过共晶铝硅合金电磁半连铸过程中初生硅形貌和偏聚的基础研究

Metallurgical method to purify Si has many advantages, such as low energy-loss, environmental-friendly, low cost, and so on, which has become one of the most potential and inexpensive method in the solar industry. The project will be based on the solute segregation of Al-Si alloy during solidification to obtain the solar-Si crystal, and suggests a method to use the electromagnetic field to control the nucleation and growth of the primary Si phase during semi-continuous casting process. The nucleation, growth, segregation, collision and combination mechanism of primary Si phase under electromagnetic field, and the inbeing relationship with the purification result will be uncovered. The relationship between the segregation coefficient of impurity element and impurity content in the inter-region of primary Si phase will be clarified. The heat conduction between alloy and mold and liquid metal flow under electromagnetic field will be investigated. The formation condition and evolution law of Si-rich layer will be revealed, and the corresponding mathematic and physical models will be established. Finally, the project will provide a new independent technology to purify polycrystalline Si from hypereutectic Al-Si alloy by electromagnetic continuous casting, and to supply the cheap polycrystalline Si for the solar industry of our country.

冶金法具有能耗低、环境污染小、成本低、投资小、生产灵活等优点，已成为太阳能光伏产业最有应用潜力的低成本制备多晶硅技术之一。本项目利用Al-Si合金凝固过程中溶质再分配获得晶体硅的思路，提出电磁场控制过共晶铝硅合金半连续铸造过程初生硅的形核与偏聚的方法，制备太阳能级多晶硅。研究电磁场作用下过共晶铝硅合金凝固过程中初生硅的形核、生长、偏聚富集机制，建立各杂质元素在初生硅与铝硅熔体之间的分凝系数与初生硅晶间杂质含量之间的本征关系。把握电磁半连续铸造过程中熔体的传质现象和其与结晶器的传热规律，以及初生硅富集层的形成条件与演化规律，建立相对应的数学、物理模型。研究出具有自主知识产权的过共晶Al-Si合金电磁连续铸造过程中初生硅偏聚富集的新方法，为我国太阳能电池产业提供低成本多晶硅原料。

探索建立低成本、高效率、工艺稳定的太阳能级多晶硅制备技术对促进光伏产业可持续性发展具有重要的现实意义。相比于传统复合冶金法逐步升级冶金硅思路，以过共晶Al-Si合金为代表的合金凝固提纯法可以在单次凝固过程中实现对所有杂质元素发挥去除作用，具有提纯温度低、除杂效率高、能耗低等优点，极具成本竞争力和发展前景。但在凝固提纯过程中，由于低温生长动力学因素对杂质去除效率的影响和析出的初生硅均匀分布在合金基体中难以收集的限制，最终制约了该方法的实际推广应用。本项目以过共晶Al-Si合金凝固过程为研究对象，在合金凝固过程中施加电磁场，研究强制对流对合金凝固过程中杂质元素分凝行为的影响，揭示电磁搅拌作用下杂质分凝行为的强化机制；通过电磁场/温度场耦合控制过共晶Al-Si合金凝固过程，实现初生硅高效分离；进一步揭示并验证初生硅电磁分离机制；在此基础上，提出过共晶Al-Si合金电磁半连铸过程中初生硅连续分离新技术，实现初生硅高效收集。为解决太阳能光伏产业高纯硅原料的低成本供应问题提供了一条潜在的途径。