Working electrode corrosion potential

In a different application, Williams and coworkers were interested in using the SECM to identify a precursor state to the pitting corrosion of stainless steel (12) and also to elucidate the mechanism by which a pit could be maintained and propagate further (13), once it had been initiated. For these studies, a commercial AFM (Quesant Resolver ) was adapted for use as an SECM. The tip electrode was a Pt-Ir wire electrolytically sharpened and insulated, as for electrochemical STM. A two-electrode mode was used with a Pt counterelectrode of much larger area than the stainless steel working electrode. The potential of the counterelectrode was standardized against an SCE. The probe UME was maintained at the same potential as the Pt counterelectrode. Typical tip-substrate separations of 0.1-0.5 /xm were employed for imaging purposes, with the distance carefully established by ap-... 

Instruments very suitable for corrosion work are readily available, with several different models produced commercially. Although most, if not all, of the available potentiostats are properly designed, it should be kept in mind that corrosion studies require the instrument to have a low internal resistance and to react quickly to changes of potential of the working electrode. 

Tower, Stephen. All About Electrochemistry. Available online. URL http //www.cheml.com/acad/webtext/elchem/. Accessed May 28, 2009. Part of a virtual chemistry textbook, this excellent resource explains the basics of electrochemistry, which is important in understanding how fuel cells work. Discussions include galvanic cells and electrodes, cell potentials and thermodynamics, the Nernst equation and its applications, batteries and fuel cells, electrochemical corrosion, and electrolytic cells and electrolysis. 

Polarization experiments on a corrosion system are carried out by using a potentiostat. The experimental arrangement of the cell consists of a working electrode, reference electrode and a counter-electrode. The counter-electrode is used to apply a potential on the working electrode both in the anodic and the cathodic direction, and measure the resulting currents. The electrochemical cell is depicted in Figure 1.26. 

Open-circuit potential (OCP) — This is the - potential of the - working electrode relative to the - reference electrode when no potential or - current is being applied to the - cell [i]. In case of a reversible electrode system (- reversibility) the OCP is also referred to as the - equilibrium potential. Otherwise it is called the - rest potential, or the - corrosion potential, depending on the studied system. The OCP is measured using high-input - impedance voltmeters, or potentiometers, as in - potentiometry. OCP s of - electrodes of the first, the second, and the third kind, of - redox electrodes and of - ion-selective membrane electrodes are defined by the - Nernst equation. The - corrosion po-... 

Direct current methods are commonly employed in corrosion testing and may be either potentiostatic, where the electrode potential is controlled, and current monitored or galvanostatic (intentiostatic), where the cell current is controlled and the working electrode potential monitored. The potential or current may also be varied with time, producing potentiodynamic or... 

To investigate the steady-state corrosion layers, quenching experiments were performed. Shortly after immersion, the working electrode potential was fixed at a chosen value for 4 hours. After this period the specimens were taken out of the melt while still being under potential control and cooled down to room temperature in air as fast as possible. The carbonate adhering to the specimen prevented contact and interaction... 

Counter electrodes should be made from a corrosion resistant metal, for example a noble metal, and their design should allow for uniform current (potential) distribution and free convection of aggressive agents to the working electrode. 

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