potential region, accompanied by electrode mass increase, which was primarily due to water absorption into the film. The anodic current decay, by three orders of magnitude, was due to an increase of the film resistance. The reaction with the metal surface of water which had been stored in the film during cathodic charging, to form aluminum oxide, was considered to be responsible for the increase of resistance.;The rates of pit initiation and pit growth during the first 30 ms anodic polarization at...