Boron removal in purifying metallurgical grade silicon by CaO-SiO_2 slag refining

Boron removal from metallurgical grade silicon （MG-Si） using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of CaO-SiO2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron （LB） and the activities of SiO2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of LB reaches 1.57 with a slag composition of 60%CaO-40%SiO2 （mass fraction）. The boron content in the refined silicon is reduced from 18×10^-6 to 1.8×10^-6 using slag refining at 1600 ℃ for 3 h with a CaO-SiO2/MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.

Boron removal from metallurgical grade silicon by oxidizing refining

A purification process was developed to remove impurity element boron from the metallurgical grade silicon by the electric arc furnace refining. The thermodynamic equilibria calculation and experiment to remove boron in the oxidizing atmosphere were performed and analyzed. Boron is removed as the gaseous species BxOy and BxHzOy in O2 and H2O-O2 atmosphere respectively. The equilibrium pressure of BxHzOy is 105-1010 times that of BxOy. Boron is removed and its content in silicon is reduced from 18× 10-6 to 2×10-6 in the Ar-H2O-O2 atmosphere in the electric arc furnace.

Vacuum distillation refining of metallurgical grade silicon(Ⅰ)——Thermodynamics on removal of phosphorus from metallurgical grade silicon

The removal of impurity phosphorus from metallurgical grade silicon is one of the major problems on purification of metallurgical grade silicon for solar grade silicon preparation. The thermodynamics on vacuum refining process of the metallurgical grade silicon was studied via separation coefficient of impurity phosphorus in the metallurgical grade silicon and vapor-liquid equilibrium composition diagram of Si-P binary alloy at different temperatures. The behaviors of impurity phosphorus in the vacuum distillation process were examined. The results show that the vacuum distillation should be taken to obtain silicon with less than 10-7 P,and the impurity phosphorus is volatilized easily by vacuum distillation in thermodynamics. Phosphorus is distilled from the molten silicon and concentrated in vapor phase.

Vacuum distillation refining of metallurgical grade silicon(Ⅱ)——Kinetics on removal of phosphorus from metallurgical grade silicon

The kinetics on vacuum refining process of metallurgical grade silicon was studied using maximum evaporation rate,critical pressure and mean free path of phosphorus in the metallurgical grade silicon at different temperatures. The behaviors of impurity phosphorus in the vacuum distillation process were examined in detail. The results show that the fractional vacuum distillation should be taken to obtain silicon with high purity. Impurity phosphorus volatilize with the maximum evaporation rate of 1.150×105- 1.585×106 g/(cm2·min) in the temperature range of 1 073-2 173 K and the pressure below 2.1 Pa. Because the value of ωmax,P is at least 108 times of ωmax,Si,Si hardly evaporates and remains in the residual,which indicates that phosphorus can be removed from metallurgical grade silicon(MG-Si) completely.

Boron Removal From Metallurgical Grade Silicon by Molten Slag Refining in Induction Furnace

The impurities Al,Ca,Ti,B,P etc in metallurgical grade silicon(MG-Si)can be effectively removed by refining using molten slag based CaO-SiO_2,and it is especially effective for boron removal.The experiments of boron removal were studied using CaO-SiO_2 binary slag in induction furnace.The results showed that the distribution coefficient of boron(L_B)between slag and silicon increased with more proportion of CaO/SiO_2(mass%).It was advantaged to boron removal for higher basicity of slag,so the boron in MG-Si was reduced from 18ppmw to 1.4ppmw with the addition of Li_2O and K_2O to CaO-SiO_2 slag.The proportion of SiO_2 in slag affected the oxidizing capacity of slag,which reduced the efficiency of boron removal.

Numerical Simulation for Induction Refining Process of Metallurgical-Grade Silicon in Vacuum Furnace

The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling fields have been developed by using the finite element method(FEM)and a 2D numerical simulation for electromagnetic、 temperature and velocity fields of metallurgical-grade silicon melting in vacuum induction furnace were performed with a software Multi-physics Comsol 3.5a in this paper.The results showed that the temperature field was dependent observably on input power of coils and induction heating times and the maximum temperature gradient in melting pool was 215K in holding time.With the silicon molted gradually a clockwise vortex was come into being for electromagnetic stirring in the smelting poor.The variation of velocity field in melting silicon is mainly influenced with the change of the current intensity and power frequency.The numerical predications of temperature distribution are in good agreement with experiments.

