Solar-grade silicon production by metallothermic reduction

Various types of processes for solargrade silicon (SOG-Si) production/purification have been developed with the aim of overcoming the low productivity of the Siemens process. These processes can be divided into three groups: decomposition and/or hydrogen reduction of silane gases by improving the currently used commercial processes; purification of metallurgical-grade silicon using metallurgical purification methods; and metallothermic reduction of silicon halides by metal reductants such as zinc and aluminum. This paper reviews the features of various SOG-Si production processes, particularly the processes based on metallothermic reduction, by classifying them according to the types of reductants and the silicon compounds used. Prospects for development of new processes for producing high-purity silicon are presented.     

An Evolving Method for Solar-Grade Silicon Production: Solvent Refining

Use of photovoltaic (PV) power generation has recently been increasing rapidly because it provides clean, renewable energy. While production of solar-grade silicon (SOG-Si) has been dominated recently by the modified Siemens process and a fluidized bed reactor process, obtaining a stable supply of SOG-Si at lower cost is essential to further increases in PV installation. Metallurgical production offers benefits in productivity and possibly also in process cost. Several metallurgical processes, such as directional solidification, vacuum melting, and plasma melting, have been developed, but significant cost reductions or dramatic improvements in productivity are required to enable metallurgical refining to become the major route for SOG-Si production. The solvent refining process offers the possibility of cost reduction due to its high purification efficiency and low processing temperature. This paper reviews solvent refining processes for SOG-Si purification, emphasizing their advantages and identifying the problems that must be solved for process development.     

Winning the global race for solar silicon

While there are numerous contestants in the race to produce low-cost solar silicon, the chemistries involved can be grouped into three categories: new Siemens-like processes, new approaches to reduction of silica, and upgrades of metallurgical-grade silicon. This review is focused on the thermo-chemistries being employed in the last two categories, with emphasis on removal of boron and phosphorous, as these elements are the two most difficult to remove from silicon by unidirectional solidification.     

冶金法制备太阳能级硅的原理及研究进展

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.本文分析了全球光伏产业的发展现状和趋势,对目前获得太阳能级多晶硅的化学路径和冶金路径进行了对比分析;重点介绍了冶金法制备太阳能级硅的工艺原理,以及目前常用的提纯技术;同时,简单介绍低成本生产太阳能级多晶硅的新工艺,并指出了冶金法可能是今后提纯多晶硅的主要研究方向.     

冶金法制备太阳能级多晶硅的热力学研究进展

冶金法制备太阳能级硅是目前多晶硅材料的研究热点。为更深入理解冶金法制备太阳能级硅的原理,本文综述了几种常见的冶金法提纯多晶硅的热力学研究进展,重点对定向凝固过程中杂质的分凝系数问题、真空精炼中杂质蒸气压与温度的关系、以及合金造渣和氧化造渣中杂质的分配规律,以及渣相和硅相体系中各组元的活度测定方法进行了分析,提出了多晶硅热力学研究中尚存在的问题。     

微波场在冶金级硅酸浸提纯过程的应用

为了降低冶金级硅粉中金属杂质的含量,本文比较了微波场、球磨活化、恒温水浴等不同反应条件对冶金级硅中金属杂质去除效果的影响.实验结果表明,微波场作用下杂质Fe、Al、Ca、Ti的去除效率分别为83%,73%,93%,54%;球磨活化作用下杂质Fe、Al、Ca、Ti的去除最率分别为78%,69%,83%,46%;恒温水浴作用下Fe、Al、Ca、Ti的去除效率分别为72%,54%,67%,38%.微波场作用效果要明显优于球磨活化和恒温水浴作用,且微波场作用时间少干另外两者,探讨了微波场湿法提纯冶金级硅、球磨活化湿法提纯冶金级硅的原理.     

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.     

