Crystallization behavior of silica glass

Silica glass powder and bulk were heat-treated and cold static pressure briquettes were pressureless sintered. XRD, EPMA and TEM were used to investigate the effect of heat treatment and sintering temperature on crystallization behavior. The results indicated that all the crystallization products were low-temperature cristobalites. With the increasing of heat treatment temperature, the amount of cristobalites in silica glass powder and bulk increased dramatically in 1400°C-1550°C and 1350°C-1500°C, respectively, and reached the maximum value when treated in 1575°C and 1525°C. Thereafter, the amount of crystal decreased. With the sintering temperature increasing, the amount of crystal in briquettes increased gradually. The prime crystallization temperature of silica glass was low. Cristobalites appeared in silica glass powder held for 30 min at 1150°C, but fewer cristobalites appeared for glass bulk held at 1200°C. Only a few cristobalites could be observed at 1400°C for briquettes and obvious crystallization occurred at 1500°C. The amount of cristobalites was larger (about 70.49%) when sintered at 1600°C. In the meantime, the cristobalites were large in size and no complete grain boundary could be observed.