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The crystal structures of type II N[sub 2-], O[sub 2-], and air-clathrate hydrates have been studied under their thermodynamic conditions of stability by neutron powder diffraction. The isothermal compressibilities were deduced from the refined lattice constants and found to be significantly different for N[sub 2] and O[sub 2] clathrate hydrates. The water host lattice structure rearranges as a function of pressure with a resulting change of the volume ratio of small and large cages. The cage fillings were established on an absolute scale for the first time. The large cages were found to be partly occupied by two molecules. The results are compared with predictions based on the statistical thermodynamic theory of van der Waals and Platteeuw. While the filling follows the predicted trend significant differences exist in detail. [ABSTRACT FROM AUTHOR]

Thermodynamic measurements and Raman spectroscopy are performed to investigate the structure, selectivity and capture efficiency in mixed gas hydrates containing CO 2 and N 2 . Clathrates forming conditions and dissociation pressures are provided between 270.5 K and 278.3 K (−2.5 °C and 5.3 °C). Specific CO 2 Raman signatures show structure sII to be thermodynamically stable at feed gas composition of 1% and kinetically favored at ∼2%. Structure sI is stable at feed gas CO 2 ranging from ∼2% up to 70%. Our Raman quantitative analysis demonstrates the removal of CO 2 from a typical flue gas mixture (1–20% CO 2 ) and from samples of 47% and 70% CO 2 during hydrate crystallization. For the first time, quantitative bulk guest compositions in hydrates are directly obtained by Raman using relative cross sections of the guests’ (CO 2 and N 2 ) vibrational modes. The equilibrium data thereby generated satisfactorily compare with predictions based on thermodynamic models (CSMGem) and thus remove any ambiguity from previous literature data. It appears that CO 2 molecules preferentially occupy sI large cages (5 12 6 2 ) for a CO 2 feed gas concentration in the range of 2–20% (i.e. ∼1–16% equilibrium gas compositions), whereas CO 2 molecules severely compete with N 2 to fill sI small cages (5 12 ) at equilibrium CO 2 concentrations greater than 30%. As a consequence, the derived selectivity shows a significant decrease from ∼7.2 (at 20% CO 2 ) to ∼3.8 for CO 2 -rich feed gas compositions (i.e. above 20%). In addition, the selectivity is reduced in structure sII formed at 1% CO 2 feed gas composition. Then, the influence of thermodynamic parameters on hydrate selectivity and recovery fraction is described qualitatively at typical CO 2 flue gas concentrations found in conventional power plants. [ABSTRACT FROM AUTHOR]

Semi-clathrates of tetrabutylammoniumbromide (TBAB) are investigated for their potential application inthe CO2capture context based on hydrate technology. Thethree-phase lines of semi-clathrates of CO2–TBAB–H2O and N2–TBAB–H2O areestablished simultaneously with their structure using in situ Ramanscattering performed at high pressure. The preferred crystal phaseobtained at ambient pressure from solutions of 5 and 40 wt % TBABinitial concentrations is shown to change upon enclathration of CO2or N2, or by applying a higher pressure on thesystem. Deep in the stability field, metastable hydrate phases areoccurring at the onset of the formation and correspond to the onesexpected under ambient pressure conditions. Depending on the pressure,they progressively transformed into the most stable ones when approachingequilibrium and dissociation points. Besides, it is shown that a 5wt % TBAB original solution forms preferentially a mixed structureof both type B and type A at low gas pressure with CO2asthe guest gas. A new structure is spectroscopically characterizedat pressures higher than ∼2 MPa CO2. Type A is demonstratedto be stable at 5 wt % initial TBAB concentration with N2as the guest molecule and pressure between 8 and 12 MPa. These structuraldata address new insights on the relationship between the hydrophilic-anionand hydrophobic-cation intercalation with a guest gas producing hydrophobicinteraction in a distorted water lattice. [ABSTRACT FROM AUTHOR]

