Zhang Jing, Fuller Jon, An Qi
Department of Chemical and Materials Engineering, University of Nevada-Reno, Reno, Nevada 89557, United States.
J Phys Chem B. 2021 Aug 12;125(31):8876-8887. doi: 10.1021/acs.jpcb.1c03748. Epub 2021 Jul 30.
Eutectic LiCl-KCl molten salt is often used in molten salt reactors as the primary coolant due to its high thermal capacity and high solubility of fission products. Thermophysical properties, such as density, heat capacity, and viscosity, are important parameters for engineering applications of molten salts but may be significantly influenced by metal solutes from corrosion of metallic structural materials. The behavior of the LiCl-KCl eutectic composition is well researched, yet the effects on these properties due to chlorocomplex formation from metals dissolved in the salt are less well known. These properties are often difficult to accurately measure from experimental methods due to the issues arising from the dissolved species, such as volatility. Here, we applied a combination of quantum mechanics molecular dynamics (QM-MD) and deep machine learning force field (DP-FF) molecular dynamics simulations to investigate the structural and thermophysical properties of LiCl-KCl eutectic as well as the influence of dissolved transition metal chlorocomplexes NiCl and CrCl at low concentrations. We find that the dissolution of Ni and Cr in the LiCl-KCl system forms the local tetrahedral (NiCl) and octahedral (CrCl) chlorocomplexes, respectively, which do not have a significant impact on the overall liquid salt structures. In addition, the thermodynamic properties including diffusion constant and specific heat capacity are not significantly affected by these chlorocomplexes. However, the viscosity significantly increases in the temperature range of 673-773 K. This study thus provides essential information for evaluating the effects of dissolved metals on the thermophysical and transport properties of molten salts.
共晶LiCl-KCl熔盐由于其高热容量和裂变产物的高溶解度，常用于熔盐反应堆作为主冷却剂。密度、热容量和粘度等热物理性质是熔盐工程应用的重要参数，但可能会受到金属结构材料腐蚀产生的金属溶质的显著影响。LiCl-KCl共晶成分的行为已得到充分研究，但对于溶解在盐中的金属形成氯配合物对这些性质的影响却知之甚少。由于溶解物种引起的问题，如挥发性，这些性质通常很难通过实验方法准确测量。在这里，我们应用量子力学分子动力学（QM-MD）和深度机器学习力场（DP-FF）分子动力学模拟相结合的方法，研究LiCl-KCl共晶的结构和热物理性质，以及低浓度下溶解的过渡金属氯配合物NiCl和CrCl的影响。我们发现，Ni和Cr在LiCl-KCl体系中的溶解分别形成了局部四面体（NiCl）和八面体（CrCl）氯配合物，它们对整个液态盐结构没有显著影响。此外，包括扩散常数和比热容在内的热力学性质不受这些氯配合物的显著影响。然而，在673-773K的温度范围内，粘度显著增加。因此，本研究为评估溶解金属对熔盐热物理和传输性质的影响提供了重要信息。
