硅合金电渣重熔精炼与偏析耦合强化B、P同步脱除

Interface mass-transfer dynamics control and thermodynamics restriction of interphase distribution coefficient are the common problems in the process of producing high-purity silicon at present, especially for high harmfulness and low concentration impurities B and P. Traditional metallurgical purification method is difficult to remove impurities B and P simultaneously, which can lead to low efficiency and high energy consumption problem. For the highlighted problems about low concentration impurity mass transfer kinetics and the distribution coefficient thermodynamics, based on the characteristic of composite solvent refining and solidification segregation, the new method of electroslag remelting purification short process for silicon alloy and new idea of coupling polyphase interfacial mass transfer reinforcement and high temperature electric slag increasing balance of impurities distribution were proposed to remove impurities B and P simultaneously. The mass transfer law of B and P in slag and alloy under dynamic condition was investigated by slag washing dripping experiment and mass transfer mechanism of the impurities in the interface was revealed through the interface composition analysis. The morphology transformation rule of oxygen anion in the slag and B and P in silicon in the dynamic interface was revealed by interface microstructure analysis under the condition of different slag composition, basicity, oxygen potential and temperature. The interface oxidation co-strengthening mechanism of active oxygen ions and oxygen molecules was explored by slag composite blowing oxygen, electric field enhancement and thermodynamic calculation. These research results laid a theoretical foundation for the silicon alloy electroslag remelting refining technology producing high purity silicon materials.

界面传质动力学控制与相间分配热力学限制是高纯硅制备过程的共性问题，传统冶金提纯技术难以实现B、P同步高效深度去除，造成提纯效率低、能耗高等问题。基于多相界面反应传递协同与过程耦合强化学术思想，提出硅合金电渣重熔提纯短流程新方法，耦合高温电渣精炼与合金凝固偏析过程，利用多相界面传质与反应强化大幅提高杂质在渣/金相间及金属液/固相间的二次分配，实现同步去除B、P杂质。结合在线取样和界面微区成分分析方法，揭示B、P在渣金两相的传质特征，掌握合金凝固过程杂质浓度梯度及其在近渣侧的偏析富集规律；通过改变熔渣组成、碱度、氧势、温度等精炼条件，采用渣金界面微观结构分析方法，揭示渣中活性氧离子和氧分子与合金中B/P的形态转化与界面反应机制，推测反应路径探明速控步骤；通过熔渣吹氧等调控环境氧势方法并结合热力学计算，探索活性氧离子/分子协同强化界面反应机制。为电渣重熔精炼制备高纯硅材料提供基础数据和理论支撑。

本项目基于多相界面反应传递协同与过程耦合强化学术思想，耦合高温电渣精炼与合金凝固偏析过程，提出硅合金电渣重熔提纯短流程新方法，根据三部分研究内容开展了相应工作。第一，活性氧离子与氧分子协同强化界面氧化机制的研究基本完成，掌握了渣金界面处氧离子对B、P氧化重构机制，揭示了精炼除磷过程基于FeO添加的氧势与氧离子协同调控机理，实现B和P的进一步同步去除；第二，动态条件下杂质在渣金两相界面传质与反应机制的研究基本完成，基于电渣精炼过程渣洗逆流操作，设计了硅合金液滴穿过渣层的渣洗滴落实验，通过创造渣金反应动态界面强化除B，建立了硅合金液滴滴落过程的运动规律计算模型，揭示了动态界面强化除杂机制；第三，合金凝固偏析过程杂质浓度梯度及其在近渣侧的偏析富集规律的研究基本完成，建立了Al-Si合金体系凝固偏析过程晶体硅结构与杂质去除之间构效关系，形成了硅合金固液界面形貌与硅晶体生长控制等界面结构调控方法，实现了金属杂质（Fe、Ti、Ca）与非金属杂质（B、P）的同步高效去除，两类杂质最高去除率分别达到98%和80%以上。