Abstract: Gas hydrates and gas bubbles were collected during the MARNAUT cruise (May–June 2007) in the Sea of Marmara along the North Anatolian Fault system, Turkey. Gas hydrates were sampled in the western part of the Sea of Marmara (on the Western High), and three gas-bubble samples were recovered on the Western High, the Central High (center part of the Sea of Marmara) and in the Çinarcik Basin (eastern part of the Sea of Marmara). Methane is the major component of hydrates (66.1%), but heavier gases such as C2, C3, and i-C4 are also present in relatively high concentration. The methane contained within gas hydrate is clearly thermogenic as evidenced by a low C1/C2 +C3 ratio of 3.3, and carbon and hydrogen isotopic data (δ 13CCH4 of −44.1‰ PDB and δDCH4 of −219‰ SMOW). A similar signature is found for the associated gas bubbles (C1/C2 +C3 ratio of 24.4, δ 13CCH4 of −44.4‰ PDB) which have the same composition as natural gas from K. Marmara-af field. Gas bubbles from Central High show also a thermogenic origin as evidenced by a C1/C2 +C3 ratio of 137, and carbon and hydrogen isotopic data (δ 13CCH4 of −44.4‰ PDB and δDCH4 of −210‰ SMOW), whereas those from the Çinarcik Basin have a primarily microbial origin (C1/C2 +C3 ratio of 16,600, δ 13CCH4 of −64.1‰ PDB). UV-Raman spectroscopy reveals structure II for gas hydrates, with CH4 trapped in the small (512) and large (51264) cages, and with C2H6, C3H8 and i-C4H10 trapped in the large cages. Hydrate composition is in good agreement with equilibrium calculations, which confirm the genetic link between the gas hydrate and gas bubbles at Western High and the K.Marmara-af offshore gas field located north of the Western High. We calculate the characteristics of the hydrate stability zone at Western High and in the Çinarcik Basin using the CSM-GEM computer program. The base of the structure II hydrate stability field is at about 100 m depth below the seafloor at the Western High site, whereas in the Çinarcik Basin, P–T conditions at the seafloor correspond to the uppermost range for structure I hydrate formation from microbial gas. [Copyright &y& Elsevier]

Abstract: Intact natural gas hydrates recovered on the West African margin in the South Atlantic Ocean (ZaiAngo and Neris II projects) and from the Norwegian Sea (Hakon Mosby Mud Volcano) are investigated by micro-Raman spectroscopy at ambient pressure and low temperature. The gas hydrates collected at different geological sites contain a high methane concentration relative to other minor components that are slightly dispersed in the samples. They crystallize in a type I cubic lattice structure as also confirmed by our preliminary synchrotron diffraction results obtained on the ZaiAngo specimen. However, detailed analysis of selected microscopic areas reveals a variation in the gas distribution among the different specimens. Trace amounts of CO2 and H2S can be identified by their characteristic vibrational signatures in the 1000–3800 cm−1 spectral range. They are found to be co-clathrated with methane. Their presence produces a compositional effect on the relative cage occupancy of CH4, as determined from the integrated band intensity ratio corresponding to the molecular stretching modes of methane in the hydrate. The comparative Raman analysis of synthetic hydrates of H2S, CH4 and CH4-deuterohydrates allows the unambiguous assignment of weak band overtones of trapped methane and co-clathrated H2S molecular vibrations. [Copyright &y& Elsevier]

Abstract: Solid deposits have been formed at 88K and 10−1 Torr from ethanol–water gas collected above aqueous solutions of ethanol (EtOH) (0.6, 2, 4.5, 9 and 17mol%). The composition of different gas mixtures varying between 1:16 and 1:0.8 EtOH:H2O are determined at 295K using our experimental vapor–liquid equilibrium (VLE) data in combination with the Wilson model . The Wilson constants derived at this temperature are Λ 12 =0.37(4) and Λ 21 =0.58(5). The concentration of EtOH in the ice mixture can be calculated using these data and a kinetic model of condensation. It is found to vary between 9 and 65mol% EtOH. The ice mixtures are analyzed in situ in a modified cryostage by micro-Raman spectroscopy. The distinct vibrational signatures of pure EtOH, EtOH aqueous solutions and EtOH–ice mixtures are identified in the 400–3800cm−1 spectral range. Internal vibrational motions of EtOH molecules are affected by temperature and concentration. The presence of amorphous EtOH–ice phases at 88K is demonstrated by the characteristic vibrational signatures of the ν OH stretching modes. The crystallization of an EtOH hydrate is proposed during annealing at ∼140K of a 65mol% EtOH–ice mixture. According to our preliminary X-ray diffraction work, this phase has apparently a distinct structure from that of solid EtOH or from EtOH–clathtrate structures usually found in frozen aqueous solutions. For ice mixtures of lower EtOH content, a distinct hydrate phase crystallizes at ∼170K. These results suggest that ice mixtures obtained by vapor deposition reflect the existence of EtOH clusters of a distinctive structural nature with respect to those encountered in frozen aqueous mixtures. [Copyright &y& Elsevier]

