Thermal analysis and phase diagram of the LiF–BiF3 system

Abstract

Differential thermal analysis up to complete melting was performed for the complete pseudobinary system LiF-BiF 3 . Melts with high bismuth fluoride concentration show severe evaporation, nevertheless even pure BiF 3 could be molten at 655 • C. The system contains one intermediate compound BiLiF 4 which melts by peritectic decomposition under the formation of LiF at 415 • C. The eutectic between BiLiF 4 and BiF 3 melts at 415 • C. By thermodynamic assessment the following parameters were found for BiLiF 4 : ∆H = −1514900 J mol −1 , S = 158.5 J mol −1 K −1 , c p = 166.173 − 0.01072 · T (in J mol −1 K −1 ). The melt has negative excess Gibbs free energy.

Lanthanide-Doped Bismuth-Based Fluoride Nanocrystalline Particles: Formation, Spectroscopic Investigation, and Chemical Stability

“…At temperatures lower than 300 K, both the compounds show a similar behavior due to the carbonization and volatilization of EG, while at higher temperature, they are characterized by a different thermal response. Unlike BiF 3 that does not show any particular feature, as expected by considering its melting point over 650 °C, NaBiF 4 evidences a strong endothermic peak with an onset at about 440 °C during the heating cycle and two exothermic peaks with onset at about 453 and 429 °C during the cooling cycle. The endothermic peak is assigned to the melting temperature of the compound in agreement with the melted residual found on the crucible after the measurement and with the temperature of the incongruent melting (440 °C) reported by Chartier et al…”