Calorimetric Investigation of NdI3-MI Liquid Systems (M = Li, Na, K, Rb, Cs)

Abstract

The molar enthalpies of mixing, Δmix Hm, of the liquid alkali metal iodide - neodymium iodide binary systems have been measured over the whole composition range at 1068 K with an accuracy of about 6%. The apparatus used was a Calvet - type high - temperature microcalorimeter. In all the systems under investigation the enthalpies of mixing are negative, with minimum values close to −1.1, −4.8, −10.3, −16.2, and −20.0 kJ mol−1 for LiI-NdI3, NaI-NdI3, KI-NdI3, RbI-NdI3, and CsI-NdI3, respectively, at the mole fractions xNdI3 ⋍ 0.30 - 0.40 except the LiI-NdI3 system, where it is at the NdI3-rich compositions. The molar enthalpies of formation ΔformHm at 1068 K for M = Li, Na, K, Rb, and Cs, arising from the reaction 3 MI(l) + NdI3(l), are found to be −4.5, −17.5, −39.1, −59.9, and −73.3 kJmol−1, respectively They are compared with the formation enthalpies determined previously for the (3MCl, NdCl3) and (3MBr,NdBr3) liquid mixtures. These enthalpies become less negative with increase of the radius of the halide ion.