Crystallization characteristics and physico-chemical properties of the glasses based on Li2O-CaO-SiO2 eutectic (954 °C) system containing magnesium oxide

The crystallization process of glasses in the Li2O-CaO-SiO2 (954 degrees C) eutectic system containing MgO at the expense of Li2O and/or CaO were investigated by means of DTA, XRD, and SEM. Minor additives of CaF2 or TiO2 were added on the batch of the eutectic glass as nucleating agents. The relationship between the crystalline phases formed, heat-treatment applied and their effect on the properties were discussed. The crystallization of the glasses was greatly enhanced by modification processes, thus fine fibrous and prismatic-like growths were obtained therefrom. The dilatometric thermal expansion of the glasses and their corresponding glass-ceramics were determined. The thermal expansion properties of the glasses depend on the glass compositions. The addition of CaF2 or TiO2 as nucleating agent to the eutectic glass led to increase the alpha-values of the glasses. However, both the T-g and T-s values decreased. The alpha-values of the glasses were decreased with the increase of MgO at the expense of Li2O and/or CaO, while both the transformation (T-g) and softening (T-s) temperatures increased. The thermal expansion coefficients of the crystalline materials exhibited a wide range depending upon the type and relative proportions of the crystalline phases formed. The chemical durability test, using acid solution, of the glass-ceramics was determined. The data obtained depend on the nature and concentration of crystalline phases present and microstructure. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.