Surface fluorination is regarded as an effective means for the enhancement of vacuum flashover strength. However

due to the changes of surface roughness and different chemical compositions

their separate influence and corresponding mechanism are still unclear. Consequently

UV-cured nanocomposite coating was sprayed onto the surface of polymeric insulation. Rougher morphology was formed by nano-Al2 O3 flakes in the coating layer. Furthermore

a fluorination layer could be gained by fluorosilane treatment of Al2 O3 flakes due to surface segregation in UV curing process. The influence of surface morphology and surface fluorinated chains on the surface flashover strength and charge behaviors in vacuum were investigated systematically. Experimental results reveal that the morphology will change and the surface roughness of the coating layer will gradually increase as nano-Al2 O3 flakes pile up

and the fluorinated chains are segregated to the surface. Surface morphology is the domain factor for the enhanced pulsed flashover strength and surface charging mitigation. Experiments indicate that the presence of fluorination layer traps more internal secondary electrons with low energy in the case of high roughness level

thereby further improving flashover strength. A theoretical model considering outside secondary electron multipactor and inside electron transport was proposed

which is in good agreement with surface charging characteristics.