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SF6/N2 mixture is an alternative gas of SF6, which is already used in electrical equipment. When a malfunction occurs, SF6/N2 will decompose and further react with trace water and oxygen to produce nitrogen-containing gases such as NO, NO2, N2O and NF3. It is necessary to monitor these gases to ensure the safe operation of the equipment. This paper is based on density functional theory (DFT), the nanomaterial Ti3C2T x doped with Au atom was selected as sensing material. The result shows that Au/Ti3C2T x has larger adsorption energy when NO and NO2 adsorbed on the surface, the stable structures were conformed more easily with NO and NO2 compared with N2O and NF3. The density of states analysis and the frontier molecule orbital analysis reveal more change of the system before and after NO and NO2 adsorption, suggesting the material showed good sensitivity performance to NO and NO2. Thus, Au/Ti3C2T x is considered to have the potential for sensing NO and NO2. [ABSTRACT FROM AUTHOR]

Context: SF6 gas has a strong greenhouse effect, and how to treat SF6 in an environmentally friendly way has been a hot topic of current research. In this paper, the adsorption behavior of SF6 on the surface of Pd-doped hydroxyl-terminated modified Ti3C2Tx (i.e., Ti3C2(OH)2) was investigated based on the density functional theory using two-dimensional MXene as the catalyst. The structures of different Pd-doped Ti3C2(OH)2 were analyzed and the most structurally stable doped structures were selected as the basis for subsequent calculations. A large number of adsorption configurations were constructed and geometrically optimized, and the adsorption energy, charge transfer, differential charge density, and density of states of the systems were calculated in order to analyze the gas–solid interactions and find the surface active sites; compared with the adsorption performance of undoped Ti3C2(OH)2 on SF6, it was found that Pd doping played a less inhibitory role in the adsorption of SF6 on the Ti3C2(OH)2 surface. The results of this study can provide theoretical support for the use of Pd-doped Ti3C2(OH)2 as a catalyst for the degradation of SF6. Methods: In this paper, simulations of SF6 adsorption on Ti3C2Tx surfaces are based on density functional theory and are carried out in the Dmol3 module of Material Studio. To better describe the non-uniform electron density of the actual system, the PBE functional in the generalized gradient approximation (GGA) was chosen for the optimization of the structure of the gas–solid interface system and the calculation of the relevant electronic properties, combined with the Grimme dispersion correction in the DFT-D dispersion correction for the electron exchange correlation term. Because both Pd and Ti are transition metal elements, the mode-conserving pseudopotential DNP basis set containing relativistic effects was chosen for the electronic wave function expansion. In this paper, an all-electron model is used for the inner core treatment of gas molecules and a density generalized semi-nuclear pseudopotential DSSP is used for the solid surface treatment. [ABSTRACT FROM AUTHOR]

C5F10O is a promising insulating medium in the manufacturing of environmentally friendly gas-insulated switchgears (GISs). The fact that it is not known whether it is compatible with sealing materials used in GISs limits its application. In this paper, the deterioration behaviors and mechanism of nitrile butadiene rubber (NBR) after prolonged exposure to C5F10O are studied. The influence of C5F10O/N2 mixture on the deterioration process of NBR is analyzed through a thermal accelerated ageing experiment. The interaction mechanism between C5F10O and NBR is considered based on microscopic detection and density functional theory. Subsequently, the effect of this interaction on the elasticity of NBR is calculated through molecular dynamics simulations. According to the results, the polymer chain of NBR can slowly react with C5F10O, leading to deterioration of its surface elasticity and loss of inside additives, mainly ZnO and CaCO3. This consequently reduces the compression modulus of NBR. The interaction is related to CF3 radicals formed by the primary decomposition of C5F10O. The molecular structure of NBR will be changed in the molecular dynamics simulations due to the addition reaction with CF3 on NBR's backbone or branched chains, resulting in changes in Lame constants and a decrease in elastic parameters. [ABSTRACT FROM AUTHOR]

In gas-insulated equipment, the decomposition of SF6 is closely related to the residual traces of O2 and H2O in the equipment. However, the decomposition mechanism has not yet been clarified. In this paper, the adsorption and defluorination of SF6 on the preadsorbed Cu(111) surface were calculated based on density flooding theory and transition state theory. Besides, the influence mechanism of O atoms and H2O molecules on the defluorination process is analyzed by comparing the energy barrier, reaction heat, and density of states. The results show that pre-adsorption of O atoms changes the adsorption sites of SFx, but has no significant effect on the adsorption energy. In addition, the O atom has a certain inhibitory effect on the decomposition process, and SF → S + F is the key to determining the reaction rate. In contrast, H2O will not only promote the adsorption of SFx to the surface but also reduce the total reaction heat of the decomposition reaction by 135.37 kcal·mol−1, driving the decomposition process of SF6. In this paper, stable co-adsorption configurations of low-fluorosulfide and co-adsorption groups were determined, and the effects of O and H2O preadsorption on SF6/Cu gas–solid interactions were initially revealed. [ABSTRACT FROM AUTHOR]

