EXPERIMENTAL AND MODEL STUDIES OF SOLID-L IQUID EQUILIBRIA OF THE BINARY-SYSTEMS WATER-YTTRIUM NITRATE, WATER-BARIUM NITRATE AND WATER-COPPER NITRATE .1. THE BINARY-SYSTEMS H2O-BA(NO3)2 AND H2O-Y(NO3)(3)

An experimental study of solid-liquid equilibria of H2O-Ba(NO3)(2) and H2O-Y(NO3)(3) systems has been conducted using conductimetry and cont rolled thermal flux analysis. The solid phases were studied using X-ra y diffraction, thermogravimetry and chemical analysis such as calcinat ion and DCP. Calorimetric analysis using DSC on the water-barium nitra te eutectic has given the transformation enthalpy (303 J g(-1)) and th e specific heat capacities of the solid and the liquid mix between -20 and 15 degrees C. The invariant transformation temperatures of the H2 O-Y(NO3)(3) system have been determined or qualified and the measured metastable melting point of the tetra-, penta- and hexahydrate are res pectively 120.4, 77.8 and 51.8 degrees C. A thermodynamic study of the phase equilibria of the two systems has been achieved taking into acc ount ionic dissociation and solvation phenomena. It shows that the bar ium nitrate in aqueous solution behaves as a binary electrolytic compo und, that the yttrium nitrate in aqueous solution is dissociated and t hat the yttrium ion tends to solvate itself mainly into tetra-, octa- and dodecahydrate. The model used provides an excellent representation of the equilibrium curves. The metastable fusion enthalpies of the va rious hydrates have been computed and the validity check of these valu es has been successfully conducted on yttrium nitrate pentahydrate.