# Accelerated Charge Dissipation by Gas-Phase Fluorination on Nomex Paper
## 4 Conclusions  
In this paper, the influence of gas-phase fluorination on the surface charge and space charge characteristic of oil-impregnated Nomex paper were studied. The main conclusions are summarized as follows:  
1. Gas-phase fluorination could be an effective approach to modify the surface charge dynamics of oil-impregnated Nomex paper. The considerable molecular chain scission and cleavage during fluorination are evident from ATR-IR spectra. The positive and negative surface potential decay  
Figure 8: Space charge dissipation: (**a**) Original sample; (**b**) 30 min fluorinated sample.  
Figure 7: Space charge accumulation: (**a**) Original sample; (**b**) 30 min fluorinated sample.  
rates are accelerated with the increase of fluorination duration and slowed down with continuous extension of fluorination duration. The samples fluorinated for 30 min show highest decay rate.
2. The trap energy level and density distribution obtained by the isothermal surface potential decay method show that gas-phase fluorination exerts a great influence on the trap characteristic of oil-impregnated Nomex paper, which is mainly attributed to the competition between physical and chemical defects change caused by fluorination. The difference between the hole trap and electron trap energy level and density of the original and the fluorinated samples are mainly caused by the different conduction path of hole and electron.
3. The space charge measured by the pulsed electro-acoustic (PEA) system shows that the charge mobility of the fluorinated samples is higher than that of the original sample. The negative charge of the fluorinated samples accumulated near the cathode shows obvious inward migration tendency, while the peak value is smaller compared to the non-fluorinated samples. The space charge decay rate of the fluorinated samples is also faster than the non-fluorinated one. Nevertheless, the influence of gas-phase fluorination on other electrical properties of oil-impregnated Nomex paper will be explored, because previous research has shown that gas-phase fluorination brings about remarkable improvement of flashover strength, partial discharge resistance or corona resistance of the polymer such as polyimide and epoxy resin.  
Conceptualization, L.H. and F.W.; methodology, T.Z. and L.H.; software, M.Z.K.; validation, Y.H.; formal analysis, L.H. and F.W.; investigation, Q.Z.; resources, J.L.; data curation, L.H.; writing--original draft preparation, L.H.; writing--review and editing, F.W.; visualization, M.Z.K.; supervision, J.L.; project administration, F.W.; funding acquisition, F.W., Z.H. and H.Z.  
This research was funded by the National Key R&D Program of China, grant number 2017 YFB0903801, the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, grant number ammt2017A-3 and the Science and Technology Project of SGCC under Grant SGTYHT/14-JS-188.  
The authors gratefully acknowledge supports from the National Key R&D Program of China (2017 YFB0903801), the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology (ammt2017A-3) and the Science and Technology Project of SGCC (SGTYHT/14-JS-188).  
The authors declare no conflict of interest.