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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]

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]

To clarify the influence of pressure on SF6 decomposition under positive DC partial discharge (PD), SF6‐positive DC partial discharge decomposition experiments at different pressures were carried out. We found that the contents of SF6 primary decomposition products are proportional to E / P 3 / 2 exp − B d P / E. Keeping the chamber volume and external temperature constant, the difference of air chamber pressure means that the electronic mean free path is different. So, different pressures make a difference in the energy of free electrons obtained in a single flight, which results in the difference in the reaction rates of SF6 primary decomposition and further influences the formation of SF6 PD characteristic decomposition components. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The decomposition characteristics of SF6 gas-insulated equipment remarkably vary under different working pressures (0.3?0.7 MPa). Thus, the influence of pressure should be considered when adopting decomposed components for spark discharge fault diagnosis. A series of experiments on SF6 spark discharge decomposition under various pressures were performed on the spark discharge simulation experimental platform. The influence of pressure on SF6 spark discharge decomposed components were analyzed quantitatively combined with molecule chemical decomposition mechanisms. Results show that the species of spark decomposed components do not vary under different pressures. However, pressure directly affects the accumulated energy of the electrons in the spark channel, leading to diverse dissociation intensities of electrons on SF6. This phenomenon further affects the rate of neutral-neutral molecule and ion-molecule reactions responsible for the decomposed components. Finally, the yields and effective generation rates of decomposed components CF4, SOF4, SO2F2, SOF2, and SO2 decline with varying degrees under increasing pressure. Moreover, mathematic regression equations were derived for the effective generation rates of the components influenced by pressure. [ABSTRACT FROM AUTHOR]

We explored the thermal decomposition characteristics of SF6 with partial overthermal fault in organic solid insulating materials. Results show that when organic solid insulating materials were around the fault point, the main overthermal decomposition characteristic products of SF6 were CS2, CO2, CF4, H2S, SO2F2, SOF2, and SO2. The difference in the generating reaction and degree of reaction of the seven decomposition components resulted in the complexity of concentration and growth regularity. Surface component analysis after the experiment showed that the thermode surface contained numerous S, O, C and F. Fe existed in the form of Fe2O3 and FeF2. The organic insulating materials added new elements, such as F and S, because HF and H2S easily reacted with O in the epoxy group. [ABSTRACT FROM AUTHOR]

Sulfur hexafluoride (SF₆) gas-insulated equipment (GIE) has been widely used in extra/ultra high voltage power transmission systems. During its operation, GIE inevitably experiences partial overthermal faults caused by poor contact. In this study, the SF₆ decomposition characteristic of partial overthermal faults was used to solve problems that cannot be detected effectively in GIE. First, a large number of experiments were conducted on an SF₆ overthermal decomposition system to obtain the overthermal decomposition characteristic of SF₆ below 400 °C. Then, from the perspective of the physical significance of engineering, three feature parameters, namely, total decomposition amount, effective formation rate, and ratio of characteristic components, were proposed to reveal the deterioration degree of the gas insulation medium as well as to represent the development trend and severity of a partial overthermal fault. Results show that total decomposition amount CT, CT1, and CT2 can depict the degradation degree of the GIE insulation medium and the carbonic metal structure caused by a partial overthermal fault, which can be a good index to differentiate partial overthermal fault temperatures. The effective formation rate of each characteristic component RRMS is closely related to temperature and can reflect the development trend of a partial overthermal fault. The feature ratio CO2/(SO₂F₂+SOF₄+SOF₂+SO₂+H2S) can reveal whether a partial overthermal fault involves organic insulation materials. H2S/(SO₂F₂+SOF₄) can depict the severity of a partial overthermal fault. Log10(SOF₂+SO₂)/(SO₂F₂+SOF₄) and its effective value TCRRMS3 can represent the deterioration degree of GIE and provide excellent correlation with the severity of a partial overthermal fault, and thus, it can be used to evaluate the severity of a partial overthermal fault quantitatively. [ABSTRACT FROM PUBLISHER]

