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.