Glass Ceramic Systems

A number of other phosphate-based glass-ceramic systems have been investigated. Fine-grained glass-ceramics based on crystals isostructural with NZP (NaZt O ) can be prepared from certain transition-metal orthophosphate and silicophosphate glasses (27). The extensive solid solution possible in the NZP phase provides for a wide range in thermal expansion, with coefficients ranging from —20 to 60 x 10-7 /°C. 

Preparation of Giass Ceramics 17.3.3.1. Glass Ceramic Systems... 

Various investigations have been conducted in an effort to combine two specific properties in the fluorosilicate glass-ceramic system and in the mica glass-ceramic system in particular, that is, high strength and machinability as a result of mica precipitation. 

The above glass-ceramic system was selected with the intention of producing biomaterials to replace bone in human medicine. It was particularly important to achieve a high content of apatite in the glass-ceramic as well as a Ca reservoir to assure the subsequent ion release of the implant by adding CaO and P2O5 to the glass-ceramic. 

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. 

In a study on the effects of oxidation on crystallization, Keding and Russel (1997) found that reduction produced the ion, which acted as a nucleating agent. Russel (1997) managed to control the orientation of the main crystal phases in a specific axial direction in various glass-ceramic systems. The fresnoite system as well as apatite glass-ceramics and lithium disilicate glass-ceramics were particularly suitable. 

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