Gas Sensing Properties Studies On Nitrogen And Fluoride Doped TiO₂ Nanotube Gas Sensors For Detecting SF₆ Decomposition Components

SF₆ electrical insulation equipment combines a variety of electrical appliances in a closed manner,which has reduced the footprint and the impact of the external environment and is now widely used in power systems.However,during its long-term operation,internal latent insulation defects would cause partial discharge,which could causes decomposition of SF₆ insulating gas,and reduce its insulation performance.In order to ensure the safety and stability of the power system,it is necessary to test the operating status of the SF₆ electrical insulation equipment.Unlike other offline and periodic detection methods,the gas sensor method could enable real-time long-term online monitoring of equipment.In recent years,a large amount of research has been conducted due to the wide application field of TiO₂.Resistive gas sensor based on TiO₂ nanomaterials has become a research hotspot in the field of gas sensing due to its high stability,large resistance change and reversibility.However,defects such as intrinsic energy gap?more than 3.0eV?of intrinsic TiO₂ limit its application in the field of gas sensing.Studies have shown that modifying the surface of TiO₂ by metal or non-metal doping is an effective way to solve this problem.Therefore,the TiO₂ nanotubes are doped with fluorine and co-doped with nitrogen and fluorine by dielectric barrier discharge low temperature plasma method,and then the gas sensitivity of the modified TiO₂ nanotube sensor will be investigated from theoretical simulation and macroscopic experiments.The main research contents and conclusions of this paper include:?1?The adsorption mechanism of the three decomposition products of SF₆ on the fluorine-doped and nitrogen and fluorine co-doped TiO₂ crystal planes were studied.Based on the simulation software Materials Studio,a microscopic model of fluorine doping and nitrogen and fluorine co-doping TiO₂ was established.The adsorption process of gas molecules on the TiO₂ crystal plane was calculated by density functional theory.Some parameters such as state density and molecular frontier orbital of the adsorption system were analyzed.The simulation results show that the electron structure of the adsorption system changes significantly after the SO₂ gas molecules are adsorbed onto the fluorine doping and the nitrogen and fluoride co-doped TiO₂ crystal plane.After doping,the direction of charge transfer changes from gas molecules to crystal planes to from crystal to gas molecules,and the adsorption of SOF₂ and SO₂F₂molecules on doped crystal is slightly enhanced.?2?The surface modification experiment of TiO₂ nanotubes was carried out.In the specific implementation,the dielectric barrier discharge is used to generate CF₄ plasma and the N₂ and CH₄ mixed plasma,which are used for fluorine doping and nitrogen fluoride co-doping on the surface of the TiO₂ nanotube.The SEM and XRD characterization results show that the structure and properties of TiO₂ nanotubes have not changed.The XPS spectra of F 1s and N 1s orbitals indicate that some O atoms in the TiO₂ lattice are replaced by N atoms and F atoms after plasma discharge treatment,and forming new F-Ti bonds and N-Ti bonds,which indicate that TiO₂ nanotubes have successfully achieved fluorine doping and co-doping of nitrogen and fluorine.?3?The gas sensing experiment of TiO₂ nanotubes was carried out.The macroscopic gas sensing properties of fluorine-doped and nitrogen and fluorine co-doped TiO₂ nanotube gas sensors were studied.Firstly,the temperature characteristics of the three decompossition components on the modified TiO₂ nanotube gas sensor were measured.The results showed that the operating temperature of the modified TiO₂ nanotube gas sensor is significantly lower than that before doping.Among them,the operating temperature of the fluorine-doped TiO₂ nanotubes to three components decreased from 200^°C to 110^°C,and the nitrogen and fluoride co-doped TiO₂ nanotubes to three components decreased from 200^°C to 80^°C.Then,the gas-sensitive response of the modified TiO₂ nanotubes to the three decomposition components was measured.The results show that sensitivity responses of the fluorine-doped TiO₂ nanotubes to SO₂,SOF₂ and SO₂F₂ were-26.78%,-15.83%,and-10.47%,respectively.The gas-sensitive responses of nitrogen and fluorine co-doped TiO₂ nanotube gas sensors to SO₂,SOF₂,and SO₂F₂ gases were-52.98%,-26.05%and-2.75%,respectively.The research work in this paper is a positive exploration of the gas sensor method applied to the on-line monitoring of SF₆ insulated electrical equipment.The research results provide theoretical support and experimental basis for the state evaluation of SF₆ insulated electrical equipment.