CRYSTALLIZATION OF A LITHIUM SILICATE GLASS-CERAMIC UNDER PRESSURE

A lithium silicate glass has been crystallized under increasing pressu re using a constant thermal cycle in a hot isostatic press, As pressur e increases, the amount of cristobalite that crystallizes decreases, t he amount of quartz increases, and the total volume fraction of crysta lline phases increases. Crystallization without added pressure gives a mixture of Lithium metasilicate, Lithium disilicate, cristobalite, an d residual glass; quartz is not normally observed with atmospheric-pre ssure crystallization. The threshold pressure for the appearance of qu artz is about 50 MPa, which is in qualitative agreement with the value obtained from thermodynamic calculation, In this glass-ceramic, quart z is favored over cristobalite at high pressures because it is more de nse.