Solid-liquid phase equilibria in the potassium + rubidium and the rubidium + caesium alloy systems

Thermal methods were used to determine with high precision the solid-liquid phase equilibria diagram for the potassium + rubidium and the rubidium + caesium systems. Both form solid solutions of continuously varying composition with the minima in the liquidus curves occurring at 307.00 K and 0.667 mol fraction rubidium in the K + Rb system and 282.85 K and 0.530 mol fraction caesium in the Rb + Cs system. In the K + Rb system, the liquidus and solidus points are close together, giving a very narrow temperature range for the two phase region. The freezing point minimum in this system, occurring at 0.667 mol fraction Rb, suggests the possible formation of a KRb2 intermetallic compound.