CO2 laser-induced interaction between sulfur hexafluoride and carbon disulfide

Interaction between carbon disulfide and sulfur hexafluoride is excited by cw CO₂ laser radiation and has been investigated for different ratios over a pressure range from 3.1 to 34.6 kPa. The reaction yields sulfur tetrafluoride, sulfur, carbon, thiocarbonyl fluoride, tetrafluoromethane and hexafluoroethane, the ratio of these latter products is dependent on the partial pressure of sulfur hexafluoride in the initial CS₂-SF₆ mixture. Interaction is considered to include both the SF₆-sensitized decomposition of carbon disulfide and reaction between sulfur hexafluoride and carbon disulfide.     

Nucleophilic Activation of Sulfur Hexafluoride: Metal‐Free,Selective Degradation by Phosphines

The development of new methods for the chemical activation of the extremely inert greenhouse gas sulfur hexafluoride (SF₆) not only is of current environmental interest, but also offers new opportunities for applications of SF₆ as a reagent in organic synthesis. We herein report the first nucleophilic activation of SF₆ by Lewis bases, namely by phosphines, which results either in its complete degradation to phosphine sulfides and difluorophosphoranes or in the selective conversion of SF₆ into a bench‐stable, crystalline salt containing the SF₅^? anion. Quantum chemical calculations reveal a nucleophilic substitution mechanism (S_N2) for the initial fluorine abstraction from SF₆ by the phosphine. Furthermore, a scalable one‐pot procedure for the complete decomposition of SF₆ into solid, nonvolatile products is presented based on cheap and commercially available starting materials.     

Nucleophilic Activation of Sulfur Hexafluoride: Metal‐Free,Selective Degradation by Phosphines

The development of new methods for the chemical activation of the extremely inert greenhouse gas sulfur hexafluoride (SF₆) not only is of current environmental interest, but also offers new opportunities for applications of SF₆ as a reagent in organic synthesis. We herein report the first nucleophilic activation of SF₆ by Lewis bases, namely by phosphines, which results either in its complete degradation to phosphine sulfides and difluorophosphoranes or in the selective conversion of SF₆ into a bench‐stable, crystalline salt containing the SF₅⁻ anion. Quantum chemical calculations reveal a nucleophilic substitution mechanism (S_N2) for the initial fluorine abstraction from SF₆ by the phosphine. Furthermore, a scalable one‐pot procedure for the complete decomposition of SF₆ into solid, nonvolatile products is presented based on cheap and commercially available starting materials.     

A full dimensional direct ab initio dynamics study of the electron capture by SF6

The dynamics of electron capture by sulfur hexafluoride (SF₆) have been investigated by means of full dimensional direct ab initio dynamics calculations at the HF/6-311G(d)+sp (a diffuse sp-function is further added to sulfur atom) level. A rigid SF₆ structure and narrow Franck–Condon region for electron capture was assumed in choosing initial conditions for the trajectories. The direct ab initio dynamics calculations for the electron capture processes by SF₆ indicated that the SF⁻₆ ion formed by the vertical electron attachment to SF₆ decomposes into SF⁻₅ and F via short-lived complex formation (SF⁻₆). The lifetime of SF⁻₆ was distributed from 0.1–0.2 ps, which is quite short as lifetime of the intermediate complex. The dynamics calculations showed that 12% of the total available energy is partitioned into the relative translational mode between SF₅⁻ and F. The effect of solid phase on the dynamics has been examined by introducing a model bath-relaxation time for energy dispersion. There was a possibility that the SF₆⁻ anion exists in solid phase. The mechanism of the electron capture by SF₆ in gas phase and in solid phase was discussed on the basis of the results.     

Electron scattering on C6F6 and SF6 molecules

Total absolute cross sections for electron scattering on hexafluorobenzene, C₆F₆, and sulfur hexafluoride, SF₆, molecules, have been measured as a function of impact energy from 0.6 to 250 eV. The total cross section for C₆F₆ exhibits a very broad peak stretching from 10 to 100 eV with some weak features near 9.5 and 15 eV superimposed on the peak. Apart from the well-known low-energy resonant structures in the SF6 total cross section function, a new weak resonant feature close to 25 eV has been noticed in the present experiment, in accordance with earlier theoretical calculations.     

