Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 - A)SiO2 center dot X(Al2O3 + P2O5) center dot 5B(2)O(3) center dot 15Na(2)O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al2O3-P2O5-SiO2 and forms a continuous phase. Glasses containing a larger amount of Al2O3-P2O5 (X = 40 and 50) readily crystallize and precipitates tridymite type AIPO(4) crystals. It is estimated that the phase separation occurs forming continuous Al2O3-P2O5-SiO2 phase at first, and then tridymite type AIPO(4) crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 2030 nm and about 50%, respectively. (c) 2006 Elsevier B.V. All rights reserved.