Snežana R. Grujić

DTA study of the crystallization of Li2O–Nb2O5–SiO2–TiO2 glass

Abstract In this study, the crystallization of 30Li2O·15Nb2O5·50SiO2·5TiO2 (mol%) glass was examined. The parent glass was prepared by the standard melt quenching method, and the investigations were performed under non-isothermal and isothermal conditions using the DTA, XRD, SEM and EDS methods. The results revealed primary crystallization of this glass and the dendritic morphology of crystal growth. Three crystalline phases were formed in the glass matrix during crystallization, whereby LiNbO3 was formed as the primary phase, followed by Li2Si2O5 and SiO2 as the secondary. The surface and volume mechanisms of crystallization occur. The condition that both the mechanisms were dominant was determined. In the case of volume crystallization, the characteristics of the nucleation process were examined. The kinetic parameters of crystallization under different mechanisms of crystallization were determined.

Thermodynamics of mixed and pure aqueous solutions of K2HPO4 at T = 298.15 K

Experimental results on isopiestic measurements for three ternary aqueous solutions of K2HPO4 with KCl, KBr, and KNO3 at T = 298.15 K were modeled with the Clegg–Pitzer–Brimblecombe equation based on mole-fraction-composition scale yielding appropriate mixing parameters, for the estimation of thermodynamic activities of solute components. The results for mean ionic activity coefficients of electrolytes in ternary solutions, calculated this way, are showing specific behavior depending on total ionic strength and ionic strength fractions of electrolytes. The activity coefficients of KCl in {yKCl + (1–y)K2HPO4}(aq) and of KBr in {yKBr + (1–y)K2HPO4}(aq) are changing consistently from the ionic strength and their ionic strength fractions contrary to activity coefficients of KNO3 in {yKNO3 + (1–y)K2HPO4}(aq). In addition, molality of K2HPO4 aqueous saturated solution, in equilibrium with K2HPO4 · 3H2O(cr), and appropriate osmotic coefficient at T = 298.15 K, were determined by the isopiestic method.