Low-frequency modes of gas hydrates with Xe, Ar, O[SUB2], and N[SUB2] atoms/molecules have been studied by inelastic neutron-scattering and molecular dynamics simulations. Type I and type II clathrate hydrates show some small but significant differences of the low-frequency host contribution to the density of states. Both differ markedly from that of ice Ih and depend only weakly on the guest. The vibrational modes associated with Xe atoms were observed at 2.2, 2.9, and 4.0 meV (T = 100 K). They are in good agreement with predictions from molecular dynamics simulations. In the case of N[SUB2] hydrate we found a well-defined peak at about 2 meV, which shows a remarkable shift to higher frequency with increasing temperature. This peak and a broad peak that is overlapped with the host lattice modes (6.5 and 10.5 meV) are assigned to the vibration of N[SUB2] molecules in the large and small cages, respectively. The calculated vibrational spectra of N[SUB2] molecules in doubly occupied large cages show a significant distinct spectral distribution. The anharmonic shift of the guest atoms in large cages is significantly less pronounced in Xe hydrates suggesting that guest-host interactions can vary considerably from one system to another. [ABSTRACT FROM AUTHOR]

Abstract: The insertion of different elements in the cobalt ferrite spinel structure can drastically change the electric and magnetic characteristics of CoFe2O4 bulks and thin films. Pulsed Laser Deposition (PLD) is a widely used technique that allows the growth of thin films with complex chemical formula. We present the results obtained for stoichiometric and Gadolinium-doped cobalt ferrite thin films deposited by PLD using a femtosecond laser with 1kHz repetition rate. The structural properties of the as obtained samples were compared with other thin films deposited by ns-PLD. The structural characteristics and chemical composition of the samples were investigated using profilometry, Raman spectroscopy, X-Ray diffraction measurements and ToF-SIMS analysis. Cobalt ferrite thin films with a single spinel structure and a preferential growth direction have been obtained. The structural analysis results indicated the presence of internal stress for all the studied samples. By fs-PLD, uniform thin films were obtained in a short deposition time. [Copyright &y& Elsevier]

Two distinct ethanol aqueous solutiondroplets ((XEtOH)L= 8.7 wt% and 46.5 wt %) are investigatedby in situ Raman spectroscopy and X-ray diffraction between 253 and88 K. Structural changes are identified by modifications in the O–Hand C–H stretching modes (2800–3800 cm–1spectral region) during freezing and annealing events. They areattributed to the formation of ice and/or different hydrate structuresin the EtOH–water system. At high initial ethanol concentration,the particle is found to be composed of a modified clathrate I (cubicstructure) at 211 K on cooling and transformed into an ethanol hydrateII (monoclinic structure) on annealing between ∼143 and 173K. This latter decomposes at ∼200 K and leaves an aqueous solutionand ice Ih which further dissociates above ∼230 K. At low initialconcentration, ice first forms on cooling and the particle consistsof a crystalline ice core embedded in a liquid layer of high ethanolcontent at ~200 K (or an amorphous layer at lower T). A new hydrate(IV) of distinct structure (orthorhombic) is observed on annealing(from 100 K) between ∼123 K and ∼142 K (depending oninitial composition), which transforms into the ethanol hydrate IIat ∼160 K. The hydrate II decomposes at ∼200 K, andice Ih remains (and dissociate above ∼220 K) in coexistencewith the liquid layer of high ethanol content. It is proposed thatthe complex crystalline ice particles formed may have the potentialto impact several atmospherical processes differently in comparisonto the pure ice case. [ABSTRACT FROM AUTHOR]

CoFeO thin films with preferential texture structure, small grain size, and perpendicular magnetic anisotropy can be obtained by the pulsed laser deposition (PLD) technique. In this work, we studied the influence of the Fe ions substitution by three elements from lanthanide group (Dy, La, and Gd) on the structural properties of the thin films. The samples were deposited by Nd:YAG laser ( λ=532 nm, 10 ns) ablation of CoFeREO, (RE=Dy, La, Gd) targets at various substrate temperatures ranging from room temperature to 600 °C. The microstructure and chemical composition of the thin films were investigated by Raman spectroscopy, XRD, SEM-EDS, and ToF-SIMS. The XRD patterns and Raman spectra of the thin films indicated the formation of a single spinel structure. Thus, the desired substitution of the iron ions in the spinel lattice with the RE elements was achieved in the thin films, although in the bulk material, their presence determined the formation of a residual phase with a perovskite-type structure. [ABSTRACT FROM AUTHOR]

