Experimental and theoretical analysis on decomposition and by-product formation process of (CF3)2CFCN mixture

Although sulfur hexafluoride (SF6) is widely used in gas-insulated electrical equipment due to the excellent electrical insulation and arc-interruption behaviors, its strong greenhouse effect with high glow warming potential (GWP) has been driving the research on environmentally friendly gases for SF6 alternatives. Recently, the heptafluoro-isobutyrontrile (CF3)(2)CFCN (3M Novec (TM) 4710) is reported to have the potential to replace SF6. The decomposition characteristic of gas insulating medium is one of the basic conditions to measure whether it has the feasibility of replacing SF6. However, the decomposition characteristic of (CF3)(2)CFCN and the formation mechanism of by-products are still unclear. In this paper, a series of AC corona discharge experiments were performed, and the gas by-products of (CF3)(2)CFCN mixed with CO2, N-2 and air were qualitatively analyzed by gas chromatography mass spectrometry (GC/MS) method, respectively. Then, the decomposition mechanism of (CF3)(2)CFCN molecule and the formation mechanism of gas by-products were studied via density functional theory (DFT) method. The results show that the major gas by-products are CO, CO2, C2O3F6, CF4, C2F6, C3F6, C3F8, C2F4, (CF3)(3)CF, CF3CN, C2F5CN and CNCN, in addition to trace amounts of F3CC=CCF3 and CF3CF=CFCF3. Among the three initial dissociation pathways of (CF3)(2)CFCN molecule, a C-CF3 bond fission pathway that produces CF3CFCN and CF3 radicals is identified as the thermodynamically favorable channel. The bond energy of C-CF3 bond calculated at M06-2X/def2-QZVP//M06-2X/6-311G(d,p) level is 94.7 kcal/mol. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).