Monolithic Glass-Ceramics

NaCaPO in a sample pjgg g 2-35 DSC functions of the base glass heated at heated to 580 C. The SSO C for 15 min. 

At higher temperatures, above 610°C, a new interesting phenomenon was discovered. XRD investigations (Fig. 2-36 (B)) showed the precipitation of an additional crystalline phase at 640°C and no NaCaPO crystals were present any longer. 

The primary crystals of apatite were determined at 700 C for 8 h heat treatment (Fig. 2-38). But these crystals did not show a needlelike habit. Needlelike fluoro- 

This phenomenon is also visible at 800 C at the beginning of the apatite precipitation. 

Heat treatment of glass powders results in the precipitation of leucite from the surface of the glass-ceramics and the volume crystallization of needlelike apatite. 

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Limited and controllable shrinkage No porosity in monolithic glass-ceramics... 

Pressing (viscous flow at 900°C for glaSs-ceramic A or 1000°C for glass-ceramic B) monolithic glass-ceramic... 

In addition to the largest monolithic glass-ceramic telescope mirrors in the world today, measuring 8.2 m in diameter, light-weight structures made up of individual segments are also produced (Schott product information 1988). 

J. Lankford, Strength of Monolithic and Fiber-Reinforced Glass Ceramics at High Rates of Loading and Elevated Temperatures, Cer. Eng. Sci. Proc., 9[7-8], 843-852 (1988). 

Liquid-feed/ceramic melter (PAMELA 11) (FRG-DWK/ Eurochemic/KFK, Mol) Borosilicate glass or glass ceramic Monolithic cylinder Joule-heated ceramic Liquid Chemical or thermal... 

Ceramic matrix composites (CMCs), in which carbon or ceramic fibers are embedded in a ceramic matrix, have been designed to overcome the intrinsic brittleness of monolithic ceramics with a view toward structural uses at extremely high service temperatures. The most commonly used are carbon (C/C) and SiC matrix composites (C/SiC and SiC/SiC). Ceramic matrix composites with a silica based glass or glass-ceramic matrices have also been studied [12] [53-56]. 

Figure 1-40 Crystal size of phlogopite in the glass ceramic after different heat treatments of the base glass. Results of 765°C, 795 C, 810°C, 825"C, 840 C are related to thin films, results for 910 C were determined for monolithic samples.

These mechanisms are presented by using the examples of cordierite and leucite glass-ceramics. To clearly demonstrate the mechanisms, experiments were conducted with monolithic test specimens rather than the fine-powdered glasses required in the industrial manufacturing of glass-ceramics. The following descriptions, therefore, refer only to the mechanism as demonstrated in monolithic specimens. 

Glass-ceramics of the P203-Al203-Ca0-type are produced as monolithic bulk glass-ceramics and as composites of glass-ceramics and metals. Both types are used as biomaterials for bone substitution in human medicine. 

On the other hand, a melt-derived glass body of the same composition is fractured or softened during heating to high temperatures. Crystallization took place only on the surface of the glass sample. This indicates that the gel monolith has many inner surfaces (pore surface) and as a result, crystallization takes place throughout the gel body, which leads to the formation of glass-ceramic without fracture or deformation. 

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