Highly stable, sheathed, beryllia insulated, tungsten-rhenium alloy thermocouples

The fabrication and performance testing of 1.6mm diameter tantalum sheathed, beryllium oxide (BeO) insulated, W-3% Re/W-25% Re thermocouples are reported. Fully assembled thermocouples constructed from aged thermoelements, specially heat treated, sintered BeO insulators, and specially cleaned and etched tantalum sheaths were tested for 2059h at 1800 deg C in a helium environment. The measured thermal emf drifts were less than the equivalent of 1 deg C per thousand hours of exposure at 1800 deg C. No gross chemical attack or degradation of the component materials was evident. The fabrication techniques, thermal emf test results, and post-test analyses of the component materials are discussed