Interaction Mechanism between the C₄F₇N-CO₂ Gas Mixture and the EPDM Seal Ring

C₄F₇N (fluorinated nitrile) has been introduced as a remarkable substitute gas for the greenhouse gas SF₆ (sulfur hexafluoride) which is used in gas-insulated equipment (GIE). Intensive investigations about the compatibility between C₄F₇N and materials used in GIE are required to decide their long-term behavior. In this paper, the interaction mechanism between EPDM, used as a sealing ring in GIE, and C₄F₇N-CO₂ was explored. The composition and morphology properties of EPDM were first revealed based on scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that EPDM rubber is incompatible with the C₄F₇N-CO₂ gas mixture at temperatures higher than 70 °C. There exist chemical reactions between EPDM and C₄F₇N, resulting in the generation of gaseous byproducts including C₃F₆, CF₃H, and C₂F₅H and corrosion of EPDM. DFT calculation also shows that the interaction between C₄F₇N and EPDM could cause the dissociation of C₄F₇N. Relevant results provide important guidance for the engineering application of the C₄F₇N gas mixture.