Phase equilibria in rare-earth chloride-fluoride and rare-earth chloride-magnesium fluoride systems

Article abstract of DOI:10.1111/j.1151-2916.1996.tb09019.x

Equilibrium phase diagrams for the systems LaCl₃-LaF₃, CeCl₃-CeF₃, NdCl₃-NdF₃, LaCl₃-MgF₂, CeCl₂-MgF₂, and NdCl₃-MgF₂ were determined by differential thermal analysis. A eutectic was observed at 654° ± 4°C and 31 molpercent LaF₃ in the LaCl₃-LaF₃ system, 620° ± 3°C and 31.5 molpercent CeF₃ in the CeCl₃-CeF₃ system, 615° ± 5°C and 29 molpercent NdF₃ in the NdCl₃-NdF₃ system, 723° ± 5°C and 30 molpercent MgF₂ in the LaCl₃-MgF₂ system, 690° ± 3°C and 26 molpercent MgF₂ in the CeCl₃-MgF₂ system, and 655° ± 3°C and 26.5 molpercent MgF₂ in the NdCl₃-MgF₂ system. A compound, NdCl₃·NdF₃, decomposing at 595° ± 5°C, also was observed in the NdCl₃-NdF₃ system. On the basis of agreement between the activities calculated by the Temkin model and the Clausius-Clapeyron equation, the melts of the rare-earth (RE) chloride and fluoride consisted of RE³⁺, Cl^-, and F^-. The melts formed with a rare-earth chloride and magnesium fluoride consisted of RE³⁺, Mg²⁺, RECl₆^3-, and MgF₄^2-.