Theoretical study of the decomposition mechanism of SF₆/Cu gas mixtures

Abstract

The compositions of SF 6 arc plasma are contaminated by Cu vapor through electrode erosion and thus affect the performance of the high-voltage SF 6 circuit breaker. But the essential data for chemical kinetic models to study the non-equilibrium compositions of SF 6 /Cu mixtures, namely the decomposition mechanism of SF 6 /Cu mixtures, is still not clear. Besides, SF 6 decomposition products can be used to diagnose insulation faults of GIS and to evaluate the electric life of the SF 6 circuit breaker, but the uncertainty of the decomposition mechanism of SF 6 /Cu mixtures hinders the application of the analysis method of SF 6 decomposition products. Therefore, this work is devoted to investigating the decomposition mechanism of SF 6 /Cu mixtures by means of density functional theory in conjunction with 6-311G(d,p) basis set (for S and F atoms) and Lanl2DZ basis set (for the Cu atom). The optimized molecular structures, harmonic vibrational frequencies and energetic information of reactants, intermediate products (IM), transition states (TS) and products are thoroughly studied. And the complete decomposition pathways of SF 6 /Cu mixtures involving 15 reactions are derived. Detailed potential energy surfaces of SF 6 + Cu decomposition reactions are also depicted as a result. Among all the decomposition pathways, the favorable decomposition reactions of SF 6 + Cu mixtures are found: reaction R1 contributes more than reaction R2 in the decomposition of SF 6 + Cu mixtures due to its lower energy released; reaction R3 is dominant in the decomposition of SF 5 + Cu other than multi-step reactions; the chemical processes of SF 4 + Cu → IM x → TS y (where x stands for 9, 10 and 13, and y denotes 7, 8 and 9) may play the same role in SF 4 + Cu decomposition, but the reaction rate of R6 is higher than other reactions; reaction R9 and R11 are relative favorable among SF 3 + Cu decomposition reactions; reaction R13 is dominant in the decomposition of SF 2 + Cu because of its high potential well. This work hopes to outline a theoretical basis to investigate the non-equilibrium compositions of SF 6 /Cu arc plasma and the SF 6 decomposition products analysis method.

Theoretical study on decomposition pathways and reaction rate constants of C4F7N with O atom

“…Reaction formula Experiments to detect the decomposition products of C 4 F 7 N have been carried out recently, but those generated under the influence of an O atom are seldom reported. As mentioned in the introduction, Anderson [7] detected the degradation products of C 4 F 7 N by TIR/smog chamber experiments which supports our finding that COF 2 is one of the decomposition 311G(d,p) method was verified in our previous work [5,16,19] that the optimized structures and harmonic vibrational frequencies of C/F/N/O chemical system calculated with this method are in good agreement with experimental data from CCCBDB or those carried out with different calculation methods. The harmonic vibrational frequencies of reactants, products and TS are shown in table S1 in the supplementary material (stacks.iop.org/JPhysD/53/105202/mmedia).…”

“…As introduced in our previous work [5,[16][17][18][19], the molecular structures (interatomic distances, angles between bonds, etc) of reactants, products and TS in C 4 F 7 N decomposition pathway are optimized to the minimum potential energy with DFT/B3LYP method [20][21][22][23] in conjunction with 6-311G(d,p) basis set [16,17,24] implemented in the Gaussian09 packages [25] as the prerequisite for harmonic frequencies and energetic information calculations and decomposition mechanism analysis. Products, reactants and intermediate products are stationary points on PES as shown by the real harmonic vibrational frequencies [26,27] while TS is the saddle point on PES connecting reactants and products with only one imaginary vibrational frequency [28] and confirmed by intrinsic reaction coordinate calculations [29].…”

Theoretical study by density functional theory calculations of decomposition processes and primary products of C5F10O with moisture content

“…Sulfur hexafluoride, SF 6 , is widely used as insulating medium in switchgear, circuit breakers, gas insulated high-voltage transformers and gas-insulated transmission lines due to its virtues such as high dielectric strength, excellent arcquenching performance and thermal stability properties [1][2][3]. However, SF 6 , with a very high global warming potential (GWP) of 23 900, is one of the strongest greenhouse gases on a per molecule basis [4]. SF 6 is also an extremely stable anthropogenic gas with a long atmospheric lifetime of 3200 years, so that it was targeted to be restricted under the Kyoto Protocol in 1997 [5].…”

“…SF 6 is also an extremely stable anthropogenic gas with a long atmospheric lifetime of 3200 years, so that it was targeted to be restricted under the Kyoto Protocol in 1997 [5]. Hence, finding an environmentally-friendly replacement has been a subject of intensive research over the past few years to meet increasingly strict environmental requirements [6,7]. Potential substitutes for SF 6 need to own high dielectric strength, chemical stability, low toxicity, low GWP and short atmospheric [8].…”