Study On Electrical Property And The Thermocouple Of ZrB₂-based Ceramic Materials

In this paper，the electrical property and the performance of the thermocouplesprepared by ZrB₂-based materials were studied. We hope to overcome theshortcomings of traditional temperature measurements, such as low temperature rangeof contact temperature measurements and low precision of non-contact temperaturemeasurements.There are some insurmountable problems in traditional temperature measurementmethods, which make it is hard to apply in the higher temperature and more harshenvironment and temperature measurement accuracy is difficult to meet the demand.For example, traditional resistance temperature measurement method can not applyabove1000℃due to its low melting points，the poor antioxidation and corrosionresistance under high temperature of their own material. And the thermocoupletemperature measurement method is difficult to use in the oxidizing atmosphereabove1600℃because of the limitation of thermocouple materials. Non-contacttemperature measurement method has a bigger temperature measurement range （up to3500℃） than that of contact temperature measurement method, but a relative lowertemperature measurement accuracy.ZrB₂, with the potential used in extreme environments, has excellentperformances, such as high melting point, high hardness, high stability, high thermalconductivity and good corrosion resistance to the molten metal and slag. In thiscontext, ZrB₂-based material has been studied extensively. ZrB₂-based materials, alsohaving excellent electrical properties, are potential to use as high temperaturethermocouple material, so I hope to deepen understanding of the electrical propertiesof ZrB₂-based material. And study the performance of ZrB₂-based materials duringtemperature measurement through the preparation of thermocouple.In this paper, the electrical property of the different components of ZrB₂-basedmaterials is studied, analyzed the impact of the composition and particle size on theconductivity. For ZS10, ZS20and ZS30, their resistivity increases with the increasingof the SiC content. For10G,15G and20G, with the graphite content increasing, theresistivity increases. And the extent of increased resistance temperature coefficientbecomes bigger, when the graphite content increases. At the same temperature, theresistivity of different components changes with the vol.ume fraction of ZrB₂inversely. ZrB₂content determines the change of the resistivity. The resistivity ofnano-ZS20is significantly larger than that of micron ZS20. The resistancetemperature coefficient of nano-ZS20is also much larger than that of ZS20.The15G and ZS20are selected as thermocouple positive and negative materials,respectively. And a thermocouple, can be used for measurement and used in theexperiment, is made. And its temperature dependence of thermoelectric power weremeasured. Experimental results show that the thermocouple of the thermoelectricpower temperature curve has a good reproducibility in different tests, especially in the temperature range above1000℃; Similarly, the temperature dependence ofthermoelectric power in the heating and cooling process also has good reproducibility.Oxyacetylene heating on the hot end of the thermocouple can provide a highertemperature. We test the thermoelectric power relations below2000℃using thismethod. The results show that for thermocouple, the thermoelectric powertemperature curves have the same trend no matter using oxyacetylene to provide thetemperature of the hot end or using the muffle furnace.The change of ZS20and15G materials depending on temperature within therange of room temperature to1300℃was studied by thermogravimetric anddifferential thermal analysis method. The oxidation state of the material at differenttemperatures were analyzed, showing that the oxide film formed can at least protectthe material in the oxidizing atmosphere to1600℃. The oxidation products arenon-conductive, and have no effect on the electrical properties that are not part of theoxide film, so the final thermocouple thermoelectric properties are not subject tosurface oxidation.