The effect of TiO 2 addition on the crystallization and phase formation in lithium aluminum silicate (LAS) glasses nucleated by P 2O 5

Abstract

We have prepared lithium aluminum silicate (LAS) glasses of compositions (wt%) 10.6Li 2O–71.7SiO 2–7.1Al 2O 3–4.9K 2O–3.2B 2O 3–2.5P 2O 5(LAS-P) and 10.6Li 2O–71.7SiO 2–7.1Al 2O 3–4.9K 2O–3.2B 2O 3–1.25P 2O 5–1.25TiO 2 (LAS-PT) by the conventional melt quench technique. P 2O 5 and TiO 2 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 TiO 2, in addition to P 2O 5, 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 ( T g) is produced.