Crystallization Kinetics and Mechanism of Strontium Zinc Silicate Glass

The non-isothermal crystallization kinetics of the strontium zinc silicate (SZS) glasses, having composition 51SrO-9ZnO-40SiO(2) (wt%), was studied using the differential thermal analysis (DTA). Glasses prepared by quenching the melt in air, were subjected to different heat treatments for studying the crystallization behavior. Formation of crystalline phases and microstructure were studied by using powder X-ray diffraction and scanning electron microscopy. The activation energy and mechanism of crystallization were determined according to Kissinger, Ozawa and Matusita-Sakka equations. The DTA exotherm observed at around 920 degrees C consists of two overlapping crystallization peaks corresponding to two different crystalline phases. Strontium silicate (Sr3Si3O9) and SZS (Sr2ZnSi2O7) phases crystallize almost simultaneously as major phases. The activation energies for the these crystallization peaks are 700 kJ/mol and 704 kJ/mol. Higher activation energies indicate that the kinetics are more thermally activated making the control of crystallization more difficult. The values of growth morphology parameters n (Avarami parameter) and m (dimensionality of crystal growth) suggest a diffusion controlled bulk crystallization with three- and two-dimensional growth. This is also confirmed by an interconnected growth of stubby granular/prismatic shaped crystals in the glass-ceramic. The microstructural evolution of the glass upon heating suggests the occurrence of phase separation with an apparently spinodal decomposition mechanism prior to the crystallization.