A Tungsten Rhenium Thermocouples Positive and Negative Comparative Stability

Tungsten- rhenium thermocouple in the air oxidation will occur after a certain time thermopower mutation to constitute the positive and negative tungsten -3% -25 % rhenium and tungsten rhenium alloy oxidation rate is different. Which can be expected, the stability of the thermocouple will they produce different effects . It can be seen from Figure 1 : Tungsten rhenium thermocouples having different stability of positive and negative . 1000 ℃, tungsten rhenium 3 pole poor stability, thermopower mutation first occurred , and tungsten rhenium 25 very good stability , a later mutates. Stability of the positive and negative differences are two kinds of tungsten and rhenium alloy oxidation behavior consistent . 800,900 ℃ , with the decrease in the content of rhenium , tungsten rhenium alloy antioxidant capacity enhancement. -3% Tungsten rhenium relatively good adhesion due to the formation of a layered structure oxide film having less than 25% of rhenium, tungsten corrosion rate ; 1000 ℃ , the rhenium content is higher, the stronger the oxidation resistance of alloys . As a result of 25% tungsten, rhenium oxide layer formed by reaction sintering of the oxide film layer structure , the outer layer is less rich tungsten rhenium oxide thin , inner layer is a dense tungsten , rhenium oxide mixed layer , relative to the base ratio, rhenium has enriched . Reaction sintering the oxide film becomes more dense , increased to 25% of tungsten rhenium at 1000 ℃ antioxidant capacity , the corrosion rate is lower than -3% of tungsten rhenium . Therefore , tungsten rhenium 3 pole less stable at 1000 ℃ , the first occurrence of thermopower mutations. Therefore, positive and negative changes in the sequence of stability is a direct reflection of the level of oxidation rate .

2 . Tungsten rhenium thermocouple thermoelectric power thermoelectric mutation causes

Positive and negative relative stability during the experiment at the same time , using two 0.8 mm nickel chromium wire 2cm long were suspended tungsten -3 % -25 % tungsten, rhenium and rhenium alloy wire of a group, working with the thermocouple placed on the same side of the temperature zone 1000 ℃ , when mutations occur when the first thermoelectric take a set of samples , the second mutation then remove another set of samples , respectively, electron microprobe analysis . The results show that : the first time thermopower mutation , -3% tungsten rhenium alloy anode has been completely oxidized, and the negative -25 % tungsten rhenium alloy wire core part still alloy phase . The second thermoelectric mutated, it is also negative alloy phase has been fully oxidized [1] . Thus , tungsten rhenium thermocouple thermoelectric power is due to the positive and negative mutations caused by oxidation .

To further confirm this phenomenon, making the overall stability test thermocouple , remove mutations moment thermocouple, will end its work made ​​metallographic sample . Based on our 1000 ℃ tungsten rhenium thermocouple potential mutations just occurred working end time by metallographic analysis of morphology , thermocouple potential mutation causes the selective oxidation of alloying elements is not caused by changes in composition , but the pole due to oxidation of a thermocouple the original tungsten rhenium alloy turned into oxides. This is a qualitative component , that is, from alloy into oxides , this phenomenon is associated with tungsten- rhenium alloy high temperature oxidation behavior consistent . Under the experimental conditions , as rhenium and tungsten oxide evaporation , resulting in the oxidation of the tungsten rhenium alloy catastrophic oxidation follows a linear law of cracking . Cracks formed during the oxidation , loose oxide layer is difficult to form the oxygen diffusion resistance, so that the oxidation reaction occurs at the metal / oxide layer interface ; since rhenium is far less than the oxygen affinity of tungsten , and their oxides generated with a more the steam thus large tungsten rhenium alloy does not occur during the oxidation of rhenium selective oxidation , the oxide layer which are made from tungsten and rhenium oxide mixture. Thus , in an oxidizing atmosphere , there is no selective oxidation caused by the diffusion of metal cations as a result of gradual change in the alloy composition . Thus, as the oxidation process proceeds, shrinking alloy wire cross-section , but the composition changed, until eventually completely oxidized into oxide , the material properties of a fundamental change , closely related thermoelectric properties also changed completely , thus tungsten- rhenium thermocouple leads thermopower mutations. Through the above experiment , the first to reveal the potential of tungsten rhenium thermocouple nature of mutations . Further, since the tungsten- rhenium alloy is generated after oxidation of rhenium oxide has a high electrical conductivity , resulting in the tungsten- rhenium thermocouple has failed circuit illusion thermopower still occurs , which would address the long outstanding problem.

