Mica glass-ceramics microstructures

The microstructure of the mica glass-ceramic of the phlogopite-type demonstrates direct interlocking of the mica crystals after heat treatment at 950 C for 4 h. This morphology is described as a house-of-cards in Section 3.2.6. 

Beall (1971) determined that different microstructures can be produced, depending on the composition crystallization process used. Furthermore, the chemical stability of the respective glass-ceramics also changes. The machin-ability of this mica glass-ceramic proved to be very favorable. A ceramic containing one-third by volume mica was shown to demonstrate satisfactory machinability. Optimum machinability was obtained at two-thirds by volume. 

A dense microstructure of mica crystals formed in the glass matrix on heat treatment of625°C for 4 h and 1100°C for 6 h. The determination of the properties of this type of alkaline-fi ee mica glass-ceramics was of particular interest. 

To sum up, the formation of the house-of-cards microstructure in mica glass-ceramics is characterized by the following solid-state reactions, which take place as consecutive reactions ... 

Holand W, Gotz W, Carl G., and Vogel W, "Microstructure of Mica Glass-Ceramics and Interface Reactions between Mica Glass-Ceramics and Bone," Cells Mater., 2, 105-12 (1992). 

Figure 1. Electron micrograph of microstructure of mica glass ceramic. Specimen was polished to 1 pm finish and etched in HF for 10 s. Most of the platelets are viewed edge on. The occasional plan view of a platelet can be seen.

Table 1. Microstructural parameters for mica glass ceramic materials. For aU materials, the volume fraction is Vf 70%, the elastic modulus E ps 70 GPa and Poisson s ratio v ps 0.26. Platelet dimensions measured from sectioned and etched samples. Yield stress was determined according to a procedure given in reference 12.

Influence of CU2O Addition on Crystallization Process and Microstructure of Transparent Mica Glass-Ceramics... 

Figure 2-20 Microstructure of mica ZrOj glass-ceramic (containing 7.5 wt% after heat treatment at OSO C.

Fluorapatite and mica crystallization are examples of a twofold controlled mechanism to develop a glass-ceramic having a combination of diflFerent properties, such as machinability and bioactivity. The microstructure of the final glass-ceramic comprising mica and apatite crystals embedded in a glass matrix is shown in Fig. 2-32. 

Figure 2-44 Microstructure of machinable fenimagnetic glass-ceramic (see the composition in Table 2-22) after heat treatment (1180 C/1 h). Cubic spinel crystal of the ferrite-type and mica crystals characterize the morphology of the glass-ceramic (SEM).

At temperatures in the range of 790°- 1000°C, curved micas demonstrating a cabbage-head microstructure were formed. A typical example of this microstructure is shown in Fig. 3-14b. The growth of a second crystal phase in the form of a secondary phase was observed in the final stage of the formation of curved micas in different glass-ceramics of this type. This phase was located between the mica crystals (Fig. 3-15a), X-ray diffraction investigations have shown the phase to be composed of cordierite crystals. The formation of... 

This glass-ceramic (Glaskeramik 1995)> like Bioverit (see Section 4.4.1), exhibits a cabbage-head microstructure of mica crystals. The special properties of this glass-ceramic are ... 

Mica-type glass-ceramics are very good insulators. MACOR is a preferred glass-ceramic for this appHcation. Its properties and microstructure were reported in Sections 2.3.1 and 3.2.6. 

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