Phase diagram, thermodynamic activities and thermodynamic modelling in the NaBr–DyBr3 system

Thermodynamic properties of the pseudo-binary NaBr–DyBr3 system were studied by differential thermal analysis (DTA), Knudsen effusion mass spectrometry (KEMS) and by thermodynamic modelling (TM). Investigations performed by DTA resulted in the phase diagram involving the binary compound 3NaBr∗DyBr3(s) in addition to the pure component metal halides NaBr(s) and DyBr3(s) and the liquid phase. The eutectic parameters of the {DyBr3(s)+3NaBr∗DyBr3(s)} mixture were determined as T e = 710 ± 3 K and x(NaBr)liq=0.62. A peritectic transition of 3NaBr∗DyBr3(s) at 765 ± 3 K was indicated. The study of the vaporisation by KEMS in the temperature range of 703–1025 K led to the identification of gaseous species in the equilibrium vapour (NaBr, (NaBr)2, DyBr3, (DyBr3)2, NaDyBr4, Na2DyBr5) and to the thermodynamic activities of NaBr and DyBr3 over the complete concentration range of the system at 863 K. The results obtained were used in the computer modelling of the NaBr–DyBr3 system carried out by the use of the BINGGS program.