基于随机共振和微纳传感器阵列的六氟化硫检测方法研究

建立了一种基于随机共振和微纳传感器阵列的六氟化硫气体检测方法.使用两个360 μm极间距离的微纳传感器构成的阵列结合随机共振算法,在室温常压,相对湿度70%的条件下检测3.0～24 g/m3 SF6气体及纯SF6气体,以信噪比极大值实现各浓度SF6气体的区分.传感器工作于微电离平衡状态,检测过程中无有害气体产生,安全性较高.为检验该方法的实用性,依据国家标准在温度20 ℃、相对湿度70%和常压条件下模拟现场检测3.0～12 g/m3SF6气体,结果表明: 本方法具有较好的重复性和实用性.     

Simultaneous determination of trace amounts of sulphur hexafluoride and cyclic perfluorocarbons in reservoir samples by gas chromatography

Summary Both sulphur hexafluoride and a group of compounds among the perfluorinated cyclic hydrocarbons: perfluorodimethyl cyclobutane, perfluoromethyl cyclopentane, perfluoromethyl cyclohexane and the 1,2- and 1,3-isomers of perfluordimethyl cyclohexane are well known to be good gas tracers, in various applications. Unfortunately different methods have been used for the analysis of SF₆ and the perfluorocarbons. Therefore, in many cases, the analytical costs may have hindered the use of both SF₆ and the perfluorocarbons in the same tracer experiments. The analytical method described in this paper enables the determination of both types of gas tracer in one single run. The new method has already replaced two former methods and was used to run the gas tracer analysis routinely, proving the reliability of the method.     

Sulfur-doped LaNiO3 perovskite oxides with enriched anionic vacancies and manipulated orbital occupancy facilitating oxygen electrode reactions in lithium-oxygen batteries

The rational design of effective bifunctional catalysts with enhanced activity toward oxygen reduction reaction and oxygen evolution reaction is of significance to develop high-performance lithium-oxygen (Li–O₂) batteries. Herein, sulfur-doped LaNiO₃ nanoparticles are elaborately synthesized, and their catalytic activity toward oxygen redox reactions in Li–O₂ batteries is comprehensively studied. As confirmed by the density functional theory calculations and experimental results, the substitution of oxygen atoms by sulfur atoms with lower Pauling electronegativity can enhance the covalent feature of bonds, thus increasing electrical conductivity of catalyst. In addition, abundant oxygen vacancies created after sulfur doping are capable of providing concentrated active sites. Simultaneously, sulfur dopants boost the hybridization between Ni 3d orbital and O 2p orbital and increase the covalency of Ni–O bonds due to the increase of Ni³⁺ with the near-unity occupancy of the e_g orbital, thereby increasing the adsorption strength of oxygen-containing intermediates on the surface. Eventually, lowered reaction energy barriers and accelerated reaction kinetics of oxygen electrode reactions are realized, contributing to the optimized electrochemical performance of Li–O₂ battery. The Li–O₂ battery based on sulfur-doped LaNiO₃ with the optimized S-doping level of 2.89 wt% (marked as S_2.89 wt%-LNO) delivers a high specific discharge capacity of 24067 mAh/g, an ultralow overpotential of 0.37 V and extended life of 347 cycles.     

Inexpensive and accurate predictions of optical excitations in transition-metal complexes: the TDDFT/PBE0 route

Time-dependent density functional theory (TDDFT) is applied to calculate vertical excitation energies of three representative transition metal complexes. The computational model (PBE0) is obtained by combining the Perdew-Burke-Erzenrhof (PBE) generalized gradient functional with a predetermined amount of exact exchange. Our results show that the TDDFT/PBE0 model represents a cheap and reliable tool for the computation of optical excitations for transition metal complexes. Received: 8 August 2000 / Accepted: 7 September 2000 / Published online: 23 November 2000     

Theoretical studies on the mechanisms of NCCO + O2 reaction

The mechanisms of the reaction of NCCO with molecular oxygen are investigated at the G3MP2//B3LYP/6-311G(d,p) levels for the first time. The calculation results show that two mechanisms are involved, namely, O attack on α atom mechanism and O attack on β atom mechanism, with six products yielded. The most feasible channel is the addition of O₂ to β atom in NCCO radical leading to the energy-rich intermediate IM1, NCC(O)OO, which can isomerize to a four-center-structure IM3, and then undergoes C–C and O–C bond fission to form P1(NCO + CO₂) finally. The barriers are 27.3 and 25.4 kcal/mol, respectively. For other channels involved in the two mechanisms, with less stable initial adducts and higher barrier, they are less conceivable dynamically and thermochemically.     

