Phase Equilibria in the Ternary Fused‐Salt System LiF‐BeF₂,‐UF₄

Abstract

The phase diagram for the ternary fused-salt system LiF-BeF2-UF4 was determined from 300°C to the liquidus by differential thermal analysis, thermal-gradient quenching studies, and high-temperature filtration techniques. The samples prepared by quenching were examined by polarized-light microscopy and X-ray diffraction techniques. The experimental methods are described. The primary-phase fields for the compounds LiF, 7LiF.6UF4, LiF.4UF4, and UF4 covered most of the liquidus surface.Small areas of the liquidus surface were covered by the compounds BeF,, 2LiF.BeFz, and 4LiF.UF4. The compound 4LiF-UF4, which was stable at the binary liquidus temperature, decomposed in the ternary system when the liquidus temperature decreased below 48OOC. No ternary compounds or solid solutions were observed. Two ternary eutectics were found. The first, containing 48 mole yo LiF, 51.5 mole yo BeFz, and 0.5 mole yo UF4, melted at 350°C. The second, containing 69.5 mole yo LiF, 22.5 mole yo BeF,, and 8 mole % UF,, melted at 427°C.

Thermodynamic properties and phase diagrams of fluoride salts for nuclear applications

“…The LiF-BeF 2 equilibrium diagram has been studied extensively by thermal analysis techniques [8][9][10][11][12][13][14]. The early studies generally agree on the overall shape of the system, but differences exists in the details, probably due to oxygen impurities in the salts.…”

Measured enthalpy and derived thermodynamic properties of solid and liquid lithium tetrafluoroberyllate, Li2BeF4, from 273 to 900 K

“…The version in a fairly recent co mpilation of phase diagr ams [3] is based on th e res ults of two gro ups of work ers [4,5]. Anoth er composite di agram [6] is based on th e res ults of th e above workers, as well as on those from two other publi cations [7 , 8] and additional work unpublished at that time.…”

Thermodynamic assessment of the LiF–BeF2–ThF4–UF4 system

“…Performing our own DTA experiments would be priority in a future study on this system. [9] and LiF-ThF 4 -UF 4 by Weaver et al [10]. b 2LiF AE BeF 2 was considered as incongruently melting compound at the time of analysis.…”

“…Tables belonging to the papers [8][9][10], which were deposited at the Library of Congress in Washington DC, contained all experimental data on LiFBeF 2 -ThF 4 (thermal gradient quenching and DTA cooling), LiF-BeF 2 -UF 4 (DTA cooling, thermal gradient quenching and high-temperature filtration) and LiF-ThF 4 -UF 4 (thermal gradient quenching). A comparison was made between liquidus surface of the calculated and the experimentally defined diagrams.…”

“…All binary subsystems were assessed according to the CALPHAD method, from which the four ternaries were derived. The results were compared to the experimental data for LiF-BeF 2 -UF 4 [9], LiFThF 4 -UF 4 [10] and BeF 2 -ThF 4 -UF 4 [11]. …”