STUDY OF HIGH TEMPERATURE THERMOCOUPLES.
Final rept. for 1 Jun 63-15 Dec 64,
HOSKINS MFG CO DETROIT MICH
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Materials suitable for use as components of thermocouples for temperature measurement in a graphite environment were investigated. The performance of the WW26Re thermocouple was evaluated up to 2500C in the presence of graphite under different atmospheric conditions. Thermoelectric effects were associated with carbon-metal reactions as revealed by metallographic studies or test materials. The behavior of the thermocouple was found to be directly dependent on the carburizing potential of the atmosphere surrounding the wires. Temperature indications were found to be reliable within at least 2 for up to 100 hours at 2400C in argon at atmospheric pressure in a graphite furnace. However, reducing the pressure or replacing the argon with hydrogen or a hydrocarbon gas caused a decrease in the thermocouple output as a function of time and temperature. This was interpreted as the formation of intermediate junctions of Tungsten Tungsten Carbide and Tungsten-26 Rhenium Tungsten Carbide in the respective wires. Several thermocouple prototypes were constructed and were found to have features that could be useful in thermocouples for a graphite environment. Author