Thermal analysis and phase diagram of the LiF–BiF3 system

Differential thermal analysis up to complete melting was thoroughly performed for the pseudobinary system LiF–BiF3. Melts with high bismuth fluoride concentration suffered from high evaporation; nevertheless even pure BiF3 could be molten at 655 °C. The system contains one intermediate compound BiLiF4 which melts by peritectic decomposition with the formation of LiF at 450 °C. The eutectic between BiLiF4 and BiF3 melts at 415 °C. Thermodynamic assessment yielded the following parameters for BiLiF4: ΔH = −1, 514, 900 J mol−1, S = 158.5 J mol−1 K−1, cp = 166.173 − 0.01072 · T (in J mol−1 K−1). The melt has negative excess Gibbs free energy.

► The LiF–BiF3 phase diagram is described and assessed for the first time.
► Intermediate compound BiLiF4 melts incongruently with peritectic formation of LiF.
► Density disparity between components leads to non-equilibrium effects.