Development of electrochemical sensors and their application for characterizing the metal/electrolyte system during localized corrosion

Electrochemical microprobes for in situ monitoring of the electrochemical conditions inside recesses are needed to better understand how localized corrosion and other charge transfer processes occur in confined spaces. The electrode potential distribution can be routinely measured in cavities of > 100 μm opening dimension, but the ability to measure the concentrations of chemical species and their change with time in the presence of potential gradients is only recently becoming possible. Microprobes for pH and chloride ion will be described and results with these sensors will be presented and discussed for creviced iron samples in aqueous electrolytes. Available results reveal, that these species change in concentration and distribution with time both during the induction period before crevice corrosion starts and during propagation of crevice corrosion. Preliminary data show that ionic concentrations peak at locations of highest metal dissolution rate on the crevice wall.