To obtain the influence regularity of trace O2 on SF6 decomposition characteristics under partial discharge (PD) and establish the foundation of using SF6 decomposed components to diagnose the insulation status of SF6 electrical equipment, first, a series of PD decomposition experiments with different O2 concentrations (%)were conducted on a special experiment platform. The variation regularity between the concentrations of characteristic components and the different content of O2 were obtained quantitatively. Second, the correlation coefficient r testing method was applied to identify the associated influence of trace O2 on the decomposed characteristic components and characteristic ratios. Based on this, an exponential regression model of the related characteristics was developed. Finally, the influence mechanism of trace O2 on SF6 decomposition progress was explained reasonably. The results show that under the PD caused by metal protrusion insulation fault without organic solid insulated materials, CO2, SO2F2, and SOF2 were the mainly decomposed components in the specific range of trace O2. Although no obvious influences of the trace O2 on the concentrations of CO2 and SOF2 as well as the ratio c(CO2)/c(SO2F2+SOF2), it is notable that the trace O2 is negatively and positively related to the concentration of SO2F2 and the ratio c(SOF2)/c(SO2F2), respectively. The exponential regression model can minimize the effect of trace O2 on the fault diagnostic result when using SF6 decomposed components. [ABSTRACT FROM AUTHOR]

Highlights: [•] CaO catalyzes NH3 decomposition, NO reduction by NH3, and NH3 oxidation by O2. [•] NH3 dissociation to NH2 is the rate-controlling step of NH3 conversion. [•] NH3 conversion on the CaO surface is mainly influenced by O2. [•] The selectivity of NH3 conversion is influenced by both O2 and NO. [•] Mechanism and kinetic model are proposed to describe the CaO-involved SNCR process. [ABSTRACT FROM AUTHOR]

Abstract: Increasing environmental pollution caused by the volatile organic compounds due to their toxicity makes their removal imperative. So it is crucial to develop processes which can degrade these compounds effectively. The paper demonstrates that the photocatalytic activity of TiO2 toward the decomposition of gaseous benzene in a batch reactor can be greatly enhanced by loading TiO2 onto the surface of Ce x Zr1−x O2 (x ≥0.25) using sol–gel technology. This research investigated the relationship between x amount and the photocatalytic activity of TiO2. The prepared photocatalysts were characterized by BET, XRD, UV–vis diffuse reflectance and XPS analyses. The specific surface area of photocatalyst decreases as x decreases. XRD results reveal the no peaks of titania were detected. Among the five catalysts prepared, only the binding energy values of Ti2p3/2 of TiO2/Ce0.5Zr0.5O2 shift toward lower value. The order of photocatalytic activity is TiO2/Ce0.5Zr0.5O2 >TiO2/Ce0.75Zr0.25O2 >TiO2/CeO2 ≈TiO2/Ce0.25Zr0.75O2 >TiO2/ZrO2 ≈TiO2. The mechanism role of Ceria–Zirconia mixed oxides in photocatalytic reaction was speculated. [Copyright &y& Elsevier]

Abstract: Increasing environmental pollution caused by the volatile organic compounds due to their toxicity is a matter of great concern. So it is crucial to develop processes which can destroy these compounds effectively. It has been found that the photocatalytic activity of TiO2 towards the decomposition of gaseous benzene can be greatly enhanced by loading Pd on the surface of TiO2. The results show that the optimum palladium loading is 0.25wt.%. The prepared photocatalysts were characterized by XRD, UV–vis diffuse reflectance and XPS. XRD results indicate that no peaks of Pd are detected in the 2θ region from 10° to 90°. Pd/TiO2 absorbs much more light than TiO2 in the visible light region. The XPS spectrum shows that there are Ti, O, C and Pd elements on the surface of the Pd/TiO2, the binding energy values of Ti2p of 0.25%Pd/TiO2 transfer to a lower value. In addition, the photocatalytic performance of 0.25%Pd/TiO2 was investigated, the result illustrates that 0.25%Pd/TiO2 demonstrates 2.32 times the photocatalytic activity of pure TiO2. The reason of promotion of photocatalytic performance was discussed. [Copyright &y& Elsevier]