Thermal Analysis and Phase Diagram of the LiF-BiF3 System

TL;DR

This study investigates the thermal behavior and phase diagram of the LiF-BiF3 system, identifying key compounds, melting points, and thermodynamic parameters through differential thermal analysis and assessment.

Contribution

It provides the first comprehensive thermal analysis and thermodynamic assessment of the LiF-BiF3 system, including phase diagram details and compound properties.

Findings

BiF3 melts at 655°C with evaporation issues.

BiLiF4 is an intermediate compound melting at 415°C.

Thermodynamic parameters for BiLiF4 were determined.

Abstract

Differential thermal analysis up to complete melting was performed for the complete pseudobinary system LiF-BiF3. Melts with high bismuth fluoride concentration show severe evaporation, nevertheless even pure BiF3 could be molten at 655 deg. C. The system contains one intermediate compound BiLiF4 which melts by peritectic decomposition under the formation of LiF at 415 deg. C. The eutectic between BiLiF4 and BiF3 melts at 415 deg. C. By thermodynamic assessment the following parameters were found for BiLiF4: \Delta H=-1514900 J/mol, S=158.5 J/mol K, c_p=166.173 -0.01072 T (in J/mol K). The melt has negative excess Gibbs free energy.