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

Abstract The phase separation and crystallization behavior in the system (80 − X )SiO 2 · X (Al 2 O 3 + P 2 O 5 ) · 5B 2 O 3 · 15Na 2 O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al 2 O 3 –P 2 O 5 –SiO 2 and forms a continuous phase. Glasses containing a larger amount of Al 2 O 3 –P 2 O 5 ( X = 40 and 50) readily crystallize and precipitates tridymite type AlPO 4 crystals. It is estimated that the phase separation occurs forming continuous Al 2 O 3 –P 2 O 5 –SiO 2 phase at first, and then tridymite type AlPO 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 20–30 nm and about 50%, respectively.