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- Corrosion monitoring (2) (entfernen)
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Sensors for the detection of general corrosion are well established. However, the detection of early phases of localized corrosion still remains a challenging task since the initiation steps can proceed without showing significant contribution to the electrochemical signal of a macroscopic surface. Along with electrochemical noise based methods, utilization of multielectrode arrays can be used to address this problem.
The aim of this study is to develop and test multielectrode arrays for early detection of corrosion processes. By means of a multielectrode analyser the current flow, potential and impedance spectra on each single electrode can be measured as a function of time. Thus, maps of the probe can be generated with real time information for instance showing individual electrodes persistent anodic or cathodic signals. This approach has been utilized in combination with scanning electrochemical techniques such as scanning electrochemical microscope or scanning vibrating electrode to select active electrodes for detailed investigation.
As the sensitivity is strongly dependent on the wire diameter and array configuration, a systematical investigation has been performed to optimize the preparation procedures and probe geometry. Stainless steel X5CrNi18-10 (1.4301) wires of different diameters have been embedded in a carrier material made of epoxy resin providing electrical insulation. The multielectrode probes consisting of at least 3 x 3 and a maximum of 10 x 10 single electrodes have been tested in corrosive media, with different chloride concentrations, as well as in the presence of metal reducing bacteria to assess their applicability in the detection of the onset of corrosion. This contribution will summarize our optimization study and the evaluation of the sensor performance.
High resolution analysis of corrosion processes on stainless steels is a challenging task. The application of local electrochemical techniques such as scanning electrochemical microscopy (SECM) has opened new possibilities for the detection of corrosion products and activity on metallic surfaces. However, due to its stochastic nature, the analysis of pitting corrosion requires being at the right place at the right time. Scanning over large areas at a high resolution not only leads to long scan durations but also leaves many short-lived processes undetected. In this paper we present the combined automated operation of SECM and wire multi-electrodes connected to a multi-electrode analyzer (MMA). The inter-electrode currents between 25 wire electrodes connected via zero resistance ammeters (ZRA) are measured by the MMA at open circuit potential (OCP) and the electrodes reporting anodic currents are detected automatically to be analyzed by means of SECM. The results demonstrate the successful application of this methodology for the detection of unstable and stable pitting processes on 304 stainless steel in a corrosive aqueous environment.