Study on the Compatibility of C6F12O Gas Mixture with EPDM
Year: 2024
Type: article
Abstract: Objective SF6 is widely used in electrically insulated equipment due to its excellent insulating properties. However, its global warming potential is 23 500 times greater than that of CO2, with an atmospheric lifespan of up to 3200 years. As the severity of global warming intensifies, finding a new environmentally friendly insulating gas to reduce the using of SF6 has become a hot research topic in recent years. C6F12O has both environmental benign characteristics and insulating properties, which has attracted the attention of scholars. However, the liquefaction temperature of pure C6F12O gas is 49 ℃ at atmospheric pressure, which is difficult to use as an insulating medium in practical engineering scenarios. It must be mixed with low-boiling point buffer gases, including CO2 and N2. It has been shown that a gas mixture comprising 4% C6F12O/CO2, when pressurized above 0.14 MPa, can be used as an insulating gas in 10 kV switchgear. For new eco-friendly insulation gas, its compatibility with the internal sealing materials of the equipment is also need to be considered.Method The experimental study on the compatibility between the C6F12O/CO2 gas mixture and the sealing rubber EPDM was carried out by building a thermally accelerated compatibility experimental platform in this paper. The effect of trace O2 on the compatibility of C6F12O gas mixture and EPDM was investigated by adding a small amount of O2 into the gas mixture. The changes in the surface morphology, the elements of rubber samples, the gas mixture components, and the mechanical properties were analyzed before and after the experiments. The interaction between C6F12O/CO2/O2 gas mixture and rubber was also calculated based on the MD theory.Results and Discussions The results from scanning electron microscopy showed that the scaly structures appeared on the surface of EPDM when mixed with C6F12O/CO2 at 110 °C. A flocculent structure appeared when EPDM was mixed with C6F12O/CO2/O2 at only 90 °C. This observation suggested that the inclusion of O2 promotes the interaction between the C6F12O/CO2 gas mixture and EPDM, which in turn leads to the corrosion of EPDM. The results of X-ray photoelectron spectroscopy showed that a decrease in the carbon content alongside increases in oxygen and fluorine within the C6F12O/CO2 mixed EPDM with increasing temperature. This trend indicated that C6F12O/CO2 reacts with EPDM. In group of C6F12O/CO2/O2, the changes were more significant, which indicate that O2 promoted the reaction between the C6F12O/CO2 mixture and EPDM. Post-experimental analyses identified new spectral peaks at 284.5 eV, 285.8 eV and 289.2 eV, corresponding to C—C, C—H and —COO— ester bonds, respectively. Three characteristic peaks of elemental F were detected on the EPDM surface for metal fluoride at 683 eV, organofluoride at 684.5 eV, and —CF2CH2— at 687 eV. The intensity of C characteristic peak was significantly lower, while the intensity of O and F were higher in the C6F12O/CO2/O2 gas mixture after testing. These findings indicated that O2 actively participates in the reaction between the C6F12O/CO2 mixture and the EPDM, fostering an intensified interaction. The results of tensile properties showed that the mechanical properties of EPDM decreased significantly with increasing temperature. The mechanical property of EPDM in C6F12O/CO2 atmosphere was slightly worse than those of the original samples. The mechanical property of EPDM under C6F12O/CO2/O2 was worse than that of C6F12O/CO2. The reaction between the C6F12O/CO2 mixture and EPDM was more intensive after adding O2, leading to a significant decrease in the mechanical properties of EPDM. At the end of the experiment, a small amount of the resultant gas was collected and subjected to Gas chromatography–mass spectrometry for further analysis. The small amount of H2O remaining inside the gas tank was involved in the decomposition reaction of the C6F12O gas mixture. Throughout the reaction, ${\rm H}^{\,\cdot} $ and ${\rm OH}^{\,\cdot} $ were generated from the decomposition of H2O, which can interact with particles such as ${\rm CF}_3^{\,\cdot} $ , ${\rm C_{3}F}_7^{\,\cdot} $ , and ${\rm F}^{\,\cdot} $ produced by C6F12O to produce decomposition products such as C3F6 and C3F7H. Meanwhile, the reaction rate of the C6F12O gas mixture with EPDM and the concentration of C3F6 and C3F7H were increased by both the increasing temperature and O2 introduction. The diffusion coefficient D indicates that the diffusion speed of gas molecules in EPDM can reflect the physicochemical relationship between the gas and the solid material. The diffusion coefficients of both C6F12O and CO2 in EPDM increased with rising temperatures. At 110 °C, the diffusion coefficients of C6F12O and CO2 were increased by 1.71 and 2.49 times, respectively, following O2 addition. It indicates that the internal energies of gas molecules were increased by adding O2, and the C6F12O and CO2 gas molecules could be easier to diffuse on the EPDM surface and interact with EPDM. The Flory–Huggins interaction parameter ( $\chi $ ) quantifies alterations in molecular interaction energy during miscibility and aids in determining the solubility of binary mixtures. A value of $\chi $ tending towards 0 indicates good compatibility between the mixed systems. Meanwhile, the parameter ( $\chi $ ) tends to be linear with the mixing energy (ΔEmix). Both $\chi $ and ΔEmix values of the EPDM mixing system decreased with increasing temperature. The $\chi $
Authors: Shuangshuang TIAN, Benli LIU, Guangyu DENG, Xiaoxing ZHANG, Huihui LI, Weihao LIU, Hui CHEN
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7024849529
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