Study On The Electrical Properties Of CNFs-Fe₃O₄/polythylene Nanocomposites

The carbon nanofibers(CNFs)were synthesized by chemical vapor deposition method,Its surface were processed in different ways to obtain pure CNFs,CNFs-COOH and CNFs-Fe3O4.They were used to modified the semi-conducting layer materials to research the influence of space charge properties of the composites by doping different surface morphology CNFs in semi-conducting layer and orientation.1.This study used nano-copper catalyst and chemical vapor deposition(CVD)to prepare straight carbon nanofibers(CNFs).Then CNFs were disposed in concentrated nitric acid under certain temperature to obtain CNFs-COOH.Finally,the surface of carbon nanofibers(CNFs)were modified with Fe3O4 magnetic nanoparticles uniformly by the chemical coprecipitation which dispersed the CNFs-COOH,Fe2+ and Fe3+in aqueous solution according to certain proportion soaking 24 h and adjusting the pH with ammonia under certain temperature.Results showed that the surface of CNFs were evenly modified with Fe3O4 magnetic nanoparticles.Moreover,when the temperature of concentrated nitric acid was 110?,and CNFs-COOH:Fe3O4=5:1 the best modification effect would be obtained.2.CNFs/polymer nanocomposite materials were successfully prepared by mechanical blending method.The three kinds of CNFs were doped into LDPE semi-conducting materials by mixer to modify them.The semi-conductive materials was pressed into semi-conductive layer samples under the condition of high temperature molten state.Magnetic field was applied on both ends of the mold when CNFs-Fe3O4/polymer nanocomposite materials were pressure.The semi-conducting layer and pure LDPE insulation layer were jointed together to form double layer sample.The morphology of the fracture surface of the sample which doped with CNFs-Fe3O4 was analyzed by SEM.the results showed that the CNFs were arranged along the direction of orientation,the CNFs had good compatibility with semi-conductive shield,the interface interaction between them was strong and the CNFs were uniformly dispersed.3.Pulsed electroacoustic(PEA)method and thermal stimulation current(TSC)were used to measure the space charge distribution at room temperature.The experimental results showed that the semi-conductive layer modified by oriented CNFs-Fe3O4 can inhibit space charge injection from conductive metal layer to insulating layer.With increasing amount of carbon fiber doping concentration the space charge injection into the insulating layer first decreases and increases in the trend.When the CNFs-Fe3O4 content is 0.75 wt%,CNFs-Fe3O4/LDPE semi-conductive layer has the most inhibiting effect on the space charge injection.