The principal properties of ceramics

The principal properties of ceramics arise from a combination of chemical bonding and the atomic defects and microstmcture resulting from the fabrication techniques described above. 

The bonding, whether described as ionic or covalent, is strong, which ensures that the solids are chemically inert and often stable to high temperatures (refractory). Refractory ceramics are widely used in furnaces and other high-temperamre equipment. In addition, in aerospace applications refractory components are used both externally, to protect the outside of re-entry modules, and internally, in rocket motors. 

The lack of free electrons endows basic ceramics with poor thermal and electronic conductivity. The chemical flexibihty of ceramics, however, allows them to be selectively doped with other ions. In particular, doping with transition metal or lanthanide ions generates a wide variety of colours and can radically alter electronic and magnetic properties. Thus, insulators can be transformed into superconductors. How this comes about is described in Part 4, Chapters 10-15. 

Ceramics do not deform very easily at ordinary temperatures, as strong chemical bonds must be broken and, unlike metals, dislocation movement 

Some widely used silicate glasses are listed in Table 6.3. 

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