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Oftentimes, a molybdenum sheathed thermocouple is used in a furnace with graphite liners or heating elements. At temperatures above 1,600 degrees Celsius any graphite present emits dust molecules which attack the sheath and rapidly carburizes the sheath. This causes the sheath to become crystallized and porous. The thermal elements lose their protection and they also become crystallized and then break during cycling. Coating the protecting sheath with a thick layer of tungsten minimizes this carburization process and extends the life of the probes significantly. Field tests at 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 degrees Celsius.
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