Crystallization of a Lithium Silicate Glass-Ceramic under Pressure

A lithium silicate glass has been crystallized under increasing pressure using a constant thermal cycle in a hot isostatic press. As pressure increases, the amount of cristobalite that crystallizes decreases, the amount of quartz increases, and the total volume fraction of crystalline phases increases. Crystallization without added pressure gives a mixture of lithium metasilicate, lithium disilicate, cristobalite, and residual glass; quartz is not normally observed with atmospheric‐pressure crystallization. The threshold pressure for the appearance of quartz is about 50 MPa, which is in qualitative agreement with the value obtained from thermodynamic calculation. In this glass‐ceramic, quartz is favored over cristobalite at high pressures because it is more dense.