Fusion Science and Technology / Volume 41 / Number 2 / March 2002 / Pages 141-150
The pressures of the vapor species in equilibrium with Flibe at ~600°C are determined from work by Buchler and Stauffer and by Baes and coworkers. The former authors show that the principal vapor species are BeF2(g) and LiBeF3(g). The measurements and the theoretical model of Baes provide accurate values of the activity coefficient of BeF2 in Flibe. When combined with the vapor pressure of pure BeF2, the equilibrium pressure of BeF2 is determined as a function of melt composition and temperature. The activity coefficient of LiF is not measured, but it is obtained by application of the Gibbs-Duhem equation to the measured activity coefficient of BeF2. Thus, the partial pressure of LiF(g) is also known. The pressure of the mixed dimer LiBeF3 is calculated from the gas phase equilibrium for the formation of the dimer from the two monomers, with the equilibrium constant given by Buchler and Stauffer. The vapor pressure at 600°C extrapolated from high-temperature Oak Ridge National Laboratory data is ~60% higher than the predicted values.