Background

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.
Melting Points

The melting points of a selection of Advanced Ceramics are shown in the Table below:

Table 1. Melting points of some commonly used advanced ceramics.

Material


Melting Temp (°C)

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 Dynamic-Ceramic 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 c.1400°C.
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 800°C. 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 months of successful service has been reported at temperatures of up to 1800°C.
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 2000°C.

Production techniques have been developed to permit the fabrication of thin walled tubes, with both open and closed ends to exacting tolerances.