Thermal Toughening of Low-Expansion Glass Ceramics

The maximum compressive stresses, CTmax developed in this way within a surface layer of a flat glass sheet can be calculated by (3.12) under the assumption that the heat transfer between the surface of the glass and the cooling medium will be oo, from [3.36]  

Low-expansion glass ceramics, however, show an excellent thermal shock resistance and a high thermal load capacity. For that reason they are used as table and oven ware, oven plates, or fire resistant glasses. With all these applications, low-expansion glass ceramics are exposed to relatively high temperatures. In most of these cases, compressive stresses due to thermal toughening would be reduced. 

The low compressive stresses obtainable by thermal toughening and the reduction of prestressing in daily use are the reasons why low-expansion glass ceramics are usually not prestressed by thermal toughening. 

Low-expansion glass ceramics, however, show excellent thermal shock resistance and high thermal load capacity. For that reason they are used as table 

With glasses chemical strengthening can be performed by an exchange of ions for larger ions below Tg or smaller ions above Tg. 

Chemical Strengthening of Crystallized Glass Ceramics with Large Ions Below Tg 

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