REPASSIVATION TRANSIENTS MEASURED WITH THE BREAKING-ELECTRODE TECHNIQUE ON ALUMINUM THIN-FILM SAMPLES

The breaking-electrode technique was used to study repassivation trans ients of small, fresh metal areas of Al exposed to a conductive electr olyte at a range of potentials. The peak current density measured with in the first few microseconds after breaking was found to be ohmically limited, with an ohmic resistance that is substantially higher than t hat measured minutes after breaking. The current decay during the firs t 3 s was recorded and found to be exponential in nature. By plotting the data as log i vs. (it)(-1/2), it is concluded that oxide growth wa s better represented by the direct logarithmic law than by high-field kinetics. Cathodic current transients having a complex shape were obse rved at low potentials. It is suggested that oxide growth at potential s slightly above the reversible potential for oxide formation retards the water reduction reaction. The advantages and limitations of the br eaking-electrode technique are discussed.