Miscibility of Molten Lithium and Sodium

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Abstract
Results of a calculation from first principles of the change on mixing of the electronic energy for seven molten lithium-sodium mixtures are presented. These results, along with the assumption of an ideal entropy of mixing, are used to predict the miscibility curve which forms the boundary on the phase diagram between the region of a single homogeneous melt and the region of two separated melts. Favorable agreement with experiment is obtained. Calculated energies for the lithium-sodium system are compared with energies previously found for the sodium-potassium system, a system for which the melts are miscible in all concentrations. This comparison reveals that it is chiefly the change on mixing of the average kinetic energy of the electrons which is responsible for the lithium-sodium miscibility gap. For the lithium-sodium system, the kinetic energy is found to increase on mixing, while for sodium-potassium and other liquid binary alkali mixtures for which no gap exists, the kinetic energy was found to decrease. In all other respects the mixing behavior of lithium and sodium seems to follow the general pattern previously established for other molten binary alkali mixtures.