Calorimetric Investigation of the CeBr3-MBr Liquid Mixtures (M = Na, K, Rb, Cs)

The molar enthalpies of mixing (Delta H-mix(m)) in the liquid cerium(III)-alkali metal bromide mixtures were measured with a Calvet-type high temperature microcalorimeter over the entire composition range at 1073 K. Mixing the two liquid components was achieved by using the "break-off ampule technique". All the melts are characterized by negative enthalpies of mixing with a minimum value of approximately -5.3 kJ.mol(-1), -12.7 kJ.mol(-1), -16.1 kJ.mol(-1), and -18.4 kJ.mol(-1), for M = Na, K, Rb, and Cs, respectively. For all the systems, the minimum of the enthalpy of mixing is shifted toward the alkali bromide-rich compositions and located in the vicinity of x(CeBr3) similar to 0.4. The composition dependence of the interaction parameter lambda, with a broad minimum at x(CeBr3) similar to 0.2 for the systems with KBr, RbBr, and CsBr is indicative of LnBr(6)(3-) complexes formation in the melts.