The effect of strontium oxide replacing calcium oxide on the crystallization and thermal expansion properties of Li2O–CaO–SiO2 glasses

The crystallization process and thermal expansion characteristics of glass compositions based on 17.80Li2O–(32.20−x) CaO (xSrO)–50SiO2 system (where x=3, 6, 9 and 12mol%) were investigated. The crystallization characteristics of the glasses, the type of crystalline phases formed as well as the resulting microstructure were traced by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The addition of SrO at the expense of CaO has led to a slight decrease in both the transition (Tg) and softening (Ts) temperatures of the glasses. The main crystalline phases, formed after controlling heat-treatment are lithium metasilicate-Li2SiO3, wollastonite-CaSiO3 together with pseudowollastonite-like phase. The incorporation of Sr into CaSiO3 structure has partially promoted has partially promoted the phase transition from wollastonite to pseudowollastonite-like phase. A slight increase of thermal expansion coefficients (α-values) of the glasses and their corresponding glass–ceramics has been detected. The α-values of the obtained glasses are 114 to 130×10−7°K−1 in the 25–300°C temperature range while those of the crystalline materials are 90 to 121×10−7°K−1 in the 25–700°C temperature range. The present results provide valuable information about the role of Sr2+ in determining the type of crystalline phases formed in the glasses and the thermal expansion data of the material were obtained.