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Corrosion Sites (corrosion + site)
Selected AbstractsFrequency-Dependent Alternating-Current Scanning Electrochemical Microscopy (4D AC-SECM) for Local Visualisation of Corrosion SitesCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Kathrin Eckhard Dr. Abstract For a better understanding of the initiation of localised corrosion, there is a need for analytical tools that are capable of imaging corrosion pits and precursor sites with high spatial resolution and sensitivity. The lateral electrochemical contrast in alternating-current scanning electrochemical microscopy (AC-SECM) has been found to be highly dependent on the frequency of the applied alternating voltage. In order to be able to obtain data with optimum contrast and high resolution, the AC frequency is swept in a full spectrum at each point in space instead of performing spatially resolved measurements at one fixed perturbation frequency. In doing so, four-dimensional data sets are acquired (4D AC-SECM). Here, we describe the instrument set-up and modus operandi, along with the first results from the imaging of corroding surfaces. Corrosion precursor sites and local defects in protective organic coatings, as well as an actively corroding pit on 304 stainless steel, have been successfully visualised. Since the lateral electrochemical contrast in these images varies with the perturbation frequency, the proposed approach constitutes an indispensable tool for obtaining optimum electrochemical contrast. Um die Entstehung lokaler Korrosionsphänomene untersuchen zu können, bedarf es ortsauflösender Methoden, die beispielsweise Lochfraß oder Korrosionsvorstufen mit hoher lateraler Auflösung visualisieren können. Bei der Abbildung lokaler elektrochemischer Aktivität mittels wechselstrombasierter elektrochemischer Rastermikroskopie (AC-SECM) ist der Kontrast in hohem Maße abhängig von der gewählten Anregungsfrequenz. Um den Informationsgehalt der erhaltenen Bilder zu erhöhen und optimalen elektrochemischen Kontrast zu erzielen, wird vorgeschlagen, an jedem Punkt des Rastergitters, ein komplettes Frequenzspektrum aufzunehmen, anstatt die Oberfläche mit einer einzigen, willkürlich gewählten Anregungsfrequenz abzurastern. Dadurch werden vierdimensionale Datensätze erhalten (4D AC-SECM). Wir berichten hier über den Aufbau des neu entwickelte Instrumentes, seine Funktionsweise und über erste Ergebnisse zur Abbildung korrodierender Oberflächen. Korrosionsvorstufen und Defekte in organischen Schutzschichten konnten ebenso erfolgreich visualisiert werden wie ein Korrosionsherd auf einer 304 Edelstahl-Oberfläche. Die hier vorgestellte Herangehensweise garantiert die Erfassung des optimalen elektrochemischen Kontrastes und damit eine hohe Auflösung bei der Visualisierung korrodierender Oberflächen. [source] Potential mapping technique for the detection of corrosion in reinforced concrete structures: Investigation of parameters influencing the measurement and determination of the reliability of the methodMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2009Y. Schiegg Abstract The potential distribution around a corrosion site in concrete was modeled by means of a simple mathematical model for a rod-shaped anode. Based on these calculations the influencing parameters and the limits of the potential mapping technique were determined. They demonstrate that the location of anodes depends on the anode length, the concrete coverage, and the measuring grid. Moreover small anodes with less than 1 cm length are virtually impossible to localize. Investigations on concrete elements without reinforcing steel showed that heterogeneous water content and chloride distribution can result in potential differences of up to 150 mV on the concrete surface. This effect was related to the streaming potential and the diffusion overpotential in the concrete. In order to determine the reliability of the potential mapping technique in the field application, the concrete on a tunnel wall was removed after the measurement of the potential distribution and the corrosion loss of the steel was determined. It was found that all corrosion sites with more than 2 mm material loss were detected by the potential mapping technique. Only some smaller corrosion sites were not found. Based on this investigation, the applicability of the potential mapping technique for detecting corrosion sites was confirmed. The observed high reliability of the potential mapping technique can be explained by a combination of the heterogeneous wetting of the concrete, the inhomogeneous contamination with chloride, and the macrocell formation. [source] Spatial Imaging of Cu2+ -Ion Release by Combining Alternating Current and Underpotential Stripping Mode Scanning Electrochemical MicroscopyELECTROANALYSIS, Issue 2-3 2007Dirk Ruhlig Abstract Anodic underpotential stripping voltammetry was integrated into SECM in order to characterize local corrosion of metallic copper deposits on metal surfaces as a model for copper containing alloys. Primarily, the alternating current mode of SECM was applied in an electrolyte of low ionic strength for localizing possible corrosion sites without any perturbation of the corroding surface, e.g., by the presence of any redox mediator. Sequentially, the release of Cu2+ -ions was confirmed and locally visualized at