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1.
The structure, stability, and paths of formation of 11 (HF)m(DMF)n heterocomplexes (m = 1–4, n = 1, 2) were studied in terms of the B3LYP/6-31++G(d, p) density functional calculation. The results of this calculation suggest that: a) addition of hydrogen fluoride molecules to the (HF)mDMF cyclic fragment is the basic tendency in complex formation in the HF-DMF system; b) data about the structure and properties of stable molecular forms that prevail in N,N-dimethylformamide solutions of hydrogen fluoride can be obtained by quantum chemical calculations for (HF)mDMF complexes (m = 5–10). 相似文献
2.
A gas chromatographic method is described for the determination of alcohols up to C20H41OH. The procedure is rapid and indicates the molecular weight distribution and the contents of straight-chain and branched-chain alcohols. A programmed temperature control with a silicone substrate was satisfactory. n-C14H20OH and n-C5H11OH were used as internal standards. 相似文献
3.
《Journal of membrane science》1998,141(1):91-99
A series of amine-containing polyurethanes and poly(urethane-urea)s based on 4,4′-diphenylmethane diisocyanate and either poly(ethylene glycol) of molecular weights 400 or 600 were prepared as gas separation membranes. The amine functional groups of N-methyldiethanolamine (MDEA) and/or tetraethylenepentamine (TEPA) were introduced into the hard segment as a chain extender. The gas transport data of He, H2, O2, N2, CH4 and CO2 in these polymer membranes were determined by using the Barrer's high-vacuum technique and the time-lag method. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft segment and hard-segment domains, resulting in the increase in the density, glass transition temperature of soft segments (Tgs). The separation mechanism of various gas pairs used in industrial processes is also discussed. Effect of pressure on permeability of the gases above and below Tgs was studied. It was found that the gas permeability increased or decreased with upstream pressure above Tgs, and should be described by a modified free-volume model. On the other hand, the condensable CO2 exhibits a minimum permeability at a certain upstream pressure below Tgs. The permeability of He and H2 were pressure independent above and below the Tgs. 相似文献
4.
《Electrochemistry communications》2007,9(7):1607-1612
The effect of inert gas flow rate on hydrogen underpotential deposition (Hupd) measurements in polymer electrolyte fuel cells (PEFCs) was investigated using a novel experimental technique. The method combines local voltammetric measurements in PEFCs with the use of sectioned electrodes. The results give experimental proof that the high inert gas flow rate usually employed in voltammetric measurements in PEFCs at the working electrode results in high hydrogen reduction currents in both the cathodic and the anodic sweep, which hampers an accurate determination of the electrochemically active surface area (ECA). Strong spatial inhomogeneities occur at low potentials as a consequence of formation and accumulation of molecular hydrogen along the flow field. The results show that the flow of inert gas should be minimized or even stopped during a measurement to allow molecular hydrogen to accumulate at the working electrode and to provide uniform conditions along the flow field. 相似文献
5.
Investigating the nature of intermolecular and intramolecular bonds in noble gas containing molecules
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This article presents a theoretical study on a number of selected noble gas containing systems of the general formula FNgR and NgR (Ng = He, Ne, Ar, Kr, Xe and R = CH3, CN, CCH, BO, BNH, H, BeO, and AuF). The principal structures, bond energies, spectroscopic, and electronic properties of 28 noble gas containing molecules were investigated using density functional theory at the BMK level. Quantum theory of atoms in molecules, natural bond orbital, and several other analysis methods have been used to provide more insight into the nature of noble gas bonds. Although both F? Ng and Ng? R bonds in the investigated molecules are assigned to have partially covalent and partially electrostatic nature, the covalent character is dominant in Ng? R bonds. In the second part, the intermolecular interactions between FNgR molecules and hydrogen fluoride are overviewed with emphasis on the hydrogen bonding through the fluorine side of noble gas molecule with hydrogen of HF. The calculated interaction energies were found to decrease in magnitude going down the noble gas series. For all noble gases, the strongest hydrogen bond has been observed in the case R=CH3. On the contrary, using R=CN in the FNgR moiety weakens the interaction strength. © 2014 Wiley Periodicals, Inc. 相似文献
6.
