Interaction Mechanism between the C(4)F(7)N–CO(2) Gas Mixture and the EPDM Seal Ring

[Image: see text] C(4)F(7)N (fluorinated nitrile) has been introduced as a remarkable substitute gas for the greenhouse gas SF(6) (sulfur hexafluoride) which is used in gas-insulated equipment (GIE). Intensive investigations about the compatibility between C(4)F(7)N 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 C(4)F(7)N–CO(2) 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 C(4)F(7)N–CO(2) gas mixture at temperatures higher than 70 °C. There exist chemical reactions between EPDM and C(4)F(7)N, resulting in the generation of gaseous byproducts including C(3)F(6), CF(3)H, and C(2)F(5)H and corrosion of EPDM. DFT calculation also shows that the interaction between C(4)F(7)N and EPDM could cause the dissociation of C(4)F(7)N. Relevant results provide important guidance for the engineering application of the C(4)F(7)N gas mixture.