Strengthening glass phase

Many other methods of strengthening are based on formation of composites by inclusion of fibers or whiskers or by crystallization to form glass-ceramics. Phase separation may also affect strength by altering crack propagation mechanisms. Transformation toughening has also been attained by formation of a small concentration of zirconia crystals in glasses. 

The subscripts c, f, and m refer to the composite, fiber, and matrix, respectively, and V is the volume fraction of each phase. If we assume 45 vol% of steel fibers and Of = 530 MPa and Om = 42 MPa, then Oc = 262 MPa. This value, which is close to experimentally measured values, represents a significant strengthening above that of the glass alone. 

Relaxation properties of epoxy rubber compounds and mechanisms of the rubber strengthening effect. Usually ERC displays two regions of relaxation. The first is at a temperature much higher than room temperature and depends on the glass-transition of the matrix (epoxy) component of the compound. The glass-transition of the rubber phase is related to the second relaxation region, which is detected at temperatures below room temperature. 

It is relatively easy to apply a glaze to these materials, as richterite glass-ceramics exhibit a high coefficient of thermal expansion of 115 x 10 (0°(D-300°C) due to the formation of a cristobalite secondary phase. Therefore, a glaze with a lower coefficient of thermal expansion can be applied to produce compressive strain in the surface of the material. As a result, the material is strengthened as described in Section 2.3.3. 

Low-expansion glass ceramics have a crystalline as well as a vitreous phase. In this vitreous phase normal ion exchange can take place. But for the chemical strengthening of low-expansion glass ceramics at transformation temperatures above 700 °C, salt melts of potassium nitrate cannot be used, because the salt melts of nitrates decompose at temperatures above 500 °C and produce the toxic NO . Other potassium salts such as sulphates and chlorides and their eutectics have melting temperatures above 700 °C. 

---