| On the basis of previous studies,the monodispersed a-alumina nanoparticles with high purity and less aggregation were produced and applied in the epoxy nanocomposite to enhance the electrical insulation properties.The boehmite/epoxy nanocomposite,?-alumina/epoxy nanocomposite and neat epoxy were also fabricated and characterized for comparison.The changing mechanism of nanoparticles on the electrical insulation properties of epoxy resin was discussed on these characterizations.Results are summarized as follows:(1)Boehmite nanoparticles was prepared by the reaction of high purity aluminum powder and water.The alumina precursor made by the boehmite nanoparticles was transformed to y-alumina nanoparticles after calcination under 1000?.The ?-alumina nanoparticles began conversion to a-alumina temperature above 1100?.The transformation was completed at 1150?.The particle size of boehmite,y-alumina and a-alumina nanoparticles were about 100nm.The a-alumina nanoparticles were smaller than the boehmite and y-alumina nanoparticles because of crystallization.The X-ray photoelectron spectroscopy(XPS)results showed that there was three O elemental species on the surface of the nanoparticles,which was lattice-oxygen(Olatt),adsorbed-oxygen(Oads)and hydroxyl-oxygen(O-OH),respectively.The boehmite nanoparticles had the most amount of O-OH.And the a-alumina nanoparticles had the most amount of Olatt and the least amount of Oads.(2)When the content of a-alumina in epoxy resin increased from 0 to 1 wt.%,the resistivity of epoxy nanocomposite showed increasing trend.And the same trend cannot be found when the content of a-alumina continuly increased to 2 wt.%.The epoxy/?-alumina nanocomposite with 2 wt.%of a-alumina showed the highest resistivity at 30?,which was 2.2×1018?·cm.And the epoxy/?-alumina nanocomposite with 0.5wt.%of ?-alumina showed the highest resistivity at 80?,which was 7.3×1017?·cm.The electrical corrosion of epoxy resin can effectively be hindered by a-alumina nanoparticles,so that the breakdown strength of epoxy/?-alumina nanocomposite can be increased to 79.2kV·mm-1.The ?-alumina nanoparticles showed little effect on the tensile modulus of epoxy/?-alumina nanocomposite.However,the tensile strength,the glass transition temperature,the activation energy of glass transition and epoxy crosslinking density of epoxy/a-alumina nanocomposite were increased and then decreased with the increasing of the content of a-alumina.And their values all reached the maximum when the content of?-alumina nanoparticles became 1 wt.%.The maxima value of the tensile strength and the glass transition temperature are 78.64MPa and 153.8 0C,respectively.The ±400kV column insulator made of this epoxy/?-alumina nanocomposite passed all performance test.The column insulator's line frequency withstand voltage is greater than 500 kV,lightning impulse withstand voltage is greater than 903 kV,the switching impulse withstand voltage is greater than 825KV.The column insulator can withstand 612 kV DC voltage for 120min,and partial discharge>2000pC has not occured in the last 30min of this process.Results showed that the ?-alumina nanoparticles restricted the movement of epoxy molecule chains in the ?-alumina/epoxy interaction zone by affecting the cross-linking state of epoxy molecular chains.(3)The ?-alumina nanoparticles showed obvious advantages in enhancing electrical insulation performance of epoxy nanocomposites,comparing to the boehmite or ?-alumina nanoparticles.The direct current volume resistivity and breakdown strength of epoxy nanocomposite with 2.0 wt%?-alumina nanoparticles was improved to 2.2×10?·cm(at 30?),4.6×1017?·cm(at 80?)and 76.1kV mm-1 respectively.And these improved values of electrical insulation properties are much higher than these of epoxy nanocomposites reported in previous studies.The tensile strength of epoxy nanocomposite with 2.0 wt%a-alumina nanoparticles was also improved to76.63MPa.(4)On the basis of Jonscher's universal law of relaxation,it was found that the ?-alumina nanoparticles may limit the mobility of the polymer chains in the epoxy/a-alumina interaction zone by enhancing the intermolecular correlation without restricting the movement of local chains.The transfer of the carriers in the interaction zone was also hindered by the restriction of the movement of the molecular chain.On the contray,the intermolecular correlation of the polymer chains in the epoxy/boehmite and epoxy/y-alumina nanocomposites were weakened.All these effects may due to the hydrogen bonds between polymer chains and O elemental species on the surface of these nanoparticles.The a-alumina nanoparticles became the best nanofiller in the epoxy nanocomposite due to the highest proportion of lattice-oxygen on their surface. |
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