Phase Changes and Electrical Conductivity of Concentrated Lithium—Ammonia Solutions and the Solid Eutectic

Abstract

The electrical conductivities of concentrated solutions of lithium in ammonia have been measured over the temperature range 65° to 300°K by both conventional dc techniques and electrodeless techniques. In the liquid phase, conductivities ranged from 400 to 15 000 Ω⁻¹·cm⁻¹ at 240°K; the temperature coefficient of conductivity varied from +1.0% deg⁻¹ to zero. Phase changes were indicated by discontinuities in either the conductivity or the temperature derivative of conductivity. No sign of a maximum in the melting‐point‐vs‐concentration curve near the tetra‐amine lithium [Li(NH₃)₄] concentration was found. The eutectic was found to be 89.6°±0.3°K. The conductivity of the solid was 6.7 times as large as that of the liquid at the melting point. In addition to phase changes in the liquid, two solid‐phase changes were observed; one at 82°K and the other at 69°K. Conductivities in the solid were decreasing functions of the temperature in each solid phase, yet were higher in the high‐temperature solid phases. The highest conductivity observed was 90 000 Ω⁻¹·cm⁻¹ (at 83°K). The solid does not behave as do the eutectics of sodium—ammonia or potassium—ammonia solutions. A comparison with other metal—ammonia solutions is made.