LiCl-KCl-CeCl_3熔盐结构与热力学的分子动力学模拟

Molecular Dynamics Simulation on the Structure and Thermodynamics of Molten LiCl-KCl-CeCl_3

采用分子动力学模拟的方法,研究了LiCl-KCl-CeCl_3熔盐中CeCl_3的结构性质和热力学,获得了LiClKCl-CeCl_3熔盐中密度与组成、密度与温度的关系数据;径向分布函数g_(Ce-Cl)(r)的第一个峰位置为0.259nm,Ce^(3+)对应的第一个配位数约为6.9;混合熔盐中计算数据与纯熔盐中数据的差异可以解释为混合熔盐中Ce^(3+)和Cl^-的相互作用比纯的CeCl_3更强;LiCl-KCl熔盐中Ce^(3+)的自扩散活化能为22.5 k J?mol^(-1),从活化能的本质来说,Ce^(3+)自扩散所需要克服的能垒要略低于U^(3+)(25.8 k J?mol^(-1))。当Ce^(3+)的摩尔分数从0.005增加到0.05时,其指前因子从31.9×10^(-5)cm^2?s^(-1)减少到21.8×10^(-5)cm^2?s^(-1);随着Ce^(3+)摩尔分数从0.005增长到0.05,单位体积内(忽略总体积的变化)Ce^(3+)的增加意味着其扩散阻力增加,而自扩散的能力降低,导致了指前因子的减小。

The structure and thermodynamics of CeCl_3 in molten LiCl-KCl-CeCl_3 mixtures were studied by molecular dynamics simulation. The relationship formulas of temperature and density, and composition and density were obtained. The first peak for the g_（Ce-Cl）（r） radial distribution function was located at 0.259 nm and the corresponding first coordination number of Ce^3＋was ~6.9. This inconsistency between molecular dynamics and experimental data could be attributed to the fact that our values were obtained for molten LiCl- KCl- CeCl_3 mixtures, in which the interaction between Ce^3＋and Cl^- was more powerful than that in pure molten CeCl_3.Regarding self-diffusion coefficients, the activation energy of Ce^3＋was 22.5 k J·mol^-1, which is smaller than that of U^3＋（25.8 k J·mol^-1）. Furthermore, the pre-exponential factors for Ce^3＋decreased from 31.9 ×10^-5 to 21.8 ×10^-5cm^2·s^-1 as the molar fraction of Ce^3＋increased from 0.005 to 0.05. This means that in the unit volume（ignoring the change of total volume）, the diffusion resistance of Ce^3＋increased, and the self-diffusion ability decreased, which resulted in a decrease of pre-exponential factors.