微合金化-多场强化铝硅合金精炼过程析出相演变规律及除杂机制

With the urgent need in our country to develop a technology of manufacturing solar grade silicon (SoG-Si), Al-Si solvent refining method, for its low cost and energy consumption, has attracted wide attention. But during the refining process, impurity removal is strongly controlled by kinetic factors at lower solidification temperature range, which leads to the fact that the impurity removal capacity of Al-Si solvent purification method cannot be fully utilized under general solidification condition. Therefore, a new method that coupling microalloying technology and multiple fields enhancement technologyis proposed to achieve simultaneous and efficient removal of B/P impurities and convenient separation of primary silicon/melt. By theoretical calculation and phase analysis, distribution and morphology of the key impurities B/P in the melt with the microalloying (Ti, Zr, Ca, Mg) system and their reaction mechanism are revealed. The growth and migration mechanism of precipitated compounds under the multiple fields (electromagnetic field/temperature field/flow field) is studied.By solidified structure observation and impurity content measurement, the mechanism of directional growth of primary silicon and the regulation mechanism of the impurity content is revealed. By adjusting and optimization the microalloying parameters and the multiple fields’ parameters, the solidification morphology, precipitation phase growth and migration process of primary silicon can be controlled. Therefore the goal of reducing impurity content in the primary silicon can be achieved. These results will not only enrich and develop the solidification theory of multiphase growth system under multiple fields, but also contribute to the development of economical, high-efficiency techniques to purify SoG-Si by Al-Si solvent refining method.

针对目前我国对太阳级硅制造技术的迫切需求，铝硅合金精炼法因其低能耗、低成本的优点，引起了广泛关注。但在凝固提纯过程中，硅中关键杂质元素B、P的去除在低温端存在很强的动力学效应，限制了其提纯能力。为解决此问题，本项目提出了微合金化-多场强化Al-Si合金精炼的新方法，耦合了微合金化与多场强化两种除杂技术，实现B/P杂质同步高效去除和初晶硅/熔体的便捷分离。采用理论计算和析出相分析的方法，揭示微合金化体系下B、P的赋存状态及其反应机理，掌握多场（电磁场/温度场/流场）下析出相生长、迁移机制；采用凝固组织观测和杂质含量检测，揭示初晶硅定向生长机制及其杂质含量调控机制；通过解析优化微合金化、多场参数，调控初晶硅凝固形貌，析出相生长、迁移过程，达到降低初晶硅中杂质含量的目标。本项目不仅丰富和发展了多场条件下多相生长体系的现代凝固理论，同时对开发经济、高效、快速的铝硅合金精炼技术具有重要指导意义。

Al-Si合金法是一种可以大规模、低成本制备太阳级硅的方法，但在凝固提纯的过程中，硅中关键杂质元素B、P的去除一直是一个难题。本项目采用采用微合金化结合多场凝固的工艺，采用添加微合金化元素与关键杂质元素B、P结合形成硼化物、磷化物，降低体系中的B、P含量；采用多场凝固调控熔体的温场流场，降低动力学效应，提高杂质元素的去除效率。研究了Ti/Zr/V微合金化对除B的影响，发现除B能力上Zr>Ti>V，仔细研究了Al-Si-Ti、Al-Si-Zr体系在不同冷却速率条件下的除杂情况，获得了极高的B去除效果（99.6%），总结了析出相生长规律并建立了数学模型用于描述和预测析出相的生长过程。研究了Mg/Ca/Sr微合金化对P去除的影响，发现Mg对于Al-Si体系中P去除几乎没有效果，Ca则会在硅相界面处形成Al2Si2Ca相，对P的除杂反而有负面作用，添加Sr以后会一方面促进硅相细化，另一方面会生成Al2Si2Sr相，获得了极高的P去除效果（98%），总结了不同凝固速率下析出相生长规律并建立了模型用于描述析出相的生长过程。研究了多场条件下，熔体的流场、温度场情况，析出相的生长迁移过程，特别详细研究了多场情况下Zr单加入和Zr、Sr共掺等不同微合金化体系，发现了多场条件下析出相生长机理及多元素共掺的情况下不同析出相之间的相互作用。研究微合金化提纯后初晶硅和共晶硅的杂质含量区别，开发了一种二次酸洗的方法，解决微合金化凝固后合金元素残留的问题，进一步提高了合金法提纯硅的效果和产率。最后借鉴合金法调节凝固参数和微合金组分可以改变硅相形貌与析出相种类的思路，开发合金法的新应用场景——低成本大规模锂电池用硅负极材料制备；同时利用合金法积累的检测技术和提纯理论，指导我们在石英砂提纯方面也取得了突破性的成果。