Experimental and theoretical study of the interaction between SF₆/N₂ and EPDM: A comparative study with SF₆

Mixing nitrogen (N ₂ ) into sulfur hexafluoride (SF ₆ ) is considered a beneficial measure to reduce the consumption of SF ₆ . Minimal interaction and airtightness are key factors in maintaining the long-term stable operation of the equipment. To provide a theoretical support for the application of EPDM in SF ₆ /N ₂ insulated equipment, the interaction mechanism and permeability of SF ₆ /N ₂ with EPDM at different temperatures are investigated. The experimental results are comparatively analyzed using FTIR and tensile properties tests. In the meantime, the bond length distribution and diffusion coefficient of gas molecules in EPDM are analyzed using molecular dynamics. The adsorption performance (adsorption energy, transfer charge and density of states) of EPDM on gas molecules are also analyzed by DFT. The results show that, the infrared spectra of the experimental groups almost overlapped before and after experiments with little gas products. The mechanical properties are slightly worse than SF ₆ /N ₂ . The averages of SF ₆ and N ₂ bond lengths at 383 K increase by 5.97% and 0.57% compared to those at 298 K, respectively. The permeation coefficient of N ₂ is 5.28 times higher than that of SF ₆ in SF ₆ /N ₂ gas mixture at room temperature. The adsorption energy and transfer charge of EPDM on the SF ₆ (-0.902 eV, 0.0456 e) are higher than those of the N ₂ (-0.214 eV, 0.0204 e) indicating that EPDM has a stronger adsorption effect on SF ₆ . The analysis of the density of states further confirms it. The interaction between EPDM and SF ₆ as well as N ₂ is mainly van der Waals force and a small amount of hydrogen bonding, and the force strength of SF ₆ is stronger than that of N ₂ . Overall, the interaction of EPDM with both SF ₆ and N ₂ is minimal. However, it is necessary to take appropriate measures to prevent SF ₆ and N ₂ leakage.