Investigation of a novel levitation technique for generation of solar grade silicon

太阳能被认为是一种更清洁、取之不尽、用之不竭的重要能源。然而，高纯度、低成本的原材料短缺制约了清洁能源产业的实质性发展。光伏产业使用昂贵的原材料导致光伏发电成本高。使用相对便宜的冶金级硅（MG-Si）作为生产太阳级硅的起始材料，可能是制造太阳能电池最经济的方法之一。例如，凝固精炼是一种从熔融硅中去除大部分杂质的有效方法，并且不需要化学处理。然而，这种技术不能去除磷和硼。本提案的新颖之处是利用真空悬浮技术从冶金级硅中去除磷。这种方法消除了容器材料对硅的污染，也避免了有害工业副产品的产生。为了实现这一目标，有几个短期目标：1)开发合适的感应线圈，以悬浮和精确控制熔融硅和硅合金液滴的温度；2)测量Si-P和Si-Fe-P体系中磷行为的热力学数据；3)测定硅及硅合金液滴除磷动力学；4)优化条件，加速磷蒸发，限制硅的损失；5)进行计算机模拟，以提高对悬浮液滴内流体流动、温度分布和质量传热的理解。该项目的长期目标是为材料开发、环境研究和太阳能光伏工程等关键领域提供适合就业的高素质人才。

Solar energy is recognized as an important source of cleaner and inexhaustible energy. However, a shortage of raw materials with high purity and low cost restricts substantial development of this clean energy industry. The use of expensive raw material for the photovoltaic industry results in a high cost for photovoltaic electricity. Using relatively inexpensive metallurgical grade silicon (MG-Si) as a starting material for the production of solar grade silicon, is potentially one of the most economical ways to make solar cells. For example, solidification refining is an effective way to remove most of the impurities from molten silicon and does not require chemical processing. However phosphorus and boron are not removed by this technique. The novelty of the present proposal is to remove phosphorus from metallurgical grade silicon using a vacuum levitation technique. This method eliminates contamination of silicon by container materials and also avoids generation of hazardous industrial by-products. In order to achieve this goal, there are several short-term objectives: 1) Develop suitable induction coils to levitate and precisely control the temperature of molten silicon and silicon alloy droplets; 2) Measure thermodynamic data for phosphorus behaviour in the Si-P and Si-Fe-P systems; 3) Determine the kinetics of phosphorus removal from silicon and silicon alloy droplets; 4) Optimize conditions to accelerate phosphorus evaporation and limit silicon loss; and 5) Conduct a computer simulation to improve understanding of fluid flow, temperature distribution and mass and heat transfer within levitated droplets. A longer-term objective of the project is to provide highly qualified personnel with training suitable for employment in the critical areas of Materials Development, Environmental Studies and Solar Photovoltaic Engineering.