Effect of heat treatment on the microstructure and properties of lithium disilicate glass-ceramics

The effect of heat treatment on microstructure and properties of SiO2-Li2O-K2O-Al2O3-ZrO2 glass-ceramics was investigated. The glasses were subjected to a multi-stage heat treatment. At the first stage at 650 °C, Li2SiO3 was the main crystalline phase of all samples, which had a dimensional change with prolonging the heating time from 3 h to 72 h. After the second stage treatment at 830 °C for 3 h, all the Li2SiO3 crystals decomposed and Li2Si2O5 crystals formed with an opposite dimensional change from that of Li2SiO3. These Li2Si2O5 crystals were small, which could contribute to forming high translucency. The third stage at 550 °C would release the internal strain and improve samples' bending strength, which could reach up to above 560 MPa. The sample treated for 48 h at the first stage had the smallest crystals and also obtained a highest real in-line transmission of 29% at 650 nm with a thickness of 1.45 mm and a bending strength above 581 ± 25 MPa.