Peer Schmidt Michael Sch?neich Melanie Bawohl Tom Nilges Richard Weihrich 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1511-1521
Several methods are established in thermal analysis to investigate phase formation, phase transition, and decomposition reactions. The analysis of phase equilibria with volatile components is particularly feasible by using standard method of thermogravimetry. Hardly any investigations of phase formation reactions are possible to realize if one of the components is lost by vaporization. By using the ??High-Temperature Gas-Balance?? (HTGB), the vapor phase is enclosed in a silica ampoule and thus forms an equilibrium gas phase in permanent contact with the solid phase. The measurement signal ??m meas is caused by change of the leverage of the horizontal balance support during evaporation and condensation. The application of the HTGB allows the analysis of solid?Cgas equilibria in the working range from 0.01 till 15?bar at temperatures up to 1,100?°C. The first comparison of evaporation reactions determined by standard thermogravimetric analyses and by measurements using the HTGB is given for the inorganic systems: P, As, SeO2, PtI2, and Hg/I. 相似文献
7.
Determination of gaseous carbonyl compounds by their pentafluorophenyl hydrazones with gas chromatography/mass spectrometry 总被引:2,自引:0,他引:2
Jian Li Chun Juan Xie Jian Zhen Yu Guo Ying Sheng Jia Mo Fu Ming Hong Wu 《Analytica chimica acta》2009,635(1):84-5009
A sensitive and reliable method has been developed for the simultaneous determination of 20 airborne carbonyl compounds in the C1-C10 range. The carbonyls were collected onto solid sorbent coated with pentafluorophenyl hydrazine (PFPH), followed by solvent extraction and gas chromatographic (GC)/mass spectrometric (MS) analysis of the PFPH derivatives. The sorbent is packed into two separate sections in a glass sampling tube. The two-section design allows convenient checking of collection efficiency and breakthrough. The sampling tube, with a coating amount of 971 nmol PFPH per 100 mg Tenax TA and operated at a sampling flow rate of 80 mL min−1, collects the 20 carbonyls with efficiencies above 95%. Hexane extracts the collected carbonyls in their PFPH derivatives in the sampling tube with better than 95% extraction efficiency. It is necessary to let the sampling tube sit at ambient temperature for 3 days before solvent extraction to ensure complete derivatization of the carbonyls. The limits of detection (LODs) of the tested carbonyls are in the range of 3.7-11.6 ng per sample. The method has been field-tested both in ambient environment and in an indoor environment from burning mosquito-repellent incense. Eighteen carbonyls were detected in the ambient air samples with the exception of o-tolualdehyde and m-tolualdehyde, while all the 20 target carbonyls were found in the incense smoke. Compare field test with classical DNPH-HPLC/UV method, good agreement exited between the two methods for lower molecular carbonyls but PFPH method is found to be a better analytical method for determination of high molecular weight carbonyls. 相似文献
8.
Aleksandar Staykov Junichiro Yamabe Brian P. Somerday 《International journal of quantum chemistry》2014,114(10):626-635
A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the steel in the presence of oxygen, hydrogen, and oxygen adsorption, dissociation, and coadsorption on the Fe(100) surface were investigated using density functional theory. The results show that traces of O2 would successfully compete with H2 for surface adsorption sites due to the grater attractive force acting on the O2 molecule compared to H2. The H2 dissociation would be hindered on iron surfaces with predissociated oxygen. Prompted by the notable results for H2 + O2, other practical systems were considered, that is, H2 + CO and CH4. Calculations were performed for the CO chemisorption and H2 dissociation on iron surface with predissociated CO, as well as, CH4 surface dissociation. The results indicate that CO inhibition of H2 dissociation proceeds via similar mechanism to O2 induced inhibition, whereas CH4 traces in the H2 gas have no effect on H2 dissociation. © 2014 Wiley Periodicals, Inc. 相似文献
9.
Hydrogen fluoride in a standard or sample gas stream at 200 ml min?1 permeates through a teflon membrane (0.8 μm pore size, 0.08 mm thick) into an absorption solution (citrate/acetate buffer at pH 5.4) flowing at 30 ml min?1. The fluoride produced is measured with the fluoride-selective electrode. The response time is about 12 min. The absorption efficiency of hydrogen fluoride is about 70% between 6.5 and 0.25 ppm by volume (5.2 and 0.2 mg m?3). In this range, the Nernst equation is valid with a relative standard deviation of less than 1.8%. The lower determination limit for hydrogen fluoride is 0.1 ppm (0.08 mg m?3). 相似文献
10.