Accurately grasping the decomposition path of SF6 on the surface of typical metals and metal oxides is the key to reveal the decomposition mechanism of overheating fault. In this paper, the decomposition paths of SF6 on Cu and its oxides are theoretically analyzed by combining density functional theory and transition state theory. The results show that the participation of Cu surface reduces the energy required for the initial decomposition of SF6 by about 98.70 kcal/mol compared to that in free space. The decomposition reaction of SF5 on the Cu surface is energy barrier free, thus SF5 cannot stably exist in SF6 over-thermal decomposition system. Further, it was found that when Cu was oxidized at high temperature, reactions between SF6 and metal surface would be more intense. At this time, the total reaction heat of SF6 completely decomposed into S was -220.07 kcal/mol, significantly lower than -100.60 kcal/mol on Cu surface. This illustrates the catalytic effect of Cu and its oxides. On the surface of CuO, the interaction of O and F atoms may be the main reason to further reduce the activation energy. This article explained the over-thermal decomposition process of SF6 from microscopic level, laying a theoretical foundation for further study on the influence of the over-thermal decomposition of SF6-metal system. [ABSTRACT FROM AUTHOR]

Self-recovery ability after over thermal fault decomposition is a fundamental factor determining the stability of environmentally friendly insulation medium C5F10O in engineering applications. This article proposes 42 possible reaction pathways for the decomposition products of C5F10O to reform C5F10O after overheating fault based on its thermal decomposition and industrial synthesis pathways. Dominant reaction paths and reactants in the recovery process at temperature of 298–1000 K are theoretically analyzed according to the chemical equilibrium constant and rate constant, which were calculated based on the density functional theory using the thermodynamics properties of the reactions such as activation energy and enthalpy. According to the results, at low temperatures, 26 of the 42 proposed reactions have the equilibrium constants greater than 1, and the rate constants of them are much higher than that of the decomposition reactions, proving that decomposed C5F10O can be partly recovered after the overheating fault is removed. Among the recovery pathways, reactions with primary or secondary decomposition products of C5F10O as the reactants hold higher equilibrium constants and are the dominant reactions for the recovery process. R11, R8, and R5 hold the largest rate constants in similar reactions and contribute the most to the restoration of C5F10O, that is, (CF3)2CFCO $\cdot $ , (CF3)2CFCOF $\cdot $ , and CF3OCCF(CF3)2 are the dominant reactants for the formation of C5F10O. And the synthesis reactions R22, R17, R7, and R15 of these reactants are also necessary for the self-recovery process of C5F10O. [ABSTRACT FROM AUTHOR]

As a promising environmentally friendly insulating medium, C5F10O needs to be mixed with buffer gases such as technical air to avoid liquefaction. Notably, such a high proportion of oxygen can promote the decomposition of C5F10O and may even eradicate its stability under over-thermal fault. At present, there is still a lack of experimental research investigating the influence of oxygen on the thermal stability of C5F10O, and the mechanism is still unclear. To this end, experiments are carried out on the thermal decomposition properties of C5F10O while mixed with different proportions of O2. And to reveal the mechanism, the dissociation of C5F10O and the reaction of O2 with CF3CO $\cdot $ radical are studied theoretically based on the density functional theory (DFT) and transition state theory (TST). The results signify that oxygen of 4% and above ravages the thermal stability of C5F10O medium, causing it to decompose in a large amount at high temperature, which generates stable products such as CO2, C3F6, C3F8, and C2F6. The mechanism is that O2 is extremely easy to combine with CF3CO $\cdot $ radical to form a complex, which further decomposes, leading to the continuous development of the decomposition of C5F10O. The study revealed the important mechanism of O2 during the decomposition process of C5F10O, providing experimental and theoretical support for the use of C5F10O mixed gas. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of missing parameters in the Reax force field containing S and F elements. First, density functional theory was used to scan SF6 and low-fluoride sulfide molecules to obtain the basic dataset for the Reax force field. The Monte Carlo method was then used to perform fitting optimization and quality verification of the established force field. Based on the established force field, molecular dynamics studies were carried out on the over-thermal decomposition of a SF6 gas-insulating medium, and infrared spectra were obtained, describing the vibration characteristics of SF6 and low-fluoride sulfide molecules. According to the vibration modes revealed by the infrared spectra, a potential-energy surface scan was performed. This paper focuses on the analysis of the total energy, potential energy and kinetic energy of SF6 and low-fluoride sulfide molecules moving at different temperatures. The results show that the energy error of the established force field is about 10% when describing the bonding and breaking processes of SF6, SF5, SF4, SF3 and SF2 molecules, which verifies the reliability of the reactive force field method when used to describe molecular behavior. The research work detailed in this paper lays the foundation for the next systematic study of the microscopic physical mechanisms of SF6 over-thermal decomposition. [ABSTRACT FROM AUTHOR]

