GLASS DEVELOPMENT AND CONTROLLED CRYSTALLIZATION IN THE SIO2-LI2O-ZRO2-P2O5 SYSTEM

The objective of this investigation was to analyze glass formation and crystallization in the SiO2-Li2O-ZrO2-P2O5 system for the development of high-strength glass-ceramics produced with glass powder. In the co urse of this study, it was found that the base glass or the semicrysta lline glass-ceramic could be pressed to form glass-ceramic final produ cts. The analysis of glass formation demonstrated that in a relatively large composition range, up to almost 30 wt%, ZrO2 could be incorpora ted into the base glass and increased the glass forming tendency. Othe r additives were also tested.The presence of ZrO2 crystals, ZrSiO4 cry stals and lithium phosphate crystals as well as other secondary phases in the microstructure following heat treatment at approximately 1000 degrees C was established in SEM and XRD examinations. This glass-cera mic possesses flexural strengths of 280 MPa. Translucency was observed in 0.5 mm thick layers. Growth rates of the main crystal phases were determined with cast monolithic samples in a semiquantitative kinetic evaluation of phase development. In contrast to the kinetics of mica c rystal growth processes in machinable glass-ceramics, no time lags wer e observed.