Interdiffusion Measurements in Fused Alkali Nitrates by Wave-Front-Shearing Interferometry

Interdiffusion coefficients in molten alkali nitrate systems have been measured by recording the phase variations introduced on an initially plane wave front when passing through a diffusion vessel. The recording of the path differences is performed with a wave-front-shearing interferometer giving a high degree of accuracy. Two different methods have been used to initiate bottom layer diffusion experiments, one of which has been developed in the course of this work. The interdiffusion studied here has been that of rubidium and cesium ions and in some cases that of sodium and potassium ions diffusing into the pure melts of lithium nitrate, sodium nitrate, and potassium nitrate. The diffusion coefficients have been measured over a temperature range of some 100°C above the melting point.