High Temperature Thermocouple Probes

Vacuum • Carburizing • Annealing • Hardening • Sintering
Reference

A11 Info

Our line of High Temperature Thermocouples are especially designed for the temperature range from 1000°F to 4235°F. Sheath materials available from stock include tantalum, molybdenum, zirconia, alumina and quartz. Chief characteristics of the sheath materials are summarized below. Please note, the size of the wire diameter of the thermocouple element is key to the life of the device. Nanmac offers both a standard gage, #30 (0.010 inch) and a heavy gage #24 (0.020 inch) wire diameter for high temperature thermocouples.

Alumina (Al2O3)
This high purity sintered aluminum oxide (99.5% AI2O3, dense) has a melting point of 3686°F (2030°C) and an upper working service temperature of 3482°F (1900°C). It can be used in oxidizing, reducing or high vacuum applications. (Not recommended for use in high vacuum environments in the presence of graphite at temperatures exceeding 2372°F (1300°C). AI2O3 has high thermal conductivity and therefore fairly good resistance to thermal shock. It has excellent resistance to chemical attack. Poor for thermal cycling applications.

Fused Quartz
(Fused silica) consists of 99,9%SiOi. Most acids, metals, chlorine and bromine are reactive with fused silica at ordinary temperatures. It is slightly attacked by alkaline solutions, the reaction rate increasing with temperature and concentration of solution. Fused silica has an extremely low coefficient of thermal expansion, 0.55 x 10-6 cm/cm/°F (0-572°F). This is l/34th that of copper, 1/17th of platinum and 1/9th of tungsten. This low expansion produces a high thermal shock resistance, it can be heated to 2700''F, and immersed into ice water without cracking. Good for oxidizing, inert or neutral atmospheres to 3050°F. Excellent for thermal shock applications. Devitrifies rapidly at temperatures above 1800°F causing microscopic surface cracking (hazy film) upon cooling.

Molybdenum (Mo)
Excellent mechanical properties at elevated temperatures. Melting point at 4750°F. Excellent in reducing or neutral atmospheres. It has low thermal-neutron capture cross-section and excellent thermal shock resistance. Poor in oxidizing atmospheres. Excellent for thermal cycling applications.

Tantalum (Ta)
Melting point of 5430°F. The most corrosive resistant of the refractory metals. Corrosion resistant to most chemicals up to 3000°F. Good in reducing or neutral atmospheres at elevated temperatures. Poor in oxidizing atmospheres. Excellent for thermal cycling applications.

Tungsten
Coating the protecting sheath with a thick layer of tungsten minimizes the carburization process and extends the life of the probes significantly. Field tests of 2,000 degrees Celsius using the coated probes produced continuous temperature data for up to two months. Even during cycling, whereas the uncoated probes failed within hours of reaching temperature. Longer life times were also experienced at temperatures below 2,000 degree Celsius.

Zirconia (ZRO2)
Zirconium oxide is fully stabilized with exceptional refractory properties, which include the highest melting point and lowest thermal conductivity of any refractory. It is not wetted by most molten metals, is generally inert to oxidizing and reducing atmospheres, and resists most chemical reactions. Usable to 4400°F. It is impervious (0% water absorption). Poor for thermal cycling applications.

Applications:
Oxidizing, vacuum, reducing and inert gas furnaces, gas burners, ovens, nuclear power generating plants, exhaust gases, wind tunnels, pollution control, and high temperature process control applications.

Note:
All information supplied herein is intended as a guide only. All information should be verified by the user through the users own engineering efforts, prior to implementation.