Molten Salt Electrodeposition of Silicon in Cu-Si

Widespread use of solar energy has not been realized to date because its cost is not competitive with conventional energy sources. The high price of solar grade silicon has been one of the barriers against photovoltaic industry achieving its much anticipated growth. Therefore, developing a method, which is energy efficient and will deliver inexpensive silicon feedstock material is essential. The electrodeposition of Si from a cryolite-based melt was investigated in the present work as a possible solution. This study proposed electrowinning of Si in molten Cu-Si alloy, to decrease the working temperature and increase the efficiency. Solvent refining can be used to recover Si from Cu-Si and also as a second purification method. The physicochemical properties of the potential electrolyte, cryolite-SiO2 melts, were studied in the first step of this work. The deposition potential of Si on a graphite cathode was measured to determine the working potential and the effect of SiO2 concentration on it. In the next step, the deposition potential of Si from cryolite-SiO2 melt on Cu and Cu-Si cathodes was determined using cyclic voltammetry. Next, the cathodic and the anodic current inefficiencies of the process were measured. Continuous analysis of the evolved gas enabled the instantaneous measurement of the current efficiency and the kinetics of the deposition. Finally, the effectiveness of the process in delivering high purity Si was investigated. Si dendrites were precipitated out of the Cu-Si cathode and recovered to determine the purity of the final product as the final step of this study. The produced Si was separated from the alloy matrix by crushing and acid leaching and the purity was reported. The findings of this research show that the proposed method has the potential to produce high purity silicon with low B content. Further development is required to remove some metallic impurities that are remained in Si.Ph.D

Charge transport properties of cryolite–silica melts

Electrodeposition of silicon from a cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from cryolite–SiO2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO2 contents. It was found that addition of silica to cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al

One-Pot-Multicomponent Synthesis of 2,6-Diamino-4-arylpyridine-3,5-dicarbonitrile Derivatives Using Nanomagnetic Fe₃O₄@SiO₂@ZnCl₂

Nanomagnetic Fe3O4@SiO2@ZnCl2 was used as a simple, cost-effective, and reusable heterogeneous catalyst for the synthesis of 2,6-diamino-4-arylpyridine-3,5-dicarbonitriles by a one-pot-three-component condensation reaction of malononitrile, ammonium acetate, and aldehydes under solvent-free conditions at 110 °C. Simple and mild reaction conditions, facile preparation of the catalyst, the use of a cheap catalyst and easy workup and isolation are notable features of this method

Electrochemistry of Molten Sulfides: Copper Extraction from BaS-Cu[subscript 2]S

The electrolytic extraction of liquid copper at 1105°C from a molten sulfide electrolyte composed of 57 wt% BaS and 43 wt% Cu[subscript 2]S was investigated. DC cyclic voltammetry, Fourier transformed AC voltammetry, and galvanostatic electrolysis revealed that the electrodeposition of copper is possible in the selected molten sulfide electrolyte. The half wave potential for the reaction on graphite was determined, and liquid copper of high purity was obtained by galvanostatic electrolysis. These preliminary results confirm that molten sulfides free of alkaline elements could be used as an electrolyte for faradaic applications, despite the semi-conducting nature of the melt. In addition to demonstrating the need for enhanced understanding of the transport properties of such electrolyte, the results show the critical impact of the cell design to improve the process faradaic efficiency.Norco ConservationUnited States. Office of Naval Research (Contract N00014-12-1-0521

High-Temperature Refining of Metallurgical-Grade Silicon: A Review

Among currently known alternatives for renewable energy sources, solar power is generally regarded as having the most potential to satisfy the ever-growing demand. While solar photovoltaic power is a well-established technology, its widespread uptake has been hindered by prohibitively high price of units and, thusly, the price of electricity. This is due mainly to the high cost of the silicon used to fabricate the devices. This article presents a review of the development of established pyrometallurgical techniques as applied to refining metallurgical silicon to solar grade for the purposes of reducing the reliance on expensive traditional silicon feedstock. Four basic high temperature methods: solvent refining, slag treatment, vaporization, and electrorefining are described and the limitation and advantages of each method are presented. It is apparent that these techniques are very useful for removing impurities from silicon, but are often selective and not able to remove all problematic elements. Therefore, refining may need to be as a sequence of steps, targeting specific elements each time, or as novel methods combining multiple techniques simultaneously. Ultimately, the successful approach will have to achieve large-scale production by cost-effective means to replace current methods