Sintering and Phase Transformation in B ₂ O ₃ /P ₂ O ₅ ‐Doped Li ₂ O ^. Al ₂ O ₃ ^. 4SiO ₂ Glass‐Ceramics

Abstract

The effects of the additives B 2 O 3 and P 2 O 5 on the sintering and phase transformation in Li 2 O . Al 2 O 3 . 4SiO 2 glass‐ceramics were investigated. The addition of B 2 O 3 enhanced the crystallization of the parent glasses, whereas the addition of P 2 O 5 delayed it; however, both additives improved the sinterability. Glass‐ceramics that contained appropriate amounts of B 2 O 3 and P 2 O 5 showed good sinterability at temperatures as low as 750°C. The phase transformation of metastable high‐quartz solid solution (h‐Q ss) to stable β‐spodumene (β‐S) occurred when the crystallization of parent glass to h‐Q ss was almost complete. Both B 2 O 3 and P 2 O 5 affected the relative amount of β‐S that transformed to h‐Q ss. A glass that contained a larger amount of B 2 O 3 revealed an increase in the relative ratio of β‐S to h‐Q ss with increasing temperature, which was consistent with the generally known phase development in Li 2 O–Al 2 O 3 –SiO 2 (LAS) glass‐ceramics. A glass that contained a larger amount of P 2 O 5 showed an anomalous temperature dependence of the transformation of metastable h‐Q ss to stable β‐S; this dependence had not been observed in other LAS glass‐ceramics. A possible explanation for this anomaly is that h‐Q ss (and β‐S) that has been formed at different temperatures may have different phase compositions.