Study on the Microstructure and Thermal Transport Properties of Magnesium Chloride-Based Molten Salts Using Machine Learning Approaches

Abstract

Molten chloride eutectics, particularly those based on MgCl₂, have attracted considerable interest for their applications in thermal storage and heat transfer, benefiting from their high thermal stability and cost-effectiveness. This comprehensive study employs deep potential molecular dynamics (DPMD) simulations, integrating principles from first-principles calculations, classical molecular dynamics, and machine learning, to systematically explore the interrelationship between structural features and thermophysical properties of molten MgCl₂–NaCl (MN) and MgCl₂–KCl (MK) eutectics across the temperature spectrum of 800–1000 K. The analyses extend to a broader temperature range, employing DPMD to accurately replicate densities, radial distribution functions, coordination numbers, potential mean forces, specific heat capacities, viscosities, and thermal conductivities with enhanced scale and temporal depth (5.2 nm and 5 ns, respectively). Notably, the superior heat capacity of molten MK is attributed to the stronger Mg–Cl bond forces, whereas the enhanced heat transfer capabilities of molten MN are ascribed to its higher thermal conductivity and reduced viscosity, which in turn result from diminished Mg–Cl interactions.

Additionally, the role of magnesium as a corrosion inhibitor in molten MgCl₂–NaCl–KCl (MNK) is investigated, elucidating its impact on the structure and thermodynamics of molten MgCl₂–NaCl–KCl (MNK) eutectic. A pivotal discovery is the Mg-induced alteration in the coordination environment, effectively reducing the coordination number and weakening the cation-Cl bonds. This transition, particularly beyond a critical magnesium concentration (~0.79 mol%), leads to a pronounced destabilization in coordination structures, impacting the thermophysical behaviours of molten salts. Specifically, the addition of magnesium modifies the heat capacity and viscosity, with significant changes observed at a concentration of 2.33 mol% Mg. This dual-focus investigation not only delineates the molecular intricacies governing the thermal and flow properties of molten chlorides but also extends the application potential of DPMD simulations, providing vital insights into the formulation and optimization of new molten salts with tailored properties for advanced thermal management systems.

Date of Award	9 Sept 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Zhongfeng TANG (External Supervisor) & Ruiqin ZHANG (Supervisor)