Potential Oscillations of a Stainless Steel Electrode during Galvanostatic Polarization in a Mixed Solution of Sulfuric and Chromic Acids

Potential oscillations of a stainless steel electrode galvanostatically anodized have been observed in a mixture of chromic and sulfuric acids. The potential regularly oscillated between 1.6 V vs. SCE (lower) and 2.1V (upper) with a certain frequency. The potential values are affected neither by the composition of chromic and sulfuric acids nor by the magnitude of applied current density although the potential frequency is very sensitive to these parameters. This phenomenon is interpreted in terms of the repeated formation and disappearance of the saturated layer of dichromate ions on the electrode surface. Such scheme is consistent with the in situ FTIR spectroscopic result that the concentration of Cr₂O₇^2- ions on the electrode surface increased with time during the polarization at the lower potential but the change in concenetion of Cr₂O₇^2- ions was negligible at the higher potential.