Diffusion and Absorption Behaviors of Small Gas Molecules in EPDM and NBR Sealing Materials for C₅F₁₀O Insulated Switchgears

The performance of the sealing materials is a crucial factor that determines the reliability of C5F(10)O gas mixture insulated switchgears. In this article, we investigate the transport behaviors of small gas molecules present in C5F10O gas mixture within ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR). By conducting molecular dynamic (MD) and grand canonical Monte Carlo (GCMC) simulations on the established EPDM and NBR cells, the diffusion coefficients, solubilities, and permeability coefficients of O-2, N-2, CO, CO2, CF3H, CF4, and CF2O in EPDM and NBR were calculated. The molecular diameter, free volume, radial distribution function (RDF), isosteric heat, and absorption site of the simulation models were further analyzed to understand the factors contributing to the differences in transport behavior. The results suggest that the diffusion coefficients of gases within NBR are lower than those of EPDM, because NBR has greater structural density, stronger intermolecular forces, and less free volume. Moreover, the solubility of the seven gases is primarily determined by isosteric heat and absorption site distribution between the gas and rubber. Based on the calculation results of the permeability coefficients, NBR is a better choice over EPDM for sealing C5F10O/N-2 or C5F10O/air insulated equipment, while the latter is preferable for C5F10O/CO2 insulated equipment. The leakage of CF3H, CF4, and CO is much slower and poses minimal to no hazards. Notably, the toxic gas CF2O has high permeability coefficients in both EPDM and NBR, making it advisable to take appropriate safety measures when using either of the sealing medium for C5F(10)O-related equipment.