Influence of fluorine content on crystallization and mechanical properties of SiO2–Li2O glass-ceramics

The effect of fluorine content on the crystallization, microstructure and mechanical properties of SiO2–Li2O glass-ceramics was investigated. Four parent glass samples with different fluorine content were prepared by melt quenching method. The glass-ceramic samples are obtained by heat treatment including nucleation and crystallization process. It was found that lithium disilicate (Li2Si2O5) is the main phase crystallizing in the course of heat treatment, while lithium metasilicate (Li2SiO3), petalite (LiAlSi4O10), and fluorapatite (Ca5(PO4)3F) appear in some of the samples as minor phases. The addition of fluorine increases the crystallinity and promotes the formation of Li2Si2O5 and Ca5(PO4)3F crystals, and thereby regulates the microstructure and mechanical properties. A proper amount of fluorine significantly enhanced mechanical properties. The SiO2–Li2O glass-ceramic sample with 0.5 mol% fluorine content has the highest Vickers hardness HV value of 6.64 GPa and highest fracture toughness KIC value of 0.932 MPa m1/2 after crystallization process at 670 °C for 8 h. The SiO2–Li2O glass-ceramic sample with 1.0 mol% fluorine content has the highest Young's moduli E value of 102.1 GPa after crystallization process at 670 °C for 8 h.