Use of Galvanokinetic Methods for the Determination of Characteristic Potentials for Pitting Corrosion on Aluminum

Three different galvanokinetic methods have been used to determine the pitting potential (Ep) and the protection potential against pitting (Epp) for unalloyed aluminum in a deareated solution of 3% NaCI at 0 and 30 C (32 and 86 F). These three methods are (1) the continuous galvanokinetic, (2) the quasistationary galvanokinetic, and (3) the stationary galvanokinetic. From results of these investigations, determination of the potentials appears dependent on which of these three methods is used. It seems the quasistationary method gives the results with the best reproducibility. The results also supports the theory that aluminium does not have more than one characteristic potential for pitting corrosion under these special conditions. This theory was previously published by Broli and Holtan.1 The stationary method provides the possiblity for an approximation of the critical current density for aluminium dissolution.