Reduction of silicon dioxide by electrochemical deoxidation

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2010

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Ergül, Emre

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Electrochemical reductions of porous SiO2 pellets and bulk SiO2 plate were investigated in molten CaCl2 and/or CaCl2-NaCl salt mixture. The study focused on effects of temperature, particle size of the starting material, electrolyte composition and cathode design on the reduction rate. The behavior of the cathode contacting materials was also examined. Moreover, cyclic voltammetry study was conducted to investigate the mechanism of the electrochemical reaction. Mainly, XRD analysis and SEM examinations were used for characterizations. The rates of electrochemical reduction were interpreted from the variations of current and accumulative electrical charge that passed through the cell as a function of time under different conditions. The results showed that reduction rate of SiO2 increased slightly with increasing temperature or decreasing the particle size of SiO2 powder. Higher reduction rate was obtained when porous pellet was replaced by bulk SiO2 plate. Use of Kanthal wire mesh around the SiO2 cathode increased but addition of NaCl to the electrolyte decreased the reduction rate. X-ray diffraction results confirmed the reduction of SiO2 to Si in both CaCl2 salt and CaCl2-NaCl salt mixture. However, silicon produced at the cathode was contaminated by the nickel and stainless steel plates which were used as the cathode contacting materials. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO2 in molten salts may become a method to produce solar grade silicon (SOG-Si). In addition, overall reduction potential of SiO2 pellet against the graphite anode and the potential of the cathode reaction at 750°C in molten CaCl2-NaCl salt mixture were determined as 2.3 V (at 1.19 A current) and 0.47 V, respectively by cyclic voltammetry.

Subject Keywords

Metallurgy.

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http://etd.lib.metu.edu.tr/upload/12612154/index.pdf
https://hdl.handle.net/11511/19737

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

E. Ergül, “Reduction of silicon dioxide by electrochemical deoxidation,” M.S. - Master of Science, Middle East Technical University, 2010.