Preparation And Electrical Properties Of Al-Nb Co-Doped SiO₂/Polyimide Composites

Insulation materials subjected to high voltage and high breakdown field for long periods of time can be easily damaged by external electric fields,gradually aging,and even breakdown.Improving the insulation performance of polymers is crucial for the long-term reliability of electrical equipment.However,it is still difficult to improve both the dielectric constant and the breakdown field strength of polymer-based dielectrics.Polyimide（PI）has excellent insulation properties among many polymers,so it is a challenge to further optimize its electrical properties.SiO₂,Al₂O₃,and Nb₂O₅were synthesized into Al_0.5xNb_0.5xSi_1-xO₂（x=0.5,1,1.5,2mol%）（NASO（x mol%））fillers by ball milling and sintering,and NASO/PI composite films with different concentrations were prepared after that.A series of characterizations,including scanning electron microscopy（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）were performed,and electrical and mechanical properties were tested.The effect of NASO on the electrical properties of polyimide matrix composites was investigated by using the carrier generation generated by packing ionization to regulate the carrier transport of polyimide matrix composites.The carrier transport in polymer matrix composites is regulated and controlled by using the carrier generated by ionization of the filler.To search for the influential mechanism of NASO on the electrical performance of polyimide matrix composites by using the regularity of the variation of microstructure and electrical performance,and to model the mechanism for improving the electrical performance of polyimide matrix composites.According to the result of XRD,no diffraction peak of Al₂O₃and Nb₂O₅is observed in NASO particles,indicating that there is no residual Al₂O₃and Nb₂O₅in the prepared filler.With the increase in the contents of Al and Nb,the peaks of the composite films steamed buns gradually shifted to the right,indicating that the distance between the molecular chains of PI matrix decreased.There exists a small amount of Al³⁺and Nb⁵⁺in the full spectrum of XPS.In this part,Al³⁺and Nb⁵⁺have successfully substituted Si⁴⁺,indicating the successful preparation of NASO co-doping filler.The SEM results of the composite films show that the NASO packing particles are uniformly dispersed in the PI matrix.The result of FTIR indicates that the imidization of the PI matrix has completed and a hydrogen bond has been formed between the filler and the PI matrix.The dielectric properties,short-term and long-term breakdown properties and mechanical properties of polyimide and polyimide-based composites were tested.Compared with pure PI composites,the dielectric constant of NASO/PI composites is higher,which increases by 38.5%.The breakdown properties of NASO/PI composites first increase and then decrease with the increasement of Al,Nb content and filler volume fraction.The breakdown field of 1 vol%NASO（1 mol%）/PI composites with the best insulation properties reached 334.38 k V/mm.Compared with Si O₂/PI composites with the same filler volume fraction,the increasement is 11.97%and 19.6%,respectively.The corona resistance life reaches 14.5 h,which increases 43.56%and63.84%compared with Si O₂/PI composites with the same filler volume fraction.The tensile properties of NASO/PI composites with the same filler volume fraction decrease slightly with the increasement of the content of Al and Nb,but are still higher than those of PI.Combined with the results of characterizations and tests,it can be found that adjusting the concentration of defects in NASO filler and the volume fraction in polyimide matrix will lead to the formation of positive or negative charge centers and then generate an ion charge shielding layer.The carrier is effectively bound at the interface,and finally synergically improve the electrical and mechanical properties of composite materials,which have a vast application prospect.