Vapor pressure measurements on mixtures of LiF, NaF, and BeF2

Abstract

Knowledge of the vapor pressure of fluoride salts is necessary in order to assess the suitability of these salts as a liquid first wall for fusion energy schemes. A combination of Thermogravimetric Analysis (TGA) and Knudsen Cell Mass Spectrometry (KCMS) was used to characterize the vapor phase above mixtures of LiF, NaF, and BeF2. The scope was limited to mixtures containing between 0.3 and 0.9 mole fraction BeF2. Measurements were performed on pure BeF2 as well as the binary systems of LiF-BeF2 and NaF-BeF 2. For BeF2, values of DeltaHvap were obtained by TGA and KCMS; and the vapor pressure was measured using TGA. Results were in agreement with literature values within experimental uncertainty. KCMS on the binary and ternary systems showed that the vapor phase was composed primarily of BeF2, and to a lesser extent the mixed dimers LiBeF3 and NaBeF3. Data for the binary systems were in agreement with the available literature sources. The ternary system was treated as a pseudobinary system by fixing the ratio of LiF to NaF. Data for both the ternary and binary systems were correlated in terms of the BeF2 activity coefficient