Molecular dynamics simulation of homogeneous nucleation of melting in superheated sodium crystal

Abstract

The melting process and nucleation behaviour of sodium (Na) crystals are crucial for the frozen start-up of high-temperature sodium heat pipes and the working performance of molten sodium batteries. Equilibrium melting and the homogeneous nucleation of melting in superheated Na crystal are studied by molecular dynamics simulation. The thermodynamic properties and nucleation of Na crystal during the heating process are investigated by the characterization of the density, radial distribution function (RDF), self-diffusion coefficient (D), nucleation rate (Ihom), etc. Firstly, the equilibrium melting of Na crystal is simulated and verified by the single-phase method. Results show that Na's equilibrium melting temperature, densities, and RDF simulated match well with experimental values, demonstrating that the EAM/FS potential is suitable for studying the melting processes of Na crystal. Secondly, the calculated D of liquid Na increases approximately linearly with rising temperature within 440 K∼540 K and fits with experimental data well. The activation energy for the diffusion of Na obtained by linear fitting is 1.6406·10-20 J, which agrees well with the observed values. Finally, the homogeneous nucleation of melting in superheated Na crystal is analyzed. It is found that the Ihom of melting in superheated Na crystal rises exponentially with increasing temperature, which is consistent with the prediction in literature. The kinetic stability limit of superheated Na crystal is 468.3 K, and the relation between the Ihom of melting in superheated Na crystal and temperature is given. The physical properties and nucleation theory of Na crystal simulated during the melting can provide theoretical support for sodium's heat and mass transfer-related applications, such as sodium heat pipes and sodium batteries.