Study On The Construction Of PI Surface Nanocomposite Layer And Its Influence On The Electrical Resistance Characteristics Along The Vacuum Surface

Solid along-surface insulation is the weakest link in vacuum-solid composite insulation system,and solid insulation material along-surface flashover in vacuum is a major problem limiting electrical equipment and pulsed power devices.The study of the discharge mechanism along the surface of solid media in vacuum is important to improve the electrical resistance of solid insulating materials along the surface of vacuum.Therefore,it is necessary to investigate the methods and approaches to improve the vacuum electrical resistance performance of solid insulating materials along the surface,Enables safe and stable operation of electrical equipment under vacuum conditions.In this paper,polyimide（PI）,which has excellent overall performance,is used as the matrix material,and a layer of oxide is constructed on the surface of polyimide by ion exchange technology,It is beneficial to improve the electrical resistance performance along the surface of vacuum electrical equipment.The main work of this paper is as follows.A nanoscale metal oxide layer（Zn O or Al₂O₃）was constructed on the surface of polyimide（PI）film by ion exchange method,and the feasibility of this method was verified by various characterization methods such as SEM,AFM,EDS and XPS,i.e.,the oxide constructed on the pure PI surface was Zn O or Al₂O₃,and Zn O was uniformly distributed on the polyimide surface,while Al₂O₃ made the polyimide surface morphology becomes rough i.e.,uneven,forming peaks with different degrees of convexity.The isothermal surface potential decay test shows that Zn O can generate more deep energy level traps on the polyimide surface compared to alumina,and the introduction of deep traps has a stronger capturing effect on the secondary electrons during the secondary electron emission avalanche.The surface resistivity measurements show that the resistivities from small to large are Zn O@PI-360,PI,and Al₂O₃@PI-360,and that the low resistivity of Zn O allows pure PI to generate more lateral conductive paths while maintaining inherent excellent insulating properties.The surface potential build-up test indirectly reflects the charge density variation caused by the secondary electron avalanche in the pre-flashover period along the surface,with the most severe charge build-up in pure PI and less charge build-up in the nanocomposite film Zn O@PI-360 than in Al₂O₃@PI-360.Through the flashover voltage test results along the vacuum surface,it is known that the flashover voltage along the surface of the nanocomposite film Zn O@PI-360 is increased by 23.6% compared with pure PI,while the Al₂O₃@PI-360 is only 7.2%higher than that of pure PI.That is,the low resistivity of Zn O can effectively enhance the vacuum along-surface flashover voltage of pure PI,and the morphological change caused by constructing alumina on the surface of PI film also enhances the along-surface flashover voltage.The surface morphology is also an influencing factor of the electrical resistance along the vacuum surface of the insulating medium.Different heat treatment temperatures have different degrees of influence on the surface morphology of nanocomposite films,so nanocomposite films Al₂O₃@PI with different heat treatment temperatures（280 ℃,320 ℃,360 ℃,400 ℃）were prepared.Structural characterization showed that the surface morphology complexity was highest at the heat treatment temperature of 320 °C,and the trap density introduced by alumina on the pure PI surface was the highest,at which time the resistivity gradually decreased with increasing temperature,and the flashover voltage along the vacuum surface of the nanocomposite film increased by 25.4% relative to the pure PI.When the temperature rises to 400 ℃,the surface tends to be uniform due to high temperature,the trap energy level becomes shallow and the density decreases,and the flashover voltage along the vacuum surface at this time is 0.4% lower than that of pure PI.