Solar grade silicon is currently produced mainly through blending semiconductor grade silicon waste with metallurgical grade silicon. As the demand for solar cells continues to increase rapidly, soon demand will outstrip supply of semiconductor grade silicon waste. A process for producing solar grade silicon efficiently and without relying on other industries is needed. It is proposed to produce solar grade silicon of 6N purity (99.9999%) by reacting silicon tetrachloride with aluminum monochloride via the following reaction: 2 AlCl(g) + SiCl4(g)= Si(s) + 2 AlCl3(g) Aluminum monochloride is proposed as the reductant for silicon tetrachloride because it is an extremely strong reducing agent and the reaction will produce all gaseous by-products. Additionally, the aluminum trichloride produced can be recycled to form more aluminum monochloride, which is produced by reacting aluminum metal with aluminum trichloride in the following reaction: AlCl3(g) + 2 Al(l)= 3 AlCl(g) High yields of AlCl have only been found above 1200°C, with very little AlCl present in equilibrium with Al and AlCl3 at lower temperatures. The high temperatures under which AlCl can be found in larger quantities makes it difficult to determine if the AlCl3 reacting with Al is actually producing AlCl as opposed to another subhalide such as AlCl2. Numerous IR spectroscopy studies have been undertaken to confirm that the reaction of aluminum trichloride gas with molten aluminum does produce aluminum monochloride, with all such studies confirming that this theoretical path is correct. Unlike previous studies, which pass the AlCl3 gas over molten aluminum, it is proposed to bubble the AlCl3 gas into the molten aluminum. This should increase yield of aluminum monochloride, which was not a priority in previous studies. In order to achieve the project objectives a literature review of silicon manufacturing techniques as well as aluminum monochloride production was completed. Experiments to determine the rate of sublimation of aluminum trichloride were to be done in order to determine what temperature at which to sublime the aluminum trichloride. Aluminum trichloride was bubbled into aluminum metal to form aluminum monochloride with experimental conditions being varied to increase yield. Yield was determined through analysis of the reaction products, which was difficult due to the instability of aluminum monochloride, which dissociates at room temperature back into aluminum trichloride and aluminum metal. After the yield of aluminum monochloride was maximized, silicon tetrachloride was introduced into the reactor to react with the aluminum monochloride to form silicon metal. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-09-18 18:16:36.31

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.

Current methods of solar-grade silicon (SG-Si) production are energy intensive and costly. The possibility of using metallurgical techniques for refining metallurgical-grade Si (MG-Si) to SG-Si has been investigated. The main steps in the metallurgical refining route include alloying with copper to produce a 50-50wt% Cu-Si alloy, controlled solidification, crushing, and acid leaching. The controlled solidification process involved 5 variations to determine the best process to maximize Si dendrite agglomeration in the sample and produce the purest Si. This was determined by using various techniques, such as: optical imaging, dendrite analysis, EPMA and SEM analysis and ICP analysis. The crushing and acid leaching steps were carried out to remove the unwanted Cu3Si eutectic from the pure Si dendrite phase. Upon completion of the analysis techniques, the optimal cooling method was determined to be the top cooled, 0.5°C/min sample.

Current methods of solar-grade silicon (SG-Si) production are energy intensive and costly. The possibility of using metallurgical techniques for refining metallurgical-grade Si (MG-Si) to SG-Si has been investigated. The main steps in the metallurgical refining route include alloying with copper to produce a 50-50wt% Cu-Si alloy, controlled solidification, crushing, and acid leaching. The controlled solidification process involved 5 variations to determine the best process to maximize Si dendrite agglomeration in the sample and produce the purest Si. This was determined by using various techniques, such as: optical imaging, dendrite analysis, EPMA and SEM analysis and ICP analysis. The crushing and acid leaching steps were carried out to remove the unwanted Cu3Si eutectic from the pure Si dendrite phase. Upon completion of the analysis techniques, the optimal cooling method was determined to be the top cooled, 0.5°C/min sample.

