Effects of heat treatment on the crystallization behavior, microstructure and thermal properties of a complex Li2O-SiO2 glass system

Abstract

In this paper, glass-ceramics in the SiO2-Li2O-MgO-Al2O3-Rb2O-P2O5 system were fabricated by the two- and three-stage heat treatment at different temperatures and holding times. The effects of heat treatment on the crystallization behavior, microstructure and thermal properties of the glass-ceramics were investigated in detail by DSC, XRD, Raman spectroscopy, SEM and CTE. The results suggest that the lithium metasilicate (LM) phase with a lower crystallization activation energy precipitated from the parent glass before the lithium disilicate (LD) phase. Additionally, only LM crystals with the spherical nano-grains were precipitated after two-stage heat treatment. After three-stage heat treatment, LD was the primary crystalline phase with the minor phases of lithium phosphate, coesite and LM. Raman spectroscopy shows that Q2 and Q3 tetrahedra were the primary microstructural units of LM and LD glass-ceramics, respectively. With increasing temperature and prolonging holding time, LD crystals evolved from the uniform submicron equiaxed grains to the coarse rod-like grains. LD glass-ceramics have a lower CTE (9.51~9.70 × 10-6K-1) and higher softening point (730 ~ 760 °C) than LM glass-ceramics and the parent glass.