Experimental and model studies of solid-liquid equilibria of the binary systems water-yttrium nitrate, water-barium nitrate and water-copper nitrate. Part 1. The binary systems H"2OBa(NO"3)"2 and H"2OY(NO"3)"3 - Bouchet, R.; Tenu, R.; Counioux, J.J. (Elsevier)
An experimental study of solid-liquid equilibria of H"2OBa(NO"3)"2 and H"2OY(NO"3)"3 systems has been conducted using conductimetry and controlled thermal flux analysis. The solid phases were studied using X-ray diffraction, thermogravimetry and chemical analysis such as calcination and DCP.Calorimetric analysis using DSC on the water-barium nitrate eutectic has given the transformation enthalpy (303 J g^-^1) and the specific heat capacities of the solid and the liquid mix between -20 and + 15^oC.The invariant transformation temperatures of the H"2OY(NO"3)"3 system have been determined or qualified and the measured metastable melting point of the tetra-, penta- and hexahydrate are respectively 120.4, 77.8 and 51.8^oC.A thermodynamic study of the phase equilibria of the two systems has been achieved taking into account ionic dissociation and solvation phenomena. It shows that the barium nitrate in aqueous solution behaves as a binary electrolytic compound, that the yttrium nitrate in aqueous solution is dissociated and that 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 various hydrates have been computed and the validity check of these values has been successfully conducted on yttrium nitrate pentahydrate. | L'etude experimentale des equilibres solide-liquide des systemes H"2OBa(NO"3)"2 et H"2OY(NO"3)"3 a ete effectuee par conductimetrie et analyse thermique a flux controle. Les phases solides ont ete controlees par diffraction de rayons X, thermogravimetrie et analyse chimique: calcination et DCP.Une analyse calorimetrique par DSC de l'eutectique eau-nitrate de baryum a permis de determiner l'enthalpie de la transformation (303 J g^-^1) et les capacites thermiques du melange solide et liquide entre -20 et + 15^oC.Les temperatures des transformations invariantes du systeme H"2OY(NO"3)"3 ont ete determinees ou precisees et les temperatures de fusion metastables des tetra-, penta- et hexahydrate mesurees sont respectivement 120,4, 77,8 et 51,8^oC.Une etude thermodynamique des equilibres entre phases des deux systemes a ete effectuee en prenant en compte les phenomenes de solvatation et de dissociation. Elle montre que le nitrate de baryum se comporte en solution aqueuse comme un electrolyte binaire, que le nitrate d'yttrium est dissocie en solution aqueuse et que l'ion yttrium a tendance a se solvater preferentiellement en tetra-, octa- et dodecahydrate.Le modele utilise permet une excellente representation des courbes d'equilibre. Les enthalpies de fusion metastable des differents hydrates ont ete calculees et un controle de la validite des valeurs obtenues a pu etre effectue dans le cas du pentahydrate du nitrate d'yttrium.
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