Molten Salt Material

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Background

Molten salts are promising thermal energy storage(TES)materials. Thermophysical properties of molten halide salts closely related to device and system design should be determined accurately covering the entire operating temperature range. Although multi-components salts are actually used, structural and thermophysical properties of pure salts are essential for complementing the basic thermodynamic data and developing new type halide materials. Moreover, thermophysical properties of multi-components salts can be roughly estimated without any experiments by additive principle7 and other expirical methods8 where the corresponding properties of individual components are needed in case someone has no experimental conditions. Furthermore, in order to elucidate evolution law of thermophysical properties of molten halide salts with temperature, microstructures should be either measured or simulated. Unfortunately, to our best knowledge, some thermophysical properties are hard to measure by experiment so far. As an alternative, molecular simulations have been proposed and used to predict thermal and transport properties over the entire operating temperature range.

Results

In this work, we use high-throughput molecular dynamics (HT-MD) to compute thermophysical properties and microstructure information of molten halide salts in an exhaustive manner. Thirty MXn systems are simulated in total. Of which cations cover majority of group I and II and minority of transition metal elements, lanthanides and actinicles while anions cover majority of halogen (see Fig. 1 (https://github.com/pangchq/Molten-Salt-Simulation-Toolkit/raw/master/Fig.1.jpg) ). Thermophysical properties (~2,500) including constant pressure specific heat capacity, density, thermal expansion coefficient, self-diffusion coefficient, and viscosity as well as microstructure information including partial radial distribution function and coordination curve under atmospheric pressure condition are obtained with respect to different temperature. These calculations are automated using our own code, Molten Salt Simulation Toolkit (MSST), developed at the National Supercomputer Center in Guangzhou. MSST is built upon Tianhe-2 high-performance computing (HPC) clusters and can automatically handle input/output processing of CP2K molecular dynamics and manage job submission to cluster queues. Fig. 2 shows the workflow used to implement the HT-MD. (https://raw.githubusercontent.com/pangchq/Molten-Salt-Simulation-Toolkit/master/Fig.2.jpg)

Conclusions

The simulated constant pressure specific heat capacity, density, viscosity, thermal expansion coefficient, self-diffusion coefficient, and microstructures are in good agreement with experimental values.

Usage notes

We recommend usage of the fitting formula of thermophysical properties in the database as some viscosities of simulations near the melting point are not very accurate due to the reason mentioned above. Researchers who concern the precision and would like to obtain more accurate results can rerun the code (https://github.com/pangchq/Molten-Salt-Simulation-Toolkit/) and increase the simulation time.