Calorimetric investigation of TmCl3-MCl liquid mixtures (M = Li, Na, K, Rb)

Abstract The molar enthalpies of mixing (ΔmixHm) in the liquid alkali chloride‑thulium (III) chloride mixtures have been measured with a Calvet-type high temperature microcalorimeter over the entire composition range at 1130 K. Mixing of the two liquid components was achieved by using the “break-off ampoule technique”. All the melts are characterized by negative enthalpies of mixing with a minimum value of approximately: −1.8, −10.3, −23.4, and −26.0 kJ·mol−1, for systems with LiCl, NaCl, KCl and RbCl, respectively. For all systems, the minimum of the enthalpy of mixing is shifted towards the alkali chloride-rich compositions and located in the vicinity of xTmCl3 ~0.350. The composition dependence of the interaction parameter λ, with a broad minimum at xTmCl3 ~0.2 for all of the systems is indicative of TmCl63− complexes formation in the melts. The results were discussed with using Papatheodoru-Ostvold model of complexes formation and Associate Solution Model. The configurational mixing entropy of investigated systems has been calculated and commented.