ENTHALPIES OF MIXING IN PRCL3-CACL2 AND NDCL3-CACL2 LIQUID-SYSTEMS

The molar enthalpies of mixing DELTA(mix)H(m) in the PrCl3-CaCl2 and N dCl3-CaCl2 liquid binary systems were measured at 1073 K over the whol e composition range under argon at atmospheric pressure. The apparatus used was a Calvet-type high-temperature micro-calorimeter and mixing of the two liquid components was obtained by the break-off ampoule tec hnique. In both systems the plots of enthalpies of mixing versus compo sition were ''S-shaped'' curves. The enthalpy of mixing values are pos itive for NdCl3- and PrCl3-rich compositions, and negative for other c ompositions. These values are very small (from about -200 to about 180 J mol-1). In the PrCl3-CaCl2 and NdCl3-CaCl2 liquid binary systems, D ELTA(mix)H(m) almost-equal-to 0 at x(PrCl3) almost-equal-to 0.6 and at x(NdCl3) almost-equal-to 0.4, respectively. These results are discuss ed in terms of equilibrium between the LnCl3 (where Ln is Pr, Nd) poly mers and anionic complexes as a function of the composition of the mel ts.