A. A. Ivanov 《Moscow University Chemistry Bulletin》2013,68(2):83-86
The ineffectiveness of the traditional probe electron-diffraction experiment on free molecules (atoms), which prevents the development of the diffraction structural method in gas phase electron diffraction, has been shown. The application of a molecular beam enabled the determination of a quantitative performance indicator of the scattering process using the given experimental equipment. The quantitative value of the effective cross section on residual gas molecules σext(S max, Å?1) has been suggested as a technical characteristic for the electron diffraction equipment complex. A nomographic chart for determining the number of molecules of any substance has been drawn up in order to obtain a given density of scattered charge on the detector within the maximum sector radium. The author refers to the GED community with the need for agreement on a unified estimation of the efficiency of electron scattering experiment on the free molecules. 相似文献
11.
The surface grafting onto ultrafine silica via reverse ATRP of methyl methacrylate initiated by peroxide groups introduced onto the surface and conventional ATRP of Styrene initiated by the hybrid nanoparticles were investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polymer layer. The polymerization was closely controlled in solution at quite low temperature such as 70 °C. In both cases, linear kinetic plots, linear plots of molecular weight (Mn) versus conversion, in hydrodynamic diameter with increasing conversion, and narrow molecular weight distributions (Mw/Mn) for the grafted polymer samples were observed. Hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved polymer using GPC. Ultrathin films of hybrid nanoparticles were examined using TEM and AFM. 相似文献
12.
A manual method for the determination of hydrogen chloride in air, based on diffusion/denuder tube separation from particulate chloride aerosol is described. When air is drawn through a tube coated with a selective absorbent (sodium fluoride), separation is achieved because gaseous hydrogen chloride diffuses much more rapidly to the tube walls than particulate chloride aerosol, which passes through virtually unabsorbed. After the sampling period (the length of which depends on the concentration of gaseous hydrogen chloride expected), the sorbed hydrogen chloride is washed from the tube and measured with a highly sensitive chloride ion-selective electrode with a mercury (I) chloride membrane. The method is examined theoretically and experimentally. The experimentally derived absorption efficiencies of the diffusion/denuder tubes were > 90% and the standard deviation of the method was 0.023 μg m?3 for hydrogen chloride concentrations of 0.16–0.55 μg m?3. Interference from particulate chloride salts was negligible; this was confirmed by tests with artificially generated aerosol particles from an aerosol generator. The diffusion/denuder tubes have high capacity; level as high as 330 μg m?3 hydrogen chloride can be sampled for 60 min without affecting performance. A detection limit of (50/t) μg m?3 can be achieved, where t is the sampling rime (min); e.g., 1μg m?3 hydrogen chloride can be detected with a sampling period of 50 min. 相似文献
13.
David Uhlmann Shaomin Liu Bradley P. Ladewig João C. Diniz da Costa 《Journal of membrane science》2009
Cobalt-doped silica membranes were synthesized using tetraethyl orthosilicate-derived sol mixed with cobalt nitrate hexahydrate. The cobalt-doped silica structural characterization showed the formation of crystalline Co3O4 and silanol groups upon calcination. The metal oxide phase was sequentially reduced at high temperature in rich hydrogen atmosphere resulting in the production of high quality membranes. The cobalt concentration was almost constant throughout the film depth, though the silica to cobalt ratio changed from 33:1 at the surface to 7:1 at the interface with the alumina layer. It is possible that cobalt has more affinity to alumina, thus forming CoOAl2O3. The He/N2 selectivities reached 350 and 570 at 160 °C for dry and 100 °C wet gas testing, respectively. Subsequent exposure to water vapour, the membranes was regenerated under dry gas condition and He/N2 selectivities significantly improved to 1100. The permeation of gases generally followed a temperature dependency flux or activated transport, with best helium permeation and activation energy results of 9.5 × 10−8 mol m−2 s−1 Pa−1 and 15 kJ mol−1. Exposure of the membranes to water vapour led to a reduction in the permeation of nitrogen, attributed to water adsorption and structural changes of the silica matrix. However, the overall integrity of the cobalt-doped silica membrane was retained, given an indication that cobalt was able to counteract to some extent the effect of water on the silica matrix. These results show the potential for metal doping to create membranes suited for industrial gas separation. 相似文献
14.
The thermal behaviour of poly (ε-caprolactam) studied by the technique of “inverse gas-chromatography” indicates a dependence of the Tg/Tm ratio on the molecular weight of the sample. Comparison of the measured Tm-values with DTA-data suggests that, because of the specific working conditions, zero-entropy-production Tm values are determined by the inverse gas-chromatographic method. 相似文献
15.
