Scanning Electrochemical Microscopy Study of Corrosion Dynamics on Type 304 Stainless Steel

Abstract

Scanning electrochemical microscopy was utilized to study dynamics of corrosion on type 304 SS. The I Ϫ /I 3 Ϫ redox couple was used in the substrate generation/tip collection mode to determine active sites. Scanning the sample sequentially revealed that the electrochemical activity ͑where I 3Ϫ was detected͒ was localized and dynamic in nature. Subsequent microscopy indicated pitting occurred at many of the sites where electrochemical activity was detected. Currently, the technique is limited by the time required to raster a single probe through the scan area. In future studies, parallel ͑multielectrode͒ image acquisition is proposed to address this issue.The investigation of localized electrochemical reactions on metal surfaces is of great fundamental interest to corrosion science. Traditionally, corrosion is studied by accelerated tests using an external electric field and possibly followed by postmortem analysis of the surface to determine material loss and morphology. These techniques provide insight into corrosion rates and morphological changes at surfaces, but do not offer much detail about the localized dynamics of corrosion processes. This type of information is of interest to a fundamental understanding of corrosion processes. Recently, in situ probes ͓scanning tunneling microscopy, atomic force microscopy, and scanning electrochemical microscopy ͑STM, AFM, and SECM͔͒, have been developed for allowing real-time study of surface reactions at interfaces. 1-3 In terms of studying pitting corrosion, the SECM appears most suitable due to its ability to analyze larger areas of the sample than other in situ methods and can be tuned for chemical specificity. Large area measurements are important because the microstructure of most samples of interest are heterogeneous with multiple phases present. In addition, larger areas provide more statistically defensible results, a problem that high resolution techniques have when studying complex surfaces.In recent years, several SECM studies have probed local electrochemical activities of metal surfaces using redox molecules. [3][4][5][6][7][8][9] These papers show that only a small fraction of the surface was electrochemically active, localized to point sites on the surface. While the reason for this heterogeneous activity has not been determined, it was suggested that electrons tunnel through the oxide layer via areas that have either a thinner oxide layer or are more metallike ͑conductive͒. 4,7,9 Correlation of local electrochemical activity with areas of oxide breakdown has been made is some cases, thus suggesting that SECM could be used as a predictive tool to determine where corrosion might occur. In certain cases, a dynamic change in surface reactivity was observed with a variation in potential. The dynamics appear to be a delicate balance between oxide thickening and increased potential drop across the oxide which promotes electron transfer to redox species. 4 In this study, local electrochemical activity of type 304 SS was probed using the I Ϫ /I 3 Ϫ redox probe...

Elektrochemische Rastermikroskopie zur direkten Abbildung von Reaktionsgeschwindigkeiten

“…[201,202] für Korrosionsuntersuchungen ergänzen oder ersetzen. [203][204][205][206][207] Ti, [208][209][210][211][212] Ta, [213,214] Ni [215] und Al [216,217] À an der UME erfolgt dieser Nachweis mit lokaler Auflösung. [206,219] Lister und Pinhero erweiterten dieses Detektionsverfahren um eine Technik zur Messung lokaler elektrischer Feldstärken.…”

Investigation of Localized Catalytic and Electrocatalytic Processes and Corrosion Reactions with Scanning Electrochemical Microscopy (SECM)

“…A similar concept was followed by Lister and Pinhero [197,235]. In addition to the detection of sulfidic species above sulfide inclusions in stainless steel as mentioned above, a current inversion at the UME was observed at higher sample current densities close to the inclusions.…”

“…The temporal evolution was fol- [201,202] and Lister and Pinhero [197,235]. lowed over a time frame of several hours, but due to the large distance of 400 μm between the single array electrodes, the lateral resolution of the resulting images is considerably inferior to typical SECM images.…”

Corrosion Product Formation Monitored Using the Feedback Mode of Scanning Electrochemical Microscopy with Carbon Microelectrodes

“…XEDS maps of the AOI (see Figure S1), following a 2 h immersion, identify the two bottom features as being Al-Mn intermetallics and the two top particles containing a high concentration of O, which could be attributed to corrosion product. 35 To confirm that the variations in current in the SECM map ( Figure 5A) are related to an intrinsic change in surface reactivity, localized probe approach curves were performed over the different microstructure features, the α-phase ( [3]), β-phase ( [2]) and intermetallic ([1]), Figure 5B. Consistent with the results presented in Figure 3, an intermediate behavior is observed when performing a probe approach curve over each of these locations on the Mg alloy, Figure 5B.…”