Thermal Transformations in the System NaF-CaF₂-AlF₃and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production

The details of ternary fluoride crystallization in the system NaF-CaF2-AlF3 have been specified. The phases NaCaAlF6, Na2Ca3Al2F14 and NaAlF4 have been obtained by high-temperature synthesis. Their thermal transformations have been studied using high-temperature X-ray diffraction. The occurring transformations can be considered in a quasibinary system CaF2-NaAlF4, where at T = 745°C - 750°C invariant equilibrium is established with the phases CaF2-NaCaAlF6-Na2Ca3Al2F14-(NaAlF4). The compounds NaCaAlF6 and Na2Ca3Al2F14 are stable in different temperature ranges. The phase NaCaAlF6 was fixed by rapid quenching from the melt. It decomposes at heating before 640°C yielding Na2Ca3Al2F14 and NaAlF4. Direct and inverse transformations between NaCaAlF6 and Na2Ca3Al2F14 occur in the bulk samples of the electrolyte. A thermal treatment procedure was proposed for the solid electrolyte sample to get a sample corresponding to the composition of the melt and providing high phase crystallinity for the purposes of quantitative X-ray phase diffraction analysis.

LiF－CaF_2，NaF－CaF_2和KF－CaF_2系熔体热力学参量及相图的计算

本文将ＤＣＡ模型应用于ＬｉＦ－ＣａＦ２，ＮａＦ－ＣａＦ２和ＫＦ－ＣａＦ２熔体，并假设在这些熔体中存在络合离子．利用已有的上述混合熔体量热和熔盐相图的实验数据估计了熔体模型中的参数，并计算了熔体的混合热力学参量及相图．计算结果与实验结果吻合较好．

NaF—CaF_2熔盐溶液结构的分子动力学模拟研究

使用分子动力学方法,研究了NaF—CaF_2熔盐体系给出了体系各离子间的偶对分布函数和各种健角几率分布,并在此基础上讨论了体系中的桥和络合模拟结果表明,Ca^(2+)离子周围的F^(-)离子未形成四面体配位,出现象CaF_4^(2-)这样小的络合原子团的可能性不大Ca^(2+)离子周围F^(-)离子排布的一种可能的结构是3个Ca^(2+)离子通过F^(-)离子桥联成一个正三角形,正三角形中心上下各有一个F^(-)离子,每个Ca^(2+)离子在三角形外侧还各有2个F^(-)