In order to systematically investigate the modulating role of fluorination temperature and time on surface electrical properties of the epoxy resin insulator, epoxy resin sheets were surface fluorinated in a laboratory vessel using a F 2 /N 2 mixture with 12.5% F 2 by volume at 0.1 MPa and different temperatures of 25-95 °C for different times of 5-120 min. Conductivity measurements have shown that the intrinsic surface conductivity of the epoxy resin insulator could be modulated from an even lower value to a nearly four orders of magnitude higher value than the value prior to fluorination by changing the fluorination temperature and time. Surface conductivity increased with increasing fluorination temperature at the same fluorination time, while decreased to some extent with increasing fluorination time at a given fluorination temperature. Surface potential decay measurements showed consistent results with the surface conductivity measurements. ATR-IR analyses revealed substantial changes in surface chemical composition and structure, depending on the fluorination temperature and time. SEM images clearly showed an increase of the fluorinated layer thickness with increasing fluorination temperature and time. Surface cracks appeared only at elevated fluorination temperatures and increased with fluorination temperature, while the surface became compact with the duration of the fluorination. These results, compared with the previous results on an epoxy resin insulator made of DGEBA epoxy resin with a lower epoxy value, also indicated a significant influence of the epoxy resin insulator itself or the epoxy resin raw material on surface electrical properties and surface physicochemical characteristics after fluorination.Index Terms -Epoxy resin insulator, surface fluorination, fluorination temperature and time, surface electrical properties, surface charge accumulation.
The photoinduced evolutions of surface physicochemical characteristics and electrical properties of the fluorinated epoxy resin have been investigated. Cured epoxy resin sheets were surface fluorinated in a laboratory vessel using a F 2 /N 2 mixture with 12.5% F 2 by volume at 0.1 MPa and 95 °C for 30 min. The fluorinated epoxy sample together with the unfluorinated (original) one for a comparison were exposed to ultraviolet (UV) radiation with wavelengths of 320 to 390 nm. During UV exposure, the evolution of surface physicochemical characteristics was investigated by attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray energy dispersive spectroscopy, and the sessile drop technique. The corresponding evolution of surface electrical properties was evaluated by measurements of surface potential decay and surface conductivity. These results have shown that the crosslinking reaction rather than photodegradation occurred for the fluorinated sample, compared to a continuous degradation of the original sample during the UV exposure. These results also indicate that surface conduction and its sensitivity to humidity increased very significantly with UV exposure time for the original sample, while the opposite changes in surface conduction and its moisture sensitivity with the exposure time were found for the fluorinated sample. A relationship between the evolutions of surface electrical properties and surface physicochemical characteristics has been established.
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