Research Of Influential Factors On The DC Dielectric Properties Of MgO/LDPE And SiO₂/LDPE Nanocomposite

Interface dominates the dielectric properties of nanocomposite. Figuring out if interfacial charge exists in the nanocomposite and studying the link between the physical properties（such as crystallization properties, surface molecular structure and electrochemical properties） of different nano-particles and the dielectric performance of nanocomposite have scientific research significance and engineering application value. In this paper, the investigations focused on figuring out the main factor influenced the dielectric properties of SiO₂/LDPE and MgO/LDPE nanocomposites. We carried out several aspect s as follows:Studying the crystallization property, surface molecular characteristics and isoelectric point of MgO and SiO₂ nanoparticles with different physical chemical properties;Applying Zeta potential testing technology, we measured the Zeta potential of nano MgO or SiO₂ particles in polyethylene wax. Applying electrostatic force microscope and synchrotron radiation Small Angle X-ray Scattering we studied the interfacial charge phenomenon of MgO/LDPE and SiO₂ / LDPE nanocomposite. As a combination of the three measurement results, it is supposed to provide some experimental evidences on the interface charge phenomenon in nanocomposite;The formation mechanism of interfacial charge layer in nanocomposite and its impact on the dieclectric properties performance of nanocomposite were studied. It is found that the polarity of the interfacial charge layer associated with the isoelectric point of nanoparticles, and the chargeing abi llity of interfacial charge layer associated with the Zeta potential value; Experiments also found that SiO₂/LDPE nanocomposites with interfacial charge layer have better dc dielectric performance compared with MgO/LDPE nanocomposite without interfacial charge layer;The influence of moisture absorption on the dielectric properties of nanocomposite and the moisture absorption mechanism of nanoparticles were studied. Experiment results showed that the moisture absorption property of nano powder was associated with the crystal morphology and surface water molecules adsorption energy of nano-MgO and nano-SiO₂. Being affected with moisture, it will lead to a decrease of the dielectric properties of nanocomposite under the electric field larger than 20 k V/mm;The influence of surface treatment process on the dispersion, moisture absorption and dc dielectric properties of SiO₂/LDPE nanocomposite were studied by us. Experiments results revealed that, nano SiO₂ powder treated by Hexamethyldisilazane got better dispersion than nano SiO₂ powder treated by KH550. There are positive effects on improving the dielectric properties of nanocomposite by promoting the dispersion of nanoparticles. SiO₂/LDPE nanocomposite with this kind of nanopowder can still maintained excellent dc dielectric performance in the case of being slightly affected with damp;The DC conductivity characteristic of LDPE nanocomposite and its effect on electric field distribution in HVDC cable were studied. Experiments results revealed that, under DC condition, the electric field distribution is conductivity-dependent. Conductivity changes caused by the temperature, which will lead to electric field distribution is temperature–dependent. Meanwhile, conductivity and electric field strength has nonlinear relationship, it can stabilize the distortion of the electric field caused by the geometric structure or temperature gradient.