Mixing Enthalpies of TbBr3-MBr Liquid Mixtures (M=Li, Na, K, Rb, Cs)

Abstract

The molar enthalpies of mixing, ΔmixHm in the binary liquid systems TbBr3-MBr (M = Li, Na, K, Rb, Cs) have been measured with a Calvet - type high-temperature microcalorimeter over the entire composition range with an accuracy of about 6%. Mixing of the two liquid components was achieved by using the "break-off ampoule" technique. All the investigated systems show negative enthalpies of mixing except the LiBr system that also includes slightly positive mixing enthalpies in the TbBr3-rich composition range. For all the systems, enthalpy minimum occurs at molar fraction of TbBr3, xTbBr3 ≈ 0.3–0.4. The molar enthalpies of formation Δform Hm (3MBr, TbBr3, 1) for M = Li, Na, K, Rb and Cs (arising from the reaction 3MBr(1) + TbBr3(1) = (3MBr, TbBr3)(1)) were calculated at 1113K. The interaction parameter of these bromide systems are discussed in terms of ionic potentials. A general comparison of the formation enthalpy is made for all (3MX, TbX3) alkali lanthanide-halide melts.