Ceramic forming

Ceramic forming iavolves consoHdation and mol ding of ceramic powders to produce a cohesive body of the desired size and shape. Ceramic forming operations (38,40—66) are conducted with dry powders, plastic bodies, pastes, and slurries. 

This reaction has a lower free energy of formation (—218 kJ/mol at 1000°C) compared to the simple oxidation-rednction reaction (—118 kJ/mol) analogous to Eq. (3.48) above. It is also possible that the molten metal can completely reduced the metal oxide ceramic, forming an alloy and gaseous oxygen ... 

Table 7.3 Nominal Processing Pressures and Shear Rates in Some Ceramic Forming Processes...

Table 7.13 Some Structural Ceramics Formed in Gas-Phase Synthesis...

The effects of temperature and frequency on the permittivity and dissipation factor of a high-purity alumina ceramic are shown in Fig. 5.24. The discrepancies between the permittivity levels in Fig. 5.24 and values given elsewhere are probably due to differences in microstructure and measurement technique. Reliable room temperature values for er for single-crystal sapphire at 3.4GHz are 9.39 perpendicular to the c axis and 11.584 parallel to it, which are close to the values measured optically. The average er to be expected for a fully dense ceramic form is therefore 10.12, and values close to this have been determined. Nothwithstanding the uncertainties there is no doubt that the general behavioural pattern indicated by Fig. 5.24 is correct and typical of ceramic dielectrics. 

Rutile is anisotropic, with the values of er at room temperature being approximately 170 and 90 in the c and a directions respectively. In the polycrystalline ceramic form er averages to intermediate values with a... 

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