Formation Of SF Research Articles

Kinetic Selectivity of SF6 during Formation and Dissociation of SF6 + N2 Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Kinetic Selectivity of SF₆ during Formation and Dissociation of SF₆ + N₂ Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Influence of trace O<inf>2</inf> on SF<inf>6</inf> decomposition characteristics under partial discharge based on oxygen isotope tracer

As an excellent electrical insulation and arc-interruption medium, sulfur hexafluoride (SF 6 ) has been widely used in gas-insulated switchgear (GIS). Insulation failures in GIS are usually evolved from the partial discharges which are induced by hidden defects, such as metal protrusions, free conducting particles, floating components. In the presence of discharges, SF 6 decomposes into various by-products. Accordingly, these decomposition by-products are often used to detect and identify partial discharges in GIS based on SF 6 decomposition characteristics. Oxygen (O 2 ) as an impurity plays an important role in the formation of SF 6 decomposition by-products. In this paper, the influence of O 2 on SF 6 decomposition characteristics under partial discharge has been investigated based on oxygen isotope tracer 18O 2 and 16O 2 . In our experiments, SF 6 isotopic decomposition by-products were induced, as severity degree of partial discharge or ratio of 18O 2 to 16O 2 varied. The isotopic decomposition by-products were measured by gas chromatograph mass spectrometer. Based on the results, the sequences of reactions that lead to SO 2 F 2 and SO 2 were described. It is shown that the formation of SO 2 F 2 depends not only on O 2 but also H 2 O, whereas the formation of SO 2 has little dependence on O 2 .

Application of Hybrid Nano-Promoter to the Kinetic Formation of SF6 Gas Hydrates

Application of Hybrid Nano-Promoter to the Kinetic Formation of SF₆ Gas Hydrates

Activation of SF6 at Platinum Complexes: Formation of SF3 Derivatives and Their Application in Deoxyfluorination Reactions

AbstractThe activation of SF6 at [Pt(PR3)2] R=Cy, iPr complexes in the presence of PR3 led selectively and in an unprecedented reaction route to the generation of the SF3 complexes trans‐[Pt(F)(SF3)(PR3)2]. These can also be synthesized from SF4 and the SF2 derivative trans‐[Pt(F)(SF2)(PCy3)2][BF4] was characterized by X‐ray crystallography. trans‐[Pt(F)(SF3)(PR3)2] complexes are useful tools for deoxyfluorination reactions and novel fluorido complexes bearing a SOF ligand are formed. Based on these studies a process for the deoxyfluorination of ketones was developed with SF6 as fluorinating agent.

Activation of SF6 at Platinum Complexes: Formation of SF3 Derivatives and Their Application in Deoxyfluorination Reactions.

The activation of SF6 at [Pt(PR3 )2 ] R=Cy, iPr complexes in the presence of PR3 led selectively and in an unprecedented reaction route to the generation of the SF3 complexes trans-[Pt(F)(SF3 )(PR3 )2 ]. These can also be synthesized from SF4 and the SF2 derivative trans-[Pt(F)(SF2 )(PCy3 )2 ][BF4 ] was characterized by X-ray crystallography. trans-[Pt(F)(SF3 )(PR3 )2 ] complexes are useful tools for deoxyfluorination reactions and novel fluorido complexes bearing a SOF ligand are formed. Based on these studies a process for the deoxyfluorination of ketones was developed with SF6 as fluorinating agent.

Metal-free reduction of the greenhouse gas sulfur hexafluoride, formation of SF5containing ion pairs and the application in fluorinations

A protocol for the fast and selective two-electron reduction of the potent greenhouse gas sulfur hexafluoride (SF6) by organic electron donors at ambient temperature has been developed.

On the formation of SFn– (n = 1–6) anions via a novel route and their properties

Sulfur hexafluoride (SF6 ) being a potential greenhouse gas, coupled with its numerous applications, makes the study of the formation and fragmentation of SF6 -based species important. The formation of SF6 -based anionic species has been studied using the gas feed-sputtering route and the mechanisms at play during the sputter-ejection of guest molecule-derived particles have also been probed. Studies of the formation of SFn (-) (n = 1-6) anions were conducted from various surfaces (metal and compound) that were subjected to Cs(+) ion sputtering in the presence of SF6 gas employing the gas feed-cesium sputter technique. The anions generated were mass analyzed using a double-focusing magnetic sector mass spectrometer. Quantum mechanical computations were performed to study the ground state structure and stability of neutral and negatively charged SFn (n = 1-6) systems applying density functional theory (DFT) and ab initio methods (MP2 and CC). This technique readily generated (32) SFn (-) (n = 1-6) anions for all sizes of 'n' with practicable yields. Mass spectrometric measurements of the yield of sputter-ejected (32) SFn (-) (n = 1-6) anions reveal an oscillatory pattern as a function of 'n', with odd values of 'n' being relatively more abundant. The relative yield of (34) SFn (-) (n = 1-6) anions with respect to size was also measured albeit with low signal intensity. Also observed were F(-) , S(-) , F2 (-) , (33) SF5 (-) and (33) SF6 (-) anionic species. The relevant electron affinity and bond dissociation energy (BDE) values were also computed. Gas-phase SFn (-) (n = 1-6) anions can be effectively generated by using the gas spray-cesium sputter technique. Both experimental measurements and calculations indicate the existence of odd-even oscillations in the stability and electronic structure of the SFn (n = 1-6) systems. The highest yield recorded was for the sputter-ejected SF5 (-) species and this may be attributed to its 'superhalogen' anionic character coupled with the relatively favorable F(0) fragmentation pathway of sputtered SF6 (-) . A signature pertaining to intact SF6 (-) anion ejection is also observed.

