Influence Of Trap Characteristics On Electrical Properties Of Polyimide/Al2O3 Composite Films

Nanocomposite is an effective way to enhance the electrical properties of insulation materials used in the electrical equipments. In this thesis, the polyimide?PI? is chosen as the matrix. The main effort is devoted to the investigations on the effects of trap characteristics on electrical properties of polyimide/Al₂O₃ nanocomposite. By taking the trap characteristics as the entry point, the mechanisms corresponding to the electrical properties of nanodielectrics are studied.The PI/Al₂O₃ nanocomposite films with different doping content were prepared by in-situ polymerization method and the thickness were about 30?m. The structure of composite film was studied by using scanning electron microscopy, X ray diffraction, infrared spectroscopy, X ray scattering device. The test results show that nano Al₂O₃ particles uniformly dispersed in the polyimide matrix. Nano-Al₂O₃ closely contact with polyimide matrix, and produce inorganic- organic interface. The trap characteristics of polymer were proposed by the isothermal discharge current methods. Research indicates that with the increase of nano doping content, PI/Al₂O₃ composite film trap energy density increases, the emergence of a large number of shallow traps in the interface.The effect of doping content on the electrical properties and charge transportation characteristics of the composite films were investigated by electrical performance test. The results show that the electrical properties of polyimide are greatly improved after doping with nanoparticles. The introduction of Al₂O₃ nanoparticles decrease the volume resistivity of the thin films, the electrical conductivity increase, the electrical conductivity increase, the electrical aging threshold decrease. The breakdown field strength decrease with the increase of the composition, but still maintain good insulation. The corona aging life of the PI/Al₂O₃ composite film is the longest when the doping content of 20%, which is about 10 times of the pure PI film.The energy band model of PI/Al₂O₃ nanocomposites was proposed via the experimental and theoretical analysis of the influence of the trap characteristics onthe electrical properties of the composite film. Research concludes that the introduction of nano-particles make the original trap energy level depth shallow, and effectively increase the density of the trap energy level. In the electric field, the chance of electrons are captured by traps becomes larger, the trap electrons can jump out of the trap and become a free electron involving in conducting, and generate space charge filed contrasted with the direction of applied electric field, which make the insulation life of polyimide film improve.