Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior, microstructure and mechanical performance

Abstract

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al2O3 for SiO2. The relationships between glass network structure and crystallization behavior of Li2O–Na2O–Al2O3–SiO2 (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al2O3. LNAS glasses with the addition of Al2O3 from 16 to 18 mol% exhibited increasing Q4 (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al2O3 content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)3PO4 phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al2O3 showed high transparency ∼84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.