A method for probing vertical potential profile within the metal/solution interphas of localized corrosion systems

摘要

Based on a home-built hybrid system of scanning reference electrode technique and scanning tunneling microscope (SRET/STM), a method for in situ measurement of vertical potential and corrosion species concentration profiles within the met al/solution interphase for studying localized corrosion has been successfully estab lished in this work. There are two prominent advantages of this method: (1) probe approaching in STM mode is able to bring the probe tip very close to the surface pre cisely and reproducibly; (2) Two-dimension potential mapping helps to position the probe tip accurately to a region where localized corrosion occurs. An obviously dif ference of the vertical profiles of potential and corrosion species concentration over corrosion active sites and passive sites were observed. At corrosion active sites, the vertical potential profile exhibits a V-shape dependence on the distance between probe tip-substrate (d_(t-s)). There exists one stationary point on the potential-distance curve, at which the charge transfer and mass transport reach a balance during loca lized corrosion. In contrast, the potential decreases monotonously with decreasing dt s at the passive area. This distinct difference is attributed to the concentration profile of electroactive couple and corrosion current flow at the metal/solution interface.