The influence of Al2O3, MgO and ZnO on the crystallization characteristics and properties of lithium calcium silicate glasses and glass-ceramics

Abstract

Abstract The crystallization characteristics of glasses based on the Li2O–CaO–SiO2 eutectic (954 ± 4 °C) system containing Al2O3, MgO and ZnO has been investigated by differential thermal analysis (DTA), X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The partial replacement of Li2O by Al2O3 and CaO by MgO or ZnO in the studied glass-ceramics led to the development of different crystalline phase assemblages, including lithium meta- and di-silicates, lithium calcium silicates, α-quartz, diopside, clinoenstatite, wollastonite, β-eucryptite ss, β-spodumene, α-tridymite, lithium zinc orthosilicate, hardystonite and willemite using various heat-treatment processes. The dilatometric thermal expansion of the glasses and their corresponding glass-ceramics were determined. A wide range of thermal expansion coefficient values were obtained for the investigated glasses and their corresponding crystalline products. The thermal expansion coefficients of the investigated glasses were decreased by Al2O3, MgO or ZnO additions. The α-values of the investigated glasses were ranged from (+18) to (+108) × 10−7 K−1 (25–300 °C), while those of the glass-ceramics were (+3) to (+135) × 10−7 K−1 (25–700 °C). The chemical durability of the glass-ceramics, towards the attack of 0.1N HCl solution, was markedly improved by Al2O3 with MgO replacements. The composition containing 11.5 mol% Al2O3 and 6.00 mol% MgO exhibited low thermal expansion values and good chemical durability.