Effect of heat-treatment condition on crystallization behavior and thermal expansion coefficient of Li2O-ZnO-Al2O3-SiO2-P2O5 glass-ceramics

Utilizing P-2-O-5 as nucleation agent, a Li2O-ZnO-Al2O3-SiO2 glass was prepared by conventional melt quenching technique and subsequently converted to glass-ceramics with different crystal phases. During the processing, two-step heat-treatments including nucleation and crystallization were adopted. The effects of heat-treatment on the crystal type, the microstructure and the thermal expansion behavior of the glass-ceramics were studied by means of differential scanning calorimetry, X-ray powder diffraction analysis, scanning electron microscopy and thermal expansion coefficient tests. It was shown that the crystallization of beta(')(parallel to)-Li2ZnSiO4 occurred after the glass was treated at 580 degrees C. As the temperature increased from 580 degrees C to 630 degrees C, cristobalite and beta(')(parallel to)-Li2ZnSiO4 were identified as main and second crystal phases, respectively, in the glass-ceramic. An increase in the temperature to 700 degrees C, the beta-quartz solid solution in the glass-ceramic accompanied by a decrease in cristobalite content. The transformation from P1-LiZnSi04 to gamma(0)-Li2ZnSiO4 took place from 700 degrees C to 750 degrees C. The resulting crystallization phases in the glass-ceramics obtained at the temperature higher than 750 degrees C were beta-quartz solid solution and gamma(0)-Li2ZnSiO4. The glass-ceramics containing beta(')(parallel to)-Li2ZnSiO4 or beta-quartz solid solution crystal phase possessed a microstructure formed by the development of dendritic crystals. The thermal expansion coefficient of the glass-ceramics varied from 36.7 to 123.8 x 10(-7) degrees C-1 in the temperature range of 20-400 degrees C, this precise value is dependent on the type and the proportion of the crystalline phases presented. (c) 2007 Elsevier B.V. All rights reserved.