| However, with the increasingly depletion of some kinds of traditional resources, such as petroleum, gasoline and coal, our living environment has become worse and worse, which badly restricts the development of society and economy. Consequently, various countries have been devoted to developing and utilizing new resources. As a new-type reproducible resource, solar energy has these excellent qualities, such as no pollution, clean and safe, relatively persistent and inexhaustible, so it is hailed as one of the optimal reproducible resources. Si is the most important raw material for photovoltaic industry. Si becomes increasingly needed with the booming of photovoltaic industry. However, due to the reasons like long flow and complexity of traditional industrial crafts, the cost for preparation of Si has always been high, which restricts the development of photovoltaic industry and some other relatively industries. Therefore, it is imperative to research and develop new industrial crafts and new equipment for preparation of Si.This experiment applies solid SiO2 powder as raw material, which doesn't need some prophase dispositions such as sintering and palletizing. Calculated by thermodynamics, we can know that the decomposition voltage of SiO2 is-1.683 V. The outcome of this experiment indicates that under the condition that the cell voltage is more than 2.8V, SiO2 can be produced all the time. By comparing the amount of impurity content of raw material and product before reaction and after reaction: Before the reaction the contents of Fe, P and B were 1050ppm,13.62ppm and 6.62ppm, but after the reaction which change into 204ppm,5.54ppm and 12.52ppm. We can know that impurities are mainly from raw material. During the electrolytic process, no obvious impurities have been brought in. From the experiment of velocity cold of fused salt CaCl2-CaO-SiO2, we find that the SiO2 inside fused salt is:from top to bottom, it gradually decreases and produces intermediate product Ca2SiO4. Studying experiment mechanism by cyclic voltammogram, we can know the reaction mechanism is as follows:1. At high temperature, the intermediate products Ca2SiO4 can be formed by the reaction of CaO and SiO2 powders. And Ca2SiO4 can migrate to the graphite cathode due to the influence of the concentration gradient. 2CaO+SiO2â†'Ca2SiO42. The negative electrode potential is favorable to the decomposition of intermediate products Ca2SiO4. Ca2SiO4+4e-â†'CaO+Si+2O2Ca2SiO4 can be reduced to Si, CaO and oxygen ions in the surface of the graphite cathode. The obtained Si can deposite on the surface of graphite cathode and the oxygen ion can migrate to the anode by the electric field force.3. CaO obtained from the decomposition of the Ca2SiO4 will dissolve in the molten CaCl2 again, and continue to react on SiO2 powders to form the new intermediate products Ca2SiO4.4. Repeat steps 1-3 untill Si can be whole formed by the reduction of the SiO2 powders.This experiment adopts its designed reaction vessel and initially adopts blend fused salt (CaCl2-CaO) as electrolytic system, which solves the problems such as the difficulty of solid mass transfer and non-conducting of SiO2, etc. It improves the reaction condition and fully demonstrates this method's creativity and rationality. Compared to traditional industrial crafts, the new industrial crafts of preparation of high-purity through electrolytic SiO2 by using fused salt has many advantages such as short flow, low consumption, simple equipment and friendly environment. It has been more and more concerned and can relieve the pressure of the whole world's demand for Si. |
PDF Full Text Request