Enthalpies of Mixing in the LaI3–MI (M = Li, Na, K, Rb, Cs) Binary Systems

The molar enthalpy of mixing (ΔmixHm) in the LaI3–MI (M = Na, K, Cs) liquid systems was measured over the whole composition range at 1060 K with a Calvet-type high temperature microcalorimeter. The mixing of two liquid components was achieved by using the “break-off ampoule technique”. The dependence of the interaction parameter on composition λ = A + Bx + Cx2 + Dx3 (x = mole fraction of LaI3) was determined. Unknown molar enthalpy of mixing (ΔmixHm) in the LaI3–LiI and LaI3–RbI liquid systems was calculated using the conformal solution theory of Davis. In all systems under investigation the enthalpies of mixing are negative except the LaI3–LiI system at LaI3-rich compositions. The minimum of enthalpy is shifted toward the alkali metal iodide-rich part and is located at the composition of x(LaI3) ≈ 0.35–0.40. Measured and calculated molar enthalpies of mixing were compared with the molar enthalpies of mixing in the LaCl3–MCl and LaBr3–MBr (M = Li, Na, K, Rb, Cs) liquid systems.