C_(6)F_(12)O混合气体与三元乙丙橡胶的相容性研究

Study on the Compatibility of C_(6)F_(12)O Gas Mixture with EPDM

C_(6)F_(12)O作为一种新型环保绝缘气体,与缓冲气体混合后具有作为绝缘介质运用于中低压电气设备的潜力。然而,环保气体绝缘设备内的密封材料是否与C_(6)F_(12)O长期兼容还有待深入研究。为此,本文研究了C_(6)F_(12)O/CO_(2)混合气体与气体绝缘设备中常用的三元乙丙橡胶(EPDM)的相容性和O_(2)对C_(6)F_(12)O/CO_(2)混合气体与EPDM相容性的影响。本文搭建了气固相容性实验平台,并结合实际运行温度进行不同温度下C_(6)F_(12)O混合气体与EPDM的相容性实验,测试了实验后EPDM的表面形貌、表面元素、力学性能和气体成分的变化,以确定C_(6)F_(12)O混合气体与EP-DM的长期相容性。同时,构建了C_(6)F_(12)O混合气体与EPDM分子链的仿真模型,基于分子动力学(MD)理论计算了C_(6)F_(12)O、CO_(2)与EPDM之间的扩散系数、相互作用参数和混合能。结果表明:在110℃热加速实验后EPDM表面产生鳞状结构,并在EPDM表面检测到C—F键、有机氟化物和金属氟化物,EPDM的力学性能降低,实验后主要气体产物为C_(3)F_(6)和C_(3)F_(7)H。加入O_(2)后,EPDM在90℃时表面出现凸起,并且有大量O、F元素积累在表面,EPDM力学性能下降,气体产物增多。理论计算也表明升高温度和加入O_(2)会加速C_(6)F_(12)O混合气体在EPDM中的扩散,导致气体分子与EPDM相容性变差。本文的研究成果将为C_(6)F_(12)O气体绝缘设备的设计和制造过程提供参考。

Objective SF6 is widely used in electrically insulated equipment due to its excellent insulating properties.However,its global warming potential is 23500 times greater than that of CO_(2),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.C_(6)F_(12)O has both environmental benign characteristics and insulating properties,which has attracted the attention of scholars.However,the liquefaction temperature of pure C_(6)F_(12)O 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 CO_(2)and N2.It has been shown that a gas mixture comprising 4%C_(6)F_(12)O/CO_(2),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 C_(6)F_(12)O/CO_(2)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 O_(2)on the compatibility of C_(6)F_(12)O gas mixture and EPDM was investigated by adding a small amount of O_(2)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 C_(6)F_(12)O/CO_(2)/O_(2)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 C_(6)F_(12)O/CO_(2)at 110℃.A flocculent structure appeared when EPDM was mixed with C_(6)F_(12)O/CO_(2)/O_(2)at only 90℃.This observation suggested that the inclusion of O_(2)promotes the interaction between the C_(6)F_(12)O/CO_(2)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 C_(6)F_(12)O/CO_(2)mixed EPDM with increasing temperature.This trend indicated that C_(6)F_(12)O/CO_(2)reacts with EPDM.In group of C_(6)F_(12)O/CO_(2)/O_(2),the changes were more significant,which indicate that O_(2)promoted the reaction between the C_(6)F_(12)O/CO_(2)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—CF_(2)CH_(2)—at 687 eV.The intensity of C characteristic peak was significantly lower,while the intensity of O and F were higher in the C_(6)F_(12)O/CO_(2)/O_(2)gas mixture after testing.These findings indicated that O_(2)actively participates in the reaction between the C_(6)F_(12)O/CO_(2)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 C_(6)F_(12)O/CO_(2)atmosphere was slightly worse than those of the original samples.The mechanical property of EPDM under C_(6)F_(12)O/CO_(2)/O_(2)was worse than that of C_(6)F_(12)O/CO_(2).The reaction between the C_(6)F_(12)O/CO_(2)mixture and EPDM was more intensive after adding O_(2),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 H_(2)O remaining inside the gas tank was involved in the decomposition reaction of the C_(6)F_(12)O gas mixture.Throughout the reaction,H^(·)and OH^(·)were generated from the decomposition of H_(2)O,which can interact with particles such as,CF_(3)^(·),C_(3)F_(7)^(·)and F^(·)produced by C_(6)F_(12)O to produce decomposition products such as C_(3)F_(6)and C_(3)F_(7)H.Meanwhile,the reaction rate of the C_(6)F_(12)O gas mixture with EPDM and the concentration of C_(3)F_(6)and C_(3)F_(7)H were increased by both the increasing temperature and O_(2)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 C_(6)F_(12)O and CO_(2)in EPDM increased with rising temperatures.At 110℃,the diffusion coefficients of C_(6)F_(12)O and CO_(2)were increased by 1.71 and 2.49 times,respectively,following O_(2)addition.It indicates that the internal energies of gas molecules were increased by adding O_(2),and the C_(6)F_(12)O and CO_(2)gas molecules could be easier to diffuse on the EPDM surface and interact with EPDM.The Flory-Huggins interaction parameter(χ)quantifies alterations in molecular interaction energy during miscibility and aids in determining the solubility of binary mixtures.A value ofχtending towards 0 indicates good compatibility between the mixed systems.Meanwhile,the parameter(χ)tends to be linear with the mixing energy(ΔE_(mix)).BothχandΔE_(mix)values of the EPDM mixing system decreased with increasing temperature.The andΔE_(mix)of the CO_(2)/EPDM mixing system at different temperatures were higher than those of the C_(6)F_(12)O/EPDM blend system,which suggested that C_(6)F_(12)O was soluble with EPDM while CO_(2)struggles to establish a stable system.TheχandΔE_(mix)values of the system were decreased after adding O_(2),indicating that the internal energy of C_(6)F_(12)O and CO_(2)gas molecules was enhanced by O_(2),thereby enhancing their interaction with EPDM molecular chains.Conclusions The corrosion of the EPDM surface intensifies with the increase of temperature and the addition of O_(2)leading to a decline in the elongation at break and tensile strength.The fluorine-containing groups generated by the decomposition of C_(6)F_(12)O and EPDM not only interact with EPDM molecules,but also react with the additives inside EPDM to form metal fluorides and organic fluorides.Given its large molecular diameter,C_(6)F_(12)O possesses a diffusion coefficient significantly lower than that of CO_(2)at various temperatures,making it difficult to react with EPDM molecules.Conversely,the compact CO_(2)molecules boast a large diffusion coefficient,yet CO_(2)'s chemical stability precludes its combination with EPDM.The increase in temperature and the addition of O_(2)will reduce the interaction parameters and mixing energy of the C_(6)F_(12)O/EPDM and CO_(2)/EPDM binary blends,making it easier to interact with EPDM.