Investigation of oxidation potentials of substances accumulated during cathodic polarization of aluminium

High-purity aluminium immersed in a neutral sodium chloride solution was submitted to galvanostatic pulses of different duration in a current density range between 10⁻⁵ and 10⁻¹ A cm⁻², as well as to a defined anodic current following immediately each cathodic pulse. Potential transients were recorded at time scales ranging between ms and 10³s. Interfacial and kinetic parameters for the cathodic reaction were extracted from cathodic transients. Anodic transients revealed several levels of oxidation potentials at which different substances produced in the cathodic process, were oxidized. It was found that, when the cathodic processes take place at the bare metal surface (at c.d. sufficient to cause complete hydration of the oxide film), the amount of substances formed is proportional to the square root of the total cathodic charge passed during a pulse.