Effect of interface chloride ion perturbation on oscillatory electrodissolution

This paper investigated the effect of chloride ion perturbation on the electrodissolution behavior of carbon steel in 5.0 M H3PO4 solution. The results indicated that the oscillatory electrodissolution changes significantly when the electrode/electrolyte interface was disturbed by injecting small quality of chloride ion-containing solution. The mode of current oscillations changed from the mono-periodic to the nonperiodic behavior with higher frequencies but lower amplitudes. After a transient response disappeared, the permanent influence in the current oscillations was observed. Potential distributions on the surface of the electrode were monitored in situ by using scanning reference electrode technology during the electrodissolution process. The potential maps show clearly that localized corrosion was induced after the chloride perturbation. The enforced solution homogenization by bubbling nitrogen at the electrode/electrolyte interface after a few seconds of the chloride perturbation could not eliminate such influence, indicating that chloride ions may enter the passive film and resulted in degradation in chemical stability of the film because of permanent damage. Such a degradation of the passive film only appears when the transient concentration gradient of the chloride ions on the surface is sufficiently high. The long duration of impact on electrodissolution caused by chloride ion perturbation suggests that the passive film does not totally dissolve during the active period in each oscillatory cycle.