A Modified Chemical Imaging Sensor System for Real‐Time pH Imaging of Accelerated Crevice Corrosion of Stainless Steel

The measurement system of a chemical imaging sensor is combined with the circuitry for polarization of a metal test piece. The surface of the metal test piece is brought into contact with the sensor surface forming a crevice of about 12 µm width. The course of initiation and propagation of corrosion are observed as serial images of pH in the crevice. A local change of the pH value down to 2 is observed in synchronization with the change of the anodic current. In situ visualization of pH change in the course of crevice corrosion is presented here. The pH distribution in the vicinity of a test piece of stainless steel under potentiostatic polarization is measured by a chemical imaging sensor. In synchronization with the increase of the corrosion current, the pH value drops to about 2 at the location where corrosion is initiated.