Dachang Chen

Reactive molecular dynamics study of the decomposition mechanism of the environmentally friendly insulating medium C3F7CN

The extensive use of sulfur hexafluoride (SF6) gas in the power industry has a strong greenhouse effect. Hence, many scholars are committed to studying SF6 alternative gases to achieve green power development. In the past two years, C3F7CN (heptafluoroisobutyronitrile) has attracted the attention of many scholars due to its excellent insulation and environmental protection characteristics as a potential alternative gas. This study theoretically explores the decomposition characteristics of C3F7CN and the C3F7CN/CO2 gas mixture based on the reactive molecular dynamics method and density functional theory. The main decomposition pathways of C3F7CN and the enthalpy of each path at different temperatures were analyzed. The yield of the main decomposition products was obtained under several temperature conditions. The decomposition of C3F7CN mainly produced CF3, C3F7, CN, CNF, CF2, CF, F, and other free radicals and a few molecular products, such as CF4 and C3F8. The C3F7CN/CO2 gas mixture has more excellent decomposition characteristics than that of the pure C3F7CN. The addition of CO2 effectively ensures that the gas mixture has a low liquefaction temperature, which is considerably suitable for use as a gas insulation medium. The relevant research results provide guidance for the further exploration on the electrical properties and practical engineering application of the C3F7CN gas mixture.

Investigation of Gas-Sensing Property of Acid-Deposited Polyaniline Thin-Film Sensors for Detecting H2S and SO2

Latent insulation defects introduced in manufacturing process of gas-insulated switchgears can lead to partial discharge during long-time operation, even to insulation fault if partial discharge develops further. Monitoring of decomposed components of SF6, insulating medium of gas-insulated switchgear, is a feasible method of early-warning to avoid the occurrence of sudden fault. Polyaniline thin-film with protonic acid deposited possesses wide application prospects in the gas-sensing field. Polyaniline thin-film sensors with only sulfosalicylic acid deposited and with both hydrochloric acid and sulfosalicylic acid deposited were prepared by chemical oxidative polymerization method. Gas-sensing experiment was carried out to test properties of new sensors when exposed to H2S and SO2, two decomposed products of SF6 under discharge. The gas-sensing properties of these two sensors were compared with that of a hydrochloric acid deposited sensor. Results show that the hydrochloric acid and sulfosalicylic acid deposited polyaniline thin-film sensor shows the most outstanding sensitivity and selectivity to H2S and SO2 when concentration of gases range from 10 to 100 μL/L, with sensitivity changing linearly with concentration of gases. The sensor also possesses excellent long-time and thermal stability. This research lays the foundation for preparing practical gas-sensing devices to detect H2S and SO2 in gas-insulated switchgears at room temperature.

Pristine and Cu decorated hexagonal InN monolayer, a promising candidate to detect and scavenge SF6 decompositions based on first-principle study

We carried out the first-principle study of four types of SF6 decompositions adsorbed on pristine and Cu atom decorated hexagonal InN monolayer. The adsorption structures, adsorption energy, electron transfer, band structure, density of states and desorption properties were discussed to evaluate the possible application of InN monolayer in field of adsorbent and gas sensor. The results revealed that the pristine InN monolayer has the largest adsorption energy to SO2 with evident chemical interactions. The introduction of Cu adatom on InN monolayer significantly enhanced the chemical interactions between the InN monolayer and the SO2, SOF2, SO2F2 gas molecule but declined the adsorption energy of HF. We also investigated the electronic properties of all adsorption configurations and estimated the desorption time of every gas molecule from pristine and Cu decorated InN monolayer to evaluate the potential application in noxious gas detecting and scavenging in gas insulated switch-gear (GIS).

Pt Decorating Effect on CNT Surface Towards Adsorption of SF 6 Decomposed Components

Carbon nanotubes (CNTs) based sensors are drawn considerable attentions for gas adsorption and sensing due to their large specific surface area. In this paper, the adsorptions of three SF6 decomposed components (SO2F2, SOF2 and SO2) on Pt doped CNT are theoretically studied based on density function theory method. The density of state, frontier molecular orbital theory as well as Mulliken population analysis were considered in order to comprehensively understand the adsorbing processes. Results indicated that Pt-CNT has the best sensitivity to SOF2 owing to their strong chemisorption, followed by SO2 and the last one comes to SO2F2 due to their weak physisorption. Pt dopant that acts as an activated catalytic additive can effectively improve the adsorption ability to gas molecules through providing several active adsorption sites of CNT. Our calculation results would be meaningful not only to explain the sensing mechanism of CNT but also to suggest advanced SWCNTs based sensing materials to be applied in the field of electrical engineering.

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

ABSTRACT Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C3F7CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF6 environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C2F5CN, CF3CN, COF2 and CF4 with the aluminium widely used in electrical equipment. It was found that the interaction between C2F5CN, CF3CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF2, CF4 and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C3F7CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C3F7CN decomposition products and aluminium. GRAPHICAL ABSTRACT

Simulation and experiment on the catalytic degradation of high-concentration SF6 on TiO2 surface under UV light

The high-temperature effect gas SF6 is used in the power industry, and its emissions are increasing daily. Therefore, the degradation of SF6 is particularly important. In this work, SF6 with a high concentration of 2% was degraded using the catalytic principle of TiO2 under UV light at normal temperature and pressure. Experimental results proved that this method can effectively degrade SF6. Moreover, the addition of TiO2 can effectively increase the degradation rate of SF6. The degradation of eight pieces of TiO2 with a unit area of 3 cm2 was 8.98% after 3 h of catalysis. FTIR spectral analysis showed that the main degradation products were SO2F2, SiF4, SF4, and SO2. Adding H2O can further increase the degradation rate, which can reach 27.22% in 3 h. The main degradation products were SO2F2, SiF4, SF4, SiH4, HF, and SO2. Finally, simulations verified the catalytic decomposition of SF6 on the surface of TiO2.The high-temperature effect gas SF6 is used in the power industry, and its emissions are increasing daily. Therefore, the degradation of SF6 is particularly important. In this work, SF6 with a high concentration of 2% was degraded using the catalytic principle of TiO2 under UV light at normal temperature and pressure. Experimental results proved that this method can effectively degrade SF6. Moreover, the addition of TiO2 can effectively increase the degradation rate of SF6. The degradation of eight pieces of TiO2 with a unit area of 3 cm2 was 8.98% after 3 h of catalysis. FTIR spectral analysis showed that the main degradation products were SO2F2, SiF4, SF4, and SO2. Adding H2O can further increase the degradation rate, which can reach 27.22% in 3 h. The main degradation products were SO2F2, SiF4, SF4, SiH4, HF, and SO2. Finally, simulations verified the catalytic decomposition of SF6 on the surface of TiO2.