Transpiration vapour pressures and activities in the molten salt systems ZnCl₂ + NaCl and ZnCl₂ + KCl

Abstract

Vapour pressure measurements were made by a transpiration method for molten zinc chloride and molten mixtures of this salt with sodium and potassium chlorides, respectively. Activities of zinc chloride in the mixtures were calculated and from these values, those of the alkali chloride were calculated by Gibbs-Duhem integration. For this purpose a convenient computer method has been devised. Although the large deviations of activity and activity coefficients qualitatively support independent evidence that complex ions are formed in these systems, the results cannot quantitatively be explained using a calculation due to Braunstein in terms of interactions in the melt to form complex ions of a unique type, e.g. ZnCl₃- or ZnCl₄²- etc. This indicates that the departure from ideal behaviour needs to be explained by a more detailed theory.