Remaking Yamato, remaking Japan

Recent years have seen the development and production of several Hollywood remakes of Japanese cultural commodities, among which are some based on sf Japanese animations. Some of these remakes have provoked criticism from fan communities for their ‘whitewashing’ of casts, settings and storylines. Given the hegemonic position that Hollywood occupies within the world-media system, these criticisms are undoubtedly warranted. Yet insofar as they operate on the basis of a politics of representation, they at once run the risk of fetishising a notion of Japanese authenticity that re-inscribes mutually reinforcing techno-orientalist and cultural nationalist undercurrents in the discourse surrounding Japanese animation. My essay argues that rather than an approach that privileges notions of originality and authenticity, the transnational cultural politics of remakes and reboots can be more effectively apprehended when the intertextuality built into the very structural logic of the sf genre is properly recognised. Taking up the recent live-action remake of Space Battleship Yamato (2010) as an illustrative example, I suggest that the nostalgic desire and staging of retroactive continuities that drive both its story and its critical reception call attention to its repetitions of tropes from not only the preceding titles from within the Yamato franchise, but also a longer legacy of nautical adventure stories from the late nineteenth and early twentieth centuries. Informed by this textual genealogy, I highlight the text’s engagement with the linkages between the history of imperialism and the formation of sf as a genre in Japan and beyond.

CREEP MECHANISM OF A Ni-Co BASE WROUGHTSUPERALLOY

Ni-based wrought superalloys are widely used in the hot section of aircraft gas turbine engines for their capability in retaining strength and resisting creep,fatigue,and oxidation at elevated temperature.With the development of the newer generation turbine disk alloys,it is highly imperative for aircraft engine manufacturers to substantiate the use of the materials by conducting a thorough examination of their mechanical properties.As these components are subjected to elevated temperatures and complex stress state in the service process where time dependent creep is the primary deformation failure mechanism and life-limiting factor for the component,it is of great importance to evaluate the relationship between microstructure,creep behavior and the underlying creep deformation mechanism.Therefore,the main objective of the present research aims at investigating the fundamental relationship between external creep condition and internal creep deformation mechanism in a new wrought superalloy with low stacking fault energy(SFE).In order to study the influences of the loading stress level and temperature on the creep deformation mechanism,stress range of 345—840 MPa and temperature range of 650—815℃were selected to carry out the creep experiment.The results show that two kinds ofγ' with different diameters distributed in the matrix and the larger one began to coarsen when the creep temperature increased to 725℃.Under creep temperature of 650℃, the formation of SF resulted from the shearing ofγ' by dislocations dominated the creep deformation. When the temperature range was raised up to 725—760℃,SF and microtwins were the main microstructures after creep deformation.With further increasing the temperature and load,instead of accommodating only in theγ',the SF and microtwins penetrated the wholeγ' and matrix area.When the temperature was increased to 815℃,the climb/bypass mechanism controlled the creep process.

New insights into the superoxide generation sites in bovine heart NADH-ubiquinone oxidoreductase (Complex I): The significance of protein-associated ubiquinone and the dynamic shifting of generation sites between semiflavin and semiquinone radicals

Considerable disagreement still exists concerning the superoxide generation sites in the purified bovine heart NADH-ubiquinone oxidoreductase (complex I). Majority of investigators agree that superoxide is generated at the flavin site. Here we present a new hypothesis that the generation of superoxide reflects a dynamic balance between the flavosemiquinone (semiflavin or SF) and the semiquinone (SQ), like a “tug-of-war” through electrons. All preparations of bovine heart complex I, which have been isolated at Yoshikawa's laboratory, have one protein-bound endogenous ubiquinone per complex I (Shinzawa-Itoh et al., Biochemistry, 49 (2010) 487–492). Using these preparations, we measured (i) EPR signals of the SF, the SQ and iron–sulfur cluster N2 simultaneously with cryogenic EPR and (ii) superoxide production with both the room temperature spin-trapping technique and the partially acetylated cytochrome c method. Our experimental evidence was (1) without added decylubiquinone (DBQ), no catalytic oxidation of NADH occurs. The NADH addition produced mostly SF and it generated superoxide as reported by Kussmaul and Hirst (PNAS, 103 (2006) 7607–7612). (2) During catalytic electron transfer from NADH to DBQ, the superoxide generation site was mostly shifted to the SQ. (3) A quinone-pocket binding inhibitor (rotenone or piericidin A) inhibits the catalytic formation of the SQ, and it enhances the formation of SF and increases the overall superoxide generation. This suggests that if electron transfer was inhibited under pathological conditions, superoxide generation from the SF would be increased.

