Isothermal and non-isothermal crystallization kinetics of zinc-aluminosilicate glasses

Isothermal and non-isothermal differential thermal analysis (DTA), and X-ray diffraction (XRD) were used to study the nucleation and crystallization behavior of multicomponent Li2O-ZnO-Al2O3-B2O3-SiO2 glasses with ZrO2 and TiO2 as nucleating agents. The temperature of maximum nucleation rate for investigated glasses was found to be 1028 K. The crystallization of two phases (mullite s.s. and gahnite) occurs in a narrow temperature and time interval, respectively, therefore, the DTA curves are characterized by the superposition of exothermic peaks. Recently derived mathematical models have been applied for resolving the overlapping. The models enabled establishing the kinetic parameters for crystal growth of individual phases. The activation energies for crystal growth were found to be in the range of 459-471 and 368-386 kJ mol(-1) for mullite and gahnite, respectively. Avrami exponent n reveals three-dimensional growth of both phases. (C) 2001 Elsevier Science B.V. All rights reserved.