Surface tension calculations for molten salts: Critique and modification of the Fowler model

Abstract

The Fowler model, the ubiquitous first approximation for calculations of surface properties, allows the calculation of surface tension and surface energy in terms of properties of the bulk fluid. It is here applied to a two-component fluid with Coulombic forces (molten salts), the bulk fluid being described by the generalized mean spherical approximation. In sharp contrast to universal experience with simple fluids, totally unreasonable results are attained. The situation is not improved by going to a more realistic model of the bulk fluid or by modifying the one-particle part of the pair distribution function. Inconsistencies in the Fowler model are discussed. Concluding that the difficulty lies in the violation of the electroneutrality condition demanded by the Coulombic forces, we give a simple method to guarantee its fulfillment. While hardly complicating the calculation, it gives drastic improvement in both surface tension and surface energy.