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

The molar enthalpies of mixing (Delta H-mix(m)) in the liquid alkali chloridethulium (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 x(TmCl3) similar to 0.350. The composition dependence of the interaction parameter lambda, with a broad minimum at x(TmCl3) similar to 0.2 for all of the systems is indicative of TmCl63- complexes formation in the melts. The results were discussed with using Papatheocloru-Ostvold model of complexes formation and Associate Solution Model. The configurational mixing entropy of investigated systems has been calculated and commented. (C) 2020 The Authors. Published by Elsevier B.V.