A simple kinetic model describing the molecular gas phase reactions during the formation of fumed silica (AEROSIL®) was developed. The focus was on the formation of molecular SiO2, starting from SiCl4, hydrogen and oxygen. Wherever available, kinetic and thermodynamic parameters were taken from the literature. All other parameters are based on quantum chemical calculations. From these data, an adiabatic model for the combustion reaction has been developed. It was found that a significant amount of molecular SiO2 forms after about 0.1 and 0.6 ms at starting temperatures between 1000 and 2000 K. The initial reaction of the SiCl4 combustion in a hydrogen/oxygen flame was found to be different from the combustion in air: The high reactivity of SiCl4 towards water is favored over the SiCl4 dissociation, which is the initial and rate‐determining step during the combustion of SiCl4 in air. 相似文献
16.
Structure of dense hydrogen fluoride gas from neutron diffraction and molecular dynamics simulations
Kreitmeir M Heusel G Bertagnolli H Tödheide K Mundy CJ Cuello GJ 《The Journal of chemical physics》2005,122(15):154511
The gas phase of hydrogen fluoride has been investigated by neutron diffraction experiments at three different particle densities. All investigated states are within the liquid-gas coexistence region of hydrogen fluoride. From the obtained diffraction data we deduced information about the local structure of the gas phase, which consists of small agglomerates. This has been expected as liquid hydrogen fluoride forms the strongest hydrogen bonds known. Molecular dynamics simulations with a modified potential have been carried out for all experimentally investigated states. The results confirmed that the size of the formed agglomerates in the gas phase is growing with increasing density of the gas phase. 相似文献
17.
New macrocyclic stationary chemically bonded phases were synthesized and tested in gas chromatography conditions. The complexes of 1,4,8,11-tetraazacyclotetradecane with Cu(II) and Co(II) were bonded to the silica support through the (3-chloropropyl)triethoxysilane reactant. The packings obtained were analyzed by diffuse-reflectance ultraviolet–visible spectroscopy (DRUV–Vis), differential thermal gravimetry (DTG), porosimetry, and elementary analysis. Preliminary study of the novel silica gas chromatography (GC) stationary phases containing cyclam complexes was carried out using packed 1/8 in. i.d. columns. The study was conducted on: cyclic, linear and branched olefins, aromatic hydrocarbons and ethers. Characterization of interactions between the compounds mentioned and new stationary phases was based upon analysis of Kováts retention indices (I), difference between retention indices for two phases (ΔI), and molecular retention indices (ΔMe). Results have shown that the new stationary phases interact sufficiently strongly with molecules of high electron density and can be applied in capillary gas chromatography for the analysis of light hydrocarbons. 相似文献
18.
19.
《Journal of membrane science》2001,184(1):69-78
Transport rates (permeability) and ideal separation factors for several gas pairs through dense polyaniline membranes are reported. The ideal separation factors for all gas pairs tested were found to be independent of the polyaniline membrane thickness whereas the permeability of the single gases showed significant variations. Both dedoped and redoped films (film thickness between 9 and 67 μm) were studied. The highest selectivities α(A/B) found were 7.6 for the gas pair H2/CO2 in the case of the dedoped membrane and 10 for the gas pair H2/CO2, 6 for O2/N2 and 200 for H2/N2 in the case of the redoped membrane. Statistical analysis of a large number of membranes allowed the critical comparison with results obtained by other groups.Comparison with other membrane materials shows that an approximately sixfold enhancement of the respective separation factors is possible for gas pairs containing hydrogen. Similar separation factors are observed for the gas pairs CO2/O2, CO2/N2 and N2/O2.Membranes for which Knudsen diffusion was observed exhibited regularly distributed micropores (400 nm diameter). 相似文献
20.
R. J. Gritter M. Seeger E. Gipstein 《Journal of polymer science. Part A, Polymer chemistry》1978,16(2):353-360
Both co- and terpolysulfones have been flash-pyrolyzed at high temperature followed by separation and identification of the products by gas chromatography and/or gas chromatography/mass spectrometry. As expected, most of the products were the corresponding olefin and SO2. Additionally, higher molecular weight products, including aromatics, and olefin isomerization products, were produced. Mechanisms for initiation and formation of the higher molecular weight products are presented which include the back reaction of intermediate free radicals to abstract hydrogen or to form C? C bonds followed by expulsion of SO2. The free-radical intermediates formed by the SO2 expulsion undergo transformations to give the aromatic products. No breakdown products were found with either O or S present, nor was SO2H found. 相似文献