High Temperature Ceramic Oxide Thermocouple By Screen Printing

In the fields of aerospace,nuclear power and chemical industry,a large number of large-scale high-temperature components with extreme high temperature and indestructible structure are involved.Most of their working environments are above1300°C,and the temperature field distribution of high-temperature hot-end components can be obtained.High-precision monitoring has a crucial impact on the performance improvement and prolonging the working life.In view of the temperature measurement requirements of such large-scale high-temperature components,there are extremely high requirements for the upper limit of temperature measurement of the temperature sensor and the preparation method.The traditional temperature measurement technology cannot meet the above requirements,but the use of graphic screen printing technology to print the thermoelectric sensitive ceramic oxide powder in the form of electronic paste on the surface of the measured hot end component,which has the advantages of not destroying the component structure,low cost,strong oxidation resistance and easy preparation.In this thesis,based on the application background of high-temperature testing requirements of large high-temperature components,new ceramic oxide La_0.7Ca_0.3Mn O₃（LCMO）:ITO screen printing thermocouple,new ceramic oxide La_0.67Sr_0.33Mn O₃（LSMO）:ITO screen preparation and performance study of printed thermocouple and screen-printed Pt:ITO thermocouple.First,the preparation of ceramic oxide LCMO powder and the preparation and thermoelectric properties of a new LCMO:ITO screen-printed ceramic oxide thermocouple were carried out.LCMO powder was prepared by high-temperature solid-state reaction,and then LCMO:ITO screen-printed thermocouple was fabricated on Al₂O₃ceramic substrate by screen-printing technology.Through atmospheric annealing treatment,the organic components in the slurry are effectively excluded,and the film thickness is reduced while the film continuity is effectively ensured.After annealing at1300℃for 2 h,the resistance of the LCMO film decreased from 8.4 KΩto 2.2 KΩ.Through dynamic calibration test,the sensitivity performance of thermocouple is studied.The results show that the output thermoelectric potential increases with the temperature difference between the hot end and the cold end of the thermocouple,and has good repeatability and sensitivity.The Seebeck coefficient of the thermocouple reaches 50.21μV/℃,which is an order of magnitude higher than that of the precious metal thermocouple.And the new ceramic oxide LCMO:ITO screen-printed thermocouple can still work stably at 1300℃.Secondly,the ceramic oxide LSMO was explored as a new thin-film thermocouple material,and the preparation and thermoelectric properties of a new ceramic oxide LSMO:ITO screen-printed thermocouple were studied.The research results show that the output thermoelectric potential of the new ceramic oxide LSMO:ITO screen-printed thermocouple well follows the change trend of the temperature difference between the hot and cold ends of the thermocouple,and has good repeatability,stability and sensitivity..In the temperature rise and fall range,the four calibration results have good repeatability,and the output thermoelectric potential increases with the increase of the temperature difference.The calibration results show that the Seebeck coefficient of the LSMO:ITO screen-printed thermocouple reaches 40.65μV/℃.At a high temperature of1300℃and constant temperature calibration for 2 h,the thermoelectric performance of the thermocouple is stable,and the service life exceeds 50 h.Finally,a Pt:ITO screen-printed thermocouple was fabricated by screen-printing technology,and its thermoelectric properties were studied.The study found that the Pt and ITO films after annealing at 1300℃can completely discharge the organic components of the slurry inside the film,repair the internal defects of the film,improve the continuity of the film layer,and enhance the electrical conductivity of the film.The research results show that the output thermoelectric potential of the screen-printed Pt:ITO screen-printed thermocouple in the dynamic calibration temperature range from room temperature to 1300℃increases nonlinearly with the change trend of the temperature difference between the hot end and the cold end.The fitting correlation coefficient of the fitting reaches 0.9999;the Seebeck coefficient of the screen-printed Pt:ITO screen-printed thermocouple is 48.75μV/℃,and the temperature drift rate is0.167K/h at 1287℃.Compared with the magnetron sputtering Pt:ITO screen-printed thermocouple,it has a higher upper limit of temperature measurement,the upper limit of temperature measurement is increased by 200℃,and the service life is also more than45h.