Sintering and phase transformation in B2O3/P2O5-doped Li2O•Al2O3•4SiO2 glass-ceramics

The effects of the additives B2O3 and P2O5 on the sintering and phase transformation in Li2O . Al2O3. 4SiO(2) glass-ceramics were investigated. The addition of B2O3 enhanced the crystallization of the parent glasses, whereas the addition of P2O5 delayed it; however, both additives improved the sinterability. Glass-ceramics that contained appropriate amounts of B2O3 and P2O5 showed good sinterability at temperatures as low as 750 degrees C. The phase transformation of metastable high-quartz solid solution (h-Q ss) to stable beta-spodumene (beta-S) occurred when the crystallization of parent glass to h-Q ss was almost complete. Both B2O3 and P2O5 affected the relative amount of beta-S that transformed to h-Q ss. A glass that contained a larger amount of B2O3 revealed an increase in the relative ratio of p-S to h-Q ss with increasing temperature, which was consistent with the generally known phase development in Li2O-Al2O3-SiO2 (LAS) glass-ceramics. A glass that contained a larger amount of P2O5 showed an anomalous temperature dependence of the transformation of metastable h-Q ss to stable beta-S; this dependence had not been observed in other LAS glass-ceramics. A possible explanation for this anomaly is that h-Q ss (and beta-S) that has been formed at different temperatures may have different phase compositions.