Recent Developments in Understanding the Initiation of Localized Corrosion Using the Wire Beam Electrode Method

This paper provides a brief review of some new experimental investigations on localized corrosion initiation processes using the wire beam electrode (WBE, a coupled multielectrode array) in conjunction with the scanning reference electrode technique (SRET).  WBE and SRET have been used to probe pitting potential and anodic dissolution profile by mapping anodic dissolution currents over the anodically polarised WBE.  For WBE surface under free corrosion or low anodic polarisation conditions, the initiation of localised corrosion was found to be due to the disappearance of minor anodes, which lead to accelerated dissolution of a few major anodes.  For WBE surface under large anodic polarisation, the initiation of localised corrosion was found to be due to the formation of active new anodic sites.  WBE have also been used to study electrochemical noise patterns from localised corrosion initiation processes.  The characteristic sharp peaks in potential noise data were found to correlate with the sudden disappearance of unstable anodes in WBE current distribution maps.  This result suggests that, in some corrosion system, electrode noise activities were associated with the disappearance of minor anodic sites, which lead to the eventual disappearance of most anodic sites and accelerated anodic dissolution of a small number of remaining anodic sites.