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

Area of Science:

• Materials Science
• Nuclear Engineering
• Computational Chemistry

Background:

• Molten salt technologies are experiencing a resurgence for nuclear reactors.
• Accurate thermodynamic models require understanding atomistic behavior of molten salts.
• Predicting molten salt mixtures' structure is key for reactor development.

Purpose of the Study:

• To elucidate the molten structure of magnesium chloride (MgCl2) and potassium chloride (KCl) mixtures.
• To investigate the atomistic-level behavior of these salts under various conditions.
• To provide insights for improving thermodynamic models of molten salt systems.

Main Methods:

• High-energy X-ray scattering experiments were conducted.
• Molecular dynamics simulations were employed.
• Computational analysis was performed to understand structural correlations.

Main Results:

• Potassium chloride (KCl) exhibits simple charge alternation.
• Magnesium chloride (MgCl2) and its mixtures show complex correlations, including intermediate-range order.
• Formation of Cl--decorated Mg2+ chains and correlations between these chains were observed.
• Mg2+ coordination structure revealed multiple accessible states with distinct geometries.

Conclusions:

• The complex structure of MgCl2-KCl mixtures goes beyond simple charge alternation.
• Intermediate-range order is linked to correlations between Mg2+ chains.
• The coordination environment of Mg2+ is more intricate than previously understood.