Electrochemical Behavior of Silicon in the (NaCl-KCl-NaF-SiO 2 ) Molten Salt
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INTRODUCTION
MOLTEN salts are known as suitable media for metal electrowinning and electrorefining, the metallurgical properties of the deposit strongly being dependent on the operating conditions.[1] If electrolysis is performed using complex systems, such as those that include alkali metal halides and oxygen-containing refractory metal ions, the deposition of refractory metal is possible.[2–5] Silicon is a widely applied semiconducting material, which finds application as a promising material for a functionally gradient material (FGM) and low-cost solar cell to establish the solar–hydrogen energy system. For the demand of production, it is important to produce Si thin film with uniform, large area and appropriate characteristics for FGM and solar cells. Electrodeposition is one of the most widely accepted techniques for the economical and efficient growth of thin films from liquid phase, and many reports are available on the deposition of various thin films by this method.[6–8] However, the electrodeposition of silicon has not been well understood because of considerably negative reduction potential and the high reactivity of most silicon compounds with water. Molten salt electrolyte medium is employed for the electrodeposition of Si. It has been known for many years that silicon films can be fabricated by electrodeposition.[9–16] All researchers have conducted the deposition of silicon by electroplating in a mixed solvent that consists of alkali ZONGYING CAI, Instructor, is with the School of Metallurgical & Energy Engineering, Hebei Polytechnic University, Tangshan, Hebei, 063009, P.R. China, and with the Institute of Advanced Materials, Mechanical Engineering College, Shijiazhuang, Hebei, 050003, P. R. China. Contact e-mail: [email protected] YUNGANG LI, Professor, and XIAOFENG HE and JINGLONG LIANG, Research Scholars, are with the School of Metallurgical & Energy Engineering, Hebei Polytechnic University. Manuscript submitted November 18, 2009. Article published online July 7, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
fluorides and silicon fluoride. However, the electrolysis of a simple molten system containing an oxide and an alkali metal halides mixture and the theoretical research on electrochemical process are not been studied, which can give a better understanding the influence of process parameters on chemical composition and the morphology of the final product. The character of thin film mainly depends on the nucleation kinetics and the growth mechanism of the first metallic nuclei formed on the substrate. The aim of this study is to obtain the silicon thin film and relate it to the electrochemical behavior of super saturated SiO2 in the NaCl-KCl-NaF melt. Tetrachlorosilane can be produced easily in this molten salt system by adding SiO2 that was dissolved in the halides. The electrochemical reduction and nucleation mechanisms of Si (IV) in the molten salt with SiO2 as the electroactive constituent were explored using cyclic voltammetry and chronoamperometry techniques.
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EXPERIMENTAL
All electrochemical
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