Investigation into designed current oscillations during anodic dissolution of Al in NaCl + NaNO2 solutions

We previously proposed that current oscillations occurred when there were both an active factor and a passive factor that depended on each other and influenced the anodic dissolution processes of metallic materials alternatively. In this study, an electrochemical system, Al|NaCl + NaNO2, was designed to verify this proposal. The chloride ions are aggressive ions (active factor), assisting the dissolution of the oxide film, while nitrite ions are inhibitive ones (passive factor), assisting the formation of the oxide film. The dissolution and the formation of the oxide film on the surface of the Al electrode occurred alternatively, and the current oscillations were observed to occur in this system, which proved the above point. The Al|NaCl + NaNO2 system is a new electrochemical oscillator, in which hydrogen evolves periodically from the surface of the electrode during the current oscillations. The results were discussed in terms of the formation and the dissolution of the oxide film. The current oscillations were induced by pitting corrosion of Al in chloride ions containing solutions. It is expected that more oscillatory systems can be found and further studies into the nonlinear dynamic behaviour of metallic materials can be conducted in the light of the proposal.