On the Surface Tension of Pure Molten Alkali Halides

摘要

In the present paper the detailed structural - thermodynamic model for the surface tension of pure molten alkali halides has been developed based on the (M~+-X~-) associates. It has been shown that the empirical average slope of 0.06 between the surface tension and the heat of evaporation (divided by the molar surface area) can be divided into three independent quantities. It has been shown as well that a 'zero-term' of about 29 mJ/m~2 is needed to describe surface tension values properly, due to the anti-shrinkage effect, while the (M~+-X~-) associate is transferred from the bulk of the melt to the liquid/gas interface. From the correlations found in this paper, the heat of formation of gaseous NaI was estimated (missing from major thermochemical tables) as Δ_fH~0(NaI, g, 298 K, 1 bar) = -94 +- 13 kJ/mol.