In-situ radial pH monitoring inside the crevice of stainless steel combined with potentiometric scanning electrochemical microscopy

The development of crevice corrosion is closely related to changes in the microchemical environment in crevices. However, it is difficult to detect the microchemical information inside the crevice using conventional electrochemical techniques. To this end, a Pt/IrOx-pH ultramicroelectrode (UME) with a radius of 690 nm was developed to study the local radial pH distribution in the crevice using the potentiometric mode of SECM in situ. This pH UME showed excellent sensitivity and stability over a wide pH range between 1.0 and 13.0. The feasibility of this pH UME was demonstrated in the study of the radial pH distribution within the slit with a slit of 101.30 mu m for 201 stainless steel (201-SS). The result showed that a significant radial pH difference was observed within the gap: the largest pH drop was observed at the opening from pH = 4.2 to 1.6, followed by the middle and the bottom. This result agreed well with the images of in-situ corrosion morphology seen in optical microscopy. This combination of SECM and submicron pH UME could be used to explore the mechanisms of crevice corrosion in various metals as well as the early stages of pitting corrosion.