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碳热还原二氧化硅和其他含二氧化硅的氧化物（如煤灰）中的行为。本工作旨在为硅的大规模生产和粉煤灰材料的回收利用进行基础研究。研究结果如下：B_2O_3-SiO_2熔液碳热还原时，B与SiO同时从熔体中蒸发，而k_2o_3 - sio_2熔液还原时，K的蒸发比SiO更有利。对模型煤灰的碳热还原进行了研究。对SiO凝结物的微观观察表明，该凝结物主要由颗粒状和纤维状物质组成，说明SiO的凝结物发生在气相中形成颗粒状，同时，气态SiO也沉积在附着在坩埚壁上的颗粒状SiO上，增强了SiO的外延生长。在含磷模型煤灰在1800℃的碳热还原过程中，由于熔体和SiO中的P完全蒸发，在低温区回收的SiO不受P的污染。另一方面，当模型灰分中含有B时，SiO中B的含量比初始模型灰分低50%左右。进一步观察气相缩合SiO的形貌，可以发现缩合SiO中存在纳米级纤维、纳米级颗粒和纳米颗粒链状聚集体三种形态。纳米颗粒SiO_x的平均组成为x = 1.2 ~ 1.5。纳米纤维和纳米链的SiO_x的平均组成为x = 1.7 ~ 1.9。将纳米SiO颗粒收集起来，用HF溶液处理，使SiO_2溶解在材料中。用XRD对处理后的残渣进行了研究。XRD分析结果表明，残渣由金属Si和少量SiO组成。结果表明，本研究得到的SiO根据歧化反应分离为SiO_2和Si，因此用HF溶液处理SiO即可得到金属Si。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