Combustion of hydrocarbons produces both particulate- and gas-phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose coupling a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate- and gas-phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through and then trap the most volatile components on a second black-carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling–multi-technique approach in conjunction with advanced statistical methods, we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile, and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry. [ABSTRACT FROM AUTHOR]

Combustion of hydrocarbons produces both particulate and gas phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose to couple a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate and gas phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through, and then trap the most volatile components on a second black carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling/multi-technique approach in conjunction with advanced statistical methods we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry. [ABSTRACT FROM AUTHOR]

Pollen grains are covered with lots of different biochemical compounds, like proteins, saccharides and lipids, which are only loosely attached to the pollen. Therefore, they can be separated from the pollen by suspending them in water. Since these compounds play a key role in many atmospheric processes (e.g. cloud condensation nucleation, ice nucleation, aerial allergen exposure), their separation and analyzing are of interest. The chemical composition of whole pollen grains is compared by both Raman and infrared spectroscopy with material that could be extracted from pollen with water. The dominant signals in the pollen grain Raman spectra are those from sporopollenin and carotenoids. These bands decrease in the washing water spectra, since sporopollenin is high molecular and thus is not extractable. The released material shows in turn a chemical composition that differs significantly between species, what is quite expected, since they differ even in the optical properties of their aqueous suspensions. The FTIR spectra show some additional bands to appear in comparison to the Raman spectra. Furthermore, we investigated the pollen rupturing and material release in the aqueous suspensions by drying them up and picturing the residues with a scanning electron microscope. We saw that corn pollen ejected loads of micrometer-sized organelles, which are most likely starch granules. The more the pollen disrupted, the more the measured samples were covered with an amorphous film, which consists of the extracted pollen material, like lipids, sugars, and proteins - the same substances we detected by spectroscopy. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A joint industrial project with IFREMER and Total provides insights into the tectonic setting and the geochemistry of a large active pockmark offshore W-Africa in the Niger Delta. The study combines both geophysical (seismic) and geochemical data to infer the dynamics of a 300 m wide pockmark located at 667 m water depth. Two Calypso cores, one at the centre and one outside the pockmark, along with three box-cores, two inside the pockmark and one outside, were collected to study the geochemistry of gas hydrates, carbonates and pore waters. Two seismic lines, a 3D high resolution random line and a 2D high resolution seismic line, provide a good description of the plumbing of the system. The integrated results depict a very active pockmark characterized by several gas charged-bodies, a well identified BSR marking a hydrate accumulation zone, charged from deeper sources via a network of faults. Hydrates and carbonate concretions have been detected inside the pockmark while only the latter has been found outside. The hydrate analyses show that the hydrate-forming gases are of thermogenic origin, albeit overwhelmingly composed of methane. Pore-water analyses reveal the occurrence of anaerobic oxidation of methane coupled with sulphate reduction at shallow depth (∼200 cm). The chloride concentration profile exhibits both values lower than that of seawater which is inherent to hydrate dissociation after core recovery and positive anomalies (values 7% higher than that of seawater background) at the lowermost part of the core. The latter evidence suggests current or recent hydrate formation at this area. The carbonate dating provides additional temporal information and indicates that this pockmark has been active since ∼21 kyr. [Copyright &y& Elsevier]

Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueous H2CO solutions of different concentrations (from 10-5 to 0.3 molar fraction) using mass spectrometry and IR diode laser spectroscopy. Both experimental techniques allow direct probing of the gas phase concentration collected at equilibrium above the aqueous solutions. A correlation is observed between the polymerization processes occurring in the solution and the partial pressure of H2CO measured at vapor liquid equilibrium (VLE). A similar correlation is observed from total pressure measurements for which the equilibrium vapor pressure decreases as [...]liq is increased. A saturation regime of the H2CO partial pressure is reached as the dissolved fraction of formaldehyde increases above ∼0.15 mol frac. Henry's law constants are derived at 295K for the diluted solutions. [ABSTRACT FROM AUTHOR]

