Tungsten-Rhenium Thermocouples for Use at High Temperatures

Tungsten-rhenium thermocouple systems were evaluated for use in measuring temperatures between 1600 and 3000°C. Temperature-millivolt relationships were extended from 2300 to 3000°C for bare-wire W3Re/W25Re and W5Re/W26Re thermocouples in vacuum. The performance of W26Re sheathed, high-fired beryllia-insulated thermocouples was limited only by the melting point of the beryllia insulation (∼2550°C). The thermoelectric output of high-fired thoria-insulated thermocouples sheathed in W26Re was determined and found to be reliable up to at least 2850°C, when corrected for electrical shunting through the insulation. Stability of high temperature thermocouples using thoria insulation was within ±0.3 mV (±40°C) when held at 2425°C for 148 h.