Removal of iron and aluminum impurities from metallurgical grade-silicon with hydrometallurgical route

A new method for production of solar grade silicon(SoG-Si) at low cost from metallurgical grade silicon(MG-Si) via vacuum metallurgical technique was proposed,which is a promising process to feedstock solar energy silicon material independence of traditional Siemens method. In this procedure,pre-treatment of MG-Si using hydrometallurgical routes to remove the metallic impurities such as iron and aluminum to reduce the production cost is an important process. The influences of acid agents,acid concentration,reaction time and temperature and particle size of raw material ground on the removal efficiency of iron and aluminum impurities were investigated,respectively. The results show that the optimum operation conditions for leaching in acid C are:acid concentration 6 mol/L,temperature 60 ℃,time 4 d,diameter for raw material 50 μm. The removal efficiencies of impurities iron and aluminum are up to 85% and 75%,respectively.

Low-temperature purification process of metallurgical silicon

The removal of B and P consumes most of heat energy in Si metallurgical purification process for solar-grade Si. Metal-liquating purification of metallurgical grade silicon （MG-Si）, also called Si-recrystallization from metal liquid, was a potential energy-saving method for the removal of B and P efficiently, since Si could be melted at lower temperature by alloying with metal. The selection criteria of metal-liquating system was elaborated, and Al, Sn and In were selected out as the optimum metallic mediums. For Sn-Si system, the segregation coefficient of B decreased to 0.038 at 1 500 K, which was much less than 0.8 at the melting point of Si. The mass fraction of B was diminished from 15×10^-6 to 0.1×10^-6 as MG-Si was purified by twice, while that of most metallic elements could be decreased to 0.1×10^-6 by purifying just once. During the metal-liquating process, the formation of compounds between impurity elements and Si was also an important route of impurity removal. Finally, one low-temperature metallurgical process based on metal-liquating method was proposed.

Removal of impurities from metallurgical grade silicon by electron beam melting

Solar cells are currently fabricated from a variety of silicon-based materials.Now the major silicon material for solar cells is the scrap of electronic grade silicon（EG-Si）.But in the current market it is difficult to secure a steady supply of this material.Therefore,alternative production processes are needed to increase the feedstock.In this paper,EBM is used to purify silicon.MG-Si particles after leaching with an initial purity of 99.88%in mass as starting materials were used.The final purity of the silicon disk obtained after EBM was above 99.995%in mass.This result demonstrates that EBM can effectively remove impurities from silicon.This paper mainly studies the impurity distribution in the silicon disk after EBM.

Boron Removal From Metallurgical-Grade Silicon Using CaO-SiO_2 Slag

The removal of boron impurity from metallurgical-grade silicon for solar cell application in slag system of CaO-SiO_2 is investigated.The experiments are conducted in an electromagnetic induction furnace which is used to heat. The distribution coefficient of boron(L_B)between slag and silicon phase is particularly examined in terms of the optical basicity of slag.With the increase of optical basicity,L_B increases to a local maximum value of 1.58 when the optical basicity is 0.71 after getting to the minimum value of 0.72 when the optical basicity is 0.56.In that above optical basicity of 0.71,L_B decrease sharply which indicates that increasing the basicity of slag is not always effective in boron removal from silicon.

太阳能级多晶硅生产工艺

阐述了挥发性硅化物还原或分解法和冶金级硅精炼法生产太阳能级多晶硅的生产工艺。目前生产多晶硅的主要方法是改良的西门子法,但该方法在降低生产成本上显得力不从心。冶金级硅精炼法是一种制备低成本太阳能级多晶硅的方法,然而该方法不能有效地去除B和P,只能选择B和P含量很少的冶金级硅为原料制备多晶硅。锌还原法是生产低成本太阳能级多晶硅的优势方法,分析表明锌还原法与西门子法相结合不失为生产多晶硅的好方法。

冶金法制备太阳能级多晶硅新工艺原理及研究进展

随着光伏市场需求不断增加,能满足光伏电池技术经济指标要求的硅材料出现严重短缺,冶金法制备太阳能级多晶硅新工艺技术由于其能耗低、成本低,越来越受到国内外的广泛重视,成为研究开发的热点。综述了近年来国内外有关冶金法提纯冶金级硅至太阳能级硅的各种工艺路线的原理及成果,并进行了比较分析,展望了其应用前景。

冶金级硅氧化精炼提纯制备太阳能级硅研究进展

综述了目前冶金级硅氧化精炼制备太阳能级硅的研究进展,详细介绍了熔渣精炼、吹气氧化精炼和热等离子体精炼的方法和装置以及杂质的去除效果。研究发现:上述氧化精炼方法对硅中杂质元素Al、Ca、Cu、B、P等具有很好的去除效果;熔渣和吹气氧化精炼对Fe不明显,须借助于定向凝固方法才能彻底的去除;吹气氧化精炼和等离子体精炼对硅中B的去除效果十分明显,可使其降低至0.1ppmw以下,这为当前冶金法提纯制备太阳能级硅在技术和工艺上提供了很好的思路;通过氧化精炼,硅中杂质元素完全可以达到太阳能级硅的要求。本文提出,吹气氧化精炼(或等离子体精炼)与定向凝固精炼联合使用并形成规模化和连续化精炼装置是加快我国太阳能级硅产业化进程最切实可行的办法和措施。

