In this study, a lithium disilicate glass-ceramic in the SiO2-Li2O-K2O-ZnO-P2O5 system was investigated with regard to the biaxial flexural strength, the Vickers hardness and the microstructure by heat treating the the glass isothermally at temperatures between 500 and 850 degrees C. The crystallization behaviour of the base glass was characterized by differential scanning calorimetry (DSC) in a non-isothermal mode. The microstructure and crystalline phases of the lithium disilicate glass-ceramics were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The biaxial flexural strength and the Vickers hardness were interpreted with correlation to the microstructure of the glass-ceramics. It was found that the mechanical strength increased remarkably when crystallization was carried out at a temperature higher than 600 degrees C. The glass-ceramic with the highest strength of 360 + 67 MPa was attained with an isothermal heat treatment of 850 degrees C for 1 h. This glass-ceramic consisted of elongated lithium disilicate crystals with a length of 2.5 to 3um and an aspect ratio of 3 to 4. The volume content of lithium disilicate was 70 + 5%. The crystals were precipitated by the mechanism of bulk crystallization. The interlocking lithium disilicate crystals were randomly orientated which was of advantage for high mechanical strength.
