Density Measurements in the Molten ZnCl₂-MCl (M=Li, Na, K, Cs) Binary Systems

Abstract

Densities of the molten ZnCl₂-MCl (M=Li, Na, K, Cs) binary systems on the alkali chloride-rich side have been measured by means of the Archimedean method with two spherical bobs of different sizes made of platinum. From the experimental results obtained in the present work and the density data on the ZnCl₂-rich side obtained by Bloom and Weeks with a pycnometer, the composition dependences of the molar volume, excess molar volume, partial molar volume and thermal expansion coefficient of these melts were calculated for the whole composition range.
The excess molar volume and the partial molar volume of these binary melts exhibit very complicated behavior with the changes in both temperature and composition. These results may be attributed to the peculiar properties of molten ZnCl₂.
The thermal expansion coefficients increase markedly with increasing content of MCl in the composition range of 0∼50 mol%MCl and change monotonously in the composition range of 50∼100 mol%MCl. This fact implies that these melts are associated liquids on the ZnCl₂-rich side and become ionic ones in the composition range of more than 50 mol%MCl.
The change of the species involved in these melts is briefly inferred.