Graduate Thesis Or Dissertation
 

Electrochemistry at a reticulated vitreous carbon flow electrode

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/j9602428n

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  • The electrochemistry of cadmium at a Reticulated Vitreous Carbon (RVC) electrode has been studied to determine the suitability of RVC as a working electrode for the electrochemical preconcentration of cadmium in the corrosive environment of zirconium dissolved in hydrofluoric acid. The electrochemistry in this investigation deals with deposition of solid reduction products on the working electrode. The theory of cyclic voltammetry (CV) when solid products are deposited differs from the theory when soluble products are produced because diffusion of the solid reduction product does not occur. Schiffrin (1986) has developed the theory of cyclic voltammetry for the case of solid product forma tion under the assumptions of instantaneous nucleation and no over-potential effects. Cadmium, however, has a significant nucleation over-potential at RVC. This nucleation over-potential causes 1) an apparent dependence between the CV scan speed and the observed reduction potential and 2) cyclic voltammograms which cross themselves after scan reversal. Flow cells of several different styles were built and evaluated before it became obvious that a theoretical evaluation of the sources of potential drop within the cell was essential to the design of a flow cell. The theoretical evaluation revealed that the most critical problem in flow cell operation was the iR drop in the electrolyte within the pores of the porous working electrode. Simple computer programs demonstrated that cells with cylindrical symmetry could reduce the electrolyte iR drop to a minimum. Flow cells with cylindrical symmetry were constructed, and they were found to be stable and capable of 100% conversion efficiency. The sensitivities of these flow cells compare favorably to literature reports of flow cells. These cells also perform according to the theoretical predictions of variation of current and conversion efficiency with flow rate. The suitability of RVC as a working electrode for electrochemical preconcentration of cadmium in zirconium solutions is not verified by this work because the poor reliability of the cells constructed in this study. This work suggests that automation of cell manufacture may improve consistency between cells so that the factors affecting reliability may be investigated. This work also suggest that automation of flow cell control would reduce the number of operator caused cell failures.
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