Infrared spectra of SF6−⋅HCOOH⋅Arn (n=–2): Infrared triggered reaction and Ar-induced reactive inhibition

We present the infrared spectra of SF(6)(-) x HCOOH x Ar(m) (m=0-2) complexes. We find that the binding motif involves a single hydrogen bond between the SF(6)(-) anion and the OH group of the formic acid, with the CH group weakly tethered to a neighboring F atom. Similar to the case of hydrated SF(6)(-), the SF bond involved in the (OH-F) bond is significantly stretched and weakened by the attachment of the HCOOH ligand. The bare complex undergoes reaction upon infrared absorption in the CH/OH stretching region of the formic acid moiety, leading predominantly to the formation of SF(4)(-) + 2HF + CO(2). The reaction can be inhibited by attachment of two Ar atoms. We discuss a likely reaction mechanism in the framework of ab initio calculations, suggesting that reaction proceeds via tunneling through the potential barrier.

Experimental and theoretical study of the ion-ion mutual neutralization reactions Ar++SFn− (n=6, 5, and 4)

The ion-ion mutual neutralization reactions Ar(+)+SF(n) (-)-->Ar+SF(n) (n=6, 5, and 4) have been studied in a flowing afterglow-Langmuir probe (FALP) apparatus at 300 K and 1 Torr of He buffer gas. Electron concentrations and product ion fractions were measured, and neutralization rate constants of 4.0 x 10(-8), 3.8 x 10(-8), and 4 x 10(-8) cm(3) s(-1) for SF(6) (-), SF(5) (-), and SF(4) (-), respectively, were derived, with uncertainties of +/-25% (+/-35% for SF(4) (-)). During the neutralization process, excited neutrals are generated that are able to dissociate to neutral fragments. In the case of SF(6), the formation of SF(5) and SF(4), and similarly in the case of SF(5), the formation of SF(4) and SF(3) were observed and quantified. The mechanism of primary and secondary reaction was analyzed in detail, and rate constants for the dissociative electron attachments e(-)+SF(5)-->F(-)+SF(4) (k=3 x 10(-9) cm(3) s(-1),+/-40%) and e(-)+SF(3)-->F(-)+SF(2) (k=2 x 10(-8) cm(3) s(-1),+400%,-75%) were also derived. The experimental ion-ion neutralization rate constants were found to be in good agreement with estimates from an optimum two-state double-passage Landau-Zener model. It was also found that energy partitioning in the neutralization is related to the extent of electronic excitation of Ar generated by the electron transfer processes.

Electron transfer and bond-forming reactions following collisions of SF 2+ with Ar

Collisions between SF 2+ and Ar have been investigated using time-of-flight mass spectrometry over a collision energy range of 2.6–6.2 eV in the centre-of-mass frame. The formation of SF +, S + and Ar + in single electron transfer reactions has been detected and the cross-sections, in arbitrary units, for forming these species have been evaluated. This electron transfer reactivity has been rationalized by Landau–Zener calculations. The reactivity in this collision system also involves an unusual bond-forming reaction which generates ArS 2+. Quantum chemical calculations of the relevant energetics show that the lowest lying singlet and triplet states of ArS 2+ are bound and are energetically accessible to this collision system at the above collision energies. This energetics analysis also shows that electron transfer in the exit channel between the separating ArS 2+ and F atom is likely to be inefficient, explaining why we detect the observed products and not ArS + + F +.

The anomalous shape of the cross section for the formation of SF3+ fragment ions produced by electron impact on SF6 revisited.

The partial ionization cross section for the formation of SF(3) (+) fragment ions following electron impact on SF(6) is known to have a pronounced structure in the cross section curve slightly above 40 eV. We used the mass-analyzed ion kinetic energy (MIKE) scan technique to demonstrate the presence of a channel contributing to the SF(3) (+) partial ionization cross section that we attribute to the Coulomb explosion of doubly charged metastable SF(4) (2+) ions into two singly charged ions SF(3) (+) and F(+), with a threshold energy of about 45.5 eV. Thus the observed unusual shape of the SF(3) (+) partial ionization cross section is the result of two contributions, (i) the direct formation of SF(3) (+) fragment ions via dissociative ionization of SF(6) with a threshold energy of 22 eV and (ii) the Coulomb explosion of metastable SF(4) (2+) ions with a threshold energy of about 45.5 eV. A detailed analysis of the MIKE spectrum reveals an average kinetic energy release of about 5 eV in the Coulomb explosion of the SF(4) (2+) ions with evidence of a second channel corresponding to an average kinetic energy release of about 1.1 eV.

