Theoretical study on the compatibility of C4F7N decomposition products with metal oxides: First-principles

Abstract

The compatibility between the gas and solid materials within the gas chamber is key to ensuring the safe operation of electrical equipment. Current research primarily focuses on the compatibility between the C₄F₇N (Heptafluoroisobutyronitrile) and the solid materials used in equipment. However, C₄F₇N decomposes under electrical and thermal fault conditions, while metal materials are also prone to oxidation during the manufacturing and operation processes. In this paper, the interaction systems between the main decomposition products of C₄F₇N (CO, CF₄ and C₃F₆(perfluoropropene)) and typical metal surface oxides (Al₂O₃, CuO) are established. Based on first-principles, the interaction energy, charge transfer, electronic density of states, differential charge density, and weak interaction forces are evaluated as five microscopic parameters. The interaction mechanisms between the decomposition products of C₄F₇N and the surface oxides of typical metal materials are analyzed at the microscopic level, further assessing their compatibility. The results show that both CO and CF₄ exhibit weak interactions with the Al₂O₃(0 0 0 1) interface, demonstrating good compatibility. However, the interaction energy between C₃F₆ and the Al₂O₃(0 0 0 1) interface reaches -3.13 eV with a charge transfer of 0.336e, showing significant charge accumulation, as well as stronger interactions, and the apparent overlap between the 2p orbitals of F atoms and the 3p orbitals of Al atoms between 0eV-6eV. This suggests the potential formation of chemical bonds, leading to poor compatibility. The interactions between CO, CF₄ and C₃F₆ with the CuO(1 1 1) interface are all weak, indicating good compatibility. In conclusion, to ensure the safe operation of C₄F₇N/CO₂ environmentally friendly gas-insulated equipment, it is recommended to maximize the use of copper materials in metal equipment and avoid prolonged exposure of the equipment to environments prone to oxidation, thereby further enhancing the stability and reliability of the equipment.