Other Glass Ceramics

In recent years LAS glass ceramics received some new attention by the observation that keatite s.s. [1.38] and h-quartz s.s. [1.39] containing glass ceramics can be formed by the photonucleation process. But it still has to be shown that low-expansion glass ceramics can be obtained via the photonucleation process. 

Because of the unique property achievable with low-expansion glass ceramics this material class attracted most attention at the beginning of the development of glass ceramics but of course many researchers tried to apply the basic ideas of the formation of glass ceramics to other composition fields, and often they were very successful. Nowadays there is no principal reason why the glass ceramic approach could not work in other composition fields, although the specific details have to be worked out for each field separately. 

Only a few examples of the many successful developments in the field of glass ceramic materials, which have been performed over the last 35 years, are mentioned here, further information can be found in [1.16-23,57]. 

Biocompatibility and bioactivity are outstanding properties on their own. Several glass ceramics have been developed which show high biocompatibility or bioactivity but which are not machinable with conventional metal-working tools [1.47]. 

The idea to produce ceramic-like materials with a fine microstructure by controlled devitrification of base glasses was soon extended to procedures other than the controlled volume nucleation and crystallization of base glasses. Relatively fine-grained glass ceramics can also be obtained by sintering and crystallization of glass powders to dense bodies. 

The LAS glass ceramic was tested as one of the first matrices for fibre-reinforced glass ceramics [1.31-33]. This matrix seemed to be very attractive because of its low expansion, thus giving the opportunity to develop strong and tough composites with low thermal expansion up to about 1100 °C. In the meantime, the effort in the development of these materials has been reduced considerably because of two drawbacks. One drawback is observed in most, perhaps all, fibre-reinforced glass ceramics with Nicalon SiC fibres. The high 

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Other glass-ceramics may find potential use in Hquid crystal and electroluminescent displays. 

Fig. 2-51), the growth rate of the Zr02 macrocrystals was the fastest at 3.5-5.0 pm/h (Table 2-26) (Holand et al., 1996). Non-steady-state time lags were not observed for any of the growing crystal phases as they had been in other glass-ceramic systems. This fact indicated that nucleation proceeds rapidly and does not determine the rate of subsequent crystal growth. 

The properties of other glass ceramic products have also been tailored to special household applications the properties of the glass ceramic Robax were adapted to its use as stove windows. Chemical strengthening of the surface of another glass ceramic used for cooktops can improve their functionality. 

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