Effect Of Plasma And Hydrothermal Fluorination Of Micron Al₂O₃ On The Insulation Of Epoxy Composites

In gas-insulated transmission lines,micron Al₂O₃/epoxy resin composite materials are used as the main base material of basin insulators due to their excellent insulation and thermodynamic properties.The new direct current transmission system regards GIL as the main transmission method.However,the traditional micron Al₂O₃/epoxy resin composite material does not perform well under direct current conditions.Under the long-term effect of a unipolar electric field,the surface of the composite insulating material is likely to accumulate a large amount of net residual charges.Due to the strong electret polarity of the material itself,these surface charges are difficult to effectively dissipate,and then disturb the surface electric field distribution of the insulator,leading to the occurrence of surface flashover and secondary accidents.In order to improve its charge dynamic characteristics and improve its surface insulation performance,the modification method of plasma and hydrothermal fluorination of filler and characterizes the microscopic nature and macroscopic effects of the two modification methods were proposed in this paper.The fluorination process parameters were studied.Firstly,in this paper,the plasma filler modification platform based on atmospheric pressure dielectric barrier discharge,which can generate fluorine-containing low-temperature plasma with adjustable composition and ratio to modify the surface of micron Al₂O₃was built.The high-temperature hydrothermal fluorination platform was built,and fluorine-containing chemical reagents were used to modify the surface of micron Al₂O₃through a long-term hydrothermal reaction.The modified micron Al₂O₃filler was doped into epoxy resin to prepare modified Al₂O₃/epoxy resin composite materials.In terms of the choice of filler particle size,the thermal conductivity in the basic properties of the material was used as the optimization guide,and the best median particle size was selected within the industry-allowed particle size range.Then,the ergodic study of the key parameters of plasma fluorination,including fluorination time and fluorine source gas concentration,was carried out.We used particle size distribution test,X-ray electron spectroscopy（XPS）,Fourier infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）diffractometer and scanning electron microscope（SEM）to characterize the micron Al₂O₃filler and its composite material before and after modification,and the reaction principle of plasma fluorination was analyzed.Based on the surface flashover and surface charge characteristic test platform built by our research group,the surface insulation characteristic test experiment of micron Al₂O₃/epoxy resin composite material was carried out.The effects of fluorination time and fluorine source gas concentration on the DC flashover voltage,charge dissipation characteristics and trap distribution characteristics of the composite materials were analyzed.The ergodic study of the key parameters of chemical hydrothermal fluorination,including hydrothermal time and introduction of plasma pretreatment was carried out.The modified filler and its composite material were micro-characterized,and the essence of the micro-reaction of the filler hydrothermal fluorination was explored.The surface insulation characteristics test experiment of the hydrothermal fluorinated Al₂O₃/epoxy resin composite material was carried out.The influence of hydrothermal time on the DC flashover voltage,charge dissipation characteristics and trap distribution characteristics of the composite material was analyzed,and the effectiveness of plasma pretreatment on improving the fluorination effect was revealed.And through the dielectric and water contact angle tests,the performance of the composite material sample with the best modification effect of plasma and hydrothermal fluorination was characterized.Finally,based on finite element and molecular dynamics methods,starting from the electric field equalization effect caused by fluorination and the strengthening effect of the filler-matrix interface caused by fluorination,the creeping insulation strength improvement mechanism of the micron Al₂O₃/epoxy resin composite material was described.