硅注入原位合成Sn-Si合金熔体的电磁半连续定向凝固行为研究

As one of the most potential and inexpensive method to purify metallurgical silicon for photovoltaic applications, alloying refining has been widely studied, and some progress has been made. However, the removal fractions of impurities in previous studies are still inadequate, the separation of refined silicon crystals from the melt needs to be further enhanced and the separation efficiency needs to be increased for practical application. Furthermore, some intrinsic mechanisms related to this refining process have not been deeply revealed. This project is proposed to study the basic issues related to a silicon refining process, in which Sn-Si alloying refining and electromagnetic semi-continuous directional solidification are coupled with each other. First, through analyzing the solidification behaviors of Sn-Si melt under different refining conditions and the primary silicon characteristics in refined ingots, the effect of process parameters on the nucleation, growth and migration behaviors of primary silicon will be studied, and the influence mechanisms of induction heating and directional solidification on the primary silicon separation will be discussed and explored. Second, through analyzing the impurities characteristics in the cast ingots and near the solid/liquid interfaces at different moments, the effect of process parameters on the transfer and segregation behaviors of impurities during this combined refining process will be studied, and the influence mechanism of the enrichment of impurities in the melt pool on the following impurities removal behaviors will be explored. At last, based on the above research, the relationships between the nucleation, growth and migration behaviors of primary silicon and the transfer and segregation behaviors of impurities will be studied for obtaining the final ideal refining parameters. Considering the purpose to realize refining metallurgical silicon with compact processing, high efficiency and low cost, to enrich the basic theory of metallurgical refining method, this project is of significant to both theory and practical application.

合金法作为一种很有发展潜力的低成本提纯工业硅方法，近年来受到广泛关注，取得了阶段性成果。但现有研究中杂质去除率还不够理想，初生硅分离效果与分离效率亦有待进一步提高，且对相关内禀机理尚缺乏深入的揭示。本项目拟将Sn-Si合金法与电磁半连续定向凝固耦合，开展工业硅提纯研究。首先，利用各不同工艺条件下合金凝固行为与凝固组织中初生硅特征分析，获得各参数对耦合提纯过程初生硅析出偏聚行为的影响规律，探索感应加热与定向凝固对初生硅的分离作用机理；其次，利用提纯铸锭中及不同拉锭长度固液界面附近杂质特征分析，获得各参数对杂质迁移与再分配行为的影响规律，探索熔池中杂质富集对后续除杂行为的影响机理；最后，在以上研究基础上，探索初生硅析出偏聚行为与杂质迁移及再分配行为间的内在联系，寻求理想的耦合提纯工艺条件。本研究对于发展短流程、高效率及低成本提纯工业硅技术方法，丰富冶金法提纯的基础理论具有重要的实际与科学意义。

合金法作为一种很有发展潜力的低成本提纯工业硅方法，近年来受到广泛关注，取得了阶段性成果。但现有研究中杂质去除率还不够理想，初生硅分离效果与分离效率亦有待进一步提高，且对相关内禀机理尚缺乏深入的揭示。本项目将Sn-Si合金法与电磁半连续定向凝固耦合，开展工业硅提纯研究。通过对耦合提纯过程中初生硅析出偏聚行为、杂质的迁移与再分配行为、初生硅析出偏聚行为与杂质迁移及再分配行为间相关性的实验研究与理论分析，阐明了锡含量、电磁场与温度场对初生硅析出偏聚行为的影响规律与机理，揭示了耦合提纯过程中各杂质的去除机制及锡含量、电磁场及提纯过程熔池中杂质富集等对除杂行为的影响，获得了综合考虑初生硅分离效果、除杂率及提纯效率的理想耦合提纯工艺条件。当锡含量为30 wt.%, 凝固速率为1.5mm/min时，耦合提纯初生硅富集度由原料中的29%提升至91%，Al、Fe、Ca、B与P的去除率分别达到了96.55%、99.05%、98.81%、43.33%及60.53%。本研究对于发展短流程、高效率及低成本提纯工业硅技术方法，丰富冶金法提纯的基础理论具有重要的实际与科学意义。