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

Utilizing P2O5 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 β∥′-Li2ZnSiO4 occurred after the glass was treated at 580 °C. As the temperature increased from 580 °C to 630 °C, cristobalite and β∥′-Li2ZnSiO4 were identified as main and second crystal phases, respectively, in the glass–ceramic. An increase in the temperature to 700 °C, the β-quartz solid solution in the glass–ceramic accompanied by a decrease in cristobalite content. The transformation from β∥′-Li2ZnSiO4 to γ0-Li2ZnSiO4 took place from 700 °C to 750 °C. The resulting crystallization phases in the glass–ceramics obtained at the temperature higher than 750 °C were β-quartz solid solution and γ0-Li2ZnSiO4. The glass–ceramics containing β∥′-Li2ZnSiO4 or β-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 × 10−7 °C−1 in the temperature range of 20–400 °C, this precise value is dependent on the type and the proportion of the crystalline phases presented.