稀土金属蒸馏提纯过程中杂质的运动行为及分布规律研究

Ultra-pure rare earth metals have been widely used in high technique field, which is a key raw material of higher-performance magnetostrictive materials, luminescent materials, superconducting materials, and etc. Vacuum distillation is an important method for purifying rare earth metals, most previous studies used separation coefficient of impurity to judge whether the impurity can be separated or not, however, there is few report on behaviors of impurity in liquid metal and quantitative analysis of impurity in distillate, aiming at above problems, a mathematical model is proposed based on the redistribution theory of solute in solidification front. In present project, a combined research method of theoretical calculation, numerical simulation and experiment has been used; the diffusion coefficients of impurity in liquid dysprosium, including volatile impurity and non-volatile impurity, are measured by capillary-pool method, activity coefficient of impurity is theoretically calculated by molecular interaction volume model, temperature filed at evaporate surface is calculated by numerical simulation, and the vacuum distillation experiments are conducted by ultra-high vacuum distillation furnace, the concentration of impurities in the remained liquid metal and distillate are determined by chemical analysis method, and the distribution rules of impurities in liquid metal are discussed; base on the redistribution theory of solute in solidification front, the distribution function of impurity in distillate is founded, and the effect rules of diffusion coefficient and activity coefficient of impurity, distillation temperature, experimental process, distillation velocity on impurity distribution function are researched, and it will provide theoretical guidance for the vacuum distillation purification and the preparation of ultra-pure rare earth metals.

超高纯稀土金属在高新技术领域应用广泛，是获得高性能磁性、发光、超导等稀土功能材料的关键原材料。真空蒸馏是稀土金属重要的提纯方法，针对目前采用杂质分离系数定性判断杂质元素能否被分离，而对杂质的运动行为以及在液态金属和蒸馏产物中的分布缺乏定量研究的现状，提出了利用凝固前沿溶质的再分布理论建立蒸馏产物中杂质分布的数学模型；通过毛细管-熔池法测定稀土金属镝中易挥发及蒸气压较低的两类金属杂质的扩散系数，分子相互作用体积模型理论计算杂质元素的活度系数，数值模拟获得蒸发面的温度分布，并开展超高真空蒸馏提纯实验，化学分析存留液态金属及蒸馏产物中的杂质含量，探讨液态金属内部杂质元素的分布以及影响规律，建立蒸馏产物中杂质分布的数学模型，揭示杂质在液态金属中的扩散系数和活度系数、蒸馏温度、蒸馏进程、蒸馏速度对杂质分布的影响规律，为稀土金属真空蒸馏提纯以及超高纯稀土金属的制备提供理论指导。

超高纯稀土金属在高新技术领域应用广泛，是获得高性能磁性、发光、超导等稀土功能材料的物质基础。本项目重点研究稀土金属镝蒸馏提纯过程中的温度分布，稀土金属镝中易挥发及蒸气压较低的两类金属杂质的在液态金属中的扩散系数、传质系数、活度系数及其温度影响规律，开展真空蒸馏实验，研究杂质在蒸馏产物中的分布规律，建立蒸馏产物中杂质分布的数学模型。首先建立了二维轴对称传热模型，并根据金属镝的饱和蒸气压，确定了稀土金属蒸气的热物性参数，获得了真空蒸馏提纯过程中，液态金属、蒸发面及金属蒸气的温度分布；采用理论计算方法，计算了液态稀土金属镝中常见金属杂质的活度系数和扩散系数，并确定温度、浓度对扩散系数的影响规律；对杂质挥发过程进行动力学分析，计算了液相传质及界面挥发的杂质传质系数，确定饱和蒸气压较低的杂质的限制性环节为界面挥发，易挥发性杂质的限制性环节为液相传质，并开展实验研究，测定坩埚内残留稀土金属中杂质的浓度分布，对计算结果进行验证；开展真空蒸馏实验，研究杂质在蒸馏产物的分布规律，提纯修正的分离系数，建立两类杂质在蒸馏产物中的分布函数。本项目的成功实施将有丰富稀土金属提纯理论，为稀土金属真空蒸馏提纯工艺技术优化以及超高纯稀土金属的制备提供理论指导。