Heats of Mixing in Binary-Liquid—Alkali-Metal Mixtures

Abstract

The enthalpies of mixing in all the binary-liquid alloys formed among the alkali metals sodium, potassium, rubidium, and cesium have been measured by reaction calorimetry at 111°±2°C. All systems except rubidium—cesium show positive enthalpies of mixing. There is a tendency for the mixing enthalpies to become more positive and also more unsymmetrical as the two metals become more separated in the periodic table. A comparison of the new enthalpy data with reported phase-diagram information indicates that the three liquid alloys which contain sodium all exhibit nearly ideal entropies of mixing. For potassium—rubidium, potassium—cesium, and rubidium—cesium, the new heat data, combined with the available phase diagrams, permit estimates to be made of the excess free energies of mixing in the solid solutions.