Microelectrochemical investigation of corrosion processes: metal passivation and corrosion inhibition by organic substances

Abstract

The corrosion resistance of metallic materials is primarily derived from the development of passive films on their surface formed by oxides and oxy-hydroxides of the metal. Their adhesion and chemical stability in the environments they are exposed to will determine their ability to counteract the driving force to corrosion. Furthermore, these surface films maybe modified through the interaction of organic molecules which may operate as corrosion inhibitors when they contribute to the formation of more resistant surface films, or they effectively originate a barrier film on the surface of the material, physically separating it from the aggressive environment. The organic compounds may either be dissolved in the electrolyte or adsorbed on the metal surface. In this Thesis the interaction of model inhibitors with metal surfaces was further investigated in order to establish the stability of the passive oxy-hydroxide surface layers and their modification by organic molecules. Special attention was devoted to the analysis of local effects and surface distribution by the combination of scanning microelectrochemical techniques such as the the scanning electrochemical microscope (SECM) and the scanning vibrating electrode technique (SVET). New operation modes including the use of potentiometric monitoring using ion-selective electrodes (ISE), application of AC potential signals to the scanning probe (AC-SECM), or the association with atomic force microscopy (AFM), have been implemented so as to detect local differences in electrochemical activity in the metal surface.