Chemically assisted ion beam etching of silicon and silicon dioxide using SF6

A chemical flux of sulfur hexafluoride (SF₆) in conjunction with low-energy Ar-ion bombardment has been used for chemically assisted ion beam etching (CAIBE) of silicon and silicon dioxide. The study has shown a large degree of independent control over the selectivity and anisotropy in dry etching. The total etch rate could be controlled by varying either the Ar-ion milling parameters or the chemical flux of SF₆. Etch rate enhancement of 7–8 for silicon and 3–4 for silicon dioxide have been obtained over pure physical etching.     

Inorganic volatile fluorides obtained from electrical decomposition of sulfur hexafluoride in a quartz tube

Recent investigations on sulfur hexafluoride decomposition have shown the need of a rapid and efficient method for the qualitative and quantitative analysis of the reaction products. An analytical method for characterizing the gas mixture obtained from the decomposition of sulfur hexafluoride in a quartz reactor submitted to an r.f. discharge, is presented. A combination of gas-chromatographic, mass spectrometric and infrared spectrophotometric techniques has shown the presence of SF₆, SO₂F₂, SOF₄, SOF₂, SiF₄ and F₂ in the gas mixtures examined. For quantitative purposes a gas-chromatographic method has been found to be most suitable.     

Extraction of polychlorinated biphenyl with supercritical carbon dioxide, sulfur hexafluoride and subcritical water

In the extraction of spiked PCB from soil, three extracting fluids were investigated: supercritical carbon dioxide (CO₂), supercritical sulfur hexafluoride (SF₆) and subcritical water. Among the tested fluids SF₆ appeared to be appropriate especially for the extraction of low polar PCB. CO₂ and water were found to be suitable for the quantitative extraction of all PCB. Water was judged as the best because of its low price, good availability and environmental safety.     

Plasma processed carbon thin films applied to dye-sensitized solar cells

Plasma-treated carbon thin films are investigated as counter electrodes for dye-sensitized solar cells. The films were grown onto fluorine-doped tin oxide (FTO) substrates by magnetron sputtering using pure graphite target and argon atmosphere and subsequently annealed at 600 °C for 30 min in vacuum. These films were then submitted to a plasma texturing process in a reactive ion etching reactor using three different gas combinations: sulfur hexafluoride/argon (SF₆ + Ar), sulfur hexafluoride/hydrogen (SF₆ + H₂), and sulfur hexafluoride/oxygen (SF₆ + O₂). The morphology and structure of the obtained films were characterized by scanning electron microscopy and Raman spectroscopy. Cyclic voltammetry technique allowed accessing the improvements in their catalytic properties, while the photocurrent-voltage curves under simulated solar illumination AM 1.5G (100 mW/cm²) evaluated the performance of the respective assembled solar cells. The results show that photovoltaic performance is significantly affected by the different plasma texturing conditions used. The carbon counter electrode obtained after SF₆ + O₂ plasma texturing achieved the best power conversion efficiency of 2.23%, which is comparable to the 2.31% obtained using the commercial platinum counter electrode.

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Graphical abstract Reactive Ion Etching reactor for plasma texturing process of carbon thin films

     

Experimental investigation and simulation of hollow fiber membrane process for SF6 recovery from GIS

In this present study, polyethersulfone hollow fiber membrane was used to recover sulfur hexafluoride (SF₆) from gas‐insulated switchgear (GIS). SF₆, N₂ pure gas and mixed gas (12.5 vol.% of SF₆) experiment was initiated to observe permeation behavior according to temperature and pressure difference and retentate flow rate. Scanning electron microscopy was used to investigate the morphological characteristics and the structure of asymmetric hollow fibers. The permeation rates of SF₆ and N₂ were measured by the variable pressure method. As a result, permeance of N₂ was 9.5–16.3 GPU, and selectivity of N₂/SF₆ was 10.5–13.3. Moreover, the concentration of SF₆ in the retentate stream reached to 99.2% by the control of the operating condition. Based on the experimental results, tree‐stage membrane process was designed using simulation program. As a result, demanded membrane area reduced about 74% according to operating condition difference. Copyright © 2013 John Wiley & Sons, Ltd.     

