Influence of SiO2 contents on the microstructure and mechanical properties of lithium disilicate glass-ceramics by reaction sintering

Preparation of lithium disilicate glass-ceramics was attempted via solid-state reaction between Li2SiO3 crystals and SiO2 glass. By addition of 0.5 mol Li2Si2O5 glass as binding, the mixtures were hot-pressing sintered at 840 degrees C for 1 h. The effect of SiO2 contents (1-2 mol) on the reaction sintering behavior, microstructure and mechanical properties of Li2Si2O5 glass-ceramics was studied. Part of SiO2 glass crystallized to quartz so that at least 1.5 mol SiO2 was needed for the complete reaction with the 1 mol LM crystals. The grain size of Li2Si2O5 crystals increased with increasing the SiO2 content depending on the degree of reaction. The flexural strength and fracture toughness of the samples both increased firstly then decreased with the increasing SiO2. After reaction, rod-like Li2Si2O5 crystals of tens microns long could be obtained, which were several times longer than the directly crystallized ones from the parent glass. Such reaction formed large Li2Si2O5 crystals apparently had an effective toughening effect without sacrificing other properties. Due to the complete reaction of 1 mol Li2SiO3 crystals by 1.5 mol SiO2 glass in the specimens of M1S1.5D0.5, high flexural strength of 373 +/- 12 MPa and improved fracture toughness of 3.35 +/- 0.12 MPa.m(1/2) were obtained. The improved properties were attributed mainly to crack deflexion and grain-bridging toughening mechanisms.