Electron attachment cross sections and negative ion states of SF 6

A comprehensive and critical assessment of published data on the total, dissociative and nondissociative electron attachment cross sections for SF 6 allowed us to recommend or suggest room temperature values for these cross sections over an energy range from 0.0001 eV to 15 eV. The total electron attachment cross section is dominated by the formation of SF 6 − below ∼0.2 eV, by the formation of SF 5 − between ∼0.3 eV and 1.5 eV, and by the formation of F − beyond ∼2.0 eV. This work, along with electron scattering and theoretical data, allowed us also to identify the energies and symmetry assignments of the negative ion states of SF 6 below ∼15 eV.

Theoretical Study of the Heats of Formation of SF, FSO, FSO2 and HSO Radicals

Standard heats of formation of SF, FSO, FSO

How inert is an argon matrix?

SF 6 as an IR-active bulk and surface probe indicates the presence of porosity and diverse local environments in an Ar matrix prepared under experimental conditions favouring perfect isolation of guest molecules. This is in agreement with previous X-ray and neutron diffraction studies. A huge variety of different cage and surface sites are generated during formation of the matrix. On annealing, two generally contradictory phenomena occur: (a) perfectly isolated monomer species are enriched by sealing the micropores through which the monomers penetrated in the preceding deposition process; (b) cluster formation of SF 6 probes takes place, resulting in the appearance of extended crystalline phases in the larger pores and on the surfaces.

Formation of SF 5− in electron attachment to SF 6; swarm and beam results reconciled

Based on the results of recent swarm experiments, it has been proposed that the increase in the cross section for SF 5 − formation observed at an electron energy, E e of about 0.3 eV in electron beam studies of electron attachment to SF 6 is due to the combined (opposing) effects of the vibrational heating of the molecule by the attached electron, which enhances the dissociation of the nascent (SF 6 −) ∗ ion, and the reduction of the cross section for capture (s-wave) of the electron by SF 6 with increasing E e. Further, it has been shown that the dissociation reaction is endothermic by 0.12 eV, and that, contrary to previous suggestions, there is no potential barrier to this dissociation reaction. Now we have carried out electron beam studies of the SF 6 attachment reaction in Berlin at gas temperatures, T g, over the range 300 to 920 K and in Innsbruck at T g below 300 K. These studies have provided support for the above proposals concerning the appearance of the SF 5 − peak and for a reaction endothermicity of 0.12 eV. Thus these studies have clarified the doubts about the products of the SF 6 attachment reaction at low electron energy.

Negative ion chemistry of SF4

A selected ion flow tube was used to conduct an extensive study of negative ion–molecule reactions of SF4 and SF−4. Rate constants and product ion branching fractions were measured for 56 reactions. The reactions bracket both the electron affinity of SF4 (1.5±0.2 eV or 34.6±4.6 kcal mol−1) and the fluoride affinity of SF3 (1.84±0.16 eV or 42.4±3.2 kcal mol−1). These results may be combined to give the neutral bond energy D(SF3–F)=3.74±0.34 eV or 86.2±7.8 kcal mol−1, independent of other thermochemical data except for the accurately known electron affinity of F. The heat of formation of SF−4 is derived from the electron affinity of SF4: ΔfH(SF−4)=−9.2±0.3 eV or −212.9±7.5 kcal mol−1. Lower limits to EA(SF2) and EA(SF3) are deduced from observation of SF−2(35%) and SF−3(65%) ion products of the reaction S−+SF4. Rapid fluoride transfer from both SF−2 and SF−3 to SF4 places upper limits on the electron affinities of SF2 and SF3. The combined results are 0.2 eV≤EA(SF2)≤1.6 eV and 2.0 eV≤EA(SF3)≤3.0 eV. We review the status of measurements of EA(SFn), n=1–7.

Two isomers of SF•5 and SF+5: Structures and energetics

The apparently conflicting results for the ionization energy of SF•5 and the standard enthalpy of formation of SF+5 reported over the last 25 years have been reinterpreted and brought into line in terms of the existence of square pyramidal (C4v) and trigonal bipyramidal (D3h) isomers of SF•5 and SF+5. New experimental results and theoretical calculations are reported which are consistent with this interpretation. Values are recommended for the ionization energy and standard enthalpies of formation for the two isomers of SF•5 and SF+5.