Thermal decomposition characteristics and kinetic analysis of C4F7N/CO2 gas mixture

In recent years, the C4F7N/CO2 gas mixture has been considered one of the most promising candidates to replace the strong greenhouse gas SF6 in high-voltage power equipment. However, there are few studies on the thermal stability of the C4F7N/CO2 gas mixture. In this paper, the characteristics and mechanism of the thermal decomposition of C4F7N/CO2 gas mixture are analyzed by both experiment and calculation. Gas chromatography-mass spectrometry (GC-MS) is applied to detect the decomposition products at different temperatures and pressures. The measurements show that the C4F7N/CO2 mixture undergoes significant decomposition above about 700C and the main products are CO, C2F6, C3F6, C3F8, C2F3N, C3F5N and C2N2. Previous studies have explored the possible decomposition pathways of C4F7N and predicted the free radicals produced after the decomposition. However, the subsequent processes in which the free radicals recombine and form stable products have not been considered. In this study, both the decomposition and recombination pathways are considered and the corresponding reaction rate constants are calculated. Based on this, precise chemical kinetic composition results at steady state during the thermal decomposition of C4F7N/CO2 mixture are obtained. Further, the influences of pressure and temperature on the decomposition products are theoretically investigated. It is also found that C4F7N/CO2 gas mixtures are more stable under higher pressures. The results provide an important reference for the engineering application of C4F7N/CO2 gas mixtures.