The designation ceramics comprises a hugh number of anorganic compounds which are typically oxides or carbides from various metalls. The properties of ceramics are much different from the metalls based on. For examples ceramics are almost inert, i.e. not at all corrosive and very good electric and thermal isolators. Ceramics cannot be melted or softened by temperature and are temperature resistant up to very high temperature.
Ceramics have been used for thousends of years. Historically aluminium oxides and caolite have been won from clay minerals and been used for forming and burning all types of dishes and vessels.
The perfect insulating performance of these ceramics have been the base of early technical applications of porcelain materials when the technical application of electricity started.
Thermal and electrical insulation is still an important application mainly of aluminium oxide ceramics but the most important applications are due to the extraordinary hardness, abrasion resistance and low friction.
- Aluminiumoxide Al2O3 (Korund): Abrasives
- Zirconiumdioxice ZnO2: High Performance Abrasives
- Siliconcarbide SiC: High performance Abrasives
Moulded pieces can be produced by sintering, however the variety of contures is limited. The introduction of injection moulding of ceramic parts abolished this limitation so that almost any geometrical structure is possible. These products take profit from the following characteristics superior to any other material:
- Thermal resistance and stability
- Little thermal expansion
- high hardness and stiffness
- high resistant against almost all chemicals
- little friction and abrasion
- However it is also a specific characteristic of all ceramic, that their resistance against deformations, elongation and bending strngth is very limited
A rapidly growing field of ceramics applications is ceramic coating by CVD- and PACVD technologies by using low pressure plasma. By this method silicon carbide- and boron carbide layers of extreme hardness and wear resistance can be produced.
Some unique ceramic applications are:
- Beryllium oxide (BeO) for vessels of highest possible temperature resistance
- Silicon carbide (SiC) for bearings for extreme dynamic load (speed and force)
- Boron nitride and boron carbide: Harness close to diamond
- Zirconium dioxide (ZnO2) for medical implants because of perfect biocompatibility