Research On Sensing Preparation Of ZnO Based Methane Gas Sensor And Its Sensing Mechanism With The First-principle

Dissolved gas analysis in oil is the most convenient and the most effective way to judge oil-immersed transformer's latently faults in early times.Gas sensing detection technology is the core of the dissolved gas analysis in oil,it directly affects the accuracy and reliability of the diagnosis.At present,most of the oil dissolved gas on-line monitoring device when used in gas sensor for on-line monitoring will have faulty gases dissolved in transformer oil is affected by temperature,concentration,sensitivity of gas selectivity,the weak choices between various gases and poor stability of device problems and so on.So it is unable to evaluate the insulation of the transformer working state monitoring effectively.Therefore,studying gas sensor detection technology and developing new gas sensor have great significances to improve the on-line monitoring of dissolved gas in transformer oil.Depending on the Natural Science Fund Project in Chongqing,this thesis mainly aim at detecting fault characteristics of methane gas in the oil in the oil-immersed power transformer and conducting the study of oxide zinc based methane gas detection sensor and gas-sensing mechanism which are based on the first principle.Applying the hydrothermal method,first step is to prepare different morphology as well as metal platinum oxide doped zinc base gas sensitive materials.After that,analyzing characterization analysis like morphology,crystal structure,particle size and element composition,later it made into heater gas sensor and the methane gas sensitive performance experiment.At the same time,which based on the first principles of density functional theory,establishing the corresponding oxide zinc base of gas-sensitive sensor model,studying the model surface atomic structure and electronic properties,constructing CH₄ gas adsorption model and electronic performance calculation analysis.The main achievements of the thesis are as follows:1.Using the hydrothermal preparation of flake and spherical ZnO gas sensitive material then analyzing it in the X-ray diffraction,scanning electron microscopy?SEM?and analyzing it in X photoelectric spectrometer,and make it into heater gas sensor which is based on laboratory test platform to test its CH₄ gas gas-sensing properties.Study found that compared with spherical ZnO,flake ZnO based gas sensitive materials has larger specific surface area?25.2 m²/g?and average pore diameter?8nm?.Which is made from sheet ZnO under different concentrations of CH₄ gas sensor has higher response value and the low concentration(2²0 parts per million?ppm?,and good linear relation with the CH₄ under the best working temperature?270??on 50ppm CH₄ gas sensitivity is as high as 42.3.Compared with spherical ZnO gas sensor,the best working temperature is60?,at the same time,it has faster responding speed and good repeatability.2.Using the hydrothermal method to prepare the lamellar ZnO gas sensitive materials with metal Pt doping,which based on the laboratory gas testing platform,so the detection studies the characteristics of CH₄ gas.Test results show that:compared with pure doping sheet ZnO,6mol%of the Pt doping ZnO gas sensor of CH₄ gas have a higher response value under different concentrations,detecting of 50 ppm CH₄ gas when the best working temperature down to 240?the detection sensitivity increased to 64.2 and the response-recovery time is 8 to 12s,as well as the low concentration of CH₄ gas shows better linearity.3.Based on the First Principles density functional theory to build the metal Pt doping ZnO model and CH₄ gas adsorption material surface model before and after,staying the doped ZnO base gas sensor which based on the model simulation properties and adsorption properties.Study found:the?001?surface of the ZnO is the stability surface in low index.Pt atoms replaced Zn_3d bit and then it can formed Eform less than Pt atom adsorption which is doped in O_2s.The doping method is more stable,O_2s an atom surface has larger adsorption to CH₄ gas adsorption.CH₄ gas adsorption on Pt doping ZnO?001?adsorption on the surface is larger then on the pure ZnO.The charge transfer is 0.136e and it is obviously more than 0.121e of pure ZnO.It shows that CH₄ gas is more likely to adsorbe on the metal Pt doping of ZnO surface,the results of the study lay the foundation of high performance ZnO CH₄ gas sensor research and development.