Ultrasonic Velocity and Absorption in Liquid Mixtures of K–Rb and Na–Cs

Abstract

Ultrasonic absorption and velocity measurements have been made in potassium–rubidium and sodium–cesium alloys at temperatures from 25 (or the liquidus points) to 250°C. It has been found that the potassium–rubidium system behaves as an ideal liquid mixture. For both potassium–rubidium and sodium–cesium alloys, Rao's constant and Wada's constant calculated from measured velocity data vary linearly with concentration and are temperature independent to within 2% over the temperature range 100–200°C. The ultrasonic measurements in the sodium–cesium system suggest a substantial molecular association and the absorption peak at 75 at.% sodium concentration is attributed to a molecular association of the form of 3Na+Cs⇋Na3Cs. The Na3Cs has been identified as the critical composition of an assumed submerged miscibility gap under the inflection point of the melting-point curve.