• Exchange kinetic in CH 4 -hydrates using CO 2 or CO 2 -N 2 gas. • Impact of the initial CH 4 -hydrate system properties on the kinetic. • Structure, cage occupancy and phase composition monitored by Raman spectroscopy. • Quantitative and qualitative estimates of factors influencing the kinetic. Recovering methane from natural gas hydrate deposits using carbon dioxide injection is currently of great environmental and energetic interest as it shows potential for producing an energy resource while mitigating CO 2 emissions through CO 2 sequestration. This work investigates the exchange kinetic between CH 4 and CO 2 (or CO 2 -N 2 (v)) in synthetic hydrates, with an emphasis on the impact of CH 4 hydrate formation conditions (e.g. driving force Δ p) on the subsequent exchange reactions. Different driving forces Δ p are utilized and show that the exchange kinetic is improved by a factor of ~3 when the exchange is performed with low Δ p CH 4 hydrates, for which there is a higher relative amount of free H 2 O(liq) (277 K); the kinetic is further improved when stirring is applied. Isobaric CH 4 hydrates exhibit a fast primary hydrate dissociation and CH 4 release, followed by a slower exchange kinetic, possibly limited by solid-state exchange diffusion or secondary CO 2 -rich hydrate formation within the stability field of CH 4 hydrates. Upon exposure to a mixed CO 2 -N 2 (v) gas stream, secondary hydrate production is governed by the effective Δ p remaining after dissolution of the gas mixture, and results in an even slower exchange reaction rate. These results may help optimizing recovery processes in field trial experiments, where both hydrates and liquid water coexist, and aid in predicting the risk of geo-hazards induced by unstable secondary hydrate formation. Furthermore, the exchange kinetic dependencies highlighted here are important as they affect the overall energy efficiency and energy cost of CH 4 recovery processes in gas hydrate field trials. [ABSTRACT FROM AUTHOR]

• Semi-clathrate hydrates separation efficiency is studied from a CO 2 -N 2 gas mixture. • Influence of formation parameters evaluated by in-situ Raman spectroscopy. • Structure, equilibrium gas and hydrate compositions inferred from Raman analyses. • Higher selectivity in semi-clathrates type A compare to type B/polymorphs. • CO 2 capture efficiency depends on crystallization parameters. Carbon dioxide (CO 2) capture from flue gas mixture analogs based on ionic clathrate hydrates crystallization (using tetra-n-butyl ammonium bromide, TBAB) is investigated by optical microscopy and Raman spectroscopy. The purpose of this research is to investigate the influence of the crystallization protocol (slow versus fast cooling/heating) on the subsequent semi-clathrate structures formed from a 35 wt% TBAB-H 2 O solution and CO 2 separation efficiency from an initial gas mixture of 10%CO 2 + 90%N 2. In-situ Raman analyses reveal that structure type B (sometimes associated with several polymorph phases) is readily observed at the onset of the formation process regardless of the crystallization protocol. Structure type B remains stable up to a temperature close to that of dissociation, whereas polymorphs form and evolve continuously until then. Just before dissociation, structure type A is additionally observed. The protocol involving slow cooling and heating steps (similar to the isochoric pressure search method) performs slightly better in terms of selectivity than the one using the multi-cycling temperature approach (fast cooling and heating). However, within the same protocol, the selectivity greatly depends on the specific semi-clathrate structures formed. We find that the best CO 2 selectivity is achieved when structure type A is formed compared to all other semi-clathrate phases. The CO 2 recovery fraction is found at lower value than that measured in canonical clathrate hydrates. [ABSTRACT FROM AUTHOR]

Ge-Sb-Te thin films were obtained by ns-, ps-, and fs-pulsed laser deposition (PLD) in various experimental conditions. The thickness of the samples was influenced by the Nd-YAG laser wavelength, fluence, target-to-substrate distance, and deposition time. The topography and chemical analysis results showed that the films deposited by ns-PLD revealed droplets on the surface together with a decreased Te concentration and Sb over-stoichiometry. Thin films with improved surface roughness and chemical compositions close to nominal values were deposited by ps- and fs-PLD. The X-ray diffraction and Raman spectroscopy results showed that the samples obtained with ns pulses were partially crystallized while the lower fluences used in ps- and fs-PLD led to amorphous depositions. The optical parameters of the ns-PLD samples were correlated to their structural properties. [ABSTRACT FROM AUTHOR]