Influence of Oxygen on the Thermal Decomposition Properties of C4F7N–N2–O2 as an Eco-Friendly Gas Insulating Medium

The C 4 F 7 N (fluorinated nitrile) gas mixture has been recognized as the most potential substitute gas to SF 6 used in gas-insulated equipment. In this paper, we explored the thermal stability and decomposition properties of the C 4 F 7 N-N 2 -O 2 gas mixture. The influence mechanism of oxygen content and temperature on the byproduct generation was obtained and analyzed. It was found that thermal decomposition of the C 4 F 7 N-N 2 -O 2 gas mixture mainly produces CO, C 3 F 6 , C 3 F 8 , CF 3 CN, (CN) 2 , and COF 2 . The addition of oxygen could accelerate the decomposition of C 4 F 7 N. The content of C 3 F 6 and (CN) 2 decreases, while the yield of CF 4 , CO, C 3 F 8 , and COF 2 increases with the oxygen content. Thermal decomposition of the C 4 F 7 N-N 2 -O 2 gas mixture at temperatures lower than 425 °C results from the interaction between C 4 F 7 N and the metal heating element, while the bond cleavage reactions occur at higher temperature. As for engineering application, the oxygen added in the 6%C 4 F 7 N-94%N 2 gas mixture should not exceed 6% to avoid the negative effect of oxygen on the thermal stability of C 4 F 7 N.