LiCl-KCl-CeCl3熔盐结构与热力学的分子动力学模拟

采用分子动力学模拟的方法,研究了LiCl-KCl-CeCl₃熔盐中CeCl₃的结构性质和热力学,获得了LiCl-KCl-CeCl₃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, Ce³⁺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Ce³⁺和Cl^-的相互作用比纯的CeCl₃更强; LiCl-KCl熔盐中Ce³⁺的自扩散活化能为22.5 kJ·mol^-1,从活化能的本质来说, Ce³⁺自扩散所需要克服的能垒要略低于U³⁺(25.8 kJ·mol^-1)。当Ce³⁺的摩尔分数从0.005增加到0.05时,其指前因子从31.9×10^-5 cm²·s^-1减少到21.8×10^-5 cm²·s^-1;随着Ce³⁺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)Ce³⁺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。

Molecular Dynamics Simulation on the Structure and Thermodynamics of Molten LiCl-KCl-CeCl3

The structure and thermodynamics of CeCl₃ in molten LiCl-KCl-CeCl₃ 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 Ce³⁺ 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-CeCl₃ mixtures, in which the interaction between Ce³⁺ and Cl^- was more powerful than that in pure molten CeCl₃. Regarding self-diffusion coefficients, the activation energy of Ce³⁺ was 22.5 kJ·mol^-1, which is smaller than that of U³⁺ (25.8 kJ·mol^-1). Furthermore, the pre-exponential factors for Ce³⁺ decreased from 31.9×10^-5 to 21.8×10^-5 cm²·s^-1 as the molar fraction of Ce³⁺ increased from 0.005 to 0.05. This means that in the unit volume (ignoring the change of total volume), the diffusion resistance of Ce³⁺ increased, and the self-diffusion ability decreased, which resulted in a decrease of pre-exponential factors.