我国硅热法炼镁现状及发展趋势

我国镁冶金工业是在特定的环境和条件下发展起来的，是以牺牲环境和燃料资源为代价的。目前，我国硅热法炼镁的发展趋势为开发高效、节能、环保的皮江法炼镁工艺。     

低温净化冶金硅工艺(英文)

硼、磷杂质的去除在冶金净化法生产太阳能级多晶硅工艺中耗能最大。金属熔析净化法可以实现冶金硅在金属液中低温下熔化,而后再结晶净化,是一种可行的低能耗硼磷去除方法。对熔析体系的选择原则进行总结,筛选出铝、锡和铟金属作为合适的熔析介质。对于Sn-Si体系,1500K时硼的分凝系数为0.038,远小于纯硅熔点的对应值0.8。冶金硅二次熔析净化处理可使硼的质量分数由15×10-6降至0.1×10-6,而多数金属杂质可一次性去除至0.1×10-6以下。在熔析过程中,杂质和硅生成化合物是主要的杂质去除方式。提出一种以金属熔析法为基础的低温冶金硅净化工艺。     

Thermodynamics of solar-grade-silicon refining

Solar energy will shortly be in great demand since it is inexhaustible and cleaner than any conventional energy resources. At present, an expensive grade of silicon for semiconductor (SEG-Si) is used for a solar cell to convert solar energy into electricity. However, the amount of supply is limited and we have to develop an innovative process for silicon production with low energy cost in order to spread the solar cell system widely. Using relatively inexpensive metallurgical grade silicon (MG-Si) as a starting material for making solar grade silicon (SOG-Si) is believed to be one of the ways to make solar cells less expensive. Impurities in MG-Si will shorten the lifetime of excited carriers in silicon solar cell and disturb electric generation. Hence, the removal of impurities from silicon is a significant issue in silicon solar cell fabrication. To discuss the possibility and efficiency of the impurity elimination process, evaluation of thermodynamic properties of impurities in molten silicon such as the activity coefficients and the interaction parameters of harmful impurities has been performed.     

熔盐电解精炼提纯金属硅(英文)

对熔盐电解质中硅的沉积过程进行电化学研究。在 973~223K,在硅氯化物熔盐中采用电解精炼提纯金属硅。结果表明,液态硅铜合金阳极有利于 CaCl2-NaCl-CaO-Si 熔盐体系的电解精炼。ICP-AES 分析结果显示,通过电解精炼可有效去除原料中大量的钛、铝、铁等金属杂质,硅中的硼和磷含量分别由 36×106和 25×106降低至 4.6×10 6和 2.8×10 6,电解能耗约为 9.3 kW·h/kg。     

High-Temperature Refining of Metallurgical-Grade Silicon: A Review

Among currently known alternatives for renewable energy sources, solar power is generally regarded as having the most potential to satisfy the ever-growing demand. While solar photovoltaic power is a well-established technology, its widespread uptake has been hindered by the prohibitively high price of units and thus electricity. This is due mainly to the high cost of the silicon used to fabricate the devices. This article presents a review of the development of established pyrometallurgical techniques as applied to refining metallurgical silicon to solar grade for the purposes of reducing reliance on expensive traditional silicon feedstock. Four basic high-temperature methods??solvent refining, vaporization, electrorefining, and slag treatment??are described, and the limitations and advantages of each method are presented. It is apparent that these techniques are very useful for removing impurities from silicon, but are often selective and not able to remove all problematic elements. Therefore, refining may need to be as a sequence of steps, targeting specific elements each time, or as novel methods combining multiple techniques simultaneously. Ultimately, the successful approach will have to achieve large-scale production by cost-effective means to replace current methods.     

Kinetics of iron removal from metallurgical grade silicon with pressure leaching

In this paper, the kinetics of pressure leaching for purification of metallurgical grade silicon with hydrochloric acid was investigated. The effects of particle size, temperature, total pressure, and concentration of hydrochloric acid on the kinetics and mechanism of iron removal were studied. It was found that the reaction kinetic model followed the shrinking core model, and the apparent activation energy of the leaching reaction was 46.908 kJ/mol. And the apparent reaction order of iron removal with pressure leaching was 0.899. The kinetic equation was ob-tained and the mathematical model of iron removal from metallurgical grade silicon (MG-Si) was given as follows: 1-2/3x-(1-x)2/3=exp(5.1654-4811.4591/T+1.287lnp+1.046ln[C])·t/r02· The values calculated from the equation were consistent with the experimental results.     

Weld structure of joined aluminium foams with concentrated solar energy

Concentrated solar energy was applied to welded foam plates in non-protective atmosphere. The filler was a pore-generating aluminium–silicon alloy placed between two commercial aluminium foam plates. The heating device provided enough energy to melt and foam the filler. The heat affected surfaces on foam plates and welding mechanisms were correlated with heating conditions. Test plate thickness controlled filler foaming, and two runs were necessary to complete foaming. Weld characterization through tensile tests and microstructural study was performed. The role of the oxide layer on the weld was analyzed and the main welding mechanisms identified: a mechanical form-fit and a metallurgical connection.     