The cost reductions and the environmental benefits aligned with global concerns about climate change have made solar photovoltaic technology the most installed source of energy in the power sector worldwide. Brazil has the largest know reserves of silicon in the world. Therefore, there is a huge potential for developing a national technology for purifying and manufacturing silicon wafers within an increasingly competitive and efficient photovoltaic industry. The IPEN initiative of investigating the production of metallic silicon and metallurgical route purification required a characterization of samples in different stages of production from quartz to wafer and understanding the characterization methods for silicon wafers taking into account the main defect mechanisms such as light-induced degradation. Metalic silicon is produced in IPEN via magnesiothermal reduction through acid leaching to form a metallurgical grade silicon with relatively low impurities. One more acid leaching step resulted in a specific ultra-metallurgical grade silicon. The same acid leaching was processed in a commercially available Brazilian-made metallurgical grade silicon produced via carbothermal reduction. All samples impurities was measured by ICP-OES. The result is a material with ultra-metallurgical grade silicon content with excess of B and P. While wafer characterization was studied, an extensive investigation was taken on LeTID, which causes remain unknown, at Institute for Energy Technology, Norway. Neighboring high performance mc-Si p-type wafers were tested in different firing process conditions. The effects was investigated in terms of defects activation and a corresponding lifetime degradation and recovery at illuminated annealing. A sample with almost fully suppressed LeTID is shown. A new method have been proposed to separate Boron Oxygen-Light Induced Degradation effects of LeTID, enabling to measure even where it was thought to be fully suppressed. New models for LeTID defect formation and suppression are proposed. Both silicon purification and light-induced degradation characterization in mc-Si studies shows a wide range of research on new production routes that may require tailored processes of crystallization and solar cell manufacturing such as gettering and firing. / As reduções de custos e benefícios ambientais alinhadas às preocupações globais com as mudanças climáticas tornaram a tecnologia solar fotovoltaica a fonte de energia mais instalada no setor de energia do mundo. O Brasil possui as maiores reservas conhecidas de silício. Portanto, existe um enorme potencial para o desenvolvimento de uma tecnologia nacional para purificação e fabricação de wafers de silício dentre a indústria fotovoltaica cada vez mais competitiva e eficiente. A iniciativa do IPEN de investigar a produção de silício metálico e a purificação de rotas metalúrgicas exigiu a caracterização de amostras em diferentes estágios de produção, do quartzo ao wafer e a compreensão dos métodos de caracterização dos wafers de silício, levando em consideração os principais mecanismos de defeitos, como a degradação induzida pela luz. O silício metálico é produzido no IPEN através da redução magnesiotérmica através da lixiviação ácida para formar um silício de grau metalúrgico com impurezas relativamente baixas. Mais uma etapa de lixiviação ácida resultou em um silício de grau ultra-metalúrgico específico. A mesma lixiviação foi feita em um silício de grau metalúrgico fabricado no Brasil, disponível comercialmente, produzido por redução carbotérmica. Todas as amostras foram medidas por ICP-OES. O resultado é um material com teores de silício de grau ultra-metalúrgico e excesso de B e P. Enquanto a caracterização do wafer foi estudada, uma extensa investigação foi realizada sobre o LeTID, que tem causas desconhecidas, no Institute for Energy Technology, Noruega. Os wafers vizinhos de mc-Si do tipo-p de alto desempenho foram testados em diferentes condições do processo de firing. Os efeitos foram investigados em termos de ativação de defeitos e uma correspondente degradação e recuperação no lifetime sob recozimento iluminado. Uma amostra com LeTID quase totalmente suprimido é mostrada. Um novo método foi proposto para separar os efeitos de Degradação Induzida por Luz relacionados ao Oxigênio e Boro do LeTID, permitindo até medir onde se pensava que estivesse totalmente suprimido. Novos modelos para formação e supressão de defeitos LeTID são propostos. Tanto a purificação de silício quanto a caracterização de degradação induzida pela luz nos estudos de mc-Si mostram uma ampla gama de pesquisas sobre novas rotas de produção que podem exigir processos personalizados de cristalização e fabricação de células solares, como gettering e firing.

Purification of metallurgical grade silicon (MG- Si) by a combination of solvent refining and physical separation has been studied. MG-Si was alloyed with iron and solidified under different cooling rates to grow pure Si dendrites from the alloy. The Si dendrites and FeSi2 that were formed after solidification were then separated by a gravity-based method. The separation method relies on significantly different densities of Si and FeSi2, and uses a heavy liquid with specific gravity between the two phases to float the former on the surface of a heavy liquid, while the latter sinks to the bottom. The effect of particle size and cooling rate on the Si yield and separation efficiency of the Si phase was investigated. The floated Si particles were further purified by removing the physically adherent Fe-Si phase, using an acid leaching method. Analysis of the produced silicon indicates that several impurity elements including P and B can be efficiently removed using this simple and low-cost technique.

Purification of metallurgical grade silicon (MG- Si) by a combination of solvent refining and physical separation has been studied. MG-Si was alloyed with iron and solidified under different cooling rates to grow pure Si dendrites from the alloy. The Si dendrites and FeSi2 that were formed after solidification were then separated by a gravity-based method. The separation method relies on significantly different densities of Si and FeSi2, and uses a heavy liquid with specific gravity between the two phases to float the former on the surface of a heavy liquid, while the latter sinks to the bottom. The effect of particle size and cooling rate on the Si yield and separation efficiency of the Si phase was investigated. The floated Si particles were further purified by removing the physically adherent Fe-Si phase, using an acid leaching method. Analysis of the produced silicon indicates that several impurity elements including P and B can be efficiently removed using this simple and low-cost technique.

Impurity optimized silicon is needed for the advancement of terrestrial photovoltaic power generation. In this study the possibility of producing solar grade silicon from rice husks has been pursued. An integrated process flowsheet was developed and practiced that included initial leaching, reduction of Rice husk ash (RHA) and post-reduction purification of silicon. Metallothermic reduction of purified RHA with magnesium was investigated within the temperature range of 500-950 oC. The reduction product was purified by two stage acid leaching sequence. Analysis of the final silicon powder product by XRD and ICP-OES showed crystalline silicon with boron content to be less than 3ppm- corresponding to reduction by a factor greater than 10, whilst the phosphorus content was reduced by a factor of over 20 and reaching less than 73ppm. The effects of temperature, magnesium amount and leaching agents were optimized in this study. A one step test melting was also carried out to convert the silicon powder into silicon chunks.

Impurity optimized silicon is needed for the advancement of terrestrial photovoltaic power generation. In this study the possibility of producing solar grade silicon from rice husks has been pursued. An integrated process flowsheet was developed and practiced that included initial leaching, reduction of Rice husk ash (RHA) and post-reduction purification of silicon. Metallothermic reduction of purified RHA with magnesium was investigated within the temperature range of 500-950 oC. The reduction product was purified by two stage acid leaching sequence. Analysis of the final silicon powder product by XRD and ICP-OES showed crystalline silicon with boron content to be less than 3ppm- corresponding to reduction by a factor greater than 10, whilst the phosphorus content was reduced by a factor of over 20 and reaching less than 73ppm. The effects of temperature, magnesium amount and leaching agents were optimized in this study. A one step test melting was also carried out to convert the silicon powder into silicon chunks.