Gas Sensing Properties On Cobalt-doped Zinc Oxide Composites Detecting Gases Dissolved In Transformer Oil

Gas sensor technology is the core of online monitoring of dissolved gases in transformer oil.However,when it comes to the use of conventional semiconductor metal oxide gas sensors to detect the dissolved gases in transformer oil,it still remains some performance issues so far,such as poor sensitivity,high operating temperature,slow response-recovery time,and low selectivity.Those factors have restricted the application of their use in this field.ZnO-based composites have become a research hot-spot due to its excellent physical and chemical properties,easy preparation,and potential gas-sensing performance to dissolved gases in transformer oil.In this work,the main characteristic gases dissolved in transformer oil are taken as the object of study.From the perspective of gas sensing properties,a planar gas sensor based on Cobalt-doped ZnO is developed and tested for four gases?H₂,CO,CH₄,and C₂H₂?under the experimental conditions to study its gas sensing properties such as temperature-sensitivity,concentration-minimum limited detection,response-recovery time,selectivity,and stability.At the same time,based on the first-principles of density functional theory,an intrinsic,Co-doped ZnO model,and adsorption models of six gases?H₂,CO,CO₂,CH₄,C₂H₂,and C₂H₄?were established and simulated from the atomic and electronic levels.The characteristics of Co doping and the adsorption of gases also be investigated.Finally,the macroscopic gas properties and microcosmic theoretical calculations are combined to explore its intrinsic gas-sensing mechanism and provide theoretical guidance for exploration of specific functional modification methods for detecting gases dissolved in transformer oil.The main work are as follows:Different morphologies of ZnO and Co-doped ZnO nanomaterials were synthesized by hydrothermal method,and XRD,SEM,TEM,and SAED tests were carried out.A planar Co-doped ZnO composite gas sensor also is manufactured:The XRD pattern of Co-doped ZnO show that there are new three-doped characteristic peaks,and the doping and fusion of Co strengthen the intensity of the three main peaks of the intrinsic ZnO material.The prepared crystals are pure phase hexagonal wurtzite structure with good crystallinity;Co-doped ZnO nanostructures with a variety of morphologies are clearer,more dispersive than intrinsic ZnO nanomaterials,a larger specific surface area,more gas channels,and more BET surface.The more effective active sites in a surface which will contribute to the more intense charge exchange and physicochemical reactions between gases and materials;less doping has less influence on the morphology and crystallinity of the intrinsic material,and the as-prepared material is exposed to grow along the?0001?surface.The gas sensing characteristics of four main characteristic gases were tested and analyzed from five perspectives:At 200?L/L,the temperature-sensitivity characteristics are:C₂H₂?160 ^oC,9.886?<CH₄?200 ^oC,6.054?<CO?240 ^oC,4.077?<H₂?260 ^oC,3.369?;The concentration characteristics were tested in 0⁴00?L/L,and at 0²0?L/L,a good goodness of curve fitting?linearity of sensor?was demonstrated:C₂H₂?2.62?L/L?<CH₄?9.43?L/L?<CO?17.12?L/L?<H₂?24.68?L/L?;at 200?L/L,the response-recovery time is:C₂H₂?22²6 s?<CH₄?22³3 s?<CO?24³3 s?<H₂?35⁴3 s?;The method of sensitivity standardization is introduced to analyze the selectivity of the sensor.The selectivity to the four gases was good under 50,100,200?L/L;The sensor has a little degree of drifted and fluctuated within 60 days of the stability test at 100?L/L.Based on the first-principles calculations,structure models of intrinsic ZnO,cobalt-doped ZnO and adsorption models of six main characteristic dissolved gases in transformer oil?H₂,CO,CO₂,CH₄,C₂H₂,and C₂H₄?on Co-doped ZnO?0001?surface were established and simulated:Through a comprehensive study of the results of five single-parameter?E_a,Q_t,T?L?DOS,E_g,and visualization HOMO-LUMO?,the gas sensing properties of the six gases which through the conductivity changed of the composites achieved are evaluated to increase in the following order:C₂H₂>CO₂>CH₄>C₂H₄>CO>H₂.The doping of Co introduces a band of impurity and lowers the energy barrier.The electron density is increased,the charge transfer is enhanced,the resistance of adsorption substrate is reduced,and the interaction between the material adsorption substrate and the gas adsorbent is enhanced.Comparing the macroscopic gas sensitivity test,the feasibility of using a ZnO-based model based on the first principles of density functional theory to calculate the selection of doping element and the macroscopic detection characteristics of the measured gas was verified.It provides a new idea and method for the research of high performance ZnO-based composites gas sensors for DGA.