Tungsten Rhenium Thermocouple Wire
Application Information
Concept Alloys was founded in 2002 by technical professionals with decades of experience in specialty alloys. The company manufactures its products in Whitmore Lake, Michigan, USA, and specializes in the production of tungsten-rhenium alloys and tungsten rhenium thermocouple wire used for high-temperature measurement applications. Using proprietary manufacturing, testing and calibration methods, Concept Alloys produces materials designed for reliable performance in demanding environments.
Extensive industry knowledge and hands-on experience allow Concept Alloys to provide strong application support along with detailed failure analysis and laboratory testing services for customers using tungsten rhenium thermocouple wire and other specialty alloy products.
Tungsten Rhenium Thermocouple Wire for Extreme Temperature Measurement
Tungsten rhenium thermocouple wire and alloy combinations can operate across an extremely wide temperature range, from –196°C to over 2,760°C. Standard temperature reference tables defined by ASTM E230 and ASTM E1751 cover the range from 0°C to 2315°C. These materials provide excellent stability in reducing or inert environments such as hydrogen, inert gases and vacuum. However, tungsten-rhenium alloys oxidize rapidly at high temperatures and are not recommended for use in oxidizing atmospheres. Compared with noble metal thermocouples, tungsten rhenium thermocouple wire offers a much lower material cost while maintaining reliable performance at very high temperatures.
Three primary tungsten-rhenium thermocouple combinations are commonly used: pure W vs. W26Re, W3Re vs. W25Re and W5Re vs. W26Re. Among these, the W5Re/W26Re combination has become the most widely accepted in industry. Unless otherwise specified, materials produced by Concept Alloys conform to ASTM E696, ASTM E230 and ASTM E1751 standards. The earlier W vs. W26Re design used pure tungsten as the positive leg, but this configuration can become brittle and experience an emf shift when exposed to temperatures above roughly 1,100°C. Its main benefit is a higher Seebeck coefficient at temperatures above about 500°C, though modern instrumentation has reduced the importance of this advantage.
The W5Re and W26Re thermoelements provide better ductility compared with pure tungsten and maintain good handling characteristics after heating to temperatures above 1650°C. These thermocouples can be used bare, with hard-fired ceramic insulators, or in mineral-insulated metal-sheathed (MIMS) cable. At lower temperatures, alumina or magnesia insulation is commonly used, though their performance limits are tied to the melting point of alumina (2010°C) and the declining electrical resistivity of magnesia above about 1980°C.
Insulation & Sheath Materials for High Temperature Tungsten Rhenium Thermocouples
For temperatures above 1650°C, specialized insulators such as beryllia, hafnia or thoria may be used. Beryllia offers strong electrical resistivity performance, but due to health concerns it is often replaced with hafnia. In MIMS assemblies, sheath materials must be compatible with the thermocouple wire, insulation and operating atmosphere. Materials that have been used successfully include tantalum, tungsten and tungsten alloys, niobium, molybdenum and certain ceramics, depending on the application environment.