Thermal properties of technical ceramics
Four terms are crucial when it comes to thermal properties of technical ceramics:
- Thermal conductivity
- Thermal expansion
- Thermal shock resistance
- Maximum temperature of use
Some ceramic materials are used as thermal insulation material because of their low thermal conductivity. The thermal conductivity of ceramic is generally lower than that of metals such as copper or steel.
Regarding their capacity to conduct heat, silicate ceramic materials i.e. steatite as well as superpyrostat, cordierite and forsterite exhibit consistent low values on the same level. Zirconia, a chemical compound belonging to the group of oxide ceramics, exhibits similar behavior, whereas alumina (same group) and silicon nitride(group of non-oxide ceramics) show relatively high thermal conductivity.
Cordierite: low thermal expansion
The thermal expansion of technical ceramics is normally lower than that of grey cast iron or steel – a detail that needs to be considered when designing composite constructions. Thermal expansion is a specific material constant with values depending on the respective temperature range. The thermal expansion of oxide ceramic alumina and non-oxide ceramic silicon nitride is comparatively low. Silicate ceramics such as steatite, superpyrostat and cordierite show low thermal expansion. Forsterite exhibits higher values and, in this respect, is complemented by zirconia from the group of oxide ceramics.
Ideally suited for high insulation through low thermal conductivity
Thermal stresses depending on geometrical, thermal and physical boundary conditions control a property known as thermal shock resistance. The mineral cordierite being a silicate ceramic and the compound silicon nitride, a non-oxide ceramic, exhibit average values, whereas alumina and zirconia (both oxide ceramics) as well as silicate ceramic materials i.e. steatite, superpyrostat and forsterite come out slightly less well. Ceramic materials are used in many demanding applications because of their excellent thermal insulation. All silicate ceramics – steatite, superpyrostat, cordierite and forsterite – as well as high-tech oxide ceramic materials such as zirconia achieve exceptionally low thermal conductivity.
Technical ceramics show exceptional thermal load capacity
The maximum temperature of use is another important criterion when selecting materials for high-temperature applications. Pure alumina is ideally suited because it can withstand temperatures up to 1,800° C in air.
The thermal load capacity of non-oxide silicate ceramics is significantly higher when exposed to protective atmosphere rather than air; the material oxidizes at temperatures exceeding 1,400° C as soon as it comes into contact with oxygen. Depending on operating conditions, we supply specific zirconia materials with extremely high thermal load capacity (up to 2,000° C). Silicate ceramic materials are generally not comparable with oxide ceramics in this area.
Selecting the perfect ceramic material according to its thermal properties to fit in with each application is a complex project. Please contact us to discuss and find individual solutions.
Further information can also be found in our material data sheet.
Would you like detailed information about the properties of materials used at Sembach Technical Ceramics, or do you have other questions or a specific inquiry? Please contact us, we would be pleased to help you.