Corrosion Behavior Of Tungsten-rhenium Thermocouple Wire And Protective Countermeasures

As perfect alternative to the platinum-rhodium thermocouple, the tungsten-rhenium thermocouples has the advantage of high thermoelectric potential, high melting point, fast response speed, low price and so on. It is easy to oxidation under the condition of high temperature, only applies to atmosphere of vacuum, inert, reduction of high temperature measurement. It must be protected to use in the air or oxidizing atmosphere. Under the precondition of not affect the thermocouple measurement response speed, In view of oxidation behavior of the tungsten-rhenium thermocouples, we research and develop the materialization antioxidant tungsten-rhenium thermocouples, and makes it possible to use in the air or the oxidizing environment, and prolongs temperature measuring work.At first, we know the oxidation process of the tungsten-rhenium thermocouple wire in the air through the DSC/TG experiment; Through the XRD experiment to make sure that the composition of oxidation products the tungsten-rhenium thermocouple wire; Through the SEM experiment to observe oxidation film of the tungsten-rhenium thermocouples wire; Through measuring the change of the micro resistance under high temperature to qualitatively analysis the oxidation rate of the tungsten-rhenium thermocouple wire. The results show:the DSC curve of W-5%Re wire begin to show heat release at 873℃, and the TG curve begin to show weight gain at 901℃, but the DSC curve of W-26%Re wire is fluctuant from 674℃ to 1062℃; The oxidation film of the tungsten-rhenium thermocouples wire is radioactive growth, and could not protect substrate; the thermo electromotive force and body resistance is mutational when the tungsten-rhenium thermocouples fail.The second, we determine the protection tube and filling type by physical and chemical and the experimental verification. So we choose the corundum protection tube as the protection tube and choose inert materials, functional materials 1 and functional materials 2 as filling materials. The tungsten-rhenium thermocouple wire is put in corundum protection tube and is filled respectively with inert materials, functional materials 1 and functional materials 2, then sealed with the epoxy resin to complete the materialization tungsten-rhenium thermocouples.The materialization tungsten-rhenium thermocouples are oxidated for 11 cycles, then analyzing the wire by SEM to understand the oxide film of the materialization tungsten-rhenium thermocouples wire; and analyzing the element content of different location of the materialization tungsten-rhenium thermocouples wire by EDS and EMPA experiments to ensure whether have the phenomenon of elements redistribution when the wires of W-5%Re and W-26%Re are in the high temperature environment for a long time. In order to simulate industrial applications, the materialization tungsten-rhenium thermocouples should be oxidated 200 hours continuously, then analyzing the oxidation film of the materialization tungsten-rhenium thermocouples wire by SEM. The results show that, the tungsten-rhenium thermocouples with functional materials 1 and functional materials 2 is oxidated after 200 hours, the elements of materials center do not move, functional materials 1 and functional materials 2 can be a very good protection of the tungsten-rhenium thermocouples, the oxidation degree of tungsten-rhenium thermocouples should be minimized.Finally, the materialization tungsten-rhenium thermocouples with filling functional materials 1 and functional materials 2 are tested, and verify the oxidation resistance. The results show that the materialization tungsten-rhenium thermocouples with filling functional materials 2 can be used faultlessly in the air and oxidizing atmosphere for a long time.