Tungsten Rhenium Thermocouple Wire Background and Use 2017-02-10T15:27:39+00:00

Application Information

Tungsten Rhenium Thermocouple Wire

Concept Alloys was formed in 2002 by former technical staff of Hoskins Manufacturing Company. The company manufactures its’ products in their facility located in Whitmore Lake, Michigan, USA. It specializes in the production of tungsten-rhenium alloys for temperature measurement using proprietary manufacturing and testing/calibration methods.

Knowledge and experience in the field allow Concept Alloys to provide unrivaled application support, failure analysis and laboratory testing.

Tungsten-rhenium alloy combinations can be used over a wide temperature range that extends from –196°C to over 2,760°C. Standard temperature tables (ASTM E230 and E1751) are available from 0°C to 2315°C. These alloy combinations are susceptible to rapid oxidation at high temperatures and are not recommended for use in oxidizing environments. They are very stable at high temperatures in reducing or inert atmospheres such as hydrogen, inert gases and vacuum. The cost of these materials is relatively low compared to noble metals.

Of the three common combinations of these alloys (pure W vs. W26Re, W3Re vs. W25Re and W5Re vs. W26Re) the W5/W26Re combination has received the widest acceptance by industry. Unless otherwise stated, all materials produced by Concept Alloys conform to ASTM E696, E230 and E1751.

The pure W vs. W26Re thermocouple was the earliest combination developed in this system. It suffers, however, from the brittle behavior of the pure tungsten positive leg. For this reason, the positive leg is generally shipped in the as-drawn condition. This results in an emf shift when the thermocouple is exposed to elevated temperatures (generally in excess of 1,100°C.) in use. The primary advantage in using this combination is the higher Seebeck coefficient obtained at temperatures in excess of about 500°C. Modern instrumentation minimizes the importance of this advantage.

Both the W5Re and W26Re thermoelements retain good room temperature ductility (in comparison to unalloyed tungsten) after heating to over 1650°C and are shipped in a stabilized condition. So long as use is restricted to 1650°C or lower this ductility is retained and handling problems are minimized.

W5Re/W26Re thermocouples may be used bare, with hard fired ceramic insulators or in mineral insulated, metal sheathed (MIMS) cable. At low temperatures common alumina or magnesia insulation is generally satisfactory. Their use is limited by the melting point of alumina (2010°C) and the low electrical resistivity of magnesia above 1980°C.

At temperatures over 1650°C insulators of beryllia, hafnia or thoria may be used. From a performance standpoint beryllia is desirable due to its higher electrical resistivity. However, due to health concerns with beryllia ,halfnia is often used in its place. Before selecting any insulator a thorough investigation should be conducted relative to material properties, chemical compatibility and necessary safety precautions. In MIMS constructions the selected sheath should be compatible with the insulators, wires and atmosphere. Materials that have been used successfully include tantalum, tungsten and some tungsten alloys, niobium, molybdenum and various ceramics.

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