The open-circuit elecrtode potential of aluminium cut under deoxygenated 1N.KC1 solution rises from a minimum potential of -1.65v 20μs after the metal is cut, to a steady potential of -0.9v after several minutes in solution. This behaviour has been investigated. Square-wave current methods were used to determine the change with time in the overvoltage parameters for cathodic, hydrogen ion discharge and for anodic, aluminium dissolution processes. The results indicate that the rise in

more »

... t potential can be attributed to a decreasing anodic exchange current from 2.2 x 10⁻² amps/cm² at the bare metal surface to 1 x 10⁻⁷ amps/cm² after some minutes in solution. It is concluded that this effect is caused by the formation on the metal surface of a films which conducts electrons, but impedes the dissolution of aluminium. The suggestion is made that for aluminium, hydrogen ion may be discharged only from the film covered surface. An explanation of the potential of -0.5v which has often been observed for aluminium in aerated chloride solution is offered.