(500d) Solid-Liquid Phase Equilibria of Salt Mixtures Using Molecular Dynamics Simulations

The use of alkali nitrate salt mixtures as heat transfer fluids in solar thermal power plants is limited by their relatively high melting point. Certain compositions of quarternary and higher dimensional mixtures of alkali and alkaline earth nitrates and nitrites have lower melting points. However, the high dimensionality of the search space makes it difficult to find lowest melting compositions. Molecular simulations offer an efficient way to screen for promising mixtures.

We have developed the capability to compute the minimum in liquid phase free energy and hence obtain an estimate of the eutectic point using molecular dynamics simulations. This method is based on alchemical transformations using thermodynamic integration. The method involves swapping idenitites of particles gradually and computing the free energy of such a transformation via thermodynamic integration.

Currently, we have computed the liquid phase free energy curves for all three binary mixtures of lithium, sodium and potassium nitrates as a function of composition. For all the three binary mixtures, our calculations of the minima in free energy are in close proximity to the experimental eutectic points. Results for ternary mixtures will also be presented.