Sintering and crystallisation of a P2O5-added Li2O-ZrO2-SiO2 glass powder system

Sintering and crystallisation of a 11.5 wt % Li2O, 22.8 wt % ZrO2, 65.7 wt % SiO2 glass powder with P2O5 added were investigated. By means of thermal shrinkage measurements, sintering was found to start at about 650°C and was completed in a very short temperature interval (ΔT ≈ 100°C) in less than 30 min. Crystallisation took place just after completion of densification and was almost completed at about 900°C in 20 min. Secondary porosity prevailed over the primary porosity during the crystallisation stage. The glass powder compacts first crystallised into lithium metasilicate (Li2SiO3) and/or zircon (ZrSiO4) and tridymite (SiO2) which transformed and/or grew into lithium disilicate (Li2Si2O5), zircon and tridymite after the crystallisation process was essentially complete, so that, a crystallinity degree between 52.4 ± 2.0 and 68.5 ± 3.2 wt % was obtained. P2O5 doping little affected the densification. However, adding P2O5 remarkably enhanced the zircon and tridymite crystallisation while delaying the Li2SiO3 to Li2Si2O5 transformation. The microstructure is characterised by fine crystals uniformly distributed arbitrarily oriented throughout the residual glass phase.