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冶金硅熔析精炼去除硼、磷等杂质的基础研究
Alternative TitleFoundational Research for B, P and Other Impurities Removal from Metallurgical-Grade Silicon by Solvent Refining
胡磊
Subtype硕士
Thesis Advisor王志
2013-04-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword冶金硅   杂质   熔析精炼   化学重构   分离提纯
Abstract随着光伏产业的快速发展,对太阳能级多晶硅的需求急剧增大,由于西门子法等化学法生产太阳能多晶硅工艺存在能耗高、成本高和污染严重等问题,冶金法制备多晶硅技术成为关注的焦点。 熔析精炼作为一种对合金杂质分离提纯的新体系,通过改变杂质的存在形式和位置,使冶金硅在低温下熔化,强化了杂质分离特性,并且合金化使硅晶体在低温下熔化和析出,实现了低温操作净化,因此有可能大幅降低净化过程的总能耗。本论文根据冶金硅杂质的赋存状态,计算了熔析体系下杂质的分凝系数;研究了Sn-Si和Al-Si组合熔析体系对杂质的去除效果并重点探讨了杂质的去除机理;通过在熔析体系中添加金属Ti、Ca研究了其对B、P的强化去除效果以及杂质化学重构的过程;最后对熔析过程析出硅和熔析介质的分离做了探索性研究。 (1)解析了冶金硅中杂质的物理赋存状态与分布规律。B、P在冶金硅中主要以固溶的形式存在,极少量的B、P会与硅、金属杂质等形成二元、多元化合物偏析在硅的晶界处。在冶金硅中,偏析的磷主要存在于CaAl2Si2相中,冶金硅中金属杂质主要以合金杂质相的形式富集于晶界处,当硅中Ca、Al的含量比不同时,冶金硅中金属间化合物的种类不同。 (2)研究了Sn-Si和Al-Si熔析体系下杂质的热力学。采用Factsage软件计算了Sn-Si体系和Al-Si体系下B、P的分凝系数,与纯硅体系相比,B、P的分凝系数在Al-Si体系中的下降趋势更明显。在1200K时,B的分凝系数值由0.8下降到0.033,P的分凝系数由0.35下降到0.002,从热力学的角度证明了Sn-Si和Al-Si熔析体系提纯工艺的可能性。 (3)首次采用Sn-Si和Al-Si组合熔析方法提纯冶金硅,组合熔析可使B、P的最终含量下降至0.28ppmw和0.46ppmw,达到了太阳能级多晶硅的要求。组合熔析可使金属杂质(除熔析剂Sn和Al)的含量下降至0.5ppmw以下。 (4)探讨了熔析过程中杂质的主要去除方式。在熔析过程中,B、P和其他元素形成杂质相偏析出来,然后通过酸洗去除是其主要的脱除方式,CaAl2Si2相是Al-Si体系析出硅中含磷的主要杂质相之一。在Sn-Si体系中SiB6是B形成的主要杂质相;而在Al-Si体系中,AlB12是B形成的主要杂质相之一。金属杂质在熔析过程中主要形成了中间化合物(如二元金属硅化物)或多元杂质相偏析在析出硅的晶界处或者附着在硅的表面。 (5)研究了熔析过程中杂质的化学重构。在Sn-Si熔析体系中添加Ca后,P的去除率由72.1%增加到84.6%。P和Ca富集在杂质相区域,P在熔析体系中的化学重构过程是强化其去除的原因。 (6)对硅和熔析介质的分离进行了探索性研究。熔析过程中使用超重力有利于结晶硅的聚并,而较小的冷却速率有利于析出硅和熔析介质的分离,并减少了熔析介质的夹带。
Other AbstractWith the rapid development of photovoltaic industry, there is an immense need for solar grade polycrystalline silicon. Since the problems including high energy consumption, high cost and serious environmental pollution existed in the chemical methods like Siemens method, metallurgical methods become the focus of attention. Solvent refining, as a new system for separation and purification of impurities in alloy, strengthens the segregation characteristic of impurities by transforming the existing state and position of impurities, and the alloying makes silicon crystals melt and segregate at low temperature and implements the purification process in low temperature, so it is possible for reducing the total energy consumption of the purification process significantly. In this paper, according to the existing state of impurities in metallurgical-grade silicon (MG-Si), the segregation coefficients of impurities were calculated, and the removal efficiency of impurities by the Sn-Si and Al-Si refining processes was studied, and the removal mechanism of impurities was mainly discussed. The strengthened removal effect of boron and phosphorus and the chemical reconstruction process of impurities were studied by adding titanium or calcium to the solvent refining system. Finally, the exploratory research for separation of refined silicon and solvent in the solvent refining process was conducted. (1) The physical existing state and distribution regularity of impurities were analyzed. B and P existed in MG-Si in the form of solid solution, a little amount of them formed binary and multielement compounds with silicon and metallic impurities and segregated in the grain boundaries of Si. In MG-Si, CaAl2Si2 phase was the main existing phase of P segregated out, metallic impurities enriched in the grain boundaries of MG-Si in the form of alloy impurity phases, the types of the intermetallic compounds in MG-Si were different when the content ratio of Ca to Al was different. (2) The thermodynamics of impurities in the solvent systems was studied. The segregation coefficients of B and P in the Sn-Si and Al-Si systems were calculated by Factsage soft, compared with the pure silicon system, the segregation coefficients of B and P in the Al-Si system reduced more obviously. The segregation coefficient of B reduced from 0.35 to 0.033 and that of P reduced from 0.8 to 0.002 at 1200 K. The possibility of purification process by Sn-Si and Al-Si solvent systems was proved in the thermodynamic point of view. (3) The purification of MG-Si by the combined Sn-Si and Al-Si solvent refining method was first proposed. The final contents of B and P reduced to 0.28 ppmw and 0.46 ppmw, respectively, which achieved the demand of solar-grade silicon, and the contents of metallic impurities (except of the solvents) were below 0.5 ppmw by the combined solvent refining processes. (4) The main removal approach of impurities in the solvent refining processes was discussed. B or P formed impurity phases with other impurities which segregated in the grain boundaries of refined Si or attached to the surface of refined Si, this is the main removal approach of impurities. CaAl2Si2 phase was the main existing phase of P in the refined Si in the Al-Si system. SiB6 was the main formed impurity phase of B in the Sn-Si system, while AlB12 was one of the main formed impurity phases of B in the Al-Si system. (5) The chemical reconstruction process of impurities in MG-Si was studied. The removal efficiency of P increased from 72.1 pct to 84.6 pct by adding Ca to the Sn-Si system. Meanwhile, P and Ca enriched in the region of impurity phases when adding Ca to the Sn-Si system, the chemical reconstruction process of P in the solvent refining process led to the strengthened removal effect of P. (6) The exploratory research for separation of refined Si and the solvent was conducted. The use of gravity force was beneficial for the coalescence of silicon crystals, and the smaller cooling rate was beneficial for separation of refined silicon and the solvent, and more, reducing the entrainment of the solvent in refined silicon.
Pages105
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8364
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
胡磊. 冶金硅熔析精炼去除硼、磷等杂质的基础研究[D]. 中国科学院研究生院,2013.
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