Rotating ring-disc electrode corrosion

The rotating ring disc electrode is also a powerful tool for the study of corrosion. The disc is made from the material of interest, while the ring electrode is an inert material. The principal application of the ring disc electrode is to allow, with absolute certainty, distinction between corrosion products which are solids (and remain at the disc surface) and those which are soluble in the solution (and may therefore be detected at the ring electrode). Moreover, the Ir-E characteristic allows the solution free products to be identified. Commonly the disc is left at open circuit so that corrosion is not electrochemically accelerated. 

F. Huet, M. Keddam, X. R. Novoa, and H. Takenouti, Frequency and time resolved measurements at rotating ring-disc electrodes for studying localized corrosion,... 

In a typical experiment with semiconductor-liquid junctions, one of the most important experimental problems is the differentiation between reactions that involve chemical changes at the semiconductor electrode (corrosion with insoluble products) and chemical changes in the electrolyte that might be subject to mass transfer limitations. The technique of Rotating Ring Disc Electrode (RRDE) (17-19) provides an opportunity to differentiate between these two types of reactions under controlled hydrodynamic conditions. In its simplestform, the metallic ring is isolated... 

Another example for the HMRRD electrode is given in Fig. 9 for Fe in alkaline solutions [12, 27]. The square wave modulation of the rotation frequency co causes the simultaneous oscillation of the analytical ring currents. They are caused by species of the bulk solution. Additional spikes refer to corrosion products dissolved at the Fe disc. This is a consequence of the change of the Nemst diffusion layer due to the changes of co. This pumping effect leads to transient analytical ring currents. Besides qualitative information, also quantitative information on soluble corrosion products may be obtained. The size of the spikes is proportional to the dissolution rate at the disc, as has been shown by a close relation of experimental results and calculations [28-30]. As seen in Fig. 7, soluble Fe(II) species are formed in the po-... 

THE POTENTIOSTAT AND CORROSION STUDIES Rotating Disc-ring Electrodes... 

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