PHASE-EQUILIBRIA IN RARE-EARTH CHLORIDE-FLUORIDE AND RARE-EARTH CHLORIDE-MAGNESIUM FLUORIDE SYSTEMS

Equilibrium phase diagrams for the systems LaCl3-LaF3, CeCl3-CeF3, NdC l3-NdF3, LaCl3-MgF2, CeCl2-MgF2, and NdCl3-MgF2 were determined by dif ferential thermal analysis. A eutectic was observed at 654 degrees +/- 4 degrees C and 31 mol% LaF3 in the LaCl3-LaF3 system, 620 degrees +/ - 3 degrees C and 31.5 mol% CeF3 in the CeCl3-CeF3 system, 615 degrees +/- 5 degrees C and 29 mol% NdF3 in the NdCl3-NdF3 system, 723 degree s +/- 5 degrees C and 30 mol% MgF2 in the LaCl3-MgF2 system, 690 degre es +/- 3 degrees C and 26 mol% MgF2 in the CeCl3-MgF2 system, and 655 degrees +/- 3 degrees C and 26.5 mol% MgF2 in the NdCl3-MgF2 system. A compound, NdCl3 . NdF3, decomposing at 595 degrees +/- 5 degrees C, a lso was observed in the NdCl3-NdF3 system. On the basis of agreement b etween the activities calculated by the Temkin model and the Clausins- Clapeyron equation, the melts of the rare-earth (RE) chloride and fluo ride consisted of RE(3+), Cl-, and F-. The melts formed with a rare-ea rth chloride and magnesium fluoride consisted of RE(3+), Mg2+, RECl(6) (3-), and MgF42-.