Significantly Improved Surface Flashover Characteristics of Epoxy Resin/Al2O3 Nanocomposites in Air, Vacuum and SF6 by Gas-Phase Fluorination

In this work, epoxy resin incorporated with nano-Al2O3 of various concentrations, 0 wt.%, 1 wt.%, 3 wt.% and 5 wt.%, were prepared and subsequently fluorinated for 15 min, 30 min and 60 min at 40°C in a F2/N2 gas mixture (20/80 v/v) with pressure of 0.05 MPa. Fourier-transform infrared spectroscopy was employed for the chemical characterization of epoxy resin/Al2O3 nanocomposites which showed the molecular-chain scission during the gas-phase fluorination. Later, the effect of gas-phase fluorination on DC flashover characteristics of epoxy resin/Al2O3 nanocomposites was analyzed. It was found that gas-phase fluorination of pure epoxy resin can improve its DC flashover voltage in air and sulfur hexafluoride (SF6). In addition, nano-Al2O3 incorporation leads to a slight decrease of the DC flashover strength but it is still higher than that of non-fluorinated epoxy resin. This proves that suppression of charge accumulation can increase the DC flashover voltage of epoxy resin. The vacuum DC flashover voltage of epoxy resin/Al2O3 nanocomposites decreased by 35.8% after 30 min fluorination. However, the vacuum DC flashover voltage of epoxy resin incorporated with 1 wt.% nano-Al2O3 was 17.5% higher than that of unfilled epoxy resin. Based on the secondary electron emission avalanche model of vacuum flashover, the experimental results were analyzed. It was found that the fluorination modifies the surface molecular structure of epoxy resin/Al2O3 nanocomposites, which may weaken its adsorption capacity for gases and make it easier to desorb gases and reduce flashover voltage.