Roy Santanu, Wu Fei, Wang Haimeng, Ivanov Alexander S, Sharma Shobha, Halstenberg Phillip, Gill Simerjeet K, Milinda Abeykoon A M, Kwon Gihan, Topsakal Mehmet, Layne Bobby, Sasaki Kotaro, Zhang Yong, Mahurin Shannon M, Dai Sheng, Margulis Claudio J, Maginn Edward J, Bryantsev Vyacheslav S
Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd., Oak Ridge, TN 37830, USA.
Phys Chem Chem Phys. 2020 Oct 21;22(40):22900-22917. doi: 10.1039/d0cp03672b.
Molten salts are of great interest as alternative solvents, electrolytes, and heat transfer fluids in many emerging technologies. The macroscopic properties of molten salts are ultimately controlled by their structure and ion dynamics at the microscopic level and it is therefore vital to develop an understanding of these at the atomistic scale. Herein, we present high-energy X-ray scattering experiments combined with classical and ab initio molecular dynamics simulations to elucidate structural and dynamical correlations across the family of alkali-chlorides. Computed structure functions and transport properties are in reasonably good agreement with experiments providing confidence in our analysis of microscopic properties based on simulations. For these systems, we also survey different rate theory models of anion exchange dynamics in order to gain a more sophisticated understanding of the short-time correlations that are likely to influence transport properties such as conductivity. The anion exchange process occurs on the picoseconds time scale at 1100 K and the rate increases in the order KCl < NaCl < LiCl, which is in stark contrast to the ion pair dissociation trend in aqueous solutions. Consistent with the trend we observe for conductivity, the cationic size/mass, as well as other factors specific to each type of rate theory, appear to play important roles in the anion exchange rate trend.
在许多新兴技术中，熔盐作为替代溶剂、电解质和传热流体备受关注。熔盐的宏观性质最终由其微观层面的结构和离子动力学所控制，因此在原子尺度上理解这些性质至关重要。在此，我们展示了高能X射线散射实验，并结合经典和从头算分子动力学模拟，以阐明碱金属氯化物家族中的结构和动力学相关性。计算得到的结构函数和传输性质与实验结果相当吻合，这为我们基于模拟对微观性质的分析提供了信心。对于这些体系，我们还研究了不同的阴离子交换动力学速率理论模型，以便更深入地理解可能影响电导率等传输性质的短时间相关性。阴离子交换过程在1100K时发生在皮秒时间尺度上，速率按KCl < NaCl < LiCl的顺序增加，这与水溶液中的离子对解离趋势形成鲜明对比。与我们观察到的电导率趋势一致，阳离子的大小/质量以及每种速率理论特有的其他因素，似乎在阴离子交换速率趋势中起着重要作用。
