Elucidating Ionic Correlations Beyond Simple Charge Alternation in Molten MgCl₂–KCl Mixtures

Abstract

The development of technologies for nuclear reactors based on molten salts has seen a big resurgence. The success of thermodynamic models for these hinges in part on our ability to predict at the atomistic level the behavior of pure salts and their mixtures under a range of conditions. In this letter, we present high-energy X-ray scattering experiments and molecular dynamics simulations that describe the molten structure of mixtures of MgCl2 and KCl. As one would expect, KCl is a prototypical salt in which structure is governed by simple charge alternation. In contrast, MgCl2 and its mixtures with KCl display more complex correlations including intermediate-range order and the formation of Cl–-decorated Mg2+ chains. A thorough computational analysis suggests that intermediate-range order beyond charge alternation may be traced to correlations between these chains. An analysis of the coordination structure for Mg2+ ions paints a more complex picture than previously understood, with multiple accessible states of distinct geometries.

X-ray scattering reveals ion clustering of dilute chromium species in molten chloride medium

“…What may at rst seem counterintuitive, the observed shrinking of the cation-anion closecontact distances is quite typical for inorganic salts and is associated with a decrease in the coordination numbers on melting, oen leading to shorter nearest-neighbour bond lengths than those observed in the solid state. 25,[28][29][30] The characteristically broad peaks in D(r) at the highest temperature associated with the liquid state make the interpretation of scattering results difficult, requiring more sophisticated procedures in the data analysis.…”

“…The MgCl 2 (anhydrous, >98%) was purchased from Sigma-Aldrich and further puried by fractional distillation described previously. 25,29 The KCl (anhydrous, 99.999%) and CrCl 3 (anhydrous, 99.9%) were both purchased from Sigma-Aldrich and used for experiments as received. Great care was taken so that the salts were maintained under a vacuum or inert atmosphere for the duration of sample preparation.…”

DFT Accurate Interatomic Potential for Molten NaCl from Machine Learning

“…The ionic conductivity for a symmetric electrolyte may be estimated from the Nernst-Einstein equation expressed as (8),…”

Molecular Dynamics Simulations of Molten Magnesium Chloride Using Machine‐Learning‐Based Deep Potential

“…[ 10 ] An effort was made by Wu et al. [ 11 ] to address this issue, who developed an interatomic potential for MgCl 2 ‐KCl binary salt base on the polarizable ion model (PIM). [ 12 ] However, fitting parameters of the PIM are usually a daunting task that is very time consuming and requires tremendous expertise.…”