Abstract:The phase diagrams of the binary systems RECl₃-MCl_n(M=Li,Mg,Ca,Pb;n=1 or 2)were investigated by means of DTA and X-ray diffraction analysis.It was found that they are of simple eutectic type with eutectic points 50.1 Mol.-% TBCl₃(445℃),67.5Mol.-% TbCl₃ (589℃),65.9Mol.-% TbCl_(563℃)and 35.6 Mol.-% TbCl₃(445℃)respectively.Unstable compounds,formed in the solid slate,are MgTbCl₇,CaTb₂Cl₈,LiTb₂Cl₇ and PbTbCl₅.Their decomposition temperatures are 388℃ with a phase transition at 352,500 and 521℃ with a phase transition at 483 and 405℃ respectively.Some rules of the phase diagrams were explored.

Key words: TbCl₃; TbCl₃-LiCl; TbCl₃-MgCl₂; TbCl₃-CaCl₂; TbCl₃-PbCl₂; system phase diagram Rule of phase diagram