Molten Salt Material

Background

Molten salts are promising thermal energy storage materials. The structures and thermophysical properties of pure molten halide salts are essential for complementing the basic thermodynamic data and developing new types of high-performance multi-component halide molten salts. Although the thermophysical properties of multi-components molten halide salts can be roughly estimated by additive principle and other empirical methods without any experiments, the corresponding properties of individual components are momentous in exploiting new compounds. Furthermore, microstructures of molten halide salts need to be simulated and measured to elucidate the evolution law of thermophysical properties under different temperatures. Unfortunately, people could not measure all the thermophysical properties by experiment so far. As an alternative, molecular simulations are proposed and used to predict thermophysical 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 () ). 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. ()

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.