Molecular dynamics simulation of the Ni – FLiNaK interface: adsorption layers as origin of metal passivity

Abstract

The method of classical molecular dynamics was used to study the Ni (solid) – FliNaK (melt) phase separation boundary at temperatures of 800 K, 1000K , and 1200 K. An ab initio-based pairwise model is developed to describe the interactions that take place at the Ni – FLiNaK interface. It was shown that at temperatures of 800 K and 1000 K, lithium and fluorine ions are predominantly adsorbed on the nickel surface in the form of a two-dimensional ordered structure. Such a dense layer prevents the dissolution of nickel and the metal solid has no defects in the surface layer. However, at a temperature of 1200 K the structure of the adsorption layer is noticeably disturbed with the partial replacement of lithium ions by sodium ones. Along with higher temperature, this leads to the formation of point defects and degradation of the surface layers of the nickel crystal lattice.