Theoretical study of the chemical reaction mechanisms and reaction rates of CFx + SFy (where x = 1–3 and y = 1–6) in SF6–polytetrafluoroethylene arc plasma

Abstract

The microscopic properties of nonequilibrium arc plasma have great significance for researching the breaking capacity of SF6 circuit breakers and constructing arc plasma simulation models. The polytetrafluoroethylene (PTFE) vapor generated by the ablation of the nozzle material significantly affects the SF6 arc plasma particles and thus affects the microscopic properties of the nonequilibrium arc plasma. At present, the calculation of the microscopic properties of nonequilibrium SF6–PTFE arc plasma has not been reported, mainly because the basic data for the chemical reaction mechanism and chemical reaction rate in the plasma cannot be obtained effectively. In this paper, quantum chemistry was used to theoretically research the reaction mechanisms and rates between CF3, CF2, and CF radicals and SF6, SF5, SF4, SF3, SF3, SF2, and SF in SF6–PTFE arc plasma at 298–10 000 K. A total of 18 chemical reactions are included. Structural optimizations, vibrational frequency calculations, and zero-point energy calculations for the reactants, products, and transition states were performed at the B3LYP/6-311++G(d,p) level of theory. The single-point energies of all species were obtained at the CCSD(T)/aug-cc-PVTZ level. The reaction rates of all reactions between 298 and 10 000 K were obtained by using transition state theory. The reaction rates were successfully fitted using the Arrhenius equation and the three-parameter Arrhenius equation. It has found that reactions between CF2 and fluoro sulfides have higher potential energies. Reactions R13, R7, R14, and R8 exhibit higher reaction rates at 298–10 000 K, whereas R3, R4, R5, and R6 have lower reaction rates. This work can provide theoretical guidance for research on nonequilibrium SF6–PTFE and SF6–CF4 arc plasma microscopic properties.