Composition-dependent microstructure evolution in liquid MgCl2-KCl: A first-principles molecular dynamics study

摘要

The structural evolution of MgCl2-based materials is of considerable interest due to their current and potential applications in numerous technologies, such as electrolyte in magnesium electrolysis, secondary coolant for high-temperature reactors, and a new generation heat transfer fluid for concentrated solar power systems. However, their intrinsic feature is poorly understood and difficult to obtain with experimental techniques. In this work, first-principles molecular dynamics simulations (FPMD) are adopted to investigate the structural evolution of molten MgCl2-KCl fused salt. Examination of the radial distribution function, probability distribution of coordination numbers and bond angle distribution of the melts reveals that the local geometry of the Mg converts from mainly tetrahedral to a distorted octahedral with one-two anion vacancies as the concentration of MgCl2 is increased. Accompanied by this structural change, there arc also corresponding variations in the stability and dynamics of the system. Further analysis of the stability and the lifetime of the Mg-Cl bond indicate that the coordinated Cl- anions around Mg2+ cations are more dynamic in MgCl2 richer compositions. Moreover, this study shows that the addition of MgCl2 will inhibited the formation of isolated structural units and promote the extension of Mg chains. In conclusion, the simulations successfully reproduce the structural features of MgCl2-KCl melts and highlight the application prospects of FPMD simulations in revealing the local structure of molten salts. (C) 2020 Elsevier B.V. All rights reserved.