NdF_3-LiF二元系相图测定和计算的再研究

Determination and Calculation of NdF_3-LiF Binary System

氟盐-氧化钕熔盐电解是目前稀土金属钕工业生产的主要方法,优化工艺的确定、产品质量的保证以及更好综合性能熔盐组成的选择直接有赖于NdF3-LiF二元系相图的分析和应用。为了获得精确的NdF3-LiF二元系相图和热力学信息,采用差热分析法（DTA）测定不同配比NdF3-LiF二元熔盐体系的初晶温度,同时通过扫描电子显微镜（SEM）表征方法观察确认初晶温度的准确性,并依据DTA测试结果绘制出实验相图;再根据CALPHAD法利用FactSage软件中的Compound、Solution、Equilib、OptiSage和Phase diagram等模块优化计算最终确定出NdF3-LiF二元系的相图,发现实际的NdF3-LiF熔盐体系符合正规溶液;在1000～1100℃下,LiF的活度系数趋于稳定,而NdF3的活度系数随温度升高有明显增多的趋势,其电离形成离子的多寡与电解过程密切相关。另外,用计算机处理拟合出相图中NdF3-LiF二元系初晶温度的数学模型,讨论提出了工业熔盐电解钕适合的配比为w（NdF3）∶w（LiF）=10∶1或者是比之略小的w（NdF3）∶w（LiF）=9∶1。

Electrolysis of Nd2O3 in fluoride melts was the main process for the production of neodymium metal in recent industry. Determination of the optimal production technology,the guarantee of product quality and better comprehensive performance of molten salt selection depend on the utilization and analysis of NdF3-LiF binary system fusibility figure directly. In order to obtain the precise NdF3-LiF binary phase diagram and thermodynamic information,differential thermal analysis（ DTA） was used to determine the DTA curve of NdF3-LiF binary system with different ratios,from which the liquidus temperatures of the binary system at the ratio can be analyzed,and at the same time characterizing method of scanning electron microscopy（ SEM） was used to verify the exactness of the experiment,and the experimental phase diagram was drawn out on the basis of DTA test results. Then,the calculated phase diagrams can be obtained according to the CALPHAD method with the Compound,Solution,Equilib,OptiSage and Phase diagram module optimization in FactSage; it was found that the actual NdF3-LiF molten salt system accords with the regular solution. Under 1000 ～ 1100 ℃,the activity coefficient of LiF tended to be stable,and NdF3 activity coefficient which varied with temperature had obvious increasing trend,and the ionized form was closely related to the amount of ions and the electrolytic process. In addition,Computer processing was used to fit the mathematical model of liquidus temperature in phase diagram,and it was put forward that the suitable mixture ratio of industrial fused salt electrolysis neodymium was w（ NdF3） ∶ w（ LiF） =10∶1 or slightly smaller ratio w（ NdF3） ∶ w（ LiF） =9∶1.