The effect of TiO2 addition on the crystallization and phase formation in lithium aluminum silicate (LAS) glasses nucleated by P2O5

We have prepared lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li2O–71.7SiO2–7.1Al2O3–4.9K2O–3.2B2O3–2.5P2O5(LAS-P) and 10.6Li2O–71.7SiO2–7.1Al2O3–4.9K2O–3.2B2O3–1.25P2O5–1.25TiO2 (LAS-PT) by the conventional melt quench technique. P2O5 and TiO2 are added as nucleating agents to transform them into glass ceramics. We have studied the interdependence of different phases formed, microstructure, thermal expansion coefficient (TEC), and microhardness (MH) using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-mechanical analysis (TMA), and MH (μ-hardness) measurements. The incorporation of TiO2, in addition to P2O5, greatly affects phase evolution and morphology, thereby affecting the thermo-physical properties. Its presence resulted in the formation of only lithium disilicate phase in LAS-PT samples as compared to lithium disilicate and quartz in LAS-P samples on heat treatment at 820 °C. This produced low-aspect-ratio plate-like crystallites in LAS-PT vis-à-vis granular microstructure in LAS-P. Consequently due to the combined effect of both phase formation and morphology a single-phase glass ceramic with overall higher MH, TEC, and glass transition temperature (Tg) is produced.