Surface Tensions of Molten Salt Mixtures

It is always found that the surface tension of a mixture of molten salts lies below the mean of the surface tensions of the pure components, weighted by mole fractions. Part of this effect is certainly due to the well-known fact that the composition near the surface is enriched in the component of lower surface tension. We show that an effect of the long-range forces, present for fluids involving Coulombic interactions, is of greater importance. The effect is due to the electroneutrality constraint on the distribution functions. As we show by separate calculations, both effects must be considered to obtain good agreement with experimental results for alkali halide melts.