Gas-sensitive Characteristics And Simulation Of Antase TiO₂Nanotube Sensor On Detecting SF₆Decomposed Components

Sulfur hexafluoride (SF6) gas, which has excellent insulation and extinguishingperformance, is widely used as the main insulating medium in gas insulated switchgear(GIS). However, inevitable defects inside the GIS may lead to partial discharge (PD),which brings the huge hidden trouble to the long-term reliable operation of GIS. TheSF6will decompose into SF5, SF4, SF2, and so on, under PD. The decompositionproducts oxidize in electrical discharges in the presence of oxygen or water vapor toform various reactive and stable by-products such as SO2, SOF2and SO2F2. The speciesand concentrations of SF6decomposed gases can be detected to diagnose the insulationstate of GIS. Although there are lot methods to detect the SF6decomposed gases, it stillhas many deficiencies to realize the online detecting of GIS internal failures. In thispaper, a gas sensor based on anatase TiO2is developed to detect the SF6decomposedgases. The gas sensing response and mechanism are studied by experiment and theorycalculation, and we conclude that the TiO2-based gas sensor can be effectively appliedto detect the SF6decomposed gases.In this paper, TiO2nanotube arrays (TNTAs) are prepared through theelectrochemical anodization of titanium foil. The TNTAs are highly ordered anddirectionally grown, the pipe diameter of which is about80nm, length is about300nm,and thickness is about10nm. Then the TNTAs gas sensor is designed and its sensingproperty is tested by our SF6gas composition test platform. SO2, SOF2, and SO2F2arechosen as probe gases. Temperature characteristics and sensing responses of the TNTAsgas sensor to these three gases is studied. The sensing responses under differenttemperatures at50uL/L and the sensing responses under different concentrations at200°C are showed in this paper. From experiment results, we find that the responses ofTNTAs gas sensor increase at first and then remain nearly unchanged; at the sametemperature and the concentrations is low, the responses of the three gases and theirconcentration values have a linear relationship. When the temperature is200°C and theconcentrations of the probe gases are50uL/L, the response of TNTAs gas sensor to SO2(74.6%) is more than that to SOF2(7.9%) and SO2F2(5.5%). It implies that the TNTAsgas sensor based on anatase TiO2has a better selectivity to SO2.In addition, first principles density functional theory (DFT) calculations areadopted for the theoretical investigation of the process of anatase (101) surface adsorbing SO2, SOF2and SO2F2. The adsorption energy, charge transfer and bandingdistance are calculated in this paper. The density of states analysis and molecular orbitalanalysis of the simulation results shows that the anatase (101) surface has bettersensitivity and selectivity to SO2than SOF2and SO2F2. This theoretical finding iscorroborated by the sensing experiment, which explains the sensing mechanism of theTNTAs gas sensor at atom level and improves our insight into the fundamentalunderstanding of interactions between the gas and the TNTAs surface.