Photoredox Catalytic Pentafluorosulfanylative Domino Cyclization of α-Substituted Alkenes to Oxaheterocycles by Using SF6

Virtually inert sulfur hexafluoride becomes a precious pentafluorosulfanylation agent, if properly activated by photoredox catalysis, to access α-fluoro and α-alkoxy SF₅-compounds. This advanced protocol converts SF₆ in the presence of alkynols as bifunctional C−C- and C−O-bond forming reagents directly into pentafluorosulfanylated oxygen-containing heterocycles in a single step from α-substituted alkenes. The proposed mechanism is supported by theoretical calculations and gives insights not only in the pentafluorosulfanylation step but also into formation of the carbon-carbon bond and is in full agreement with Baldwin's cyclization rules. The key step is a radical type 5-, 6- respectively 7-exo-dig-cyclization. The synthesized oxaheterocycles cannot be simply prepared by other synthetic methods, show a high level of structural complexity and significantly expand the scope of pentafluorosulfanylated building blocks valuable for medicinal and material chemistry.     

The Activation of Sulfur Hexafluoride at Highly Reduced Low‐Coordinate Nickel Dinitrogen Complexes

The greenhouse gas sulfur hexafluoride is the common standard example in the literature of a very inert inorganic small molecule that is even stable against O₂ in an electric discharge. However, a reduced β‐diketiminate nickel species proved to be capable of converting SF₆ into sulfide and fluoride compounds at ambient standard conditions. The fluoride product complex features an unprecedented [NiF]⁺ unit, where the Ni atom is only three‐coordinate, while the sulfide product exhibits a rare almost linear [Ni(μ‐S)Ni]²⁺ moiety. The reaction was monitored applying ¹H NMR, IR and EPR spectroscopic techniques resulting in the identification of an intermediate nickel complex that gave insight into the mechanism of the eight‐electron reduction of SF₆.     

高压变电站事故预警监测探讨-新型氟化氢气体在线监测仪的研制

通过监测六氟化硫（SF₆）气体的变化发现高压变电站系统中设备的异常. 气体绝缘开关设备（GIS）中的高压开关、电闸及其它各种设备因接触不良、电阻值增加、发热、融解、拉弧、连续拉弧等原因会造成设备短路. 因保护这些电器的SF₆气体不可能非常纯净,如存在H₂O. 在上述这些故障发生时变成催化条件,使SF₆与H₂O作用后生成氟化氢气体. 通过监测氟化氢气体的突发变化,可以预警GIS系统设备可能出现的故障.     

Catalytic Degradation of Sulfur Hexafluoride by Rhodium Complexes

The development of a safe and efficient method for the degradation of SF₆ is of current environmental interest, because SF₆ is one of the most potent greenhouse gases. SF₆ is thermally and chemically extremely inert, and therefore, it has been used in various industrial applications. However, this inertness results in a major challenge for its depletion. We report on a process for a catalytic degradation of SF₆ in the homogeneous phase by using rhodium complexes as precatalysts. The SF₆ activation reactions feature mild reaction conditions, low catalyst loadings, and a high selectivity. The employment of phosphines and hydrosilanes for scavenging the sulfur and fluorine atoms of the SF₆ molecule allows the selective transformation of SF₆ into nongaseous and nontoxic compounds.     

Chemical vapour deposition of germanium-containing films by IR laser-induced decomposition of ethoxy(trimethyl)germane

Carbon Dioxide (CO₂) laser-induced decomposition of ethoxy(trimethyl)germane (ETG) results in a substantial stripping of organic substituents from germanium and leads to deposition of organogermanium films, the composition of which is dependent on the mode of laser irradiation. Direct absorption of laser radiation in ETG affords material rich in Germanium, while a sulfur hexafluoride (SF₆)-photosensitized process produces a deposit composed of Germanium, Carbon, Hydrogen and Oxygen. The deposited materials can be modified by chemical reactions with acetic anhydride and atmospheric moisture.     

