Glass-ceramics based on spodumene–enstatite system from natural raw materials

Glasses of compositions (wt%) corresponding to 50–90 spodumene and 50–10 enstatite were prepared depending on natural raw materials and Li2CO3 as small ingredient. The crystallization behavior was studied using DTA and XRD. The effect of addition of the nucleating agents (LiF) to a selected glass was also examined. Polarizing microscope and dilatometeric techniques were used to study the microstructures and the thermal expansion coefficient, respectively. XRD showed that the crystalline materials are mainly enstatite, clinoenstatite, β-eucryptite ss and β-spodumene ss. The shift of the glass composition to that of enstatite results in increased bulk crystallization. The presence of LiF does not greatly affect the mineral assemblages yet it improves the thermal expansion coefficients (TEC) of the crystalline samples and promotes the initial crystallization. Low and even negative values, ranging from −5.91 × 10−7/K to 2.48 × 10−7/K in the temperature range 293–573 K and 300–737 K, respectively, could be obtained, which make such materials applicable for thermally stable articles.