Effect of micro-H2O and micro-O2 on the decomposition characteristics of insulating medium C3F7CN gas using molecular dynamics and transition state method.

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In recent years, heptafluoroisobutyronitrile (C3F7CN) has been proved to be a potential eco-friendly insulating medium to replace sulfur hexafluoride (SF6, the strong greenhouse gas). In this paper, the effect of micro-H2O and micro-O2 on the decomposition of C3F7CN was investigated based on the reactive force field molecular dynamics (ReaxFF-MD) and transition state theory (TST). It was found that H2O obviously promoted the decomposition of C3F7CN, and new products HF, COF2, CO, and NO were generated. The influence of O2 on the C3F7CN dissociation was weaker than that of H2O, and O2 slightly promoted the C3F7CN decomposition only when 50 O2 molecules were added. The simultaneous presence of H2O and O2 promoted the decomposition of C3F7CN, the promotion of which was closed to H2O existing alone. The calculation results showed that the energy barriers of the two reactions forming COF2 were 31.38kcal/mol and 23.85kcal/mol, respectively, which indicated that the reactions were difficult to proceed spontaneously. The energy barrier of F + H2O → HF + OH was relatively lower than that of COF2. These values corresponded well to the ReaxFF simulation results. This study provides theoretical support for the effect of H2O and O2 on the decomposition of C3F7CN.