Phase equilibria and solidification behavior in the PbF2−AlF3 system

Abstract

The relationship between phase equilibria in the PbF2−AlF3 system and the solidification behavior of several ternary lead aluminum fluoride compounds was explored. A partial binary phase diagram for the PbF2−AlF3 system was determined from differential thermal analysis, annealing and directional solidification studies. The compounds AlF3, Pb3Al2F12, Pb9Al2F24, and a PbF2 solid solution were identified by x-ray diffraction, energy dispersive and microprobe analysis. The previously reported phases PbAlF5 and PbAl2F8 were not observed. Directional solidification studies showed that it is possible to grow crystals of AlF3, Pb3Al2F12, and the PbF2 solid solution from nonstoichiometric PbF2−AlF3 melts. The compound Pb9Al2F24 was found to decompose on heating by a peritectoid reaction (forming two other solids) and thus could not be solidified directly from a PbF2−AlF3 melt.