MNE Nitrido Bridges with Transition Metal Nitrogen Multiple Bonds and E = Phosphorus,Sulfur, and Chlorine

A compilation is given on new syntheses, properties, and structures of complexes with M≡N—E ? M=N=E nitrido bridges with transition metal nitrogen multiple bonds and participation of the main group elements E of phosporus, sulfur, and chlorine. 1. MNP: This atomic sequence is realized in phosphoraneiminato complexes with transition metals in high oxidation states and termal bond of the (NPR₃^—) ligand. A series of new complexes of this type is reported with M = zirconium, hafnium, molybdenum, tungsten, and rhenium, among these the homoleptic species [Hf(NPPh₃)₄] and [M(NPPh₃)₄]²⁺ with M = Mo and W. Therefrom the isolobal complexes [:N≡Mo(NPPh₃)₃], [:O≡W(NPPh₃)₃]⁺, [(O)₂Mo(NPPh₃)₂], and [(O)₃Re(NPPh₃)] are derived. 2. MNS: Adding to compounds with this atomic sequence, new complexes were developed on the basis of the functional ligand groups thionitrosyl ( a ), dinitridosulphate(II) ( b ), dinitridosulphate(IV) ( c ), and cyclothiazeno ( d ) (cyclo‐3, 5‐dithia‐2, 4, 6‐triazino):

     

Picogram Detection of Sulfur Hexafluoride by High Pressure Charge Exchange Mass Spectrometry

Abstract

Since air quality in industrial atmospheres is important for personal comfort and safety, tracer experiments using sulfur hexa-fluoride (SF₆) are commonly used to monitor air distributions and flow patterns.

This method involves the determination of SF₆ by high pressure charge exchange mass spectrometry at levels as low as 3 × 10^?12 grams. It employs specific ion detection in combination with gas chromatography to insure a high degree of specificity.     

Sulfur hexafluoride as a mobile phase for supercritical fluid chromatography

Summary The capabilities of sulfur hexafluoride as a mobile phase for supercritical-fluid chromatography are investigated. An evaluation of its overall utility on the basis of separations of standard aromatic hydrocarbon odel mixtures performed on a variety of bonded-phase, packed columns with UV detection is presented. The dependence of separation performance upon operational parameters is also examined. A comparative evaluation of the chroamtographic properties of supercitrical sulfur hexafluoride and those of supercritical carbon dioxide is developed from these separations under corresponding supercritical state conditions.     

Cyclodextrin-based thiacavitands as building blocks for the construction of metallo-nanotubes

Two new cyclodextrin-based ligands with dual exo/endo binding domains were synthesised in high yields by reacting dimesylated or tetramesylated α-CD derivatives with sodium sulfide in either dimethylsulfoxyde or acetone/18-crown-6. The capping of adjacent glucose units was shown to be strongly favoured in both cases. Depending on the nature of the metal precursor being used, one of the synthesised thiacavitands forms either rigid nanotubular dimers or chelate complexes having receptor properties upon metal complexation.     

Synthesis,Structure and Reactivity of Sulfur-Rich Cyclopentadienyl-Transition Metal Complexes: Sulfur Chemistry from an Organometallic Point of View

Metal-sulfur centers play an important role in the activity of metalloproteins in enzymatic catalysis and the activity of metal sulfides as heterogeneous catalysts. The systematic search for M? S model compounds led to the discovery of an interesting and novel structural chemistry, which stems from the numerous coordination possibilities of sulfur ligands. The intention of this review article is to present and outline new approaches to sulfur chemistry from the organometallic point of view. Reactive cyclopentadienyl-transition metal fragments incorporate elemental sulfur to give polynuclear sulfur-rich complexes, which can contain either mono-, di- or polysulfido ligands or several such ligands in combined form. The versatile structural chemistry of the complexes formed and their reactivity towards organic, inorganic and organometallic compounds are discussed, and examples of some simple and rational procedures for their synthesis starting from cyclopentadienylcarbonyl- and cyclopentadienylhydrido-complexes are outlined. Their reactivity is manifested in numerous metal- and ligandcentered reactions. Finally the, albeit far less extensive, complex chemistry of the other chalcogens (O, Se, Te) is also considered for comparison, thus providing a more detailed survey of particular aspects of this area of chemistry.     

On additives, morphological evolution and dielectric breakdown in low density polyethylene

A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes.     

