Non-isothermal free-models kinetic analysis on crystallization of europium-doped phosphate glasses

A kinetic analysis under non-isothermal conditions has been performed on europium-doped phosphate glasses with molar composition 20.42 Li2O-10.25 Al2O3-58.49 P2O5-7.23 BaO-1.44 La2O3-2.16 Eu2O3 and particle size <30 mu m, >50 mu m. Differential scanning calorimetry measurements at four heating rates, from room temperature up to 900 degrees C using synthetic air have revealed that no significant mass change occurs during the heat treatment, as normally expected for glass samples. The step changes in heat flow signals are associated with the presence of three important effects: the first one, that occurs as a slope corresponds to the glass transition effect (T-g) is followed by two exothermic peaks, first of them more pronounced, associated with the first crystallization process (T-p1), while, the second one, lower in intensity corresponds to the second crystallization (T-p2) process. As expected, all peaks (T-g, T-p1 and T-p2) increase with the increasing of the heating rate. Both the activation energy of crystallization process and the crystallization mechanism were comparatively analyzed by two free-model estimations and using the formal theory of transformations for heterogeneous nucleation. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.