Importance

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Abstract

The invention is an improved theroelement which comprises a graphite/boron carbide thermocouple, the arms of which are constructed as a tube and a rod, arranged concentrically inside the tube, which are electrically connected at one end. One of the arms of the thermocouple consists essentially of boron carbide formed from self bonding boron carbide by pressureless sintering. Prefabricated sleeves of high-purity, boron-oxide-free hexagonal boron nitride are used between the arms of the thermocouple as spacers. Only the end of the arm of the thermocouple constructed as a rod is secured in an electrically conductive connecting piece and the arm is freely mobile in the direction towards the cold junction. As the material for the arm of the thermocouple constructed as a rod, there can be used, for example, boron carbide having a coarse-grained structure and a density of from 60 to 80% TD, which has been manufactured from boron carbide powder having bimodal particle size distribution by means of extrusion, followed by pressureless sintering at from 2000.degree. to 2250.degree. C. The thermoelement can also be manufactured in one operation by means of pressureless sintering of the boron carbide powder in situ. Such a thermoelement comprises, for example, a flexible graphite cord for the arm of the thermocouple constructed as a rod, a boron-nitride envelope and a boron-carbide casing, the envelope and casing having been formed from powders sintered in situ without pressure.

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First Claim