精炼法提纯冶金硅至太阳能级硅的研究进展

随着光伏市场需求不断增加,满足光伏电池技术经济指标要求的硅材料出现严重短缺,低成本提纯冶金硅至太阳能级硅工艺技术越来越受到广泛重视,成为研究开发热点。综述了近年来国外有关基于定向凝固原理开发的精炼法提纯冶金硅至太阳能级硅的技术成果,并进行了比较分析,展望了应用前景。

冶金法制备太阳能级多晶硅研究现状及发展趋势

冶金法是我国走出硅原料依赖,发展低成本、环境友好的太阳能级多晶硅制备技术的必经之路,冶金法自诞生以来在世界范围内经历了三次研究高潮,第三次正是在以我国科研和产业工作者为主导和推动下发展的,并形成了大量有益的科学结论和实践经验。本文从冶金法的界定开始,详细分析了冶金法提纯的理论基础,饱和蒸汽压机理、偏析机理和氧化性差异机理,介绍了以上机理所衍生出的技术方法及进展,并对冶金法的发展前景进行了展望。

冶金法制备太阳能硅过程的湿法除硼研究

湿法提纯作为冶金法路线制备太阳能级硅前处理工序,可去除大部分铁铝等碱金属及硼杂质,提高最终产品收率。实验考察了湿法除硼过程主要工艺因素:浸出剂浓度、温度、时间、搅拌等对产品纯度的影响,采用SEM对产品进行表征。当工艺条件为c(HNO3)=6.5 mol/L,c(H2SO4)=6 mol/L,温度120℃、时间4 h,处理后产品中杂质质量分数为3.574×10-6,湿法过程单元的去除率为44.58%。实验结果为高等级太阳能级硅制备工业化开发大幅度降低成本提供了技术基础。

冶金法制备太阳能硅过程的湿法提纯研究

湿法提纯作为冶金法路线制备太阳能级硅的前处理工序,可以去除大部分金属杂质,提高最终产品收率。考察了硅粉粒径、浸出剂浓度、温度、时间、搅拌等因素的影响,采用ICP、SEM等对产品进行了表征。当工艺条件为:硅粉平均粒径44μm、w(HCl)=5%、温度80℃、时间6h,处理后产品中杂质w(Fe)=2.4×10-5,去除率为99.2%,杂质w(Al)=6.4×10-5,去除率为80%。描述了酸浸过程在前后不同阶段分别为受反应速度和内扩散控制历程。为太阳能级硅制备工业化开发,大幅度降低成本提供了参考。

太阳能级多晶硅冶金制备技术的研究进展

随着光伏市场需求不断增加,满足光伏电池技术经济指标要求的硅材料出现严重短缺,低成本提纯冶金硅至太阳能级硅的工艺技术越来越受到广泛重视。分析了国内外光伏产业的发展现状和趋势,重点介绍了冶金法提纯太阳能级硅工艺中的湿法精炼、定向凝固、真空熔炼、造渣法、电子束精炼和离子束精炼等常用技术的原理与研究现状,并进行了比较分析,展望了应用前景。

造渣氧化精炼提纯冶金级硅研究进展

冶金级硅是生产晶体硅太阳能电池的重要原材料,需精炼处理以降低其中的杂质含量。造渣氧化精炼是一种相对能耗低,耗时少的冶金级硅提纯技术,对新能源时代太阳能的发展具有重要影响。本文对目前造渣氧化精炼冶金级硅制备太阳能级硅的最新研究进展作了较为全面的阐述,详细介绍了国内外研究人员利用CaO-SiO2,CaO-SiO2-CaF2,CaO-SiO2-Al2O3,CaO-SiO2-Na2O等渣系氧化精炼去除冶金级硅中杂质的方法、工艺和效果;其中更着重介绍了最难去除元素之一—硼的去除,分析了这些渣系的应用特点和研究现状;最后对造渣精炼的优缺点进行了简要的总结并对其发展趋势做了展望。

提纯工业硅除铝的实验研究

为了去除工业硅中的杂质制备太阳能级硅,根据工业硅凝固过程中铝在固相和液相中溶解度的差异,采用定向凝固法去除工业硅中的杂质铝。实验结果表明,铝的去除效率可达98%,说明利用定向凝固法去除工业硅中的铝是可行的。但由于在结晶过程中晶界上会富集部分铝元素,因而定向凝固法并不能除去这一部分杂质。结合金相实验中样品腐蚀前后晶界上的变化,可以知道利用酸浸可以除去晶界上的杂质铝。还研究了先酸浸后定向凝固法相结合除铝,实验结果表明铝的含量可以降到1.6×10-5,铝的去除率达98.6%。