Viscosity and Density in Molten BeF2–LiF Solutions

Abstract

The viscosity of the molten salt system, BeF2–LiF, was determined with a coaxial‐cylinder viscometer. The concentration range studied was 36–99 mole % BeF2, each composition being measured over a 200° temperature interval within over‐all limits of 376°–967°C. The viscosity isotherms exhibit an exponential decrease in viscosity with increasing LiF concentration; the decreases are attributed to the rupturing of fluoride bridges in the BeF2 network structure. Each composition displayed Arrhenius behavior ( E η , energy of activation for viscous flow, was independent of temperature). E η decreased with LiF concentration in a way that paralleled the decreases in the analogous systems, SiO2–alkaline‐earth oxide. Densities were measured between 50 and 100 mole % BeF2. From these measurements and other density determinations in BeF2–LiF, it was found that the molar volumes were additive. Volume expansivity, however, increases markedly with increasing LiF concentration. The decrease of E η with LiF content in this system is correlated with an increase in volume expansivity; for the composition range 100–70 mole % BeF2, E η is linear with the reciprocal of expansivity.