New Technologies for Solar Grade Silicon Production
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New Technologies for Solar Grade Silicon Production
Sergey M. Karabanov Ryazan Metal Ceramics Instrumentation Plant Joint Stock Company, 51B Novaya St., Ryazan 390027, Russia
ABSTRACT
The paper presents the results of study of carbothermic reduction method for solar grade silicon (SG-Si) production. The interconnection between the purity of source materials and derivable silicon has been established. The technological concept of SG-Si production, including source materials preparation, carbothermic process, silicon filtration and crystallization is suggested. The comparative analysis data of different methods of SG-Si is given.
INTRODUCTION
In the world the works on creation of new technologies for solar grade silicon production are widely carried out [1-4]. The following technological trends are being developed: - improved Siemens-process [1]; - chlorine free alkoxy silane technology [2]; - direct carbothermic reduction of silicon from quartzites [3]; - SG-Si production from silicon fluorides [4]. There are certain achievements in some approaches to the problem. The aim of the work is to study the method of carbothermic reduction of silicon for SG-Si production. The method is based on the reaction: T SiO2 + 2C → Si + 2CO In metallurgical silicon production technology charcoal, wood, etc. using as carbon, have large impurity content. This method seems to be rather perspective when clean source components, SiO2 and С, are used. In this work the influence of source materials purity on the composition of the silicon produced is studied, the approaches to the development of technological concept of SG-Si production are considered, comparative analysis of different SG-Si production methods is carried out, the basic trends of further research are determined. o
EXPERIMENTAL DETAILS
The experimental studies of carbothermic process were conducted using an electric arc furnace with the power of 200 kW and payload volume of 0,2 m3. Graphite with the purity of B11.8.1 Downloaded from https:/www.cambridge.org/core. University of Arizona, on 19 Mar 2017 at 05:20:22, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-716-B11.8
99,99% was used as the electrode material. Quartz sand with the purity of 99,8%, quartz with the purity of 99,99% were used in this work. Table I shows the purity data of silicon produced from different materials. The impurities content was analyzed by the method of optical spectroscopy. It was established that the silicon purity corresponds to the purity of materials being used. The studies of the phase composition of the manufactured silicon have revealed the presence of the following phases: Si; SiOx, SiC. The concentration of phases is at the level of 0,1-0,2%. Table I. The results of the experimental studies. Element ppm
Al 1
Fe 10
Cu 0.7
Ti 0.09
Mg 0.04
Mn 0.2
B 0.6
P 1960 C SiC + SiO T → Si + CO , SiC + SiO2 → Si + CO2 . SiO is formed at the deficiency of the restorer at T>1700°C according to the reaction
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