The decomposition mechanism of C4F7N-Cu gas mixtures

Abstract

C4F7N is one of the most remarkable replacements for SF6, and its decomposition mechanism has a great influence on insulating performance and environmental properties. It is noteworthy that discharges or high temperature also evaporates metal electrodes (e.g., Cu) in the equipment, and the generated metal gases interact with C4F7N and thus affect the C4F7N decomposition mechanism, but the decomposition mechanism is still not clear. In this paper, therefore, the B3LYP method in conjunction with 6-311G(d, p) basis set (for C, N, and F atoms) and Lanl2DZ basis set (for Cu atom) combining transition state theory is used to study the decomposition mechanism of C4F7N-Cu mixtures. 31 reactions are determined in decomposition pathways of C4F7N-Cu mixtures, and their potential energy surface as well as reaction mechanisms are obtained. The rate constants over 300 K-3500 K relevant to the insulation breakdown temperature are calculated based on the above calculations, and dominant reactions in different temperature regions are selected. The results show that (R14) C4F7N + Cu → CF3CFCN + CF2CuF plays a major role in the decomposition of C4F7N-Cu mixtures below 1500 K, while (R1) C4F7N + Cu → TSa1 → CuCN + C3F7 and (R21) C4F7N + Cu → TSc1 → CF3CF(CN)CF2 + CuF are dominant above 1500 K; (R23) CF3CF(CN)CF2 + Cu → CF2(Cu)C(F)CN + CF3 is the most important reaction leading to the generation of CF3 below 1500 K with the overwhelming rate constant, but other reactions also generating CF3 are dominant above 1500 K.