Solar pyrometallurgy—An historic review

As an alternative to fossil fuels, solar energy can help minimize global warming triatomic gas emissions (CO₂ and H₂O) when used in metallurgical processes. This paper reviews the technical development in this field from the first patents filed in the late 1800s to present-day pilot work of solar zinc production. Dr. Neelameggham is also the JOM advisor from the Reactive Metals Committee of the TMS Light Metals Division.     

Metal Recovery from Scrap and Waste

The depletion of high grade ores and accumulation of huge quantities of metallic scrap and metallurgical wastes have generated significant interest in their processing. In this paper, both pyrometallurgical, as well as hydrometal-lurgical, methods for metal recovery from scrap and wastes (viz., slag, dusts, aqueous effluents, sludge and residues) are reviewed. Scrap recycling and the processing of metallurgical wastes will pollute the environment to a lesser extent and consume less energy compared to the primary metal production. Reprocessing metallurgical waste (viz., slag, red mud, etc.) serves a social objective and ensures raw materials conservation. Research trends reveal that hydrometallurgy may play a dominant role in the waste treatment. Recently developed processes like continuous ion exchange and fluidized bed electrolysis may be used in the future for recovering metals from dilute solutions.     

铝生产结构调整与节能对策研究

针对我国铝工业面临的整体性问题,在冶金流程工程学的理论体系框架下,分析研究铝生产设备与流程的节能方向和技术路线,促进铝工业生产流程结构调整。基于现有铝工业的生产流程结构特征及能源利用情况,对比分析铝、钢铁生产流程的冶金本质,划分铝生产流程工序区段,综合分析铝工业能源结构及能量耗散规律。参照钢铁节能技术的实践,指出铝工业在流程优化与改进、能源结构优化、废弃物资源化利用及余能回收综合利用等方面具有系统节能潜力,提出铝后工序高效、有序运行的生产流程结构模式。     

Spray-atomized and codeposited 6061 Al/SiCp composites

Spray atomization and codeposition processes have received considerable attention for the synthesis of discontinuously reinforced metal-matrix composites. This methodology involves the mixing of reinforcements and matrix under thermal conditions such that the matrix contains both solid and liquid phases. In principle, such an approach avoids the extreme thermal excursions, with concomitant degradation in interfacial properties and extensive macrosegregation, normally associated with casting processes. Furthermore, this approach also eliminates the need to handle fine reactive particulates normally associated with powder metallurgical processes. To investigate the utility of this process for the preparation of metal-matrix composites, several silicon carbide particulate-reinforced 6061 Al composites were prepared. The spray-atomized and codeposited materials exhibited attractive combinations of strength, elastic modulus and elongation, although further work is needed to optimize their properties.     

Potential Applications of Concentrated Solar Thermal Technologies in the Australian Minerals Processing and Extractive Metallurgical Industry

The Australian minerals processing and extractive metallurgy industries are responsible for about 20% of Australia’s total greenhouse gas (GHG) emissions. This article reviews the potential applications of concentrated solar thermal (CST) energy in the Australian minerals processing industry to reduce this impact. Integrating CST energy into these industries would reduce their reliance upon conventional fossil fuels and reduce GHG emissions. As CST technologies become more widely deployed and cheaper, and as fuel prices rise, CST energy will progressively become more competitive with conventional energy sources. Some of the applications identified in this article are expected to become commercially competitive provided the costs for pollution abatement and GHG mitigation are internalized. The areas of potential for CST integration identified in this study can be classed as either medium/low-temperature or high-temperature applications. The most promising medium/low-grade applications are electricity generation and low grade heating of liquids. Electricity generation with CST energy—also known as concentrated solar power—has the greatest potential to reduce GHG emissions out of all the potential applications identified because of the 24/7 dispatchability when integrated with thermal storage. High-temperature applications identified include the thermal decomposition of alumina and the calcination of limestone to lime in solar kilns, as well as the production of syngas from natural gas and carbonaceous materials for various metallurgical processes including nickel and direct reduced iron production. Hybridization and integration with thermal storage could enable CST to sustain these energy-intensive metallurgical processes continuously. High-temperature applications are the focus of this paper.     

Electric discharge decomposition of metallurgical grade silicon

A new approach to the selective electric discharge disintegration of metallurgical grade silicon is put forward; this technology ensures its decomposition to fractions necessary for the production of pure silicon.