Вр5 tungsten rhenium thermocouple wire
The heat resistance of alloys ВР5 and ВР20
The advantages of the alloys are determined by tungsten and rhenium. Tungsten is one of the most difficult, refractory, hard metal. Temperature its melting point is 3410 °C, boiling point is the same as on the surface of the Sun — 6690 °C. Tungsten alloys for refractoriness and hardness in the lead among all other alloys. Slightly inferior to him rhenium, the melting point of which 3170 °C and the boiling point is equal to the 5870 °C. For the heat resistance of rhenium is far ahead of other metals, has high strength and resistance to corrosion.
The features of doping
Alloying tungsten with rhenium — 5% increases the ductility of the alloy, increasing the temperature of its recrystallization, which is especially important when it is applied to a positive electrode of the thermocouple. The use of alloy as a negative electrode to achieve the maximum thermo-EMF, require the maintenance of up to 35% rhenium.
Tungsten-rhenium alloy is resistant to helium, dry nitrogen, hydrogen, argon. Doping of silica-alloy additives to increase its stability in two-three times at temperatures up to 2000 °C.
Sensors ВР5 and ВР20 can be operated in vacuum conditions. To ensure at temperatures of 1800 °C and above more effective work in a vacuum, it is necessary to use electrodes of larger diameter. ВР5/20 successfully used as differential thermocouple — it may be two equivalent thermocouple connected opposite each other. These thermocouples are able to measure the level of temperature difference between two junctions: conditional and work.
Upon cooling to 1600 °C the nominal value of the thermal EMF also decreases to the level of 24.59 MB. The figure at t° 1500 °C is not more than from 23.31 mV at t°1400°C nominal thermal EMF is of 21.97 mV.
Significant disadvantages of these alloys relates a poor reproducibility of the thermoelectric power, therefore you want to group thermocouples in categories A-1,2,3. The first category a-1 makes it possible to apply the alloy at the maximum temperature of 2200 °C, the mode of application of A-2 and 3 is limited to 1800 °C. it is Strictly forbidden to use wire of different parties because each of them has its «own» rate of thermal EMF. Since rhenium and tungsten are rare metals, their price is very high. Although the cost ВР5/20 much more than the cost of the thermocouples, consisting of other elements, but still less than the price of alternative instrumentation for temperature regimes in a similar industrial environment.
ВР5, ВР20 used in the production processing and measuring devices, as well as TVR (contact sensors thermocouples) for measuring the highest temperatures in industrial metallurgy — liquid metals. The uncertainty of measurement up to 2500 °C is very small (±0,01°C). This makes the instruments for measuring the most accurate TVR in such an aggressive environment.
The calibration table tungsten-rhenium thermocouples VAR-5 (BP-5)/20 when the temperature of the free ends 0°C
|The temperature of the working end °C||T. E. D. S. mV temperature, °C|
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