With ultra high melting points advanced
ceramics are often the only material of choice for high
temperature applications. Dynallox® alumina components
have operated in furnace environments at up to 1800°C.
Technox® 802 thermocouple sheaths are often used at 2100°C.
One of the main driving forces for the development of
Advanced Ceramics has been their ability to operate at
elevated temperatures. The interatomic bonding of these
materials provides an excellent platform for high temperature
operation, well above the regime of superalloys or other
metallics.
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Melting Points
The melting points of a selection of Advanced
Ceramics are shown in the Table below:
| Material |
Melt.Temp (ºC) |
| Alumina |
2050 |
| Silicon Carbide |
2300 |
| Silicon Nitride |
1800 |
| Zirconia |
2700 |
As with metallic materials there is often a reduction
in room temperature properties at elevated temperatures so it
is wise to discuss your application with our engineers before
specifying an individual material.
One should also take into account the oxidation
behaviour of Non-Oxide ceramics (Si3N4 and
SiC), as this behaviour limits the temperature of application
to +/- 1400ºC.
Case Histories
There are many examples of the use of Advanced
Ceramics in elevated temperature applications, from relatively
"low tech" Kiln Furniture for the electronics industry, to "high
tech" in the form of Silicon Nitride turbocharger rotors which
operate at 150,000 rpm and 800ºC. The following examples
provide an insight to the range of high temperature applications.
Furnace Roof Hangers
Produced from one of the several grades of Dynallox®
Alumina manufactured by Dynamic-Ceramic, these components operate
as load bearing supports for furnace roof insulation. To date
many years of successful service has been reported at temperatures
of up to 1800ºC.
Thermocouple/Inspection Tubes
Technox® 802 zirconia tubes are now
used extensively in optical fibre production, both as inspection
devices and for thermocouple protection. In these applications
the material experiences temperatures in excess of 2000ºC.
Production techniques have been developed to
permit the fabrication of thin walled tubes, with both open
and closed ends to exacting tolerances.
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