Ceramics are inorganic compounds made by firing clay minerals together with other secondary minerals such as sand at temperatures greater than 700 degrees C. Technical ceramics are high-performance compounds with a large variety of applications, from dentistry to the linings of nuclear reactors.
Technical ceramics are thermally and electrically insulating, with extreme hardness and minimal thermal expansion. They hold to a very stable state because they have a limited plastic deformation capacity.
These properties make technical ceramics particularly suitable for applications involving metals. They are more abrasion- and corrosion-resistant than metals and are not influenced by temperature to the same extent as metals.
Silicon carbide is by far the most important of the carbide sub-groups of technical ceramics. Different types of this compound are produced depending on the application. However, in general, the compound has extremely high hardness and resistance to oxidation and wear, even at the highest temperatures.
Technical ceramics have a special application as coating materials. There are different methods for applying thin or thick films of the material. Thick films (greater than 20 microns thickness) are generally applied by plasma spraying. Various components of the ceramics are heated to around 10,000 °C and sprayed on a surface, usually metal, that would have been sandblasted previously.
Thin films (of thicknesses less than 20 microns) can be applied using physical vapour deposition (PVD) or chemical vapour deposition (CVD). The two processes are similar in that they involve the deposition of a coating by using it in its gaseous phase.
The PVD method starts with solid material that is vaporised and deposited on a substrate. The CVD method works by aiming precursor gases at a substrate. These react and decompose it and deposit a solid on to the substrate. The resulting coating is impervious, fine-grained and of high purity. These materials also have very high working temperatures of approximately 1,500 °C.
Silicon carbide ceramics produced with the CVD method are especially resistant to chemical erosion and can be used in etching processes using chlorine and fluorine plasmas that would normally disintegrate other compounds.
Such materials are very useful in the production of gas distribution plates because their resistance to erosion means that components have a long operational life as well as an extended preventative maintenance period.
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