Research On Detection Characteristics And Sensing Mechanism Of Cr-SnO₂ Based Sensor To C₂H₂

The analysis of dissolved characteristic gas in oil is one of the effective methods for oil-immersed power transformer state maintenance.C₂H₂ is the main fault characteristic gas dissolved in transformer oil,which can effectively reflect the discharge fault problem of power transformer.Semiconductor SnO₂ gas sensors have attracted extensive attention due to their low cost and high stability.For on-line analysis of dissolved gases in oil,there are problems such as poor selectivity and length of use.Therefore,studying the gas sensing mechanism and detection characteristics of SnO₂-based C₂H₂ gas sensors is of great significance for improving the insulation operation level of transformers.The paper relies on the National Natural Science Foundation of China to carry out the first principle study of the detection characteristics and gas sensing mechanism of SnO₂-based C₂H₂ gas sensors.Firstly,the SnO₂ gas sensing materials with different morphologies were prepared by hydrothermal method.After characterization,the planar gas sensor was fabricated,and its growth mechanism was analyzed and its gas sensing properties for C₂H₂ gas were tested.After pure Cr₂O₃ particles were synthesized by sol-gel method,pure and Cr₂O₃-SnO₂ fibrous gas-sensitive materials were prepared by electrospinning method.The structure of the Cr₂O₃-SnO₂ fiber-like gas sensing materials was studied.Based on the first principle of density functional theory,the SnO₂ surface model,C₂H₂ adsorption model,Cr-SnO₂ doping model and C₂H₂ gas adsorption model were established.The surface atomic configuration and electronic properties were analyzed by first-principles.The main results of the paper are as follows:1.Fiber,rod,microsphere and flower-like SnO₂ gas sensitive materials were prepared by hydrothermal method,and characterized by XRD,SEM and BET to prepare a planar gas sensor.The gas sensing properties of acetylene gas were tested based on a laboratory trace gas gas sensing test platform.The results show that the fiber-like and flower-like SnO₂ sensor has lower operating temperature,better gas sensitivity response and faster response recovery time than the microsphere and rod SnO₂ sensor when testing C₂H₂ gas,among which fibrous and flower-like SnO₂ detection The optimum operating temperature of 100ppm C₂H₂ is reduced to 260°C,the sensitivity is 47 and 34,respectively,while showing good stability and repeatability for C₂H₂ gas.The test found that the fibrous SnO₂ material has a large specific surface area(36.67m²/^-1g)and a large pore size?8.9nm?,thus exhibiting better gas sensitivity to C₂H₂ gas.2.After pure Cr₂O₃ particles were synthesized by sol-gel method,pure and Cr₂O₃-SnO₂ fibrous gas-sensitive materials were prepared by electrospinning method,and characterized by XRD,SEM,EDS and XPS to prepare planar gas.The sensor was tested for its detection characteristics for C₂H₂ gas.The test results show that compared with the fibrous pure SnO2 gas sensor,the Cr₂O₃-SnO₂ sensor has better gas sensitivity when detecting C₂H₂.When the C₂H₂ concentration of 20ppm is detected,the optimal operating temperature of the Cr₂O₃-SnO₂ gas sensor is reduced to 220°C,the sensitivity is increased to 48.54,and the response recovery time is 10s and 12s.It showed good linearity to C₂H₂in the low concentration range of 1-50 ppm.The linear fitting function was y=5.07+2.02x and the linear correlation coefficient was 0.993.3.Based on the first principle of density functional theory,a rutile SnO₂ crystal model was established.The adsorption model of C₂H₂ gas molecules at SnO₂?110?surface Sn_5c,Sn_6c,O_2c,O_3c was simulated.The simulation found that The O_2c position is the optimal adsorption site for the SnO₂?110?surface C₂H₂ gas.The doping model of Sn-substituted SnO₂?110?surface Sn_5c and Sn_6c sites was established.The Sn_5c position was found to be the optimal doping position of Cr-SnO₂ crystal model.Based on the optimal doping configuration,the C₂H₂ gas adsorption model was established.The results show that compared with the pure SnO₂?110?surface C₂H₂ gas adsorption model,when Cr-SnO₂?110?surface adsorbs C₂H₂,the band gap decreases by 0.044eV,and the charge transfer amount increases to 0.251e,so that the C₂H₂ adsorption to the Cr-SnO₂ sensor exhibits better gas sensitivity.