CALORIMETRIC INVESTIGATION OF NDCL3-MCL LIQUID-MIXTURES (WHERE M IS NA, K, RB, CS)

The molar enthalpies of mixing DELTA(mix)H(m) in the liquid NaCl-NdCl3, KCl-NdCl3, RbCl-NdCl3 and CsCl-NdCl3 binary systems have been measured over the whole composition range at 1124, 1065, 1122 and 1122 K, respectively, with an accuracy of about 6%. The apparatus used was a Calvet-type high-temperature microcalorimeter and mixing of the two liquid components was obtained by the break-off ampoule technique. In the investigated systems, the enthalpies of mixing are negative with minimum values at about - 5.7, - 16.6, - 20.2 and - 23.4 kJ mol-1, respectively, at x(NdCl3) = 0.4. These values are almost identical, within the experimental accuracy, to those in other previously investigated MCl-LnCl3 mixtures. The molar enthalpies of formation DELTA(f)H(m)(K3NdCl6, 1, 1065)/kJ mol-1, DELTA(f)H(m)(Rb3NdCl6, 1, 1122)/kJ mol-1 and DELTA(f)H(m)(Cs3NdCl6, 1, 1122)/kJ mol-1, according to the reaction 3MCl(1) + LnCl3(1) = M3LnCl6(1), are equal to - 55.2, - 68.8 and - 80.8 kJ mol-1, respectively. The least-squares coefficients A, B, C, D, E of the equation for the interaction parameter lambda = A + Bx + Cx2 + Dx3 + Ex4 (in kJ mol-1) are presented.