Basic study on the behavior of impurities in silicon produced with carbothermic reduction of silica

在本报告中，作者研究了杂质元素在二氧化硅和其他含二氧化硅的氧化物如火山灰的碳氢还原中的行为。本工作旨在为硅的规模化生产和灰渣中材料的回收利用进行基础研究。研究结果表明，在碳热还原B_2O_3-SiO_2熔体的情况下，B与SiO同时从熔体中蒸发，而在K_2O-SiO_2熔体还原的情况下，K蒸发比SiO更有利。对SiO凝结物的微观观察表明，SiO凝结物主要由颗粒物和纤维状物质组成，说明SiO在气相中发生凝聚形成颗粒，同时，气态SiO也沉积在附着在炉壁上的颗粒SiO上，促进了外延生长。在碳热R-…中在1800℃时，由于P从熔体和SiO中完全蒸发，在低温区回收的SiO由于P的完全蒸发而产生更多的含P的模型灰。而在模型灰中含有B的情况下，SiO中的B含量比原始模型灰中的B含量低约50%。进一步观察气相凝聚的SiO的形貌发现，凝聚的SiO中存在三种形态，即纳米尺寸的纤维、纳米颗粒和纳米颗粒的链状聚集物。纳米粒子的平均组成为SiO_x，x=1.2~1.5。纳米纤维和纳米链的平均组成为SiO_x，x=1.7~1.9。收集纳米SiO，用HF溶液处理，使材料中的SiO_2溶解。用X射线衍射仪对处理后的残留物进行了分析。X-射线衍射仪分析表明，残渣由金属硅和少量SiO组成。这一结果表明，本研究得到的SiO通过歧化反应分离为SiO_2和Si，因此我们可以简单地用HF溶液处理SiO来获得金属硅。较少

In the present report, the author investigates the behavior of impurity elements in the carbotrhermic reduction of silica and other oxide containing silica like coal ash. The present work is aimed at the basic study for the mass production of silicon and the materials recycling in coal ashes. The followings are the results of the present study In the case of carbothermic reduction of molten B_2O_3-SiO_2, B evaporates from the melt simultaneously with SiO, while, in the case of the reduction of molten K_2O-SiO_2, K evaporation is more favorably than SiO.Carbothermic reduction of model coal ash is also investigated. Microscopic observation of the condensate of SiO shows that the condensate consists basically of particulate and fibrous materials, which indicates that the condensation of SiO takes place in the gas phase to form particles and, simultaneously, gaseous SiO also deposits on the particulate SiO attached to the crucible wall to enhance the epitaxial growth. In the carbothermic r … More eduction of model coal ash containing P as an impurity at 1800 °C, SiO recovered at low temperature zone is free from the contamination of P because of complete evaporation of P from the melt and SiO. On the other hand, in the case of B in the model coal ash, the content of B in SiO is about 50% lower than that of the initial model ash.More close observation of the morphology of SiO condensed from gas phase reveals that there are three forms in the condensed SiO, i.e. fiber of nano-meter size, nano-particle, and, chain-like agglegate of nano-particles. The nano-particles have an average composition of SiO_x with x = 1.2 to 1.5. The nano-fibers and nano-chains have average composition of SiO_x with x = 1.7 to 1.9. The nano-particulate SiO is collected and treated with HF solution to dissolve SiO_2 in the material. The residue after the treatment is investigated with XRD. The results of XRD shows that the residue consists of metal Si with small amount of SiO. This result indicates that the SiO obtained in the present study separates into SiO_2 and Si according to disproportionation reaction, and thus we can obtain metal Si simply by the treatment of SiO with HF solution. Less