CATHODIC POLARIZATION OF ALUMINUM IN ACETATE-BUFFERED CHLORIDE MEDIA

Polarization behaviour of 1S aluminium has been studied in chloride solutions containing equal molar amounts of acetic acid and sodium acetate. The effects of stirring and buffer capacity have been tested. The oxide film becomes highly permeable to the passage of protons when acetate is added compared to solutions of neutral pH containing NaCl alone. The transport of Al3+ to the solution is negligible in relation to the proton flux towards the metal in the presence of a cathodic field, and the film is thus protective against significant metal dissolution. As the potential is decreased to more negative values, a limiting-current behaviour is observed followed by film breakdown below a certain threshold potential. The limitation is ascribed to the blockage of the paths for proton transport through the film by the hydrogen gas diffusing away from the metal surface. Possible causes of cathodic film breakdown are discussed. © 1979.