Abstract:Polyethylene (PE) samples were surface fluorinated by the F2/N2 mixture for 30, 60, 120 or 240 min to investigate the influence of the fluorinated layer characteristics on space charge accumulation. After polarization at 50 kV mm−1 dc electrical field and 40 °C for 240 min, the charge amounts of the samples fluorinated for the different times, normalized to the charge amount of the original sample, are 1.17, 0.51, 0.49 and 0.22, respectively, showing significant suppression of the charge accumulation by the lo… Show more
“…[11][12][13] By controlling treatment factors during the direct fluorination process, a surface layer containing C-F bonds with preferable surface properties can be obtained. 14,15 In An's research, by controlling direct fluorination time and temperature, different surface conductivities are obtained in epoxy resins. [16][17][18] The dc surface flashover voltage of the epoxy resin is also found improved after direct fluorination.…”
Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.
“…[11][12][13] By controlling treatment factors during the direct fluorination process, a surface layer containing C-F bonds with preferable surface properties can be obtained. 14,15 In An's research, by controlling direct fluorination time and temperature, different surface conductivities are obtained in epoxy resins. [16][17][18] The dc surface flashover voltage of the epoxy resin is also found improved after direct fluorination.…”
Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.
“…It needs to be pointed out that there is a small oscillating signal just after the laser target electrode signal in measured current traces, which was found to be pertinent to the length of the wire connecting the HV electrode to the power supply isolating capacitor (in Figure 1). Although we have tried to shorten the wire length so that the oscillating signal is compressed and becomes closer to the target electrode signal, in comparison with our previous published results [19], it still has a small contribution to the signals just after the laser target electrode signal, as shown by the arrow in Figure 4b in the following text.…”
Section: Space Charge Measurementsmentioning
confidence: 72%
“…However, when oxygen as impurity was present in the fluorinating gas mixture at a low concentration, a thick fluorinated layer or a long treatment time was needed to reduce the space charge densities by the same amount [19]. We also found that fluorination time needed for effective suppression of the space charge could be significantly reduced by increasing fluorination temperature, for instance, from 240 minutes at 55 °C [19] to 120 minutes at 70 °C [20].…”
Section: Introductionmentioning
confidence: 97%
“…When a fluorinating gas mixture (F 2 /N 2 ) contained no detectable oxygen, a very thin fluorinated surface layer of PE or a surface fluorination for a short time could reduce space charge accumulation very effectively [17,18]. However, when oxygen as impurity was present in the fluorinating gas mixture at a low concentration, a thick fluorinated layer or a long treatment time was needed to reduce the space charge densities by the same amount [19]. We also found that fluorination time needed for effective suppression of the space charge could be significantly reduced by increasing fluorination temperature, for instance, from 240 minutes at 55 °C [19] to 120 minutes at 70 °C [20].…”
Polyethylene (PE) plates were surface fluorinated in a laboratory vessel using a F 2 /N 2 mixture at 95 °C and 0.1 MPa for 60 minutes. Attenuated total reflection infrared analysis and scanning electron microscopy cross-section observation indicated a substantial change in chemical composition of the plate surface layer by the fluorination and a formation of 0.70 μm thick fluorinated layer. Space charge measurements on the surface fluorinated plate sample and on a layered sample consisting of a PE film and the surface fluorinated plate revealed that the fluorinated layer at the semicon electrode interface can effectively block the charge injection, and the fluorinated layer at the film/surface fluorinated plate interface also has an obvious blocking effect on charge transport from the film into the plate, although not as significantly as the former. As a result, there is only limited space charge accumulation in the surface fluorinated plate of the layered sample, mainly in the vicinity of the dielectric interface, during the 1440 minutes poling at 50 kV/mm dc and 40 °C. In addition, the results also indicated that charges can be injected from the semicon electrode into the PE so long as the electric field at the electrode interface is nonzero. This can explain a significant charge accumulation observed at the film/surface fluorinated plate interface just after the dc field was applied.
“…The research works and applications are mainly concentrated on the improvements of the barrier properties, wettability, adhesiveness, chemical stability or biocompatibility of polymers [18,19] and dealing with the electrical properties of polymers. For example, An et al [20,21] indicated that surface fluorination of PE has a significant influence on the charge injection and accumulation. Du et al [22,23] found that surface fluorination is an effective method for modulating the electrical properties and restraining the surface charge and space charge accumulation of the PI film.…”
Abstract:In this work, multi-layered polyimide (PI) films were surface fluorinated at 328 K and 0.05 MPa using F 2 /N 2 mixture with 20% F 2 by volume, for a fluorination time of 0, 30 and 60 min, respectively. Then, they were subjected to discharge plasma as barrier dielectrics of surface dielectric barrier discharge (SDBD) at ambient atmospheric air. The dielectric lifetime of SDBD greatly extends after 60 min surface fluorination. In addition, optical emission spectroscopy (OES) results indicate that during the plasma processing, SDBD with fluorinated PI can obtain more stable plasma parameters, including gas temperature and electron temperature. Dielectric surface properties were further evaluated by infrared thermography, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). It is considered that both physical and chemical effects lead to the extension of dielectric lifetime. The physical effect is reflected in low surface temperature and increased surface roughness, while the chemical effect is reflected in the graft of fluorine groups.
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