FPMD studies on the microstructures and transport properties of molten MgCl2-NaCl-KCl with addition of active metals

Abstract

A purification protocol of molten MgCl2-NaCl-KCl (MNK) by adding active metals has been proposed to reduce the corrosion of alloy materials in the application of generation III concentrating solar power plants. In this work, the ionic transport properties and micro structural characteristics of metals (Mg, Na, and K) and molten MNK mixtures (metal-MNK) are investigated at 723 K by first principles molecular dynamics (FPMD) simulations. According to the evolution of total energy, the Mg-MNK is the most stable mixture, while the Na-MNK mixture has larger energy fluctuations resulting in a higher specific heat capacity. Studies have shown that the small amount of metal existing in the molten MNK has almost no effect on the ionic diffusion order, but total diffusion coefficients and thermal conductivities of metal-MNK mixtures are improved. Meanwhile, the intensity of diffracted light of molten MNK is weakened by metals, and the microstructures of molten MNK added with alkali metals are more susceptible than that with metallic Mg by analyzing the total and partial static structure factors. Furthermore, the intermediate range orders of metal-MNK are demonstrated, especially for Mg-Mg pairs hinting the formation of the Mg2+-void-Mg2+ structure or Mg2+-centered clusters. Overall, the FPMD results deeply elaborate the dynamic interactions of molten MNK and metallic particles, which give insights for the development of salt purification and corrosion inhibition technology.