3 tungsten rhenium thermocouples oxidation technology and antioxidant tungsten rhenium thermocouples

Tungsten- rhenium thermocouple thermoelectric effect in the air is the main factor unstable oxidation, and in order to replace platinum-rhodium thermocouple they can only work in an oxidizing atmosphere , so can be used as oxidation technology : ① Coating Protection Act ; ② evacuated sealed protection Act ; ③ evacuated inflatable seal protection law ; ④ filling sealing protection laws.

Coating Protection Act technically there are still some problems, and taking the time to fill or seal protection law has passed the batch test, every year at least one thousand or more antioxidant tungsten rhenium thermocouple temperature measurement for industrial furnaces . Since the protective tube for the artificial creation of tungsten- rhenium thermocouple working non-oxidizing atmosphere , resistance to oxidation of the tungsten rhenium thermocouple term stability. Author entities using patented technology to produce tungsten rhenium thermocouple type antioxidant , after sintering plant in Anshan pellet furnace ( oxidizing atmosphere ) using seven months (5000h), after removal of the test results showed that it stable performance, precision up to 1% , and can continue to use.


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Tungsten- rhenium thermocouples in order to solve the problems encountered in actual use , the paper discusses the tungsten rhenium thermocouple temperature stability in air law . The results showed that : tungsten rhenium thermocouples as a result of a very complete oxidation of the material properties undergone a sea change , which led to the thermoelectric properties with the corresponding radical change ; for the first time revealed the stability of tungsten- rhenium thermocouples poles at different temperatures are different ; discovered tungsten rhenium thermocouple having a volume resistivity and thermoelectric properties of both mutations and thus , by measuring the change in resistance to predict its lifetime . Results of this study for the production of tungsten- rhenium thermocouples and provides a theoretical basis for the rational use .

Tungsten- rhenium thermocouples fifties developed excellent refractory metal thermocouples , is currently more than 1800 ℃ can be measured to a better industrial thermocouples. Since platinum-rhodium thermocouple prices, user urgent need to find alternative products, resulting in oxidation of tungsten rhenium thermocouples very active in the development , the current temperature is hot research field . Now, the country has produced various forms of anti-oxidation of tungsten rhenium thermocouples few thousand a year to expend in metallurgy , building materials, petrochemical and other industries , and showed a broad application prospects . The reserves and production of tungsten are in the world, but also about antioxidant tungsten rhenium thermocouples and consumable tungsten rhenium thermocouples development and application is also a leader in the world . In order to solve the tungsten rhenium thermocouple problems in practical use , it has been explored in a non- oxidizing atmosphere stability, but in an oxidizing atmosphere stability has not been reported , which is an antioxidant tungsten rhenium thermocouple emergence of new issues , with a clear theoretical significance and practical value.


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In order to be consistent with the actual application , the present study, major domestic and foreign manufacturers to provide wire tungsten rhenium thermocouple wire as an object of study, the positive and negative growth 45cm thermocouple match between the poles of high purity Al2O3 insulated pipe insulation, work side exposed to the air . Experiment, the tungsten rhenium thermocouple placed in the working end of the furnace body temperature zone, the reference terminal is at room temperature , which fluctuated within ± 5 ℃ . With high-precision digital voltmeter thermopower of the thermocouple and the bulk resistance for real-time detection , in order to examine the stability of the thermocouple at different temperature variation and high purity platinum wire as reference electrode tungsten- rhenium thermocouples negative comparison the relative stability of the pole , while using electron probe microanalysis techniques and metallographic studies thermocouple thermoelectric potential reason for the change .