• All results suggested that the process of NF 3 adsorbing on Rh-SWCNT is exothermic. • Based on the simulation, the interaction between NF 3 and Rh-SWCNT is chemisorption. • F adsorption mode are probably the best mode for NF 3 adsorbing on Rh-SWCNT. • The recovery time are 8.633 s and 0.506 s in F adsorption mode and N adsorption mode respectively. • Considering the nice adsorption properties and short recovery time, Rh-SWCNT could be used to detect NF 3. The gas sensing properties of Rh doped single walled carbon nanotube to NF 3 , one of the key decomposition gas production of SF 6 /N 2 gas mixtures, are explored based on density functional theory in this paper. The results suggest that the process of NF 3 adsorbing on Rh-SWCNT is exothermic, and the F adsorption mode are probably the best mode for NF 3 adsorbing on Rh-SWCNT. Rh-SWCNT surface has a nice gas sensing upon NF 3 gas. All the works provide a theoretical adsorption information of Rh-SWCNT as gas sensor material for the detection of NF 3 in the application of condition monitoring and defect diagnosis in SF 6 /N 2 gas mixtures insulated equipment based on decomposition components. [ABSTRACT FROM AUTHOR]

[Display omitted] • SF 6 and Ti 3 C 2 (OH) 2 surface have strong interaction during adsorption process. • Structure of SF 6 changes obviously with low-fluorine sulfide formed as a result of chemical adsorption. • Ti 3 C 2 T x terminated by hydroxyl is potential to be a catalyst for SF 6 decomposition. At present, searching for efficient methods to degrade sulfur hexafluoride (SF 6) is a worldwide hotspot. Due to the abundant active groups on the surface, MXene is regarded as an ideal catalyst support. In this paper, the potential active sites of Ti 3 C 2 T x (T = OH, F, O) for SF 6 degradation were studied using density functional theory (DFT) method. The results show the adsorption of SF 6 on Ti 3 C 2 (OH) 2 is significantly stronger than that on Ti 3 C 2 F 2 and Ti 3 C 2 O 2. Among typical adsorption sites on Ti 3 C 2 (OH) 2 , SF 6 exhibited the strongest interaction at OH-1 site. Complex electron orbital interactions occurred between SF 6 and Ti 3 C 2 (OH) 2. Adsorption energy reached −6.739 eV and about 1.414e transferred from Ti 3 C 2 (OH) 2 to SF 6. Structure of SF 6 changed obviously and chemical adsorption occurred in this process. However, on Ti 3 C 2 F 2 and Ti 3 C 2 O 2 , gas–solid interactions were weak and the structures had little change, which was mainly physical adsorption. Compared with common catalysts such as Ag, α ‑Al 2 O 3 and BaTiO 3 , Ti 3 C 2 (OH) 2 showed better catalytic activity for SF 6 degradation. By strong adsorption of the active site on the surface, the degradation products were separated from each other, which weakened SF 6 recombination and promoted the further degradation. The results provide theoretical support for MXene acting as a catalyst to efficiently degrade SF 6. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption of CS 2 and COF 2 on the surface of α-Al 2 O 3 (0 0 0 1) presents a state of energy release. • CS 2 is more easily adsorbed on the α-Al 2 O 3 (0 0 0 1) Surface by C atoms ;the surface of α-Al 2 O 3 (0 0 0 1) has a good adsorption effect on all three atom adsorption directions of COF 2 gas. • It is believed that new bonds may be generated during the adsorption process of the CS 2 and COF 2 gas molecules, and the structure after adsorption is more stable. As the typical carbon-containing decomposition components of SF 6 under partial discharge in high-voltage insulation devices, CS 2 and COF 2 , will not only corrode devices, but also pollute the environment. Remove these gases through SF 6 adsorbent is an effective approach to eliminate the above hazards. In this paper, the adsorption performance of CS 2 and COF 2 on α-Al 2 O 3 (0 0 0 1) surface was calculated by first-principle based density functional theory, including the adsorption enthalpy change, charge transfer and structural parameters, and five relatively stable adsorption structures were initially obtained through analysis. Results indicate that all adsorption processes are exothermic. To further understand the adsorption mechanism, the density of states, frontier molecular orbital and deformation charge density diagram were analyzed. Calculations show that both CS 2 and COF 2 has a fine adsorption effect on α-Al 2 O 3 (0 0 0 1) surface, besides, for CS 2 , it is easier to be adsorbed on α-Al 2 O 3 (0 0 0 1) surface through C atom while there is no significant difference in performance parameters of the adsorption configuration for COF 2. Furthermore, frontier molecular orbital analysis also confirmed that the adsorbed system is more stable. This work provide theoretical basis for the experiments of SF 6 adsorbents adsorbing typical carbon-containing decomposition components. [ABSTRACT FROM AUTHOR]