ANOMALOUS ELECTROCHEMICAL PHENOMENA DURING CORROSION OF ALUMINUM IN NAOH SOLUTIONS AT LOW CATHODIC AND ANODIC POLARIZATION

The rates of corrosion of aluminium in aqueous 0.03 to 0.4 M-NaOH solu tions were measured at 20-degrees-C, under imposed cathodic as well as anodic current densities up to 160 muA cm-2. The rates were determine d from the loss in mass of aluminium, as well as by measuring the volu me of evolving hydrogen. The results were in contradiction with the fu ndamentals of electrode kinetics. Thus, within certain current density range, the cathodic reaction (viz. hydrogen evolution) is retarded by cathodic currents, and activated by anodic currents. On the other han d, the anodic reaction is accelerated with cathodic currents, and inhi bited with anodic ones although the surface is active. To avoid breakd own of electrode kinetics, it is suggested that the entities initiatin g the cathodic and anodic reactions originate simultaneously from the surface metal atoms. A surface equilibrium is always established betwe en the charged entities and the neutral metal atoms. Pronounced change s in the surface pattern at low polarization lead to anomalous electro chemical phenomena.