Tungsten- rhenium thermocouple thermoelectric EMF and body resistance R in the oxidation process variation with time t showed significant mutagenicity . Very stable prior to the mutation occurs ; thermoelectric potential and volume resistivity at the same temperature mutated . Its direction varies with temperature : 800 ℃ and 900 ℃ , the thermoelectric power is drift occurs ; 1000 ℃ negative drift occurs .

Thermopower mutation manifested again and negative drift occurred . But bipolar mutations occur thermopower time is different , the first thermoelectric potential positive changes , and the negative electrode . As can be seen , under the same conditions , its stability and domestic wire variation of the same , nor found over domestic wire has obvious advantages , this shows that our wire stability has reached the international advanced level of similar products .


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Tungsten- rhenium thermocouples is 60 years developed a high-temperature thermocouples, tungsten / ( tungsten- rhenium -26 ) , ( -3 tungsten rhenium ) / ( -25 tungsten rhenium ) , ( tungsten- rhenium -5 ) / ( W - 26 rhenium ) and ( tungsten rhenium -5 ) / ( -20 tungsten rhenium ), etc. Long-term use temperature of 2000 ~ 2400 ℃, short-term use up to 3000 ℃. In the low-temperature thermocouples , ( copper -2.1 cobalt ) / Cu thermocouple, the 10K or more thermoelectric power greater than 10μV / K; gold contains trace amounts ( about 0.07 atomic percent ) alloy of iron and nickel-chromium alloy thermocouples at liquid helium temperature (4K) thermoelectric power greater than 10μV / K, all the better . ( Pt -0.1 Mo ) / ( Pt -5 Mo ) , ( Pt -1 Mo ) / ( Pt -5 Mo ) and tungsten , and 0.5 to 1 ( atomic% ) alloy of osmium and rhenium tungsten alloy thermocouples etc. can be used in the nuclear radiation conditions . In addition to metallic materials, graphite and other non-metallic materials, refractory compounds can also be used as high temperature thermocouples. The advantage of such materials are high melting point , high temperature stability, high thermal potential and thermoelectric power , etc. ; drawback is brittle materials , graphite is easy to absorb moisture and changes in thermal resistance , poor reproducibility , but also in research and development into . Such thermocouples with carbon / graphite , graphite / carbide , carbide / carbide .

Tungsten- rhenium thermocouples ! Generally in a vacuum or reducing atmosphere used , if the transmission distance is long , it requires specialized wire compensation .

Tungsten- rhenium thermocouple as an excellent high-temperature measurement sensor , the maximum temperature can reach 2800 ℃, is currently measured temperature above 1800 ℃ better contact industrial thermocouples, are widely used in aero-engine plume exploration , petrochemical heavy oil cracking furnace, coal gasification , metallurgical atmosphere furnace , nuclear reactor core temperature measurement. tungsten rhenium thermocouple wire in an inert gas and dry hydrogen thermoelectric properties stable, but vulnerable in an oxidizing atmosphere oxidation at different oxygen partial oxidization of the linear , when a very complete oxidation of the material properties which cause a qualitative change , it will lead to fundamental changes in thermoelectric properties .

1 In order to make the tungsten rhenium thermocouple wire used in an oxidizing atmosphere , and foreign scholars have done a lot of research, using a variety of oxidation technology so that it can be applied to an oxidizing atmosphere , for example , the coating protection law, taking the sealing Protection Act , taking the inflatable seal protection law, fill seal protection law.

2 , but on the tungsten rhenium thermocouple wire in nitrogen , high temperature stability of carbon in the environment has not been reported in this study through the tungsten rhenium thermocouples field failure analysis , discussion in nitrogen, high-temperature carbon environment, tungsten failure of rhenium thermocouples , has obvious theoretical significance and practical value !

Are many types of thermocouples , thermocouple domestic industry is widely used for the current product quality and classification of the different manufacturers , product quality and performance has a different problem , as technology continues to improve , the product and quality of life has made ​​great progress !


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