Molecular dynamics simulations of the local structures and thermodynamic properties on molten alkali carbonate K2CO3

Abstract

Molten carbonate salts have received particular attention for high-temperature thermal energy storage and heat transfer applications due to desirable thermal characteristics, such as wide operating temperature range, low causticity and excellent thermal stability. In this study, molecular dynamics (MD) simulations were performed on molten alkali carbonate K2CO3 based on an effective pair potential model, a Born-Mayer type combined with a Coulomb term. The radial distribution functions (RDF) and coordination number curves of the molten salt were characterized to explore the temperature dependences of macroscopic properties from microscopic view. The results suggest that the distance between K2CO3 particles is getting larger with temperature increasing, resulting in the increase of molar volume and the diminished ability of resistance to shear deformation and heat transfer by vibration between ions. Besides, it can be concluded that the structure of CO32− is inferred reasonably to be ortho-triangular pyramid from the comprehensive analysis of local structures including the angular distribution functions (ADF). Moreover, the thermodynamic properties were simulated in detail from 1200 to 1600 K including the density, thermal expansion coefficient, specific heat capacity, sheer viscosity, thermal conductivity and ion self-diffusion coefficient, which was hard to be measured from experiments under high-temperature extreme conditions. All the simulation results are in satisfactory agreement with available experimental data with high accuracy, and the minimum simulation error is as low as 1.42%.