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

Equilibrium phase diagrams for the systems LaCl 3 -LaF 3 , CeCl 3 -CeF 3 , NdCl 3 -NdF 3 , LaCl 3 -MgF 2 , CeCl 2 -MgF 2 , and NdCl 3 -MgF 2 were determined by differential thermal analysis. A eutectic was observed at 654° ± 4°C and 31 mol% LaF 3 in the LaCl 3 -LaF 3 system, 620° ± 3°C and 31.5 mol% CeF 3 in the CeCl 3 -CeF 3 system, 615° ± 5°C and 29 mol% NdF 3 in the NdCl 3 -NdF 3 system, 723° ± 5°C and 30 mol% MgF 2 in the LaCl 3 -MgF 2 system, 690° ± 3°C and 26 mol% MgF 2 in the CeCl 3 -MgF 2 system, and 655° ± 3°C and 26.5 mol% MgF 2 in the NdCl 3 -MgF 2 system. A compound, NdCl 3 .NdF 3 , decomposing at 595° ± 5°C, also was observed in the NdCl 3 -NdF 3 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 RE 3+ , Cl - , and F - . The melts formed with a rare-earth chloride and magnesium fluoride consisted of RE 3+ , Mg 2+ , RECl 6 3- , and MgF 4 2- .