Transport Coefficients of High Temperature SF6–He Mixtures Used in Switching Applications as an Alternative to Pure SF6

Sulfur hexafluoride (SF₆) gas has a quite high global warming potential and hence it is required that applying any substitute for SF₆ gas. Much interest in the use of a mixture of helium and SF₆ as arc quenching medium were investigated indicating a high performance of arc interruption. The calculated values of transport coefficients of mixtures of SF₆–He mixtures, at high temperatures are presented in this paper: to the knowledge of the authors, related data have not been reported in the literature. The species composition and thermodynamic properties are determined by the method of Gibbs free energy minimization, using standard thermodynamic tables. The transport properties including electron diffusion coefficients, viscosity, thermal conductivity and electrical conductivity, are evaluated by using the Chapman–Enskog method expanded up to the third-order approximation (second-order for viscosity). Particular attention is paid to the collision integral database by the use of the most accurate and recent cross-sections or interaction potentials available in the literature. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 300 to 30,000 K for different pressures between 0.1 and 16 atm. An evaluation of the current interruption performance by adding He into SF₆ is discussed from a microscopic point of view. The properties with regard to SF₆–He mixtures calculated here are expected to be reliable because of the improved collision integrals employed.     

Real-time monitoring traces of SF6 in near-source ambient air by ion mobility spectrometry

The leakage of sulphur hexafluoride (SF₆) gas threats the global climate changes and personnel safety. Monitoring the concentration of SF₆ in its application places is an industry regulation. In this study, ion mobility spectrometry (IMS) was developed for fast monitoring traces of SF₆ in near-source ambient air. Due to the water is an important part of the natural air and affects most atmospheric measurements, the operating parameters of IMS monitoring SF₆ were optimised for quantitative analysis of SF₆ at different relative humidity (RH). It is discovered two main product ions SF₆^? and SOF₄^? by IMS at different RH. The calibration curves of SF₆ were investigated by its relationship with the peak intensity of SOF₄^– for real application. The time resolution of the measurement was obtained less than 1 s and the limit of detection (LOD) achieved 0.16–0.68 ppm with a data averaging of 30 times. At last, the simulated application of monitoring SF₆ leakage was tested in the fume hood of our lab. The results showed a great potential application prospect of IMS in monitoring SF₆ in the ambient air of its application places.     

Synthesis of Platinum(II) N-Heterocyclic Carbenes Based on Adenosine

Organometallic derivatization of nucleosides is a highly promising strategy for the improvement of the therapeutic profile of nucleosides. Herein, a methodology for the synthesis of metalated adenosine with a deprotected ribose moiety is described. Platinum(II) N-heterocyclic carbene complexes based on adenosine were synthesized, namely N-heterocyclic carbenes bearing a protected and unprotected ribose ring. Reaction of the 8-bromo-2′,3′,5′-tri-O-acetyladenosine with Pt(PPh₃)₄ by C8−Br oxidative addition yielded complex 1, with a Pt^II centre bonded to C-8 and an unprotonated N7. Complex 1 reacted at N7 with HBF₄ or methyl iodide, yielding protic carbene 2 or methyl carbene 3, respectively. Deprotection of 1 to yield 4 was achieved with NH₄OH. Deprotected compound 4 reacted at N7 with HCl solutions to yield protic NHC 5 or with methyl iodide yielding methyl carbene 6. Protic N-heterocyclic carbene 5 is not stable in DMSO solutions leading to the formation of compound 7, in which a bromide was replaced by chloride. The cis-influence of complexes 1–7 was examined by ³¹P{¹H} and ¹⁹⁵Pt NMR. Complexes 2, 3, 5, 6 and 7 induce a decrease of ¹J_Pt,P of more than 300 Hz, as result of the higher cis-influence of the N-heterocyclic carbene when compared to the azolato ligand in 1 and 4.