Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li2O-K2O-Na2O-CaO-MgO-ZrO2-Al2O3-P2O5-SiO2 glass system has been reported here. Increased amount of MgO enhanced the participation of Al2O3 as a glass network former along with [SiO4] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (-10 GPa) and elastic modulus (-127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.

Automated summary

The effect of MgO content on glass structure, crystallization behavior, microstructure, and mechanical properties was investigated. Increased MgO content enhanced the participation of Al2O3 and [SiO4] tetrahedra, reducing non-bridging oxygen and increasing bridging oxygen in glass. The increased bridging oxygen resulted in a polymerized glass structure, suppressing crystallization and improving the properties of glass and glass-ceramics.