Scanning Reference Electrode Technique SRET

Noise analysis obtained from microelectrochemical investigations of stainless steels under potentiostatic conditions revealed that the current noise, expressed as standard deviation a of the passive current, increases linearly with the size of the exposed area, whereas the pitting potential decreases.47 However, to complete the electrochemical studies and distinguish between repassivating superficial pits and penetrating ones, microscopic studies are highly desirable. The scanning reference electrode technique (SRET) should be an appropriate complementary tool.28... 

The scanning reference electrode technique (SRET). The SRET has enabled the measurement of localized corrosion current densities in the vicinity of pits in stainless... 

Scanning electrochemical microscopy (SECM) - Direct mode - Feedback mode - Generation/collection mode Scanning reference electrode technique (SRET) Scanning vibrating electrode technique (SVET) Scanning photoelectrochemical microscopy (SPECM) Scanning electrochemical induced desorption (SECMID)... 

Scanning reference electrodes make it possible to measure the potential as a function of the location. The utilization of glass capillaries in combination with reference electrodes, such as the calomel electrode, make it possible to measure corrosion potentials, while pseudo-reference electrodes such as platinum wires are used to measure the potential difference between two points in solution. Included in this latter category are closely spaced reference electrodes which give a direct measure of the current density from the potential gradient and distance between them, as shown in Fig. 7-25 a. Such electrodes are used for the scanning reference electrode technique (SRET). 

Microcapillaiy electrochemical cells are widely used in biology for local potential measurements at a very reduced size. In corrosion, pioneering work was performed for promoting the Scanning Reference Electrode Technique (SRET) in this case the microcapil-laiy is immersed in the bulk electrolyte and local potential or local electrochemical polarization or local electrochemical impedance has been measnred. 

These potential profiles may be measured with two REs, one with a fixed position and the other scanning parallel to the surface. With increasing distance to the surface, it may also scan the profile perpendicularly. A variation of this method uses two scanning REs with their FIL capillaries close to each other. One may also use two small isolated Ft tips, which allow a smaller set-up. This scanning reference electrode technique (SRET) samples... 

The earliest forms of SECM experiments were carried out in the potentiometric mode. Evans reported how he used a traveling reference electrode to map equipotential surfaces in solution and calculate corrosion rates on a water pipeline. Isaacs and coworkers revived the idea in 1972 and coined the acronym SRET for scanning reference electrode technique. Instruments used to be homemade, often with rudimentary traveling devices such as the arm of an X-Y recorder and the spatial resolution was at best submillimeter. A computer-controlled instrument was commercially produced by Uniscan Instruments with a spatial resolution around 20 pm. The SRET has now been superseded by the scanning vibrating electrode technique, known as SVET, which achieves higher spatial resolution and improved sensitivity. A SVET manufactured by Uniscan Instruments is now commercially available from Uniscan Instruments and Princeton Applied Research. 

SRET is a technique in which a reference electrode is scanned over a surfece. A second reference electrode is used to monitor the overall corrosion potential. In this way, small differences in the potential can be visualized. An alternative type of SRET has a tip with two platinum needles that are both placed close to the surface. If local potential differences exist over the surface, a corrosion current will run through the solution. In that case a small potential drop will occur in the solution between the two platinum wires. Assuming an ohmic behavior for the solution resistance, this potential difference is proportional to the potential differences on the surface. 

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