A New Surface Treatment Method for Improving Surface Flashover Performance of Polymers in Vacuum

In this paper, Low density polyethylene (LDPE) films were surface treated in ozone atmosphere for different times (Oh, 1h, 2h, 4h, and 6h) to investigate the effect of surface oxidation on DC surface flashover characteristics in vacuum. Infrared (IR) was used to characterize surface chemical structure of specimens before and after ozone treatment. IR results show that oxygen atoms (O) are introduced into LDPE surface layer and carbonyl groups (C=O) are formed after surface treatment. Surface conductivity of specimens was tested and the results show surface conductivity increases with the extending of surface ozone treatment time. For untreated LDPE, surface conductivity is 4.39× 10-18S, and it increases to 1.01×10-15Swhen LDPE specimen is surface treated for 6h with ozone. Surface potential decay (SPD) was used to characterize surface trap distribution of specimens, and the results show surface potential decays faster and faster with the increasing treatment time, which is resulted from the shallower trap centers introduced into LDPE surface layers after ozone treatment. Surface flashover performance measurement results show that surface flashover voltage of LDPE specimens is improved by surface ozone treatment, and the optimum value of flashover voltage for treated 4 hours specimen is improved by 25.59% compared with untreated LDPE. Finally, the mechanism of surface flashover is discussed and it concludes that the change of surface chemical structure resulting from surface ozone treatment leads to the variation of surface trap distribution and surface conductivity which influences the surface charge accumulation properties, and then improves surface flashover performance of LDPE in vacuum.