the previously detected electrochemically active sites by means of spatially resolved anodic underpotential stripping voltammetry performed during SECM scanning. Underpotential stripping voltammetry of Cu2+ -ions was performed at a specifically developed 15,,m gold-coated Pt microelectrode used as SECM tip with a detection limit of 0.15,nM Cu2+ (N=4, RSD=6%) for an accumulation of 45,s at ,0.4,V. SECM images of model samples such as copper coated microelectrodes and lacquered metallic copper workpieces demonstrated the feasibility and applicability of combining AC- and underpotential stripping mode of SECM for local visualization of Cu2+ -ion release from corroding surfaces. [source] In situ detection of bacteria involved in cathodic depolarization and stainless steel surface corrosion using microautoradiographyJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008B.V. Kjellerup Abstract Aims:, To examine the activity of bacteria involved in cathodic depolarization and surface corrosion on stainless steel in an in situ model system. Methods and Results:, The microautoradiographic technique (MAR) was used to evaluate the activity of bacterial populations on stainless steel surfaces with a single cell resolution. Anaerobic uptake and fixation of 14C-labelled bicarbonate occurred within corrosion sites in the absence of atmospheric hydrogen or other external electron donors, whereas it was taken up and fixed by bacteria at all other stainless steel surfaces in the presence of atmospheric hydrogen. This indicates that the bacteria utilized electrons originating from the corrosion sites due to the ongoing corrosion (cathodic depolarization). Conclusion:, Under in situ conditions, bacteria were fixating 14C-labelled bicarbonate at corrosion sites in the absence of atmospheric hydrogen. This indicates that electrons transferred to the bacteria provided energy for bicarbonate fixation due to cathodic depolarization. Significance and Impact of the Study:, Application of the MAR method showed ongoing biocorrosion in the applied in situ model system and allowed in situ examination of bacterial activity on a single cell level directly on a metal surface providing information about potential corrosion mechanisms. Furthermore, application of fluorescence in situ hybridization in combination with MAR allows for identification of the active bacteria. [source] Potential mapping technique for the detection of corrosion in reinforced concrete structures: Investigation of parameters influencing the measurement and determination of the reliability of the methodMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2009Y. Schiegg Abstract The potential distribution around a corrosion site in concrete was modeled by means of a simple mathematical model for a rod-shaped anode. Based on these calculations the influencing parameters and the limits of the potential mapping technique were determined. They demonstrate that the location of anodes depends on the anode length, the concrete coverage, and the measuring grid. Moreover small anodes with less than 1 cm length are virtually impossible to localize. Investigations on concrete elements without reinforcing steel showed that heterogeneous water content and chloride distribution can result in potential differences of up to 150 mV on the concrete surface. This effect was related to the streaming potential and the diffusion overpotential in the concrete. In order to determine the reliability of the potential mapping technique in the field application, the concrete on a tunnel wall was removed after the measurement of the potential distribution and the corrosion loss of the steel was determined. It was found that all corrosion sites with more than 2 mm material loss were detected by the potential mapping technique. Only some smaller corrosion sites were not found. Based on this investigation, the applicability of the potential mapping technique for detecting corrosion sites was confirmed. The observed high reliability of the potential mapping technique can be explained by a combination of the heterogeneous wetting of the concrete, the inhomogeneous contamination with chloride, and the macrocell formation. [source] Theoretical description of the practical possibility of stress corrosion cracking from crevice corrosion sitesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2005S. Wang Abstract Stress corrosion cracking (SCC) from crevice corrosion sites had been found in an experimental work at polarization potential of + 200 mVSCE. In that work, an occluded U-bend specimen of Type 316L (UNS S31603) stainless steel was used. The testing was done in sodium chloride (NaCl) solution. Based on that work, the practical possibility of SCC from the occluded U-bend specimen was described theoretically. It was shown that it would also be possible for SCC to occur in practice (i.e. at practical corrosion potential), but the crevice needs to be tighter. Meanwhile, it would take a longer time for obvious SCC to emerge. For a practical crevice usually formed by placing a crevice former on a large uniform metal surface, the crevice geometry may have little effect on SCC although the crevice can sustain an acidified solution more easily than pitting. The possibility of SCC should mainly depend on the corrosion system itself, i.e. material and environment. [source] | ||||||||||