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Domestic tungsten-rhenium alloys are produced in two types: BP5 (95% W, 5% Re) and BP20 (80% W, 20% Re). Rolled wire is presented. Wire for stabilization when working in a high-temperature environment is doped with silica-alkali additives: 0.1% — 0.5% SiO2; Al2O3: KCl. The alloy is designated as VAR. VR-wire for thermocouples graduated and annealed with the nominal properties of thermal conversion VR (A) -1 meets the specifications of YaO.021.142 for the production of thermocouples VR-20 / VR-5 (VAR-5).
The basis of tungsten-rhenium alloy BP5 is tungsten, which has extreme refractoriness, its melting point is 3410 ° C. The heat resistance of rhenium combined with the highest resistance to corrosion allows it to form a worthy pair of tungsten, a melting point of 3170 ° C. Tungsten-rhenium alloys in terms of refractoriness and hardness are superior to other materials. When alloying tungsten 5% Re, the plasticity of the alloy increases. BP5 is used in a thermocouple in the form of a positive electrode.
To achieve the maximum thermo-emf of a tungsten-rhenium alloy and use as a negative electrode in it should be up to 35% Re. Domestic metallurgy produces alloys containing up to 20% Re. This makes it possible to measure t ° of the order of 2500 ° C while maintaining the stability to the medium Ar2, He2, N2 and H2. When alloying with siliceous additives, the stability of the alloy increases significantly at up to t ° 2000 ° C.
Category of alloys
Due to the fluctuations in the thermo-emf values of tungsten-rhenium thermoelectrode pairs, BP alloys are divided into categories. Category A-1 is used at t ° 2200 ° C; A-2 and 3 — up to t ° 1800 ° C. Do not combine wire from different lots, because Each of the lots has its own indicators of thermo-emf.
Tungsten-rhenium thermocouples are indispensable for measuring very high temperatures in metallurgical furnaces. The error to 2500 ° C is ± 0.01 ° C. The cost of VR thermocouples depends on the price of tungsten and rhenium. Because they are quite expensive, and their production is associated with a number of difficulties. The cost of thermocouples based on the alloys of BP5, BP20 is not small. Nevertheless, it is much lower than the cost of alternative instruments for high-temperature thermometry.
|Temperature ° С||1400||1500||1600|
|Nominal value of thermo-emf, mV||21.97||23.31||24.59|
|Deviation of the thermo-emf from the nominal, μV||± 96||± 99||± 102|
It is not allowed to complete the thermocouple from different series of thermoelectrode wire, even with the same nominal static characteristic of thermoelectrodes.
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