Gas Sensitivity Studies On Amino And Gold Modified Carbon Nanotubes Detecting SF₆Decomposed Components

Sulfur hexafluoride（SF6） is widely used in gas insulated switchgear (GIS) due toits excellent insulation arcing performance. In the long time operation, the insulationdefects inside GIS may cause discharge or over-thermal faults, decomposing the SF6into a variety of by-production gases. The detection and analysis of theSF6decomposition componentsis of great significance in condition assessment and faultdiagnosis of GIS.In this thesis, considering the shortcomings of general detectionmethods, a carbon nanotube gas sensor was usedto detectthe SF6decompositioncomponents.Both theoretical calculation and sensing experiment were adopted to studythe micro adsorption mechanism and macro gas sensing properties.Considering the detecting limitations of intrinsic CNTs,this thesis developed aminomodified single-wall CNTs (SWCNTs-NH2) and gold-dopedsingle-wall CNTs(Au-SWCNTs). And studied their gas sensitivities tothe SF6decomposition components(H2S, SO2, SOF2, SO2F2).At first, the adsorptions between four kinds of gases and SWCNTs-NH2werecalculated based on density functional theory.Results show that the adsorptionenergybetween SO2and SWCNTs-NH2is the largest, and so is the charge transfer. It indicatesthat SWCNTs-NH2has the highest sensitivity to SO2, next is SOF2. The adsorptionbetween SO2F2and SWCNTs-NH2is physisorption,there is nearly no charge transferbetween them and the sensitivity is the lowest. Then adsorption energy and chargetransfer are analyzed based on molecular frontier orbitaland the density of states toexplain the micro adsorption mechanism between SWCNTs-NH2and the four gases.Then the SWCNTs-NH2gas sensor wasfabricatedusing interdigital electrodeconfiguration. The response sensitivity, response time and recovery feature of thissensor to the four gases were test. Experiment results show that the sensitivity ofSWCNTs-NH2gas sensor follows the order SO2＞SOF2＞H2S＞SO2F2. When the gasconcentration decreases, the sensitivity of SWCNTs-NH2gas sensordecreases and theresponse time increase, while the selection and response characterstic of the sensor tothe gases do not change. In addition, the SWCNTs-NH2gas sensorhas a good recoveryfeature that through vacuum and nitrogen flushing, the sensor can be basicallyrecovered in6minutes to the initial state.Therefore, SWCNTs-NH2is suitable forfabrication of gas sensorsto detect SF6decomposition components, which laysthefoundation for the fault diagnosis and condition assessment of GIS. Finally, considering the excellent properties of metal-doped carbon nanotubes, thisthesis showed a further theoretical study about the Au-doped SWCNTs detecting SF6and its decomposition components. The adsorption between Au-SWCNTs and gasmolecules were calculated. Adsorption energy, charge transfer, molecular frontier orbitaland density of state were analyzed to explain the adsorption mechanism. The calculatedresults show that Au-SWCNTs have a good sensitivity to SF6and its decompositioncomponents. SO2increase the conductivity of Au-SWCNTs, while H2S decrease that.When SOF2, SO2F2and SF6adsorb on the Au-SWCNTs, their S-F bonds may break.Thus, Au-SWCNTs is not suitable to detect the SF6decomposition but can be used forthe leakage detection of SF6and the removal of waste SF6.