Site directed synthesis of mono and disubstituted SF5-polyfluoroalkyl benzenes

A novel method for the preparation of o-, m-, p-SF₅CF₂CFYC₆H₄X (Y = Br, F and X = m-Br, p-Br, Cl, CH₃, CF₃, NO₂, o-NO₂, F, CF₃, CH(CH₃)₂) derivatives was devised by a two-step reaction: SF₅Br-addition to o-, m-, p-CF₂CFC₆H₄X followed by reaction of AgBF₄ with the o-, m-, p-SF₅CF₂CFBrC₆H₄X adducts. Additional studies have been carried out with several derivatives and includes the preparation of SF₅CF₂C(O)C₆H₅, p-CF₃CFBrC₆H₄NO₂, SF₅CF₂CF₂C₆H₃(NO₂)₂, SF₅CF₂CF₂C₆H₃(NH₂)₂, and an SF₅CF₂CF₂-containing polyimide and dye. The complete characterization (IR, NMR, and MS) of these compounds is given.     

Crystallization kinetics of PHB/PVAc blends using time resolved dielectric spectroscopy

Crystallization kinetics of poly(hydroxy butyrate), PHB, and its blends with poly(vinyl acetate), PVAc, have been thoroughly investigated using broadband dielectric technique over a wide range of frequencies (10⁻²-10⁵ Hz) as functions of crystallization temperature and blend composition. The dielectric strength of the amorphous segments, Δε, which is directly proportional to the volume fraction of the mobile amorphous phase in the blend decreases exponentially with increasing the crystallization time. However, on the other hand, the dielectric strength of the rigid amorphous segments, Δε_α′, which is related to the percentage of crystallinity in the blend increases dramatically with increasing crystallization time. A great variation in the dynamical constraints of relaxation segments with increasing crystallization time has been observed as a result of different environments, which would lead to a variation in the consistency of the cooperative regions. The value of the dielectric constant, ε′, decreases dramatically with increasing crystallization time, after that it reaches an equilibrium value at the end of the crystallization process. This dramatic decrease in the value of ε′ as a result of crystallization at a given crystallization temperature, was taken as an accurate evaluation for the amount of the amorphous phase that has undergone crystallization considering the theoretical approach of Avrami. The Avrami exponent, n, was found to be crystallization temperature, T_c, independent (n ∼ 3) indicating a three-dimensional crystal growth for pure PHB. The crystallization rate constant, k, increases greatly with increasing T_c due to the high crystallization rate. In the blend the value of n was found to be concentration dependent (n ∼ 1.8-3.2). The different values of n indicate that the shapes of the growing crystals are affected by blend concentration. For n ∼ 1.8, the crystals can either grow sporadically as rods or instantaneously as disks, while for n ∼ 3 a three-dimensional crystal growth takes place.     

The application of novel methodology for the synthesis of o-, m-, and p-(SF5-perfluoroethyl) benzene derivatives

The reaction of o-, m-, and p-F₂CCFC₆H₄X with SF₅Br produces an intermediate adduct, F₅SCF₂CFBrC₆H₄X, which, on treatment with AgBF₄, affords the first useful, high yield preparation of o-, m-, and p-F₅SCF₂CF₂C₆H₄X.     

Ground state C2 density measurement in carbon plume using laser-induced fluorescence spectroscopy

The temporal evolution and spatial distribution of C₂ molecules produced by laser ablation of a graphite target is studied using optical emission spectroscopy, dynamic imaging and laser-induced fluorescence (LIF) investigations. We observe peculiar bifurcation of carbon plume into two parts; stationary component close to the target surface and a component moving away from the target surface which splits further in two parts as the plume expands. The two distinct plumes are attributed to recombination of carbon species and formation of nanoparticles. The molecular carbon C₂ moves with a faster velocity and dies out at ~ 800 ns whereas the clusters of nanoparticle move with a slower velocity due to their higher mass and can be observed even after 1600 ns. C₂ molecules in the d³Π_g state were probed for laser-induced fluorescence during ablation of graphite using the Swan (0,0) band at 516.5 nm. The fluorescence spectrum and images of fluorescence d³Π_g − a³Π_u(0,1)(λ = 563.5 nm) are recorded using a spectrograph attached to the ICCD camera. To get absolute ground state C₂ density from fluorescence images, the images are calibrated using complimentary absorption experiment. This study qualitatively helps to get optimum conditions for nanoparticle formation using the laser ablation of graphite target and hence deducing optimum conditions for thin film deposition.     

原子吸收光谱法间接测煤中形态硫

利用 SO2 -4 在 Ba Cr O4溶液中 ,可定量置换出 Cr O2 -4 ,进行原子吸收光谱法测铬 ,间接测定煤中形态硫的研究。方法较现行使用的重量法简便、快速 ,干扰少 ,硫含量在 1× 1 0 - 4 ～ 3× 1 0 - 3mg·ml- 1 呈良好线性关系。用于样品分析 ,结果满意。