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Chemical imaging of corrosion processes involving copper species using scanning electrochemical microscopy has been hampered by the lack of soluble oxidation states for copper that can be achieved by amperometric conversion at the tip. Indeed, the only possibility is to reduce the corrosion products at the tip, thus modifying the chemical response of the electrode material and requiring subsequent redissolution of the copper deposits. Consequently, the limitations arising from the system prevented a full-scale quantification, requiring the development of new methodologies or the optimisation of those currently available, as we pursued with the present work. Therefore, the voltammetric behaviours of gold macro- and microelectrodes were evaluated with respect to the collection and redissolution of Cu2+ ions, with the aim of using them as sensing probes in scanning electrochemical microscopy (SECM) to investigate the activity of copper surfaces in acidic chloride-containing environments. Cyclic and square-wave voltammetric techniques were explored for copper collection and subsequent stripping on Au microelectrode tips in SECM with the objective to capture in situ image electrochemical reactivity distributions across copper surfaces undergoing corrosion. [ABSTRACT FROM AUTHOR]

The formation of a localized differential aeration cell on metals, susceptible to both anodic and cathodic corrosion, is a serious threat because of multiple degradation processes commencing with the passivation layer destruction. By using local electrochemical and X-ray dispersive techniques, it has been demonstrated that the differential aeration cell formed on high brass (α-brass, Cu65-Zn35) in the presence of 1 H-benzotriazole or 5-methyl-1 H-benzotriazole plays both corrosion-inhibiting and accelerating roles, depending on the inhibitor exposure time. Alternating-current scanning electrochemical microscopy was used to image local electrochemical activity, whereas energy-dispersive X-ray spectroscopy provided evidence for the mechanism of the observed phenomena. Short-term exposure to the inhibitor (5 min) promotes the formation of a passivation layer in the waterline region. In contrast, after prolonged exposure (45 min), a deficient passivation layer develops for both inhibitors. An excess of zinc(II)-inhibitor complexes in the passivation layer is accountable for the corrosion resistance of the region with high differential aeration. Rapid dezincification and local alkalinization facilitate the initial rapid formation of a passivation layer in the area under differential aeration to preserve its composition upon further modification. [ABSTRACT FROM AUTHOR]

Generation of single corrosion pits and in situ monitoring of pit growth on iron exposed to 0.5 m NaCl solution was achieved by using combined atomic force and scanning electrochemical microscopy (AFM-SECM). Pits as small as 2.7 μm in diameter were formed at arbitrary locations on the substrate through the local generation of highly concentrated nitric acid in the vicinity of the AFM-SECM probe. Addition of nitrite ions to the environment, which act as corrosion inhibitors for iron, ensures passivation of the metal and hinders metal corrosion, despite exposure to the chloride-containing media. Localized acidification was achieved by oxidizing nitrite ions at the probe. Acidification in combination with the high chloride content in the solution led to a local rapid attack at the surface and pit generation below the AFM-SECM probe. Besides improved spatial resolution and precise control of the pit nucleation site, combined AFM-SECM allows simultaneous imaging of the generated pits by the AFM tip. [ABSTRACT FROM AUTHOR]

Alternating current scanning electrochemical microscopy (AC-SECM) is used to investigate the inhibition of copper corrosion by four potential inhibitors, namely benzotriazole (BTAH), 5-methyl-benzotriazole (MBTAH), 2-mercaptobenzimidazole (MBI), and ethyl xanthate (EX). It is shown that the formation of inhibitor films on the metal can be followed from the decrease of the substrate's local electrochemical activity associated with the formation of inhibitor-containing surface layers. Sensitive imaging can be performed that accounts for changes in electrochemical activity of the modified surfaces, as well as for their corrosive attack from the environment. AC-SECM is shown to be a powerful technique for the investigation of corrosion processes. [ABSTRACT FROM AUTHOR]

Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-alloy. [ABSTRACT FROM AUTHOR]

The cover picture shows the passivation effect of a liquid in a brass tube in the presence of oxygen in the gas phase. The resulting differential aeration conditions promote the passivation of brass at short exposure times as revealed in images recorded by alternating current scanning electrochemical microscopy (AC‐SECM) which were generated by holding the SECM tip over the temporarily passivated area. Details are given in the Full Paper by Wolfgang Schuhmann et al. on page 49 in Issue 1, 2016 (DOI: 10.1002/cplu.201500398). [ABSTRACT FROM AUTHOR]