Materials

3.2 Materials Groups

Technical ceramics are often subdivided into groups in accordance with the definitions mentioned above. However since this does not permit unambiguous classification, they are alternatively grouped according to their mineralogical or chemical composition.

The following groups belong to the materials defined as technical ceramics:

Silicate ceramics, as the oldest group amongst all the ceramics, represent the largest proportion of fine ceramic products. The major components of these polyphase materials are clay and kaolin, feldspar and soapstone as silicate sources. Additionally such components as alumina and zircon are used to achieve special properties such as higher strength. During sintering a large proportion (> 20%) of glass phase material, with silicon dioxide (SiO2) as the major component, is formed in addition to the crystalline phases.

Included in the silicate ceramic materials category are:

Due to the relatively low sintering temperatures, the good understanding of how to control the process, and the ready availability of the natural raw materials, silicate ceramics are much cheaper than the oxide or non-oxide ceramics. The latter require expensive synthetic powders and high sintering temperatures.

Silicate ceramics are found, for example, in heat engineering applications, measurement and control engineering, process and environmental technologies, high and low voltage applications with typical uses such as insulators, fuse cartridges, catalysts, enclosures and in a wide range of applications in the electrical equipment industry. Silicate ceramics also continue to be used as refractory materials.

Oxide ceramics are defined as all materials that are principally composed of a single phase and a single component (>90 %) metal oxide. These materials have little or no glass phase. The raw materials are synthetic products with a high purity. At very high sintering temperatures a uniform microstructure is created which is responsible for the improved properties.

Some examples of oxide ceramics include

Oxide ceramics are found in the electrical and electronics industries, and often as structural ceramics, i. e.i.e. for non-electrical applications. They offer the typical properties suited to these applications, such as high fracture toughness, wear resistance, high-temperature resistance and corrosion resistance.

Non-oxide ceramics include ceramic materials based on compounds of boron, carbon, nitrogen and silicon. (Products made of amorphous graphite do not belong to this category!)

Non-oxide ceramics usually contain a high proportion of covalent compounds. This allows their use at very high temperatures, results in a very high elastic modulus, and provides high strength and hardness combined with excellent resistance to corrosion and wear.

The most important non-oxide ceramics are: