WorldWideScience

Sample records for clathrates

  1. Tetrahydrofuran Clathrate Hydrate Formation

    OpenAIRE

    Conrad, Heiko; Lehmkuhler, Felix; Sternemann, Christian; Sakko, Arto; Paschek, Dietmar; Simonelli, Laura; Huotari, Simo; Feroughi, Omid; Tolan, Metin; HÀmÀlÀinen, Keijo

    2009-01-01

    We report on the formation of tetrahydrofuran clathrate hydrate studied by x-ray Raman scattering measurements at the oxygen K edge. A comparison of x-ray Raman spectra measured from water-tetrahydrofuran mixtures and tetrahydrofuran hydrate at different temperatures supports stochastic hydrate formation models rather than models assuming hydrate precursors. This is confirmed by molecular dynamics simulations and density functional theory calculations of x-ray Raman spectra. In addition, chan...

  2. Methane clathrates in the Solar System

    CERN Document Server

    Mousis, Olivier; Holm, Nils G; Bouquet, Alexis; Waite, Jack Hunter; Geppert, Wolf Dietrich; Picaud, Sylvain; Aikawa, Yuri; Ali-Dib, Mohamad; Charlou, Jean-Luc; Rousselot, Philippe

    2015-01-01

    We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form in the building blocks of comets, icy bodies, and giant planets. Methane clathrates may play an important role in the evolution of planetary atmospheres. On Earth, the production of methane in clathrates is essentially biological, and these compounds are mostly found in permafrost regions or in the sediments of continental shelves. On Mars, methane would more likely derive from hydrothermal reactions with olivine-rich material. If they do exist, martian methane clathrates would be stable only at depth in the cryosphere and sporadically release some methane into the atmosphere via mechanisms that remain to be determined.

  3. Thermodynamic modeling for clathrate hydrates of ozone

    International Nuclear Information System (INIS)

    Highlights: • We present a phase-equilibrium model for ozone-containing clathrate hydrates. • We determine intermolecular potential parameters for O3. • There is good agreement between the developed model and the experimental data. • The results show the capability of O3 as a guest substance for clathrate hydrates. • We perform parametric studies for O3 storage capacity with various thermodynamic conditions. -- Abstract: We report a theoretical study to predict the phase-equilibrium properties of ozone-containing clathrate hydrates based on the statistical thermodynamics model developed by van der Waals and Platteeuw. The Patel–Teja–Valderrama equation of state is employed for an accurate estimation of the properties of gas phase ozone. We determined the three parameters of the Kihara intermolecular potential for ozone as a = 6.815 · 10−2 nm, σ = 2.9909 · 10−1 nm, and ε · kB−1 = 184.00 K. An infinite set of ε–σ parameters for ozone were determined, reproducing the experimental phase equilibrium pressure–temperature data of the (O3 + O2 + CO2) clathrate hydrate. A unique parameter pair was chosen based on the experimental ozone storage capacity data for the (O3 + O2 + CCl4) hydrate that we reported previously. The prediction with the developed model showed good agreement with the experimental phase equilibrium data within ±2% of the average deviation of the pressure. The Kihara parameters of ozone showed slightly better suitability for the structure-I hydrate than CO2, which was used as a help guest. Our model suggests the possibility of increasing the ozone storage capacity of clathrate hydrates (∼7% on a mass basis) from the previously reported experimental capacity (∼1%)

  4. Clathrate hydrate tuning for technological purposes

    Science.gov (United States)

    di Profio, Pietro; Germani, Raimondo; Savelli, Gianfranco

    2010-05-01

    Gas hydrates are being increasingly considered as convenient media for gas storage and transportation as the knowledge of their properties increases, in particular as relates to methane and hydrogen. Clathrate hydrates may also represent a feasible sequestration technology for carbon dioxide, due to a well defined P/T range of stability, and several research programs are addressing this possibility. Though the understanding of the molecular structure and supramolecular interactions which are responsible of most properties of hydrates have been elucitated in recent years, the underlying theoretical physico-chemical framework is still poor, especially as relates to the role of "conditioners" (inhibitors and promoters) from the molecular/supramolecular point of view. In the present communication we show some results from our research approach which is mainly focused on the supramolecular properties of clathrate hydrate systems - and their conditioners - as a way to get access to a controlled modulation of the formation, dissociation and stabilization of gas hydrates. In particular, this communication will deal with: (a) a novel, compact apparatus for studying the main parameters of formation and dissociation of gas hydrates in a one-pot experiment, which can be easily and rapidly carried out on board of a drilling ship;[1] (b) the effects of amphiphile molecules (surfactants) as inhibitors or promoters of gas hydrate formation;[2] (c) a novel nanotechnology for a reliable and quick production of hydrogen hydrates, and its application to fuel cells;[3,4] and (d) the development of a clathrate hydrate tecnology for the sequestration and geological storage of man-made CO2, possibly with concomitant recovery of natural gas from NG hydrate fields. Furthermore, the feasibility of catalyzing the reduction of carbon dioxide to energy-rich species by hydrates is being investigated. [1] Di Profio, P., Germani, R., Savelli, G., International Patent Application PCT/IT2006

  5. Volatile inventories in clathrate hydrates formed in the primordial nebula

    CERN Document Server

    Mousis, O; Picaud, S; Cordier, D

    2010-01-01

    Examination of ambient thermodynamic conditions suggest that clathrate hydrates could exist in the martian permafrost, on the surface and in the interior of Titan, as well as in other icy satellites. Clathrate hydrates probably formed in a significant fraction of planetesimals in the solar system. Thus, these crystalline solids may have been accreted in comets, in the forming giant planets and in their surrounding satellite systems. In this work, we use a statistical thermodynamic model to investigate the composition of clathrate hydrates that may have formed in the primordial nebula. In our approach, we consider the formation sequence of the different ices occurring during the cooling of the nebula, a reasonable idealization of the process by which volatiles are trapped in planetesimals. We then determine the fractional occupancies of guests in each clathrate hydrate formed at given temperature. The major ingredient of our model is the description of the guest-clathrate hydrate interaction by a spherically a...

  6. Investigating the Metastability of Clathrate Hydrates for Energy Storage

    Energy Technology Data Exchange (ETDEWEB)

    Koh, Carolyn Ann [Colorado School of Mines

    2014-11-18

    Important breakthrough discoveries have been achieved from the DOE award on the key processes controlling the synthesis and structure-property relations of clathrate hydrates, which are critical to the development of clathrate hydrates as energy storage materials. Key achievements include: (i) the discovery of key clathrate hydrate building blocks (stable and metastable) leading to clathrate hydrate nucleation and growth; (ii) development of a rapid clathrate hydrate synthesis route via a seeding mechanism; (iii) synthesis-structure relations of H2 + CH4/CO2 binary hydrates to control thermodynamic requirements for energy storage and sequestration applications; (iv) discovery of a new metastable phase present during clathrate hydrate structural transitions. The success of our research to-date is demonstrated by the significant papers we have published in high impact journals, including Science, Angewandte Chemie, J. Am. Chem. Soc. Intellectual Merits of Project Accomplishments: The intellectual merits of the project accomplishments are significant and transformative, in which the fundamental coupled computational and experimental program has provided new and critical understanding on the key processes controlling the nucleation, growth, and thermodynamics of clathrate hydrates containing hydrogen, methane, carbon dioxide, and other guest molecules for energy storage. Key examples of the intellectual merits of the accomplishments include: the first discovery of the nucleation pathways and dominant stable and metastable structures leading to clathrate hydrate formation; the discovery and experimental confirmation of new metastable clathrate hydrate structures; the development of new synthesis methods for controlling clathrate hydrate formation and enclathration of molecular hydrogen. Broader Impacts of Project Accomplishments: The molecular investigations performed in this project on the synthesis (nucleation & growth)-structure-stability relations of clathrate

  7. Practical reactor production of {sup 41}Ar from argon clathrate

    Energy Technology Data Exchange (ETDEWEB)

    Mercer, J.R. E-mail: jmercer@pharmacy.ualberta.ca; Duke, M.J.M.; McQuarrie, S.A

    2000-06-01

    The radionuclide {sup 41}Ar has many ideal properties as a gas flow tracer. However, the modest cross-section of {sup 40}Ar for thermal neutron activation makes preparation of suitable activities of {sup 41}Ar technically difficult particularly for low flux reactors. Argon can however be trapped in a molecular complex called a clathrate that can then be irradiated. We prepared argon clathrate and explored its irradiation and stability characteristics. Argon clathrate can be used to provide gigabecquerel quantities of {sup 41}Ar even with low power reactors.

  8. Crystal structure of clathrates of Hofmann dma-type

    International Nuclear Information System (INIS)

    Seven new clathrates Cd(DMA)2Ni(CN)4·xG (x=1, G=aniline, 2,3-xylidine, 2,4-xylidine, 2,5-xylidine, 2,6-xylidine, 3,5-xylidine, and x=2, G=2,4,6-trimethylaniline) of Hofmann type are synthesized by amine substitution for dimethylamine (DMA). On the base of x-ray diffraction data it is shown that geometry of guest molecule in cage-like hollow determines the structure of the host and crystal structure of clathrates. Two-dimension metallocomplex of the host of studied clathrates is characterized by elastic folded structure appearing as a result of angular deformation of bond between Cd atoms and host cyanide bridge. Guest molecule orientation is fixed by hydrogen bond. Structural elasticity of the host complex directs to differences in crystal structure of clathrates formed and to considerable variety of incorporated guests

  9. Equilibrium composition between liquid and clathrate reservoirs on Titan

    CERN Document Server

    Mousis, Olivier; Lunine, Jonathan I; Sotin, Christophe

    2015-01-01

    Hundreds of lakes and a few seas of liquid hydrocarbons have been observed by the Cassini spacecraft to cover the polar regions of Titan. A significant fraction of these lakes or seas could possibly be interconnected with subsurface liquid reservoirs of alkanes. In this paper, we investigate the interplay that would happen between a reservoir of liquid hydrocarbons located in Titan's subsurface and a hypothetical clathrate reservoir that progressively forms if the liquid mixture diffuses throughout a preexisting porous icy layer. To do so, we use a statistical-thermodynamic model in order to compute the composition of the clathrate reservoir that forms as a result of the progressive entrapping of the liquid mixture. This study shows that clathrate formation strongly fractionates the molecules between the liquid and the solid phases. Depending on whether the structure I or structure II clathrate forms, the present model predicts that the liquid reservoirs would be mainly composed of either propane or ethane, r...

  10. Regimes of Decomposition of Clathrate in Natural Strata Purged by Methane

    Science.gov (United States)

    Khasanov, M.; Shagapov, V.

    2016-06-01

    The process of decomposition of a methane clathrate in a finite-length stratum initially saturated with methane clathrate and methane, which is purged by warm methane, is studied. The influence of the initial parameters of the stratum and purging conditions on the evolution of methane clathrate temperature and saturation is examined. The existence of solutions is demonstrated, which predict methane clathrate decomposition both on the frontal surface and in the volume zone.

  11. Rattling 'guest' impurities in Si and Ge clathrate semiconductors

    International Nuclear Information System (INIS)

    In addition to their ground state, diamond structure, Si, Ge and Sn can form crystalline solids called clathrates. As in the diamond structure, in the clathrates, the Group IV atoms are tetrahedrally coordinated and sp3 covalently bonded to their neighbors. However, the clathrates contain pentagonal atomic rings and have open-framework lattices containing 20-, 24- and 28-atom 'cages'. There are two clathrate lattices: Type I, a SC lattice with 46 atoms per unit cell and Type II, a FCC lattice with 136 atoms per cubic cell. The pure clathrates are semiconductors. The cages can contain weakly bound impurities ('guests'), usually alkali or alkaline earth atoms. The choice of guest may be used to tune the material properties. The guests are electronic donors, but because of their weak bonding, they have small effects on the electronic band structures. However, they can produce low frequency vibrational ('rattling') modes which can strongly affect the vibrational properties. Some guest-containing clathrates have been shown to be excellent candidates for thermoelectric applications precisely because the guests only perturb the electronic properties weakly, while strongly affecting the vibrational (heat transport) properties. For thermoelectric applications, semiconductor materials are needed. When all cages are filled, the clathrates become semi-metallic due to the excess valence electrons of the guests. To compensate for this, Group III atoms (usually Ga or In) are substituted on the framework sites. After an introduction to clathrates, the results of calculations of the vibrational properties of some experimentally relevant Si- and Ge-based Type I and Type II clathrates are presented. The calculations were carried out using a first-principles, plane wave, pseudopotential method. Results for the Si-based Type II materials Cs8Ga8Si128 and Rb8Ga8Si128, and for the Ge-based Type I materials Ba8Ga16Ge30 and Ba8Ga16Si5Ge25 will be discussed with an emphasis on the very low

  12. Complex admixtures of clathrate hydrates in a water desalination method

    Science.gov (United States)

    Simmons, Blake A.; Bradshaw, Robert W.; Dedrick, Daniel E.; Anderson, David W.

    2009-07-14

    Disclosed is a method that achieves water desalination by utilizing and optimizing clathrate hydrate phenomena. Clathrate hydrates are crystalline compounds of gas and water that desalinate water by excluding salt molecules during crystallization. Contacting a hydrate forming gaseous species with water will spontaneously form hydrates at specific temperatures and pressures through the extraction of water molecules from the bulk phase followed by crystallite nucleation. Subsequent dissociation of pure hydrates yields fresh water and, if operated correctly, allows the hydrate-forming gas to be efficiently recycled into the process stream.

  13. Desalination utilizing clathrate hydrates (LDRD final report).

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, Blake Alexander; Bradshaw, Robert W.; Dedrick, Daniel E.; Cygan, Randall Timothy (Sandia National Laboratories, Albuquerque, NM); Greathouse, Jeffery A. (Sandia National Laboratories, Albuquerque, NM); Majzoub, Eric H. (University of Missouri, Columbia, MO)

    2008-01-01

    Advances are reported in several aspects of clathrate hydrate desalination fundamentals necessary to develop an economical means to produce municipal quantities of potable water from seawater or brackish feedstock. These aspects include the following, (1) advances in defining the most promising systems design based on new types of hydrate guest molecules, (2) selection of optimal multi-phase reactors and separation arrangements, and, (3) applicability of an inert heat exchange fluid to moderate hydrate growth, control the morphology of the solid hydrate material formed, and facilitate separation of hydrate solids from concentrated brine. The rate of R141b hydrate formation was determined and found to depend only on the degree of supercooling. The rate of R141b hydrate formation in the presence of a heat exchange fluid depended on the degree of supercooling according to the same rate equation as pure R141b with secondary dependence on salinity. Experiments demonstrated that a perfluorocarbon heat exchange fluid assisted separation of R141b hydrates from brine. Preliminary experiments using the guest species, difluoromethane, showed that hydrate formation rates were substantial at temperatures up to at least 12 C and demonstrated partial separation of water from brine. We present a detailed molecular picture of the structure and dynamics of R141b guest molecules within water cages, obtained from ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Density functional theory calculations were used to provide an energetic and molecular orbital description of R141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer, 1,2-dichloro-1-fluoroethane, does not form at ambient conditions because of extensive overlap of electron density between guest and host. Classical molecular dynamics simulations and laboratory trials support the results for the isomer hydrate. Molecular dynamics simulations

  14. Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type-I Clathrates

    OpenAIRE

    Prokofiev, Andrey; Svagera, Robert; Waas, Monika; Weil, Matthias; Bernardi, Johannes; Paschen, Silke

    2015-01-01

    Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the...

  15. Storage of molecular hydrogen into leaky clathrate hydrate cages

    International Nuclear Information System (INIS)

    Full text: Efficient storage of hydrogen into compact media is an essential challenge to establish a hydrogen economy. A nanostructured compound made of water and gas molecules, which is called as clathrate hydrate, is one reasonable choice for this important task. Its structure consists of three-dimensional network of hydrogen-bonded water molecules (host cages) and small nonpolar molecules (guests) encaged within this network. The clathrate hydrate medium is chemically durable, environmentally benign, and also free from the necessity of expensive rare metals. Large amount of molecular hydrogen up to 3.8 wt.% was successfully stored into the structure II hydrogen clathrate hydrate (Fd3m space group, lattice constant ∼ 1.7 nm), while it is only synthesized at low temperature and/or high pressure conditions which are not suitable for industrial applications. Required pressure to put significant amount of hydrogen into the hydrate structure is much reducible by blending in additional guest species acting as a hydrate promoter. The promoter molecules added to the system occupy some of the cages to stabilize the hydrate structure at lower pressures, so that the hydrogen storage capacity is partly reduced instead. In addition to the problem of storage capacity, kinetic aspect of hydrogen clathrate hydrate synthesis is also essential for the expected application. Its conventional production scheme was by freezing promoter's solution contacting with pressurized hydrogen gas; it then takes long time for crystal growth. We have established an alternative scheme enabling much faster synthesis (Okuchi et al., Appl. Phys. Lett., 91, 171903, 2007). We found that when hydrogen-free clathrate hydrate powders including a promoter (tetrahydrofuran) was contacted with pressurized hydrogen gas, hydrogen was quickly absorbed into the hydrate medium. We observed the absorption kinetics by nuclear magnetic resonance spectroscopy as a function of hydrogen pressure and temperature. In

  16. The chemistry of low dosage clathrate hydrate inhibitors.

    OpenAIRE

    Perrin, A.; Musa, O. M.; STEED, J. W.

    2013-01-01

    This review aims to introduce the chemistry of low dosage inhibitors of clathrate hydrate formation within the context of their role in the oil and gas industry. The review covers both kinetic hydrate inhibitors and anti-agglomerants from the point of view of structure–function relationships, focussing on recent refinements in mechanistic understanding and chemical design, and the consequently evolving and increasingly fine-tuned properties of these fascinating compounds.

  17. Nanostructured clathrate phonon glasses: beyond the rattling concept.

    Science.gov (United States)

    He, Yuping; Galli, Giulia

    2014-05-14

    Using first-principles calculations, we investigated the thermoelectric properties of a newly synthesized Si-based ternary clathrate K8Al8Si38, composed of ∼1 nm hollow cages with a metal atom inside. This compound contains solely Earth abundant elements. We found that, similar to other nanostructured type I clathrates, this system is a semiconductor and has a low thermal conductivity (∼1 W/mK). It was long believed that the mere presence of rattling centers was responsible for the low lattice thermal conductivity of type I clathrates. We found instead that the cage structural disorder induced by atomic substitution plays a crucial role in determining the conductivity of these materials, in addition to the dynamics of the guest atoms. Our calculations showed that the latter is substantially affected by the charge transfer between the metal and the cages. Our results provide design rules for the search of new types of promising nanocage structured thermoelectric materials. PMID:24762084

  18. Electrochemical stability of ionic clathrate hydrates and their structural consideration

    International Nuclear Information System (INIS)

    Although electrochemical stability is an essential factor in relation to the potential applications of ionic clathrate hydrates to solid electrolytes, most studies regarding the proton conductors have focused on their ionic conductivity and thermal stability. Solid electrolytes in various electrochemical devices have to endure the applied potentials; thus, we examined the linear sweep voltammograms of various tetraalkylammonium hydroxide hydrates in order to shed light on the trend of electrochemical stability depending on the hydrate structure. We revealed that the electrochemical stability of Me4NOH hydrates is mainly affected by both their ionic concentration and cage occupancy. In particular, the true clathrate structures of β-Me4NOH hydrates are more electrochemically stable than their α-forms that possess partially broken hydrogen bonds. We also observed that the binary THF–Pr4NOH and pure Bu4NOH clathrate hydrates exhibit greater electrochemical stability than those of pure Me4NOH hydrates having lower or similar ionic concentrations. These results are considered to arise from the fact that each of the Pr4N+ and Bu4N+ ions occupies an extended space comprising four cages, which leads to stabilization of the larger unit, whereas a Me4N+ ion is completely included only in one cage

  19. Vibrational spectroscopic and quantum theoretical study of host-guest interactions in clathrates: I. Hofmann type clathrates

    Directory of Open Access Journals (Sweden)

    VLADIMIR M. PETRUSEVSKI

    2000-06-01

    Full Text Available Hofmann type clatharates are host-guest compounds with the general formula M(NH32M'(CN4·2G, in which M(NH32M'(CN4 is the host lattice and G is benzene, the guest molecule. In previous studies, host-guest interactions have been investigated by analyzing the RT and LNT vibrational (infrared, far infrared and Raman spectra of these clathrates. All the observed changes in the vibrational spectra of these clathrates are referred to a host-guest interaction originating from weak hydrogen bonding between the ammonia hydrogen atoms from the host lattice and the p electron cloud of the guest (benzene molecules. In order to obtain an insight into the relative importance of the local crystalline field vs. the anharmonicity effects on the spectroscopic properties of the guest species upon enclathration, as well as to explain the observed band shifts and splittings, several quantum theoretical approaches are proposed.

  20. Chemical-clathrate hybrid hydrogen storage: storage in both guest and host.

    Science.gov (United States)

    Strobel, Timothy A; Kim, Yongkwan; Andrews, Gary S; Ferrell, Jack R; Koh, Carolyn A; Herring, Andrew M; Sloan, E Dendy

    2008-11-12

    Hydrogen storage from two independent sources of the same material represents a novel approach to the hydrogen storage problem, yielding storage capacities greater than either of the individual constituents. Here we report a novel hydrogen storage scheme in which recoverable hydrogen is stored molecularly within clathrate cavities as well as chemically in the clathrate host material. X-ray diffraction and Raman spectroscopic measurements confirm the formation of beta-hydroquinone (beta-HQ) clathrate with molecular hydrogen. Hydrogen within the beta-HQ clathrate vibrates at considerably lower frequency than hydrogen in the free gaseous phase and rotates nondegenerately with splitting comparable to the rotational constant. Compared with water-based clathrate hydrate phases, the beta-HQ+H2 clathrate shows remarkable stability over a range of p-T conditions. Subsequent to clathrate decomposition, the host HQ was used to directly power a PEM fuel cell. With one H2 molecule per cavity, 0.61 wt % hydrogen may be stored in the beta-HQ clathrate cavities. When this amount is combined with complete dehydrogenation of the host hydroxyl hydrogens, the maximum hydrogen storage capacity increases nearly 300% to 2.43 wt %. PMID:18928261

  1. Paraffin molecule mobility in channel clathrates of urea on spectroscopic NMR relaxation data

    CERN Document Server

    Kriger, Y G; Chekhova, G N

    2001-01-01

    The temperature dependences of the protons spin-lattice relaxation time (T sub I) in the channel clathrates of urea with paraffins are measured. The data on the T sub I are interpreted within the frames of the model of the paraffins molecules and their fragments orientation in the clathrate channels. The dynamics peculiarities are connected with the disproportion effects of these compounds

  2. Accelerated formation of THF-H2 clathrate hydrate in porous media.

    Science.gov (United States)

    Saha, Dipendu; Deng, Shuguang

    2010-06-01

    Porous media were used to control the hydrogen clathrate particle size in order to accelerate its formation kinetics. Stoichiometric tetrahydrofuran-hydrogen binary clathrate hydrates with approximately 1 wt % hydrogen loading formed in the mesopores of four porous media with median pore diameters of 49, 65, 100, and 226 A at 270 K and hydrogen pressure of 65 bar. The minimum formation time for the tetrahydrofuran-hydrogen binary clathrate hydrates was 27 min in a porous medium with a median pore diameter of 49 A, which is 6-22 times faster than the tetrahydrofuran-hydrogen binary clathrate hydrates formed in the bulk ice. The clathrate formation time was found to increase with pore size of the porous media. A modified shrinking core kinetic model was used to calculate the diffusivity of hydrogen in the tetrahydrofuran-hydrogen binary clathrate hydrates. Hydrogen diffusivities in the tetrahydrofuran-hydrogen binary clathrate hydrates were found to be on the order of 10(-18)-10(-19) m(2)/s and decrease with increasing pore size or clathrate particle size. PMID:20148547

  3. Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

    Science.gov (United States)

    Blake, David; Allamandola, Louis; Sandford, Scott; Hudgins, Doug; Freund, Friedemann

    1991-01-01

    Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

  4. Micro-Tomographic Investigation of Ice and Clathrate Formation and Decomposition under Thermodynamic Monitoring

    Directory of Open Access Journals (Sweden)

    Stefan Arzbacher

    2016-08-01

    Full Text Available Clathrate hydrates are inclusion compounds in which guest molecules are trapped in a host lattice formed by water molecules. They are considered an interesting option for future energy supply and storage technologies. In the current paper, time lapse 3D micro computed tomographic (µCT imaging with ice and tetrahydrofuran (THF clathrate hydrate particles is carried out in conjunction with an accurate temperature control and pressure monitoring. µCT imaging reveals similar behavior of the ice and the THF clathrate hydrate at low temperatures while at higher temperatures (3 K below the melting point, significant differences can be observed. Strong indications for micropores are found in the ice as well as the THF clathrate hydrate. They are stable in the ice while unstable in the clathrate hydrate at temperatures slightly below the melting point. Significant transformations in surface and bulk structure can be observed within the full temperature range investigated in both the ice and the THF clathrate hydrate. Additionally, our results point towards an uptake of molecular nitrogen in the THF clathrate hydrate at ambient pressures and temperatures from 230 K to 271 K.

  5. First-principles stability study of clathrate hydrates under pressure

    Science.gov (United States)

    Thonhauser, Timo; Li, Qi; Kolb, Brian

    2010-03-01

    We present a first-principles DFT study of the structural stability of clathrate hydrates under pressure. These materials form under high pressure and low temperature and consist of polyhedral water cages that form an ice-like framework of hydrogen bonds. Clathrate hydrates can be filled with guest molecules such as methane or molecular hydrogen, in which case these materials and their stability are of interest for energy-storage solutions. Since the interactions between the water molecules themselves---but also between the water molecules and the guest molecules---is at least partly determined by van der Waals forces, we utilize the recently developed self-consistent van der Waals density functional vdW-DF (T. Thonhauser, V.R. Cooper, S. Li, A. Puzder, P. Hyldgaard, and D.C. Langreth, Phys. Rev. B 76, 125112 (2007)). For our simulations we consider the empty host lattice, as well as the host lattice filled with methane and molecular hydrogen, for pressures up to 1 GPa. Our results show that the system undergoes phase transitions from structure I to structure II and finally to structure H, in good agreement with experiment.

  6. Geochemistry of clathrate-derived methane in Arctic Ocean waters

    Energy Technology Data Exchange (ETDEWEB)

    Elliott, S.M.; Reagan, M.T.; Moridis, G.J.; Cameron-Smith, P.J.

    2010-03-15

    Alterations to the composition of seawater are estimated for microbial oxidation of methane from large polar clathrate destabilizations, which may arise in the coming century. Gas fluxes are taken from porous flow models of warming Arctic sediment. Plume spread parameters are then used to bracket the volume of dilution. Consumption stoichiometries for the marine methanotrophs are based on growth efficiency and elemental/enzyme composition data. The nutritional demand implied by extra CH{sub 4} removal is compared with supply in various high latitude water masses. For emissions sized to fit the shelf break, reaction potential begins at one hundred micromolar and falls to order ten a thousand kilometers downstream. Oxygen loss and carbon dioxide production are sufficient respectively to hypoxify and acidify poorly ventilated basins. Nitrogen and the monooxygenase transition metals may be depleted in some locations as well. Deprivation is implied relative to existing ecosystems, along with dispersal of the excess dissolved gas. Physical uncertainties are inherent in the clathrate abundance, patch size, outflow buoyancy and mixing rate. Microbial ecology is even less defined but may involve nutrient recycling and anaerobic oxidizers.

  7. A new class of low compressibility materials: Clathrates of silicon and related materials

    OpenAIRE

    San Miguel, Alfonso; Mélinon, Patrice; Blase, Xavier; Tournus, Florent; Connétable, Damien; Reny, Édouard; Yamanaka, Shoji; Itié, Jean-Paul; Cros, Christian; Pouchard, Michel

    2002-01-01

    We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation, The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature o...

  8. Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII

    OpenAIRE

    Härkönen, Ville J.; Karttunen, Antti J.

    2015-01-01

    The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and iterative solution of the linearized Boltzmann transport equation(BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than silicon diamond structure (d-Si) by factors of 1/2 and 1/5, respectively. The main reason for the lower lattice thermal conductivity o...

  9. Preservation of carbon dioxide clathrate hydrate in the presence of trehalose under freezer conditions

    Science.gov (United States)

    Nagashima, Hironori D.; Takeya, Satoshi; Uchida, Tsutomu; Ohmura, Ryo

    2016-01-01

    To investigate the preservation of CO2 clathrate hydrate in the presence of sugar for the novel frozen dessert, mass fractions of CO2 clathrate hydrate in CO2 clathrate hydrate samples coexisting with trehalose were intermittently measured. The samples were prepared from trehalose aqueous solution with trehalose mass fractions of 0.05 and 0.10 at 3.0 MPa and 276.2 K. The samples having particle sizes of 1.0 mm and 5.6-8.0 mm were stored at 243.2 K and 253.2 K for three weeks under atmospheric pressure. The mass fractions of CO2 clathrate hydrate in the samples were 0.87-0.97 before the preservation, and CO2 clathrate hydrate still remained 0.56-0.76 in the mass fractions for 5.6-8.0 mm samples and 0.37-0.55 for 1.0 mm samples after the preservation. The preservation in the trehalose system was better than in the sucrose system and comparable to that in the pure CO2 clathrate hydrate system. This comparison indicates that trehalose is a more suitable sugar for the novel frozen carbonated dessert using CO2 clathrate hydrate than sucrose in terms of CO2 concentration in the dessert. It is inferred that existence of aqueous solution in the samples is a significant factor of the preservation of CO2 clathrate hydrate in the presence of sugar.

  10. Tropospheric impact of methane emissions from clathrates in the Arctic Region

    Directory of Open Access Journals (Sweden)

    S. Bhattacharyya

    2012-10-01

    Full Text Available A highly potent greenhouse gas, methane, is locked in the solid phase as ice-like deposits containing a mixture of water and gas (mostly methane called clathrates in both ocean sediments and underneath permafrost regions. Clathrates are stable under high pressures and low temperatures. In a warming climate, increases in ocean temperatures could lead to dissociation of the clathrates and release methane into the ocean and subsequently the atmosphere. This is of particular importance in the shallow parts of the Arctic Ocean, since clathrates are expected to start outgassing abruptly at depths of around 300 m. In this paper, we present a comparison of simulations from the Community Earth System Model (CESM1 for present-day conditions with and without additional methane emissions from a plausible clathrate release scenario based on a state-of-the-art ocean sediment model. The CESM model includes a fully interactive physical ocean and we added a fast atmospheric chemistry mechanism that represents methane as a fully interactive tracer (with emissions rather than concentration boundary conditions along with the main chemical reactions for methane, ozone, and nitrous oxide. The results show that such Arctic clathrate emissions increase methane concentrations non-uniformly, and that increases in surface ozone concentrations are greatest in polluted regions. We also find that the interannual variability in surface methane and ozone increases.

  11. Dynamic free energy surfaces for sodium diffusion in type II silicon clathrates.

    Science.gov (United States)

    Slingsby, J G; Rorrer, N A; Krishna, L; Toberer, E S; Koh, C A; Maupin, C M

    2016-02-21

    Earth abundant semiconducting type II Si clathrates have attracted attention as photovoltaic materials due to their wide band gaps. To realize the semiconducting properties of these materials, guest species that arise during the synthesis process must be completely evacuated from the host cage structure post synthesis. A common guest species utilized in the synthesis of Si clathrates is Na (metal), which templates the clathrate cage formation. Previous experimental investigations have identified that it is possible to evacuate Na from type II clathrates to an occupancy of less than 1 Na per unit cell. This work investigates the energetics, kinetics, and resulting mechanism of Na diffusion through type II Si clathrates by means of biased molecular dynamics and kinetic Monte Carlo simulations. Well-tempered metadynamics has been used to determine the potential of mean force for Na moving between clathrate cages, from which the thermodynamic preferences and transition barrier heights have been obtained. Kinetic Monte Carlo simulations based on the metadynamics results have identified the mechanism of Na diffusion in type II Si clathrates. The overall mechanism consists of a coupled diffusive process linked via electrostatic guest-guest interactions. The large occupied hexakaidechedral cages initially empty their Na guests to adjacent empty large cages, thereby changing the local electrostatic environment around the occupied small pentagonal dodecahedral cages and increasing the probability of Na guests to leave the small cages. This coupled process continues through the cross-over point that is identified as the point where large and small cages are equally occupied by Na guests. Further Na removal results in the majority of guests residing in the large cages as opposed to the small cages, in agreement with experiments, and ultimately a Na free structure. PMID:26658349

  12. Formation, properties, and function of vacancies in Si/Ge Clathrates: The importance of broken symmetries

    Science.gov (United States)

    Bhattacharya, Amrita; Carbogno, Christian; Scheffler, Matthias

    Inclusion compounds, such as clathrates, are cage-like crystal structures that can encapsulate guest atoms. Since this allows to tune their electronic and vibrational properties, they are regarded as interesting materials for thermoelectric applications. Progress in this field is, however, hindered by the fact that filling of group-IV clathrates often results in complex and unexpected structural changes, e.g., the spontaneous formation of vacancies in certain hosts: In Ge46 clathrates filled with K or Ba, the most favourable phases K8Ge44/ Ba8Ge43 feature two/three vacancies. Conversely, the framework of the isoelectronic Si46 clathrate remains intact (K8Si46/Ba8Si46) upon filling with the exact same guests. Our first-principles calculations of the formation energies and of the thermodynamic phase stabilities confirm this experimental scenario and shed light on the underlying mechanisms. Due to the spatially more delocalized 4sp3 orbitals in Ge compared to the more localized 3sp3 orbitals in Si, fundamentally different symmetry breaking distortions become possible to stabilize the vacancies. Eventually, we discuss the implications of these findings for the thermoelectric properties of clathrates.

  13. First-Principles Study of Electronic Structure of Type I Hybrid Carbon-Silicon Clathrates

    Science.gov (United States)

    Chan, Kwai S.; Peng, Xihong

    2016-08-01

    A new class of type I hybrid carbon-silicon clathrates has been designed using computational methods by substituting some of the Si atoms in the silicon clathrate framework with carbon atoms. In this work, the electronic structure of hybrid carbon-silicon clathrates with and without alkaline or alkaline-earth metal guest atoms has been computed within the density functional theory framework. The theoretical calculations indicate that a small number of carbon substitutions in the Si46 framework slightly reduces the density of states (DOS) near the band edge and narrows the bandgap of carbon-silicon clathrates. Weak hybridization of the conduction band occurs when alkaline metal (Li, Na, K) atoms are inserted into the structure, while strong hybridization of the conduction band occurs when alkaline-earth metal (Mg, Ca, Ba) atoms are inserted into the hybrid structure. Empty C y Si46- y clathrates within the composition range of 2 ≤ y ≤ 15 can be tuned to exhibit indirect bandgaps of 1.5 eV or less, and may be considered as potential electronic materials.

  14. Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII

    Science.gov (United States)

    Härkönen, Ville J.; Karttunen, Antti J.

    2016-01-01

    The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and an iterative solution of the linearized Boltzmann transport equation (BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than the silicon diamond structure (d -Si) by factors of 1/2 and 1/3, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d -Si was found to be the harmonic phonon spectra, while in the case of the clathrate structure VIII, the difference is mainly due to the harmonic phonon spectra and partly due to the shorter relaxation times of phonons. In the studied clathrate frameworks, the anharmonic effects have larger impact on the lattice thermal conductivity than the size of the unit cell. For the structure II, the predicted lattice thermal conductivity differs approximately by a factor of 20 from the previous experimental results obtained for a polycrystalline sample at room temperature.

  15. A model for the formation and stabilization of charged water clathrates

    Science.gov (United States)

    Holland, P. M.; Castleman, A. W., Jr.

    1980-01-01

    A model for the formation and stabilization of charged water clathrates is presented which accounts for observed anomalies in H(+)(H2O)n ion distributions. These anomalies are observed in both ion cluster and neutral expansions and are consistent with the sizes expected for clathrate ions. That the same sizes are observed in both ion cluster and neutral expansions strongly suggests that a rapid ionic process is responsible for their formation. The proposed model is based on the high mobility and bonding effects of the excess proton in water. Computer simulations suggest that excess proton movement in a water clathrate would be suitable for stabilizing the clathrate structure as well as giving it access to a large number of nearly degenerate proton configurations. The formation of clathrates in charged water clusters of proper size can be ascribed to the following: rapid excess proton movement, a strong preference of the H3O(+) for a three-coordinate bonding structure (which is compatible with hydrogen bonding), and finally, relatively slow processes leading to thermal disorder.

  16. Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type-I Clathrates

    Science.gov (United States)

    2015-01-01

    Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the phase Ba8–xRExTMySi46–y (RE = rare earth element; TM = Au, Pd, Pt) reveals that the RE content x is mainly governed by two factors, the free cage space and the electron balance. PMID:26823658

  17. Modeling IR spectra of CO2 isotopologues and CH4 trapped In type I clathrate

    Directory of Open Access Journals (Sweden)

    Lakhlifi A.

    2014-02-01

    Full Text Available To test the hypothesis of atmospheric carbon dioxide or methane storage in metastable clathrate, a theoretical formalism is developed to model and simulate the spectra of the CO2 or CH4 molecule trapped in clathrates. 12-6 Lennard-Jones atomatom potentials are used to account for short and long range interactions between the atoms of the trapped molecules and atoms of H2O molecules of the cage. Effective electric charges are used for electrostatic interactions with H2O molecules. The calculations were performed on clathrates of type I, with a small and a large cage to determine equilibrium configurations for both CO2 and CH4 and vibrational shifts were determined for CO2 in an undistorted trapping nano-cage.

  18. Van't Hoff law for temperature dependent Langmuir constants in clathrate hydrate nanocavities

    CERN Document Server

    Lakhlifi, Azzedine

    2015-01-01

    This work gives a van't Hoff law expression of Langmuir constants of different species for determining their occupancy in the nanocavities of clathrate hydrates. The van't Hoff law's parameters are derived from a fit with Langmuir constants calculated using a pairwise site-site interaction potential to model the anisotropic potential environment in the cavities, as a function of temperature. The parameters can be used for calculating clathrates compositions. Results are given for nineteen gas species trapped in the small and large cavities of structure types I and II [1]. The accuracy of this approach is based on a comparison with available experimental data for ethane and cyclo- propane clathrate hydrates. The numerical method applied in this work, was recently validated from a comparison with the spherical cell method based on analytical considerations [1

  19. Interpreting Temperature Strain Data from Meso-Scale Clathrate Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Leeman, John R [ORNL; Rawn, Claudia J [ORNL; Ulrich, Shannon M [ORNL; Elwood Madden, Megan [University of Oklahoma, Norman; Phelps, Tommy Joe [ORNL

    2012-01-01

    Gas hydrates are important in global climate change, carbon sequestra- tion, and seafloor stability. Currently, formation and dissociation pathways are poorly defined. We present a new approach for processing large amounts of data from meso-scale experiments, such as the LUNA distributed sensing system (DSS) in the seafloor process simulator (SPS) at Oak Ridge National Laboratory. The DSS provides a proxy for temperature measurement with a high spatial resolution allowing the heat of reaction during gas hydrate formation/dissociation to aid in locating clathrates in the vessel. The DSS fibers are placed in the sediment following an Archimedean spiral design and then the position of each sensor is solved by iterating over the arc length formula with Newtons method. The data is then gridded with 1 a natural neighbor interpolation algorithm to allow contouring of the data. The solution of the sensor locations is verified with hot and cold stimulus in known locations. An experiment was preformed with a vertically split column of sand and silt. The DSS system clearly showed hydrate forming in the sand first, then slowly creeping into the silt. Similar systems and data processing techniques could be used for monitoring of hydrates in natural environments or in any situation where a hybrid temperature/strain index is useful. Further ad- vances in fiber technology allow the fiber to be applied in any configuration and the position of each sensor to be precisely determined making practical applications easier.

  20. Effects of nocloprost clathrate on absorption of acetylsalicylic acid.

    Science.gov (United States)

    Siegmund, W; Zschiesche, M; Franke, G; Amon, I

    1994-01-01

    The cytoprotective prostaglandin E2 analog nocloprost clathrate (NOCLO) is tested as a prophylactic for gastrointestinal lesions of NSAID. The effects of 400 micrograms NOCLO versus respective placebos with and without equivalent amounts of beta-cyclodextrin on the pharmacokinetic behavior of acetylsalicylic acid (ASA), given 30 min after NOCLO, were studied in two single-blind, parallel-group trials. The trials were performed in 15 male healthy volunteers (age 21-25 years, body weight 62-94 kg, body height 172-187 cm) with known N-acetylation and debrisoquine type hydroxylation phenotype. ASA, salicylic acid (SA), and salicyluric acid (SU) in plasma and SA and SU in urine were measured by HPLC. NOCLO delayed the absorption of ASA (increased tmax, lower Cmax) significantly in comparison with both placebos. AUC and clearance values were not changed by NOCLO premedication. There were neither differences between the two placebo groups nor between the two groups pretreated with NOCLO with regard to any pharmacokinetic parameter. The changes in drug absorption are caused by the sum of those cytoprotective effects of prostaglandin which are also determinants of drug absorption. PMID:8199752

  1. Pulse radiolysis study on electrons trapped in semiclathrates and non-clathrate hydrates

    International Nuclear Information System (INIS)

    Trapping of electrons in specific water molecule vacancies, observed previously in crystalline aqueous clathrates, has also been found in semiclathrates (e.g., tetramethylammonium hydroxide pentahydrate), in clathrates showing hydrogen bonds between host and guest molecules (e.g., piperazine clathrate), and also in inorganic hydrates (e.g., sodium carbonate decahydrate). The lifetime of the electron is sometimes longer than in the case of true clathrates; e.g., t/sub 1/2/ = 3.5 ms (first-order decay in piperazine clathrate). The existence of comparatively long-lived electrons at room temperature may be considered a general phenomenon. The condition for its occurrence is the presence of OH- or F- anion, which can substitute for H2O in the aqueous part of the compound and when displaced leaves an electron trap. In other ionic and nonionic compounds, the condition for the trapping of long-lived electrons is protonation of the principal compound, thereby leaving the solution or melt alkaline during the crystallization of the hydrate. Interpretation in terms of preexistent traps invokes the crystal imperfections chemistry, which in the case of hydrates has not yet been noticed. It has been assumed that electrons occupy the vacancies temporarily revealing their presence. In some clathrates and other hydrates, the long-lived electron traps do not occur; instead, the electron shows a similar spectrum (620 nm maximum), decaying by 2-3 orders of magnitude faster than in long-lived traps. It is assumed that this is a case of electron digging its own hole, although an alternative explanation may be through trapping in other kinds of crystal imperfections in the aqueous moiety of the hydrate

  2. Thermodynamic studies on semi-clathrate hydrates of TBAB + gases containing carbon dioxide

    International Nuclear Information System (INIS)

    CO2 capture has become an important area of research mainly due to its drastic greenhouse effects. Gas hydrate formation as a separation technique shows tremendous potential, both from a physical feasibility as well as an envisaged lower energy utilization criterion. Briefly, gas (clathrate) hydrates are non-stoichiometric, ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s) under low-temperatures and elevated pressures. As the pressure required for gas hydrate formation is generally high, therefore, aqueous solution of tetra-n-butyl ammonium bromide (TBAB) is added to the system as a gas hydrate promoter. TBAB generally reduces the required hydrate formation pressure and/or increases the formation temperature as well as modifies the selectivity of hydrate cages to capture CO2 molecules. TBAB also takes part in the hydrogen-bonded cages. Such hydrates are called 'semi-clathrate' hydrates. Evidently, reliable and accurate phase equilibrium data, acceptable thermodynamic models, and other thermodynamic studies should be provided to design efficient separation processes using the aforementioned technology. For this purpose, phase equilibria of clathrate/semi-clathrate hydrates of various gas mixtures containing CO2 (CO2 + CH4/N2/H2) in the presence of pure water and aqueous solutions of TBAB have been measured in this thesis. In the theoretical section of the thesis, a thermodynamic model on the basis of the van der Waals and Platteeuw (vdW-P) solid solution theory along with the modified equations for determination of the Langmuir constants of the hydrate formers has been successfully developed to represent/predict equilibrium conditions of semi-clathrate hydrates of CO2, CH4, and N2. Later, several thermodynamic consistency tests on the basis of Gibbs-Duhem equation as well as a statistical approach have been applied on the phase equilibrium data of the systems of mixed/simple clathrate hydrates to conclude about

  3. Guest-Host Interaction Study in Clathrate Hydrates Using Lattice Dynamics Simulation

    Institute of Scientific and Technical Information of China (English)

    Maofeng Jing; Shunle Dong

    2005-01-01

    Lattice dynamics simulation of several gas hydrates (helium, argon, and methane) with different occupancy rates has been performed using TIP3P potential model. Results show that the coupling between the guest and host is not simple as depicted by the conventional viewpoints. For clathrate hydrate enclosing small guest, the small cages are dominantly responsible for the thermodynamic stability of clathrate hydrates. And the spectrum of methane hydrate is studied compared with argon hydrate,then as a result, shrink effect from positive hydrogen shell is proposed.

  4. First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

    Science.gov (United States)

    Akai, K.; Kishimoto, K.; Koyanagi, T.; Kono, Y.; Yamamoto, S.

    2014-06-01

    We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

  5. Measurement of Clathrate Hydrate Thermodynamic Stability in the Presence of Ammonia

    Science.gov (United States)

    Dunham, Marc

    2012-01-01

    There is a lack of data available for the stability of clathrate hydrates in the presence of ammonia for low-to-moderate pressures in the 0-10 MPa range. Providing such data will allow for a better understanding of natural mass transfer processes on celestial bodies like Titan and Enceladus, on which destabilization of clathrates may be responsible for replenishment of gases in the atmosphere. The experimental process utilizes a custom-built gas handling system (GHS) and a cryogenic calorimeter to allow for the efficient testing of samples under varying pressures and gas species.

  6. Cryolava flow destabilization of crustal methane clathrate hydrate on Titan

    Science.gov (United States)

    Davies, Ashley Gerard; Sotin, Christophe; Choukroun, Mathieu; Matson, Dennis L.; Johnson, Torrence V.

    2016-08-01

    To date, there has been no conclusive observation of ongoing endogenous volcanic activity on Saturn's moon Titan. However, with time, Titan's atmospheric methane is lost and must be replenished. We have modeled one possible mechanism for the replenishment of Titan's methane loss. Cryolavas can supply enough heat to release large amounts of methane from methane clathrate hydrates (MCH). The volume of methane released is controlled by the flow thickness and its areal extent. The depth of the destabilisation layer is typically ≈30% of the thickness of the lava flow (≈3 m for a 10-m thick flow). For this flow example, a maximum of 372 kg of methane is released per m2 of flow area. Such an event would release methane for nearly a year. One or two events per year covering ∼20 km2 would be sufficient to resupply atmospheric methane. A much larger effusive event covering an area of ≈9000 km2 with flows 200 m thick would release enough methane to sustain current methane concentrations for 10,000 years. The minimum size of "cryo-flows" sufficient to maintain the current atmospheric methane is small enough that their detection with current instruments (e.g., Cassini) could be challenging. We do not suggest that Titan's original atmosphere was generated by this mechanism. It is unlikely that small-scale surface MCH destabilisation is solely responsible for long-term (> a few Myr) sustenance of Titan's atmospheric methane, but rather we present it as a possible contributor to Titan's past and current atmospheric methane.

  7. Physicochemical and structural studies of clathrate hydrates of tetrabutylammonium polyacrylates.

    Science.gov (United States)

    Terekhova, Irina S; Manakov, Andrey Yu; Komarov, Vladislav Yu; Villevald, Galina V; Burdin, Alexander A; Karpova, Tamara D; Aladko, Eugeny Ya

    2013-03-01

    In this work, physicochemical and structural studies have been carried out for semiclathrate hydrates of linear (un-cross-linked) and cross-linked tetrabutylammonium polyacrylates with different degrees of cross-linking of the polymeric guest molecules (n = 0.5, 1, 2, 3%) and different degrees of substitution of proton ions of carboxylic groups in poly(acrylic acid) for TBA cations (x = 1, 0.8, 0.6). The changes in the hydrates' stability and composition depending on the outlined parameters were examined in the course of phase diagram studies of the binary systems water-tetrabutylammonium polyacrylates using differential thermal analysis method and calorimetric measurements of fusion enthalpies of the hydrates. Phase diagram studies of the binary system water-linear tetrabutylammonium polyacrylate revealed the formation of four hydrates. Based on the data of chemical analysis of hydrate crystals the compositions of all hydrates have been determined. Single-crystal X-ray diffraction studies revealed a tetragonal structure, space group 4/m, and unit cell parameters are close for different hydrates and lie in the ranges a = 23.4289-23.4713 Å and c = 12.3280-12.3651 Å (150 K). The structure can be related to tetragonal structure I typical for the clathrate hydrates of tetraalkylammonium salts with monomeric anions. Powder X-ray diffraction analyses confirmed the identity of the above crystal structure to that of the hydrates with cross-linked tetrabutylammonium polyacrylates. The behavior of TBA polyacrylate hydrates under the pressure of methane was studied and quantitative assessment of the gas content in the hydrates was made using volumetric analysis method. PMID:23383955

  8. Kinetic and thermodynamic behaviour of CF4 clathrate hydrates

    International Nuclear Information System (INIS)

    Highlights: • The kinetics and thermodynamics of CF4 hydrates are investigated. • Experimental hydrate dissociation conditions for CF4 are reported. • Good agreement between the experimental data and model predictions is observed. • The effect of initial conditions (T and P) on the CF4 hydrate kinetics is studied. - Abstract: This study presents experimental kinetic and thermodynamic data for CF4 clathrate hydrates. Experimental measurements were undertaken in a high pressure equilibrium cell with a 40 cm3 inner volume. The measurements of experimental hydrate dissociation conditions were performed in the temperature range of (273.8 to 278.3) K and pressures ranging from (4.55 to 11.57) MPa. A thermodynamic model based on van der Waals and Platteeuw (vdW–P) solid solution theory was used for prediction and comparison of hydrate dissociation conditions and the Langmuir constant parameters for CF4 based on Parrish and Prausnitz equation are reported. For the kinetics, the effect of initial pressure and temperature on the induction time, CF4 hydrate formation rate, the apparent rate constant of reaction, storage capacity, and water to hydrate conversion during the hydrate formation were studied. Kinetic experiments were performed at initial temperatures of (275.3, 276.1 and 276.6) K and initial pressures of (7.08, 7.92, 9.11, 11.47 and 11.83) MPa. Results show that increasing the initial pressure at constant temperature decreases the induction time, while CF4 hydrate formation rate, the apparent rate constant of reaction, storage capacity, and water to hydrate conversion increase. The same trends are observed with a decrease in the initial temperature at constant pressure

  9. Formation and function of vacancies in Si/Ge Clathrates: The importance of broken symmetries

    Science.gov (United States)

    Bhattacharya, Amrita; Carbogno, Christian; Scheffler, Matthias; Dr. Matthias Scheffler Team, Prof.

    2015-03-01

    One promising material class for improved thermoelectrics are the clathrates, i.e., semiconducting host lattices encapsulating guest atom. Even in simple clathrates, such as, Si46 and Ge46, the introduction of guests can result in important but not yet understood effects: In Si hosts, the addition of K (or Ba) results in defect-free K8Si46 (Ba8Si46) phases. In spite of their structural and electronic similitude, Ge hosts behave fundamentally different upon filling, where, the spontaneously formed framework vacancies completely (or partially) balance the electron donated by K (or Ba) guests leading to K8Ge44(orBa8Ge43) clathrates. In this work, we use density-functional theory, carefully validating the exchange correlation functional, to compute the formation energies of vacancies and vacancy complexes in Si- and Ge-hosts as function of the filling of guests. By taking into account of the structural disorder, geometric relaxations, and vibrational entropies, we verify the experimentally found vacancy concentration and the thermodynamic stabilities of these compounds. We can trace back the contrasting behaviour of Si/Ge clathrates upon filling to a curious, charged vacancy induced break in symmetry that occurs in Si but not in Ge hosts.

  10. Disorder of Hydrofluorocarbon Molecules Entrapped in the Water Cages of Structure I Clathrate Hydrate.

    Science.gov (United States)

    Takeya, Satoshi; Udachin, Konstantin A; Moudrakovski, Igor L; Ohmura, Ryo; Ripmeester, John A

    2016-05-23

    Water versus fluorine: Clathrate hydrates encaging hydrofluorocarbons as guests show both isotropic and anisotropic distributions within host water cages, depending on the number of fluorine atoms in the guest molecule; this is caused by changes in intermolecular interactions to host water molecules in the hydrates. PMID:27105807

  11. Crystal chemistry and thermoelectric properties of clathrates with rare-earth substitution

    International Nuclear Information System (INIS)

    Based on an analysis of the geometric crystallographic relations a general classification scheme is presented for intermetallides with four-coordinated networks isomorphous with hydrate clathrates. We prepared novel europium substituted clathrates, Eu2-x(Sr,Ba)6-xMySi46-y (M=Al, Ga), consistent with the standardized clathrate I--Ba8Al16Ge30 type structure (space group Pm3barn). Europium atoms in Ba compounds preferentially occupy the 2a position and thus form a new quaternary version of the Ba8Al16Ge30 structure type. All clathrates studied are metals with low electrical conductivity. The negative Seebeck coefficients indicate transport processes dominated by electrons as carriers. Eu2Ba6Al8Si36 and Eu2Ba6Ga8Si36 exhibit long-range magnetic order below 32 and 38 K of presumably ferromagnetic type. Magnetic susceptibilities indicate an Eu2+ ground state, in fine agreement with LIII absorption edge spectra

  12. Electric transport and magnetic investigation of the rapidly quenched clathrate Eu8Ga16Ge30

    International Nuclear Information System (INIS)

    Full text: Intermetallic clathrates have low thermal conductivities κ but high electrical conductivities σ ('phonon glass - electron crystal') which leads to a large ratio of σ/κ. The introduction of strong electronic correlations which is expected if adequate rare earth atoms are incorporated would in addition enhance the value of the thermopower S. To date the only rare earth containing clathrate is Eu8Ga16Ge30. However, it shows no sizeable interaction of 4f electrons with the conduction electrons. In our search for ways to substitute Eu with other rare earth elements we have found an unconventional synthesis procedure s. The poster of A. Prokofiev et al., 'Rapid quenching as an unconventional synthesis technique for Eu8Ga16Ge30-based clathrate phases'. The bonding situation in a clathrate Eu8Ga16Ge30 can be understood in a first approximation with the Zintl concept. Ga and Ge build a covalently bonded tetrahedrally coordinated cage structure. The guest Eu atoms are ionically bonded to the framework. The electronegative Ga and Ge receive electrons from the electropositive Eu in accordance with the octet rule. Since all valence electrons are used in local covalent bonds, one expects clathrates to be semiconducters. Here we present the results of the magnetic and electric transport investigations. The resistivity and Hall-resistivity were measured over a broad temperature range from 350 to 2 K at magnetic fields from 0 to 9 Tesla. In contrast to conventional procedures a semiconducting compound has been produced by quenching of the melt. (author)

  13. The HD molecule in small and medium cages of clathrate hydrates: Quantum dynamics studied by neutron scattering measurements and computation

    International Nuclear Information System (INIS)

    We report inelastic neutron scattering (INS) measurements on molecular hydrogen deuteride (HD) trapped in binary cubic (sII) and hexagonal (sH) clathrate hydrates, performed at low temperature using two different neutron spectrometers in order to probe both energy and momentum transfer. The INS spectra of binary clathrate samples exhibit a rich structure containing sharp bands arising from both the rotational transitions and the rattling modes of the guest molecule. For the clathrates with sII structure, there is a very good agreement with the rigorous fully quantum simulations which account for the subtle effects of the anisotropy, angular and radial, of the host cage on the HD microscopic dynamics. The sH clathrate sample presents a much greater challenge, due to the uncertainties regarding the crystal structure, which is known only for similar crystals with different promoter, but nor for HD (or H2) plus methyl tert-butyl ether (MTBE-d12)

  14. Thermoelectric and transport properties of sintered n-type K8Ba16Ga40Sn96 with type-II clathrate structure

    International Nuclear Information System (INIS)

    This clathrate had a maximum dimensionless figure-of-merit, ZT, of 0.93 at 637 K, which was slightly higher than that of 0.83 for the sintered type-VIII clathrate Ba8Ga16Sn30. We investigated the high-temperature thermoelectric properties, transport properties, electronic structures, and thermal stabilities of the clathrates. The type-II clathrate was found to be superior to the type-VIII clathrate as a thermoelectric material; it had a high thermal stability and melting point, 859 K, high mobility, 141 cm2V−1s−1 at 300 K, because of its low inertial mass, and low high-temperature lattice thermal conductivity, approximately 4 mW cm−1K−1, resulting from a larger unit cell and weaker bipolar thermal conduction. We discuss these properties in terms of the electronic structure and the differences between the two types of clathrate.

  15. Thermodynamic study of clathrates hydrates from hydrocarbon gas mixtures Consequences for capture CO2 and flow assurance

    OpenAIRE

    Bouillot, Baptiste; Le, Quang-Du; Le Quang, Duyen; Herri, Jean-Michel

    2014-01-01

    This work is a contribution to the global understanding of the coupling between kinetics and thermodynamics to explain the composition of the clathrate hydrates during their crystallization from an aqueous liquid and a hydrocarbon gas phase. In this work, we face new experimental facts that open questioning after comparing the classical modeling of clathrate hydrates following the approach of [1] with our experimental data following a new procedure allowing determining the hydrate composition...

  16. High pressure optical cell for synthesis and in situ Raman spectroscopy of hydrogen clathrate hydrates

    Science.gov (United States)

    Celli, Milva; Zoppi, Marco; Zaghloul, Mohamed A. S.; Ulivi, Lorenzo

    2012-11-01

    We report the design, realization, and test of a high-pressure optical cell that we have used to measure the Raman spectra of hydrogen clathrate hydrates, synthesized in situ by the application of 200-300 MPa of gas pressure on solid water. The optical apparatus is mounted on a cryogenic system so to allow measurements and sample treatment at any temperature between 300 and 20 K. A capillary pipe is connected to the inside of the cell to allow the gas flow into and out of the cell, and to regulate the internal pressure at any value from 0 to 300 MPa. In the experimental test described in this paper, the cell has been partly filled, at room temperature, with a small amount of water, then frozen at 263 K before injecting hydrogen gas, at pressure of 150 MPa, into the cell. This procedure has permitted to study hydrogen clathrate formation, by measuring Raman spectra as a function of time.

  17. Structural Collapse of the Hydroquinone-Formic Acid Clathrate: A Pressure-Medium-Dependent Phase Transition.

    Science.gov (United States)

    Eikeland, Espen; Thomsen, Maja K; Madsen, Solveig R; Overgaard, Jacob; Spackman, Mark A; Iversen, Bo B

    2016-03-14

    The energy landscape governing a new pressure-induced phase transition in the hydroquinone-formic acid clathrate is reported in which the host structure collapses, opening up the cavity channels within which the guest molecules migrate and order. The reversible isosymmetric phase transition causes significant changes in the morphology and the birefringence of the crystal. The subtle intermolecular interaction energies in the clathrate are quantified at varying pressures using novel model energies and energy frameworks. These calculations show that the high-pressure phase forms a more stable host network at the expense of less-stable host-guest interactions. The phase transition can be kinetically hindered using a nonhydrostatic pressure-transmitting medium, enabling the comparison of intermolecular energies in two polymorphic structures in the same pressure range. Overall this study illustrates a need for accurate intermolecular energies when analyzing self-assembly structures and supramolecular aggregates. PMID:26879515

  18. Molecular simulations and density functional theory calculations of bromine in clathrate hydrate phases

    International Nuclear Information System (INIS)

    Bromine forms a tetragonal clathrate hydrate structure (TS-I) very rarely observed in clathrate hydrates of other guest substances. The detailed structure, energetics, and dynamics of Br2 and Cl2 in TS-I and cubic structure I (CS-I) clathrate hydrates are studied in this work using molecular dynamics and quantum chemical calculations. X-ray diffraction studies show that the halogen-water–oxygen distances in the cages of these structures are shorter than the sum of the van der Waals radii of halogen and oxygen atoms. This suggests that the stabilizing effects of halogen bonding or other non-covalent interactions (NCIs) may contribute to the formation of the unique tetragonal bromine hydrate structure. We performed molecular dynamics simulations of Br2 and Cl2 clathrate hydrates using our previously developed five-site charge models for the dihalogen molecules [Dureckova et al. Can. J. Chem. 93, 864 (2015)] which reproduce the computed electrostatic potentials of the dihalogens and account for the electropositive σ-hole of the halogen bond donor (the dihalogen). Analysis of the radial distribution functions, enthalpies of encapsulation, velocity and orientation autocorrelation functions, and polar angle distributions are carried out for Br2 and Cl2 guests in various cages to contrast the properties of these guests in the TS-I and CS-I phases. Quantum chemical partial geometry optimizations of Br2 and Cl2 guests in the hydrate cages using the M06-2X functional give short halogen-water distances compatible with values observed in X-ray diffraction experiments. NCI plots of guest-cage structures are generated to qualitatively show the relative strength of the non-bonding interactions between dihalogens and water molecules. The differences between behaviors of Br2 and Cl2 guests in the hydrate cages may explain why bromine forms the unique TS-I phase

  19. Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory

    OpenAIRE

    Takabatake, Toshiro; Suekuni, Koichiro; Nakayama, Tsuneyoshi; Kaneshita, Eiji

    2014-01-01

    Type-I clathrate compounds have attracted a great deal of interest in connection with the search for efficient thermoelectric materials. These compounds constitute networked cages consisting of nano-scale tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the group 1 or 2 elements in the periodic table are encaged as the so-called rattling guest atom. It is remarkable that, though these compounds have crystalline cubic-structure, they exhibit glass-like phonon thermal c...

  20. Clathrate hydrates - the energy of the future an overview and a postulated formation mechanism

    International Nuclear Information System (INIS)

    Clathrate hydrates are non-stoichiometric compounds that form when water and certain low molecular weight hydrocarbons coexist at high pressures and low temperatures. The majority of the earth hydrocarbons are in the hydrate phase and are primarily located along the ocean bottoms and to a lesser degree in the permafrost regions. In addition, hydrate formation is induced in undersea gas transmission lines and causes costly pipeline plugs and requires expensive inhibition measures to be taken. Therefore, both a stick and a carrot motivate hydrate research. They are a costly and dangerous nuisance to the oil and gas industry and represent a tremendous, untapped energy resource of the future. The formation mechanism of clathrate hydrate formation has always been shrouded in mystery, and an ongoing debate has ensued as to whether their formation is a bulk or surface phenomenon. Molecular dynamics simulation and fractal modeling suggest that this may be an irrelevant issue and that two independent factors contribute to the symmetrical ordered structure of clathrate hydrates: hydrophobic hydration of hydrocarbon molecules in water and formation of linked cavities as these small clusters aggregate. (Author)

  1. A simple van’t Hoff law for calculating Langmuir constants in clathrate hydrates

    International Nuclear Information System (INIS)

    Highlights: • Tabulated Langmuir constants of simple gas hydrates for several molecules. • A van’t Hoff law in the 50–300 K temperature range is given for each case. • Practical form of van’t Hoff parameters for planetologists. • Fractional occupancies of guest species can be easily calculated. • An anisotropic guest-water atom–atom potential is used for numerical calculations. - Abstract: This work gives a van’t Hoff law expression of Langmuir constants of different species for determining their occupancy in clathrate hydrates. First, a pairwise site–site interaction potential energy model is used to calculate the Langmuir constants in an otherwise anisotropic potential environment, as a function of temperature. The results are then fitted to a van’t Hoff law expression to give a set of parameters that can be used for calculating clathrates compositions. The van’t Hoff law’s parameters are given for eighteen gas species trapped in the small and large cavities of structure types I and II. The accuracy of this approach is based on a detailed comparison with available experimental and/or previously calculated data for ethane, cyclo-propane, methane and carbon dioxide clathrate hydrates. A comparison with the analytical cell method is also carried out to better understand the importance of asymmetry and possible limitations of the van’t Hoff temperature dependence

  2. Calorimetric and X-ray studies of clathrate hydrates of tetraisoamylammonium polyacrylates.

    Science.gov (United States)

    Terekhova, Irina S; Manakov, Andrey Yu; Soldatov, Dmitriy V; Suwinska, Kinga; Skiba, Sergey S; Stenin, Yuri G; Villevald, Galina V; Karpova, Tamara D; Yunoshev, Alexander S

    2009-04-30

    The structure of clathrate hydrates with tetraisoamylammonium polyacrylate salt incorporated as guest has been studied in this work. Also, quantitative studies on the stability changes of the clathrate hydrates with different degrees of cross-linking of the guest polymer (varied from 0 to 3%) have been conducted. A single crystal X-ray diffraction study of a crystal of the hydrate with linear (uncross-linked) tetraisoamylammonium polyacrylate as guest reveals a hexagonal structure (space group P6m2, a = 12.15 A, c =12.58 A at 100 K) with 39 host framework water molecules per one guest monomeric unit. Powder X-ray diffraction analyses confirm the identity of the above crystal structure of the hydrate with linear guest polymer and the crystal structure of the hydrates with cross-linked guest (hexagonal, a = 12.25 A, c =12.72 A at 276 K). In order to quantitatively determine the stability differences of the hydrates with the included guests having various degrees of cross-linking of the anionic chain, a series of differential scanning calorimetry measurements of the fusion enthalpy of the hydrate samples has been carried out. On the basis of the results obtained, a structural model describing the decrease in the stability of the clathrate hydrates with tetraisoamylammonium polyacrylate guest as a function of the degree of cross-linking of the guest polymer has been suggested. PMID:19344169

  3. A spectroscopic study of the structure and occupancies of clathrate hydrates incorporating hydrogen

    Science.gov (United States)

    Grim, R. Gary

    With the ability to store and concentrate gases inside a clean and abundant water framework, clathrate hydrates are considered to be a promising material for many applications related to gas storage, separation, and sequestration. Hydrates of hydrogen are particularly interesting, for in addition to these potential applications, the small molecular size provides an opportunity for use as a model guest in many fundamental studies such as guest diffusion, multiple guest occupancy, and quantum mechanical effects upon confinement. In attempt to study these effects and the viability of H 2 hydrates as an energy storage material, a combined experimental and theoretical approach incorporating Raman spectroscopy, X-ray and neutron diffraction, nuclear magnetic resonance, ab-initio calculations, and molecular dynamic simulations was performed. One of the most significant challenges in the application of H2 clathrate hydrates is the demanding thermodynamic requirements needed for stability. In recent years, a mechanism known as the `tuning' effect had reportedly solved this issue where thermodynamic requirements could be reduced while simultaneously maintaining high storage capacities. In this work, the viability and validity of this technique is explored and alternative explanations in the form of epitaxial hydrate growth under high driving force conditions are discussed. A second, and equally important challenge facing clathrate hydrates as a future storage material is the overall storage capacity of H2. In previous work, H2 has only been experimentally verified to occupy the small 512 and 43566 3 cages and also in the large 51264 cages of the type II clathrate, often with an energy deficient promoter. In order to achieve more robust energy densities, other hydrate cages must be accessible. Herein a new method for increasing overall hydrate energy densities is presented involving the incorporation of H2 in the large cages of the type I clathrate with CH4 as a co

  4. On molecular recognition in clathrates of l,l'-binaphthyl-2,2'-dicarboxylic acid with cyclohexanone and diethyl ether

    International Nuclear Information System (INIS)

    1.1'-Binaphthyl-2.2 '-dicarboxylic acid (BNDA) host forms a conventional clathrate with cyclohexanone, in -hich the guest molecules do not use potential H-bonding possibilities. In the inclusion complex between diethyl ether and BNDA monohydrate, the guest molecules are H-bonded to water molecules avoiding a direct host-guest interaction. This mode being unusual for the formation of BNDA clathrates and indicating a failure of a molecular recognition through host-guest H-bonding is discussed. Single crystals of all clathrates were obtained by slow evaporation of the solvent from corresponding solutions at the room temperature. Intensity data were collected at the room temperature on a Syntex P2 and on an Enraf-Nonius CAD-4 diffractometer using Cu-Kα radiation

  5. A new phase diagram of water under negative pressure: The rise of the lowest-density clathrate s-III.

    Science.gov (United States)

    Huang, Yingying; Zhu, Chongqin; Wang, Lu; Cao, Xiaoxiao; Su, Yan; Jiang, Xue; Meng, Sheng; Zhao, Jijun; Zeng, Xiao Cheng

    2016-02-01

    Ice and ice clathrate are not only omnipresent across polar regions of Earth or under terrestrial oceans but also ubiquitous in the solar system such as on comets, asteroids, or icy moons of the giant planets. Depending on the surrounding environment (temperature and pressure), ice alone exhibits an exceptionally rich and complicated phase diagram with 17 known crystalline polymorphs. Water molecules also form clathrate compounds with inclusion of guest molecules, such as cubic structure I (s-I), cubic structure II (s-II), hexagonal structure H (s-H), tetragonal structure T (s-T), and tetragonal structure K (s-K). Recently, guest-free clathrate structure II (s-II), also known as ice XVI located in the negative-pressure region of the phase diagram of water, is synthesized in the laboratory and motivates scientists to reexamine other ice clathrates with low density. Using extensive Monte Carlo packing algorithm and dispersion-corrected density functional theory optimization, we predict a crystalline clathrate of cubic structure III (s-III) composed of two large icosihexahedral cavities (8(6)6(8)4(12)) and six small decahedral cavities (8(2)4(8)) per unit cell, which is dynamically stable by itself and can be fully stabilized by encapsulating an appropriate guest molecule in the large cavity. A new phase diagram of water ice with TIP4P/2005 (four-point transferable intermolecular potential/2005) model potential is constructed by considering a variety of candidate phases. The guest-free s-III clathrate with ultralow density overtakes s-II and s-H phases and emerges as the most stable ice polymorph in the pressure region below -5834 bar at 0 K and below -3411 bar at 300 K. PMID:26933681

  6. Study on clathrate formation of schaeffer's complexes with 4-methylpyridine (4-MePy) by IR-spectroscopy method

    International Nuclear Information System (INIS)

    IR-spectra of Schaeffer's complex compounds [M(4-MePy)n(NCS)2] (M-Co(2), Ni(2), Zn(2), Cd(2); n=2 or 4) and their clathrates with 4-MePy have been obtained. These data indicate of the presence both ''free'' and bonded 4-MePy in the structure of clathrates. To put in another way, the enclosing of 4-MePy in the cavities of the host framework takes place without appreciable chemical interaction between the guest and the host, and reforming of crystalline modification doesn't bring to changing of the spectrum in examined area

  7. Pressure induced amorphization and collapse of magnetic order in type-I clathrate Eu8Ga16Ge30

    OpenAIRE

    Mardegan, J. R. L.; Fabbris, G.; Veiga, L. S. I.; Adriano, C.; M.A. Avila; Haskel, D.; Giles, C.

    2013-01-01

    We investigate the low temperature structural and electronic properties of the type-I clathrate Eu8Ga16Ge30 under pressure using x-ray powder diffraction (XRD), x-ray absorption near-edge structure (XANES) and x-ray magnetic circular dichroism (XMCD) techniques. The XRD measurements reveal a transition to an amorphous phase above 18 GPa. Unlike previous reports on other clathrate compounds, no volume-collapse is observed prior to the crystalline-amorphous phase transition which takes place wh...

  8. Clathrate hydrates as a blocking of oil seepage from the broken tube in a bottom of see

    OpenAIRE

    Belosludov, Vladimir; Uchida, Tsutomu; Belosludov, Rodion; Kawazoe, Yoshiyuki

    2010-01-01

    Scheme of the oil flow shut-off by means of creation of conditions for formation of clathrate hydrates from the oil-accompanying gases, sufficient for oil outflow blocking. It contains a sphere open from below and standing on the cylinder (column) which is submerged into sea bottom enveloping top of the well with radius R larger than the diameter D (D diameter of well). The choice of the radius R is determined by requirement to obtain clathrate hydrates ('hydrate dome') sufficient for shutdow...

  9. High-Temperature Thermoelectric Properties of Polycrystalline Silicon Clathrate Ba8TM x Si46- x (TM = Ni, Pt)

    Science.gov (United States)

    Kikuchi, Daisuke; Fujimura, Koji; Tadokoro, Jun; Matsumoto, Miko; Yamazaki, Satoshi; Sasaki, Hirokazu; Eguchi, Tatsuhiko; Susai, Kyota

    2016-03-01

    The n-/ p-type stability of a silicon clathrate in which silicon was substituted with nickel or platinum was evaluated by density functional theory calculations. Then, Ba8Pt5Si41 and Ba8Pt1.5Ni3.5Si41 were synthesized, and their thermoelectric properties were investigated. The polycrystalline compounds, which have a type-I clathrate structure, were prepared through arc melting and spark-plasma-sintering. The crystal structures and elemental compositions of the synthesized samples were characterized via powder x-ray diffraction and electron microprobe analyses, respectively. The temperature dependence of both the electrical resistivity and the Seebeck coefficient was measured.

  10. Methanol incorporation in clathrate hydrates and the implications for oil and gas pipeline flow assurance and icy planetary bodies

    OpenAIRE

    Shin, Kyuchul; Udachin, Konstantin A.; Moudrakovski, Igor L.; Leek, Donald M.; Alavi, Saman; Ratcliffe, Christopher I.; Ripmeester, John A.

    2013-01-01

    One of the best-known uses of methanol is as antifreeze. Methanol is used in large quantities in industrial applications to prevent methane clathrate hydrate blockages from forming in oil and gas pipelines. Methanol is also assigned a major role as antifreeze in giving icy planetary bodies (e.g., Titan) a liquid subsurface ocean and/or an atmosphere containing significant quantities of methane. In this work, we reveal a previously unverified role for methanol as a guest in clathrate hydrate c...

  11. Catalytic activity of methanol in all-vapor subsecond clathrate-hydrate formation

    Science.gov (United States)

    Devlin, J. Paul

    2014-04-01

    Methanol's property as a catalyst in the formation of gas clathrate hydrates has been recognized for several years and was recently employed in a broad ranging study [K. Shin, K. A. Udachin, I. L. Moudrakovski, D. M. Leek, S. Alavi, C. I. Ratcliffe, and J. A. Ripmeester, Proc. Natl. Acad. Sci. U.S.A. 110, 8437 (2013)]. A new measure of that activity is offered here from comparative rates of formation of methanol (MeOH) clathrate hydrates within our all-vapor aerosol methodology for which tetrahydrofuran (THF) and other small ethers have set a standard for catalytic action. We have previously described numerous examples of the complete conversion of warm all-vapor mixtures to aerosols of gas clathrate hydrates on a sub-second time scale, generally with the catalyst confined primarily to the large cage of either structure-I (s-I) or structure-II (s-II) hydrates. THF has proven to be the most versatile catalyst for the complete subsecond conversion of water to s-II hydrate nanocrystals that follows pulsing of appropriate warm vapor mixtures into a cold chamber held in the 140-220 K range. Here, the comparative ability of MeOH to catalyze the formation of s-I hydrates in the presence of a small-cage help-gas, CO2 or acetylene, is examined. The surprising result is that, in the presence of either help gas, CH-formation rates appear largely unchanged by a complete replacement of THF by MeOH in the vapor mixtures for a chamber temperature of 170 K. However, as that temperature is increased, the dependence of effective catalysis by MeOH on the partial pressure of help gases also increases. Nevertheless, added MeOH is shown to markedly accelerate the s-II THF-CO2 CH formation rate at 220 K.

  12. Molecular simulations and density functional theory calculations of bromine in clathrate hydrate phases

    Energy Technology Data Exchange (ETDEWEB)

    Dureckova, Hana, E-mail: houci059@uottawa.ca; Woo, Tom K., E-mail: tom.woo@uottawa.ca [Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario K1N 5N6 (Canada); Alavi, Saman, E-mail: saman.alavi@nrc-cnrc.gc.ca [Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario K1N 5N6 (Canada); National Research Council of Canada, 100 Sussex Dr., Ottawa, Ontario K1N 6N5 (Canada); Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z3 (Canada)

    2016-01-28

    Bromine forms a tetragonal clathrate hydrate structure (TS-I) very rarely observed in clathrate hydrates of other guest substances. The detailed structure, energetics, and dynamics of Br{sub 2} and Cl{sub 2} in TS-I and cubic structure I (CS-I) clathrate hydrates are studied in this work using molecular dynamics and quantum chemical calculations. X-ray diffraction studies show that the halogen-water–oxygen distances in the cages of these structures are shorter than the sum of the van der Waals radii of halogen and oxygen atoms. This suggests that the stabilizing effects of halogen bonding or other non-covalent interactions (NCIs) may contribute to the formation of the unique tetragonal bromine hydrate structure. We performed molecular dynamics simulations of Br{sub 2} and Cl{sub 2} clathrate hydrates using our previously developed five-site charge models for the dihalogen molecules [Dureckova et al. Can. J. Chem. 93, 864 (2015)] which reproduce the computed electrostatic potentials of the dihalogens and account for the electropositive σ-hole of the halogen bond donor (the dihalogen). Analysis of the radial distribution functions, enthalpies of encapsulation, velocity and orientation autocorrelation functions, and polar angle distributions are carried out for Br{sub 2} and Cl{sub 2} guests in various cages to contrast the properties of these guests in the TS-I and CS-I phases. Quantum chemical partial geometry optimizations of Br{sub 2} and Cl{sub 2} guests in the hydrate cages using the M06-2X functional give short halogen-water distances compatible with values observed in X-ray diffraction experiments. NCI plots of guest-cage structures are generated to qualitatively show the relative strength of the non-bonding interactions between dihalogens and water molecules. The differences between behaviors of Br{sub 2} and Cl{sub 2} guests in the hydrate cages may explain why bromine forms the unique TS-I phase.

  13. Lattice dynamics study of low energy guest-host coupling in clathrate hydrate

    Institute of Scientific and Technical Information of China (English)

    Yang Yue-Hai; Dong Shun-Le; Wang Lin

    2008-01-01

    Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band (below 15 meV) and yield correct relative intensity.Based on the results,the uncertain profile at ~6 meV is assigned to anharmonic guest modes coupled strongly to small cages.Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for guest-host coupling that explains the anomalous thermal conductivity of clathrate hydrate.

  14. Adsorption sites and rotational tunneling of methyl groups in cubic I methyl fluoride water clathrate

    OpenAIRE

    Prager, M.; Baumert, J.; Press, W.; Plazanet, M.; J. S. Tse; Klug, D. D.

    2005-01-01

    Neutron spectroscopy in the mueV and meV regime and quasielastic scattering is applied to characterize the dynamics of methyl groups of methyl fluoride guest molecules in cubic I CH3F - water clathrate. Only above T similar to 60 K quasielastic spectra are unaffected by quantum effects. They are well described by two Lorentzians representing the CH3F species in the small and large cages of the structure. The intensities show that both cages are completely filled. The linear broadenings with t...

  15. In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy

    Science.gov (United States)

    Day, Sarah J.; Thompson, Stephen P.; Evans, Aneurin; Parker, Julia E.

    2015-02-01

    Context. Clathrate hydrates are believed to play a significant role in various solar system environments, e.g. comets, and the surfaces and interiors of icy satellites. However, the structural factors governing their formation and dissociation are poorly understood. Aims: We demonstrate the application of a high pressure gas cell, combined with variable temperature non-contact cooling and fast, time-resolved data collection, to the in situ study of clathrate hydrates under conditions relevant to solar system environments. Methods: Clathrates formed and processed within the sample cell are monitored in situ using time-resolved synchrotron X-ray powder diffraction and laser Raman spectroscopy. Results: X-ray diffraction allows the formation of clathrate hydrates to be observed as CO2 gas is applied to ice formed within the cell. Complete conversion is obtained by annealing at temperatures just below the ice melting point. A subsequent rise in the quantity of clathrate is observed as the cell is thermally cycled. Four regions between 100-5000 cm-1 are present in the in situ Raman spectra that carry features characteristic of both ice and clathrate formation. Conclusions: This novel experimental arrangement is well suited to studying clathrate hydrates over a wide range of temperature (80 -500 K) and pressure (1-100 bar) conditions relevant to solar system bodies and can be used with a variety of different gases and starting aqueous compositions (e.g. saline solutions). We propose the increase in clathrate formation observed during thermal cycling may be due to the formation of a quasi liquid-like phase that forms at temperatures below the ice melting point, but which allows either easier formation of new clathrate cages, or the retention and delocalisation of previously formed clathrate structures, possibly as amorphous clathrate. The structural similarities between hexagonal ice, the quasi liquid-like phase, and crystalline CO2 hydrate mean that differences in the

  16. Preparation and thermoelectric properties of sintered type-I clathrates K8Ga(x)Sn(46-x).

    Science.gov (United States)

    Hayashi, Masahiro; Kishimoto, Kengo; Kishio, Kazuma; Akai, Koji; Asada, Hironori; Koyanagi, Tsuyoshi

    2010-01-28

    Polycrystalline clathrate samples of nominal K(8)Ga(x)Sn(46-x) were prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K(8)Ga(8)Sn(38) sample was 25 cm(2) V(-1) s(-1), which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates. Moreover, the mobility was larger than those of the type-I Ba(8)Ga(16)Sn(30), which had more Ga substituting atoms in unit cell. A higher mobility might accordingly be achieved in thermoelectric clathrates with a smaller number of substituting atoms. Their electrical conductivities and Seebeck coefficients in the temperature range 300-450 K were typical of n-type doped semiconductors in the extrinsic region while their room-temperature lattice thermal conductivities were as low as approximately 11 mW cm(-1) K(-1). The maximum dimensionless figure of merit ZT was estimated to be 0.27 at 490 K from the Seebeck coefficient of -262 microV K(-1) and the electrical conductivity of 96 S cm(-1) for the K(8)Ga(8)Sn(38) sample with a carrier concentration of 2.9 x 10(19) cm(-3). PMID:20066199

  17. The presence of clathrates in comet 67P/Churyumov-Gerasimenko

    Science.gov (United States)

    Luspay-Kuti, A.; Mousis, O.; Hässig, M.; Fuselier, S. A.; Lunine, J. I.; Marty, B.; Mandt, K. E.; Wurz, P.; Rubin, M.

    2016-04-01

    Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument onboard Rosetta provide insight into the possible origin of this comet. The observed outgassing pattern indicates that the nucleus of 67P contains crystalline ice, clathrates, and other ices. The observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. If the building blocks of 67P were formed from crystalline ices and clathrates, then 67P would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the Sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate.

  18. The presence of clathrates in comet 67P/Churyumov-Gerasimenko

    Science.gov (United States)

    Luspay-Kuti, Adrienn; Mousis, Olivier; Hässig, Myrtha; Fuselier, Stephen A.; Lunine, Jonathan I.; Marty, Bernard; Mandt, Kathleen E.; Wurz, Peter; Rubin, Martin

    2016-01-01

    Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument onboard Rosetta provide insight into the possible origin of this comet. The observed outgassing pattern indicates that the nucleus of 67P contains crystalline ice, clathrates, and other ices. The observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. If the building blocks of 67P were formed from crystalline ices and clathrates, then 67P would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the Sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate. PMID:27152351

  19. The presence of clathrates in comet 67P/Churyumov-Gerasimenko.

    Science.gov (United States)

    Luspay-Kuti, Adrienn; Mousis, Olivier; Hässig, Myrtha; Fuselier, Stephen A; Lunine, Jonathan I; Marty, Bernard; Mandt, Kathleen E; Wurz, Peter; Rubin, Martin

    2016-04-01

    Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument onboard Rosetta provide insight into the possible origin of this comet. The observed outgassing pattern indicates that the nucleus of 67P contains crystalline ice, clathrates, and other ices. The observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. If the building blocks of 67P were formed from crystalline ices and clathrates, then 67P would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the Sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate. PMID:27152351

  20. Thermodynamic modeling of phase equilibria of semi-clathrate hydrates of CO2, CH4, or N2+tetra-n-butylammonium bromide aqueous solution

    DEFF Research Database (Denmark)

    Eslamimanesh, Ali; Mohammadi, Amir H.; Richon, Dominique

    2012-01-01

    Prediction of phase equilibria of semi-clathrate hydrates has been very rarely investigated in the literature. In this work, a thermodynamic model is proposed for representation/prediction of phase equilibria of semi-clathrate hydrates of the CO2, CH4, or N2+tetra-n-butylammonium bromide (TBAB) a...... agreement with the experimental semi-clathrate hydrate dissociation data investigated in this work....

  1. Quadrupole order in clathrate compound Pr3Pd20Si6

    International Nuclear Information System (INIS)

    In order to investigate ordered phases revealed at low temperatures in clathrate compound Pr3Pd20Si6, we have performed ultrasonic measurements using a single crystal in magnetic fields at low temperatures. Temperature dependence of elastic constant C11 and CL[11-bar0] = (C11 + C12 + 2C44)/2 shows the anomalies at about 150 mK in zero field. Magnetic phase diagrams are determined by measuring C11 in H || [001] and CL[l1-bar0] in H || [111]. The magnetic phase diagrams along the three principal axes indicate a closed loop and a strong magnetic anisotropy. This result suggests that antiferroquadrupole ordering appears at low temperatures in Pr3Pd20Si6.

  2. Clathrate formation of gossypol: The structure of the complex of gossypol with tropolone

    International Nuclear Information System (INIS)

    The clathrate of gossypol with tropolone is prepared for the first time and studied by X-ray diffraction. The structure is determined and refined using 7307 reflections (Siemens SMART/CCD diffractometer). The crystals are monoclinic, C30H30O8 · 2C7H6O2 , a = 35.5892(1) A, b 12.8893(2) A, c = 18.5910(2) A, β = 118.54(3) deg., Z = 8, space group C2/c, and R = 0.058. Each gossypol molecule is linked to two tropolone molecules through hydrogen bonds. The host (gossypol) and guest (tropolone) molecules form separate bilayers that are parallel to the bc plane and alternate along the a-axis

  3. Analytical Cell Potentials for Clathrate-Hydrates from Inversion of Langmuir Constant Versus Temperature Curves

    CERN Document Server

    Bazant, M Z; Bazant, Martin Z.; Trout, Bernhardt L.

    2000-01-01

    Experimental Langmuir constants for clathrate-hydrates, which are inferred from phase equilibrium data using an equation of state and the statistical thermodynamical model of van der Waals and Platteeuw (vdWP), contain a wealth of information about intermolecular forces. In the simplest (Lennard-Jones and Devonshire) approximation of a spherical cell, the Langmuir constant is related to a configurational integral involving a spherically averaged cell potential. All previous attempts to interpret experimental data based on this formalism have involved numerical fitting with ad hoc functional forms, such as the popular Kihara potential. In addition to lacking analytical insight, however, such empirical fits often produce parameters contradicting those obtained by other means. As a more appealing alternative, the spherical-cell vdWP formula for the Langmuir constant versus temperature can be viewed as a nonlinear integral equation for the cell potential. In this article, a variety of exact analytical solutions a...

  4. Modeling and Ab initio Calculations of Thermal Transport in Si-Based Clathrates and Solar Perovskites

    Science.gov (United States)

    He, Yuping

    2015-03-01

    We present calculations of the thermal transport coefficients of Si-based clathrates and solar perovskites, as obtained from ab initio calculations and models, where all input parameters derived from first principles. We elucidated the physical mechanisms responsible for the measured low thermal conductivity in Si-based clatherates and predicted their electronic properties and mobilities, which were later confirmed experimentally. We also predicted that by appropriately tuning the carrier concentration, the thermoelectric figure of merit of Sn and Pb based perovskites may reach values ranging between 1 and 2, which could possibly be further increased by optimizing the lattice thermal conductivity through engineering perovskite superlattices. Work done in collaboration with Prof. G. Galli, and supported by DOE/BES Grant No. DE-FG0206ER46262.

  5. Thermodynamic promotion of carbon dioxide-clathrate hydrate formation by tetrahydrofuran, cyclopentane and their mixtures

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Thomsen, Kaj; Abildskov, Jens;

    2013-01-01

    Gas clathrate hydrate dissociation pressures are reported for mixtures of carbon dioxide, water and thermodynamic promoters forming structure II hydrates.Hydrate (H)-aqueous liquid (Lw)-vapour (V) equilibrium pressures for the ternary system composed of water, tetrahydrofuran (THF), and carbon......) equilibrium data are presented for the ternary system of water-cyclopentane-carbon dioxide at temperatures ranging from 285.2K down to 275.5K.New four-phase H-Lw-La-V equilibrium data for the quaternary system water-THF-cyclopentane-carbon dioxide are presented in the temperature range from 275.1K to 286.6K....... It is shown that upon adding THF to the pure aqueous phase to form a 4mass percent solution, the equilibrium pressure of the formed hydrates may be lowered compared to the ternary system of water, cyclopentane and carbon dioxide. © 2013 Elsevier Ltd....

  6. Synthesis of hydrogen-carbon clathrate material and hydrogen evolution therefrom at moderate temperatures and pressures

    Science.gov (United States)

    Lueking, Angela; Narayanan, Deepa

    2011-03-08

    A process for making a hydrogenated carbon material is provided which includes forming a mixture of a carbon source, particularly a carbonaceous material, and a hydrogen source. The mixture is reacted under reaction conditions such that hydrogen is generated and/or released from the hydrogen source, an amorphous diamond-like carbon is formed, and at least a portion of the generated and/or released hydrogen associates with the amorphous diamond-like carbon, thereby forming a hydrogenated carbon material. A hydrogenated carbon material including a hydrogen carbon clathrate is characterized by evolution of molecular hydrogen at room temperature at atmospheric pressure in particular embodiments of methods and compositions according to the present invention.

  7. Thermoelectric properties of sintered type-II clathrates (K, Ba)24(Ga, Sn)136 with various carrier concentrations

    Science.gov (United States)

    Kishimoto, Kengo; Koda, Shota; Akai, Koji; Koyanagi, Tsuyoshi

    2015-09-01

    We reported the thermoelectric properties of the sintered type-II clathrate K8Ba16Ga40Sn96 in a previous paper [S. Koda et al., J. Appl. Phys. 116, 023710 (2014)]. The clathrate had a high dimensionless figure of merit ZT, namely, 0.93. In this study, we optimized the carrier concentration n by modifying the chemical compositions of (K, Ba)24(Ga, Sn)136 samples, and heat treated the sintered samples. The carrier mobilities μ were improved because of the reduction in potential barrier scattering at grain boundaries. The room-temperature (RT) n values varied from 7.7 × 1017 to 3.7 × 1019 cm-3; the maximum RT μ value was 170 cm2V-1s-1. Consequently, we obtained a high ZT value of 1.19 at 630 K for n = 2.5 × 1019 cm-3. This material therefore has good thermoelectric properties.

  8. Preparation and characterization of planetary ball milled Si-based clathrates and their spark plasma sintered materials

    Science.gov (United States)

    Shirataki, R.; Hokazono, M.; Nakabayashi, T.; Anno, H.

    2011-05-01

    Ba8Ga16Si30 clathrate particles ranging in size from several tens nanometers to submicron have been prepared by a planetary ball milling technique, and their sintered materials with microstructures have been prepared by a spark plasma sintering (SPS) technique. Relatively low temperature, short time and high pressure conditions of SPS are needed for the densification without the decomposition and/or the oxidation of clathrate phase. In comparison with Ba8Ga16Si30 prepared by SPS of micro powders, Ba8Ga16Si30 prepared by SPS of pulverized powders shows relatively large Seebeck coefficient about -100 μV/K at middle temperature range, low thermal diffusivity as low as 0.6 mm2/s (RT) and extremely low electrical conductivity of the orders of 0.1 - 1 S/cm (RT), due probably to the increased scattering at the interfaces and pores in the microstructures.

  9. Études thermodynamiques sur les Semi-Clathrate Hydrates de TBAB + gaz contenant du Dioxyde de Carbone

    OpenAIRE

    Eslamimanesh, Ali

    2012-01-01

    CO2 capture has become an important area of research mainly due to its drastic green-house effects. Gas hydrate formation as a separation technique shows tremendous potential, both from a physical feasibility as well as an envisaged lower energy utilization criterion. Briefly, gas (clathrate) hydrates are non-stoichiometric, ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s) under low-temperatures and elevated pressures. As the pressure r...

  10. Influence of process variables of ball milling and hot pressing on the thermoelectric performance of type I clathrates

    International Nuclear Information System (INIS)

    Full text: To achieve a high thermoelectric performance, materials with a low lattice thermal conductivity are needed. One promising method to reduce the lattice thermal conductivity is to use nanostructured materials. In this study, we prepare nanopowders of type I clathrates by the ball milling technique, and compact them by hot pressing. The relation between the process variables for ball milling and hot pressing, the microstructures and thermoelectric properties of the final hot pressed samples will be presented. (author)

  11. Cross-nucleation between clathrate hydrate polymorphs: Assessing the role of stability, growth rate, and structure matching

    International Nuclear Information System (INIS)

    Cross-nucleation is a phenomenon where a new crystal nucleates and grows upon the surface of a different polymorph. Previous studies indicate that faster growth rate of the new crystal is a necessary but not sufficient condition for cross-nucleation. The thermodynamic stability of the different polymorphs can also affect cross-nucleation by modulating the rates of crystal growth. The interplay between thermodynamic stability of the polymorphs involved, the growth rate of the crystals, and the need for creation of an interfacial transition layer that seamlessly connects the two structures has not yet been fully elucidated. Predicting cross-nucleation is particularly challenging for clathrate hydrates, for which there are sometimes several polymorphs with similar stability and for which growth rates are not known. In this work, we use molecular dynamics simulations to investigate which factor (stability, growth rate, or formation of interfacial transition layer) controls cross-nucleation between the four known Frank-Kasper clathrate hydrate polymorphs: sI, sII, TS, and HS-I. We investigate the growth and cross-nucleation of these four hydrates filled with a set of guest molecules that produce different order of stabilities for the four crystal structures. We determine that the growth rate of sII clathrate is the fastest, followed by TS, HS-I, and sI. We find that cross-nucleation into or from sII clathrates is preceded by the formation of an interfacial transition layer at the seed crystal/liquid interface because sII does not share a crystal plane with sI, HS-I, or TS. Cross-nucleation between the latter three can occur seamlessly and is determined only by their growth rates. Our results indicate that nucleation of an interfacial transition layer between non-matching polymorphs can control cross-nucleation or lack thereof under conditions of small driving force. Under conditions of sufficient supercooling clathrate hydrate polymorphs cross-nucleate into the fastest

  12. Effects of Water in Synthetic Lubricant Systems and Clathrate Formation: A Literature Search and Review

    Energy Technology Data Exchange (ETDEWEB)

    Rohatgi, Ngoc Dung T.

    2001-08-08

    An extensive literature search and a confidential survey were critically analyzed to determine the effects of water on the stability of hydrofluorocarbon/synthetic lubricant systems and to identify key areas requiring further investigation. Following are highlights from the analysis: Clathrate hydrates are solid solutions formed when water molecules are linked through hydrogen bonding creating cavities that can enclose various guest molecules from hydrate formers, such as hydrofluorocarbons R-32, R-125, R-134a, R-407C and R-410A. The four methods for preventing clathrate formation were drying the gas, heating it, reducing its pressure, or using inhibitors. The hydrolysis of polyolester lubricants was mostly acid-catalyzed and its reaction rate constant typically followed the Arrhenius equation of an activated process. Hydrolytic stability improved with hindered molecular structures, and with the presence of acid catcher additives and desiccants. Water vapor can effect the adsorption of long-chain fatty acids and the chemistry of formation of protective oxide film. However, these effects on lubrication can be either positive or negative. Fifty to sixty percent of the moisture injected into an air-conditioning system remained in the refrigerant and the rest mixed with the compressor oil. In an automotive air-conditioning system using R-134a, ice would form at 0 C evaporating temperature when the water content in the vapor refrigerant on the low-pressure side was more than 350 ppm. Moisture would cause the embrittlement of polyethylene terephthalate and the hydrolysis of polyesters, but would reduce the effect of amine additives on fluoroelastomer rubbers. The reactions of water with refrigerants and lubricants would cause formicary and large-pit corrosion in copper tubes, as well as copper plating and sludge formation. Moreover, blockage of capillary tubes increased rapidly in the presence of water. Twenty-four companies responded to the survey. From the responses

  13. In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy

    CERN Document Server

    Day, Sarah J; Evans, Aneurin; Parker, Julia E

    2015-01-01

    Clathrate hydrates are believed to play a significant role in various solar system environments, e.g. comets, and the surfaces and interiors of icy satellites, however the structural factors governing their formation and dissociation are poorly understood. We demonstrate the use of a high pressure gas cell, combined with variable temperature cooling and time-resolved data collection, to the in situ study of clathrate hydrates under conditions relevant to solar system environments. Clathrates formed and processed within the cell are monitored in situ using synchrotron X-ray powder diffraction and Raman spectroscopy. X-ray diffraction allows the formation of clathrate hydrates to be observed as CO2 gas is applied to ice formed within the cell. Complete conversion is obtained by annealing at temperatures just below the ice melting point. A subsequent rise in the quantity of clathrate is observed as the cell is thermally cycled. Four regions between 100-5000cm-1 are present in the Raman spectra that carry feature...

  14. Phase equilibrium measurements for semi-clathrate hydrates of the (CO2 + N2 + tetra-n-butylammonium bromide) aqueous solution system

    International Nuclear Information System (INIS)

    Highlights: ► Semi-clathrate hydrate phase equilibrium for CO2+N2+TBAB aqueous solutions. ► Measurements for temperatures from 277.1 K to 293.2 K and pressures up to 16.21 MPa. ► TBAB has a promotion effect on semi-clathrate hydrate formation. - Abstract: The application of semi-clathrate hydrate formation technology for gas separation purposes has gained much attention in recent years. Consequently, there is a demand for experimental data for relevant semi-clathrate hydrate phase equilibria. In this work, semi-clathrate hydrate dissociation conditions for the system comprising mixtures of {CO2 (0.151/0.399 mole fraction) + N2 (0.849/0.601 mole fraction) + 0.05, 0.15, and 0.30 mass fraction tetra-n-butylammonium bromide (TBAB)} aqueous solutions have been measured and are reported. An experimental apparatus which was designed and built in-house was used for the measurements using the isochoric pressure-search method. The range of conditions for the measurements was from 277.1 K to 293.2 K for temperature and pressures up to 16.21 MPa. The phase equilibrium data measured demonstrate the high hydrate promotion effects of TBAB aqueous solutions.

  15. Captage du dioxyde de carbone par cristallisation de clathrate hydrate en présence de cyclopentane : Etude thermodynamique et cinétique

    OpenAIRE

    Galfré, Aurélie

    2014-01-01

    Le CO2 est capté par formation de clathrates hydrates sous l'action d'un promoteur de cristallisation thermodynamique. Les clathrates hydrates sont des composés d'inclusion non stœchiométriques formés de molécules d'eau organisées en réseau de cavités piégeant des molécules de gaz. Ce procédé de captage consiste à piéger de façon sélective le dioxyde de carbone dans les cavités des clathrates hydrates et à le séparer ainsi des autres gaz. Les hydrates mixtes de cyclopentane (CP) + gaz ont été...

  16. Synthesis of polyphenylacetylene by radiation-induced polymerization in deoxycholic acid clathrate

    International Nuclear Information System (INIS)

    Phenylacetylene was polymerized as inclusion compound (clathrate) inside deoxycholic acid (DOCA) crystals. The polymerization was initiated by γ radiation and a total dose of 320 kGy was employed. The resulting polyphenylacetylene (PPA) was isolated by dissolution of deoxycholic acid in boiling ethanol. PPA high polymer was accompanied by a series of phenylacetylene oligomers, which were detected by liquid chromatographic analysis (HPLC). PPA was characterized by electronic absorption spectroscopy and by FT-IR spectroscopy in comparison to a reference PPA prepared by a stereospecific catalyst. The microstructure of PPA from inclusion polymerization was highly trans type, similar to that observed on PPA prepared by bulk radiolysis. No optical activity was detected by polarimetry on PPA prepared by inclusion polymerization. The host-guest complex PPA/DOCA was studied by differential thermal analysis (DTA) and by thermogravimetry (TGA). DTA provided evidences of the host-guest complex formation from the shift of the melting point of DOCA while the TGA confirmed the identity - in terms of thermal behaviour - of the PPA from inclusion polymerization with that from stereospecific polymerization

  17. NMR study of Ba8Cu5Si(x)Ge(41-x) clathrate semiconductors.

    Science.gov (United States)

    Sirusi, Ali A; Ross, Joseph H; Yan, Xinlin; Paschen, Silke

    2015-07-14

    We have performed (63)Cu, (65)Cu, and (137)Ba NMR on Ba8Cu5SixGe41-x, a series of intermetallic clathrates known for their potential as thermoelectric materials, in order to investigate the electronic behavior of the samples. The spectra and spin-lattice relaxation times were measured at 77 K and 290 K for the entire composition range 0 ≤ x ≤ 41. Magnetic and quadrupole shifts and relaxation rates of the Cu NMR data were extracted, and thereby carrier-induced metallic contributions identified. The observed shifts change in a nonlinear way with increasing Si substitution: from x = 0 to about 20 the shifts are essentially constant, while approaching x = 41 they increase rapidly. At the same time, Ba NMR data indicate greater Ba-site participation in the conduction band in Ba8Cu5Si41 than in Ba8Cu5Ge41. The results indicate surprisingly little change in electronic features vs. Si content for most of the composition range, while Ba8Cu5Si41 exhibits enhanced hybridization and a more metallic framework than Ba8Cu5Ge41. PMID:26063217

  18. NMR and computational study of Ba8CuxGe46-x clathrate semiconductors

    International Nuclear Information System (INIS)

    Highlights: • Quadrupole NMR with first-principles calculations probes local site preferences. • Cu/Ge ratio is clarified vs. the ideal Zintl composition. • Modified Becke–Johnson exchange potential agrees well with NMR Knight shifts. - Abstract: Ba8CuxGe46-x is a type-I clathrate material that forms as a semiconductor in a narrow composition range corresponding to the electron-balanced Zintl composition, with x = 5.3. We use NMR spectroscopy combined with ab initio electronic structure calculations to probe the electronic and structural behavior of these materials. Computational results based on a superstructure model for the atomic configuration of the alloy provide good agreement with the electric quadrupole-broadened NMR lineshapes. Modeling using the modified Becke–Johnson (TB-mBJ) exchange potential is also shown to agree well with experimental NMR Knight shifts. The results indicate that the Cu–Ge balance is the main factor determining the carrier density, within a narrow stability range near the ideal Zintl composition

  19. Synthesis, Transport and Magnetic Properties of Ba-Co-Ge Clathrates

    Science.gov (United States)

    Sirusi, Ali A.; Ross, Joseph H.

    2016-02-01

    Ba-Co-Ge intermetallic clathrates were synthesized in both type-I and chiral-type crystal structures to investigate thermoelectric and physical properties. Seebeck coefficients, thermal conductivities, electrical resistivities, and Hall coefficients were measured, as well as specific heat and magnetic susceptibility. Type-I Ba8Co x Ge46- y was formed with a large number of spontaneous vacancies, similar to a Zintl condition, but without the vacancy ordered superstructure of Ba8Ge43. However, the vacancies for this composition do not moderate the carrier density as expected from Zintl electron balancing. Instead, the physical properties point to a complex Fermi surface property with a large effective carrier density, a behavior consistent with other materials close to Ba8Ge43. In the case of chiral samples, Co substitution strongly suppresses the temperature of only the lower of the two structural transformations. Susceptibility and specific heat measurements, coupled with the measured transport properties, demonstrate that the electron densities of states near the Fermi energy change very little in the transformations, a significant reduction in the effect of these transitions compared to the case of unsubstituted Ba8Ge25.

  20. Connecting the Rheological Behavior of Clathrate Hydrate Slurries to Flow Performance

    Science.gov (United States)

    Geri, Michela; Venkatesan, Rama; McKinley, Gareth; MIT Team; Chevron ETC Team

    2014-11-01

    Clathrate hydrates represent a major flow assurance issue for deep water drilling operations. To develop a proper constitutive model, an extensive set of rheological measurements has been performed on a model hydrate forming emulsion. Upon hydrate formation a sharp increase in the fluid viscosity is observed (by a factor of 100 to 1000). Steady shear measurements show that the hydrate slurry has a shear thinning behavior as well as a yield stress on the order of 1-10 Pa which increases with aging of the fluid. Thixotropy becomes evident as a hysteretic behavior in the flow curve, even when no rheological aging has occurred. Creep tests also reveal that the fluid microstructure accumulates back stress. Oscillatory measurements show that in the linear viscoelastic region hydrate slurries develop viscoelastic gel-like behavior with the elastic modulus exceeding the viscous modulus. These characteristics guide the development of an elastoviscoplastic constitutive model that can capture the salient dynamic features in simple unidirectional flows (e.g. steady or transient Poiseuille) such as apparent wall slip, plug flow or excessive pressure drop in start-up flow.

  1. Hydrate-phobic surfaces: fundamental studies in clathrate hydrate adhesion reduction.

    Science.gov (United States)

    Smith, J David; Meuler, Adam J; Bralower, Harrison L; Venkatesan, Rama; Subramanian, Sivakumar; Cohen, Robert E; McKinley, Gareth H; Varanasi, Kripa K

    2012-05-01

    Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation. Systematic and quantitative studies of hydrate adhesion on smooth substrates with varying solid surface energies reveal a linear trend between hydrate adhesion strength and the practical work of adhesion (γ(total)[1 + cos θ(rec)]) of a suitable probe liquid, that is, one with similar surface energy properties to those of the hydrate. A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations. PMID:22441203

  2. Clathrate Sequestration: State-of-the-Art Review and New Technical Approaches

    Directory of Open Access Journals (Sweden)

    Annick Nago

    2011-01-01

    Full Text Available This paper focuses on reviewing the currently available solutions for natural gas production from methane hydrate deposits using CO2 sequestration. Methane hydrates are ice-like materials, which form at low temperature and high pressure and are located in permafrost areas and oceanic environments. They represent a huge hydrocarbon resource, which could supply the entire world for centuries. Fossil-fuel-based energy is still a major source of carbon dioxide emissions which contribute greatly to the issue of global warming and climate change. Geological sequestration of carbon dioxide appears as the safest and most stable way to reduce such emissions for it involves the trapping of CO2 into hydrocarbon reservoirs and aquifers. Indeed, CO2 can also be sequestered as hydrates while helping dissociate the in situ methane hydrates. The studies presented here investigate the molecular exchange between CO2 and CH4 that occurs when methane hydrates are exposed to CO2, thus generating the release of natural gas and the trapping of carbon dioxide as gas clathrate. These projects include laboratory studies on the synthesis, thermodynamics, phase equilibrium, kinetics, cage occupancy, and the methane recovery potential of the mixed CO2–CH4 hydrate. An experimental and numerical evaluation of the effect of porous media on the gas exchange is described. Finally, a few field studies on the potential of this new gas hydrate recovery technique are presented.

  3. Weak interactions between water and clathrate-forming gases at low pressures

    Energy Technology Data Exchange (ETDEWEB)

    Thurmer, Konrad; Yuan, Chunqing; Kimmel, Gregory A.; Kay, Bruce D.; Smith, R. Scott

    2015-11-01

    Using scanning probe microscopy and temperature programed desorption we examined the interaction between water and two common clathrate-forming gases, methane and isobutane, at low temperature and low pressure. Water co-deposited with up to 10-1 mbar methane or 10-5 mbar isobutane at 140 K onto a Pt(111) substrate yielded pure crystalline ice, i.e., the exposure to up to ~107 gas molecules for each deposited water molecule did not have any detectable effect on the growing films. Exposing metastable, less than 2 molecular layers thick, water films to 10-5 mbar methane does not alter their morphology, suggesting that the presence of the Pt(111) surface is not a strong driver for hydrate formation. This weak water-gas interaction at low pressures is supported by our thermal desorption measurements from amorphous solid water and crystalline ice where 1 ML of methane desorbs near ~43 K and isobutane desorbs near ~100 K. Similar desorption temperatures were observed for desorption from amorphous solid water.

  4. Constraints on sea to air emissions from methane clathrates in the vicinity of Svalbard

    Science.gov (United States)

    Pisso, Ignacio; Vadakkepuliyambatta, Sunil; Platt, Stephen Matthew; Eckhardt, Sabine; Allen, Grant; Pitt, Joseph; Silyakova, Anna; Hermansen, Ove; Schmidbauer, Norbert; Mienert, Jurgen; Myhre, Cathrine Lund; Stohl, Andreas

    2016-04-01

    Methane stored in the seabed in the form of clathrates has the potential to be released into the atmosphere due to ongoing ocean warming. The Methane Emissions from Arctic Ocean to Atmosphere (MOCA, http://moca.nilu.no/) proje sct conducted measurement campaigns in the vicinity of Svalbard during the summers of 2014 and 2015 in collaboration with the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE, https://cage.uit.no/) and the MAMM (https://arcticmethane.wordpress.com) project . The extensive set of measurements includes air (BAe 146) and ship (RV Helmer Hansen) borne methane concentrations, complemented with the nearby monitoring site at Zeppelin mountain. In order to assess the atmospheric impact of emissions from seabed methane hydrates, we characterised the local and long range atmospheric transport during the aircraft campaign and different scenarios for the emission sources. We present a range of upper bounds for the CH4 emissions during the campaign period as well as the methodologies used to obtain them. The methodologies include a box model, Lagrangian transport and elementary inverse modelling. We emphasise the analysis of the aircraft data. We discuss in detail the different methodologies used for determining the upper flux bounds as well as its uncertainties and limitations. The additional information provided by the ship and station observations will be briefly mentioned.

  5. Clathrates [MPy4(NCO)2]·2Py (M=M(2)=Mn, Fe, Co, Ni, Cu, Zn, Cd; Py=pyridine)

    International Nuclear Information System (INIS)

    Investigation of addition products of six pyridine molecule to cyanates of metals M(OCN)2·6Py (M=Mn, Fe, Co, Ni, Cu, Zn, Cd; Py=pyridine) is conducted. Compounds investigated form isostructural series and are isomorphous to other clathrates [MPy4X2]·2Py. Coordination polyhedron is slightly distorted due to difference in bond lengths. Conformation of the molecule is propeller-type. Guest molecules are arranged in in hollows of crystal structure in accordance with Van-der-Waals type of packing. Thermal decomposition of cadmium clathrate in dependence on conditions is derived in one stage up to host complex or with host dissociation

  6. Ab initio computational study on the lattice thermal conductivity of Zintl clathrates [Si$_{19}$P$_{4}$]Cl$_{4}$ and Na$_{4}$[Al$_{4}$Si$_{19}$

    OpenAIRE

    Härkönen, Ville J.; Karttunen, Antti J.

    2016-01-01

    The lattice thermal conductivity of silicon clathrate framework Si$_{23}$ and two Zintl clathrates, [Si$_{19}$P$_{4}$]Cl$_{4}$ and Na$_{4}$[Al$_{4}$Si$_{19}$], is investigated by using an iterative solution of the linearized Boltzmann transport equation (BTE) in conjuntion with ab initio lattice dynamical techniques. At 300 K, the lattice thermal conductivities for Si$_{23}$, [Si$_{19}$P$_{4}$]Cl$_{4}$, and Na$_{4}$[Al$_{4}$Si$_{19}$] were found to be 43 W/(m K), 25 W/(m K), and 2 W/(m K), re...

  7. Low-temperature structure and lattice dynamics of the thermoelectric clathrate Sn24P19.3I8

    International Nuclear Information System (INIS)

    Highlights: ► Sn24P19.3I8 retains the crystal structure of the type-I clathrate even at 10 K. ► Two Einstein and one Debye terms describe the lattice dynamics of Sn24P19.3I8. ► The thermal conductivity for Sn24P19.3I8 is almost entirely phononic. - Abstract: The crystal structure of the thermoelectric clathrate Sn24P19.3I8 was determined down to 10 K showing no variations with the temperature. Even at 10 K Sn24P19.3I8 crystallizes in the type-I clathrate structure, space group Pm3-n, with the cubic unit cell parameter ranging from 10.9173 Å at 10 K to 10.9554 Å at room temperature. In its crystal structure, tin and phosphorus atoms form the framework that traps the guest iodine atoms in the polyhedral cavities of two different shapes. The temperature-dependent crystal structure data and the results of the heat capacity measurements revealed the localized vibrations of the guest atoms inside the oversized cavities with the characteristic Einstein temperatures of θE1 = 60 K and θE2 = 78 K, whereas the characteristic Debye temperature for Sn24P19.3I8 is 265 K. The room temperature lattice thermal conductivity was calculated using the Debye model to be κL = 0.85 W m−1 K−1, which is in excellent agreement with the experimentally measured data and demonstrates that the thermal conductivity is almost entirely phononic.

  8. Anomalously low thermal conductivity and thermoelectric properties of new cationic clathrates in the Sn-In-As-I system

    International Nuclear Information System (INIS)

    Single-crystal samples of cationic clathrates in the Sn-In-As-I system with different indium contents have been synthesized. Their crystal structure has been analyzed and their thermoelectric properties have been measured. These compounds are found to be n-type semiconductors with high absolute values of the Seebeck coefficient (S = 400–600 μV/K) and anomalously low thermal conductivity (κ ≤ 0.4 W/(m/K) at 300 K, which is characteristic of amorphous materials. The reasons for the anomalously low thermal conductivity of these semiconductors are discussed and ways for optimizing their thermoelectric properties are shown.

  9. The effect of stirring on the heterogeneous nucleation of water and of clathrates of tetrahydrofuran/water mixtures

    Directory of Open Access Journals (Sweden)

    P.W. Wilson

    2016-03-01

    Full Text Available The statistics of liquid-to-crystal nucleation are measured for both water and for clathrate-forming mixtures of tetrahydrofuran (THF and water using an automatic lag time apparatus (ALTA. We measure the nucleation temperature using this apparatus in which a single sample is repeatedly cooled, nucleated and thawed. The effect of stirring on nucleation has been evaluated numerically and is discussed. We find that stirring of the solution makes no difference to the nucleation temperature of a given solution in a given tube.

  10. Hydrogen storage and carbon dioxide sequestration in TBAF semi-clathrate hydrates: Kinetics and evolution of hydrate-phase composition by in situ raman spectroscopy - Abstract -

    NARCIS (Netherlands)

    Torres Trueba, A.; Radoviæ, I.R.; Zevenbergen, J.F.; Kroon, M.C.; Peters, C.J.

    2012-01-01

    Carbon dioxide (CO2) represents almost one third of the emissions from the combustion of fossil fuels additionally, CO2 has been identified as the mayor contributor of global warming. Hydrogen (H2), on the other hand, due to its properties is considered a promising energy carrier. Clathrate hydrates

  11. Competing quantum effects in the free energy profiles and diffusion rates of hydrogen and deuterium molecules through clathrate hydrates

    CERN Document Server

    Cendagorta, Joseph R; Hele, Timothy J H; Marsalek, Ondrej; Bačić, Zlatko; Tuckerman, Mark E

    2016-01-01

    Clathrate hydrates hold considerable promise as safe and economical materials for hydrogen storage. Here we present a quantum mechanical study of H$_2$ and D$_2$ diffusion through a hexagonal face shared by two large cages of clathrate hydrates over a wide range of temperatures. Path integral molecular dynamics simulations are used to compute the free-energy profiles for the diffusion of H$_2$ and D$_2$ as a function of temperature. Ring polymer molecular dynamics rate theory, incorporating both exact quantum statistics and approximate quantum dynamical effects, is utilized in the calculations of the H$_2$ and D$_2$ diffusion rates in a broad temperature interval. We find that the shape of the quantum free-energy profiles and their height relative to the classical free energy barriers at a given temperature, as well as the rate of diffusion, are profoundly affected by competing quantum effects: above 25 K, zero-point energy (ZPE) perpendicular to the reaction path for diffusion between cavities decreases the ...

  12. Experimental measurement and thermodynamic modelling of phase equilibria of semi-clathrate hydrates of (CO2 + tetra-n-butyl-ammonium bromide) aqueous solution

    International Nuclear Information System (INIS)

    Highlights: • Hydrate phase equilibrium data are reported for the CO2 + TBAB aqueous solutions systems. • A thermodynamic model is developed to predict the dissociation conditions of the latter systems. • The properties of the aqueous phase are calculated using the AMSA-NRTL electrolyte model. • The model satisfactorily predicts the experimental data with an AARD% of approximately 13%. - Abstract: Comprehensive studies on semi-clathrate hydrates phase equilibria are still required to better understand characteristics of this type of clathrates. In this communication, new experimental data on the dissociation conditions of semi-clathrate hydrates of {carbon dioxide + tetra-n-butyl-ammonium bromide (TBAB)} aqueous solution are first reported in a wide range of TBAB concentrations and at different pressures and temperatures. A thermodynamic model is then proposed to predict the dissociation conditions of the semi-clathrate hydrates for the latter system. The (hydrate + TBAB) aqueous solution (H + Lw) phase equilibrium prediction is considered based on Gibbs free energy minimization approach. A modified van der Waals–Platteeuw solid solution theory developed based on the (H + Lw) equilibrium information is employed to predict the dissociation conditions of semi-clathrate hydrates of carbon dioxide + TBAB. The properties of the aqueous solution are estimated using the AMSA-NRTL electrolyte model (considering the association and hydration of ions). The Peng–Robinson equation of state is used for estimating the gas/vapour phase properties. Results show that the proposed model satisfactorily predicts the experimental values with an average absolute relative deviation of approximately 13%

  13. Gas hydrates and clathrates. Flow assurance, environmental and economic perspectives and the Nigerian liquefied natural gas project

    International Nuclear Information System (INIS)

    Gas hydrates are nonstoichiometric crystalline compounds that belong to the inclusion group known as clathrates. They occur when water molecules attach themselves together through hydrogen bonding and form cavities which can be occupied by a single gas or volatile liquid molecule. Gas hydrates, asphaltenes and waxes are three major threats to flow assurance that must be well assessed by design team uptime. Gas hydrates are also looked upon as a future energy source and as a potential climate hazard. The purpose of this review is to show the chemistry and mechanism of gas hydrate formation, the problems they pose, especially to flow assurance, their system implications, their environmental and economic perspectives with respect to their prospects as storage and transport alternative to the liquefied natural gas technology. (author)

  14. Observations of CO{sub 2} clathrate hydrate formation and dissolution under deep-ocean disposal conditions

    Energy Technology Data Exchange (ETDEWEB)

    Warzinski, R.P.; Cugini, A.V. [Department of Energy, Pittsburgh, PA (United States); Holder, G.D. [Univ. of Pittsburgh, Pittsburgh, PA (United States)

    1995-11-01

    Disposal of anthropogenic emissions of CO{sub 2} may be required to mitigate rises in atmospheric levels of this greenhouse gas if other measures are ineffective and the worst global warming scenarios begin to occur. Long-term storage of large quantities of CO{sub 2} has been proposed, but the feasibility of large land and ocean disposal options remains to be established. Determining the fate of liquid CO{sub 2} injected into the ocean at depths greater than 500 m is complicated by uncertainties associated with the physical behavior of CO{sub 2} under these conditions, in particular the possible formation of the ice-like CO{sub 2} clathrate hydrate. Resolving this issue is key to establishing the technical feasibility of this option. Experimental and theoretical work in this area is reported.

  15. Calculations of NMR properties for sI and sII clathrate hydrates of carbon dioxide

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • We studied the influence of a type of clathrate hydrate cage on NMR parameters of the encaged CO2. • The interaction-induced shifts of σ(17O) of CO2 form a decreasing trend from 512 through 51262 and 51264 to monomeric one. • We observed a correlation of the 1hJOH transmitted through H-bonds H⋯O with the strength of H-bonds. - Abstract: Nuclear shielding and spin–spin coupling constants (intra- and intermolecular) have been calculated for cages forming sI and sII clathrate hydrates of carbon dioxide (for all atoms of host and guest molecules). Structures of 512, 51262 and 51264 cages have been constructed using neutronographic data and DFT/B3LYP calculations conducted with HuzIII-su3 basis set for NMR parameters determination. Based on those results it is possible to discriminate between CO2 molecules residing in each type of the cage. The analysis of NMR parameters calculated for water molecules is focused on their dependence on geometry of the molecular environment. It is possible to connect changes in NMR parameters with types of H-bond patterns present in cages of hydrates and the strength of H-bonds formed. Moreover, our results show that topologically differentiable water molecules forming cages are characterized by distinct NMR parameters, for example 17O shielding constants for water molecules of different topologies differ by 1.6 and 2.1 ppm for cages 51262 and 51264, respectively. This observation could be confirmed experimentally

  16. The Location of the CO2, Fundamental in Clathrate Hydrates and its Application to Infrared Spectra of Icy Solar System Objects

    Science.gov (United States)

    Sandford, S. A.; Mastrapa, R. M. E.; Bernstein, M. P.; Cruikshank, D. P.

    2006-01-01

    CO2 is present on the surface of many Solar System objects, but not always as a segregated, pure ice. In pure CO2-ice, the fundamental absorption is located near 4.268 micron (2343.3 wavenumbers). However, on several objects, the CO2 fundamental is shifted to higher frequency. This shift may be produced by CO2 gas trapped in another material, or adsorbed onto minerals. We have seen that a mixture of H2O, CH3OH4 and CO2 forms a type II clathrate when heated to 125 K and produces a CO2 fundamental near 4.26 micron. The exact location of the feature is strongly dependent on the initial ratio of the three components. We are currently exploring various starting ratios relevant to the Solar System to determine the minimum amount of CH3OH needed to convert all of the CO2 to the clathrate, i.e. eliminate the splitting of the CO2 fundamental. We are testing the stability of the clathrate to thermal processing and UV photolysis, and documenting the changes seen in the spectra in the wavelength range from 1-5 micron. We acknowledge financial support from the Origins of Solar Systems Program, the Planetary Geology and Geophysics and the NASA Postdoctoral Program.

  17. Critical magnetic fields of superconducting aluminum-substituted Ba{sub 8}Si{sub 42}Al{sub 4} clathrate

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yang, E-mail: yang.li@upr.edu; Garcia, Jose; Lu, Kejie; Shafiq, Basir [School of Engineering, University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico 00681-9000 (United States); Franco, Giovanni; Lu, Junqiang [Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico 00681 (United States); Rong, Bo [Communications Research Centre (CRC), Industry Canada, 3701 Carling Avenue, Box 11490, Station H, Ottawa, Ontario K2H 8S2 (Canada); Chen, Ning; Liu, Yang [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Lihua; Song, Bensheng; Wei, Yuping [Department of Physics, University of Science and Technology Beijing, Beijing 100083 (China); Johnson, Shardai S.; Luo, Zhiping [Department of Chemistry and Physics, Fayetteville State University, Fayetteville, North Carolina 28301 (United States); Feng, Zhaosheng [Department of Mathematics, University of Texas-Pan American, Edinburg, Texas 78541 (United States)

    2015-06-07

    In recent years, efforts have been made to explore the superconductivity of clathrates containing crystalline frameworks of group-IV elements. The superconducting silicon clathrate is unusual in that the structure is dominated by strong sp{sup 3} covalent bonds between silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. This paper reports on critical magnetic fields of superconducting Al-substituted silicon clathrates, which were investigated by transport, ac susceptibility, and dc magnetization measurements in magnetic fields up to 90 kOe. For the sample Ba{sub 8}Si{sub 42}Al{sub 4}, the critical magnetic fields were measured to be H{sub C1} = 40.2 Oe and H{sub C2} = 66.4 kOe. The London penetration depth of 4360 Å and the coherence length 70 Å were obtained, whereas the estimated Ginzburg–Landau parameter of κ = 62 revealed that Ba{sub 8}Si{sub 42}Al{sub 4} is a strong type-II superconductor.

  18. Prediction of a large number of electron pockets near the band edges in type-VIII clathrate Si46 and its physical properties from first principles.

    Science.gov (United States)

    Norouzzadeh, Payam; Myles, Charles W; Vashaee, Daryoosh

    2013-11-27

    The material design of type-VIII clathrate Si46 is presented based on first principles. The structural, electronic, elastic, vibrational, and thermodynamic properties of this hypothetical material are presented. Our results predict that type-VIII clathrate Si46 is an indirect semiconductor with a bandgap of 1.24 eV. The band structure revealed an interestingly large number of electron pockets near both conduction and valance band edges. Such a large density of states near the band edges, which is higher than that of the best thermoelectric materials discovered so far, can result in a large thermoelectric power factor (>0.004 W m(-1) K(-2)) making it a promising candidate for thermoelectric applications. The elastic properties as well as the vibrational modes and the phonon state densities of this material were also calculated. Our calculations predict that the heat capacity at constant volume (isochoric) of this clathrate increases smoothly with temperature and approaches the Dulong-Petit value near room temperature. The electronic band structure shows a large number of valleys closely packed around the valance band edge, which is rare among the known semiconducting materials. These valleys can contribute to transport at high temperature resulting in a possibly high performance (ZT > 1.5) p-type thermoelectric material. PMID:24172765

  19. Influence of Sn-substitution on the thermoelectric properties of the clathrate type-I, Ba8Zn(x)Ge(46-x-y)Sn(y).

    Science.gov (United States)

    Falmbigl, Matthias; Grytsiv, Andriy; Rogl, Peter; Yan, Xinlin; Royanian, Esmaeil; Bauer, Ernst

    2013-02-28

    A systematic investigation is presented on the influence of Sn-substitution in the clathrate-I compound Ba(8)Zn(x)Ge(46-x-y)Sn(y), particularly for the crystal structure and thermoelectric properties including electrical resistivity, Seebeck coefficient, and thermal conductivity. Two series of samples were prepared to explore the changes for different Sn-contents, (y), and to define the optimum Zn-content, (x), for Ba(8)Zn(x)Ge(46-x-y)Sn(y). Sn-incorporation leads to a linear expansion of the unit cell parameters. Sn-atoms occupy the 6d and 24k positions of the clathrate type-I structure (SG Pm3n, standardized setting). Whereas the electrical resistivity and the Seebeck coefficient modify only slightly compared to Ba(8)Zn(x)Ge(46-x), the thermal conductivity is significantly decreased by the Sn-atoms incorporated into the clathrate-I framework. Furthermore the charge carrier mobility is larger and the effective mass (m* = 1.7 m(e)) is much smaller than those of the ternary compound Ba(8)Zn(x)Ge(46-x). The maximum thermoelectric figure of merit is improved by 80% and reaches ZT = 0.82 at 850 K for Ba(8)Zn(7.66)Ge(36.55)Sn(1.79). PMID:23243666

  20. Theoretical Study of the Properties of the Type II Clathrate A^xSn^136, (A = alkali atom; 0 <= x <= 24)

    Science.gov (United States)

    Xue, Dong; Higgins, Craig; Myles, Charley

    2012-10-01

    Motivated by recent experimental and theoretical interest in the x dependence of the properties of the Si and Ge-based Type II clathrate materials A^xSi^136 and A^xGe^136 (A = alkali atom) [1,2] we are carrying out a systematic theoretical study of the properties of the Sn-based Type II clathrate system A^xSn^136. Type II clathrates have cage-like lattices in which Si, Ge, or Sn atoms are tetrahedrally-coordinated and sp3 covalently bonded. The cages can contain ``guests''; usually alkali or alkaline earth atoms. These materials are particularly interesting because of their potential use as thermoelectrics. Recent powder X-ray diffraction experiments have found the very interesting result that, for increasing x in the range 0 10.1021/cg200756r[0pt] [2] M. Beekman, E. Nenghabi, K. Biswas, C. Myles, M. Baitinger, Y. Grin, G.S. Nolas, Inorg. Chem. 49 2010, DOI: 10.1021/ic1005049

  1. Intra-cage dynamics of molecular hydrogen confined in cages of two different dimensions of clathrate hydrates

    Science.gov (United States)

    Russina, Margarita; Kemner, Ewout; Mezei, Ferenc

    2016-01-01

    In porous materials the molecular confinement is often realized by means of weak Van der Waals interactions between the molecule and the pore surface. The understanding of the mechanism of such interactions is important for a number of applications. In order to establish the role of the confinement size we have studied the microscopic dynamics of molecular hydrogen stored in the nanocages of clathrate hydrates of two different dimensions. We have found that by varying the size of the pore the diffusive mobility of confined hydrogen can be modified in both directions, i.e. reduced or enhanced compared to that in the bulk solid at the same temperatures. In the small cages with a mean crystallographic radius of 3.95 Å the confinement reduces diffusive mobility by orders of magnitude. In contrast, in large cages with a mean radius of 4.75 Å hydrogen molecules displays diffusive jump motion between different equilibrium sites inside the cages, visible at temperatures where bulk H2 is solid. The localization of H2 molecules observed in small cages can promote improved functional properties valuable for hydrogen storage applications. PMID:27270444

  2. Structural, elastic, and electronic properties of sodium atoms encapsulated type-I silicon-clathrate compound under high pressure

    Science.gov (United States)

    Zhang, Wei; Chen, Qing-Yun; Zeng, Zhao-Yi; Cai, Ling-Cang

    2015-10-01

    We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound (Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus, Young’s modulus, Debye temperature, sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46. Project supported by National Natural Science Foundation of China (Grant Nos. 11347134 and 11304254) and the Doctor Foundation of Southwest University of Science and Technology, China (Grant No. 13zx7125).

  3. Phase equilibrium condition measurements in nitrogen and air clathrate hydrate forming systems at temperatures below freezing point of water

    International Nuclear Information System (INIS)

    Highlights: • Phase equilibrium conditions in the nitrogen and modelled air hydrate forming systems are measured. • Measurements are conducted at temperatures below the freezing point of water. • Results have relevance to the air hydrate formation in the ice sheets. • Measured data are quantitatively compared with the previously reported values. • Range of the equilibrium measurements was from (242 to 268) K. -- Abstract: Contained in this paper are the three phase equilibrium conditions of the (ice + clathrate hydrate + guest-rich) vapour in the (nitrogen + water) and the modelled (air + water) systems at temperatures below the freezing point of water. The precise determination of the equilibrium conditions in those systems are of importance for the analysis of the past climate change using the cored samples from the ice sheets at Antarctica and Greenland because the air hydrates keep the ancient climate signals. The mole ratio of the modelled air composed of nitrogen and oxygen is 0.790:0.210. The equilibrium conditions were measured by the batch, isochoric procedure. The temperature range of the measurements in the nitrogen hydrate forming system is (244.05 < T < 266.55) K and the corresponding equilibrium pressure range is (7.151 < p < 12.613) MPa. The temperature range of the measurements in the modelled air hydrate forming system is (242.55 < T < 267.85) K, and the corresponding equilibrium pressure range is (6.294 < p < 12.144) MPa. The data obtained quantitatively compared with the previously reported data

  4. Structural, elastic, and electronic properties of sodium atoms encapsulated type-I silicon-clathrate compound under high pressure

    Institute of Scientific and Technical Information of China (English)

    张伟; 陈青云; 曾召益; 蔡灵仓

    2015-01-01

    We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon–clathrate compound (Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus ,Young’s modulus, Debye temperature, sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.

  5. Intra-cage dynamics of molecular hydrogen confined in cages of two different dimensions of clathrate hydrates

    Science.gov (United States)

    Russina, Margarita; Kemner, Ewout; Mezei, Ferenc

    2016-06-01

    In porous materials the molecular confinement is often realized by means of weak Van der Waals interactions between the molecule and the pore surface. The understanding of the mechanism of such interactions is important for a number of applications. In order to establish the role of the confinement size we have studied the microscopic dynamics of molecular hydrogen stored in the nanocages of clathrate hydrates of two different dimensions. We have found that by varying the size of the pore the diffusive mobility of confined hydrogen can be modified in both directions, i.e. reduced or enhanced compared to that in the bulk solid at the same temperatures. In the small cages with a mean crystallographic radius of 3.95 Å the confinement reduces diffusive mobility by orders of magnitude. In contrast, in large cages with a mean radius of 4.75 Å hydrogen molecules displays diffusive jump motion between different equilibrium sites inside the cages, visible at temperatures where bulk H2 is solid. The localization of H2 molecules observed in small cages can promote improved functional properties valuable for hydrogen storage applications.

  6. High-pressure studies on a new superconducting clathrate: Ba sub 6 Ge sub 2 sub 5

    CERN Document Server

    Yuan, H Q; Carrillo-Cabrera, W; Paschen, S; Sparn, G; Baenitz, M; Grin, Y; Steglich, F

    2002-01-01

    The effect of pressure on the low-temperature states of the newly discovered clathrate Ba sub 6 Ge sub 2 sub 5 is investigated by means of measurements of the electrical resistivity. At ambient pressure, Ba sub 6 Ge sub 2 sub 5 undergoes a two-step structural phase transition between 230 and 180 K from metallic behaviour to a high-resistivity state characterized by a mean free path of about 3 A. Interestingly, a Bardeen-Cooper-Schrieffer-like (BCS-like) superconducting transition occurs at T sub C approx 0.24 K from the resulting 'bad metal'. With increasing pressure, the structural phase transition is depressed but T sub C increases drastically. T sub C reaches a maximum value of 3.85 K at the critical pressure p sub C approx 2.8 GPa, where the structural distortion is completely suppressed and the system exhibits metallic behaviour. Higher pressures lead to a slight decrease of T sub C.

  7. Atomic ordering and thermoelectric properties of the n-type clathrate Ba8Ni3.5Ge42.1square0.4.

    Science.gov (United States)

    Nguyen, L T K; Aydemir, U; Baitinger, M; Bauer, E; Borrmann, H; Burkhardt, U; Custers, J; Haghighirad, A; Höfler, R; Luther, K D; Ritter, F; Assmus, W; Grin, Yu; Paschen, S

    2010-01-28

    Single crystals of the type-I clathrate Ba(8)Ni(3.5)Ge(42.1)square(0.4) (space group Pm3n, no. 223, a = 10.798(2) A, l = 30 mm, slashed circle = 8 mm) were grown from the melt using the Bridgman technique. Their composition, determined by microprobe analysis, reveals a distinctly lower Ni content than previously reported for the lower limit (x = 5.4) of the homogeneity range of the clathrate-I phase Ba(8)Ni(x)Ge(46-x). From single crystal X-ray diffraction data we introduce a crystal structure model that takes point defects (vacancies) square in the Ge network into account. It reveals that both Ni and square accumulate at a single site (6c) and that, as a consequence, the Ge network distorts considerably. Ba(8)Ni(3.5)Ge(42.1)square(0.4) shows metal-like behaviour (drho/dT > 0) albeit with high resistivity at room temperature (rho(300 K) approximately 1 mOmega cm). Together with the low charge carrier concentration of 2.3 e(-)/unit cell at 300 K this is typical of a degenerate semiconductor. The lattice thermal conductivity is distinctly smaller than that of Ba(8)Ge(43)square(3), where the vacancies partially order, and smaller than those of Ba-Ni-Ge type-I clathrates without vacancies, suggesting that disordered vacancies efficiently scatter heat-transporting phonons. We provide evidence that the maximum value of the thermoelectric figure of merit reached in Ba(8)Ni(3.5)Ge(42.1)square(0.4), ZT(680 K) congruent with 0.21, can be further improved by adjusting the charge carrier concentration. PMID:20066193

  8. Precursor routes to quaternary intermetallics: Synthesis, crystal structure, and physical properties of clathrate-II Cs8Na16Al24Si112

    Science.gov (United States)

    Wei, Kaya; Dong, Yongkwan; Nolas, George S.

    2016-05-01

    A new quaternary clathrate-II composition, Cs8Na16Al24Si112, was synthesized by kinetically controlled thermal decomposition (KCTD) employing both NaSi and NaAlSi as the precursors and CsCl as a reactive flux. The crystal structure and composition of Cs8Na16Al24Si112 were investigated using both Rietveld refinement and elemental analysis, and the temperature dependent transport properties were investigated. Our results indicate that KCTD with multiple precursors is an effective method for the synthesis of multinary inorganic phases that are not easily accessible by traditional solid-state synthesis or crystal growth techniques.

  9. Crystallization of tetra-n-butyl ammonium bromide clathrate hydrate slurry and the related heat transfer characteristics

    International Nuclear Information System (INIS)

    Highlights: • Crystallization characteristics of TBAB CHS under different thermal conditions were clarified. • Overall heat transfer coefficients before and during the crystallization were obtained. • The crystallization characteristics of TBAB CHS mainly depend on the status of supercooled solution. • Dropping of TBAB CHS can accelerate the supercooling release and crystallization. - Abstract: Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is a promising phase change material slurry for cold storage and transport in air-conditioning system. This slurry can be generated from the supercooled TBAB aqueous solution. In the present study, TBAB CHS was generated under different thermal conditions, i.e. different initial mass concentrations of TBAB aqueous solution and different supercooling degrees. The crystallization of TBAB CHS and the overall heat transfer coefficient under different thermal conditions were clarified. It was concluded that the crystallization characteristics of TBAB hydrate crystals mainly depended upon the thermal condition of the supercooled TBAB aqueous solution. In addition, the dropping of pre-produced TBAB CHS into supercooled TBAB aqueous solution could immediately induce the crystallization of TBAB hydrate crystals, and the initial type of TBAB hydrate crystals was only related to the status of the supercooled TBAB aqueous solution regardless of the type of the dropped TBAB CHS. Furthermore, the overall heat transfer coefficients before crystallization and during crystallization were also measured. It was found that more hydrate crystals would adhere to the vessel wall at larger supercooling degree and higher mass concentration of aqueous solution, which would deteriorate the heat transfer significantly. Moreover, images of TBAB hydrate crystals under different thermal conditions were recorded in order to help clarifying the crystallization characteristics

  10. Pre-combustion capture of carbon dioxide in a fixed bed reactor using the clathrate hydrate process

    International Nuclear Information System (INIS)

    Hydrate based gas separation (HBGS) process with silica sand and silica gel as contact medium was employed to capture CO2 from fuel gas mixture. Gas uptake measurement at three different pressures (7.5, 8.5 and 9.0 MPa) and 274.15 K were conducted for hydrate formation kinetics and overall conversion of water to hydrate, rate of hydrate formation were determined. Water conversion of up to 36% was achieved with silica sand bed compared to 13% conversion in the silica gel bed. Effect of driving force on the rate of hydrate formation and gas consumption was significant in silica sand bed whereas it was found to be insignificant in silica gel bed. Hydrate dissociation experiments by thermal stimulation (at constant pressure) alone and a combination of depressurization and thermal stimulation were carried out for complete recovery of the hydrated gas. A driving force of 23 K was found to be sufficient to recover all the hydrated gas within 1 h. This study indicates that silica sand can be an effective porous media for separation of CO2 from fuel gas when compared to silica gel. - Highlights: ► The clathrate process for pre-combustion capture of carbon dioxide in a novel fixed bed reactor is presented. ► Performance of two contact media (silica gel and silica sand) was investigated. ► Water to hydrate conversion was higher in a silica sand column. ► A pressure reduction and thermal stimulation approach is presented for a complete recovery of the hydrated gas

  11. Lithium-ion induced conformational change of 5,17-bis(9-fluorenyl)-25,26,27,28-tetrapropoxy calix[4]arene resulting in an egg-shaped dimeric clathrate

    DEFF Research Database (Denmark)

    Faldt, A.; Krebs, Frederik C; Jørgensen, Mikkel

    2000-01-01

    Synthesis and structural investigation of a 5,17-bis(9-fluorenyl)-25,26,27,28-tetrapropoxy calix[4]arene and its lithium complex salt that forms a dimeric clathrate with a molecule of solvent inside a cavity. At least three different interactions were identified as being responsible for the...

  12. Enhanced Selectivity of the Separation of CO2 from N2 during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions

    Directory of Open Access Journals (Sweden)

    Herri J.-M.

    2014-09-01

    Full Text Available CO2 mitigation is crucial environmental problem and a societal challenge for this century. CO2 capture and sequestration is a route to solve a part of the problem, especially for the industries in which the gases to be treated are well localized. CO2 capture by using hydrate is a process in which the cost of the separation is due to compression of gases to reach the gas hydrate formation conditions. Under pressure, the water and gas forms a solid that encapsulates preferentially CO2. The gas hydrate formation requires high pressures and low temperatures, which explains the use of thermodynamic promoters to decrease the operative pressure. Quaternary ammoniums salts represent an interesting family of components because of their thermodynamic effect, but also because they can generate crystals that are easily handled. In this work, we have made experiments concerning the equilibrium of (CO2, N2 in presence of Tetra-n-Butyl Ammonium Bromide (TBAB which form a semi-clathrate hydrate. We propose equilibrium data (pressure, temperature in presence of TBAB at different concentrations and we compare them to the literature. We have also measured the composition of the hydrate phase in equilibrium with the gas phase at different CO2 concentrations. We observe that the selectivity of the separation is dramatically increased in comparison to the selectivity of the pure water gas clathrate hydrate. We observe also a benefice on the operative pressure which can be dropped down to the atmospheric pressure.

  13. Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure

    Directory of Open Access Journals (Sweden)

    Wei Zhang

    2016-07-01

    Full Text Available For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K8Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K8Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K8Si46 under different temperature and pressure were also predicted.

  14. Synthesis and Characterization of Novel Copper(II 2D Coordination Polymers from a Fluorinated Flexible Ligand with Remarkable Clathration Ability

    Directory of Open Access Journals (Sweden)

    Kayoko Kasai

    2011-11-01

    Full Text Available Two-dimensional (2D grid coordination polymers were prepared by the reaction of 1,4-bis(4-pyridylmethyltetrafluorobenzene (bpf with Cu(NO32 in the presence of aromatic compounds. Crystal structures of {[Cu(bpf2(NO32]·(biphenyl2}n (1, {[Cu(bpf2(NO32]·(m-C6H4(OMe22}n (2, {[Cu(bpf2(NO32]·PhtBu}n (3 and {[Cu(bpf2(NO3(H2O]NO3·(bpf0.5}n (4 were determined. The grid networks were held together by C–H···O and C–H···F hydrogen bonds via the NO3− anions and the tetrafluorophenylene rings of bpf, respectively. Biphenyl, m-dimethoxybenzene, t-butylbenzene, and bpf molecules were clathrated in cyclic cavities of the grid networks through arene-perfluoroarene interactions. These coordination networks have remarkable clathration ability for aromatic compounds.

  15. Suggestions for Mitigation of Methane Clathrate Destabilization Along Continental Slopes Offshore and Discrimination Between Fossil and Recent Methane in the Atmosphere with Remote Sensing

    Science.gov (United States)

    Vincent, R. K.; Vincent, R. A.

    2010-12-01

    When a hydrocarbon-rich stratum intersects the outer edge of a continental shelf, at the continental slope, methane clathrates act as a partially impermeable barrier that prevents their easy escape at the end of the “layer cake” of continental sediments. If the clathrates on the continental slope melt because of rising sea bottom temperatures, hydrocarbons (natural gas and oil) can escape into the ocean, and finally into the atmosphere in the case of methane. A mitigation method is discussed that would drill vertically into the continental shelf, then horizontally toward the continental slope, and resulting production of oil and gas would reduce the pressure and the amount of methane escape to the ocean and the atmosphere. Remote sensing for lower tropospheric methane plumes will be needed to determine where drilling is needed, as well as to assess the effects of mitigation in reducing methane escape. A remote sensing method employing carbon isotopic ratios is proposed for discriminating fossil methane in natural gas from recent methane produced by decaying organic material. This is important because recent methane is recycled over decadal time frames and does not add greatly to global warming, whereas fossil methane releases carbon that has been sequestered for millions of years and is a principal cause of increased carbon dioxide in the atmosphere and its concomitant global warming.

  16. Homo- and heterovalent substitutions in the new clathrates I Si30P16Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x): synthesis, crystal structure, and thermoelectric properties.

    Science.gov (United States)

    Abramchuk, Nikolay S; Carrillo-Cabrera, Wilder; Veremchuk, Igor; Oeschler, Niels; Olenev, Andrei V; Prots, Yurii; Burkhardt, Ulrich; Dikarev, Evgeny V; Grin, Juri; Shevelkov, Andrei V

    2012-11-01

    The new cationic clathrates I Si(30)P(16)Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x) were synthesized by the standard ampule technique. The Si(30)P(16)Te(8-x)Se(x) (x = 0-2.3) clathrates crystallize in the cubic space group Pm3̅n with the unit cell parameter a ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si(30+x)P(16-x)Te(8-x)Br(x) (x = 1-6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (x = 1-3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group Pm3n to Pm3. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10(-6) to 1.0 × 10(-5) K(-1) in the temperature range of 298-1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of p-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (ZT = 0.1) was achieved for the Br-bearing clathrate Si(32.1(2))P(13.9(2))Te(6.6(2))Br(1.0(1)) at 750 K. PMID:23072375

  17. Chemical and Thermoelectric Properties of Hot Pressed and Spark Plasma Sintered Type-I Clathrate Ba8Cu4.8Si41.2

    Science.gov (United States)

    Yan, X.; Populoh, S.; Weidenkaff, A.; Rogl, P.; Paschen, S.

    2016-03-01

    Nanostructuring has been considered as an effective way to reduce the thermal conductivity and enhance the thermoelectric performance in different material systems. Here, we present the chemical and thermoelectric properties of the nanostructured bulk type-I clathrate Ba8Cu4.8Si41.2. The samples were prepared by consolidating ball-milled nanopowders either by hot pressing or by spark plasma sintering. Fine powders and high sintering temperatures are needed to reach a high bulk density and high thermoelectric performance in the sintered samples. The highest ZT of 0.3 at 870 K is achieved in the most dense sample sintered at 800°C by hot pressing. Further improvement is expected if smaller grain sizes could be stabilized.

  18. Synthesis, structure, and transport properties of type-I derived clathrate Ge(46-x)P(x)Se(8-y) (x = 15.4(1); y = 0-2.65) with diverse host-guest bonding.

    Science.gov (United States)

    Kirsanova, Maria A; Mori, Takao; Maruyama, Satofumi; Matveeva, Maria; Batuk, Dmitry; Abakumov, Artem M; Gerasimenko, Andrei V; Olenev, Andrei V; Grin, Yuri; Shevelkov, Andrei V

    2013-01-18

    A first clathrate compound with selenium guest atoms, [Ge(46-x)P(x)]Se(8-y)□(y) (x = 15.4(1); y = 0-2.65; □ denotes a vacancy), was synthesized as a single-phase and structurally characterized. It crystallizes in the space group Fm3 with the unit cell parameter a varying from 20.310(2) to 20.406(2) Å and corresponding to a 2 × 2 × 2 supercell of a usual clathrate-I structure. The superstructure is formed due to the symmetrical arrangement of the three-bonded framework atoms appearing as a result of the framework transformation of the parent clathrate-I structure. Selenium guest atoms occupy two types of polyhedral cages inside the positively charged framework; all selenium atoms in the larger cages form a single covalent bond with the framework atoms, relating the title compounds to a scanty family of semiclathrates. According to the measurements of electrical resistivity and Seebeck coefficient, [Ge(46-x)P(x)]Se(8-y)□(y) is an n-type semiconductor with E(g) = 0.41 eV for x = 15.4(1) and y = 0; it demonstrates the maximal thermoelectric power factor of 2.3 × 10(-5) W K(-2) m(-1) at 660 K. PMID:23276305

  19. Genesis and geometry of the Meiklejohn Peak lime mud-mound, Bare Mountain Quadrangle, Nevada, USA: Ordovician limestone with submarine frost heave structures—a possible response to gas clathrate hydrate evolution

    Science.gov (United States)

    Krause, Federico F.

    2001-12-01

    . Zebra banded rocks are also accompanied by snout and socket structures and, in some instances, are folded and sheared by curving kink bands. Zebra and stromatactis limestone structures found throughout the mud-mound resemble frost heave and cryoturbation structures identified in both Holocene and Pleistocene cryosols, and in laboratory experiments with advancing freezing fronts in clay-size sediment. Significantly, modern occurrences of methane clathrate hydrate (methane-charged ice) display parallel and digitate layering similar in depositional appearance to that of zebra and stromatactis limestone from Meiklejohn Peak. Early carbonate cements are also commonly associated with these modern clathrate hydrate deposits. Consequently, gas clathrate hydrates may have been the propping agent for zebra and stromatactis structures observed in the mud-mound. In this scenario, carbonate cements would have precipitated and stabilized these structures, both with the consolidation and dissociation of gas clathrate hydrates, and with the oxidation and reduction of associated gases. Stable δ13C and δ18O isotope ratios collected from mudstone and spar of zebra and stromatactis structures indicate that they were lithified in equilibrium with Ordovician seawater. The δ13C isotope ratios recorded at Meiklejohn Peak are similar to δ13C isotopic ratios obtained from ∑CO 2 evolving from modern seafloor. These isotopic ratios may indicate that frost heave structures in the Meiklejohn Peak mud-mound are the result of consolidation and dissociation of carbon dioxide clathrate hydrates. Even though the bulk of gas clathrate hydrates identified to date in modern ocean floors are composed of methane, carbon dioxide clathrate hydrates are known from the modern seafloor of the Okinawa Trough. They may also be common in areas of abundant carbonate sediment accumulation, as suggested by recent observations from the Great Australian Bight.

  20. Phase equilibria of methane and carbon dioxide clathrate hydrates in the presence of (methanol + MgCl2) and (ethylene glycol + MgCl2) aqueous solutions

    International Nuclear Information System (INIS)

    Highlights: • Hydrate dissociation conditions for CH4 and CO2 in the presence of pure water/inhibitor aqueous solution are reported. • The inhibitors include: methanol + MgCl2 and ethylene glycol + MgCl2. • An isochoric pressure-search method was used in all the experimental data measurements. • The aqueous solutions shift the equilibrium data to high pressure/low temperature. • The aqueous solutions containing methanol has more inhibition effect than ethylene glycol. -- Abstract: In this work, the experimental data for the equilibrium conditions of methane and carbon dioxide clathrate hydrates in the presence of (0.1 mass fraction methanol + 0.03, 0.1 mass fraction MgCl2) and (0.1, 0.2 mass fraction ethylene glycol + 0.1 mass fraction MgCl2) aqueous solutions at different temperature and pressure range 263.74 to 280.54 K and 0.98 to 8.02 MPa, respectively and for various concentrations of inhibitors are reported, which is not available in open literature. The equilibrium pressure–temperature curves were generated using an isochoric pressure-search method. The experimental results of methane and carbon dioxide clathrate hydrates in the presence of pure water and the above mentioned aqueous inhibitor solutions are compared with some selected experimental data from the literature in the presence of pure water, single glycol, alcohol or salt aqueous solutions to validate the experimental result and to show the inhibition effects of the aqueous solutions used in this work. The results show that the phase equilibrium of the quaternary system (H2O + ethylene glycol/methanol + CH4/CO2 + MgCl2) is shifted to higher pressures/lower temperatures compared to the phase equilibrium of pure CH4/CO2 due to the inhibition effect. Also, it has been observed that the quaternary system containing methanol has a more inhibition effect than the quaternary system containing ethylene glycol at the same mass fraction of the inhibitor in the aqueous solution

  1. 水合物溶液分离技术研究进展%Progress in aqueous solution concentration by forming clathrate hydrate

    Institute of Scientific and Technical Information of China (English)

    李士凤; 谭哲; 申延明; 刘东斌; 樊丽辉; 白净

    2014-01-01

    水合物法溶液分离是一种新兴的分离技术。本文概述了水合物溶液分离技术的基本原理,指出水合物溶液分离技术的优缺点。重点回顾了水合物溶液分离技术在海水淡化、废水处理、果汁浓缩、生化分离等过程中的研究进展:尽管水合物海水淡化已经有工业化的报道,但是水合物生成压力较高,分离过程能耗较大,阻碍了该技术的推广应用;水合物法废水处理仅局限于制浆废水回收方面;水合物果汁浓缩以及生化分离方面的研究表明水合物法对于高附加值产品分离十分有效。分析表明,水合物溶液分离技术在上述应用过程中存在水合物生成压力大、水合物结晶夹带浓缩液等问题,指出未来水合物溶液分离技术的研究方向为寻找更加有效的水合物生成气体以及在高附加值产品分离回收过程中的应用。%The hydrate-based solution separation is a novel separation technology. This paper summarized the basic principle of aqueous concentration by forming hydrate,the benefits and drawbacks of hydrate technology. This paper emphasized the progress of seawater desalination, wastewater treatment,juice concentration,and biochemical separation by forming clathrate hydrate. Although forming hydrate desalination has been industrialized,the high and energy consumption of hydrate formation pressure limited its applications. The research on waste water treatment was only limited to pulping waste water recovery. Juice concentration and biochemical separation by forming hydrate were proven to be effective in recovery products with high added-value. The problems of high pressure of hydrate formation and hydrate crystal entrained concentrated solution by forming clathrate hydrate were also discussed. Future research directions of aqueous solution concentration by forming hydrate were proposed.

  2. Magnetic ordering of hyperfine-coupled nuclear and 4f-electron moments in the clathrate compound Pr3Pd20Ge6

    Science.gov (United States)

    Iwakami, O.; Namisashi, Y.; Abe, S.; Matsumoto, K.; Ano, G.; Akatsu, M.; Mitsumoto, K.; Nemoto, Y.; Takeda, N.; Goto, T.; Kitazawa, H.

    2014-09-01

    Complex ac susceptibility, χ =χ'-iχ'', measurements of the clathrate compound Pr3Pd20Ge6 were performed in static fields up to 10 mT for H ∥[001] and at temperatures down to 500 μK. Praseodymium (Pr) nuclear magnetic moments at the 8c site, where quadrupole moments of 4f electrons order at TQ1=250 mK, were found to order antiferromagnetically at 9 mK, as shown by a peak in χ' and a substantial increase in thermal relaxation time. The large enhancement factor (1+K8c) obtained by calculation of the hyperfine-enhanced nuclear susceptibility of Pr at the 8c site accounts for the high transition temperature of Pr nuclear magnetic moments and the large χ' below 30 mK. From analysis of the crystalline electric field and the mean-field approximation, we conclude that a χ peak at 77 mK can be ascribed to an antiferromagnetic ordering of magnetic moments of 4f electrons at the 4a site. We found that nuclear and f-electron moments order separately on two sublattices in this compound. The temperature and magnetic field dependence of χ' and χ'' between 30 and 60 mK are discussed in terms of dissipation phenomena.

  3. Rates and mechanisms of conversion of ice nanocrystals to ether clathrate hydrates: guest-molecule catalytic effects at approximately 120 k.

    Science.gov (United States)

    Gulluru, Dheeraj B; Devlin, J Paul

    2006-02-01

    A Fourier transform infrared investigation of the rates and energetics of conversion of ice nanocrystals within 3-D arrays to ether clathrate-hydrate (CH) particles at approximately 120 K is reported. After an induction period, apparently necessitated by relatively slow nucleation of the CH phase, the well-established shrinking-core model of particle-adsorbate reaction applies to these conversions in the presence of an abundance of adsorbed ether. This implies that the transport of the ether adsorbate through the product crust encasing a reacting particle core (a necessary aspect of a particle reaction mechanism) is the rate-controlling factor. Diffusion moves adsorbed reactant molecules to the reaction zone at the interface of the ice core with the product (CH) crust. The results indicate that ether hydrate formation rates near 120 K resemble rates for gas hydrates measured near 260 K, implying rates greater by many orders of magnitude for comparable temperatures. A surprising secondary enhancement of ether CH-formation rates by the simultaneous incorporation of simple small gas molecules (N2, CO2, CH4, CO, and N2O) has also been quantified in this study. The rapid CH formation at low temperatures is conjectured to derive from defect-facilitated transport of reactants to an interfacial reaction zone, with the defect populations enhanced through transient H bonding of guest-ether proton-acceptor groups with O-H groups of the hydrate cage walls. PMID:16451023

  4. Effect of Transition Metal Substitution on the Structure and Properties of a Clathrate-Like Compound Eu7Cu44As23

    Directory of Open Access Journals (Sweden)

    Igor V. Plokhikh

    2016-07-01

    Full Text Available A series of substitutional solid solutions—Eu7Cu44−xTxAs23 (T = Fe, Co, Ni—based on a recently discovered clathrate-like compound (Eu7Cu44As23 were synthesized from the elements at 800 °C. Almost up to 50% of Cu can be substituted by Ni, resulting in a linear decrease of the cubic unit cell parameter from a = 16.6707(1 Å for the ternary compound to a = 16.3719(1 Å for the sample with the nominal composition Eu7Cu24Ni20As23. In contrast, Co and Fe can only substitute less than 20% of Cu. Crystal structures of six samples of different composition were refined from powder diffraction data. Despite very small differences in scattering powers of Cu, Ni, Co, and Fe, we were able to propose a reasonable model of dopant distribution over copper sites based on the trends in interatomic distances as well as on Mössbauer spectra for the iron-substituted compound Eu7Cu36Fe8As23. Ni doping increases the Curie temperature to 25 K with respect to the parent compound, which is ferromagnetically ordered below 17.5 K, whereas Fe doping suppresses the ferromagnetic ordering in the Eu sublattice.

  5. Clathrate hydrate dissociation conditions of refrigerants R404A, R406A, R408A and R427A: Experimental measurements and thermodynamic modeling

    International Nuclear Information System (INIS)

    Highlights: • The application of refrigerant hydrates in cold storage systems is investigated. • Hydrate dissociation conditions of various refrigerants have been measured. • A correlative thermodynamic model was applied to the data. • Enthalpy of dissociation for the refrigerants studied calculated. • Experimental measurements performed over a wide range of pressures. - Abstract: Clathrate hydrate dissociation conditions were measured for four “alternative” refrigerants, viz. R404A, R406A, R408A and R427A. The experimental measurements were performed within the pressure range of (0.079 to 9.995) MPa and temperatures ranging from (272.7 to 288.7) K. An isochoric pressure-search method was used to perform the measurements. A thermodynamic model based on the van der Waals–Platteeuw (vdW–P) model was applied for the prediction of the dissociation conditions which were compared to the experimental measurements. The fluid phase was modeled using the MHV2 GE-EoS mixing rule along with the UNIFAC (original) activity model. The van der Waals–Platteeuw (vdW–P) model was used for the modeling of the hydrate phase. There was reasonable agreement between the experimental and predicted values

  6. Molecular dynamics Gibbs free energy calculations for CO2 capture and storage in structure I clathrate hydrates in the presence of SO2, CH4, N2, and H2S impurities

    International Nuclear Information System (INIS)

    Graphical abstract: Highlights: → Gibbs free energies of CO2 substitution in the structure I hydrate with other guests are computed. → Molecular dynamics based thermodynamic integration method is used. → The pressure and temperature of the CO2 substitution correspond with experimental hydrate synthesis conditions. → SO2 and H2S are more stable in the structure I hydrate. → The contributions to the electrostatic and van der Waals forces to the Gibbs free energies are evaluated separately. - Abstract: The capture of CO2 from flue gas in coal, natural gas, and other fossil fuel burning power stations and storage of CO2 in depleted gas reservoirs in the form of the solid clathrate hydrate have been suggested as methods of carbon capture and storage. These methods have the benefit of only needing water as the CO2 capturing material. The flue gas contains impurities including SO2, CH4, N2, and H2S which can interfere with the CO2 hydrate formation process. Some of these gases may also be found as residuals in depleted natural gas reservoirs. In this work, we use the molecular dynamics thermodynamic integration method to calculate the Gibbs free energy of the substitution reactions at conditions relevant to carbon capture (T = 200 K and 0.1 MPa and at 273 K and 1.0 MPa conditions), clathrate[CO2,p,T]+Y(fluid,p,T)→clathrate[Y,p,T]+CO2(fluid,p,T) where Y is the impurity species in the flue. Knowledge of the Gibbs free energy for this reaction will allow us to determine whether the impurities need to be eliminated from the flue or can participate in the hydrate formation process as neutral species without affecting the stability of the desired CO2 clathrate hydrate. For the thermodynamic integration, we use the nonlinear mixing scheme. In addition to calculating the ΔG for the above reaction, the contributions of different terms in the intermolecular potential of the guest molecules to the ΔG will be determined.

  7. A comparative study of different methods for the generation of tetra-n-butyl ammonium bromide clathrate hydrate slurry in a cold storage air-conditioning system

    International Nuclear Information System (INIS)

    Highlights: ► Four kinds of TBAB CHS generation methods are experimentally investigated. ► Accession of CHS into supercooled solution can be helpful to the generation. ► Higher flow rate results in higher energy efficiency of CHS generation. - Abstract: A cold storage air-conditioning system using tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) as cold storage medium was built to investigate the high-efficiency method of TBAB CHS generation. In the present study, four kinds of different TBAB CHS generation methods were experimentally investigated and compared, and these methods included continuously cooling, turning off refrigerator while crystals appearing, supercooling release and accession of TBAB CHS into supercooled TBAB aqueous solution. The results showed that continuously cooling would lead to severe adhesion of crystal to the heat exchanger wall, and supercooling release took place with a big stochastic characteristic, hence the first and third method were concluded not reliable. Both the second and fourth methods could maintain the temperature of heat exchanger wall at a relatively higher level, therefore the crystal adhesion to the heat exchanger wall would be reduced significantly, which led to higher coefficient of performance (COP). In addition, accession of TBAB CHS into TBAB supercooled solution could shorten the time of supercooling release, resulting in about 21.8–35.4% shorter generation time than other methods. Moreover, the influence of flow rate on the CHS generation process was investigated, and the results showed that higher flow rate generally resulted in higher system COP

  8. Clathrate-hydrate formation from a hydrocarbon gas mixture: Compositional evolution of formed hydrate during an isobaric semi-batch hydrate-forming operation

    International Nuclear Information System (INIS)

    Highlights: • Reports laboratory experiments of hydrate formation from synthetic natural gas. • Shows how hydrate composition changes during each hydrate-forming operation. • Compares the observed compositional change with thermodynamic simulations. • Shows a PXRD result indicating simultaneous formation of sI and sII hydrates. - Abstract: The clathrate hydrate formation from a model natural gas, i.e., a mixture of methane, ethane, and propane in a 90:7:3 molar ratio, under a constant pressure was experimentally investigated, focusing on the compositional evolution of hydrate crystals formed inside a gas-bubbling-type reactor during each semi-batch hydrate-forming operation. The experimental system used in this study was specially designed for obtaining several hydrate samples formed at different, arbitrarily selected stages during each hydrate-forming operation. Each hydrate sample was analyzed by a gas-chromatograph to determine the mole fractions of methane, ethane and propane encaged in the hydrate. These analyses revealed a monotonic increase in the methane fraction and decreases in the ethane and propane fractions during each operation until a quasi-steady state was established. Powder X-ray diffraction analyses showed that both structure-I and structure-II crystals were simultaneously formed during the quasi-steady period. The compositional evolution of the hydrates formed during the early stages before the quasi-steady state was reached deviated from corresponding predictions based on the thermodynamic-simulation scheme previously reported. A hypothetical explanation for the discrepancy between the experimental and simulation-based results was provided

  9. Enhanced kinetics for the clathrate process in a fixed bed reactor in the presence of liquid promoters for pre-combustion carbon dioxide capture

    International Nuclear Information System (INIS)

    In this work, we present enhanced kinetics of hydrate formation for the clathrate process in the presence of two liquid promoters namely THF (tetrahydrofuran) and TBAB (tetra-n-butyl ammonium bromide) in a FBR (fixed bed reactor) for pre-combustion capture of CO2. Silica sand was used as a medium to capture CO2 from CO2/H2 gas mixture by hydrate crystallisation. Experiments were performed at different temperatures (274.2 K and 279.2 K) and 6.0 MPa to determine the total gas uptake, induction time and rate of hydrate formation. The observed trends indicated that higher driving force resulted in higher gas consumption and significantly reduced induction time. For the same driving force, higher gas consumption and shorter induction time was achieved by THF as compared to TBAB. 5.53 mol% THF attained higher gas consumption than 1.0 mol% THF whereas 3.0 mol% TBAB attained lower gas consumption than 0.3 mol% TBAB. A highest gas uptake of 51.95 (±5.183) mmol of gas/mol of water and a highest rate of 51.21(±8.91) mol.min−1.m−3 were obtained for 5.53 mol% THF at 6.0 MPa and 279.2 K. Overall, this study indicated better hydrate formation kinetics with the use of THF in an FBR configuration for CO2 capture from a fuel gas mixture. - Highlights: • Better kinetic performance with THF compared to TBAB for CO2 capture in a fixed bed reactor. • Highest CO2 uptake (126.99 ± 12.67 mg of gas/g of water) was obtained for 5.53 mol% THF. • Highest growth rate (51.21 ± 8.91 mol min−1.m−3) for 30 min was obtained for 5.53 mol% THF. • Waste heat (ΔT = 20) is sufficient to recover all the hydrated gas

  10. Performance of local correlation methods for halogen bonding: The case of Br2–(H2O)n,n = 4,5 clusters and Br2@51262 clathrate cage

    International Nuclear Information System (INIS)

    The performance of local correlation methods is examined for the interactions present in clusters of bromine with water where the combined effect of hydrogen bonding (HB), halogen bonding (XB), and hydrogen-halogen (HX) interactions lead to many interesting properties. Local methods reproduce all the subtleties involved such as many-body effects and dispersion contributions provided that specific methodological steps are followed. Additionally, they predict optimized geometries that are nearly free of basis set superposition error that lead to improved estimates of spectroscopic properties. Taking advantage of the local correlation energy partitioning scheme, we compare the different interaction environments present in small clusters and those inside the 51262 clathrate cage. This analysis allows a clear identification of the reasons supporting the use of local methods for large systems where non-covalent interactions play a key role

  11. Hydrated coefficient of clathrates and its applications in determination of aqueous inclusions with multivolatile components%气水化合物的水合常数及其在水溶液包裹体多组分挥发分测定中的应用

    Institute of Scientific and Technical Information of China (English)

    刘斌; 徐金明

    2007-01-01

    During the microthermometric measurement (cooling) of aqueous inclusions with multivolatile components, solid crystals of gas clathrates often occur with snow-flower- or soft-ice appearances. The structural formula of these solids is M · nH2O (where n ≥5.67 ). Many hydrocarbons, related compounds and their binary or multi-component mixtures may generate gas clathrates. This phenomenum is of fundamental importance to the study of inclusions with hydrocarbon aqueous solutions, because this is related to the determination of inclusion parameters and the computation of thermodynamic parameters.In the nature most aqueous inclusions contain not merely one volatile component but multi-volatile components. Therefore, the measurement of aqueous inclusions with multivolatile components is of universal significance and great importance. There have been many studies and available formula or figures about the computation of thermodynamic parameters for aqueous inclusions with one volatile component. Nevertheless, there are few studies concerning with multivolatile components and it is very difficult to computate thermodynamic parameters for aqueous inclusions with these components.In this paper, hydrated coefficient K is introduced. Ki is the ratio of molar fraction of component i in the gas phase to that in the gas clathrate, or Ki = yi/xi. Because K is a function of temperatures and pressures, it can be used to evaluate the temperature-pressure conditions on the phase behavior with multivolatile components.Based on the regression analysis of available experimental data, the authors have developed computational expression of hydrated coefficients in relation to temperature and pressure for most hydrocarbons and other volatile components, which is helpful to conveniently compute thermodynamic parameters on stability state for clathrates with volatile components. As aqueous inclusions with multivolatile components are common in the nature, by the use of final melting

  12. Thermodynamic model for predicting equilibrium conditions of clathrate hydrates of noble gases + light hydrocarbons: Combination of Van der Waals–Platteeuw model and sPC-SAFT EoS

    International Nuclear Information System (INIS)

    Highlights: • Applying sPC-SAFT for phase equilibrium calculations. • Determining Kihara potential parameters for hydrate formers. • Successful usage of the model for systems with hydrate azeotropes. - Abstract: In this communication, equilibrium conditions of clathrate hydrates containing mixtures of noble gases (Argon, Krypton and Xenon) and light hydrocarbons (C1–C3), which form structure I and II, are modeled. The thermodynamic model is based on the solid solution theory of Van der Waals–Platteeuw combined with the simplified Perturbed-Chain Statistical Association Fluid Theory equation of state (sPC-SAFT EoS). In dispersion term of sPC-SAFT EoS, the temperature dependent binary interaction parameters (kij) are adjusted; taking advantage of the well described (vapor + liquid) phase equilibria. Furthermore, the Kihara potential parameters are optimized based on the P–T data of pure hydrate former. Subsequently, these obtained parameters are used to predict the binary gas hydrate dissociation conditions. The equilibrium conditions of the binary gas hydrates predicted by this model agree well with experimental data (overall AAD P ∼ 2.17)

  13. Phase equilibrium measurements for clathrate hydrates of flue gas (CO2 + N2 + O2) in the presence of tetra-n-butyl ammonium bromide or tri-n-butylphosphine oxide

    International Nuclear Information System (INIS)

    Highlights: • Semi-clathrate hydrate phase equilibria for ternary gas mixture of CO2, N2, and O2 are reported. • An isochoric pressure-search method was used. • TBPO outperforms TBAB in promoting the formation of flue gas hydrate. - Abstract: This paper reports the measured hydrate phase equilibria of simulated flue gas (12.6 vol% CO2, 80.5 vol% N2, 6.9 vol% O2) in the presence of tetra-n-butyl ammonium bromide (TBAB) or tri-n-butylphosphine oxide (TBPO), at (0, 5 and 26) wt%, respectively. The measurements of the phase boundary between (hydrate + liquid + vapor) (H + L + V) phases and (liquid + vapor) (L + V) phases were performed within the temperature range (275.97 to 293.99) K and pressure range (1.56 to 18.78) MPa with using the isochoric step-heating pressure search method. It was found that addition of TBAB or TBPO allowed the incipient equilibrium hydrate formation conditions for the flue gas to become milder. Compared to TBAB, TBPO was largely more effective in reducing the phase equilibrium pressure

  14. Clathration Craft for β-Cyclodextrin in Essential Oil of Fructus Forsythiae in Fufang Yuxingcao Granules%复方鱼腥草颗粒中连翘挥发油β-环糊精包合工艺优化研究

    Institute of Scientific and Technical Information of China (English)

    施晓光

    2016-01-01

    目的:用β-环糊精对复方鱼腥草颗粒中的连翘挥发油进行包合。方法采用正交试验法选择包合工艺的最佳条件,并对包合物的质量进行分析。结果得出的最佳工艺条件为挥发油与β-环糊精的比为10 mL∶80 g,包合时间为4 h,包合温度为60℃,加水量为β-环糊精的8倍。结论该包合工艺简单可行,可有效防止挥发油有效成分的散失。%Objective To clathrate the essential oil of Fructus Forsythian in Fufang Yuxingcao Granules with β-cyclodextrin. Methods The optimum condition for clathration craft was chosen by orthogonal tests and the quality of clathrates was analyzed. Results The op-timum craft condition:the proposition of essential oil and β-cyclodextrin was 10 mL ∶80 g;the process was 4 h at 60 °C;8 times of water respect to β-cyclodextrin was added. Conclusion The craft is proved to be simple,operatable and effective to avoid active gra-dients in the essential oil.

  15. Full-dimensional, high-level ab initio potential energy surfaces for H2(H2O) and H2(H2O)2 with application to hydrogen clathrate hydrates

    Science.gov (United States)

    Homayoon, Zahra; Conte, Riccardo; Qu, Chen; Bowman, Joel M.

    2015-08-01

    New, full-dimensional potential energy surfaces (PESs), obtained using precise least-squares fitting of high-level electronic energy databases, are reported for intrinsic H2(H2O) two-body and H2(H2O)2 three-body potentials. The database for H2(H2O) consists of approximately 44 000 energies at the coupled cluster singles and doubles plus perturbative triples (CCSD(T))-F12a/haQZ (aug-cc-pVQZ for O and cc-pVQZ for H) level of theory, while the database for the three-body interaction consists of more than 36 000 energies at the CCSD(T)-F12a/haTZ (aug-cc-pVTZ for O, cc-pVTZ for H) level of theory. Two precise potentials are based on the invariant-polynomial technique and are compared to computationally faster ones obtained via "purified" symmetrization. All fits use reduced permutational symmetry appropriate for these non-covalent interactions. These intrinsic potentials are employed together with existing ones for H2, H2O, and (H2O)2, to obtain full PESs for H2(H2O) and H2(H2O)2. Properties of these full PESs are presented, including a diffusion Monte Carlo calculation of the zero-point energy and wavefunction, and dissociation energy of the H2(H2O) dimer. These PESs together with an existing one for water clusters are used in a many-body representation of the PES of hydrogen clathrate hydrates, illustrated for H2@(H2O)20. An analysis of this hydrate is presented, including the electronic dissociation energy to remove H2 from the calculated equilibrium structure.

  16. Full-dimensional, high-level ab initio potential energy surfaces for H2(H2O) and H2(H2O)2 with application to hydrogen clathrate hydrates

    International Nuclear Information System (INIS)

    New, full-dimensional potential energy surfaces (PESs), obtained using precise least-squares fitting of high-level electronic energy databases, are reported for intrinsic H2(H2O) two-body and H2(H2O)2 three-body potentials. The database for H2(H2O) consists of approximately 44 000 energies at the coupled cluster singles and doubles plus perturbative triples (CCSD(T))-F12a/haQZ (aug-cc-pVQZ for O and cc-pVQZ for H) level of theory, while the database for the three-body interaction consists of more than 36 000 energies at the CCSD(T)-F12a/haTZ (aug-cc-pVTZ for O, cc-pVTZ for H) level of theory. Two precise potentials are based on the invariant-polynomial technique and are compared to computationally faster ones obtained via “purified” symmetrization. All fits use reduced permutational symmetry appropriate for these non-covalent interactions. These intrinsic potentials are employed together with existing ones for H2, H2O, and (H2O)2, to obtain full PESs for H2(H2O) and H2(H2O)2. Properties of these full PESs are presented, including a diffusion Monte Carlo calculation of the zero-point energy and wavefunction, and dissociation energy of the H2(H2O) dimer. These PESs together with an existing one for water clusters are used in a many-body representation of the PES of hydrogen clathrate hydrates, illustrated for H2@(H2O)20. An analysis of this hydrate is presented, including the electronic dissociation energy to remove H2 from the calculated equilibrium structure

  17. Full-dimensional, high-level ab initio potential energy surfaces for H2(H2O) and H2(H2O)2 with application to hydrogen clathrate hydrates.

    Science.gov (United States)

    Homayoon, Zahra; Conte, Riccardo; Qu, Chen; Bowman, Joel M

    2015-08-28

    New, full-dimensional potential energy surfaces (PESs), obtained using precise least-squares fitting of high-level electronic energy databases, are reported for intrinsic H2(H2O) two-body and H2(H2O)2 three-body potentials. The database for H2(H2O) consists of approximately 44 000 energies at the coupled cluster singles and doubles plus perturbative triples (CCSD(T))-F12a/haQZ (aug-cc-pVQZ for O and cc-pVQZ for H) level of theory, while the database for the three-body interaction consists of more than 36 000 energies at the CCSD(T)-F12a/haTZ (aug-cc-pVTZ for O, cc-pVTZ for H) level of theory. Two precise potentials are based on the invariant-polynomial technique and are compared to computationally faster ones obtained via "purified" symmetrization. All fits use reduced permutational symmetry appropriate for these non-covalent interactions. These intrinsic potentials are employed together with existing ones for H2, H2O, and (H2O)2, to obtain full PESs for H2(H2O) and H2(H2O)2. Properties of these full PESs are presented, including a diffusion Monte Carlo calculation of the zero-point energy and wavefunction, and dissociation energy of the H2(H2O) dimer. These PESs together with an existing one for water clusters are used in a many-body representation of the PES of hydrogen clathrate hydrates, illustrated for H2@(H2O)20. An analysis of this hydrate is presented, including the electronic dissociation energy to remove H2 from the calculated equilibrium structure. PMID:26328838

  18. Full-dimensional, high-level ab initio potential energy surfaces for H{sub 2}(H{sub 2}O) and H{sub 2}(H{sub 2}O){sub 2} with application to hydrogen clathrate hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Homayoon, Zahra; Conte, Riccardo; Qu, Chen; Bowman, Joel M., E-mail: jmbowma@emory.edu [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322 (United States)

    2015-08-28

    New, full-dimensional potential energy surfaces (PESs), obtained using precise least-squares fitting of high-level electronic energy databases, are reported for intrinsic H{sub 2}(H{sub 2}O) two-body and H{sub 2}(H{sub 2}O){sub 2} three-body potentials. The database for H{sub 2}(H{sub 2}O) consists of approximately 44 000 energies at the coupled cluster singles and doubles plus perturbative triples (CCSD(T))-F12a/haQZ (aug-cc-pVQZ for O and cc-pVQZ for H) level of theory, while the database for the three-body interaction consists of more than 36 000 energies at the CCSD(T)-F12a/haTZ (aug-cc-pVTZ for O, cc-pVTZ for H) level of theory. Two precise potentials are based on the invariant-polynomial technique and are compared to computationally faster ones obtained via “purified” symmetrization. All fits use reduced permutational symmetry appropriate for these non-covalent interactions. These intrinsic potentials are employed together with existing ones for H{sub 2}, H{sub 2}O, and (H{sub 2}O){sub 2}, to obtain full PESs for H{sub 2}(H{sub 2}O) and H{sub 2}(H{sub 2}O){sub 2}. Properties of these full PESs are presented, including a diffusion Monte Carlo calculation of the zero-point energy and wavefunction, and dissociation energy of the H{sub 2}(H{sub 2}O) dimer. These PESs together with an existing one for water clusters are used in a many-body representation of the PES of hydrogen clathrate hydrates, illustrated for H{sub 2}@(H{sub 2}O){sub 20}. An analysis of this hydrate is presented, including the electronic dissociation energy to remove H{sub 2} from the calculated equilibrium structure.

  19. Performance of local correlation methods for halogen bonding: The case of Br{sub 2}–(H{sub 2}O){sub n},n = 4,5 clusters and Br{sub 2}@5{sup 12}6{sup 2} clathrate cage

    Energy Technology Data Exchange (ETDEWEB)

    Batista-Romero, Fidel A.; Bernal-Uruchurtu, Margarita I.; Hernández-Lamoneda, Ramón, E-mail: ramon@uaem.mx [Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Cuernavaca, Morelos 62209 (Mexico); Pajón-Suárez, Pedro [Instituto Superior de Tecnologías y Ciencias Aplicadas (InSTEC), Habana 6163 (Cuba)

    2015-09-07

    The performance of local correlation methods is examined for the interactions present in clusters of bromine with water where the combined effect of hydrogen bonding (HB), halogen bonding (XB), and hydrogen-halogen (HX) interactions lead to many interesting properties. Local methods reproduce all the subtleties involved such as many-body effects and dispersion contributions provided that specific methodological steps are followed. Additionally, they predict optimized geometries that are nearly free of basis set superposition error that lead to improved estimates of spectroscopic properties. Taking advantage of the local correlation energy partitioning scheme, we compare the different interaction environments present in small clusters and those inside the 5{sup 12}6{sup 2} clathrate cage. This analysis allows a clear identification of the reasons supporting the use of local methods for large systems where non-covalent interactions play a key role.

  20. Preparation of Anti-mosquito Silk Fabric via Grafting β-cyclodextrin to Clathrate Natural Mosquito Repellent%利用接枝β-环糊精包合天然驱蚊剂制备防蚊真丝织物

    Institute of Scientific and Technical Information of China (English)

    刘建华; 许宏聪; 沈林; 陈瑞玉; 李超; 余志成

    2012-01-01

    采用1,2,3,4-丁烷四羧酸(BTCA)在催化剂次亚磷酸钠(SHP)的作用下将β-环糊精(β-CD)接枝到真丝纤维上,然后浸渍加入具有驱蚊功效的薰衣草精油使其包合在β-CD空腔中,制备出具有驱蚊功效的真丝织物.设计单因素试验优化β-CD接枝真丝织物的工艺参数,当BTCA和β-CD的质量浓度分别为100 g/L,SHP的质量浓度为60 g/L,170℃下焙烘3min或180℃下焙烘2 min,真丝织物的接枝增重率可达18.4%,红外光谱分析表明β-CD已成功接枝至真丝织物上,且可耐15次以上的水洗.接枝β-CD的真丝织物能够赋予薰衣草精油缓释的效果,且放置8d后对按蚊仍可保持75%以上的驱避率.此方法制备的防蚊真丝织物效果持久可重复使用,且具有对人体无毒害、环保的特点.%p-cyclodextrin (p-CD) was grafted onto silk fabric by using 1,2,3,4-butane tetracarboxylic acid (BTCA) un-der the catalysis of sodium hypophosphite (SHP),which enabled lavender essential oil,a natural mosquito repellent,to be clathrated into the cavity of β-CD for development of silk fabric with mosquito repellence.Single factor tests were designed to optimize technological parameters for grafting β-CD onto silk fabric.The results showed that the fabric weight gain rate could reach 18.4% when grafting was conducted with 100 g/Lβ-CD,100 g/L BTCA and 60 g/L SHP under 170℃for 3 min or 180℃for 2 min.Infrared spectrometric analysis demonstrated that β-CD had been grafted onto silk fabric successfully and could resist washing over 15 times.The β-CD grafted silk fabric endowed lavender essential oil a slow-release effect,which maintained an over 75% mosquito repellence rate after 8 days.The mosquito-repellence silk fabric prepared by this method not only had a long effective duration and many times of repeated use,but also had the characteristics of being safe to human body and being friendly to environment.

  1. Molecular Design Basis for Hydrogen Storage in Clathrate Hydrates

    Energy Technology Data Exchange (ETDEWEB)

    John, Vijay T [Tulane University; McPherson, Gary L [Tulane University; Ashbaugh, Hank [Tulane University; Johnes, Camille Y [Columbia University

    2013-06-28

    We attach a final technical report for the project. The report contains the list of all peer reviewed publications that have resulted from the contract. I will be happy to send the pdf files of the papers.

  2. Towards a green hydrate inhibitor: imaging antifreeze proteins on clathrates.

    Directory of Open Access Journals (Sweden)

    Raimond Gordienko

    Full Text Available The formation of hydrate plugs in oil and gas pipelines is a serious industrial problem and recently there has been an increased interest in the use of alternative hydrate inhibitors as substitutes for thermodynamic inhibitors like methanol. We show here that antifreeze proteins (AFPs possess the ability to modify structure II (sII tetrahydrofuran (THF hydrate crystal morphologies by adhering to the hydrate surface and inhibiting growth in a similar fashion to the kinetic inhibitor poly-N-vinylpyrrolidone (PVP. The effects of AFPs on the formation and growth rate of high-pressure sII gas mix hydrate demonstrated that AFPs are superior hydrate inhibitors compared to PVP. These results indicate that AFPs may be suitable for the study of new inhibitor systems and represent an important step towards the development of biologically-based hydrate inhibitors.

  3. Superconductive "sodalite"-like clathrate calcium hydride at high pressures

    CERN Document Server

    Wang, Hui; Tanaka, Kaori; Iitaka, Toshiaki; Ma, Yanming

    2012-01-01

    Hydrogen-rich compounds hold promise as high-temperature superconductors under high pressures. Recent theoretical hydride structures on achieving high-pressure superconductivity are composed mainly of H2 fragments. Through a systematic investigation of Ca hydrides with different hydrogen contents using particle-swam optimization structural search, we show that in the stoichiometry CaH6 a body-centred cubic structure with hydrogen that forms unusual "sodalite" cages containing enclathrated Ca stabilizes above pressure 150 GPa. The stability of this structure is derived from the acceptance by two H2 of electrons donated by Ca forming a "H4" unit as the building block in the construction of the 3-dimensional sodalite cage. This unique structure has a partial occupation of the degenerated orbitals at the zone centre. The resultant dynamic Jahn-Teller effect helps to enhance electron-phonon coupling and leads to superconductivity of CaH6. A superconducting critical temperature (Tc) of 220-235 K at 150 GPa obtained...

  4. CO₂ processing and hydration of fruit and vegetable tissues by clathrate hydrate formation.

    Science.gov (United States)

    Takeya, Satoshi; Nakano, Kohei; Thammawong, Manasikan; Umeda, Hiroki; Yoneyama, Akio; Takeda, Tohoru; Hyodo, Kazuyuki; Matsuo, Seiji

    2016-08-15

    CO2 hydrate can be used to preserve fresh fruits and vegetables, and its application could contribute to the processing of carbonated frozen food. We investigated water transformation in the frozen tissue of fresh grape samples upon CO2 treatment at 2-3 MPa and 3°C for up to 46 h. Frozen fresh bean, radish, eggplant and cucumber samples were also investigated for comparison. X-ray diffraction indicated that after undergoing CO2 treatment for several hours, structure I CO2 hydrate formed within the grape tissue. Phase-contrast X-ray imaging using the diffraction-enhanced imaging technique revealed the presence of CO2 hydrate within the intercellular spaces of these tissues. The carbonated produce became effervescent because of the dissociation of CO2 hydrate through the intercellular space, especially above the melting point of ice. In addition, suppressed metabolic activity resulting from CO2 hydrate formation, which inhibits water and nutrient transport through intercellular space, can be expected. PMID:27006222

  5. Optimizing the Interactions of Surfactants with Graphitic Surfaces and Clathrate Hydrates.

    Science.gov (United States)

    Di Crescenzo, Antonello; Di Profio, Pietro; Siani, Gabriella; Zappacosta, Romina; Fontana, Antonella

    2016-07-01

    Surfactants are amphiphilic molecules active at the surface/interface and able to self-assemble. Because of these properties, surfactants have been extensively used as detergents, emulsifiers, foaming agents, and wetting agents. New perspectives have been opened by the exploitation of surfactants for their capacity to interact as well with simple molecules or surfaces. This feature article gives an overview of significant contributions in the panorama of the current research on surfactants, partly accomplished as well by our research group. We look at several recent applications (e.g., adsorption to graphitic surfaces and interactions with hydrate crystals) with the eye of physical organic chemists. We demonstrate that, from the detailed investigation of the forces involved in the interactions with hydrophobic surfaces, it is possible to optimize the design of the surfactant that is able to form a stable and unbundled carbon nanotube dispersion as well as the best exfoliating agent for graphitic surfaces. By studying the effect of different surfactants on the capacity to favor or disfavor the formation of a gas hydrate, it is possible to highlight the main features that a surfactant should possess in order to be devoted to that specific application. PMID:27264111

  6. A Novel Orange Juice Concentration Method Based on C2H4 Clathrate Hydrate Formation

    Directory of Open Access Journals (Sweden)

    Shifeng Li

    2014-06-01

    Full Text Available A novel orange juice concentration method by C2H4 hydrate formation was presented. The experiments were carried out in a high-pressure stirred reactor. The changes of temperature and pressure during C2H4 hydrate formation were discussed under different pressure (2.10 and 4.43 MPa. Dehydration ratio was defined in order to evaluate the separation efficiency. It was found that secondary nucleation happened under higher initial pressure. The dehydration ratios were 20.2 and 99.3% with initial pressure at 2.10 and 4.43 MPa, respectively. The results demonstrated that removal of water by formation of C2H4 hydrate is a potential technology for orange juice concentration.

  7. LIQUID CLATHRATE FORMATION IN IONIC LIQUIDS/AROMATIC MIXTURES. (R828257)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  8. Soft x-ray photoelectron spectroscopy study of type-I clathrates

    Directory of Open Access Journals (Sweden)

    Jun Tang, Zhaofei Li, Jing Ju, Ryotaro Kumashiro, Marcos A. Avila, Kouichirou Suekuni, Toshiro Takabatake, FangZhun Guo, Keisuke Kobayashi, Koji Akai and Katsumi Tanigaki

    2008-01-01

    Full Text Available Extensive soft x-ray photoelectron spectroscopy studies are performed on Ba8 Ga16 Ge30 (BGG and Sr8Ga16Ge30 (SGG single crystals ranging from Fermi to core levels, at a high-energy facility. Valence band x-ray photoelectron spectroscopy (XPS experiments with theoretical calculations revealed that the valence band is mainly constructed by the Ge/Ga 4s and 4p wave functions with little contribution of the Ba/Sr atomic orbitals. Surprisingly, unexpected features evidencing the different shift for the 2a- and 6d- sites between Ba 4d and Sr 3d are observed. The detailed analyses including theoretical support by first-principles band-structure calculations lead to the conclusion that the component distributions of the larger tetrakaidecahedral cage are different depending on the endohedral atoms, which contrasts with the past consensus that BGG and SGG have the same framework structure. This may give thorough reconsiderations on earlier interpretations of experimental data.

  9. Evaluation of the Efficiency of Clathrate Hydrates in Storing Energy Gases

    Science.gov (United States)

    Papadimitriou, N. I.; Tsimpanogiannis, I. N.; Economou, I. G.; Stubos, A. K.

    2015-09-01

    We use Grand Canonical Monte Carlo simulations to examine the efficiency of hydrates in storing hydrogen. In this way, the hydrate lattice is treated as a solid substrate where gas adsorption takes place. Special focus is given to the study of multiple occupancy, namely the presence of more than one gas molecules in the same hydrate cavity. This phenomenon occurs in the case of hydrogen hydrates and may drastically increase their storage capacity. A parametric analysis is also carried out to quantify the correlation between the change in the lattice constant and the storage capacity since small changes in the size of the crystal unit cell may induce significant changes in the storage capacity especially in cases were multiple occupancy occurs.

  10. Decomposition of Clathrate Hydrates by High Frequency in-Liquid Plasma

    OpenAIRE

    Putra, Andi Erwin Eka

    2008-01-01

    In recent years, 81% of total energy consumption is fossil fuel. Transportation, power generation, agriculture and industry activity is driven by oil and petroleum as a fossil fuel. Nevertheless, Petroleum prices are rising due to oil crisis in 1973, the Gulf War in 1991, and depletion of petroleum reserves. In addition, the environmental issues such as global warming, the Kyoto Protocol, and the emission of greenhouse gases are also a consideration to look for alternative energy fuel. Tod...

  11. Facilitating guest transport in clathrate hydrates by tuning guest-host interactions

    International Nuclear Information System (INIS)

    The understanding and eventual control of guest molecule transport in gas hydrates is of central importance for the efficient synthesis and processing of these materials for applications in the storage, separation, and sequestration of gases and natural gas production. Previously, some links have been established between dynamics of the host water molecules and guest-host hydrogen bonding interactions, but direct observation of transport in the form of cage-to-cage guest diffusion is still lacking. Recent calculations have suggested that pairs of different guest molecules in neighboring cages can affect guest-host hydrogen bonding and, therefore, defect injection and water lattice motions. We have chosen two sets of hydrate guest pairs, tetrahydrofuran (THF)-CO2 and isobutane-CO2, that are predicted to enhance or to diminish guest–host hydrogen bonding interactions as compared to those in pure CO2 hydrate and we have studied guest dynamics in each using 13C nuclear magnetic resonance (NMR) methods. In addition, we have obtained the crystal structure of the THF-CO2 sII hydrate using the combined single crystal X-ray diffraction and 13C NMR powder pattern data and have performed molecular dynamics-simulation of the CO2 dynamics. The NMR powder line shape studies confirm the enhanced and delayed dynamics for the THF and isobutane containing hydrates, respectively, as compared to those in the CO2 hydrate. In addition, from line shape studies and 2D exchange spectroscopy NMR, we observe cage-to-cage exchange of CO2 molecules in the THF-CO2 hydrate, but not in the other hydrates studied. We conclude that the relatively rapid intercage guest dynamics are the result of synergistic guest A–host water–guest B interactions, thus allowing tuning of the guest transport properties in the hydrates by choice of the appropriate guest molecules. Our experimental value for inter-cage hopping is slower by a factor of 106 than a published calculated value

  12. An Experimental Determination of Natural Clathrate Hydrate Dissolution Rates in the Deep Sea

    Science.gov (United States)

    Peltzer, E. T.; Walz, P. M.; Brewer, P. G.; Dunk, R. M.; Hester, K.; Sloan, E. D.

    2006-12-01

    In August of 2006 we carried out a series of geochemical experiments on the massive Structure II hydrate mounds in Barkley Canyon using MBARI's ROV Tiburon deployed from the R/V Western Flyer. One of the primary questions regarding the fate of this hydrate exposure at 850m depth is the temporal persistence of un-sedimented surfaces exposed to steady currents of seawater undersaturated with methane. Previous work on the dissolution rate of laboratory prepared methane hydrate (Rehder et al., 2004) showed diameter reduction rates of ~3 m/year. These formations appeared largely unchanged from the earlier descriptions and photographs contained in media reports released in 2002 and later (Chapman et al., 2004; Lu et al., 2005) leading us to speculate that these hydrates are far slower to dissolve. In order to quantify their dissolution rates, samples of the outcropping hydrate, both a pure white hydrate and a much harder yellow, oil-stained hydrate, were collected using an ROV operated coring device and hydraulically expelled into an open mesh container for time-lapse photography over the course of the next 48 hours. By exposing these samples of natural hydrate to the flow of ambient seawater we hoped to observe the dissolution rate consistent with the local environmental conditions. Initial analysis of the time-lapse photographs obtained using a Nikon Cool-pix camera revealed an apparent diameter reduction rate for the yellow hydrate of approximately 0.040 μm/s, corresponding to a volume loss rate of 1.3×10-6cm3/cm2/s. The observed dissolution rate of the white hydrate was significantly faster, consistent with the observed large-scale undercutting of the exposed layered structures. Assuming that the yellow hydrate has a density of 0.93 g/cm3 and an average hydration number near 6, this yields a guest gas loss rate of about 9.4×10-9 mol/cm2/s. This is approximately one-fourth the rate that was observed for the dissolution of synthetic Structure I methane hydrates under similar conditions in Monterey Bay. Thus the lifetime of the exposed surfaces must be short unless there is some form of active expulsion of fresh hydrates taking place. Chapman et al. (2004). Eos, Trans. Amer. Geophys. Union. 85: 361, 365. Lu et al. (2005). J. Geophys. Res. 110: B10204, doi:10.1029/2005JB003900. Rehder et al. (2004). Geochim. et Cosmochim. Acta 68: 285-292.

  13. Clathrate hydrate equilibria in mixed monoethylene glycol and electrolyte aqueous solutions

    International Nuclear Information System (INIS)

    Highlights: ► New water activity of mixed salt(s) and MEG aqueous solutions were measured. ► New 3-phase H–Lw–V data for methane and a natural gas in equilibrium with MEG and NaCl solutions are reported. ► The CPA-EoS combined with a modified Debye Hückel electrostatic term is employed to model the phase equilibria. ► Water activity data were used to adjust parameters of the modified Debye Hückel electrostatic term. ► The modified model was independently validated using hydrate data. - Abstract: Monoethylene glycol (MEG) is commonly added in the formulation of hydraulic and drilling fluids and injected into pipelines to prevent the formation of gas hydrates. It is therefore necessary to establish the effect of a combination of salts and thermodynamic inhibitors on gas hydrate equilibria. In this communication, water activity of five ternary solutions (MEG–H2O–NaCl, MEG–H2O–CaCl2, MEG–H2O–MgCl2, MEG–H2O–KCl and MEG–H2O–NaBr) and four multicomponent solutions have been measured by a reliable resistive electrolytic humidity sensor. We also report new experimental measurements of the locus of incipient hydrate-liquid water–vapour curve for systems containing methane or natural gas with aqueous solution of ethylene glycol and NaCl over a wide range of concentrations, pressures and temperatures. A thermodynamic approach in which the Cubic-Plus-Association equation of state is combined with a modified Debye Hückel electrostatic term is employed to model the phase equilibria. These new data have been used to optimise binary interaction parameters between salts and MEG implemented in the modified Debye Hückel electrostatic term. The model developed has been evaluated using the new generated hydrate data and literature data. Good agreement between predictions of the modified model and experimental data is observed, supporting the reliability of the developed model.

  14. Sponge Effect on Coal Mine Methane Separation Based on Clathrate Hydrate Method

    Institute of Scientific and Technical Information of China (English)

    ZHANG Baoyong; CHENG Yuanping; WU Qiang

    2011-01-01

    The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carried out at 273.15K under 4.00 MPa.The key process variables of gas formation rate,gas volume stored in hydrate and separation concentration were closely investigated in twelve THF-SDS-sponge-gas systems to verify the sponge effect in these hydrate-based separation processes.The gas volume stored in hydrate is calculated based on the measured gas pressure.The CH4 mole fraction in hydrate phase is measured by gas chromatography to confirm the separation efficiency.Through close examination of the overall results,it was clearly verified that sponges with volumes of 40,60 and 80 cm 3 significantly increase gas hydrate formation rate and the gas volume stored in hydrate,and have little effect on the CH4 mole fraction in hydrate phase.The present study provides references for the application of the kinetic effect of porous sponge media in hydrate-based technology.This will contribute to CMM utilization and to benefit for local and global environment.

  15. Dynamical and energetic properties of hydrogen and hydrogen–tetrahydrofuran clathrate hydrates

    OpenAIRE

    Gorman, Paul D.; English, Niall J.; MacElroy, J. M. Don

    2011-01-01

    Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the dynamical and energetic properties in hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 30 and 200K and 0.05 kbar, and also at intermediate temperatures, using SPC/E and TIP4P-2005 water models. The potential model is found to have a large impact on overall density, with the TIP4P-2005 systems being on average 1 % more dense than their SPC/E counterparts, due to the greater guest-host in...

  16. Diffusive hydrogen inter-cage migration in hydrogen and hydrogen-tetrahydrofuran clathrate hydrates

    OpenAIRE

    H. Cao; English, Niall J.; MacElroy, J. M. Don

    2013-01-01

    Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the diffusive properties of inter-cage hydrogen migration in both pure hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 0.05 kbar from 200 K and up to 250-260 K. For mixed H2- THF systems in which there is single H2 occupation of the small cage (labelled ‘1SC 1LC’), we found that no H2 migration occurs. However, for more densely-filled H2-THF and pure- H2 systems, in which th...

  17. Diffusive hydrogen inter-cage migration in hydrogen and hydrogen-tetrahydrofuran clathrate hydrates.

    Science.gov (United States)

    Cao, Huayu; English, Niall J; MacElroy, J M D

    2013-03-01

    Classical equilibrium molecular dynamics simulations have been performed to investigate the diffusive properties of inter-cage hydrogen migration in both pure hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 0.05 kbar from 200 K and up to 250-260 K. For mixed H2-THF systems in which there is single H2 occupation of the small cage (labelled "1S1L"), we found that no H2 migration occurs. However, for more densely filled H2-THF and pure-H2 systems, in which there is more than single H2 occupation in the small cage, there is an onset of inter-cage H2 migration events from the small cages to neighbouring cavities at around 200 K. The mean square displacements of the hydrogen molecules were fitted to a mathematical model consisting of an anomalous term and a Fickian component, and nonlinear regression fitting was conducted to estimate long-time (inter-cage) diffusivities. An approximate Arrhenius temperature relationship for the diffusion coefficient was examined and an estimation of the hydrogen hopping energy barrier was calculated for each system. PMID:23485313

  18. Pressure-induced phase transformations in the Ba8Si46 clathrate

    DEFF Research Database (Denmark)

    Yang, Lirong; Ma, Y.M.; Iitaka, T.;

    2006-01-01

    parameters from Rietveld analysis. The results show that the first transition at 7 GPa is caused by the displacement of the Ba atoms in the Si-24 cages. The cause of the second transition at 15 GPa, characterized by a dramatic reduction of cell volume, is not as clear. Theoretical calculations predicted...

  19. About Some Of The Properties Of A Guest Molecule Confined In A Water Network, In Order To Form A Clathrate

    Science.gov (United States)

    Pérez, G. Bravo; Cruz-Torres, A.; Romero-Martínez, A.

    2008-03-01

    At conditions of high pressure and or low temperature, like a sea bottom from even 1 Km deep, hydrates formation may take place. Its presence is facilitated at the water/oil interface inside conducting oil pipelines. Once formed, the hydrates nucleate further to agglomerations, sticking to the inner surface of the tube. This represents a big problem to flow assurance. We present results contributing to a better understanding of the interaction of a guest molecule with a water cage confining it, that give rise to a hydrate formation. The hydrate structure, its formation energy, and the role that the H bond and its cooperative effect in the water network play in the electrostatic dipole moment of the hydrate, are presented. Molecular calculations using the HF/6-311g(d, p), B3LYP/6-311g(d, p), and B3LYP/6-311++g(d,p) methods, have been applied to compare three different hydrates, each one confining one, two CH4 molecules, and a CO2 molecule, requiring respectively n = 14, 35, and 15 water molecules for the confinement.

  20. Thermodynamic study of clathrates hydrates from hydrocarbon gas mixtures consequences for CO2 capture and flow assurance

    OpenAIRE

    Le, Quanq-Du; Le Quang, Duyen; Bouillot, Baptiste; Herri, Jean-Michel

    2014-01-01

    This work presents details on the experimental procedure to measure the composition of the hydrate that crystallizes from a hydrocarbon gas mixture. We show that the results are time dependent and tend to thermodynamic equilibrium as time tends to infinity. An immediate consequence concerns two major domains of applications, CO2 capture from power plants, as well as flow assurance in the oil and gas industry. In fact, in both the cases, the crystallization is under non equilibrium conditions,...

  1. Phase Behaviour, Thermodynamics and Kinetics of Clathrate Hydrate Systems of Carbon Dioxide in Presence of Tetrahydrofuran and Electrolytes

    NARCIS (Netherlands)

    Mohamad Sabil, K. Bin

    2009-01-01

    In view of the possibilities for new development of carbon dioxide hydrate processes, this study focused on experimental measurements to obtain fundamental insight into the phase behaviour and the kinetic of formation of carbon dioxide hydrate forming systems. These data are essential for the develo

  2. Neutron spectra and cross sections for ice and clathrate generated from the synthetic spectrum and synthetic model for molecular solids

    International Nuclear Information System (INIS)

    We present here a Synthetic Model for Molecular Solids, aimed at the description of the interaction of thermal neutrons with this kind of systems.Simple representations of the molecular dynamical modes are used, in order to produce a fair description of neutron scattering kernels and cross sections with a minimum set of input data. Using those spectra, we have generated thermal libraries for M C N P

  3. Preparation, transport properties and structure analysis by resonant x-ray scattering of the type-I clathrate Cs8Cd4Sn42

    International Nuclear Information System (INIS)

    Structural and transport properties of Cs8Cd4SN42 are reported. Cs8Cd4Sn42 has a thermal conductivity that is unusually low for a cystalline solid (1 W m-1 K-1 at room temperature). This low lattice thermal conductivity is associated with the rattling of cesium in the tetrakaidecahedral cavities, as indicated by the large atomic displacement parameters of Cs in the tetrakaidecahedra. Resonant X-ray powder diffraction measuerments indicate that all of the cadmium is located on one of three inequivalent framework sites. There is no evidence for any framework vacancies in the material

  4. Carbon dioxide, argon, nitrogen and methane clathrate hydrates: Thermodynamic modelling, investigation of their stability in Martian atmospheric conditions and variability of methane trapping

    OpenAIRE

    Herri, Jean-Michel; Chassefière, Eric

    2012-01-01

    This paper deals with the stability of clahtrate hydrates at low temperature and low pressure in the conditions prevailing in the atmosphere and at the surface of Mars. We fit the classical van der Waals model to compare deviation from experimental results published in the literature. It appears to be acceptable and allows to simulating a Martian gas, CO2 dominated (95.3%) plus nitrogen (2.7%) and argon (2%). The hydrate is a CO2-based hydrate which is unstable during Mars' summer and stable ...

  5. Viscosity Reduction with Self-Assembly of Cationic Surfactant on Tetra-n-butyl Ammonium Bromide Semi-Clathrate Hydrate Aqueous Slurry

    OpenAIRE

    Hashimoto, Shunsuke; Kawamura, Kazushi

    2012-01-01

    Aims: To utilize hydrate slurry for phase change refrigerants, the rheological properties are essential. In the present study, the viscosity characteristics of hydrate slurry are investigated. Additionally, the effect of cationic surfactant on viscosity is also evaluated. Study Design: Experimental and analytical study. Place and Duration of Study: Division of Chemical Engineering, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, between D...

  6. A molecular dynamics study of model SI clathrate hydrates: the effect of guest size and guest-water interaction on decomposition kinetics.

    Science.gov (United States)

    Das, Subhadip; Baghel, Vikesh Singh; Roy, Sudip; Kumar, Rajnish

    2015-04-14

    One of the options suggested for methane recovery from natural gas hydrates is molecular replacement of methane by suitable guests like CO2 and N2. This approach has been found to be feasible through many experimental and molecular dynamics simulation studies. However, the long term stability of the resultant hydrate needs to be evaluated; the decomposition rate of these hydrates is expected to depend on the interaction between these guest and water molecules. In this work, molecular dynamics simulation has been performed to illustrate the effect of guest molecules with different sizes and interaction strengths with water on structure I (SI) hydrate decomposition and hence the stability. The van der Waals interaction between water of hydrate cages and guest molecules is defined by Lennard Jones potential parameters. A wide range of parameter spaces has been scanned by changing the guest molecules in the SI hydrate, which acts as a model gas for occupying the small and large cages of the SI hydrate. All atomistic simulation results show that the stability of the hydrate is sensitive to the size and interaction of the guest molecules with hydrate water. The increase in the interaction of guest molecules with water stabilizes the hydrate, which in turn shows a slower rate of hydrate decomposition. Similarly guest molecules with a reasonably small (similar to Helium) or large size increase the decomposition rate. The results were also analyzed by calculating the structural order parameter to understand the dynamics of crystal structure and correlated with the release rate of guest molecules from the solid hydrate phase. The results have been explained based on the calculation of potential energies felt by guest molecules in amorphous water, hydrate bulk and hydrate-water interface regions. PMID:25767053

  7. 基于β-环糊精包合作用的防蚊真丝织物研制%Preparation of mosquito repellence silk fabric based on the clathration of β-cyclodextrin

    Institute of Scientific and Technical Information of China (English)

    许宏聪; 陈瑞玉; 沈林; 李超; 刘建华; 余志成

    2012-01-01

    The P-CD was grafted onto silk fabric with BTCA as cross-linking agent and SHP as catalytic agent, then was treated with citronella essential oil to make mosquito repellent fabric. Determine the optimum grafting process of P-CD through orthogonal experiment as: mass concentration of BTCA is 110 g/L, mass concentration of p-CD is 70 g/L, and mass concentration of SHP is 40 g/L, and curing temperature is 170 °C for 3 min, and weight gain rate of real silk fabric under this process could reach 16.04 %. SEM test indicates that: P-CD had grafted onto silk fabric successfully; after that, K/S value of P-CD grafted silk fabric dyed with cationic dyeing is increased significantly, while K/S value of acid dyes and reactive dyes are significantly lowered. After placing grafted silk fabric dyed with citronella essential oil for once week, the repellent rate of the silk fabric against culex pipiens pallens could still stay higher than 75 %.%以丁烷四羧酸(BTCA)为交联剂,次亚磷酸钠(SHP)为催化剂,将β-环糊精(β-CD)接枝到真丝织物上,再经天然香茅草提取物整理,赋予真丝织物驱蚊效果.通过正交试验确定β-CD最佳接枝工艺为:BTCA质量浓度110g/L、β-CD质量浓度70 g/L、SHP质量浓度4g/L、焙烘条件170℃、3min,此工艺下真丝织物增重率可达16.04%.扫面电镜(SEM)测试表明:β-CD己成功接枝到真丝织物上;β-CD接枝后真丝织物阳离子染料染色的K/S明显提高,而酸性染料和活性染料染色的K/S值明显下降.经香茅草提取物整理的接枝真丝织物,放置一周后,对淡色库蚊驱避率仍可保持在75%以上.

  8. On the possible noble gas deficiency of Pluto's atmosphere

    OpenAIRE

    Mousis, Olivier; Lunine, Jonathan I.; Mandt, Kathleen E.; Schindhelm, Eric; Weaver, Harold A.; Stern, S. Alan; Waite, J. Hunter; Gladstone, Randy; Moudens, Audrey

    2013-01-01

    We use a statistical-thermodynamic model to investigate the formation and composition of noble-gas-rich clathrates on Pluto's surface. By considering an atmospheric composition close to that of today's Pluto and a broad range of surface pressures, we find that Ar, Kr and Xe can be efficiently trapped in clathrates if they formed at the surface, in a way similar to what has been proposed for Titan. The formation on Pluto of clathrates rich in noble gases could then induce a strong decrease in ...

  9. Possible evidence for a methane source in Enceladus' ocean

    Science.gov (United States)

    Bouquet, A.; Mousis, O.; Waite, J. H.; Picaud, S.

    2015-10-01

    We have investigated the evolution of the composition of the putative internal ocean of Enceladus. We used a thermodynamical statistical model to assess the formation of clathrate hydrates in an ocean with the composition of the plumes observed by the Cassini probe. We find that in our initial scenario as well as in alternative ones, clathrates form and efficiently deplete methane in the ocean, below plume levels. An additional source of methane in the ocean or ulterior dissociation of the clathrates are required to explain the abundances of methane detected in the plumes..

  10. Hydrogen storage in molecular compounds

    OpenAIRE

    Mao, Wendy L.; Mao, Ho-kwang

    2004-01-01

    At low temperature (T) and high pressure (P), gas molecules can be held in ice cages to form crystalline molecular compounds that may have application for energy storage. We synthesized a hydrogen clathrate hydrate, H2(H2O)2, that holds 50 g/liter hydrogen by volume or 5.3 wt %. The clathrate, synthesized at 200–300 MPa and 240–249 K, can be preserved to ambient P at 77 K. The stored hydrogen is released when the clathrate is warmed to 140 K at ambient P. Low T also stabilizes other molecular...

  11. Tracking all-vapor instant gas-hydrate formation and guest molecule populations: A possible probe for molecules trapped in water nanodroplets

    Czech Academy of Sciences Publication Activity Database

    Uras-Aytemiz, N.; Cwiklik, Lukasz; Devlin, J. P.

    2012-01-01

    Roč. 137, č. 20 (2012), s. 204501. ISSN 0021-9606 Institutional support: RVO:61388955 Keywords : Fourier transform infrared emission spectra * clathrate hydrate * simulations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.164, year: 2012

  12. Method for solid state crystal growth

    Science.gov (United States)

    Nolas, George S.; Beekman, Matthew K.

    2013-04-09

    A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

  13. 21 CFR 314.108 - New drug product exclusivity.

    Science.gov (United States)

    2010-04-01

    ...) DRUGS FOR HUMAN USE APPLICATIONS FOR FDA APPROVAL TO MARKET A NEW DRUG FDA Action on Applications and... coordination bonds), or other noncovalent derivative (such as a complex, chelate, or clathrate) of the...

  14. The Clathration Technology of Garlic Oil and Its Influence to the Blood Rheology of Experimental Hyperlipemia Rat%大蒜油的包合工艺及其对实验性高脂血症大鼠血液流变学影响

    Institute of Scientific and Technical Information of China (English)

    饶小勇; 何颖辉; 王珏; 林色奇; 张国松; 罗小建

    2006-01-01

    大蒜油为大蒜(Allium sativum L)的有效成分之一,通过对大蒜油进行β-环糊精(简称β-CD)包合工艺的考察,确定大蒜油的最佳包合工艺;大蒜油包合物能明显降低大蒜油对胃肠道粘膜的刺激性,比纯大蒜油更具有应用价值,为了深入研究大蒜油及其包合物的药效作用及毒性,我们做了大蒜油β—CD包合物对实验性高血脂症大鼠血液流变学的影响的试验研究。

  15. Phase equilibria of carbon dioxide and methane gas-hydrates predicted with the modified analytical S-L-V equation of state

    Directory of Open Access Journals (Sweden)

    Span Roland

    2012-04-01

    Full Text Available Gas-hydrates (clathrates are non-stoichiometric crystallized solutions of gas molecules in the metastable water lattice. Two or more components are associated without ordinary chemical union but through complete enclosure of gas molecules in a framework of water molecules linked together by hydrogen bonds. The clathrates are important in the following applications: the pipeline blockage in natural gas industry, potential energy source in the form of natural hydrates present in ocean bottom, and the CO2 separation and storage. In this study, we have modified an analytical solid-liquid-vapor equation of state (EoS [A. Yokozeki, Fluid Phase Equil. 222–223 (2004] to improve its ability for modeling the phase equilibria of clathrates. The EoS can predict the formation conditions for CO2- and CH4-hydrates. It will be used as an initial estimate for a more complicated hydrate model based on the fundamental EoSs for fluid phases.

  16. The fate of ethane in Titan's hydrocarbon lakes and seas

    Science.gov (United States)

    Mousis, Olivier; Lunine, Jonathan I.; Hayes, Alexander G.; Hofgartner, Jason D.

    2016-05-01

    Ethane is expected to be the dominant photochemical product on Titan's surface and, in the absence of a process that sequesters it from exposed surface reservoirs, a major constituent of its lakes and seas. Absorption of Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this interaction on an assumed initial ethane-methane mixture in the liquid phase. We find that progressive liquid entrapment in clathrate allows the surface liquid reservoir to become methane-dominated for any initial ethane mole fraction below 0.75. If interactions between alkanofers and clathrates are common on Titan, this should lead to the emergence of many methane-dominated seas or lakes.

  17. The fate of ethane in Titan's hydrocarbon lakes and seas

    CERN Document Server

    Mousis, Olivier; Hayes, Alexander G; Hofgartner, Jason D

    2015-01-01

    Ethane is expected to be the dominant photochemical product on Titan's surface and, in the absence of a process that sequesters it from exposed surface reservoirs, a major constituent of its lakes and seas. Absorption of Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this interaction on an assumed initial ethane-methane mixture in the liquid phase. We find that progressive liquid entrapment in clathrate allows the surface liquid reservoir to become methane-dominated for any initial ethane mole fraction below 0.75. If interactions between alkanofers and clathrates are common on Titan, this should lead to the emergence of many methane-dominated seas or lakes.

  18. Physical properties of single-crystalline Ba 8 Ni 3.5 Ge 42.1 h 0.4

    OpenAIRE

    Nguyen, Lien Thi Kim; Aydemir, Umut; Baitinger, Michael; Custers, Jeroen; Haghighirad, Amir-Abbas; Höfler, Rudolf; Luther, Klaus-Dieter; Ritter, Franz; Grin, Yuri; Aßmus, Wolf (Prof. Dr.); Paschen, Silke

    2010-01-01

    Clathrates are candidate materials for thermoelectric applications because of a number of unique properties. The clathrate I phases in the Ba-Ni-Ge ternary system allow controlled variation of the charge carrier concentration by adjusting the Ni content. Depending on the Ni content, the physical properties vary from metal-like to insulator-like and show a transition from p-type to n-type conduction. Here we present first results on the characterization of millimeter-sized single crystals grow...

  19. Finding New Thermoelectric Compounds Using Crystallographic Data: Atomic Displacement Parameters

    International Nuclear Information System (INIS)

    A new structure-property relationship is discussed which links atomic displacement parameters (ADPs) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-like compounds, in which one of the atom types is weakly bound and ''rattles'' within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the ''rattler'', and the temperature dependence of the heat capacity. Neutron data and X-ray crystallography data, reported in the literature, are used to apply this analysis to several promising classes of thermoelectric materials

  20. Volcanism and igneous processes in small icy satellites

    Energy Technology Data Exchange (ETDEWEB)

    Stevenson, D.J. (California Inst. of Tech., Pasadena (USA). Div. of Geological and Planetary Sciences)

    1982-07-08

    It is argued that the most likely cause of endogenic processes in the small saturnian satellites is the igneous activity associated with a low melting point NH/sub 3/-H/sub 2/O magma. Radiogenic heating probably suffices to provide the necessary melting in Tethys, Dione, Rhea and Iapetus whereas tidal heating is needed for Enceladus and possibly Mimas. Migration of large fluid-filled cracks, leading to surface flooding, is likely. If clathrates are present, then pyroclast-forming explosive events can occur at a near-surface intrusive contact between magma and one or more of the methane, nitrogen and argon clathrates.

  1. EXPERIMENT ON METHANE GAS HYDRATE FORMATION%甲烷水合物储气实验研究

    Institute of Scientific and Technical Information of China (English)

    郑新; 樊栓狮

    2003-01-01

    @@ 1 INTRODUCTION Methane gas hydrates (MGH) are solid phase crystalline inclusion compounds (also called clathrates) that consist of a host water lattice with cavities in which methane gas is caged as a guest gas.Methane gas hydrate might contain 164 volumes (at standard pressure and temperature)of methane and 0.87 volumes of water per volume hydrate.

  2. SULFURIZATION OF IRON IN THE DYNAMIC SOLAR NEBULA AND IMPLICATIONS FOR PLANETARY COMPOSITIONS

    Energy Technology Data Exchange (ETDEWEB)

    Ciesla, Fred J., E-mail: fciesla@uchicago.edu [Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States)

    2015-02-10

    One explanation for the enhanced ratio of volatiles to hydrogen in Jupiter’s atmosphere compared to a a gas of solar composition is that the planet accreted volatile-bearing clathrates during its formation. Models, however, suggest that S would be over abundant if clathrates were the primary carrier of Jupiter’s volatiles. This led to the suggestion that S was depleted in the outer nebula due to the formation troilite (FeS). Here, this depletion is quantitatively explored by modeling the coupled dynamical and chemical evolution of Fe grains in the solar nebula. It is found that disks that undergo rapid radial expansion from an initially compact state may allow sufficient production of FeS and carry H{sub 2}S-depleted gas outward where ices would form, providing the conditions needed for S-depleted clathrates to form. However, this expansion would also carry FeS grains to this region, which could also be incorporated into planetesimals. Thus for clathrates to be a viable source of volatiles, models must account for the presence of both H{sub 2}S in FeS in the outer solar nebula.

  3. A brief review of the low temperature thermal properties of crystalline and glassy materials

    International Nuclear Information System (INIS)

    The thermal properties of crystalline and amorphous materials have been reviewed. It is found that the specific heats of many crystalline materials at low temperatures deviate from the Debye T law and can be explained using flat TA mode. The thermal conductivity of many crystalline material such as ice-Ih and clathrate hydrate at low temperatures is not well understood. (author)

  4. Liquid Water Structure from Anomalous Density under Ambient Condition

    Institute of Scientific and Technical Information of China (English)

    SUN Qiang; ZHENG Hai-Fei

    2006-01-01

    @@ From discussion of the structure of liquid water, we deduce that water under ambient condition is mainly composed of ice Ih-like molecular clusters and clathrate-like molecular clusters. The water molecular clusters remain in a state of chemical equilibrium (reversible clustering reactions). This structural model can be demonstrated by quantitative study on anomalous density with increasing temperature at ambient pressure.

  5. Sulfurization of Iron in the Dynamic Solar Nebula and Implications for Planetary Compositions

    CERN Document Server

    Ciesla, Fred J

    2015-01-01

    One explanation for the enhanced ratio of volatiles to hydrogen in Jupiter's atmosphere compared to a a gas of solar composition is that the planet accreted volatile-bearing clathrates during its formation. Models, however, suggest that S would be over abundant if clathrates were the primary carrier of Jupiter's volatiles. This led to the suggestion that S was depleted in the outer nebula due to the formation troilite (FeS). Here, this depletion is quantitatively explored by modeling the coupled dynamical and chemical evolution of Fe grains in the solar nebula. It is found that disks that undergo rapid radial expansion from an initially compact state may allow sufficient production of FeS and carry H$_{2}$S-depleted gas outward where ices would form, providing the conditions needed for S-depleted clathrates to form. However, this expansion would also carry FeS grains to this region, which could also be incorporated into planetesimals. Thus for clathrates to be a viable source of volatiles, models must account...

  6. Materials for hydrogen storage: current research trends and perspectives.

    Science.gov (United States)

    van den Berg, Annemieke W C; Areán, Carlos Otero

    2008-02-14

    Storage and transport of hydrogen constitutes a key enabling technology for the advent of a hydrogen-based energy transition. Main research trends on hydrogen storage materials, including metal hydrides, porous adsorbents and hydrogen clathrates, are reviewed with a focus on recent developments and an appraisal of the challenges ahead. . PMID:18478688

  7. Phase equilibrium modeling of gas hydrate systems for CO2 capture

    DEFF Research Database (Denmark)

    Herslund, Peter Jørgensen; Thomsen, Kaj; Abildskov, Jens;

    2012-01-01

    Two thermodynamic models capable of describing dissociation pressures of mixed gas clathrate hydrates formed from ternary mixtures of CO2, N2 and liquid water, are presented. Both of the models utilize the Cubic-Plus-Association (CPA) equation of state (EOS) for the thermodynamic description of t...

  8. On the abundances of noble and biologically relevant gases in Lake Vostok, Antarctica

    CERN Document Server

    Mousis, Olivier; Picaud, Sylvain; Pasek, Matthew; Chassefière, Eric

    2013-01-01

    Motivated by the possibility of comparing theoretical predictions of Lake Vostok's composition with future in situ measurements, we investigate the composition of clathrates that are expected to form in this environment from the air supplied to the lake by melting ice. In order to establish the best possible correlation between the lake water composition with that of air clathrates formed in situ, we use a statistical thermodynamic model based on the description of the guest-clathrate interaction by a spherically averaged Kihara potential with a nominal set of potential parameters. We determine the fugacities of the different volatiles present in the lake by defining a "pseudo" pure substance dissolved in water owning the average properties of the mixture and by using the Redlich-Kwong equation of state to mimic its thermodynamic behavior. Irrespective of the clathrate structure considered in our model, we find that xenon and krypton are strongly impoverished in the lake water (a ratio in the 0.04--0.1 range ...

  9. Nano-rattling semiconductors

    International Nuclear Information System (INIS)

    The efficiency of a thermoelectric material is given by its figure of merit, Z=S2σ/κ, where Z is in unit of (K)-1, S is its Seebeck coefficient, σ is its electrical conductivity and κ is its thermal conductivity. A good thermoelectric material must have high electrical conductivity and low thermal conductivity. Semiconducting clathrates are promising thermoelectric materials. The clathrate lattices are open frameworks containing large 'cages'. These cages can contain loosly bound impurity atoms or 'guests'. The guest atoms are 'rattling' in the cages and scatter the heat carry phonons, resulting in the amorphous like low thermal conductivity. The improvement of the thermoelectric properties of clathrates was attempted by the modification of electronic properties through the transition element substitution at the 6c site of the host lattice. The substitution of Pt atoms brings about an increase of Seebeck coefficient but only a slight decrease of carrier mobilities. The calculated electronic structure shows that transition element substituting clathrates Ba8TMGe40 (TM=Ni, Pd, Pt, Cu, Ag, Au) are p-type semiconductors and have large thermoelectric power in spite of relatively low mobilities of the charge carriers. The electronic structure and thermoelectric properties are also calculated for guest-substituted clathrates Ba6R2Au6Ge40 (R=Eu, Yb). When the Ba 2a site is replaced by Eu and Yb, the lowest conduction bands at x-point shift to lower energy side. The multivally effect in M and X points yields the increase in the density of states near the conduction band edge, resulting in the increase in the Seebeck coefficient for n-type doping. The lattice thermal conductivity decreases gradually with the increasing x of all the YbxBa8-xGa16Ge30 compounds. (Y. K.)

  10. Phase equilibrium conditions of semi-calthrate hydrates of (tetra-n-butyl ammonium chloride + carbon dioxide)

    International Nuclear Information System (INIS)

    Highlights: • Carbon dioxide hydrate stability zone was enlarged with the help of TBAC. • Carbon dioxide uptake into TBAC semi-clathrate hydrates is confirmed. • Equilibrium pressure of hydrate decreased with the increase of TBAC mass concentration. • The addition of TBAC reduces the formation pressures of carbon dioxide hydrate by 2.5 MPa. - Abstract: In the present work, hydrate equilibrium conditions for (tetra-n-butyl ammonium chloride (TBAC) + carbon dioxide + water) mixtures were investigated. Tetra-n-butyl ammonium chloride was reported to form a semi-clathrate hydrate. The experiments were carried out within the TBAC mass fraction range of (0.05 to 0.3). The experimental results showed that the presence of TBAC decreased the formation pressure of carbon dioxide double hydrate within the experimental temperature range. Moreover, pressure reduction was dependent on the TBAC concentration

  11. astrophysical significance

    Directory of Open Access Journals (Sweden)

    Dartois E.

    2014-02-01

    Full Text Available Clathrate hydrates, ice inclusion compounds, are of major importance for the Earth’s permafrost regions and may control the stability of gases in many astrophysical bodies such as the planets, comets and possibly interstellar grains. Their physical behavior may provide a trapping mechanism to modify the absolute and relative composition of icy bodies that could be the source of late-time injection of gaseous species in planetary atmospheres or hot cores. In this study, we provide and discuss laboratory-recorded infrared signatures of clathrate hydrates in the near to mid-infrared and the implications for space-based astrophysical tele-detection in order to constrain their possible presence.

  12. The future of methane as an energy resource

    International Nuclear Information System (INIS)

    The author begins this paper with an examination of the world's conventional and unconventional resources base for natural gas. Next, the environmental advantages and disadvantages of natural gas are explored, with an emphasis on new technologies that offer significant efficiency advantages. The author closes with a detailed consideration of an unconventional gas source, methane clathrates, that is not usually considered in future resource projections. Given anticipated production levels, existing conventional gas fields should peak early in the next century. Another 30 to 40 years of production can be expected from undiscovered conventional fields. In the second half of the next century, unconventional gas deposits - tight sands, shales, and coal beds - will become an important resource. As production from these deposits peaks, the enormous methane clathrate resource base will become essential, particularly if the world turns to a hydrogen-based economy

  13. Formation of porous gas hydrates

    CERN Document Server

    Salamatin, Andrey N

    2015-01-01

    Gas hydrates grown at gas-ice interfaces are examined by electron microscopy and found to have a submicron porous texture. Permeability of the intervening hydrate layers provides the connection between the two counterparts (gas and water molecules) of the clathration reaction and makes further hydrate formation possible. The study is focused on phenomenological description of principal stages and rate-limiting processes that control the kinetics of the porous gas hydrate crystal growth from ice powders. Although the detailed physical mechanisms involved in the porous hydrate formation still are not fully understood, the initial stage of hydrate film spreading over the ice surface should be distinguished from the subsequent stage which is presumably limited by the clathration reaction at the ice-hydrate interface and develops after the ice grain coating is finished. The model reveals a time dependence of the reaction degree essentially different from that when the rate-limiting step of the hydrate formation at...

  14. [Concept of mechanisms of anesthetic and therapeutic properties of xenon].

    Science.gov (United States)

    Burov, N E

    2011-01-01

    The molecular theory of L. Poling is a genius example of scientific prediction, made in the middle of 20th century, when the studies about clathrates and methods of roentgen structured analysis were doing their first steps. The views expressed in this message are some additions on the structure of xenon clathrates, function-free xenon water associates and the use of cameras in the liberated associates of the water molecules, for the process of supramolecular detoxification and attempts to develop this theory more widely, to better understand the mechanisms of xenon anesthesia and treatment for further justification of its therapeutic features as well as for the use of other inert gases (Ar, Kr) in modern medicine. PMID:21692221

  15. On the origin of Triton and Pluto

    International Nuclear Information System (INIS)

    A simple hypothesis on the origin of Triton and Pluto is that Triton and Pluto are independent representatives of large outer Solar System planetesimals. Triton is simply captured, with potentially spectacular consequences that include runaway melting of interior ices and release to the surface of clathrated CH4, CO and N2. Condensed remnants of this proto-atmosphere could account for features in Triton's unique spectrum. (author)

  16. Fuel traps: mapping stability via water association.

    Energy Technology Data Exchange (ETDEWEB)

    Rempe, Susan L.; Clawson, Jacalyn S.; Greathouse, Jeffery A.; Alam, Todd M; Leung, Kevin; Varma, Sameer; Sabo, Dubravko; Martin, Marcus Gary; Cygan, Randall Timothy

    2007-03-01

    Hydrogen storage is a key enabling technology required for attaining a hydrogen-based economy. Fundamental research can reveal the underlying principles controlling hydrogen uptake and release by storage materials, and also aid in characterizing and designing novel storage materials. New ideas for hydrogen storage materials come from exploiting the properties of hydrophobic hydration, which refers to water s ability to stabilize, by its mode of association, specific structures under specific conditions. Although hydrogen was always considered too small to support the formation of solid clathrate hydrate structures, exciting new experiments show that water traps hydrogen molecules at conditions of low temperatures and moderate pressures. Hydrogen release is accomplished by simple warming. While these experiments lend credibility to the idea that water could form an environmentally attractive alternative storage compound for hydrogen fuel, which would advance our nation s goals of attaining a hydrogen-based economy, much work is yet required to understand and realize the full potential of clathrate hydrates for hydrogen storage. Here we undertake theoretical studies of hydrogen in water to establish a firm foundation for predictive work on clathrate hydrate H{sub 2} storage capabilities. Using molecular simulation and statistical mechanical theories based in part on quantum mechanical descriptions of molecular interactions, we characterize the interactions between hydrogen and liquid water in terms of structural and thermodynamic properties. In the process we validate classical force field models of hydrogen in water and discover new features of hydrophobic hydration that impact problems in both energy technology and biology. Finally, we predict hydrogen occupancy in the small and large cages of hydrogen clathrate hydrates, a property unresolved by previous experimental and theoretical work.

  17. Influence d'additifs anti-agglomérants sur l'agrégation et les propriétés de transport des hydrates de méthane cristallisant dans des émulsions eau/dodécane

    OpenAIRE

    FIDEL-DUFOUR, Annie

    2004-01-01

    The gas hydrates are solid compounds of clathrate type which can be formed starting from cold water and hydrocarbon gas molecules under pressure. These conditions are met in certain oil conduits and can lead to a problem of production. Indeed, the oil effluent which leaves a well of production always contains light water and hydrocarbon molecules (methane, ethane, propane) suitable form a gas hydrate. The methane hydrates are not naturally present in the layers of production because the tempe...

  18. Review of Solid State Hydrogen Storage Methods Adopting Different Kinds of Novel Materials

    OpenAIRE

    Renju Zacharia; Sami ullah Rather

    2015-01-01

    Overview of advances in the technology of solid state hydrogen storage methods applying different kinds of novel materials is provided. Metallic and intermetallic hydrides, complex chemical hydride, nanostructured carbon materials, metal-doped carbon nanotubes, metal-organic frameworks (MOFs), metal-doped metal organic frameworks, covalent organic frameworks (COFs), and clathrates solid state hydrogen storage techniques are discussed. The studies on their hydrogen storage properties are in pr...

  19. Changes in atmospheric carbonyl sulfide over the last 54,000 years inferred from measurements in Antarctic ice cores

    Science.gov (United States)

    Aydin, M.; Campbell, J. E.; Fudge, T. J.; Cuffey, K. M.; Nicewonger, M. R.; Verhulst, K. R.; Saltzman, E. S.

    2016-02-01

    We measured carbonyl sulfide (COS) in air extracted from ice core samples from the West Antarctic Ice Sheet (WAIS) Divide, Antarctica, with the deepest sample dated to 54,300 years before present. These are the first ice core COS measurements spanning the Last Glacial Maximum (LGM), the last glacial/interglacial transition, and the early Holocene. The WAIS Divide measurements from the LGM and the last transition are the first COS measurements in air extracted from full clathrate (bubble-free) ice. This study also includes new COS measurements from Taylor Dome, Antarctica, including some in bubbly glacial ice that are concurrent with the WAIS Divide data from clathrate glacial ice. COS hydrolyzes in ice core air bubbles, and the recovery of an atmospheric record requires correcting for this loss. The data presented here suggest that the in situ hydrolysis of COS is significantly slower in clathrate ice than in bubbly ice. The clathrate ice measurements are corrected for the hydrolysis loss during the time spent as bubbly ice only. The corrected WAIS Divide record indicates that atmospheric COS was 250-300 parts per trillion (ppt) during the LGM and declined by 80-100 ppt during the last glacial/interglacial transition to a minimum of 160-210 ppt at the beginning of the Holocene. This decline was likely caused by an increase in the gross primary productivity of terrestrial plants, with a possible contribution from a reduction in ocean sources. COS levels were above 300 ppt in the late Holocene, indicating that large changes in the COS biogeochemical cycle occurred during the Holocene.

  20. Colossal magnetocapacitance effect at room temperature

    Science.gov (United States)

    Bishchaniuk, T. M.; Grygorchak, I. I.

    2014-05-01

    First nano-hybridized clathrate/cavitant structure of hierarchical architecture was synthesized. The results of investigations of the properties of initial nanoporous silica matrices MCM-41, with encapsulated in its pores of β-cyclodextrin in cavitand and cavitat (with FeSO4) states and change at room temperature in a constant magnetic field intensity of 2.75 kOe, have been presented. Phenomenon of enormous magnetocapacitance and giant negative variable-current magnetoresistance has been discovered.

  1. Coupled multiphysics modeling of gas hydrate bearing sediments

    OpenAIRE

    Sanchez, Marcelo; Gai, Xuerui; Santamarina, J. Carlos

    2014-01-01

    Gas hydrates are crystalline clathrate compounds made of water and a low molecular gas like methane (Sloan 1998). Gas hydrates are generally present in oil-producing areas and in permafrost regions. Methane hydrate deposits can lead to large-scale submarine slope failures, blowouts, platform foundation failures, and -borehole instability. Gas hydrates constitute also an attractive source of energy as they are estimated to contain very large reserves of methane. Hydrate formation, dissociation...

  2. Crystal structure and encapsulation dynamics of ice II-structured neon hydrate

    OpenAIRE

    Yu, Xiaohui; Zhu, Jinlong; Du, Shiyu; Xu, Hongwu; Vogel, Sven C.; Han, Jiantao; Germann, Timothy C.; Zhang, Jianzhong; Jin, Changqing; Francisco, Joseph S.; Zhao, Yusheng

    2014-01-01

    Clathrate hydrates have ice-like crystalline structures typically stabled under low-temperature and high-pressure conditions. They are of great importance as potential materials for energy storage and production and carbon dioxide sequestration. Here the first structural refinement data of neon hydrate, to our knowledge, are presented. Both the experimental observations by in situ neutron diffraction and molecular dynamics simulations demonstrate that neon atoms can be enclathrated to form ic...

  3. 微小重力下におけるエアロゾル・デポジション法による薄膜形成

    OpenAIRE

    Watanabe, Masahito; Nakano, Shizuka; Akedo, Jun; 渡邉 匡人; 中野 禅; 明渡 純

    2007-01-01

    In this research, we clarify the aerosol dynamics during thin film formation by using the Aerosol Deposition (AD) technique under the microgravity conditions. The aerosol deposition technique is useful for making thin film of ceramics materials. We are now trying this technique to make thin film of thermally unstable materials, such as clathrate compounds and/or amorphous materials. However, it is difficult to make homogeneously the aerosol of these materials in the terrestrial conditions, be...

  4. Coexistence of structure I and II gas hydrates in Lake Baikal suggesting gas sources from microbial and thermogenic origin

    OpenAIRE

    Kida, M; Khlystov, O.; Zemskaya, T.; Takahashi, N; Minami, H.; Sakagami, H; Krylov, A.; Hachikubo, A.; YAMASHITA, S.; Shoji, H; J. Poort; L. Naudts

    2006-01-01

    We report the field observation of hydrate deposits of different crystal structures in the same cores of a mud volcano in the Kukuy Canyon. We link those deposits to chemical fractionation during gas hydrate crystallization. Gas composition and crystallographic analyses of hydrate samples reveal involvement of two distinct gas source types in gas hydrate formation at present or in the past: microbial (methane) and thermogenic (methane and ethane) gas types. The clathrate structure II, observe...

  5. Interpretation of the ethane deficiency in Ligeia Mare

    Science.gov (United States)

    Mousis, O.; Lunine, J. I.; Hayes, A. G.; Hofgartner, J.

    2015-10-01

    Absorption of Cassini's 2.2 cm radar by Ligeia Mare suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this inter action on an assumed initial ethane- methane mixture in the liquid phase.

  6. The mysteries of memory effect and its elimination with antifreeze proteins

    Energy Technology Data Exchange (ETDEWEB)

    Walker, V.; Gordienko, R.; Kuiper, M.; Huva, E.; Wu, Z. [Queen' s Univ., Kingston, ON (Canada). Dept. of Biology; Zeng, H.; Ripmeester, J. [Queen' s Univ., Kingston, ON (Canada). Dept. of Biology]|[National Research Council of Canada, Ottawa, ON (Canada). Steacie Inst. for Molecular Sciences

    2008-07-01

    With the decline in easily accessible and conventional hydrocarbon supplies, exploration will focus on hydrocarbons in deep offshore waters, in permafrost or in crystalline water as gas hydrates. Crystallization of water or water-encaged gas molecules takes place when nuclei reach a critical size, but the crystal growth may be inhibited by certain antifreeze proteins (AFPs). In this study, the authors hypothesized that the crystal lattice of gas hydrates may act as an alternative for substrate antifreeze proteins (AFPs). AFP-mediated inhibition of ice and clathrate hydrate crystallization was examined. Since the AFPs had a notable ability to eliminate the memory effect (ME) or the faster reformation of clathrate hydrates after melting, the authors were prompted to examine heterogeneous nucleation. Silica, served as a model nucleator hydrophilic surface. Quartz crystal microbalance-dissipation (QCM-D) experiments showed that an active AFP was tightly adsorbed to the silica surface. However, polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap), 2 commercial hydrate kinetic inhibitors that do not eliminate ME, were not as tightly adsorbed. A mutant AFP inhibited tetrahydrofuran clathrate hydrate growth, but not ME. QCM-D analysis showed that adsorption of the mutant AFP was more similar to PVCap than the active AFP. It was concluded that although there is no evidence for memory in ice reformation, the crystallization of ice and hydrates, and the elimination of the more rapid recrystallization of hydrates, can be mediated by the same proteins. The properties of adsorbed layers can be effectively monitored by QCM-D. These study results provided useful information about the inhibition mechanism of heterogeneous nucleation of clathrate hydrate. The technique facilitates the screening of potential low dose hydrate inhibitors and residues in AFPs that are involved in silica adsorption. 24 refs., 1 tab., 4 figs.

  7. Advanced heat pumps and their economic aspects. The case for super heat pump

    International Nuclear Information System (INIS)

    The results of the economic evaluation of the Super Heat Pump Energy Accumulation System project in Japan are reviewed. It is reported that although the initial costs of super heat pumps are higher than those of conventional systems, the calculated operating costs of a unit thermal energy produced by a super heat pump is reduced considerably. All the various system concepts with thermal/chemical storage were evaluated economically with the exception of the high temperature thermal storage systems using salt ammonia complexes and solvation. These latter systems were not further developed as pilot plants. It is advocated to accelerate the introduction of super heat pumps by facilitating their market introduction. Actual clathrate chemical storage systems have shown that the annual costs are comparable to those of an ice storage system. Clathrate systems will find their way in the market. It is concluded that most of the super heat pump systems and clathrate storage systems will be economic in the future. A big challenge however still exists in further improving the cost effectiveness of heat storage in tanks by reducing their size dramatically (to 1/10th)

  8. Early Mars volcanic sulfur storage in the cryosphere and formation of transient SO2-rich atmospheres during the Hesperian

    CERN Document Server

    Schmidt, F; Tian, F; Dartois, E; Herri, J -M; Mousis, O

    2016-01-01

    In a previous paper (Chassefi\\`ere et al., Icarus 223, 878-891, 2013), we have shown that most volcanic sulfur released to early Mars atmosphere could have been trapped in the cryosphere under the form of CO2-SO2 clathrates. Huge amounts of sulfur, up to the equivalent of a ~1 bar atmosphere of SO2, would have been stored in the Noachian cryosphere, then massively released to the atmosphere during Hesperian due to rapidly decreasing CO2 pressure. It would have resulted in the formation of the large sulfate deposits observed mainly in Hesperian terrains, whereas no or little sulfates are found at the Noachian. In the present paper, we first clarify some aspects of our previous work. We discuss the possibility of a smaller cooling effect of sulfur particles, or even of a net warming effect. We point out the fact that CO2-SO2 clathrates formed through a progressive enrichment of a preexisting reservoir of CO2 clathrates and discuss processes potentially involved in the slow formation of a SO2-rich upper cryosphe...

  9. Photoluminescence properties of S2 molecule trapped in Melanophlogite

    Science.gov (United States)

    Messina, Fabrizio; Todaro, Michela; Buscarino, Gianpiero; Vaccaro, Lavinia; Cannas, Marco; Gelardi, Franco M.

    2016-03-01

    We studied the photoluminescence properties of a sample of SiO2-clathrate Melanophlogite, a crystalline microporous material which is found in nature as a rare mineral. Upon β irradiation, the material displays an intense light emission under near-UV illumination. We studied in detail this optical activity by steady-state and time-resolved photoluminescence measurements as a function of temperature. The spectroscopic properties we find can be ascribed to a population of quasi-free molecules trapped within each of the two different types of cage available in the structure of this clathrate, although the spectroscopic properties of the guest molecules are affected by their interactions with the host matrix. Based on the available data, we attribute the observed photoluminescence to trapped S2 molecules, emitting from their excited 3Σ u - or 3Π u electronic states, depending on the cage they are trapped in and on temperature. Our results have an impact on the fundamental understanding of host-guest interactions characteristic of microporous systems such as clathrates. Indeed, the data highlight that even a relatively weak coupling between quasi-free S2 molecules and the two types of cages provided by the Melanophlogite host has a surprisingly complex influence on the optical properties of the guest.

  10. The radiometric analysis of non-radioactive materials by chemical exchange

    International Nuclear Information System (INIS)

    The use of radioisotopes to measure the composition of different materials via chemical exchange within an instrument is described. The product of the reaction is a radioactive gas which is counted and serves as the indicator of measurement. This method has been applied to a number of different liquids and gases for their specific and sensitive determination. The chief limiting condition on sensitivity is imposed by the specific activity of the radiochemical component. Where high specific activities are available, sensitivity in terms of chemical quantity will be very great. The recent development of quinol- Kr85 clathrate compounds has provided a basic radiochemical source which not only provides high specific activities at low cost but also excellent half-life and energy characteristics. These clathrate compounds can be oxidized only by very strong oxidizing agents, such as ozone to release Kr85. When coupled with a salt, such as sodium chlorite, the sensing of reducing materials such as SO2 may be accomplished. Two applications of the radiometric technique employing clathrates are described. The first is the development of a balloon-borne sonde for the meteorological analysis of ozone in the upper atmosphere. The other is its use in air pollution and process control work in the form of a portable analyser. Different gases may be analysed by this device by merely changing the radiochemical reaction cell. (author)

  11. Application of gas hydrate formation in separation processes: A review of experimental studies

    International Nuclear Information System (INIS)

    Highlights: ► Review of gas hydrate technology applied to separation processes. ► Gas hydrates have potential to be a future sustainable separation technology. ► More theoretical, simulation, and economic studies needed. - Abstract: There has been a dramatic increase in gas hydrate research over the last decade. Interestingly, the research has not focussed on only the inhibition of gas hydrate formation, which is of particular relevance to the petroleum industry, but has evolved into investigations on the promotion of hydrate formation as a potential novel separation technology. Gas hydrate formation as a separation technology shows tremendous potential, both from a physical feasibility (in terms of effecting difficult separations) as well as an envisaged lower energy utilization criterion. It is therefore a technology that should be considered as a future sustainable technology and will find wide application, possibly replacing a number of current commercial separation processes. In this article, we focus on presenting a brief description of the positive applications of clathrate hydrates and a comprehensive survey of experimental studies performed on separation processes using gas hydrate formation technology. Although many investigations have been undertaken on the positive application of gas hydrates to date, there is a need to perform more theoretical, experimental, and economic studies to clarify various aspects of separation processes using clathrate/semi-clathrate hydrate formation phenomena, and to conclusively prove its sustainability.

  12. Exotic Forms of Silicon for Energy Applications

    Science.gov (United States)

    Taylor, P. Craig

    2015-03-01

    Over the last few decades many exotic forms of carbon, such as carbon-60, carbon nanotubes, and graphene, have generated novel scientific discoveries and revolutionized many important applications. Similar potentially transformative breakthroughs may be expected with exotic forms of silicon. Such structures include, but are not necessarily limited to, (1) those formed under high pressure that are metastable at ambient pressure, (2) single layers of Si (silicene), (2) clathrate Si, which has been studied for superconducting and thermoelectric properties but not in any detail for semiconductor applications, (3) nanostructured forms of Si (nanodots and nanowires), including those composed of diamond Si, (4) porous Si, and (5) any other structures that differ in their structural, optical or electronic properties from bulk diamond Si. Silicon is an abundant, non-toxic element around which an advanced technology exists for semiconducting devices based on diamond Si. One of these exotic forms of Si could form the basis for the next revolution in electronics or even opto-electronics, since some forms exhibit direct, or nearly direct, band gaps. Recent results toward producing pure and dopable semiconductors out of Si nanodots imbedded in amorphous matrices and in clathrate Si and clathrate Si-Ge alloys will be discussed. The author acknowledges important collaborations with R. T. Collins, C. A. Koh, L. Krishna, M. Lusk, and P. Stradins. DOE SUNSHOT program, under Contract DE-EE0005326 and by the NSF MRSEC program under Grant DMR-0820518.

  13. Marine methane cycle simulations for the period of early global warming

    Energy Technology Data Exchange (ETDEWEB)

    Elliott, S.; Maltrud, M.; Reagan, M.T.; Moridis, G.J.; Cameron-Smith, P.J.

    2011-01-02

    Geochemical environments, fates, and effects are modeled for methane released into seawater by the decomposition of climate-sensitive clathrates. A contemporary global background cycle is first constructed, within the framework of the Parallel Ocean Program. Input from organics in the upper thermocline is related to oxygen levels, and microbial consumption is parameterized from available rate measurements. Seepage into bottom layers is then superimposed, representing typical seabed fluid flow. The resulting CH{sub 4} distribution is validated against surface saturation ratios, vertical sections, and slope plume studies. Injections of clathrate-derived methane are explored by distributing a small number of point sources around the Arctic continental shelf, where stocks are extensive and susceptible to instability during the first few decades of global warming. Isolated bottom cells are assigned dissolved gas fluxes from porous-media simulation. Given the present bulk removal pattern, methane does not penetrate far from emission sites. Accumulated effects, however, spread to the regional scale following the modeled current system. Both hypoxification and acidification are documented. Sensitivity studies illustrate a potential for material restrictions to broaden the perturbations, since methanotrophic consumers require nutrients and trace metals. When such factors are considered, methane buildup within the Arctic basin is enhanced. However, freshened polar surface waters act as a barrier to atmospheric transfer, diverting products into the deep return flow. Uncertainties in the logic and calculations are enumerated including those inherent in high-latitude clathrate abundance, buoyant effluent rise through the column, representation of the general circulation, and bacterial growth kinetics.

  14. Origin of Molecular Oxygen in Comet 67P/Churyumov–Gerasimenko

    Science.gov (United States)

    Mousis, O.; Ronnet, T.; Brugger, B.; Ozgurel, O.; Pauzat, F.; Ellinger, Y.; Maggiolo, R.; Wurz, P.; Vernazza, P.; Lunine, J. I.; Luspay-Kuti, A.; Mandt, K. E.; Altwegg, K.; Bieler, A.; Markovits, A.; Rubin, M.

    2016-06-01

    Molecular oxygen has been detected in the coma of comet 67P/Churyumov–Gerasimenko with abundances in the 1%–10% range by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis-Double Focusing Mass Spectrometer instrument on board the Rosetta spacecraft. Here we find that the radiolysis of icy grains in low-density environments such as the presolar cloud may induce the production of large amounts of molecular oxygen. We also show that molecular oxygen can be efficiently trapped in clathrates formed in the protosolar nebula (PSN), and that its incorporation as crystalline ice is highly implausible, because this would imply much larger abundances of Ar and N2 than those observed in the coma. Assuming that radiolysis has been the only O2 production mechanism at work, we conclude that the formation of comet 67P/Churyumov–Gerasimenko is possible in a dense and early PSN in the framework of two extreme scenarios: (1) agglomeration from pristine amorphous icy grains/particles formed in ISM and (2) agglomeration from clathrates that formed during the disk’s cooling. The former scenario is found consistent with the strong correlation between O2 and H2O observed in comet 67P/Churyumov-Gerasimenko’s coma while the latter scenario requires that clathrates formed from ISM icy grains that crystallized when entering the PSN.

  15. Novel self-assembled gels and materials synthesis in unconventional environments

    Science.gov (United States)

    Irvin, Glen Clifford, Jr.

    This thesis deals specifically with the fabrication of novel nanophase and polymer materials using novel microstructured mediums. Enzymatic polymerization in a new microemulsion system using dense carbon dioxide and fluorinated surfactants was carried out. The morphology, molecular weight, and chemical structure of the polymer are characterized through electron microscopy, HPLC, FTIR, and 1HNMR. Structural characteristics indicate similarity to polymers formed in AOT-inverse micelles. Spectroscopic information of the polymerization system on a molecular level has been performed. The results indicate strong hydrogen bonding interactions between the monomer, water, and perfluorinated surfactant implying the partitioning of the monomer to the surfactant headgroup region. An extension of the microemulsion environment is found with novel microemulsion based gels. The gels contain both lecithin and AOT surfactants where roughly equal volumes of hydrocarbon and water forms a three-dimensional gel network. This microemulsion system is unique from a fundamental scientific and practical interest. Analysis of the system microstructures using 1HNMR, 13CNMR 31PNNM, Rheology, SAXS, SANS, and conductivity is presented. Nanomaterial templated syntheses were conducted and are discussed. A new technique was developed for the rapid production of clathrate hydrates either in aqueous or water-in-microemulsion environments. The systems devised for this technology have significantly greater interfacial contact between water and gas molecules (clathrate hydrate constituents). The rapid clathrate hydrate technique was utilized for synthesis of nanoclusters in aqueous and reverse micelle based systems using the remarkable phenomenon of clathrate hydrate formation. Conversion of water to crystalline ice-like (clathrate hydrate) form is exploited to arrest particle growth, thereby restricting particle size to the nanometer range. The technique is used to generate high synthesis rates of

  16. Geodetic data support trapping of ethane in Titan's polar crust

    Science.gov (United States)

    Sotin, Christophe; Rambaux, Nicolas

    2016-04-01

    Titan's surface is characterized by polar depressions that strongly influence interpretations of the gravity data. This study investigates several geodynamical models that can explain these depressions. For each model, the values of the three moments of inertia are computed numerically by discretizing the interior in spherical coordinates. The study shows that a Pratt model where the polar subsurface is made of ethane clathrates can explain the polar depression, the abrupt jump in altitude at about 60 degrees latitude, and the values of the degree 2 gravity coefficients. This model, proposed by Choukroun and Sotin [1], is based on the stability of ethane clathrate hydrates relative to methane clathrate hydrates. In addition to fitting the geodetic data, it explains the absence of ethane in Titan's atmosphere although ethane is the main product of the photolysis of methane. Other geophysical models based on latitudinal variations in the tidal heating production or in the heat flux at the base of the icy crust do not provide such a good match to the gravity and topographic observations. The ethane-clathrate model predicts that all the ethane produced by photolysis of methane at the present rate during the last billion years could be stored in the polar subsurface. It is consistent with the age of Titan's surface and that of Titan's atmospheric methane inferred from geological and geochemical observations by the Cassini/Huygens mission. The present study also emphasizes the role of mass anomalies on the interpretation of the degree 2 gravity coefficients. It shows that for Titan, a slow rotator, the values of the two equatorial moments of inertia (MoI) are largely affected by the polar depressions whereas the value of polar MoI is not. Therefore, as pointed out by previous calculations [2], calculating the moment of inertia (MoI) factor from the value of J2 could lead to major errors. This is not the case for our preferred Titan's model for which the negative polar

  17. TITAN'S BULK COMPOSITION CONSTRAINED BY CASSINI-HUYGENS: IMPLICATION FOR INTERNAL OUTGASSING

    Energy Technology Data Exchange (ETDEWEB)

    Tobie, G. [Universite de Nantes, LPGNantes, UMR 6112, F-44322 Nantes (France); Gautier, D. [LESIA, Observatoire de Paris, F-92195 Meudon Cedex (France); Hersant, F. [Universite Bordeaux, LAB, UMR 5804, F-33270, Floirac (France)

    2012-06-20

    In the present report, by using a series of data gathered by the Cassini-Huygens mission, we constrain the bulk content of Titan's interior for various gas species (CH{sub 4}, CO{sub 2}, CO, NH{sub 3}, H{sub 2}S, Ar, Ne, Xe), and we show that most of the gas compounds (except H{sub 2}S and Xe) initially incorporated within Titan are likely stored dissolved in the subsurface water ocean. CO{sub 2} is likely to be the most abundant gas species (up to 3% of Titan's total mass), while ammonia should not exceed 1.5 wt%. We predict that only a moderate fraction of CH{sub 4}, CO{sub 2}, and CO should be incorporated in the crust in the form of clathrate hydrates. By contrast, most of the H{sub 2}S and Xe should be incorporated at the base of the subsurface ocean, in the form of heavy clathrate hydrates within the high-pressure ice layer. Moreover, we show that the rocky phase of Titan, assuming a composition similar to CI carbonaceous chondrites, is a likely source for the noble gas isotopes ({sup 40}Ar, {sup 36}Ar, {sup 22}Ne) that have been detected in the atmosphere. A chondritic core may also potentially contribute to the methane inventory. Our calculations show that a moderate outgassing of methane containing traces of neon and argon from the subsurface ocean would be sufficient to explain the abundance estimated by the Gas Chromatograph Mass Spectrometer. The extraction process, implying partial clathration in the ice layers and exsolvation from the water ocean, may explain why the {sup 22}Ne/{sup 36}Ar ratio in Titan's atmosphere appears higher than the ratio in carbonaceous chondrites.

  18. THE DUAL ORIGIN OF THE NITROGEN DEFICIENCY IN COMETS: SELECTIVE VOLATILE TRAPPING IN THE NEBULA AND POSTACCRETION RADIOGENIC HEATING

    Energy Technology Data Exchange (ETDEWEB)

    Mousis, Olivier; Petit, Jean-Marc; Rousselot, Philippe [Universite de Franche-Comte, Institut UTINAM, CNRS/INSU, UMR 6213, Observatoire des Sciences de l' Univers de Besancon, F-25030 Besancon Cedex (France); Guilbert-Lepoutre, Aurelie [Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 (United States); Lunine, Jonathan I. [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Cochran, Anita L. [University of Texas McDonald Observatory, Austin, TX 78712 (United States); Waite, J. Hunter, E-mail: olivier.mousis@obs-besancon.fr [Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX 78228 (United States)

    2012-10-01

    We propose a scenario that explains the apparent nitrogen deficiency in comets in a way that is consistent with the fact that the surfaces of Pluto and Triton are dominated by nitrogen-rich ice. We use a statistical thermodynamic model to investigate the composition of the successive multiple guest clathrates that may have formed during the cooling of the primordial nebula from the most abundant volatiles present in the gas phase. These clathrates agglomerated with the other ices (pure condensates or stoichiometric hydrates) and formed the building blocks of comets. We report that molecular nitrogen is a poor clathrate former, when we consider a plausible gas-phase composition of the primordial nebula. This implies that its trapping into cometesimals requires a low disk temperature ({approx}20 K) in order to allow the formation of its pure condensate. We find that it is possible to explain the lack of molecular nitrogen in comets as a consequence of their postformation internal heating engendered by the decay of short-lived radiogenic nuclides. This scenario is found to be consistent with the presence of nitrogen-rich ice covers on Pluto and Triton. Our model predicts that comets should present xenon-to-water and krypton-to-water ratios close to solar xenon-to-oxygen and krypton-to-oxygen ratios, respectively. In contrast, the argon-to-water ratio is predicted to be depleted by a factor of {approx}300 in comets compared to solar argon-to-oxygen, as a consequence of poor trapping efficiency and radiogenic heating.

  19. A sublimation technique for high-precision measurements of δ13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

    Directory of Open Access Journals (Sweden)

    H. Fischer

    2011-07-01

    Full Text Available In order to provide high precision stable carbon isotope ratios (δ13CO2 or δ13C of CO2 from small bubbly, partially and fully clathrated ice core samples we developed a new method based on sublimation coupled to gas chromatography-isotope ratio mass spectrometry (GC-IRMS. In a first step the trapped air is quantitatively released from ~30 g of ice and CO2 together with N2O are separated from the bulk air components and stored in a miniature glass tube. In an off-line step, the extracted sample is introduced into a helium carrier flow using a minimised tube cracker device. Prior to measurement, N2O and organic sample contaminants are gas chromatographically separated from CO2. Pulses of a CO2/N2O mixture are admitted to the tube cracker and follow the path of the sample through the system. This allows an identical treatment and comparison of sample and standard peaks. The ability of the method to reproduce δ13C from bubble and clathrate ice is verified on different ice cores. We achieve reproducibilities for bubble ice between 0.05 ‰ and 0.07 ‰ and for clathrate ice between 0.05 ‰ and 0.09 ‰ (dependent on the ice core used. A comparison of our data with measurements on bubble ice from the same ice core but using a mechanical extraction device shows no significant systematic offset. In addition to δ13C, the CO2 and N2O mixing ratios can be volumetrically derived with a precision of 2 ppmv and 8 ppbv, respectively.

  20. A sublimation technique for high-precision measurements of δ13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

    Directory of Open Access Journals (Sweden)

    H. Fischer

    2011-03-01

    Full Text Available In order to provide high precision stable carbon isotope ratios (δ13CO2 or δ13C on CO2 from small bubble and clathrate ice core samples we developed a new method based on vacuum sublimation extraction of the CO2 and gas chromatography-isotope ratio mass spectrometry (GC-IRMS. In a first step the trapped air is quantitatively released from ~30 g of ice and CO2 together with N2O are separated from the bulk air components and stored in a miniature glass tube. In an off-line step, the extracted sample is introduced into a helium carrier flow using a minimised tube cracker device. Prior to measurement, N2O and organic sample contaminants are gas chromatographically separated from CO2. Pulses of a CO2/N2O mixture are admitted to the tube cracker and follow the path of the sample through the system. This allows an identical treatment and comparison of sample and standard peaks. The ability of the method to reproduce δ13C from bubble and clathrate ice is verified on different ice cores. We achieve reproducibilities for bubble ice between 0.05‰ and 0.07‰ and for clathrate ice between 0.05‰ and 0.09‰ (dependent on the ice core used. A comparison of our data with measurements on bubble ice from the same ice core but using a mechanic extraction device shows no significant systematic offset. In addition to δ13C, the CO2 and N2O mixing ratios can be volumetrically derived with a precision of 2 ppmv and 8 ppbv, respectively.

  1. MODELLING EARTH SYSTEM CHANGES THROUGH THE SHURUM-WONOKA ANOMALY

    DEFF Research Database (Denmark)

    Bjerrum, Christian J.; Canfield, D. E.

    -amplitude fluctuations in the isotopic composition of marine carbonate carbon (d13CIC ) and oxygen (d18O) and more subdued changes in the isotope composition of marine organic carbon. Normally, carbon isotope changes are considered to reflect the burial history of inorganic and organic carbon into sediments, while the...... and organic carbon at lower values of d13CIC, with a cross-plot slope of about 1. This unit slope seems to be unique to the Neoproterozoic in Earth history and not easily explained. In our model, the carbon isotope excursions were driven by methane from sediment-hosted clathrate hydrate deposits...

  2. Coronene-based charge-transfer complexes.

    Science.gov (United States)

    Yoshida, Yukihiro; Isomura, Kazuhide; Kumagai, Yoshihide; Maesato, Mitsuhiko; Kishida, Hideo; Mizuno, Motohiro; Saito, Gunzi

    2016-08-01

    Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented. PMID:27294380

  3. Coexistence of structure I and II gas hydrates in Lake Baikal suggesting gas sources from microbial and thermogenic origin

    Science.gov (United States)

    Kida, Masato; Khlystov, Oleg; Zemskaya, Tamara; Takahashi, Nobuo; Minami, Hirotsugu; Sakagami, Hirotoshi; Krylov, Alexey; Hachikubo, Akihiro; Yamashita, Satoshi; Shoji, Hitoshi; Poort, Jeffrey; Naudts, Lieven

    2006-12-01

    We report the field observation of hydrate deposits of different crystal structures in the same cores of a mud volcano in the Kukuy Canyon. We link those deposits to chemical fractionation during gas hydrate crystallization. Gas composition and crystallographic analyses of hydrate samples reveal involvement of two distinct gas source types in gas hydrate formation at present or in the past: microbial (methane) and thermogenic (methane and ethane) gas types. The clathrate structure II, observed for the first time in fresh water sediments, is believed to be formed by higher mixing of thermogenic gas.

  4. Multidisciplinary investigations exploring indicators of gas hydrate occurrence in the Krishna–Godavari Basin offshore, east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Ramana, M.V.; Ramprasad, T.; Paropkari, A.L.; Borole, D.V.; Rao, B.R.; Karisiddaiah, S.M.; Desa, M.; Kocherla, M.; Joao, H.M.; LokaBharathi, P.A.; DeSouza, M.J.B.D.; Pattan, J.N.; Khadge, N.H.; PrakashBabu, C.; Sathe, A.V.; Kumar, P.; Sethi, A.K.

    :529–531 Sethi AK, Ahmad MN (2006) Gas hydrates—a future energy source: advances in India, vol. 1(1). Petroview, Directorate General of Hydrocarbons, New Delhi, pp 5–10 Sloan ED Jr (1997) Clathrate hydrates of natural gases. Marcel Dekker, New York Sloan ED Jr... multi-channel seismic section along line GDSW-46, depicting a discrete BSR, merging with the subsurface lithology towards the NE. Deep drilling in its vicinity has revealed the presence of a thick gas hydrate column (Sethi and Ahmad 2006...

  5. Deuterium quadrupole coupling in methanol, salicyclic acid, catechol, resorcinol, and hydroquinonea)b)

    Science.gov (United States)

    Clymer, J. W.; Ragle, J. L.

    1982-11-01

    Deuteron NQR spectra of several model systems involving alcoholic of phenolic-OD groups are discussed. The spectra of alpha hydroquinone and its two isomers resorcinol and catechol show complex structure due to the presence of inequivalent O-DṡṡṡO hydrogen bonds. In the case of hydroquinone, this structure collapses to that characteristic of a single type of hydrogen bond in the beta- or clathrate-forming phase. An attempt is made to place the data in theoretical perspective by calculations of the deuterium field gradient in hydroxide ion, hydroxyl radical, methanol, and methanol dimer and by comparison with precise Hartree-Fock computations from the literature.

  6. Theoretical Study of the Structural and Electronic Properties of KxSi136, (x = 1, 8, 18)

    Science.gov (United States)

    Higgins, Craig; Myles, Charles

    2012-10-01

    Type II clathrate semiconductors have cage-like lattices in which Group IV atoms are tetrahedrally-coordinated and sp^3 covalently bonded. The cages can contain ``guest'' atoms; usually alkali or alkaline earth atoms. These materials are of interest because of their thermoelectric properties. Measurements of the lattice constant [1] as a function of Na concentration x in NaxSi136 (0 DOI: 10.1021/ic1005049[0pt] [2] S. Stefanoski and G. Nolas, Cryst. Growth Des. 2011, dx.doi.org/10.1021/cg200756r

  7. Search for volatiles in the surface of icy satellites

    International Nuclear Information System (INIS)

    It is proposed to measure the reflectance spectra of the icy satellites of Jupiter, Saturn and Uranus in the spectral region 1.8 to 2.4 micrometers. These observations use the new Cooled Grating Array Spectrometer using a 32-element InSb photodiode array detector and produce spectra of higher resolution and precision than any data yet obtained; the ultimate scientific objective is to search for the signatures of methane clathrate, ammonium hydroxide or carbon monoxide clathrate (compounds predicted to exist on icy surfaces in the outer solar system by several theories of formation of these bodies) in the region of the spectrum where water ice has a relative maximum in reflectance. At the very least, these data will allow upper limits to be placed on the amount of these chemical species that can be present. The specific targets is Europa, Ganymede, Enceladus, Ariel and Titania, bodies that have the highest probability of having some or all of these volatiles on their surface according to current formation models

  8. Water dynamics on ice and hydrate lattices studied by second-order central-line stimulated-echo oxygen-17 nuclear magnetic resonance

    International Nuclear Information System (INIS)

    Oxygen-17 stimulated-echo spectroscopy is a novel nuclear magnetic resonance (NMR) technique that allows one to investigate the time scale and geometry of ultraslow molecular motions in materials containing oxygen. The method is based on detecting orientationally encoded frequency changes within oxygen’s central-transition NMR line that are caused by second-order quadrupolar interactions. In addition to the latter, the present theoretical analysis of various two-pulse echo and stimulated-echo pulse sequences takes also heteronuclear dipolar interactions into account. As an experimental example, the ultraslow water motion in polycrystals of tetrahydrofuran clathrate hydrate is studied via two-time oxygen-17 stimulated-echo correlation functions. The resulting correlation times and those of hexagonal ice are similar to those from previous deuteron NMR measurements. Calculations of the echo functions’ final-state correlations for various motional models are compared with the experimental data of the clathrate hydrate. It is found that a six-site model including the oxygen-proton dipolar interaction describes the present results

  9. Structural transformation of isopropylamine semiclathrate hydrates in the presence of methane as a coguest.

    Science.gov (United States)

    Lee, Seungmin; Lee, Youngjun; Park, Sungwon; Seo, Yongwon

    2012-11-15

    Guest-induced structural transformation in amine semiclathrate hydrates is a unique pattern caused by modifying the hydrophobic-hydrophilic balance, and thus, it can be applied to potential gas storage and transportation areas. The experimental results of the structural transformation of isopropylamine (IPA) semiclathrate hydrates in the presence of methane (CH(4)) as a coguest are presented with a focus on the macroscopic phase behavior and microscopic analytical methods such as powder X-ray diffraction (PXRD) and NMR spectroscopy. The introduction of CH(4) molecules as coguests changed the structure of the IPA·8.0H(2)O semiclathrate hydrates (hexagonal, P6(3)/mmc) to sII gas hydrates (cubic, Fd3m). The microscopic analysis results indicate that the guest gas distribution and the clathrate hydrate composition can be altered with adjustment of the IPA concentration. The overall experimental results are valuable for increased understanding of the stability conditions, structural details, and guest-host interactions in hydrophobic guest gas + IPA clathrate hydrates. PMID:23113568

  10. Gas Hydrate Research Database and Web Dissemination Channel

    Energy Technology Data Exchange (ETDEWEB)

    Micheal Frenkel; Kenneth Kroenlein; V Diky; R.D. Chirico; A. Kazakow; C.D. Muzny; M. Frenkel

    2009-09-30

    To facilitate advances in application of technologies pertaining to gas hydrates, a United States database containing experimentally-derived information about those materials was developed. The Clathrate Hydrate Physical Property Database (NIST Standard Reference Database {number_sign} 156) was developed by the TRC Group at NIST in Boulder, Colorado paralleling a highly-successful database of thermodynamic properties of molecular pure compounds and their mixtures and in association with an international effort on the part of CODATA to aid in international data sharing. Development and population of this database relied on the development of three components of information-processing infrastructure: (1) guided data capture (GDC) software designed to convert data and metadata into a well-organized, electronic format, (2) a relational data storage facility to accommodate all types of numerical and metadata within the scope of the project, and (3) a gas hydrate markup language (GHML) developed to standardize data communications between 'data producers' and 'data users'. Having developed the appropriate data storage and communication technologies, a web-based interface for both the new Clathrate Hydrate Physical Property Database, as well as Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program was developed and deployed at http://gashydrates.nist.gov.

  11. Structural Basis for the Inhibition of Gas Hydrates by α-Helical Antifreeze Proteins.

    Science.gov (United States)

    Sun, Tianjun; Davies, Peter L; Walker, Virginia K

    2015-10-20

    Kinetic hydrate inhibitors (KHIs) are used commercially to inhibit gas hydrate formation and growth in pipelines. However, improvement of these polymers has been constrained by the lack of verified molecular models. Since antifreeze proteins (AFPs) act as KHIs, we have used their solved x-ray crystallographic structures in molecular modeling to explore gas hydrate inhibition. The internal clathrate water network of the fish AFP Maxi, which extends to the protein's outer surface, is remarkably similar to the {100} planes of structure type II (sII) gas hydrate. The crystal structure of this water web has facilitated the construction of in silico models for Maxi and type I AFP binding to sII hydrates. Here, we have substantiated our models with experimental evidence of Maxi binding to the tetrahydrofuran sII model hydrate. Both in silico and experimental evidence support the absorbance-inhibition mechanism proposed for KHI binding to gas hydrates. Based on the Maxi crystal structure we suggest that the inhibitor adsorbs to the gas hydrate lattice through the same anchored clathrate water mechanism used to bind ice. These results will facilitate the rational design of a next generation of effective green KHIs for the petroleum industry to ensure safe and efficient hydrocarbon flow. PMID:26488661

  12. Water dynamics on ice and hydrate lattices studied by second-order central-line stimulated-echo oxygen-17 nuclear magnetic resonance

    Science.gov (United States)

    Adjei-Acheamfour, Mischa; Tilly, Julius F.; Beerwerth, Joachim; Böhmer, Roland

    2015-12-01

    Oxygen-17 stimulated-echo spectroscopy is a novel nuclear magnetic resonance (NMR) technique that allows one to investigate the time scale and geometry of ultraslow molecular motions in materials containing oxygen. The method is based on detecting orientationally encoded frequency changes within oxygen's central-transition NMR line that are caused by second-order quadrupolar interactions. In addition to the latter, the present theoretical analysis of various two-pulse echo and stimulated-echo pulse sequences takes also heteronuclear dipolar interactions into account. As an experimental example, the ultraslow water motion in polycrystals of tetrahydrofuran clathrate hydrate is studied via two-time oxygen-17 stimulated-echo correlation functions. The resulting correlation times and those of hexagonal ice are similar to those from previous deuteron NMR measurements. Calculations of the echo functions' final-state correlations for various motional models are compared with the experimental data of the clathrate hydrate. It is found that a six-site model including the oxygen-proton dipolar interaction describes the present results.

  13. Water dynamics on ice and hydrate lattices studied by second-order central-line stimulated-echo oxygen-17 nuclear magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Adjei-Acheamfour, Mischa; Tilly, Julius F.; Beerwerth, Joachim; Böhmer, Roland [Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund (Germany)

    2015-12-07

    Oxygen-17 stimulated-echo spectroscopy is a novel nuclear magnetic resonance (NMR) technique that allows one to investigate the time scale and geometry of ultraslow molecular motions in materials containing oxygen. The method is based on detecting orientationally encoded frequency changes within oxygen’s central-transition NMR line that are caused by second-order quadrupolar interactions. In addition to the latter, the present theoretical analysis of various two-pulse echo and stimulated-echo pulse sequences takes also heteronuclear dipolar interactions into account. As an experimental example, the ultraslow water motion in polycrystals of tetrahydrofuran clathrate hydrate is studied via two-time oxygen-17 stimulated-echo correlation functions. The resulting correlation times and those of hexagonal ice are similar to those from previous deuteron NMR measurements. Calculations of the echo functions’ final-state correlations for various motional models are compared with the experimental data of the clathrate hydrate. It is found that a six-site model including the oxygen-proton dipolar interaction describes the present results.

  14. Inter-cage dynamics in structure I, II, and H fluoromethane hydrates as studied by NMR and molecular dynamics simulations

    International Nuclear Information System (INIS)

    Prospective industrial applications of clathrate hydrates as materials for gas separation require further knowledge of cavity distortion, cavity selectivity, and defects induction by guest-host interactions. The results presented in this contribution show that under certain temperature conditions the guest combination of CH3F and a large polar molecule induces defects on the clathrate hydrate framework that allow intercage guest dynamics. 13C NMR chemical shifts of a CH3F/CH4/TBME sH hydrate and a temperature analysis of the 2H NMR powder lineshapes of a CD3F/THF sII and CD3F/TBME sH hydrate, displayed evidence that the populations of CH4 and CH3F in the D and D′ cages were in a state of rapid exchange. A hydrogen bonding analysis using molecular dynamics simulations on the TBME/CH3F and TBME/CH4 sH hydrates showed that the presence of CH3F enhances the hydrogen bonding probability of the TBME molecule with the water molecules of the cavity. Similar results were obtained for THF/CH3F and THF/CH4 sII hydrates. The enhanced hydrogen bond formation leads to the formation of defects in the water hydrogen bonding lattice and this can enhance the migration of CH3F molecules between adjacent small cages

  15. Origin of molecular oxygen in Comet 67P/Churyumov-Gerasimenko

    CERN Document Server

    Mousis, O; Brugger, B; Ozgurel, O; Pauzat, F; Ellinger, Y; Maggiolo, R; Wurz, P; Vernazza, P; Lunine, J I; Luspay-Kuti, A; Mandt, K E; Altwegg, K; Bieler, A; Markovits, A; Rubin, M

    2016-01-01

    Molecular oxygen has been detected in the coma of comet 67P/Churyumov-Gerasimenko with abundances in the 1-10% range by the ROSINA-DFMS instrument on board the Rosetta spacecraft. Here we find that the radiolysis of icy grains in low-density environments such as the presolar cloud may induce the production of large amounts of molecular oxygen. We also show that molecular oxygen can be efficiently trapped in clathrates formed in the protosolar nebula, and that its incorporation as crystalline ice is highly implausible because this would imply much larger abundances of Ar and N2 than those observed in the coma. Assuming that radiolysis has been the only O2 production mechanism at work, we conclude that the formation of comet 67P/Churyumov-Gerasimenko is possible in a dense and early protosolar nebula in the framework of two extreme scenarios: (1) agglomeration from pristine amorphous icy grains/particles formed in ISM and (2) agglomeration from clathrates that formed during the disk's cooling. The former scenar...

  16. Towards a fundamental understanding of natural gas hydrates.

    Science.gov (United States)

    Koh, Carolyn A

    2002-05-01

    Gas clathrate hydrates were first identified in 1810 by Sir Humphrey Davy. However, it is believed that other scientists, including Priestley, may have observed their existence before this date. They are solid crystalline inclusion compounds consisting of polyhedral water cavities which enclathrate small gas molecules. Natural gas hydrates are important industrially because the occurrence of these solids in subsea gas pipelines presents high economic loss and ecological risks, as well as potential safety hazards to exploration and transmission personnel. On the other hand, they also have technological importance in separation processes, fuel transportation and storage. They are also a potential fuel resource because natural deposits of predominantly methane hydrate are found in permafrost and continental margins. To progress with understanding and tackling some of the technological challenges relating to natural gas hydrate formation, inhibition and decomposition one needs to develop a fundamental understanding of the molecular mechanisms involved in these processes. This fundamental understanding is also important to the broader field of inclusion chemistry. The present article focuses on the application of a range of physico-chemical techniques and approaches for gaining a fundamental understanding of natural gas hydrate formation, decomposition and inhibition. This article is complementary to other reviews in this field, which have focused more on the applied, engineering and technological aspects of clathrate hydrates. PMID:12122641

  17. State of the art on phase change material slurries

    International Nuclear Information System (INIS)

    Highlights: ► A bibliographic study on PCM slurries. ► Clathrate Hydrate slurry, Microencapsulated PCM Slurry, shape-stabilized PCM slurries and Phase Change Material Emulsions. ► Formation, thermo-physical, rheological, heat transfers properties and applications of these four PCS systems. ► The use of thermal energy storage and distribution based on PCM slurries can improve the refrigerating machine performances. - Abstract: The interest in using phase change slurry (PCS) media as thermal storage and heat transfer fluids is increasing and thus leading to an enhancement in the number of articles on the subject. In air-conditioning and refrigeration applications, PCS systems represent a pure benefit resulting in the increase of thermal energy storage capacity, high heat transfer characteristics and positive phase change temperatures which can occur under low pressures. Hence, they allow the increase of energy efficiency and reduce the quantity of thermal fluids. This review describes the formation, thermo-physical, rheological, heat transfer properties and applications of four PCS systems: Clathrate hydrate slurry (CHS), Microencapsulated Phase Change Materials Slurry (MPCMS), shape-stabilized PCM slurries (SPCMSs) and Phase Change Material Emulsions (PCMEs). It regroups a bibliographic summary of important information that can be very helpful when such systems are used. It also gives interesting and valuable insights on the choice of the most suitable PCS media for laboratory and industrial applications.

  18. Feasibility of Large-Scale Ocean CO2 Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Peter Brewer

    2008-08-31

    Scientific knowledge of natural clathrate hydrates has grown enormously over the past decade, with spectacular new findings of large exposures of complex hydrates on the sea floor, the development of new tools for examining the solid phase in situ, significant progress in modeling natural hydrate systems, and the discovery of exotic hydrates associated with sea floor venting of liquid CO{sub 2}. Major unresolved questions remain about the role of hydrates in response to climate change today, and correlations between the hydrate reservoir of Earth and the stable isotopic evidence of massive hydrate dissociation in the geologic past. The examination of hydrates as a possible energy resource is proceeding apace for the subpermafrost accumulations in the Arctic, but serious questions remain about the viability of marine hydrates as an economic resource. New and energetic explorations by nations such as India and China are quickly uncovering large hydrate findings on their continental shelves. In this report we detail research carried out in the period October 1, 2007 through September 30, 2008. The primary body of work is contained in a formal publication attached as Appendix 1 to this report. In brief we have surveyed the recent literature with respect to the natural occurrence of clathrate hydrates (with a special emphasis on methane hydrates), the tools used to investigate them and their potential as a new source of natural gas for energy production.

  19. The search for green inhibitors : perturbing hydrate growth with bugs

    Energy Technology Data Exchange (ETDEWEB)

    Huva, E.; Gordienko, R. [Queen' s Univ., Kingston, ON (Canada). Dept. of Biology; Ripmeester, J.; Zeng, H. [Queen' s Univ., Kingston, ON (Canada). Dept. of Biology]|[National Research Council of Canada, Ottawa, ON (Canada). Steacie Inst. for Molecular Sciences; Walker, V.K. [Queen' s Univ., Kingston, ON (Canada). Dept. of Biology]|[Queen' s Univ., Kingston, ON (Canada). Dept. of Microbiology and Immunology

    2008-07-01

    The ability of some organisms, such as insects and microbes, to survive low temperatures can be attributed to the production of either ice nucleating proteins (INPs) or antifreeze proteins (AFPs). INPs can direct crystal growth by inducing rapid ice formation. AFPs adsorb to ice embryos and decrease the temperature at which the ice grows. Certain AFPs can also inhibit the crystallization of clathrate hydrates and eliminate more rapid recrystallization or memory effect. This paper presented a study that involved the examination of bacterial species with ice-associating properties for their effect on tetrahydrofuran (THF) hydrate crystallization. As part of the study, THF hydrate formation was inhibited in the presence of cultures containing the ice-associating bacterium chryseobacterium C14. The paper discussed the methods used for the study, including hydrate formation and reformation in the presence of ice-associating bacteria and the development of a clathrate hydrate affinity purification technique. A 40 per cent reduction in crystallization was observed, indicating their potential as a commercial green inhibitor for hydrates. In addition, there was no elimination of memory effect, and little supporting evidence was seen for nucleation inhibition by any of the bacteria. 17 refs., 1 tab., 3 figs.

  20. Production of Xenon Compounds by the Beta Decay of Iodine in Iodine Compounds

    International Nuclear Information System (INIS)

    It is known that most beta decays cause no change in the electron number of the atom containing the decaying nucleus. In the beta decay I129 -Xe129 in an iodine compound the electronic structure and geometry are often appropriate for formation of a xenon compound with the same ligands. This process has been discovered and studied by use of the Mössbauer effect in Xe129. The first-excited state in Xe129 has Jπ = 3+/2, T½ = 10-9 * s, and lies 40 keV above the ½+ ground state. It is populated by decay from 1,6 x 106 y. I129. The Mössbauer effect of the 40-keV gamma ray may readily be observed with a variety of sources and absorbers in experiments done at 4.2°K. The electric quadrupole splitting of the excited state results in two absorption lines when the Doppler shift is used to scan the spectrum. The separation between lines characterizes the electronic configuration on the xenon and often unequivocally identifies the structure. In the first experiments a source of Nal129 was used with absorbers of hydroquinone clathrate, Na4XeO6, XeF4, and XeF2. Single-line spectra were observed for the clathrate and pexenate, and two-line spectra for the fluorides. The single line indicates that in the source I- -→ Xe0, its iso-electronic daughter. When Na3H2IO6 was used as source, with clathrate absorber, the recoil-less fraction increased by a factor of 3, implying stronger bonding. KIO4 also gave a single but somewhat less intense line. With NalO3 as source and clathrate absorber, splitting was observed suggesting that IO3- -→ XeO6. This was verified by the observation of identical splitting in an XeO3 absorber used with KIO4 source. An experiment with KIC14 * H2O as source and clathrate absorber showed splitting somewhat smaller than in XeF4. Here ICl-4 -→ XeCl4. Using aligned crystals of KICl4 * H2O and making quantitative intensity measurements it was established that the square planar structure of ICl4- is preserved in the transition to XeCl4 and that XeCl2 and

  1. One-hundred-km-scale basins on Enceladus: Evidence for an active ice shell

    Science.gov (United States)

    Schenk, Paul M.; McKinnon, William B.

    2009-08-01

    Stereo-derived topographic mapping of ˜50% of Enceladus reveals at least 6 large-scale, ovoid depressions (basins) 90-175 km across and 800-to-1500 m deep and uncorrelated with geologic boundaries. In contrast, the south polar depression is larger and apparently shallower and correlates with active resurfacing. The shape and scale of the basins is inconsistent with impact, geoid surface deflections, or with dynamically supported topography. Isostatic thinning of Enceladus' ice shell associated with upwellings (and tidally-driven ice melting) can plausibly account for these basins. Thinning implies upwarping of the base of the shell of ˜10-20 km beneath the depressions, depending on total shell thickness; loss of near-surface porosity due to enhanced heat flow may also contribute to basin lows. Alternatively, the basins may overly cold, inactive, and hence denser ice, but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice.

  2. Classification of Valleytronics in Thermoelectricity

    Science.gov (United States)

    Norouzzadeh, Payam; Vashaee, Daryoosh

    2016-03-01

    The theory of valleytronics as a material design tool for engineering both thermal and electrical transport properties is presented. It is shown that the interplay among the valleytronics parameters such as the degeneracy of the band, intervalley transitions, effective mass, scattering exponent, and the Fermi energy may deteriorate or ameliorate any or all of the main thermoelectric properties. A flowchart classifying the different paths through which the valleytronics can influence the thermoelectric figure-of-merit ZT is derived and discussed in detail. To exemplify the application of the flowchart, valleytronics in four different semiconductors, Mg2Si, Si0.8Ge0.2, AlxGa1‑xAs and clathrate Si46-VIII were studied, which showed different trends. Therefore, a degenerate multivalley bandstructure, which is typically anticipated for a good thermoelectric material, cannot be a general design rule for ZT enhancement and a detailed transport study is required to engineer the optimum bandstructure.

  3. Biphasic dissolution method for quality control and assurance of drugs containing active substances in the form of weak acid salts.

    Science.gov (United States)

    Franc, Aleš; Muselłk, Jan; Goněc, Roman; Vetchý, David

    2016-03-01

    Substances in the form of weak acid salts have been found to be problematic for dissolution testing. Their absorption can start only after they are turned into the form of an acid following the gastric passage although they were administered in the form of a salt. Due to poor solubility, they cannot be tested in acidic gastric environment for a biased dissolution profile. The biphasic dissolution method is promising for overcoming this obstacle. Tablets with warfarin clathrate sodium salt in two concentrations and two different particle size distributions were tested as a suitable model for finding the medium and process conditions of dissolution. The dissolution method based on the use of the upper organic layer (1-octanol) and the lower aqueous layer 0.1 mol L-1 HCl) was found suitable and discriminatory for tablets containing active substances in the form of salts of weak acids. The method also reflects physical differences in the quality of used substances. PMID:26959550

  4. (2,3,5,10,12,13,15,20-Octaphenylporphinatocopper(II 1,1,2,2-tetrachloroethane solvate

    Directory of Open Access Journals (Sweden)

    Babu Varghese

    2008-02-01

    Full Text Available The title complex, [Cu(C68H44N4]·C2H2Cl4, exhibits nearly square-planar geometry around the CuII centre and the macrocyclic ring is almost planar. The porphyrin molecule has an approximate non-crystallographic inversion centre (Ci, and a non-crystallographic twofold rotation axis (C2 within the CuII–porphyrin ring plane. Further, it has non-crystallographic twofold rotation axis and mirror plane (Cs symmetry perpendicular to the molecular plane. The molecular packing of the complexes and the solvent molecules shows weak intermolecular C—H...π, C—H...Cl and C—H...N interactions, forming a clathrate-like structure.

  5. VOLATILE TRANSPORT INSIDE SUPER-EARTHS BY ENTRAPMENT IN THE WATER-ICE MATRIX

    International Nuclear Information System (INIS)

    Whether volatiles can be entrapped in a background matrix composing planetary envelopes and be dragged via convection to the surface is a key question in understanding atmospheric fluxes, cycles, and composition. In this paper, we consider super-Earths with an extensive water mantle (i.e., water planets), and the possibility of entrapment of methane in their extensive water-ice envelopes. We adopt the theory developed by van der Waals and Platteeuw for modeling solid solutions, often used for modeling clathrate hydrates, and modify it in order to estimate the thermodynamic stability field of a new phase called methane filled ice Ih. We find that in comparison to water ice VII the filled ice Ih structure may be stable not only at the high pressures but also at the high temperatures expected at the core-water mantle transition boundary of water planets.

  6. Novel inclusion compounds with urea/thiourea/selenourea-anion host lattices

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@ The chemistry of inclusion compounds has a long history and is nowadays a subject of wide-ranging and intense study. With the awarding of the 1987 Nobel Prize in Chemistry to Donald J. Cram, Jean-Marie Lehn and Charles J. Pedersen for their fundamental work on "host-guest" or "supramolecular" systems, inclusion chemistry has come to the fore front in contemporary researches. Increasing varieties of novel inclusion compounds and new host molecules have been synthesized recently. The term "crystal engineering" was coined by Schmidt to describe the rational design and control of molecular packing arrangements in the solid state, and the structural study of clathrates has contributed substantially to our understanding of the problem. Generalizations concerning the preferred structural motifs generated by hydrogen bonding and weaker non-covalent interactions between specific functional groups or molecular fragments have led to the realization of some impressive predictions about the construction of supramolecular networks.

  7. Large methane releases lead to strong aerosol forcing and reduced cloudiness

    DEFF Research Database (Denmark)

    Kurten, T.; Zhou, L.; Makkonen, R.;

    2011-01-01

    contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is......The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller...... forcing that is comparable in magnitude to the long-wave radiative forcing ("enhanced greenhouse effect") of the added methane. Together, the indirect CH4-O-3 and CH4-OHaerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously...

  8. Martian zeolites as a source of atmospheric methane

    CERN Document Server

    Mousis, Olivier; Bellat, Jean-Pierre; Schmidt, Frédéric; Bouley, Sylvain; Chassefière, Eric; Sautter, Violaine; Quesnel, Yoann; Picaud, Sylvain; Lectez, Sébastien

    2016-01-01

    The origin of the martian methane is still poorly understood. A plausible explanation is that methane could have been produced either by hydrothermal alteration of basaltic crust or by serpentinization of ultramafic rocks producing hydrogen and reducing crustal carbon into methane. Once formed, methane storage on Mars is commonly associated with the presence of hidden clathrate reservoirs. Here, we alternatively suggest that chabazite and clinoptilolite, which belong to the family of zeolites, may form a plausible storage reservoir of methane in the martian subsurface. Because of the existence of many volcanic terrains, zeolites are expected to be widespread on Mars and their Global Equivalent Layer may range up to more than $\\sim$1 km, according to the most optimistic estimates. If the martian methane present in chabazite and clinoptilolite is directly sourced from an abiotic source in the subsurface, the destabilization of a localized layer of a few millimeters per year may be sufficient to explain the curr...

  9. Thermodynamics of a post combustion hydrate-based carbon dioxide capture process

    International Nuclear Information System (INIS)

    Hydrates selectivity towards carbon dioxide is offering a promising route for carbon dioxide removal from flue gases. Hydrate-based CO2 capture process could substitute amine facilities widely implemented in gas treatment plants but suffering from oxidative degradation problems and high energy demand. In the framework of this thesis, we focus on phase equilibria that are involved in such process. Experimental dissociation conditions for clathrate hydrates of carbon dioxide and nitrogen, in the presence of some promoting molecules (Tetrahydrofuran, Tetrabutyl ammonium bromide and Tetrabutyl ammonium Fluoride ) are reported in the experimental section of this work. The data generated in this work along with literature data are compared to the model predictions. The developed model is based on the Cubic Plus Association (CPA) equation of state (EoS) for fluid phases combined to the van der Waals and Platteeuw's theory for the hydrate phase. (author)

  10. Thermodynamic calculations in the system CH4-H2O and methane hydrate phase equilibria

    Science.gov (United States)

    Circone, S.; Kirby, S.H.; Stern, L.A.

    2006-01-01

    Using the Gibbs function of reaction, equilibrium pressure, temperature conditions for the formation of methane clathrate hydrate have been calculated from the thermodynamic properties of phases in the system CH4-H 2O. The thermodynamic model accurately reproduces the published phase-equilibria data to within ??2 K of the observed equilibrium boundaries in the range 0.08-117 MPa and 190-307 K. The model also provides an estimate of the third-law entropy of methane hydrate at 273.15 K, 0.1 MPa of 56.2 J mol-1 K-1 for 1/n CH4??H 2O, where n is the hydrate number. Agreement between the calculated and published phase-equilibria data is optimized when the hydrate composition is fixed and independent of the pressure and temperature for the conditions modeled. ?? 2006 American Chemical Society.

  11. Quantum Effects in Cosmochemistry: Complexation Energy and Van Der Waals Radii

    Science.gov (United States)

    Mittlefehldt, D. W.; Wilson, T. L.

    2007-01-01

    The subject of quantum effects in cosmochemistry was recently addressed with the goal of understanding how they contribute to Q-phase noble gas abundances found in meteorites. It was the pursuit of the Q-phase carrier of noble gases and their anomalous abundances that ultimately led to the identification, isolation, and discovery of presolar grains. In spite of its importance, Q-phase investigations have led a number of authors to reach conclusions that do not seem to be supported by quantum chemistry. In view of the subject's fundamental significance, additional study is called for. Two quantum properties of Q-phase candidates known as endohedral carbon-cage clathrates such as fullerenes will be addressed here. These are complexation energy and instability induced by Pauli blocking (exclusion principle).

  12. Global Energy Issues and Alternate Fueling

    Science.gov (United States)

    Hendricks, Robert C.

    2007-01-01

    This viewgraph presentation describes world energy issues and alternate fueling effects on aircraft design. The contents include: 1) US Uses about 100 Quad/year (1 Q = 10(exp 15) Btu) World Energy Use: about 433 Q/yr; 2) US Renewable Energy about 6%; 3) Nuclear Could Grow: Has Legacy Problems; 4) Energy Sources Primarily NonRenewable Hydrocarbon; 5) Notes; 6) Alternate Fuels Effect Aircraft Design; 7) Conventional-Biomass Issue - Food or Fuel; 8) Alternate fuels must be environmentally benign; 9) World Carbon (CO2) Emissions Problem; 10) Jim Hansen s Global Warming Warnings; 11) Gas Hydrates (Clathrates), Solar & Biomass Locations; 12) Global Energy Sector Response; 13) Alternative Renewables; 14) Stratospheric Sulfur Injection Global Cooling Switch; 15) Potential Global Energy Sector Response; and 16) New Sealing and Fluid Flow Challenges.

  13. Structural studies on inclusion compounds and solvent sorption behavior of gradually elongated wheel-and-axle-type diol hosts featuring lateral benzo[b]thiophene units

    Science.gov (United States)

    Katzsch, Felix; Gruber, Tobias; Weber, Edwin

    2016-06-01

    Based on the wheel-and-axle design strategy, a series of six new clathrate hosts featuring two di(benzo[b]thien-2-yl)hydroxymethyl units attached to both ends of a central linear building element of varying length have been synthesized and their capability to form crystalline inclusion compounds with a fixed range of organic solvents are reported. X-ray crystal structures of relevant inclusion compounds have been determined and are comparatively discussed involving structural modification of the host molecules. Organic vapor sorption behavior of the host compounds coated as solid films on the quartz crystal of a QCM device has been studied. Significant differences in the affinities towards solvent vapors dependent both on structural and polarity properties of host and solvent are observed, indicating potential application as mass sensitive materials.

  14. A review of the geochemistry of methane in natural gas hydrate

    Science.gov (United States)

    Kvenvolden, K.A.

    1995-01-01

    The largest accumulations on Earth of natural gas are in the form of gas hydrate, found mainly offshore in outer continental margin sediment and, to a lesser extent, in polar regions commonly associated with permafrost. Measurements of hydrocarbon gas compositions and of carbon-isotopic compositions of methane from natural gas hydrate samples, collected in subaquatic settings from around the world, suggest that methane guest molecules in the water clathrate structures are mainly derived by the microbial reduction of CO2 from sedimentary organic matter. In only 2 regions, the Gulf of Mexico and the Caspian Sea, has mainly thermogenic methane been found in gas hydrate. At a few locations, where the gas hydrate contains a mixture of microbial and thermal methane, microbial methane is always dominant. Continental gas hydrate, identified in Alaska and Russia, also has hydrocarbon gases composed of >99% methane, with carbon-isotopic compositions ranging from -41 to -49???. -from Author

  15. Cooling neutrons using non-dispersive magnetic excitations

    CERN Document Server

    Zimmer, Oliver

    2014-01-01

    A new method is proposed for cooling neutrons by inelastic magnetic scattering in weakly absorbing, cold paramagnetic systems. Kinetic neutron energy is removed in constant decrements determined by the Zeeman energy of paramagnetic atoms or ions in an external magnetic field, or by zero-field level splittings in magnetic molecules. Analytical solutions of the stationary neutron transport equation are given using inelastic neutron scattering cross sections derived in an appendix. They neglect any inelastic process except the paramagnetic scattering and hence still underestimate very-cold neutron densities. Molecular oxygen with its triplet ground state appears particularly promising, notably as a host in fully deuterated oxygen-clathrate hydrate, or more exotically, in dry oxygen-He4 van der Waals clusters. At a neutron temperature about 6 K, for which neutron conversion to ultra-cold neutrons by single-phonon emission in pure superfluid He4 works best, conversion rates due to paramagnetic scattering in the cl...

  16. Seasonal recession of Mars' south polar cap as seen by Viking

    Science.gov (United States)

    James, P. B.; Briggs, G.; Barnes, J.; Spruck, A.

    1979-01-01

    The spring-summer retreat of the south polar cap of Mars is portrayed in photomosaics obtained by Viking Orbiter 2 during 1977. Comparisons of these data to Mariner 9 photos and to the record of telescopic observations attest that the polar retreat viewed by Viking was significantly slower than those previously reported. A global dust storm which occurred at an unusually early season may have effected this retarded recession by introducing dust into the atmosphere of Mars which modified the polar energy balance through scattering of incident radiation. The composition of the south residual cap cannot be unambiguously determined at this time; however, some data suggest that CO2 or clathrate survived the entire summer viewed by Viking.

  17. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    Science.gov (United States)

    Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

    2014-12-01

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2 measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.

  18. 3种熊果苷的研究进展%Progress in development of three kinds of arbutin product

    Institute of Scientific and Technical Information of China (English)

    刘彩云; 吴培诚; 梁高卫; 罗欣茹; 周丹曼

    2015-01-01

    重点综述了α-熊果苷、β-熊果苷和脱氧熊果苷的制备方法、美白机制及应用现状和稳定性,并对它们进行了比较,提出新剂型和新技术如脂质体、微乳、包合物的开发为3种熊果苷提供了新的应用方向。%The preparation method,mechanism of whitening action,as well as the application status and the product stability of three kinds of arbutin were summarized and compared. The new product types and new technologies such as liposomes,microemulsions and clathrates were put forward for providing orientation for development of new applications in the future.

  19. Structure of catenary complex bis(trimethylamine)cadmium(2)-tetra-μ-cyanonickelate(2) and contact self-stabilization of molecules

    International Nuclear Information System (INIS)

    Complex [Cd(N(CH3)3)2Ni(CN)4] is synthesized and studied by x-ray diffraction method. Complex studied is crystallized in tetragonal system in space group I4/mmm. There are parallel polymeric layers in the structure which are consisted from coordinately bound metal atoms and bridge cyanides. Octahedral Cd(2) surrounding is formed by six atoms of nitrogen of the cyanide groups in laminar plate and by two trimethylamine ligands in trans-position. Layers are stacked in the correspondence with Van-der-Waals type of packing. Space complementation of layers results in dense packing of complexes and explains the absence of clathrate-forming ability

  20. Thermal transport property of Ge34 and d-Ge investigated by molecular dynamics and the Slack's equation

    International Nuclear Information System (INIS)

    In this study, we evaluate the values of lattice thermal conductivity κL of type II Ge clathrate (Ge34) and diamond phase Ge crystal (d-Ge) with the equilibrium molecular dynamics (EMD) method and the Slack's equation. The key parameters of the Slack's equation are derived from the thermodynamic properties obtained from the lattice dynamics (LD) calculations. The empirical Tersoff's potential is used in both EMD and LD simulations. The thermal conductivities of d-Ge calculated by both methods are in accordance with the experimental values. The predictions of the Slack's equation are consistent with the EMD results above 250 K for both Ge34 and d-Ge. In a temperature range of 200–1000 K, the κL value of d-Ge is about several times larger than that of Ge34. (condensed matter: structure, thermal and mechanical properties)

  1. Review of Solid State Hydrogen Storage Methods Adopting Different Kinds of Novel Materials

    Directory of Open Access Journals (Sweden)

    Renju Zacharia

    2015-01-01

    Full Text Available Overview of advances in the technology of solid state hydrogen storage methods applying different kinds of novel materials is provided. Metallic and intermetallic hydrides, complex chemical hydride, nanostructured carbon materials, metal-doped carbon nanotubes, metal-organic frameworks (MOFs, metal-doped metal organic frameworks, covalent organic frameworks (COFs, and clathrates solid state hydrogen storage techniques are discussed. The studies on their hydrogen storage properties are in progress towards positive direction. Nevertheless, it is believed that these novel materials will offer far-reaching solutions to the onboard hydrogen storage problems in near future. The review begins with the deficiencies of current energy economy and discusses the various aspects of implementation of hydrogen energy based economy.

  2. Investigating Molecular Interactions

    DEFF Research Database (Denmark)

    Clausen, Henrik Fanø

    2010-01-01

    the thesis to the two types of structures. The first chapter is a brief introduction to the theory used in this dissertation, where diffraction theory, the aspherical atom model, and the Atom in Molecules theory will be presented. Physical properties, such as thermal stability and magnetic susceptibility...... chapters concern transition metal coordination polymers and the last three describe hydroquinone co-crystals and clathrate structures. Even though, the goal of the thesis has been to give account of all the work that I have performed, I have chosen to leave out results of certain projects, and confine......, are also introduced, as a goal of the analysis of charge density distributions is to obtain further understanding of these macroscopic properties. Neutron diffraction will be used as a complementary tool to the X-ray diffraction experiment, as positional and thermal parameters of hydrogen atoms can...

  3. How to link the relative abundances of gas species in coma of comets to their initial chemical composition ?

    CERN Document Server

    Marboeuf, Ulysse

    2014-01-01

    The chemical composition of comets is frequently assumed to be directly provided by the observations of the abundances of volatile molecules in the coma. The present work aims to determine the relationship between the chemical composition of the coma, the outgassing profile of volatile molecules and the internal chemical composition, and water ice structure of the nucleus, and physical assumptions on comets. To do this, we have developed a quasi 3D model of a cometary nucleus which takes into account all phase changes and water ice structures (amorphous, crystalline, clathrate, and a mixture of them); we have applied this model to the comet 67P/Churyumov-Gerasimenko, the target of the Rosetta mission. We find that the outgassing profile of volatile molecules is a strong indicator of the physical and thermal properties (water ice structure, thermal inertia, abundances, distribution, physical differentiation) of the solid nucleus. Day/night variations of the rate of production of species helps to distinguish th...

  4. Thermal Stability, Sorption Properties and Morphology of Films of Dipeptide and Tripeptide Based on L-Glycine

    Directory of Open Access Journals (Sweden)

    Marat A. Ziganshin

    2015-12-01

    Full Text Available The effect of the number of amino acid residues in L-glycyl-L-glycine and L-glycyl-L-glycyl-L-glycine on thermal stability of powders, the sorption properties and surface morphology of thin films has been found. Dipeptide forms the film coated with disk-shaped nano-objects on the hydrophilic substrate, while tripeptide self-organizes to the film coated with nano-crystals on the hydrophobic substrate. Replacement of substrates (hydrophilic↔hydrophobic leads to the formation of smooth films of studied oligopeptides. Powders of oligopeptides do not form stable clathrates with water and organic compounds at room temperature. But their thin films are capable to bind organic or water vapors with high thermodynamic activity. Surprising difference in sorption selectivity of dipeptide and tripeptide has been observed. L-G

  5. Theoretical study of methanol as inhibitor and cyclopentane as stabilizer of dodecahedron methane hydrate cage

    Science.gov (United States)

    Pal, Snehanshu; Kundu, T. K.

    2015-02-01

    Density Functional Theory (DFT) based simulations have been performed to explain the role of methanol as an inhibitor and the role of cyclopentane as a promoter for methane hydrate. Interaction energy, Mullikan charges and electrostatic potential parameters for combined system of methanol and dodecahedron methane hydrate as well as cyclopentane and dodecahedron (512) methane hydrate cage are calculated using B3LYP functional (with and without dispersion function) and 6-31G(d) basis set. Methane hydrate formation inhibition by methanol and methane hydrate stabilization by cyclopentane is critically analyzed based on electrostatic potential and Mullikan charge. It is observed that hydrogen bond between water molecules of clathrate 512 cages become stronger in presence of cyclopentane and weaker in presence of methanol. It is also found that methanol breaks some hydrogen bonds of water molecules.

  6. The system Ba–Zn–Sn at 500 °C: Phase equilibria, crystal and electronic structure of ternary phases

    International Nuclear Information System (INIS)

    Highlights: • Phase relations for the Ba-poor part of the Ba–Zn–Sn system established at 500 °C. • New ternary compound BaZnSn2 crystallizes in CeNiSi2 structure type. • A homogeneity region has been defined for the BaZn1−xSn1+x (0.22 ⩽ x ⩽ 0.35) compound. • BaZn2Sn2 is characterized by mixed Zn/Sn occupancy and a small amount of vacancies. • The solubility of Sn in the Ba8Zn7Si39 clathrate was found to be 2Sn2 (CaBe2Ge2 type), a novel ternary compound BaZnSn2 was found to crystallize with the CeNiSi2-type. The precise determination (EPMA) of the homogeneity region at 500 °C for the compound BaZn1−xSn1+x with the ZrBeSi type (0.22 ⩽ x ⩽ 0.35) excludes the stoichiometric composition. The stannide BaZn2−xSn2+x (x = 0.05) is characterized by mixed occupancy of Zn and Sn atoms in the 2c site; accordingly the composition is slightly shifted from stoichiometry 1:2:2. Structural effects in the Ba–Zn–Sn compounds were explained on the basis of crystal chemistry analyses and electronic structure calculations employing the electron localization function ELF. The solubility of Sn in the clathrate phase Ba8Zn7Si39 was found to be insignificant (around 1 at.%; 800 °C)

  7. Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit

    Science.gov (United States)

    Hansen, T. C.; Falenty, A.; Kuhs, W. F.

    2016-02-01

    The lattice constants of hydrogenated and deuterated CH4-, CO2-, Xe- (clathrate structure type I) and N2-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron- and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO2 as compared to methane, CO2-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO2-water system. (3) The expansivity of CO2-hydrate is larger than for CH4-hydrate which leads to larger lattice constants for the former at temperatures above ˜150 K; this is likely due to the higher motional degrees of freedom of the CO2 guest molecules. (4) The cage occupancies of Xe- and CO2-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms' vibrational energy to thermal expansion is important, most prominently for CO2- and Xe-hydrates.

  8. Self-Organization of +-Crown Ether Derivatives into Double-Columnar Arrays Controlled by Supramolecular Isomers of Hydrogen-Bonded Anionic Biimidazolate Ni Complexes

    Directory of Open Access Journals (Sweden)

    Makoto Tadokoro

    2012-01-01

    Full Text Available Anionic tris (biimidazolate nickelate (II ([Ni(Hbim3]−, which is a hydrogen-bonding (H-bonding molecular building block, undergoes self-organization into honeycomb-sheet superstructures connected by complementary intermolecular H-bonds. The crystal obtained from the stacking of these sheets is assembled into channel frameworks, approximately 2 nm wide, that clathrate two cationic K+-crown ether derivatives organised into one-dimensional (1D double-columnar arrays. In this study, we have shown that all five cationic guest-included crystals form nanochannel structures that clathrate the 1-D double-columnar arrays of one of the four types of K+-crown ether derivatives, one of which induces a polymorph. This is accomplished by adaptably fitting two types of anionic [Ni(Hbim3]− host arrays. One is a ΔΛ−ΔΛ−ΔΛ⋯ network with H-bonded linkages alternating between the two different optical isomers of the Δ and Λ types with flexible H-bonded [Ni(Hbim3]−. The other is a ΔΔΔ−ΛΛΛ⋯ network of a racemate with 1-D H-bonded arrays of the same optical isomer for each type. Thus, [Ni(Hbim3]− can assemble large cations such as K+ crown-ether derivatives into double-columnar arrays by highly recognizing flexible H-bonding arrangements with two host networks of ΔΛ−ΔΛ−ΔΛ⋯ and ΔΔΔ−ΛΛΛ⋯.

  9. Subsurface Characterization of 67P/Churyumov–Gerasimenko’s Abydos Site

    Science.gov (United States)

    Brugger, B.; Mousis, O.; Morse, A.; Marboeuf, U.; Jorda, L.; Guilbert-Lepoutre, A.; Andrews, D.; Barber, S.; Lamy, P.; Luspay-Kuti, A.; Mandt, K.; Morgan, G.; Sheridan, S.; Vernazza, P.; Wright, I. P.

    2016-05-01

    On 2014 November 12, the ESA/Rosetta descent module Philae landed on the Abydos site of comet 67P/Churyumov–Gerasimenko. Aboard this module, the Ptolemy mass spectrometer measured a CO/CO2 ratio of 0.07 ± 0.04, which differs substantially from the value obtained in the coma by the Rosetta/ROSINA instrument, suggesting a heterogeneity in the comet nucleus. To understand this difference, we investigated the physicochemical properties of the Abydos subsurface, leading to CO/CO2 ratios close to that observed by Ptolemy at the surface of this region. We used a comet nucleus model that takes into account different water ice phase changes (amorphous ice, crystalline ice, and clathrates) as well as diffusion of molecules throughout the pores of the matrix. The input parameters of the model were optimized for the Abydos site, and the ROSINA CO/CO2 measured ratio is assumed to correspond to the bulk value in the nucleus. We find that all considered structures of water ice are able to reproduce the Ptolemy observation with a time difference not exceeding ∼50 days, i.e., lower than ∼2% on 67P/Churyumov–Gerasimenko’s orbital period. The suspected heterogeneity of 67P/Churyumov–Gerasimenko’s nucleus is also found possible only if it is constituted of crystalline ices. If the icy phase is made of amorphous ice or clathrates, the difference between Ptolemy and ROSINA’s measurements would rather originate from the spatial variations in illumination on the nucleus surface. An eventual new measurement of the CO/CO2 ratio at Abydos by Ptolemy could be decisive to distinguish between the three water ice structures.

  10. Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, T. C. [Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble (France); Falenty, A.; Kuhs, W. F. [GZG, Abt. Kristallographie, Universität Göttingen, Goldschmidtstrasse 1, 37077 Göttingen (Germany)

    2016-02-07

    The lattice constants of hydrogenated and deuterated CH{sub 4}-, CO{sub 2}-, Xe- (clathrate structure type I) and N{sub 2}-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron- and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO{sub 2} as compared to methane, CO{sub 2}-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO{sub 2}-water system. (3) The expansivity of CO{sub 2}-hydrate is larger than for CH{sub 4}-hydrate which leads to larger lattice constants for the former at temperatures above ∼150 K; this is likely due to the higher motional degrees of freedom of the CO{sub 2} guest molecules. (4) The cage occupancies of Xe- and CO{sub 2}-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms’ vibrational energy to thermal expansion is important, most prominently for CO{sub 2}- and Xe-hydrates.

  11. The structure of CO{sub 2} hydrate between 0.7 and 1.0 GPa

    Energy Technology Data Exchange (ETDEWEB)

    Tulk, C. A.; Molaison, J. J. [Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Machida, S. [Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015 (United States); Klug, D. D.; Lu, H. [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada); Guthrie, M. [Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015 (United States)

    2014-11-07

    A deuterated sample of CO{sub 2} structure I (sI) clathrate hydrate (CO{sub 2}·8.3 D{sub 2}O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO{sub 2} hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai et al. [J. Phys. Chem. 133, 124511 (2010)] and Bollengier et al. [Geochim. Cosmochim. Acta 119, 322 (2013)], but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO{sub 2} molecules filling the water channels. This CO{sub 2}+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts a MH-III “like” filled ice structure with considerable disorder of the orientations of the CO{sub 2} molecule. Furthermore, the disorder appears to be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al., our neutron diffraction data show that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO{sub 2} hydrate transforms directly from the sI form to the filled ice structure.

  12. A Protosolar Nebula Origin for the Ices Agglomerated by Comet 67P/Churyumov-Gerasimenko

    Science.gov (United States)

    Mousis, O.; Lunine, J. I.; Luspay-Kuti, A.; Guillot, T.; Marty, B.; Ali-Dib, M.; Wurz, P.; Altwegg, K.; Bieler, A.; Hässig, M.; Rubin, M.; Vernazza, P.; Waite, J. H.

    2016-03-01

    The nature of the icy material accreted by comets during their formation in the outer regions of the protosolar nebula (PSN) is a major open question in planetary science. Some scenarios of comet formation predict that these bodies agglomerated from crystalline ices condensed in the PSN. Concurrently, alternative scenarios suggest that comets accreted amorphous ice originating from the interstellar cloud or from the very distant regions of the PSN. On the basis of existing laboratory and modeling data, we find that the N2/CO and Ar/CO ratios measured in the coma of the Jupiter-family comet 67P/Churyumov-Gerasimenko by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument on board the European Space Agency’s Rosetta spacecraft match those predicted for gases trapped in clathrates. If these measurements are representative of the bulk N2/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the ices accreted by the comet formed in the nebula and do not originate from the interstellar medium, supporting the idea that the building blocks of outer solar system bodies have been formed from clathrates and possibly from pure crystalline ices. Moreover, because 67P/Churyumov-Gerasimenko is impoverished in Ar and N2, the volatile enrichments observed in Jupiter’s atmosphere cannot be explained solely via the accretion of building blocks with similar compositions and require an additional delivery source. A potential source may be the accretion of gas from the nebula that has been progressively enriched in heavy elements due to photoevaporation.

  13. Revealing Surface Waters on an Antifreeze Protein by Fusion Protein Crystallography Combined with Molecular Dynamic Simulations.

    Science.gov (United States)

    Sun, Tianjun; Gauthier, Sherry Y; Campbell, Robert L; Davies, Peter L

    2015-10-01

    Antifreeze proteins (AFPs) adsorb to ice through an extensive, flat, relatively hydrophobic surface. It has been suggested that this ice-binding site (IBS) organizes surface waters into an ice-like clathrate arrangement that matches and fuses to the quasi-liquid layer on the ice surface. On cooling, these waters join the ice lattice and freeze the AFP to its ligand. Evidence for the generality of this binding mechanism is limited because AFPs tend to crystallize with their IBS as a preferred protein-protein contact surface, which displaces some bound waters. Type III AFP is a 7 kDa globular protein with an IBS made up two adjacent surfaces. In the crystal structure of the most active isoform (QAE1), the part of the IBS that docks to the primary prism plane of ice is partially exposed to solvent and has clathrate waters present that match this plane of ice. The adjacent IBS, which matches the pyramidal plane of ice, is involved in protein-protein crystal contacts with few surface waters. Here we have changed the protein-protein contacts in the ice-binding region by crystallizing a fusion of QAE1 to maltose-binding protein. In this 1.9 Å structure, the IBS that fits the pyramidal plane of ice is exposed to solvent. By combining crystallography data with MD simulations, the surface waters on both sides of the IBS were revealed and match well with the target ice planes. The waters on the pyramidal plane IBS were loosely constrained, which might explain why other isoforms of type III AFP that lack the prism plane IBS are less active than QAE1. The AFP fusion crystallization method can potentially be used to force the exposure to solvent of the IBS on other AFPs to reveal the locations of key surface waters. PMID:26371748

  14. The structure of CO2 hydrate between 0.7 and 1.0 GPa

    International Nuclear Information System (INIS)

    A deuterated sample of CO2 structure I (sI) clathrate hydrate (CO2·8.3 D2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai et al. [J. Phys. Chem. 133, 124511 (2010)] and Bollengier et al. [Geochim. Cosmochim. Acta 119, 322 (2013)], but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO2 molecules filling the water channels. This CO2+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts a MH-III “like” filled ice structure with considerable disorder of the orientations of the CO2 molecule. Furthermore, the disorder appears to be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al., our neutron diffraction data show that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO2 hydrate transforms directly from the sI form to the filled ice structure

  15. Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit

    International Nuclear Information System (INIS)

    The lattice constants of hydrogenated and deuterated CH4-, CO2-, Xe- (clathrate structure type I) and N2-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron- and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO2 as compared to methane, CO2-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO2-water system. (3) The expansivity of CO2-hydrate is larger than for CH4-hydrate which leads to larger lattice constants for the former at temperatures above ∼150 K; this is likely due to the higher motional degrees of freedom of the CO2 guest molecules. (4) The cage occupancies of Xe- and CO2-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms’ vibrational energy to thermal expansion is important, most prominently for CO2- and Xe-hydrates

  16. Structure and dynamics of cold water super-Earths: the case of occluded CH{sub 4} and its outgassing

    Energy Technology Data Exchange (ETDEWEB)

    Levi, A.; Podolak, M. [Department of Geophysics and Planetary Science, Tel Aviv University, Tel Aviv 69978 (Israel); Sasselov, D., E-mail: amitlevi.planetphys@gmail.com [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2014-09-10

    In this work, we study the transport of methane in the external water envelopes surrounding water-rich super-Earths. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice), resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to the lower ice mantle of relatively low-mass planets (∼5 M{sub E} ) lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes which depend on the surface temperature and heat flux. We demonstrate that the planetary crust can be conductive throughout or partly confined to the dissociation curve of methane clathrate hydrate. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere, making modes of ice plate tectonics possible. The dynamic character of the tectonic plates is analyzed and the ability of this tectonic mode to cool the planet is estimated. The icy tectonic plates are found to be faster than those on a silicate super-Earth. A mid-layer of low viscosity is found to exist between the lithosphere and the lower mantle. Its existence results in a large difference between ice mantle overturn timescales and resurfacing timescales. Resurfacing timescales are found to be 1 Ma for fast plates and 100 Ma for sluggish plates, depending on the viscosity profile and ice mass fraction. Melting beneath spreading centers is required in order to account for the planetary radiogenic heating. The melt fraction is quantified for the various tectonic solutions explored, ranging from a few percent for the fast and thin plates to total melting of the upwelled material for the thick and sluggish plates. Ice mantle dynamics is found to be important for assessing the composition of

  17. Structure and dynamics of cold water super-Earths: the case of occluded CH4 and its outgassing

    International Nuclear Information System (INIS)

    In this work, we study the transport of methane in the external water envelopes surrounding water-rich super-Earths. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice), resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to the lower ice mantle of relatively low-mass planets (∼5 ME ) lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes which depend on the surface temperature and heat flux. We demonstrate that the planetary crust can be conductive throughout or partly confined to the dissociation curve of methane clathrate hydrate. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere, making modes of ice plate tectonics possible. The dynamic character of the tectonic plates is analyzed and the ability of this tectonic mode to cool the planet is estimated. The icy tectonic plates are found to be faster than those on a silicate super-Earth. A mid-layer of low viscosity is found to exist between the lithosphere and the lower mantle. Its existence results in a large difference between ice mantle overturn timescales and resurfacing timescales. Resurfacing timescales are found to be 1 Ma for fast plates and 100 Ma for sluggish plates, depending on the viscosity profile and ice mass fraction. Melting beneath spreading centers is required in order to account for the planetary radiogenic heating. The melt fraction is quantified for the various tectonic solutions explored, ranging from a few percent for the fast and thin plates to total melting of the upwelled material for the thick and sluggish plates. Ice mantle dynamics is found to be important for assessing the composition of the

  18. Cage-forming compounds in the Ba-Rh-Ge system: from thermoelectrics to superconductivity.

    Science.gov (United States)

    Falmbigl, M; Kneidinger, F; Chen, M; Grytsiv, A; Michor, H; Royanian, E; Bauer, E; Effenberger, H; Podloucky, R; Rogl, P

    2013-01-18

    Phase relations and solidification behavior in the Ge-rich part of the phase diagram have been determined in two isothermal sections at 700 and 750 °C and in a liquidus projection. A reaction scheme has been derived in the form of a Schulz-Scheil diagram. Phase equilibria are characterized by three ternary compounds: τ(1)-BaRhGe(3) (BaNiSn(3)-type) and two novel phases, τ(2)-Ba(3)Rh(4)Ge(16) and τ(3)-Ba(5)Rh(15)Ge(36-x), both forming in peritectic reactions. The crystal structures of τ(2) and τ(3) have been elucidated from single-crystal X-ray intensity data and were found to crystallize in unique structure types: Ba(3)Rh(4)Ge(16) is tetragonal (I4/mmm, a = 0.65643(2) nm, c = 2.20367(8) nm, and R(F) = 0.0273), whereas atoms in Ba(5)Rh(15)Ge(36-x) (x = 0.25) arrange in a large orthorhombic unit cell (Fddd, a = 0.84570(2) nm, b = 1.4725(2) nm, c = 6.644(3) nm, and R(F) = 0.034). The body-centered-cubic superstructure of binary Ba(8)Ge(43)□(3) was observed to extend at 800 °C to Ba(8)Rh(0.6)Ge(43)□(2.4), while the clathrate type I phase, κ(I)-Ba(8)Rh(x)Ge(46-x-y)□(y), reveals a maximum solubility of x = 1.2 Rh atoms in the structure at a vacancy level of y = 2.0. The cubic lattice parameter increases with increasing Rh content. Clathrate I decomposes eutectoidally at 740 °C: κ(I) ⇔ (Ge) + κ(IX) + τ(2). A very small solubility range is observed at 750 °C for the clathrate IX, κ(IX)-Ba(6)Rh(x)Ge(25-x) (x ∼ 0.16). Density functional theory calculations have been performed to derive the enthalpies of formation and densities of states for various compositions Ba(8)Rh(x)Ge(46-x) (x = 0-6). The physical properties have been investigated for the phases κ(I), τ(1), τ(2), and τ(3), documenting a change from thermoelectric (κ(I)) to superconducting behavior (τ(2)). The electrical resistivity of κ(I)-Ba(8)Rh(1.2)Ge(42.8)□(2.0) increases almost linearly with the temperature from room temperature to 730 K, and the Seebeck coefficient is negative

  19. Formation of porous gas hydrates: Diffraction experiments and multi-stage model

    Science.gov (United States)

    Staykova, D. K.; Genov, G.; Goreshnik, E.; Salamatin, A. N.; Kuhs, W. F.

    2003-04-01

    Laboratory-grown gas hydrates were examined by cryo scanning electron microscopy and found to have a sub-micron porous structure. This microstructure is undistinguishable from the one observed in natural gas hydrates suggesting similar formation processes. In-situ observations of the formation of synthetic porous methane and carbon dioxide hydrates starting from ice Ih powders with known surfaces areas were made using time-resolved neutron diffraction on the high-flux diffractometer D20 (ILL, Grenoble) at different pressures and temperatures. Some runs were also made going through the ice melting point into liquid water. At similar reduced fugacities, the reaction of carbon dioxide was distinctly faster than that of methane. The transient formation of carbon dioxide hydrate crystal structure II was observed in coexistence with the usual type-I hydrate reaching a maximum of 5% after 5 h of the reaction at 272 K. At lower temperatures a temporary inhibition of formation was observed in the case of carbon dioxide. The rate of methane hydrate growth showed little pressure sensitivity in our experiments at low temperatures ~230 K in contrast to the situation at higher temperatures. A phenomenological model for the kinetics of the gas hydrate formation from ice powders is developed with special account of sample consolidation effects. It describes the initial stage (I) of hydrate film spreading over the ice surface and the two subsequent stages which are limited (II) by the clathration reaction at the ice-hydrate interface and (III) by the gas and water transport (diffusion) through the hydrate shells surrounding the shrinking ice cores. Comparable activation energies of the CH4-hydrate formation are found in deuterated and hydrogenated systems for the reaction-limited process (stage II) to be 8.1 and 9.5 kcal/mol, respectively. In the case of a diffusion-limited clathration (stage III) the activation energy can be estimated as 14.3 kcal/mol. The relevance of our

  20. Megafauna and frozen soil: the drivers of atmospheric CH4 dynamics

    Science.gov (United States)

    Zimov, N.; Zimov, S. A.

    2010-12-01

    During the last deglaciation (LD) a strong increase in atmospheric methane (CH4) concentrations occurred simultaneously with a rise in Greenland temperatures indicating that in the north, during this time period, strong CH4 sources “awakened”, as additionally documented by the appearance of a strong gradient between northern (Greenland) and southern (Antarctica) hemisphere atmospheric CH4 concentrations. This rise could not be caused by wetland expansion. A reconstruction of peatland formation dynamics has indicated that wetlands on Earth were few in LD and only actively expanded 10,000 yr BP, after atmospheric CH4 concentrations began to decline. Destabilization of methane clathrates also could not be the source for atmospheric CH4 increase. Geological CH4 (including methane clathrates) has the highest deuterium content (δD) among all of the known sources of CH4 while atmospheric CH4 δD values determined for the LD were record low. To explain recorded atmospheric CH4 and its isotopic dynamics required a strong northern source, which was active only during the LD and that provided very low δD CH4 values. Such a source is permafrost thawing under anaerobic conditions (or better stated soils of mammoth steppe-tundra ecosystems). Permafrost thawing is the strongest, among known, wetland sources (usually over 100g CH4/m2yr) and has a unique isotopic signature (δD = -400 per mil (-338 to -479 per mil), δ13C = -73 per mil (-58 to -99 per mil)). The main sources of atmospheric CH4 have different isotopic signatures (δ13C, δD). The isotopic content of atmospheric CH4 is a simple function of the weight average for all of the sources. Inclusion of permafrost source into a budget model of the atmospheric methane and its isotopes allowed us to reconstruct the dynamics of methane’s main sources. Model indicated geological source to be negligible as in LGM so and in LD and Holocene. During the glaciation, the largest methane source was megafauna, whose 1

  1. Experimental Study of Gas Hydrate Dynamics

    Science.gov (United States)

    Fandino, O.; Ruffine, L.

    2011-12-01

    Important quantities of methane and other gases are trapped below the seafloor and in the permafrost by an ice-like solid, called gas hydrates or clathrate hydrates. The latter is formed when water is mixing with different gases at high pressures and low temperatures. Due to a their possible use as a source of energy [1] or the problematic related to flow assurance failure in pipelines [2] the understanding of their processes of formation/destabilisation of these structures becomes a goal for many laboratories research as well as industries. In this work we present an experimental study on the stochastic behaviour of hydrate formation from a bulk phase. The method used here for the experiments was to repeat several time the same hydrate formation procedure and to notice the different from one experiment to another. A variable-volume type high-pressure apparatus with two sapphire windows was used. This device, already presented by Ruffine et al.[3], allows us to perform both kinetics and phase equilibrium measurements. Three initial pressure conditions were considered here, 5.0 MPa, 7.5 MPa and 10.0 MPa. Hydrates have been formed, then allowed to dissociate by stepwise heating. The memory effect has also been investigated after complete dissociation. It turned out that, although the thermodynamics conditions of formation and/or destabilization were reproducible. An attempt to determine the influence of pressure on the nucleation induction time will be discussed. References 1. Sum, A. K.; Koh, C. A.; Sloan, E. D., Clathrate Hydrates: From Laboratory Science to Engineering Practice. Industrial & Engineering Chemistry Research 2009, 48, 7457-7465. 2. Sloan, E. D., A changing hydrate paradigm-from apprehension to avoidance to risk management. Fluid Phase Equilibria 2005, 228, 67-74. 3. Ruffine, L.; Donval, J. P.; Charlou, J. L.; Cremière, A.; Zehnder, B. H., Experimental study of gas hydrate formation and destabilisation using a novel high-pressure apparatus. Marine

  2. IMPACT REGIMES AND POST-FORMATION SEQUESTRATION PROCESSES: IMPLICATIONS FOR THE ORIGIN OF HEAVY NOBLE GASES IN TERRESTRIAL PLANETS

    International Nuclear Information System (INIS)

    The difference between the measured atmospheric abundances of neon, argon, krypton, and xenon for Venus, Earth, and Mars is striking. Because these abundances drop by at least 2 orders of magnitude as one moves outward from Venus to Mars, the study of the origin of this discrepancy is a key issue that must be explained if we are to fully understand the different delivery mechanisms of the volatiles accreted by the terrestrial planets. In this work, we aim to investigate whether it is possible to quantitatively explain the variation of the heavy noble gas abundances measured on Venus, Earth, and Mars, assuming that cometary bombardment was the main delivery mechanism of these noble gases to the terrestrial planets. To do so, we use recent dynamical simulations that allow the study of the impact fluxes of comets upon the terrestrial planets during the course of their formation and evolution. Assuming that the mass of noble gases delivered by comets is proportional to the rate at which they collide with the terrestrial planets, we show that the krypton and xenon abundances in Venus and Earth can be explained in a manner consistent with the hypothesis of cometary bombardment. In order to explain the krypton and xenon abundance differences between Earth and Mars, we need to invoke the presence of large amounts of CO2-dominated clathrates in the Martian soil that would have efficiently sequestered these noble gases. Two different scenarios based on our model can also be used to explain the differences between the neon and argon abundances of the terrestrial planets. In the first scenario, cometary bombardment of these planets would have occurred at epochs contemporary with the existence of their primary atmospheres. Comets would have been the carriers of argon, krypton, and xenon, while neon would have been gravitationally captured by the terrestrial planets. In the second scenario, we consider impacting comets that contained significantly smaller amounts of argon, an

  3. Effect of administration of water enriched in O2 by injection or electrolysis on transcutaneous oxygen pressure in anesthetized pigs

    Directory of Open Access Journals (Sweden)

    Charton A

    2014-08-01

    the three groups, but when compared to the control group, the values remained significantly higher in animals that received the water enriched in O2 by electrolysis. Conclusions: In this protocol, water enriched in O2 by electrolysis lessened the decline of peripheral tissue oxygenation. This observation is compatible with the claim that the electrolytic process generates water clathrates which trap O2 and facilitate O2 diffusion along pressure gradients. Potential applications of O2-enriched water include an alternate method of oxygen supply. Keywords: transcutaneous oxygen partial pressure determination, tissue oxygenation, oxygenated water, water clathrate 

  4. Stabilities of filled ice II structure of hydrogen and helium hydrates at low temperatures and high pressures

    Science.gov (United States)

    Hirai, H.; Umeda, A.; Fujii, T.; Machida, S.; Shinozaki, A.; Kawamura, T.; Yamamoto, Y.; Yagi, T.

    2011-12-01

    Hydrogen hydrate is expected to be a hydrogen storage material, because it can contain relatively high hydrogen and its synthetic condition is mild comparable to industrial production. Three phases of hydrogen hydrate have been known so for. One is a clathrate hydrate sII [1], and others are filled ice II structure and filled ice Ic structure [2]. The ratio of water to hydrogen molecules for these phases are1:3, 1:6, 1:1, respectively. The clathrate sII containing only hydrogen molecules is stable only in a lower temperature region. At room temperature, above about 0.8 GPa filled ice II and above 2.5 GPa filled ice Ic are formed. The latter one survives at least up to 90 GPa [3]. However, investigations in low temperature and high pressure region have been limited. In this study, low temperature and high pressure experiments were performed by using diamond anvil cells and a helium-refrigeration cryostat in a region of 0.2 to 4.5 GPa and 130 to 300 K. X-ray diffractometry (XRD) showed a series of phase change from sII to filled ice Ic via filled ice II. For example, at 220K, sII transformed to filled ice II at approximately 0.7 GPa and further transformed to filled ice Ic structure at about 2.0 GPa. The present results experimentally confirmed the previously predicted phase boundaries. For filled ice II structure, Raman spectroscopy revealed that pressure dependency of vibration mode of guest hydrogen molecules and OH stretching mode of host water molecules changed at approximately 2.5 GPa. The XRD also showed change in axial ratio at the same pressure. These result suggested that state of filled ice II structure changed at about 2.5 GPa. Helium hydrate is known to form filled ice II structure [4], but high pressure study has not been yet fully performed. Similar experiments were carried out in a region of 0.2 to 5.0 GPa and 200 to 300 K. The results showed that the filled ice II structure did not transformed to filled ice Ic structure, but decomposed into helium

  5. CO2 and C2H2 in cold nanodroplets of oxygenated organic molecules and water

    Science.gov (United States)

    Devlin, J. Paul; Balcı, F. Mine; Maşlakcı, Zafer; Uras-Aytemiz, Nevin

    2014-11-01

    Recent demonstrations of subsecond and microsecond timescales for formation of clathrate hydrate nanocrystals hint at future methods of control of environmental and industrial gases such as CO2 and methane. Combined results from cold-chamber and supersonic-nozzle [A. S. Bhabhe, "Experimental study of condensation and freezing in a supersonic nozzle," Ph.D. thesis (Ohio State University, 2012), Chap. 7] experiments indicate extremely rapid encagement of components of all-vapor pre-mixtures. The extreme rates are derived from (a) the all-vapor premixing of the gas-hydrate components and (b) catalytic activity of certain oxygenated organic large-cage guests. Premixing presents no obvious barrier to large-scale conditions of formation. Further, from sequential efforts of the groups of Trout and Buch, a credible defect-based model of the catalysis mechanism exists for guidance. Since the catalyst-generated defects are both mobile and abundant, it is often unnecessary for a high percentage of the cages to be occupied by a molecular catalyst. Droplets represent the liquid phase that bridges the premixed vapor and clathrate hydrate phases but few data exist for the droplets themselves. Here we describe a focused computational and FTIR spectroscopic effort to characterize the aerosol droplets of the all-vapor cold-chamber methodology. Computational data for CO2 and C2H2, hetero-dimerized with each of the organic catalysts and water, closely match spectroscopic redshift patterns in both magnitude and direction. Though vibrational frequency shifts are an order of magnitude greater for the acetylene stretch mode, both CO2 and C2H2 experience redshift values that increase from that for an 80% water-methanol solvent through the solvent series to approximately doubled values for tetrahydrofuran and trimethylene oxide (TMO) droplets. The TMO solvent properties extend to a 50 mol.% solution of CO2, more than an order of magnitude greater than for the water-methanol solvent mixture

  6. Some insight into the physical basis of the cryoprotective action of dimethyl sulfoxide and ethylene glycol.

    Science.gov (United States)

    Murthy, S S

    1998-03-01

    In the determination of the solid-liquid phase equilibria in the aqueous mixtures of dimethyl sulfoxide (Me2SO) and ethylene glycol (EG) one often encounters the problem of equilibrium crystallization. In the present report the above aqueous solutions are equilibrated for crystallization in a dielectric cell during which the dielectric method is used for monitoring the extent of crystallization. The melting temperatures are then measured by using the dielectric technique in combination with the differential scanning calorimeter. The equilibrium phase diagram of Me2SO is found to be eutectic with two compounds formed of water and Me2SO in the ratio of 3:1 and 2:1. In the case of EG solutions it is eutectic with a 1:1 compound formation. It is suggested that the greater depression of the freezing point of water due to the complex formation and hence the attendant increase in the viscosity near the freezing point is the reason for the sluggish crystallization in these solutions. The variation of the glass transition temperature with composition is also examined in the above solutions along with the aqueous solutions of a number of other cryoprotectants. The glass-forming tendency of these solutions is discussed in terms of complex formation. An attempt is made to distinguish between good and bad glass-forming additives in terms of complex formation and ice clathrate formation. PMID:9527870

  7. Third international workshop on ice storage for cooling applications

    Energy Technology Data Exchange (ETDEWEB)

    Gorski, A.J. (comp.)

    1986-04-01

    The third international workshop on ice storage for cooling applications which was informal and interactive in nature, was open to persons interested in all ice-growing technologies and in ice storage, both seasonal and diurnal. Presentations were made on some 20 topics, ranging from freezers in Alaska to ice cooling of commercial jet aircraft. Workshop tours included visits to ice-storage systems at Commonwealth Edison's facilities in Bolingbrook and Des Plaines Valley, the A.C. Neilsen builing in Northbrook, and the new State of Illinois Center in Chicago. The first workshop in the present series considered the future of ice storage and predicted applications in the agricultural sector, desalinization, and commercial ice production. Progress has been rapid in the intervening two years, and an important topic at the third workshop was the possible use of ''warm ices'' (clathrate hydrates) for energy storage. This report consists primarily of abstracts of presentations made at the workshop. Persons wishing to obtain further information about particular papers should contact the speakers directly; speakers' addresses and telephone numbers are listed in this report.

  8. Thermoelectric transport in rare-earth compounds

    Energy Technology Data Exchange (ETDEWEB)

    Koehler, Ulrike

    2007-07-01

    This work focuses on the thermoelectric transport in rare-earth compounds. The measurements of the thermal conductivity, thermopower, and Nernst coefficient are supplemented by investigations of other quantities as magnetic susceptibility and specific heat. Chapter 2 provides an introduction to the relevant physical concepts. Section 1 of that chapter summarizes the characteristic properties of rare-earth systems; section 2 gives an overview on thermoelectric transport processes in magnetic fields. The applied experimental techniques as well as the new experimental setup are described in detail in Chapter 3. The experimental results are presented in Chapter 4-6, of which each concentrates on a different subject. In Chapter 4, various Eu clathrates and the skutterudite-like Ce{sub 3}Rh{sub 4}Sn{sub 13} are presented, which have been investigated as potential thermoelectric materials for applications. Chapter 5 focusses on the study of the energy scales in the heavy-fermion series Lu{sub 1-x}Yb{sub x}Rh{sub 2}Si{sub 2} and Ce{sub x}La{sub 1-x}Ni{sub 2}Ge{sub 2} by means of thermopower investigations. Chapter 6 is dedicated to the thermoelectric transport properties of the correlated semimetal CeNiSn with special emphasis on the Nernst coefficient of this compound. (orig.)

  9. Evidence of fast pebble growth near condensation fronts in the HL Tau protoplanetary disk

    CERN Document Server

    Zhang, Ke; Bergin, Edwin A

    2015-01-01

    Water and simple organic molecular ices dominate the mass of solid materials available for planetesimal and planet formation beyond the water snow line. Here we analyze ALMA long baseline 2.9, 1.3 and 0.87 mm continuum images of the young star HL Tau, and suggest that the emission dips observed are due to rapid pebble growth around the condensation fronts of abundant volatile species. Specifically, we show that the prominent innermost dip at 13 AU is spatially resolved in the 0.87 mm image, and its center radius is coincident with the expected mid-plane condensation front of water ice. In addition, two other prominent dips, at distances of 32 and 63 AU, cover the mid-plane condensation fronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially with CO and N$_2$) formed from amorphous water ice. The spectral index map of HL Tau between 1.3 and 0.87 mm shows that the flux ratios inside the dips are statistically larger than those of nearby regions in the disk. This variation can be explained ...

  10. Nuclear data generation for cryogenic moderators and high temperature moderators

    International Nuclear Information System (INIS)

    The commonly used processing codes for nuclear data only allow the generation of cross section data for a limited number of materials and physical conditions.At present, one of the most used computer codes for the generation of neutron cross sections is N J O Y, which is based on a phonon expansion of the scattering function starting from the frequency spectrum.Therefore, the information related to the system's density of states is crucial to produce the required data of interest. In this work the formalism of the Synthetic Model for Molecular Solids (S M M S) was implemented, which is in turn based on the Synthetic Frequency Spectrum (S F S) concept.The synthetic spectrum is central in the present work, and it is built from simple, relevant parameters of the moderator, thus conforming an alternative tool when no information on the actual frequency spectrum of the moderator material is available.S F S 's for several material of interest where produced in this work, for both cryogenic and high temperature moderators.We studied some materials of special interest, like solid methane, ice, methyl clathrate and two which are of special interest in the nuclear industry: graphite and beryllium.The libraries generated in the present work for the materials considered, in spite of their synthetic origin, are able to produce results that are even in better agreement with available information

  11. Hydrogen bonds in methane-water clusters.

    Science.gov (United States)

    Salazar-Cano, Juan-Ramón; Guevara-García, Alfredo; Vargas, Rubicelia; Restrepo, Albeiro; Garza, Jorge

    2016-08-24

    Characterization of hydrogen bonds in CH4-(H2O)12 clusters was carried out by using several quantum chemistry tools. An initial stochastic search provided around 2 500 000 candidate structures, then, using a convex-hull polygon criterion followed by gradient based optimization under the Kohn-Sham scheme, a total of 54 well defined local minima were located in the Potential Energy Surface. These structures were further analyzed through second-order many-body perturbation theory with an extended basis set at the MP2/6-311++G(d,p) level. Our analysis of Gibbs energies at several temperatures clearly suggests a structural preference toward compact water clusters interacting with the external methane molecule, instead of the more commonly known clathrate-like structures. This study shows that CH4-(H2O)12 clusters may be detected at temperatures up to 179 K, this finding provides strong support to a recently postulated hypothesis that suggests that methane-water clusters could be present in Mars at these conditions. Interestingly, we found that water to water hydrogen bonding is strengthened in the mixed clusters when compared to the isolated water dimer, which in turn leads to a weakening of the methane to water hydrogen bonding when compared to the CH4-(H2O) dimer. Finally, our evidence places a stern warning about the abilities of popular geometrical criteria to determine the existence of hydrogen bonds. PMID:27492605

  12. Subsurface characterization of 67P/Churyumov-Gerasimenko's Abydos site

    CERN Document Server

    Brugger, B; Morse, A; Marboeuf, U; Jorda, L; Guilbert-Lepoutre, A; Andrews, D; Barber, S; Lamy, P; Luspay-Kuti, A; Mandt, K; Morgan, G; Sheridan, S; Vernazza, P; Wright, I P

    2016-01-01

    On November 12, 2014, the ESA/Rosetta descent module Philae landed on the Abydos site of comet 67P/Churyumov-Gerasimenko. Aboard this module, the Ptolemy mass spectrometer measured a CO/CO2 ratio of 0.07 +/- 0.04 which differs substantially from the value obtained in the coma by the Rosetta/ROSINA instrument, suggesting a heterogeneity in the comet nucleus. To understand this difference, we investigated the physico-chemical properties of the Abydos subsurface leading to CO/CO2 ratios close to that observed by Ptolemy at the surface of this region. We used a comet nucleus model that takes into account different water ice phase changes (amorphous ice, crystalline ice and clathrates), as well as diffusion of molecules throughout the pores of the matrix. The input parameters of the model were optimized for the Abydos site and the ROSINA CO/CO2 measured ratio is assumed to correspond to the bulk value in the nucleus. We find that all considered structures of water ice are able to reproduce the Ptolemy observation ...

  13. The biogeochemical cycling of carbon dioxide in the oceans. Perturbations by man

    International Nuclear Information System (INIS)

    The purpose of the paper is to follow up the contribution by Dyrssen and Turner to the Hemavan meeting in 1993 on CO2 chemistry. Machta's treatment from 1971 of the role of oceans and biosphere in the carbon dioxide cycle is reviewed. Using data on the emission of CO2 and the atmospheric content in addition to the value recently presented by Takahashi et al. for the net sink for global oceans the following numbers have been calculated for the period 1990 to 2000, annual emission of CO2, 6.185 PgC (Petagram=1015 g). Annual atmospheric accumulation, 2.930 PgC. Annual sinks, 3.255 PgC. Net uptake for 1990 by the oceans, 1.151 PgC/year. Solubility pump into the mixed layer, 0.828 PgC/year. Residual input (e.g. riverborne), 0.323 PgC/year. Annual uptake by land phytomass, 2.104 PgC. In addition, perturbations involving irrigation and fertilization, limestone dissolution, iron and clathrate addition are mentioned

  14. Thermodynamic stability, spectroscopic identification, and gas storage capacity of CO2-CH4-N2 mixture gas hydrates: implications for landfill gas hydrates.

    Science.gov (United States)

    Lee, Hyeong-Hoon; Ahn, Sook-Hyun; Nam, Byong-Uk; Kim, Byeong-Soo; Lee, Gang-Woo; Moon, Donghyun; Shin, Hyung Joon; Han, Kyu Won; Yoon, Ji-Ho

    2012-04-01

    Landfill gas (LFG), which is primarily composed of CH(4), CO(2), and N(2), is produced from the anaerobic digestion of organic materials. To investigate the feasibility of the storage and transportation of LFG via the formation of hydrate, we observed the phase equilibrium behavior of CO(2)-CH(4)-N(2) mixture hydrates. When the specific molar ratio of CO(2)/CH(4) was 40/55, the equilibrium dissociation pressures were gradually shifted to higher pressures and lower temperatures as the mole fraction of N(2) increased. X-ray diffraction revealed that the CO(2)-CH(4)-N(2) mixture hydrate prepared from the CO(2)/CH(4)/N(2) (40/55/5) gas mixture formed a structure I clathrate hydrate. A combination of Raman and solid-state (13)C NMR measurements provided detailed information regarding the cage occupancy of gas molecules trapped in the hydrate frameworks. The gas storage capacity of LFG hydrates was estimated from the experimental results for the hydrate formations under two-phase equilibrium conditions. We also confirmed that trace amounts of nonmethane organic compounds do not affect the cage occupancy of gas molecules or the thermodynamic stability of LFG hydrates. PMID:22380606

  15. Occurrence of organic compound (diploptene) from the East Sea core sediment and its paleoceanographic implications

    International Nuclear Information System (INIS)

    Research focusing on marine sediments has indicated that methane hydrate stored in deep sea sediments and the episodic emission of methane gas into the water column and atmosphere are related to environmental changes over geological time. Marine sediments are known to strongly affect global climatic changes and marine ecosystems. The ideal model of episodic methane hydrate instability due to the intermediate water circulation, is called the clathrate gun hypothesis. It is essential for tracking methane emissions from deep sea sediments through direct and indirect methods. Another approach to tracking methane emissions uses isotopic studies of foraminifera and organic compounds. Diploptene is a common constituent of hydrocarbons reported in marine sediments. The most important source of diploptene in marine sediments is thought to be aerobic methanotrophic bacteria. This study determined the timing of the occurrence of diploptene and related paleoceanographic environmental changes. The results of a preliminary study of two piston cores from the East Sea and their interpretation were also presented. The paper discussed the materials and methods used in the study. It also described vertical variations of diploptene concentration of the two cores and carbon isotopic value of the diploptene. It was concluded that the diploptene was likely derived from bacterial activity. Carbon isotopic values of diploptene from this study showed depleted values, and may indicate the methanogenic bacterial activity. 12 refs., 1 fig

  16. Occurrence of organic compound (diploptene) from the East Sea core sediment and its paleoceanographic implications

    Energy Technology Data Exchange (ETDEWEB)

    Hyun, S.; Yim, U.H.; Shim, W.J. [Korea Ocean Research and Development Inst., Geoje, Kyeongnam (Korea, Republic of); Bahk, J.J.; Nam, S.I.; Lee, Y.J. [Korea Inst. of Geoscience and Mineral Resources (Korea, Republic of); Uchida, M. [National Inst. for Environmental Studies, Onogawa, Tsukuba (Japan)

    2008-07-01

    Research focusing on marine sediments has indicated that methane hydrate stored in deep sea sediments and the episodic emission of methane gas into the water column and atmosphere are related to environmental changes over geological time. Marine sediments are known to strongly affect global climatic changes and marine ecosystems. The ideal model of episodic methane hydrate instability due to the intermediate water circulation, is called the clathrate gun hypothesis. It is essential for tracking methane emissions from deep sea sediments through direct and indirect methods. Another approach to tracking methane emissions uses isotopic studies of foraminifera and organic compounds. Diploptene is a common constituent of hydrocarbons reported in marine sediments. The most important source of diploptene in marine sediments is thought to be aerobic methanotrophic bacteria. This study determined the timing of the occurrence of diploptene and related paleoceanographic environmental changes. The results of a preliminary study of two piston cores from the East Sea and their interpretation were also presented. The paper discussed the materials and methods used in the study. It also described vertical variations of diploptene concentration of the two cores and carbon isotopic value of the diploptene. It was concluded that the diploptene was likely derived from bacterial activity. Carbon isotopic values of diploptene from this study showed depleted values, and may indicate the methanogenic bacterial activity. 12 refs., 1 fig.

  17. Survey of solar thermal energy storage subsystems for thermal/electric applications

    Energy Technology Data Exchange (ETDEWEB)

    Segaser, C. L.

    1978-08-01

    A survey of the current technology and estimated costs of subsystems for storing the thermal energy produced by solar collectors is presented. The systems considered were capable of producing both electricity and space conditioning for three types of loads: a single-family detached residence, an apartment complex of 100 units, and a city of 30,000 residents, containing both single-family residences and apartments. Collector temperatures will be in four ranges: (1) 100 to 250/sup 0/F (used for space heating and single-cycle air conditioners and organic Rankine low-temperature turbines); (2) 300 to 400/sup 0/F (used for dual-cycle air conditioners and low-temperature turbines); (3) 400 to 600/sup 0/F (using fluids from parabolic trough collectors to run Rankine turbines); (4) 800 to 1000/sup 0/F (using fluids from heliostats to run closed-cycle gas turbines and steam Rankine turbines). The solar thermal energy subsystems will require from 60 to 36 x 10/sup 5/ kWhr (2.05 x 10/sup 5/ to 1.23 x 10/sup 10/ Btu) of thermal storage capacity. In addition to sensible heat and latent heat storage materials, several other media were investigated as potential thermal energy storage materials, including the clathrate and semiclathrate hydrates, various metal hydrides, and heat storage based on inorganic chemical reactions.

  18. Structure and Dynamics of Cold Water Super-Earths: The Case of Occluded CH4 and its Outgassing

    CERN Document Server

    Levi, Amit; Podolak, Morris

    2014-01-01

    We study the transport of methane in the external water envelopes surrounding water-rich super-Earths and estimate its outgassing into the atmosphere. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice) resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to relatively low mass planets lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere making modes of ice plate tectonics possible. The dynamics of the tectonic plates are analysed. We derive overturn and resurfacing time scales as well as the melt fraction underneath spreading centers. Ice mantle dynamics is found to be...

  19. A HOT GAP AROUND JUPITER'S ORBIT IN THE SOLAR NEBULA

    International Nuclear Information System (INIS)

    The Sun was an order of magnitude more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by material accreting from the solar nebula. If Jupiter was already near its present mass, the planet's tides opened an optically thin gap in the nebula. Using Monte Carlo radiative transfer calculations, we show that sunlight absorbed by the nebula and re-radiated into the gap raised temperatures well above the sublimation threshold for water ice, with potentially drastic consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter in size were vaporized within a single orbit if the planet was near its present location during this early epoch. Dust particles lost their ice mantles, and planetesimals were partially to fully devolatilized, depending on their size. Scenarios in which Jupiter formed promptly, such as those involving a gravitational instability of the massive early nebula, must cope with the high temperatures. Enriching Jupiter in the noble gases through delivery trapped in clathrate hydrates will be more difficult, but might be achieved by either forming the planet much farther from the star or capturing planetesimals at later epochs. The hot gap resulting from an early origin for Jupiter also would affect the surface compositions of any primordial Trojan asteroids.

  20. Kinetics of methane hydrate decomposition studied via in situ low temperature X-ray powder diffraction.

    Science.gov (United States)

    Everett, S Michelle; Rawn, Claudia J; Keffer, David J; Mull, Derek L; Payzant, E Andrew; Phelps, Tommy J

    2013-05-01

    Gas hydrate is known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Based on results from the decomposition of three nominally similar methane hydrate samples, the kinetics of two regions, 180-200 and 230-260 K, within the overall decomposition range 140-260 K, were studied by in situ low temperature X-ray powder diffraction. The kinetic rate constants, k(a), and the reaction mechanisms, n, for ice formation from methane hydrate were determined by the Avrami model within each region, and activation energies, E(a), were determined by the Arrhenius plot. E(a) determined from the data for 180-200 K was 42 kJ/mol and for 230-260 K was 22 kJ/mol. The higher E(a) in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions. PMID:23557375

  1. Fluid Inclusions in the Gold-Bearing Quartz Veins at Um Rus Area, Eastern Desert, Egypt

    Institute of Scientific and Technical Information of China (English)

    MOHAMED EL TOKHI; ABDALLA EL MUSLEM

    2002-01-01

    Fluid inclusions in the gold-bearing quartz veins at the Um Rus area are of three types: H2O, H2O-CO2 and CO2 inclusions. H2O inclusions are the most abundant, they include two phases which exhibit low and high homogenization temperatures ranging from 150 to200℃ and 175 to 250℃, respectively. The salinity of aqueous inclusions, based on ice melting, varies between 6.1 and 8 equiv. wt% NaCl. On the other hand, H2O-CO2 fluid inclusions include three phases. Their total homogenization temperatures range from 270 to 325℃,and their salinity, based on clathrate melting, ranges between 0.8 and 3.8 equiv. wt % NaCl.CO2 fluid inclusions homogenize to a liquid phase and exhibit a low density range from 0.52 to0.66 g/cm3. The partial mixing of H2O-CO2 and salt H2O-NaCl fluid inclusions is the main source of fluids from which the other types of inclusions were derived. The gold-bearing quartz veins are believed to be of medium temperature hydrothermal convective origin.

  2. Large methane releases lead to strong aerosol forcing and reduced cloudiness

    Directory of Open Access Journals (Sweden)

    T. Kurtén

    2011-07-01

    Full Text Available The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4 levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH concentrations, while moderately increasing ozone (O3. These changes lead to a 70 % increase in the atmospheric lifetime of methane, and an 18 % decrease in global mean cloud droplet number concentrations (CDNC. The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing ("enhanced greenhouse effect" of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.

  3. Large methane releases lead to strong aerosol forcing and reduced cloudiness

    Directory of Open Access Journals (Sweden)

    T. Kurtén

    2011-03-01

    Full Text Available The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4 levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH concentrations, while moderately increasing ozone (O3. These changes lead to a 70% increase in the atmospheric lifetime of methane, and an 18% decrease in global mean cloud droplet number concentrations (CDNC. The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing ("enhanced greenhouse effect" of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.

  4. Observation of Binding and Rotation of Methane and Hydrogen within a Functional Metal–Organic Framework

    Science.gov (United States)

    2016-01-01

    The key requirement for a portable store of natural gas is to maximize the amount of gas within the smallest possible space. The packing of methane (CH4) in a given storage medium at the highest possible density is, therefore, a highly desirable but challenging target. We report a microporous hydroxyl-decorated material, MFM-300(In) (MFM = Manchester Framework Material, replacing the NOTT designation), which displays a high volumetric uptake of 202 v/v at 298 K and 35 bar for CH4 and 488 v/v at 77 K and 20 bar for H2. Direct observation and quantification of the location, binding, and rotational modes of adsorbed CH4 and H2 molecules within this host have been achieved, using neutron diffraction and inelastic neutron scattering experiments, coupled with density functional theory (DFT) modeling. These complementary techniques reveal a very efficient packing of H2 and CH4 molecules within MFM-300(In), reminiscent of the condensed gas in pure component crystalline solids. We also report here, for the first time, the experimental observation of a direct binding interaction between adsorbed CH4 molecules and the hydroxyl groups within the pore of a material. This is different from the arrangement found in CH4/water clathrates, the CH4 store of nature. PMID:27410670

  5. Coupled THCM Modeling of Gas Hydrate Bearing Sediments

    Science.gov (United States)

    Sanchez, M. J.; Gai, X., Sr.; Shastri, A.; Santamarina, J. C.

    2014-12-01

    Gas hydrates are crystalline clathrate compounds made of water and a low molecular gas, like methane. Gas hydrates are generally present in oil-producing areas and in permafrost regions. Methane hydrate deposits can lead to large-scale submarine slope failures, blowouts, platform foundation failures, and borehole instability. Gas hydrates constitute also an attractive source of energy as they are estimated to contain very large reserves of methane. Hydrate formation, dissociation and methane production from hydrate bearing sediments are coupled Thermo-Hydro-Mechanical (THM) processes that involve, amongst other, exothermic formation and endothermic dissociation of hydrate and ice phases, mixed fluid flow and large changes in fluid pressure. A comprehensive THM formulation is briefly presented here. Momentum balance, mass balance and energy balance equations take into consideration the interaction among all phases (i.e. solid, liquid, gas, hydrates and ice) and mechanical equilibrium. Constitutive equations describe the intrinsic THM behavior of the sediment. Simulation results conducted for hydrate bearing sediments subjected to boundary conditions highlight the complex interaction among THM processes in hydrate bearing sediments.

  6. Physical properties of gas hydrates

    Energy Technology Data Exchange (ETDEWEB)

    Kliner, J.T.R.; Grozic, J.L.H. [Calgary Univ., AB (Canada)

    2003-07-01

    Gas hydrates are naturally occurring, solid crystalline compounds (clathrates) that encapsulate gas molecules inside the lattices of hydrogen bonded water molecules within a specific temperature-pressure stability zone. Estimates of the total quantity of available methane gas in natural occurring hydrates are based on twice the energy content of known conventional fossil fuels reservoirs. Accurate and reliable in-situ quantification techniques are essential in determining the economic viability of this potential energy yield, which is dependent upon several factors such as sensitivity of the temperature-pressure stability zone, sediment type, porosity, permeability, concentration/abundance of free gas, spatial distribution in pore spaces, specific cage occupancy, and the influence of inhibitors. Various techniques like acoustic P and S waves, time domain reflectometry, and electrical resistance have been used to analyze the quantity and spatial distribution of the gas hydrate samples. These techniques were reviewed and the results obtained in the course of gas hydrate research were presented. 34 refs., 8 figs.

  7. Composition and structure of the shallow subsurface of Ceres revealed by crater morphology

    Science.gov (United States)

    Bland, Michael T.; Raymond, Carol A.; Schenk, Paul M.; Fu, Roger R.; Kneissl, Thomas; Pasckert, Jan Hendrik; Hiesinger, Harry; Preusker, Frank; Park, Ryan S.; Marchi, Simone; King, Scott D.; Castillo-Rogez, Julie C.; Russell, Christopher T.

    2016-07-01

    Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.

  8. Proceedings of the 6. international conference on gas hydrates : ICGH 2008

    Energy Technology Data Exchange (ETDEWEB)

    Englezos, P. (ed.) [British Columbia Univ., Vancouver, BC (Canada); Ripmeester, J. (ed.) [National Research Council of Canada, Ottawa, ON (Canada); Dallimore, S.R. [Natural Resources Canada, Ottawa, ON (Canada). Geological Survey of Canada; Servio, P. [McGill Univ., Montreal, PQ (Canada). Dept. of Chemical Engineering; Austvik, T. [Statoil, Trondheim (Norway); Collett, T.S. [United States Geological Survey, Denver, CO (United States); Mehta, A. [Shell E and P Asia Pacific, Sarawak (Malaysia); Paull, C.K. [Monterey Bay Aquarium Research Inst., CA (United States); Sloan, E.D.Jr. [Colorado School of Mines, Golden, CO (United States); Uchida, T. [Hokkaido Univ., Sapporo (Japan)] (comps.)

    2008-07-01

    This international conference provided a forum to highlight gas hydrate research that is underway at academic institutions as well as government and industrial laboratories around the world. The gas or clathrate hydrate research community includes chemical, petroleum and mechanical engineers, geologists, geophysicists, marine biologists, chemists and physicists. The conference was attended by more than 500 delegates who presented their professional knowledge in all areas of the gas hydrates field, emphasizing new aspects. The topics of discussion included resource delineation, reservoir simulation modeling and production technology. Environmental considerations involving natural gas hydrates and global climate change were also highlighted along with carbon dioxide disposal in aquifers and deep oceans. Issues facing oil and gas operations were also discussed, with reference to flow assurance in pipelines, safety issues, permafrost and marine geohazards. Novel technologies involving hydrogen storage, carbon dioxide capture and sequestration were also highlighted along with basic science and engineering aspects of gas hydrate systems. All 417 presentations from the conference have been catalogued separately for inclusion in this database. refs., tabs., figs.

  9. Proceedings of the 6. international conference on gas hydrates : ICGH 2008

    International Nuclear Information System (INIS)

    This international conference provided a forum to highlight gas hydrate research that is underway at academic institutions as well as government and industrial laboratories around the world. The gas or clathrate hydrate research community includes chemical, petroleum and mechanical engineers, geologists, geophysicists, marine biologists, chemists and physicists. The conference was attended by more than 500 delegates who presented their professional knowledge in all areas of the gas hydrates field, emphasizing new aspects. The topics of discussion included resource delineation, reservoir simulation modeling and production technology. Environmental considerations involving natural gas hydrates and global climate change were also highlighted along with carbon dioxide disposal in aquifers and deep oceans. Issues facing oil and gas operations were also discussed, with reference to flow assurance in pipelines, safety issues, permafrost and marine geohazards. Novel technologies involving hydrogen storage, carbon dioxide capture and sequestration were also highlighted along with basic science and engineering aspects of gas hydrate systems. All 417 presentations from the conference have been catalogued separately for inclusion in this database. refs., tabs., figs

  10. DFT-based inhibitor and promoter selection criteria for pentagonal dodecahedron methane hydrate cage

    Indian Academy of Sciences (India)

    Snehanshu Pal; T K Kundu

    2013-09-01

    Density functional theory (DFT)-based simulations have been performed to provide electronic structure property correlation based reasoning for conceptualizing the effect of encapsulated methane molecule on the formation of methane hydrate cages, the role of methanol and ethylene glycol as inhibitor and the role of tetra-hydro-furan (THF) and cyclopentane as promoter of methane hydrate. Geometry optimization of 512 cage, 51262 cage and 51264 cage with and without encapsulated methane and the cluster of 512 cage with ethylene glycol, methanol, cyclopentane have been performed by density functional theory using B97X-D/6-31++G(d,p) method. Methane hydrate formation inhibition by methanol and ethylene glycol as well as methane hydrate stabilization by cyclopentane and tetrahydrofuran are critically analysed based on the interaction energy, free energy change, dipole moment and infrared frequency calculation. Calculation of free energy change for formation of methane hydrate with/without reagents at various temperature and pressure using optimized structure is reported here. It is observed that hydrogen bond between water molecules of clathrate 512 cages become stronger in the presence of cyclopentane and tetrahydrofuran but weaker/broken in the presence of ethylene glycol and methanol. Simulated results correspond well with experimental findings and can be useful for designing new inhibitor and promoter molecules for gas hydrate formation.

  11. Pits formation from volatile outgassing on 67P/Churyumov-Gerasimenko

    CERN Document Server

    Mousis, O; Brugger, B; Jorda, L; Kargel, J S; Bouquet, A; Auger, A -T; Lamy, P; Vernazza, P; Thomas, N; Sierks, H

    2015-01-01

    We investigate the thermal evolution of comet 67P/Churyumov-Gerasimenko's subsurface in the Seth_01 region, where active pits have been observed by the ESA/Rosetta mission. Our simulations show that clathrate destabilization and amorphous ice crystallization can occur at depths corresponding to those of the observed pits in a timescale shorter than 67P/Churyumov-Gerasimenko's lifetime in the comet's activity zone in the inner solar system. Sublimation of crystalline ice down to such depths is possible only in the absence of a dust mantle, which requires the presence of dust grains in the matrix small enough to be dragged out by gas from the pores. Our results are consistent with both pits formation via sinkholes or subsequent to outbursts, the dominant process depending on the status of the subsurface porosity. A sealed dust mantle would favor episodic and disruptive outgassing as a result of an increasing gas pressure in the pores, while a high porosity should allow the formation of large voids in the subsur...

  12. Crystallographic studies of gas sorption in metal–organic frameworks

    International Nuclear Information System (INIS)

    Adsorption and separation of gases is one of the primary applications of the class of materials known as metal–organic frameworks (MOFs). The role of crystallography in characterizing adsorbed gas molecules and changes in framework structure upon gas sorption is reviewed. Metal–organic frameworks (MOFs) are a class of porous crystalline materials of modular design. One of the primary applications of these materials is in the adsorption and separation of gases, with potential benefits to the energy, transport and medical sectors. In situ crystallography of MOFs under gas atmospheres has enabled the behaviour of the frameworks under gas loading to be investigated and has established the precise location of adsorbed gas molecules in a significant number of MOFs. This article reviews progress in such crystallographic studies, which has taken place over the past decade, but has its origins in earlier studies of zeolites, clathrates etc. The review considers studies by single-crystal or powder diffraction using either X-rays or neutrons. Features of MOFs that strongly affect gas sorption behaviour are discussed in the context of in situ crystallographic studies, specifically framework flexibility, and the presence of (organic) functional groups and unsaturated (open) metal sites within pores that can form specific interactions with gas molecules

  13. NEW INSIGHTS ON SATURN'S FORMATION FROM ITS NITROGEN ISOTOPIC COMPOSITION

    International Nuclear Information System (INIS)

    The recent derivation of a lower limit for the 14N/15N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at ∼45 K in the protosolar nebula, provided that the O abundance was ∼2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least ∼34.9 times protosolar and that the corresponding mass of heavy elements (∼43.1 M ⊕) is within the range predicted by semi-convective interior models

  14. Soft functional polynuclear coordination compounds containing pyrimidine bridges

    Science.gov (United States)

    Navarro, Jorge A. R.; Barea, Elisa; Galindo, Miguel A.; Salas, Juan M.; Romero, M. Angustias; Quirós, Miguel; Masciocchi, Norberto; Galli, Simona; Sironi, Angelo; Lippert, Bernhard

    2005-08-01

    In this account, we describe the use of simple pyrimidine derivatives in combination with metal ions to build highly structured molecular architectures containing functional nanoenvironments, cavities and surfaces that can interact with additional species. The supramolecular structure of these systems can be rationally controlled by metal fragment geometry, reaction conditions and presence of templating agents. Thus, the use of transition metals with low coordination numbers or blocked bonding positions in combination with pyrimidines (e.g. 2-hydroxypyrimidine, 4-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimidine) leads to the formation of either discrete assemblies, 1D polymers or helixes. When metal ions with higher coordination possibilities are applied instead, 2D and 3D networks are generated. Some of the assemblies built in this way possess functional cavities, pores and surfaces that can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to recognition processes. The latter range from molecular recognition in homogeneous phase as well as clathrate formation, to heterogeneous solid-gas and solid-liquid adsorption phenomena. It should be noted that these materials are not rigid but able to undergo guest-induced reorganisation processes even in the solid state. Finally, some of these materials also combine additional interesting magneto-optical properties. Thus, dual systems can be envisaged in which two or more of these properties are present in the same material.

  15. Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Siewenie, Joan [Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Xu, Hongwu [Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Zhu, Jinlong [High Pressure Science and Engineering Center, Department of Physics and Astronomy, The University of Nevada, Las Vegas, Nevada 89154, USA and National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Page, Katharine, E-mail: pagekl@ornl.gov [Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2014-12-15

    This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO{sub 2} measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO{sub 2} sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H{sub 2} and natural gas uptake/storage.

  16. Thermal and structural study on the lattice compound 1,4-diammoniumbutane bis(theophyllinate)

    International Nuclear Information System (INIS)

    Crystalline title compound (1) prepared from aqueous solution of theophylline and 1,4-diaminobutane has been structurally and thermally characterized. Both the two-step TG decomposition curve and elemental analysis of the hexagonal crystals show that it consists of theophylline and 1,4-diaminobutane in 2:1 molar ratio. Actually, presence of one type of both theophyllinate anions and 1,4-diammoniumbutane dication have been indicated by FTIR spectroscopy. The molecular structure of lattice compound (1) has been determined by single crystal X-ray diffraction, where the hydrogen positions have been obtained from differential Fourier maps. It has confirmed that the crystal is really built up from these ionic constituents bound together with an extensive net of hydrogen bonds. The coupled TG-FTIR analysis of the evolved gases has revealed that the diamine is released as a whole molecule in the first decomposition step. Clathrate 1 and the proton migration in it might serve as a structural model of solid aminophylline whose crystal structure is still unknown

  17. Thermal and structural study on the lattice compound 1,4-diammoniumbutane bis(theophyllinate)

    Energy Technology Data Exchange (ETDEWEB)

    Ban, Margit; Madarasz, Janos; Bombicz, Petra; Pokol, Gyoergy; Gal, Sandor

    2004-10-01

    Crystalline title compound (1) prepared from aqueous solution of theophylline and 1,4-diaminobutane has been structurally and thermally characterized. Both the two-step TG decomposition curve and elemental analysis of the hexagonal crystals show that it consists of theophylline and 1,4-diaminobutane in 2:1 molar ratio. Actually, presence of one type of both theophyllinate anions and 1,4-diammoniumbutane dication have been indicated by FTIR spectroscopy. The molecular structure of lattice compound (1) has been determined by single crystal X-ray diffraction, where the hydrogen positions have been obtained from differential Fourier maps. It has confirmed that the crystal is really built up from these ionic constituents bound together with an extensive net of hydrogen bonds. The coupled TG-FTIR analysis of the evolved gases has revealed that the diamine is released as a whole molecule in the first decomposition step. Clathrate 1 and the proton migration in it might serve as a structural model of solid aminophylline whose crystal structure is still unknown.

  18. NASA Tech Briefs, December 2003

    Science.gov (United States)

    2003-01-01

    Topics covered include: Organic/Inorganic Hybrid Polymer/Clay Nanocomposites; Less-Toxic Coatings for Inhibiting Corrosion of Aluminum; Liquid Coatings for Reducing Corrosion of Steel in Concrete; Processable Polyimides Containing APB and Reactive End Caps; Rod/Coil Block Copolyimides for Ion-Conducting Membranes; Techniques for Characterizing Microwave Printed Antennas; Cylindrical Antenna With Partly Adaptive Phased-Array Feed; Command Interface ASIC - Analog Interface ASIC Chip Set; Predicting Accumulations of Ice on Aerodynamic Surfaces; Analyzing Aeroelasticity in Turbomachines; Software for Allocating Resources in the Deep Space Network; Expert Seeker; High-Speed Recording of Test Data on Hard Disks; Functionally Graded Nanophase Beryllium/Carbon Composites; Thin Thermal-Insulation Blankets for Very High Temperatures; Aerostructures Test Wing; Flight-Test Evaluation of Flutter-Prediction Methods; Piezoelectrically Actuated Microvalve for Liquid Effluents; Larger-Stroke Piezoelectrically Actuated Microvalve; Innovative, High-Pressure, Cryogenic Control Valve: Short Face-to-Face, Reduced Cost; Safer Roadside Crash Walls Would Limit Deceleration; Improved Interactive Medical-Imaging System; Scanning Microscopes Using X Rays and Microchannels; Slotting Fins of Heat Exchangers to Provide Thermal Breaks; Methane Clathrate Hydrate Prospecting; Automated Monitoring with a BSP Fault-Detection Test; Automated Monitoring with a BCP Fault-Decision Test; Vector-Ordering Filter Procedure for Data Reduction; Remote Sensing and Information Technology for Large Farms; Developments at the Advanced Design Technologies Testbed; Spore-Forming Bacteria that Resist Sterilization; and Acoustical Applications of the HHT Method.

  19. Modeling the methane hydrate formation in an aqueous film submitted to steady cooling

    Energy Technology Data Exchange (ETDEWEB)

    Avendano-Gomez, J.R. [ESIQIE, Laboratorio de Ingenieria Quimica Ambiental, Mexico (Mexico). Inst. Politecnico Nacional; Garcia-Sanchez, F. [Laboratorio de Termodinamica, Mexico (Mexico). Inst. Mexicano del Petroleo; Gurrola, D.V. [UPIBI, Laboratorio de Diseno de Plantas, Mexico (Mexico). Inst. Politecnico Nacional

    2008-07-01

    Gas hydrates, or clathrate hydrates, are ice-like compounds that results from the kinetic process of crystallization of an aqueous solution supersaturated with a dissolved gas. This paper presented a model that took into account two factors involved in the hydrate crystallization, notably the stochastic nature of crystallization that causes sub-cooling and the heat resulting from the exothermic enthalpy of hydrate formation. The purpose of this study was to model the thermal evolution inside a hydrate forming system which was submitted to an imposed steady cooling. The study system was a cylindrical thin film of aqueous solution at 19 Mpa. The study involved using methane as the hydrate forming molecule. It was assumed that methane was homogeneously dissolved in the aqueous phase. Ethane hydrate was formed through a kinetic process of nucleation and crystallization. In order to predict the onset time of nucleation, the induction time needed to be considered. This paper discussed the probability of nucleation as well as the estimation of the rate of nucleation. It also presented the mathematical model and boundary conditions. These included assumptions and derivation of the model; boundary conditions; initial conditions; and numerical solution of the model equation. It was concluded that the heat source must be considered when investigating crystallization effects. 34 refs., 2 tabs., 2 figs.

  20. Thermoelectric transport in rare-earth compounds

    International Nuclear Information System (INIS)

    This work focuses on the thermoelectric transport in rare-earth compounds. The measurements of the thermal conductivity, thermopower, and Nernst coefficient are supplemented by investigations of other quantities as magnetic susceptibility and specific heat. Chapter 2 provides an introduction to the relevant physical concepts. Section 1 of that chapter summarizes the characteristic properties of rare-earth systems; section 2 gives an overview on thermoelectric transport processes in magnetic fields. The applied experimental techniques as well as the new experimental setup are described in detail in Chapter 3. The experimental results are presented in Chapter 4-6, of which each concentrates on a different subject. In Chapter 4, various Eu clathrates and the skutterudite-like Ce3Rh4Sn13 are presented, which have been investigated as potential thermoelectric materials for applications. Chapter 5 focusses on the study of the energy scales in the heavy-fermion series Lu1-xYbxRh2Si2 and CexLa1-xNi2Ge2 by means of thermopower investigations. Chapter 6 is dedicated to the thermoelectric transport properties of the correlated semimetal CeNiSn with special emphasis on the Nernst coefficient of this compound. (orig.)

  1. Synthesis, X-Ray Structure, and Characterization of a Complex Containing the Hexakis(ureacobalt(II Cation and Lattice Urea Molecules

    Directory of Open Access Journals (Sweden)

    Labrini Drakopoulou

    2007-01-01

    Full Text Available The 12: 1 reaction of urea (U with CoI2 in EtOH yielded the “clathrate-coordination” compound [CoU6]I2·4U (1. The complex crystallizes in the monoclinic space group P21/c. The lattice constants are a = 9.844(4, b = 7.268(3, c = 24.12(1 Å, and β=98.12(1∘. The crystal structure determination demonstrates the existence of octahedral [CoU6]2+ cations, I- counterions, and two different types (two U1 and two U2 of hydrogen-bonded, lattice urea molecules. The [CoU6]2+ cations and the U1 lattice molecules form two-dimensional hydrogen-bonded layers which are parallel to the ab plane. The I- anions are placed above and below each layer, and are hydrogen bonded both to U1 molecules and [CoU6]2+ cations. Each U2 molecule is connected to a [CoU6]2+ cation through an N–H⋯O hydrogen bond resulting in a three-dimensional network. Room temperature magnetic susceptibility and spectroscopic (solid-state UV/Vis, IR, Raman data of 1 are discussed in terms of the nature of bonding and the known structure.

  2. NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (II)

    Institute of Scientific and Technical Information of China (English)

    董顺乐; 王燕

    2001-01-01

    Lattice dynamical calculations have been carried out for ice II based on the force field constructed for ice Ih. In order to fully understand ice II inelastic neutron scattering spectra, the decomposed phonon density of states was shown mode by mode. Calculated results have shown that the hydrogen bond force constant between the six-molecule rings is significantly weaker, 75eV/nm2, compared with the force constant, 220eV/nm2, within the rings. Inelastic neutron scattering spectra of clathrate hydrate H2O+He are almost the same as ice II. This means that the absorption of He atoms cannot affect the bond strengths of the ice II host lattice. Based on the force field model for ice II, the van der Waals interactions between water molecules and helium atoms are considered. The results obtained are consistent with experimental data. Lattice dynamical calculations have been carried out for ice II using seven rigid pairwise potentials.It was found that MCY makes the stretching and bending interactions in ice II too weak and makes the O-O bond length too long (~5%), thus its lattice densities are obviously lower than other potential lattices or experimental values.

  3. NEW INSIGHTS ON SATURN'S FORMATION FROM ITS NITROGEN ISOTOPIC COMPOSITION

    Energy Technology Data Exchange (ETDEWEB)

    Mousis, Olivier; Lunine, Jonathan I. [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Fletcher, Leigh N. [Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU (United Kingdom); Mandt, Kathleen E. [Southwest Research Institute, San Antonio, TX 78228 (United States); Ali-Dib, Mohamad [Université de Franche-Comté, Institut UTINAM, CNRS/INSU, UMR 6213, Observatoire des Sciences de l' Univers de Besançon (France); Gautier, Daniel [LESIA, Observatoire de Paris, CNRS, UPMC, Univ. Paris-Diderot, F-92195 Meudon Cedex (France); Atreya, Sushil, E-mail: olivier.mousis@obs-besancon.fr [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143 (United States)

    2014-12-01

    The recent derivation of a lower limit for the {sup 14}N/{sup 15}N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at ∼45 K in the protosolar nebula, provided that the O abundance was ∼2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least ∼34.9 times protosolar and that the corresponding mass of heavy elements (∼43.1 M {sub ⊕}) is within the range predicted by semi-convective interior models.

  4. New insights on Saturn's formation from its nitrogen isotopic composition

    CERN Document Server

    Mousis, Olivier; Fletcher, Leigh N; Mandt, Kathleen E; Ali-Dib, Mohamad; Gautier, Daniel; Atreya, Sushil

    2014-01-01

    The recent derivation of a lower limit for the $^{14}$N/$^{15}$N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at $\\sim$45 K in the protosolar nebula, provided that the O abundance was $\\sim$2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least $\\sim$34.9 times protosolar and that the corresponding mass of heavy elements ($\\sim$43.1 \\Mearth) is within the range predicted by semi-convective interior models.

  5. A protosolar nebula origin for the ices agglomerated by Comet 67P/Churyumov-Gerasimenko

    CERN Document Server

    Mousis, O; Luspay-Kuti, A; Guillot, T; Marty, B; Ali-Dib, M; Wurz, P; Altwegg, K; Bieler, A; Hässig, M; Rubin, M; Vernazza, P; Waite, J H

    2016-01-01

    The nature of the icy material accreted by comets during their formation in the outer regions of the protosolar nebula is a major open question in planetary science. Some scenarios of comet formation predict that these bodies agglomerated from crystalline ices condensed in the protosolar nebula. Concurrently, alternative scenarios suggest that comets accreted amorphous ice originating from the interstellar cloud or from the very distant regions of the protosolar nebula. On the basis of existing laboratory and modeling data, we find that the N$_2$/CO and Ar/CO ratios measured in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the European Space Agency's Rosetta spacecraft match those predicted for gases trapped in clathrates. If these measurements are representative of the bulk N$_2$/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the ices accreted by the comet formed in the nebula and do not originate from the interstellar medium, supporting the...

  6. Seasonal and spatial variation in species diversity, abundance, and element accumulation capacities of macroalgae in mangrove forests of Zhanjiang, China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yubin; LI Yuan; SHI Fei; SUN Xingli; LIN Guanghui

    2014-01-01

    The objective of this study was to investigate whether there was distinctive seasonal and zonal variation in the species diversity, biomass, and element accumulation capacities of macroalgae in two major intertidal mangrove stand types (Avicennia marina assemblage andSonneratia apetala assemblage) in the Zhanjiang region of southern China. Over a year, 31 species in 15 genera were identified in both mangrove assem-blages, of which the dominant species wereCladophoropsis zollingeriand Enteromorpha clathrat.Macroal-gal species were significantly most abundant in spring (p<0.05), followed by summer, winter, and autumn. Variation in the zonal distribution of macroalgal species was conspicuous in both intertidal mangrove as-semblages, with the greatest abundance in the middle zone, and the least in the front zone. Patterns in the seasonal and zonal variation in macroalgal biomass in theS. apetalaassemblage were similar to those of macroalgal species diversity in both mangrove assemblages. The seasonal patterns in tissue concentrations of 15 analyzed elements were not uniform among the macroalgaeC. zollingeri,E. clathrata, andGracilaria salicornia in theA. marina assemblage. All three species exhibited variation in their responses to ambient concentrations of different elements, implying their differential ability to absorb and selectively accumulate certain elements.

  7. Phononic Structure Engineering: the Realization of Einstein Rattling in Calcium Cobaltate for the Suppression of Thermal Conductivity

    Science.gov (United States)

    Tian, Ruoming; Kearley, Gordon J.; Yu, Dehong; Ling, Chris D.; Pham, Anh; Embs, Jan P.; Shoko, Elvis; Li, Sean

    2016-07-01

    Phonons in condensed matter materials transmit energy through atomic lattices as coherent vibrational waves. Like electronic and photonic properties, an improved understanding of phononic properties is essential for the development of functional materials, including thermoelectric materials. Recently, an Einstein rattling mode was found in thermoelectric material Na0.8CoO2, due to the large displacement of Na between the [CoO2] layers. In this work, we have realized a different type of rattler in another thermoelectric material Ca3Co4O9 by chemical doping, which possesses the same [CoO2] layer as Na0.8CoO2. It remarkably suppressed the thermal conductivity while enhancing its electrical conductivity. This new type of rattler was investigated by inelastic neutron scattering experiments in conjunction with ab-initio molecular dynamics simulations. We found that the large mass of dopant rather than the large displacement is responsible for such rattling in present study, which is fundamentally different from skutterudites, clathrates as well as Na analogue. We have also tentatively studied the phonon band structure of this material by DFT lattice dynamics simulation, showing the relative contribution to phonons in the distinct layers of Ca3Co4O9.

  8. Interstellar and Cometary Dust in Relation to the Origin of Life

    Science.gov (United States)

    Krueger, F. R.; Kissel, J.

    Cometary grains are commonly considered to be the precursors of organic materials in early life on the Earth. It is a persistent mystery, however, how chemical evolution within the earliest protocells was triggered. We discuss the type of organics measured from Comet p/Wild-2, using the Cometary and Intersellar Dust Analyzer (CIDA). This instrument is not sensitive to mineralic cores of dust particles due to their low-impact velocities (6 km/s). The CIDA data allows us to analyze the organic fraction of interstellar dust at ~1 AU from the Sun. Surprisingly, it mainly consists of quinone-type polycyclics, some of them similar to pyrrolo-Cquinoline-Cquinone. Strong redox catalysts are apparently required to trigger the earliest chemical evolutionary steps. Our understanding of the thermochemical evolution of accretion from interstellar clouds containing cosmic grains to comets qualitatively and quantitatively requires a comprehensive understanding of the production of water and CO from the comets. The"dirty snowball" model is rejected as a suitable model for "fresh" comets. Apparently the primordial source of water is twofold: (1) a signicant fraction of cometary clathrates is contained in the mineralic and the organic fractions, producing water by evaporation; (2) rich oxygen containing PAH's in the organic phase produces water by solar radiation-induced chemical processes.

  9. Modeling of CO{sub 2}-hydrate formation at the gas-water interface in sand sediment

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, T.; Sato, T.; Hirabayashi, S.; Brumby, P.E. [University of Tokyo, Department of Ocean Technology, Policy, and Environment, Kashiwa (Japan); Inui, M. [Mitsubishi Heavy Industries America, Inc., Environmental Systems Division, Austin, TX (United States)

    2012-10-15

    Sub-seabed geological storage of CO{sub 2} in the form of gas hydrate is attractive because clathrate hydrate stably exists at low temperature and high pressure, even if a fault occurs by diastrophism like a big earthquake. For the effective design of the storage system it is necessary to model the formation of CO{sub 2}-hydrate. Here, it is assumed that the formation of gas hydrate on the interface between gas and water consists of two stages: gas diffusion through the CO{sub 2}-hydrate film and consequent CO{sub 2}-hydrate formation on the interface, between film and water. Also proposed is the presence of a fresh reaction interface, which is part of the interface between the gas and aqueous phases and not covered with CO{sub 2}-hydrate. Parameters necessary to model the hydrate formation in sand sediment are derived by comparing the results of the present numerical simulations and the measurements in the literature. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Observation of Binding and Rotation of Methane and Hydrogen within a Functional Metal–Organic Framework

    KAUST Repository

    Savage, Mathew

    2016-07-27

    The key requirement for a portable store of natural gas is to maximize the amount of gas within the smallest possible space. The packing of methane (CH4) in a given storage medium at the highest possible density is, therefore, a highly desirable but challenging target. We report a microporous hydroxyl-decorated material, MFM-300(In) (MFM = Manchester Framework Material, replacing the NOTT designation), which displays a high volumetric uptake of 202 v/v at 298 K and 35 bar for CH4 and 488 v/v at 77 K and 20 bar for H2. Direct observation and quantification of the location, binding, and rotational modes of adsorbed CH4 and H2 molecules within this host have been achieved, using neutron diffraction and inelastic neutron scattering experiments, coupled with density functional theory (DFT) modeling. These complementary techniques reveal a very efficient packing of H2 and CH4 molecules within MFM-300(In), reminiscent of the condensed gas in pure component crystalline solids. We also report here, for the first time, the experimental observation of a direct binding interaction between adsorbed CH4 molecules and the hydroxyl groups within the pore of a material. This is different from the arrangement found in CH4/water clathrates, the CH4 store of nature.

  11. A consistent and verifiable macroscopic model for the dissolution of liquid CO2 in water under hydrate forming conditions

    International Nuclear Information System (INIS)

    Direct injection of liquid CO2 into the ocean has been proposed as one method to reduce the emission levels of CO2 into the atmosphere. When liquid CO2 is injected (normally as droplets) at ocean depths >500 m, a solid interfacial region between the CO2 and the water is observed to form. This region consists of hydrate clathrates and hinders the rate of dissolution of CO2. It is, therefore, expected to have a significant impact on the injection of liquid CO2 into the ocean. Up until now, no consistent and predictive model for the shrinking of droplets of CO2 under hydrate forming conditions has been proposed. This is because all models proposed to date have had too many unknowns. By computing rates of the physical and chemical processes in hydrates via molecular dynamics simulations, we have been able to determine independently some of these unknowns. We then propose the most reasonable model and use it to make independent predictions of the rates of mass transfer and thickness of the hydrate region. These predictions are compared to measurements, and implications to the rates of shrinkage of CO2 droplets under varying flow conditions are discussed. (author)

  12. Lattice Boltzmann pore-scale model for multi-component reactive transport

    Science.gov (United States)

    Kang, Qinjun; Lichtner, Peter; Zhang, Dongxiao; Tsimpanogiannis, Ioannis

    2004-11-01

    A better understanding of multi-component flow and reaction in natural and man-made porous media is critical to a wide range of fields, including hydrology (groundwater quality), fossil energy (oil, gas, coalbed methane, clathrates), economic geology (mineral processing and development), geologic carbon sequestration (hydrodynamic and mineral trapping of carbon), and materials manufacturing and degradation (polymer composites, concrete, building materials). This problem is notoriously difficult because it usually involves multiple processes (convection, diffusion, and chemical reaction) and complex geometries and boundaries. In this work, we present a multi-component lattice Boltzmann model for simulating reactive transport in porous media at the pore scale. This model takes into account convection, diffusion, homogeneous reactions among multiple aqueous species, heterogeneous reactions between the aqueous solution and the minerals, as well as the resulting geometrical changes in pore space. Homogeneous reactions are described through local equilibrium mass action relations. Mineral reactions are treated kinetically through boundary conditions at the surface. We have applied this model to a hypothetical two-component system in a synthetically constructed medium, and analyzed the effects of convection, diffusion, reaction rate constants, and chemical compositions on mineral alteration of the porous medium.

  13. Dynamical delivery of volatiles to the outer main belt

    Science.gov (United States)

    Grazier, Kevin R.; Castillo-Rogez, Julie C.; Sharp, Philip W.

    2014-04-01

    We quantify the relative contribution of volatiles supplied from outer Solar System planetesimal reservoirs to large wet asteroids during the first few My after the beginning of the Solar System. To that end, we simulate the fate of planetesimals originating within different regions of the Solar System - and thus characterized by different chemical inventories - using a highly accurate integrator tuned to handle close planet/planetesimal encounters. The fraction of icy planetesimals crossing the Asteroid Belt was relatively significant, and our simulations show that planetesimals originating from the Jupiter/Saturn region were orders of magnitude more abundant than those stemming from the Uranus and Neptune regions when the planets were just embryos. As the planets reached their full masses the Jupiter/Saturn and Saturn/Uranus regions contributed similar fractions of planetesimals for any material remaining in these reservoirs late in the stage of planetary formation, This implies that large asteroids like Ceres accreted very little material enriched in low-eutectic volatiles (e.g., methanol, nitrogen and methane ices, etc.) and clathrate hydrates expected to condense at the very low temperatures predicted for beyond Saturn’s orbit in current early solar nebula models. Further, a large fraction of the content in organics of Ceres and neighboring ice-rich objects originates from the outer Solar System.

  14. A review of the hydrate based gas separation (HBGS) process for carbon dioxide pre-combustion capture

    International Nuclear Information System (INIS)

    In this work, a systematic review of the literature work done so far on the use of hydrate crystallization as a basis to develop data for the hydrate based gas separation (HBGS) process for the capture of CO2 from fuel gas mixtures is presented. Such a gas mixture may arise in integrated gasification combined cycle (IGCC) power plants. A thorough assessment of the thermodynamic, kinetic factors and economic aspects of the HBGS process and critical comments are presented. Compared with competing technologies, high CO2 capacity and the use of water as a solvent are key advantages for the HBGS process for CO2 capture. Furthermore, in this review, a snapshot of the current state-of-the-art is presented and further research and development opportunities and pathways for commercializing the HBGS process for pre-combustion capture of CO2 from IGCC power plants are discussed. - Highlights: • A review on a novel process to capture CO2 using water via clathrates is presented. • Hydrate based gas separation process (HBGS) for pre-combustion capture has much promise. • Current state-of-the-art on HBGS process and future directions are presented. • HBGS process is the most environmentally benign approach as water is used as a solvent

  15. Compositions of Oceans on Icy Solar System Bodies (Invited)

    Science.gov (United States)

    Zolotov, M. Y.

    2010-12-01

    Interior oceans may exist on at least several solar system bodies: Europa, Enceladus, Ganymede, Titan and Triton. Compositions of the oceans could reflect bulk chemistries on the bodies, degree and timing of differendentition, current temperature and pressure conditions, and chemical exchanges between icy shells, liquid layers, and suboceanic solids (rocks, sediments, ices and clathrates). Observational signs are sparse and modeling is the major approach to evaluate oceanic compositions. On Europa, a presence of S(VI) species and CO2 at endogenic surface features [1] suggests sulfates and C species (organic and/or inorganic) in the ocean. The detection of NaCl and Na2CO3/NaHCO3-bearing grains emitted from Enceladus [2] implies the dominance of Na, Cl and carbonate/bicarbonate ions in the past and/or present alkaline fluids in the interior. These observations are consistent with independent models for water-rock interaction [3]. Evaluated low contents of other elements (Mg, Fe, Ca, K, S, P, etc.) in initial oceanic waters [3] are accounted for by low solubilities of minerals deposited from water solutions (serpentine, saponite, magnetite, carbonates, sulfides and phosphates). Oceanic redox states are affected by the composition of accreted ices and rocks, hydrogen production through oxidation of solids (mainly Fe-Ni metal) by water and an efficiency of H2 escape. Formation of a sulfate-bearing ocean (as on Europa) through oxidation of sulfides could have been driven by radiolytically-formed oxidants (H2O2, O2), high-temperature (>500 K) hydrothermal activity and H2 escape. Formation of sulfate facilitates leaching of Mg from minerals leading to the Mg-SO4-Na-Cl ocean. Although some of these factors could have played roles on the Galilean satellites, formation of sulfate-bearing oceans beyond Jupiter is unlikely. Accretion of cometary-type ices on moons allows an existence of water-methanol-ammonia liquids at ~153 K, although ammonia could have been sequestered in

  16. Dehydration of planetary ices at high pressure; the role of analogue materials (Invited)

    Science.gov (United States)

    Fortes, A. D.

    2013-12-01

    Many planet-forming compounds become unstable with respect to their components under conditions of high pressure. In the Earth, for example, Mg2SiO4 breaks down to MgSiO3 + MgO at ~ 25 GPa, a pressure corresponding to the 670 km seismic discontinuity, with significance for the dynamics of convective flow in the mantle. A similar phenomenon occurs with many hydrate compounds thought to be major ';rock forming minerals' inside outer Solar System bodies, undoubtedly with important consequences for the structure and dynamics of icy worlds. It is well known that clathrates tend to form denser polymorphs with an incrementally greater concentration of the guest molecule, exsolving high-pressure phases of water ice in the process, or else (in the case of CO2), break down to entirely to their component molecular solids. My own recent work using high-pressure neutron powder diffraction has explored not only the behaviour of methane clathrates but also the exsolution of water from ammonia dihydrate and monohydrate, both of which break down eventually to ammonia hemihydrate + ice. In some cases, understanding the sequence of changes in both crystal structure and composition at high pressure is challenging, particularly when the starting materials have a complex crystal structure. Some years ago, I identified a high-pressure phase boundary where MgSO4.11H2O (meridianiite) appeared to break down to another hydrate and high-pressure ice VI. However, the powder diffraction pattern of the hydrate formed under these conditions resembled nothing encountered previously in my high-pressure studies of the next lowest hydrate, MgSO4.7H2O (epsomite). This led me to search for hydration states between 7 and 11 which might have escaped detection over several centuries of study of simple divalent metal sulfates. A wide-ranging systematic study of M2+X6+O4.nH2O compounds at low temperatures uncovered two new hydrates, an 8-hydrate and a 9-hydrate, the former occurring only in NiSO4 solutions

  17. Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

    Science.gov (United States)

    Majorowicz, J.; Safanda, J.; Osadetz, K.

    2012-03-01

    Atmospheric methane from episodic gas hydrate (GH) destabilization, the "clathrate gun" hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ~0.9 km depth only ~1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ~290-300 m ~6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed >255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ~1.0 Myr ago and ~4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where

  18. Carbon dioxide on the satellites of Saturn: Results from the Cassini VIMS investigation and revisions to the VIMS wavelength scale

    Science.gov (United States)

    Cruikshank, D.P.; Meyer, A.W.; Brown, R.H.; Clark, R.N.; Jaumann, R.; Stephan, K.; Hibbitts, C.A.; Sandford, S.A.; Mastrapa, R.M.E.; Filacchione, G.; Ore, C.M.D.; Nicholson, P.D.; Buratti, B.J.; McCord, T.B.; Nelson, R.M.; Dalton, J.B.; Baines, K.H.; Matson, D.L.

    2010-01-01

    Several of the icy satellites of Saturn show the spectroscopic signature of the asymmetric stretching mode of C-O in carbon dioxide (CO2) at or near the nominal solid-phase laboratory wavelength of 4.2675 ??m (2343.3 cm-1), discovered with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft. We report here on an analysis of the variation in wavelength and width of the CO2 absorption band in the spectra of Phoebe, Iapetus, Hyperion, and Dione. Comparisons are made to laboratory spectra of pure CO2, CO2 clathrates, ternary mixtures of CO2 with other volatiles, implanted and adsorbed CO2 in non-volatile materials, and ab initio theoretical calculations of CO2 * nH2O. At the wavelength resolution of VIMS, the CO2 on Phoebe is indistinguishable from pure CO2 ice (each molecule's nearby neighbors are also CO2) or type II clathrate of CO2 in H2O. In contrast, the CO2 band on Iapetus, Hyperion, and Dione is shifted to shorter wavelengths (typically ???4.255 ??m (???2350.2 cm-1)) and broadened. These wavelengths are characteristic of complexes of CO2 with different near-neighbor molecules that are encountered in other volatile mixtures such as with H2O and CH3OH, and non-volatile host materials like silicates, some clays, and zeolites. We suggest that Phoebe's CO2 is native to the body as part of the initial inventory of condensates and now exposed on the surface, while CO2 on the other three satellites results at least in part from particle or UV irradiation of native H2O plus a source of C, implantation or accretion from external sources, or redistribution of native CO2 from the interior. The analysis presented here depends on an accurate VIMS wavelength scale. In preparation for this work, the baseline wavelength calibration for the Cassini VIMS was found to be distorted around 4.3 ??m, apparently as a consequence of telluric CO2 gas absorption in the pre-launch calibration. The effect can be reproduced by convolving a sequence of model detector

  19. Basins and the South Polar Terrain of Enceladus: Hotspots vs. Coldspots, and More Evidence for Crustal Spreading and Convergence

    Science.gov (United States)

    McKinnon, William B.; Schenk, P. M.

    2009-09-01

    Stereo-derived topographic mapping of 50% of Enceladus reveals at least 6 large-scale, ovoid depressions (basins) 90-175 km across and 800-to-1500 m deep and uncorrelated with geologic boundaries (Schenk and McKinnon, GRL, in press). Their shape and scale are inconsistent with impact, geoid deflection, or with dynamically supported topography. Isostatic thinning of Enceladus’ ice shell associated with upwellings (and tidally-driven ice melting) can plausibly account for the basins. Thinning implies upwarping of the base of the shell of 10-20 km beneath the depressions, depending on total shell thickness; loss of near-surface porosity due to enhanced heat flow may also contribute to basin lows. Alternatively, the basins may overly cold, inactive, and hence denser ice, but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice. In contrast to the basins, the south polar depression (SPD) is larger ( 350 wide) and shallower ( 0.4-to-0.8 km deep) and correlates with the area of tectonic deformation and active resurfacing. The SPD also differs in that the floor is relatively flat (i.e., conforms roughly to the global triaxial shape, or geoid) with broad, gently sloping flanks. The relative flatness across the SPD suggests that it is in or near isostatic equilibrium, and underlain by denser material, supporting the polar sea hypothesis of Collins and Goodman [2007]. Near flatness is also predicted by a crustal spreading origin for the "tiger stripes” [e.g., Barr, 2008]; the extraordinary, high CIRS heat flows imply half-spreading rates in excess of 10 cm/yr, a very young surface age ( 250,000 yr), and a rather thin lithosphere (hence modest thermal topography). Topographic rises in places along the outer margin of the SPD correlate with parallel ridges and deformation along the edge of the resurfaced terrain, consistent with a compressional, imbricate thrust origin for these ridges, driven by the spreading.

  20. Synthesis and spectroscopic characterization of P-doped Na 4Si 4

    Science.gov (United States)

    Wang, Jialing; Sen, Sabyasachi; Yu, Ping; Browning, Nigel D.; Kauzlarich, Susan M.

    2010-11-01

    Na 4Si 4 is a Zintl salt composed of Na + cations and Si44- tetrahedral anions and is a unique solid-state precursor to clathrate structures and nanomaterials. In order to provide opportunities for the synthesis of complex materials, phosphorus was explored as a possible substituent for silicon. Phosphorus doped sodium silicides Na 4Si 4- xP x ( x≤0.04) were prepared by reaction of Na with the mechanically alloyed Si 4- x:P x ( x=0.04, 0.08, 0.12) mixture in a sealed Nb tube at 650 °C for 3 days. Energy dispersive X-ray spectroscopy confirms the presence of P in all products. Powder X-ray diffraction patterns are consistent with the retention of the Na 4Si 4 crystal structure. As the amount of P increases, a new peak in the diffraction pattern that can be assigned to black phosphorus is apparent above the background. Raman and solid-state NMR provide information on phosphorus substitution in the Na 4Si 4 structure. Raman spectroscopy shows a shift of the most intense band assigned to the Si44- ν 1 (A 1) mode from 486.4 to 484.0 cm -1 with increasing P, consistent with P replacement of Si. Differential nuclear spin-lattice relaxation for the Si sites determined via 29Si solid-state NMR provides direct evidence for Si-P bonding in the (Si 1- xP x) 4- tetrahedron. The 23Na NMR shows additional Na…P interactions and the 31P NMR shows two P sites, consistent with P presence in both of the crystallographic sites in the (Si 4) 4- tetrahedron.

  1. Comparison of fission gas products accumulated in the irradiated UO2 fuel with the radiogenic gas trapped in minerals containing fissile atoms

    International Nuclear Information System (INIS)

    Both the old mineral materials containing fissile isotopes and the neutron irradiated uranium dioxide fuel hold fairly a lot of noble gases. Appreciable fraction of the inert gases is immobilized in the uranium dioxide fuel after irradiation exposure in excess of 1015 fissions/cm3. Spontaneous fission fluency for the minerals containing fissile atoms of about 2 billions years old is about 1015 fissions/cm3. Alike the old minerals containing fissile isotopes and the irradiated UO2 fuel reveal during annealing three peaks of gas release in the low temperature range. In the range only several percent of the total amount of gas as well in the mineral materials and the uranium dioxide fuel is released. It still holds significant part of noble gases after annealing at a temperature about 1400 deg C. Noble gas atoms can be trapped by the point defects, clusters of the point defects, clathrates and small bubbles in the irradiated material. It is suggested that above a fission fluency threshold about 1015 fissions/cm3 occurs an additional trapping process based on the irradiation induced chemical bonding process. It is inferred further that as well in the minerals and in the irradiated UO2 fuel the gas release kinetics is determined by the kinetics of thermal recovery of the radiation induced defects in the low temperature range. It is surmised that the same amount of damage caused by alpha decay of uranium is much less effective than caused by fission of uranium for the immobilization of noble gases since only during fissioning there are formed conditions for strong chemical binding between the noble gas atoms and the mineral materials. Finally it is concluded identical nature of noble gas accumulation mechanisms in the irradiated UO2 fuel and in the old mineral materials containing fissile atoms. (author)

  2. Integrative taxonomy and molecular phylogeny of genus Aplysina (Demospongiae: Verongida) from Mexican Pacific.

    Science.gov (United States)

    Cruz-Barraza, José Antonio; Carballo, José Luis; Rocha-Olivares, Axayacatl; Ehrlich, Hermann; Hog, Martin

    2012-01-01

    Integrative taxonomy provides a major approximation to species delimitation based on integration of different perspectives (e.g. morphology, biochemistry and DNA sequences). The aim of this study was to assess the relationships and boundaries among Eastern Pacific Aplysina species using morphological, biochemical and molecular data. For this, a collection of sponges of the genus Aplysina from the Mexican Pacific was studied on the basis of their morphological, chemical (chitin composition), and molecular markers (mitochondrial COI and nuclear ribosomal rDNA: ITS1-5.8-ITS2). Three morphological species were identified, two of which are new to science. A. clathrata sp. nov. is a yellow to yellow-reddish or -brownish sponge, characterized by external clathrate-like morphology; A. revillagigedi sp. nov. is a lemon yellow to green, cushion-shaped sometimes lobate sponge, characterized by conspicuous oscules, which are slightly elevated and usually linearly distributed on rims; and A. gerardogreeni a known species distributed along the Mexican Pacific coast. Chitin was identified as the main structural component within skeletons of the three species using FTIR, confirming that it is shared among Verongida sponges. Morphological differences were confirmed by DNA sequences from nuclear ITS1-5.8-ITS2. Mitochondrial COI sequences showed extremely low but diagnostic variability for Aplysina revillagigedi sp. nov., thus our results corroborate that COI has limited power for DNA-barcoding of sponges and should be complemented with other markers (e.g. rDNA). Phylogenetic analyses of Aplysina sequences from the Eastern Pacific and Caribbean, resolved two allopatric and reciprocally monophyletic groups for each region. Eastern Pacific species were grouped in general accordance with the taxonomic hypothesis based on morphological characters. An identification key of Eastern Pacific Aplysina species is presented. Our results constitute one of the first approximations to integrative

  3. Eocene climate and Arctic paleobathymetry: A tectonic sensitivity study using GISS ModelE-R

    Science.gov (United States)

    Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

    2009-12-01

    The early Paleogene (65-45 million years ago, Ma) was a ‘greenhouse’ interval with global temperatures warmer than any other time in the last 65 Ma. This period was characterized by high levels of CO2, warm high-latitudes, warm surface-and-deep oceans, and an intensified hydrological cycle. Sediments from the Arctic suggest that the Eocene surface Arctic Ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions remain uncertain. We present equilibrium climate conditions derived from a fully-coupled, water-isotope enabled, general circulation model (GISS ModelE-R) configured for the early Eocene. We also present model-data comparison plots for key climatic variables (SST and δ18O) and analyses of the leading modes of variability in the tropical Pacific and North Atlantic regions. Our tectonic sensitivity study indicates that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the seaways connecting the Arctic to the Atlantic and Tethys. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2°C in the North Atlantic and 5-10°C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We also suggest that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates in the Atlantic.

  4. Climate sensitivity to Arctic seaway restriction during the early Paleogene

    Science.gov (United States)

    Roberts, Christopher D.; LeGrande, Allegra N.; Tripati, Aradhna K.

    2009-09-01

    The opening and closing of ocean gateways affects the global distribution of heat, salt, and moisture, potentially driving climatic change on regional to global scales. Between 65 and 45 million years ago (Ma), during the early Paleogene, exchange between the Arctic and global oceans occurred through two narrow and shallow seaways, the Greenland-Norway seaway and the Turgai Strait. Sediments from the Arctic Ocean suggest that, during this interval, the surface ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions in the Paleogene Arctic remain uncertain. Here we show results from an isotope-enabled, atmosphere-ocean general circulation model, which indicate that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the Arctic seaways. We also present modelled estimates of seawater and calcite δ18O for the Paleogene. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~ 6 psu and warming of sea-surface temperatures by 2 °C in the North Atlantic and 5-10 °C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We propose that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the Paleocene Eocene Thermal Maximum (PETM).

  5. RECENT ADVANCES IN HYDRATE-BASED TECHNOLOGIES FOR NATURAL GAS STORAGE--A REVIEW

    Institute of Scientific and Technical Information of China (English)

    Yasuhiko H. Mori

    2003-01-01

    Interest in the possibility of storing and transporting natural gas in the form of clathrate hydrates has been increasing in recent years, particularly in some gas-importing and exporting countries.The technologies necessary for realizing this possibility may be classified into those relevant to the four serial processes (a) the formation of a hydrate, (b) the processing (dewatering, pelletizing, etc. ) of the formed hydrate, (c) the storage and transportation of the processed hydrate, and (d) the regasification (dissociation) of the hydrate. The technological development of any of these processes is still at an early stage. For hydrate formation, for example, various rival operations have been proposed. However,many of them have never been subjected to actual tests for practical use. More efforts are required for examining the different hydrate-formation technologies and for rating them by comparison. The general design of the processing of the formed hydrate inevitably depends on both the hydrate-formation process and the storage/transportation process, hence it has a wide variability. The major uncertainty in the storage-process design lies in the as-yet unclarified utility of the "self-preservation" effect of the naturalgas hydrates. The process design as well as the relevant cost evaluation should strongly depend on whether the hydrates are well preserved at atmospheric pressure in large-scale storage facilities. The regasification process has been studied less extensively than the former processes. The state of the art of the technological development in each of the serial processes is reviewed, placing emphasis on the hydrate formation process.

  6. Diffuse neutron scattering studies of proton ordering in ice Ih at different pressures

    International Nuclear Information System (INIS)

    Complete text of publication follows. A series of diffuse neutron scattering measurements from D2O single crystal ice Ih at different pressures were made on Prisma using the standard He pressuriser at ISIS. The measurements show that there is no clear change to the diffuse scattering pattern for pressures up to 2.8 kbar at 230 K. The pressure of 2.8 kbar is also well above the necessary pressure required for the formation of ice II at this temperature (which is 2.2 kbar). Hence the structure of the crystal appears to be stabilised by the presence of He gas which may occupy the centre cavities of the ice structure. However, when the pressure increases to 3.1 kbar at 120 K, the structure of ice Ih starts to deform, firstly the d-spacing of Bragg reflections in the direction of (hh0) increases, for instance, the (220) peak increases from 2.245 to 2.256 A (instead of a decrease under such high pressure) and the transition is completed at temperature of 180 K (i.e. the 2.245 A component completely disappears). More interestingly, all Bragg peaks were disappeared when the temperature increases to 200 K although the background remained the same, after searching for Bragg reflections without success and from examination of the sample, we believe that the sample transformed to a clathrate structure. The lack of diffraction rings indicates the sample to be single crystalline but in a considerably different orientation. (author)

  7. General survey of techniques for separation and containment of noble gases from nuclear facilities

    International Nuclear Information System (INIS)

    Radioactive noble gases produced during uranium fission constitute a waste material requiring special treatment and handling techniques if releases to the environment are to be reduced or minimized. To date, treatment has been confined to short-term holdup of reactor off-gases to allow short half-life fission products to decay. Although the required degree of noble gas separation and containment is not yet defined, considerable development effort has been expended on a variety of separation processes. With some separation processes, the technology is sufficiently advanced that commercial separation units are now being offered for sale. Early installations of these will be mainly at reactors. Eventually, separation processes may be installed at fuel processing plants to collect the long-lived krypton-85. The separation processes potentially applicable to removing noble gas fission products from off-gas streams include absorption in liquids (liquid air, carbon dioxide, or fluorocarbons), adsorption on charcoal and other solids, thermal diffusion, electrostatic diffusion, and diffusion through a selective membrane. A cryogenic liquid-air absorption process has been operated intermittently at the Idaho Chemical Processing Plant for many years to recover krypton-85 for a variety of uses. High pressure storage in steel cylinders presently appears to be the most practical means of ultimate disposal of the krypton-85. However, inclusion of the krypton-85 into glasses, resins, clathrates, molecular sieves, and metals offer ways of reducing the effective vapor pressure in a cylinder. Long-term disposal means that have been considered including placement of the cylinders into an engineered storage facility, dumping of cylinders into the sea, and direct discharge of the krypton-85 into an appropriate geologic formation

  8. Fluid inclusion and phase equilibrium studies at the Cannivan Gulch molybdenum deposit, Montana, USA: Effect of CO 2 on molybdenite-powellite stability

    Science.gov (United States)

    Darling, Robert S.

    1994-01-01

    The molybdenum deposit at Cannivan Gulch is characterized by both stockwork- and skarn type mineralization. The vein mineral assemblages, however, differ considerably between the various host rocks. In the Cannivan stock, molybdenite occurs in typical quartz + K-feldspar or quartz + muscovite veins. In the country rocks, molybdenite occurs in chlorite + pyrite + magnetite veins containing variable amounts of quartz, calcite, and epidote. Primary fluid inclusions in quartz and fluorite contain aqueous liquid, CO 2 liquid, and CO 2 vapor (average XCO2 = 0.05). Microthermometric and Laser Raman microspectrographic analyses indicate CO 2 is the principal volatile phase. First melting temperatures in the aqueous portion indicate the dissolved salt is principally NaCl. Final CO 2-clathrate melting temperatures indicate NaCl contents ranging from 2 to 7 wt% relative to H 2O. Homogenization temperatures range from 196 to 272°C. Four chlorite temperatures from two samples range from 296 to 319°C. In P- T space, the four chlorite univariants intersect four fluid inclusion isochores (from the same samples) at temperatures of 300 ± 20° C and 1500 ± 300 bars, which are the inferred P and T of molybdenite formation. Mineral equilibria in vein assemblages from country rocks at Cannivan Gulch indicate fO2 and fS2 conditions of molybdenite formation between the pyrite-pyrrhotite-magnetite and pyrite-magnetite-hematite buffers. Formation of a calcite-molybdenite assemblage over powellite suggests that even small amounts of CO 2 ( XCO2 = 0.05) in an ore fluid greatly extend the stability field of molybdenite to higher oxygen fugacities.

  9. Encapsulated discrete octameric water cluster, 1D water tape, and 3D water aggregate network in diverse MOFs based on bisimidazolium ligands

    Science.gov (United States)

    Shi, Ruo-Bing; Pi, Min; Jiang, Shuang-Shuang; Wang, Yuan-Yuan; Jin, Chuan-Ming

    2014-08-01

    Four new metal-organic frameworks, [Zn(2-mBIM)2(SO3CF3)2·(H2O)4] (1), [Zn(BMIE)(1,4-BDC)]·(H2O)3 (2), [Cd(BIM)2(OH)(H2O)2(PF6)]·(H2O)4 (3), and [Cd(PA-BIM)2 (ClO4)2]·11.33H2O (4) (2-mBIM = bis(2-methylimidazol-1-yl)methane, BMIE = 1,2-bis[1-(2-methylimidazole)-diethoxy]ethane, BIM = bis(imidazol-1-yl)methane, and PA-BIM = 1,1-bis [(2-phenylazo)imidazol-1-yl]methane) have been prepared and structurally characterized. Complex 1 exhibits an infinite 1D cationic beaded-chain structure, which encapsulated discrete octameric water clusters that are comprised of a chair-like hexameric water cluster with two extra water molecules dangling on two diagonal vertices of the chair. Complex 2 forms a 1D infinite zigzag metal-organic chain structure with a 1D T4(0)A(4) water tape. Complexes 3 show a 2D grid-like sheet structure with the 1D water tape T4(0)A(0)2(0) motif. Complex 4 is a porous 3D MOF with tetrahedron-coordinated Cd(II) centers and trans-conformation PA-BIM ligands. These holes are occupied by a fascinating three-dimensional water clathrate network, which consists of cage-shaped structural tetradecameric water cluster (H2O)14 units and six independent bridged water molecules. The results suggest that the bisimidazolium ligands and anions play crucial roles in the formation of the different host structures and different guest water aggregations. Additionally, the thermal stabilities and photoluminescence spectra of the complexes have been discussed.

  10. Dynamics of H2 adsorbed in porous materials as revealed by computational analysis of inelastic neutron scattering spectra.

    Science.gov (United States)

    Pham, Tony; Forrest, Katherine A; Space, Brian; Eckert, Juergen

    2016-06-29

    The inelastic scattering of neutrons from adsorbed H2 is an effective and highly sensitive method for obtaining molecular level information on the type and nature of H2 binding sites in porous materials. While these inelastic neutron scattering (INS) spectra of the hindered rotational and translational excitations on the adsorbed H2 contain a significant amount of information, much of this can only be reliably extracted by means of a detailed analysis of the spectra through the utilization of models and theoretical calculations. For instance, the rotational tunneling transitions observed in the INS spectra can be related to a value for the barrier to rotation for the adsorbed H2 with the use of a simple phenomenological model. Since such an analysis is dependent on the model, it is far more desirable to use theoretical methods to compute a potential energy surface (PES), from which the rotational barriers for H2 adsorbed at a particular site can be determined. Rotational energy levels and transitions for the hindered rotor can be obtained by quantum dynamics calculations and compared directly with experiment with an accuracy subject only to the quality of the theoretical PES. In this paper, we review some of the quantum and classical mechanical calculations that have been performed on H2 adsorbed in various porous materials, such as clathrate hydrates, zeolites, and metal-organic frameworks (MOFs). The principal aims of these calculations have been the interpretation of the INS spectra for adsorbed H2 along with the extraction of atomic level details of its interaction with the host. We describe calculations of the PES used for two-dimensional quantum rotation as well as rigorous five-dimensional quantum coupled translation-rotation dynamics, and demonstrate that the combination of INS measurements and computational modeling can provide important and detailed insights into the molecular mechanism of H2 adsorption in porous materials. PMID:27160665

  11. Big Impacts and Transient Oceans on Titan

    Science.gov (United States)

    Zahnle, K. J.; Korycansky, D. G.; Nixon, C. A.

    2014-01-01

    We have studied the thermal consequences of very big impacts on Titan [1]. Titan's thick atmosphere and volatile-rich surface cause it to respond to big impacts in a somewhat Earth-like manner. Here we construct a simple globally-averaged model that tracks the flow of energy through the environment in the weeks, years, and millenia after a big comet strikes Titan. The model Titan is endowed with 1.4 bars of N2 and 0.07 bars of CH4, methane lakes, a water ice crust, and enough methane underground to saturate the regolith to the surface. We assume that half of the impact energy is immediately available to the atmosphere and surface while the other half is buried at the site of the crater and is unavailable on time scales of interest. The atmosphere and surface are treated as isothermal. We make the simplifying assumptions that the crust is everywhere as methane saturated as it was at the Huygens landing site, that the concentration of methane in the regolith is the same as it is at the surface, and that the crust is made of water ice. Heat flow into and out of the crust is approximated by step-functions. If the impact is great enough, ice melts. The meltwater oceans cool to the atmosphere conductively through an ice lid while at the base melting their way into the interior, driven down in part through Rayleigh-Taylor instabilities between the dense water and the warm ice. Topography, CO2, and hydrocarbons other than methane are ignored. Methane and ethane clathrate hydrates are discussed quantitatively but not fully incorporated into the model.

  12. Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life

    Science.gov (United States)

    Kargel, J.S.; Kaye, J.Z.; Head, J. W., III; Marion, G.M.; Sassen, R.; Crowley, J.K.; Ballesteros, O.P.; Grant, S.A.; Hogenboom, D.L.

    2000-01-01

    We have considered a wide array of scenarios for Europa's chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below. We postulate that, following formation of the jovian system, the europan evolutionary sequence has as its major links: (a) initial carbonaceous chondrite rock, (b) global primordial aqueous differentiation and formation of an impure primordial hydrous crust, (c) brine evolution and intracrustal differentiation, (d) degassing of Europa's mantle and gas venting, (e) hydrothermal processes, and (f) chemical surface alteration. Our models were developed in the context of constraints provided by Galileo imaging, near infrared reflectance spectroscopy, and gravity and magnetometer data. Low-temperature aqueous differentiation from a carbonaceous CI or CM chondrite precursor, without further chemical processing, would result in a crust/ocean enriched in magnesium sulfate and sodium sulfate, consistent with Galileo spectroscopy. Within the bounds of this simple model, a wide range of possible layered structures may result; the final state depends on the details of intracrustal differentiation. Devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean/crust compositions, e.g., an ocean/crust of sodium carbonate or sulfuric acid, or a crust containing abundant clathrate hydrates. Realistic chemical-physical evolution scenarios differ greatly in detailed predictions, but they generally call for a highly impure and chemically layered crust. Some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and/or cryovolcanism. We describe some plausible geological consequences of the physical-chemical structures predicted from these scenarios. These predicted consequences and observed aspects of Europa's geology may serve as a basis for further analys is

  13. Dependence of the initial adhesion of biofilm forming Pseudomonas putida mt2 on physico-chemical material properties.

    Science.gov (United States)

    Montag, Dominik; Frant, Marion; Horn, Harald; Liefeith, Klaus

    2012-01-01

    Bacterial adhesion is strongly dependent on the physico-chemical properties of materials and plays a fundamental role in the development of a growing biofilm. Selected materials were characterized with respect to their physico-chemical surface properties. The different materials, glass and several polymer foils, showed a stepwise range of surface tensions (γ(s)) between 10.3 and 44.7 mN m(-1). Measured zeta potential values were in the range between -74.8 and -28.3 mV. The initial bacterial adhesion parameter q(max) was found to vary between 6.6 × 10(6) and 28.1 × 10(6) cm(-2). By correlation of the initial adhesions kinetic parameters with the surface tension data, the optimal conditions for the immobilization of Pseudomonas putida mt2 were found to be at a surface tension of 24.7 mN m(-1). Both higher and lower surface tensions lead to a smaller number of adherent cells per unit surface area. Higher energy surfaces, commonly termed hydrophilic, could constrain bacterial adhesion because of their more highly ordered water structure (exclusion zone) close to the surface. At low energy surfaces, commonly referred to as hydrophobic, cell adhesion is inhibited due to a thin, less dense zone (depletion layer or clathrate structure) close to the surface. Correlation of q (max) with zeta potential results in a linear relationship. Since P. putida carries weak negative charges, a measurable repulsive effect can be assumed on negative surfaces. PMID:22452391

  14. Role of megafauna and frozen soil in the atmospheric CH4 dynamics.

    Directory of Open Access Journals (Sweden)

    Sergey Zimov

    Full Text Available Modern wetlands are the world's strongest methane source. But what was the role of this source in the past? An analysis of global 14C data for basal peat combined with modelling of wetland succession allowed us to reconstruct the dynamics of global wetland methane emission through time. These data show that the rise of atmospheric methane concentrations during the Pleistocene-Holocene transition was not connected with wetland expansion, but rather started substantially later, only 9 thousand years ago. Additionally, wetland expansion took place against the background of a decline in atmospheric methane concentration. The isotopic composition of methane varies according to source. Owing to ice sheet drilling programs past dynamics of atmospheric methane isotopic composition is now known. For example over the course of Pleistocene-Holocene transition atmospheric methane became depleted in the deuterium isotope, which indicated that the rise in methane concentrations was not connected with activation of the deuterium-rich gas clathrates. Modelling of the budget of the atmospheric methane and its isotopic composition allowed us to reconstruct the dynamics of all main methane sources. For the late Pleistocene, the largest methane source was megaherbivores, whose total biomass is estimated to have exceeded that of present-day humans and domestic animals. This corresponds with our independent estimates of herbivore density on the pastures of the late Pleistocene based on herbivore skeleton density in the permafrost. During deglaciation, the largest methane emissions originated from degrading frozen soils of the mammoth steppe biome. Methane from this source is unique, as it is depleted of all isotopes. We estimated that over the entire course of deglaciation (15,000 to 6,000 year before present, soils of the mammoth steppe released 300-550 Pg (10(15 g of methane. From current study we conclude that the Late Quaternary Extinction significantly affected

  15. NMR investigations of surfaces and interfaces using spin-polarized xenon

    Energy Technology Data Exchange (ETDEWEB)

    Gaede, H C [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-07-01

    {sup 129}Xe NMR is potentially useful for the investigation of material surfaces, but has been limited to high surface area samples in which sufficient xenon can be loaded to achieve acceptable signal to noise ratios. In Chapter 2 conventional {sup 129}Xe NMR is used to study a high surface area polymer, a catalyst, and a confined liquid crystal to determine the topology of these systems. Further information about the spatial proximity of different sites of the catalyst and liquid crystal systems is determined through two dimensional exchange NMR in Chapter 3. Lower surface area systems may be investigated with spin-polarized xenon, which may be achieved through optical pumping and spin exchange. Optically polarized xenon can be up to 10{sup 5} times more sensitive than thermally polarized xenon. In Chapter 4 highly polarized xenon is used to examine the surface of poly(acrylonitrile) and the formation of xenon clathrate hydrates. An attractive use of polarized xenon is as a magnetization source in cross polarization experiments. Cross polarization from adsorbed polarized xenon may allow detection of surface nuclei with drastic enhancements. A non-selective low field thermal mixing technique is used to enhance the {sup 13}C signal of CO{sub 2} of xenon occluded in solid CO{sub 2} by a factor of 200. High-field cross polarization from xenon to proton on the surface of high surface area polymers has enabled signal enhancements of {approximately}1,000. These studies, together with investigations of the efficiency of the cross polarization process from polarized xenon, are discussed in Chapter 5. Another use of polarized xenon is as an imaging contrast agent in systems that are not compatible with traditional contrast agents. The resolution attainable with this method is determined through images of structured phantoms in Chapter 6.

  16. Macroscopic investigation of hydrate film growth at the hydrocarbon/water interface

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, C.J.; Miller, K.T.; Koh, C.A.; Sloan, E.D. [Colorado School of Mines, Golden, CO (United States). Dept. of Chemical Engineering

    2008-07-01

    Clathrate hydrates are ice-like crystalline compounds that form as thin porous crystalline films at the interface between the water phase and the hydrocarbon guest molecule phase. The growth characteristics of these hydrate films are important in seafloor carbon dioxide sequestration, gas hydrate transport, and flow assurance in oil and gas pipelines. This paper presented a study that employed digital video microscopy to investigate the hydrate film thickness as a function of time, as well as the propagation rate for methane and cyclopentane hydrate. The purpose of the study was to enhance past measurements of hydrate film growth by incorporating gas consumption measurements simultaneously with film thickness measurements to determine which phase supplied the hydrate former during hydrate formation. The study also advanced the physical knowledge of hydrate formation by relating film formation with the water droplet to hydrate shell conversion. The paper included a schematic of the hydrate film growth apparatus and image acquisition and analysis as well as an illustration of the nucleation of a water droplet immersed in cyclopentane. The results were presented for cyclopentane hydrate film growth; methane hydrate film growth; film growth in an oil/methane/ water system; film growth/development into water phase; and gas consumption for hydrate film growth. The paper also discussed the source of methane for hydrate formation; solubility of methane in water; growth rates; proposed mechanism of hydrate film growth at the hydrocarbon/water interface; and, transferability between hydrate formation for a pool of liquid versus a water droplet. It was concluded that gas consumption data during hydrate formation presented evidence of an aqueous phase supply of hydrate former to the initial hydrate growth, followed by a vapor phase supply of hydrate former in the thickening stage of hydrate film formation. 25 refs., 18 figs.,.

  17. Equilibrium, Kinetics, and Spectroscopic Studies of SF6 Hydrate in NaCl Electrolyte Solution.

    Science.gov (United States)

    Seo, Youngrok; Moon, Donghyun; Lee, Changho; Park, Jeong-Woo; Kim, Byeong-Soo; Lee, Gang-Woo; Dotel, Pratik; Lee, Jong-Won; Cha, Minjun; Yoon, Ji-Ho

    2015-05-19

    Many studies have focused on desalination via hydrate formation; however, for their potential application, knowledge pertaining to thermodynamic stability, formation kinetics, and guest occupation behavior in clathrate hydrates needs to be determined. Herein, the phase equilibria of SF6 hydrates in the presence of NaCl solutions (0, 2, 4, and 10 wt %) were monitored in the temperature range of 277-286 K and under pressures of up to 1.4 MPa. The formation kinetics of SF6 hydrates in the presence of NaCl solutions (0, 2, and 4 wt %) was also investigated. Gas consumption curves of SF6 hydrates showed that a pure SF6 hydrate system allowed fast hydrate growth as well as high conversion yield, whereas SF6 hydrate in the presence of NaCl solutions showed retarded hydrate growth rate as well as low conversion yield. In addition, structural identification of SF6 hydrates with and without NaCl solutions was performed using spectroscopic tools such as Raman spectroscopy and X-ray diffraction. The Raman spectrometer was also used to evaluate the temperature-dependent release behavior of guest molecules in SF6 and SF6 + 4 wt % NaCl hydrates. The results indicate that whereas SF6 hydrate starts to decompose at around 240 K, the escape of SF6 molecules in SF6 + 4 wt % NaCl hydrate is initiated rapidly at around 205 K. The results of this study can provide a better understanding of guest-host interaction in electrolyte-containing systems. PMID:25893445

  18. Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates

    Science.gov (United States)

    Petrenko, Vasilii V.; Severinghaus, Jeffrey P.; Schaefer, Hinrich; Smith, Andrew M.; Kuhl, Tanner; Baggenstos, Daniel; Hua, Quan; Brook, Edward J.; Rose, Paul; Kulin, Robb; Bauska, Thomas; Harth, Christina; Buizert, Christo; Orsi, Anais; Emanuele, Guy; Lee, James E.; Brailsford, Gordon; Keeling, Ralph; Weiss, Ray F.

    2016-03-01

    Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from "old" carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26-19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.

  19. One-Hundred-km-Scale Basins on Enceladus: Evidence for an Active Ice Shell

    Science.gov (United States)

    Schenk, Paul M.; McKinnon, William B.

    2009-01-01

    Stereo-derived topographic mapping of 50% of Enceladus reveals at least 6 large-scale, ovoid depressions (basins) 90-175 km across and 800-to-1500 m deep and uncorrelated with geologic boundaries. Their shape and scale are inconsistent with impact, geoid deflection, or with dynamically supported topography. Isostatic thinning of Enceladus ice shell associated with upwellings (and tidally-driven ice melting) can plausibly account for the basins. Thinning implies upwarping of the base of the shell of 10-20 km beneath the depressions, depending on total shell thickness; loss of near-surface porosity due to enhanced heat flow may also contribute to basin lows. Alternatively, the basins may overly cold, inactive, and hence denser ice, but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice. In contrast to the basins, the south polar depression (SPD) is larger (350 wide) and shallower (0.4-to-0.8 km deep) and correlates with the area of tectonic deformation and active resurfacing. The SPD also differs in that the floor is relatively flat (i.e., conforms roughly to the global triaxial shape, or geoid) with broad, gently sloping flanks. The relative flatness across the SPD suggests that it is in or near isostatic equilibrium, and underlain by denser material, supporting the polar sea hypothesis of Collins and Goodman. Near flatness is also predicted by a crustal spreading origin for the "tiger stripes (McKinnon and Barr 2007, Barr 2008); the extraordinary, high CIRS heat flows imply half-spreading rates in excess of 10 cm/yr, a very young surface age (250,000 yr), and a rather thin lithosphere (hence modest thermal topography). Topographic rises in places along the outer margin of the SPD correlate with parallel ridges and deformation along the edge of the resurfaced terrain, consistent with a compressional, imbricate thrust origin for these ridges, driven by the spreading.

  20. Sequestering carbon dioxide in industrial polymers: Building materials for the 21st century

    Energy Technology Data Exchange (ETDEWEB)

    Molton, P.M.; Nelson, D.A.

    1993-06-01

    This study was undertaken to determine the possibility of developing beneficial uses for carbon dioxide as a key component for a large-volume building product. Such a use may provide an alternative to storing the gas in oceanic sinks or clathrates as a way to slow the rate of global warming. The authors investigated the concept that carbon dioxide might be used with other chemicals to make carbon-dioxide-based polymers which would be lightweight, strong, and economical alternatives to some types of wood and silica-based building materials. As a construction-grade material, carbon dioxide would be fixed in a solid, useful form where it would not contribute to global warming. With the probable imposition of a fuel carbon tax in industrialized countries, this alternative would allow beneficial use of the carbon dioxide and could remove it from the tax basis if legislation were structured appropriately. Hence, there would be an economic driver towards the use of carbon-dioxide-based polymers which would enhance their future applications. Information was obtained through literature searches and personal contacts on carbon dioxide polymers which showed that the concept (1) is technically feasible, (2) is economically defensible, and (3) has an existing industrial infrastructure which could logically develop it. The technology exists for production of building materials which are strong enough for use by industry and which contain up to 90% by weight of carbon dioxide, both chemically and physically bound. A significant side-benefit of using this material would be that it is self-extinguishing in case of fire. This report is the first stage in the investigation. Further work being proposed will provide details on costs, specific applications and volumes, and potential impacts of this technology.

  1. Micromechanical measurements of the effect of surfactants on cyclopentane hydrate shell properties.

    Science.gov (United States)

    Brown, Erika P; Koh, Carolyn A

    2016-01-01

    Investigating the effect of surfactants on clathrate hydrate growth and morphology, especially particle shell strength and cohesion force, is critical to advancing new strategies to mitigate hydrate plug formation. In this study, dodecylbenzenesulfonic acid and polysorbate 80 surfactants were included during the growth of cyclopentane hydrates at several concentrations above and below the critical micelle concentration. A novel micromechanical method was applied to determine the force required to puncture the hydrate shell using a glass cantilever (with and without surfactants), with annealing times ranging from immediately after the hydrate nucleated to 90 minutes after formation. It was shown that the puncture force was decreased by the addition of both surfactants up to a maximum of 79%. Over the entire range of annealing times (0-90 minutes), the thickness of the hydrate shell was also measured. However, there was no clear change in shell thickness with the addition of surfactants. The growth rate of the hydrate shell was found to vary less than 15% with the addition of surfactants. The cohesive force between two hydrate particles was measured for each surfactant and found to be reduced by 28% to 78%. Interfacial tension measurements were also performed. Based on these results, microscopic changes to the hydrate shell morphology (due to the presence of surfactants) were proposed to cause the decrease in the force required to break the hydrate shell, since no macroscopic morphology changes were observed. Understanding the hydrate shell strength can be critical to reducing the capillary bridge interaction between hydrate particles or controlling the release of unconverted water from the interior of the hydrate particle, which can cause rapid hydrate conversion. PMID:26618773

  2. Lunar and Planetary Science XXXVI, Part 6

    Science.gov (United States)

    2005-01-01

    Contents include the following: A Model for Multiple Populations of Presolar Diamonds. Characterization of Martian North Polar Geologic Units Using Mars Odyssey THEMIS Data. Effect of Flow on the Internal Structure of the Martian North Polar Layered Deposits. Elemental Abundance Distributions in Basalt Clays and Meteorites: Is It a Biosignature? Early Results on the Saturn System from the Composite Infrared Spectrometer. NanoSIMS D/H Imaging of Isotopically Primitive Interplanetary Dust Particles. Presolar (Circumstellar and Interstellar) Phases in Renazzo: The Effects of Parent Body Processing. Catastrophic Disruption of Hydrated Targets: Implications for the Hydrated Asteroids and for the Production of Interplanetary Dust Particles. Chemical and Mineralogical Analyses of Particles from the Stratospheric Collections Coinciding with the 2002 Leonid Storm and the 2003 Comet Grigg-Skjellerup Trail Passage. An Analysis of the Solvus in the CaS-MnS System. ESA s SMART-1 Mission at the Moon: First Results, Status and Next Steps. Europa Analog Ice-splitting Measurements and Experiments with Ice-Hunveyor on the Frozen Balaton-Lake, Hungary. Chromium on Eros: Further Evidence of Ordinary Chondrite Composition. Dust Devil Tracks on Mars: Observation and Analysis from Orbit and the Surface. Spatial Variation of Methane and Other Trace Gases Detected on Mars: Interpretation with a General Circulation Model. Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations. Component Separation of OMEGA Spectra with ICA. Clathrate Formation in the Near-Surface Environment of Titan. Space Weathering: A Proposed Laboratory Approach to Explaining the Sulfur Depletion on Eros. Sample Collection from Small Airless Bodies: Examination of Temperature Constraints for the TGIP. Sample Collector for the Hera Near-Earth Asteroid Sample Return Mission. A Rugged Miniature Mass-Spectrometer for Measuring Aqueous Geochemistry on Mars

  3. NMR investigations of surfaces and interfaces using spin-polarized xenon

    International Nuclear Information System (INIS)

    129Xe NMR is potentially useful for the investigation of material surfaces, but has been limited to high surface area samples in which sufficient xenon can be loaded to achieve acceptable signal to noise ratios. In Chapter 2 conventional 129Xe NMR is used to study a high surface area polymer, a catalyst, and a confined liquid crystal to determine the topology of these systems. Further information about the spatial proximity of different sites of the catalyst and liquid crystal systems is determined through two dimensional exchange NMR in Chapter 3. Lower surface area systems may be investigated with spin-polarized xenon, which may be achieved through optical pumping and spin exchange. Optically polarized xenon can be up to 105 times more sensitive than thermally polarized xenon. In Chapter 4 highly polarized xenon is used to examine the surface of poly(acrylonitrile) and the formation of xenon clathrate hydrates. An attractive use of polarized xenon is as a magnetization source in cross polarization experiments. Cross polarization from adsorbed polarized xenon may allow detection of surface nuclei with drastic enhancements. A non-selective low field thermal mixing technique is used to enhance the 13C signal of CO2 of xenon occluded in solid CO2 by a factor of 200. High-field cross polarization from xenon to proton on the surface of high surface area polymers has enabled signal enhancements of ∼1,000. These studies, together with investigations of the efficiency of the cross polarization process from polarized xenon, are discussed in Chapter 5. Another use of polarized xenon is as an imaging contrast agent in systems that are not compatible with traditional contrast agents. The resolution attainable with this method is determined through images of structured phantoms in Chapter 6

  4. Observations of bubbles in natural seep flares at MC 118 and GC 600 using in situ quantitative imaging

    Science.gov (United States)

    Wang, Binbin; Socolofsky, Scott A.; Breier, John A.; Seewald, Jeffrey S.

    2016-04-01

    This paper reports the results of quantitative imaging using a stereoscopic, high-speed camera system at two natural gas seep sites in the northern Gulf of Mexico during the Gulf Integrated Spill Research G07 cruise in July 2014. The cruise was conducted on the E/V Nautilus using the ROV Hercules for in situ observation of the seeps as surrogates for the behavior of hydrocarbon bubbles in subsea blowouts. The seeps originated between 890 and 1190 m depth in Mississippi Canyon block 118 and Green Canyon block 600. The imaging system provided qualitative assessment of bubble behavior (e.g., breakup and coalescence) and verified the formation of clathrate hydrate skins on all bubbles above 1.3 m altitude. Quantitative image analysis yielded the bubble size distributions, rise velocity, total gas flux, and void fraction, with most measurements conducted from the seafloor to an altitude of 200 m. Bubble size distributions fit well to lognormal distributions, with median bubble sizes between 3 and 4.5 mm. Measurements of rise velocity fluctuated between two ranges: fast-rising bubbles following helical-type trajectories and bubbles rising about 40% slower following a zig-zag pattern. Rise speed was uncorrelated with hydrate formation, and bubbles following both speeds were observed at both sites. Ship-mounted multibeam sonar provided the flare rise heights, which corresponded closely with the boundary of the hydrate stability zone for the measured gas compositions. The evolution of bubble size with height agreed well with mass transfer rates predicted by equations for dirty bubbles.

  5. Na8Au9.8(4)Ga7.2 and Na17Au15.87(2)Ga46.63: The diversity of pseudo 5-fold 0 Cross Mark symmetries in the Na-Au-Ga system

    Energy Technology Data Exchange (ETDEWEB)

    Smetana, Volodymyr [Ames Laboratory; Corbett, John D.; Miller, Gordon J. [Ames Laboratory

    2013-08-29

    The Na-rich part (similar to 30% Na) of the Na-Au-Ga system between NaAu2, NaGa4, and Na(22)Ga39 has been found to contain the ternary phases NasAug(8)(4)Ga-7.2 (I) and NavAu(5.87(2))Ga46.63 (II), according to the results of single crystal X-ray diffraction measurements. I is orthorhombic, Cmcm, a= 5.3040(1), b=24.519(5), c=14.573(3) A, and contains a network of clusters with local 5-fold symmetry along the a-axis. Such clusters are frequent building units in decagonal quasicrystals and their approximants. II is rhombohedral, a =16.325(2), c=35.242(7) A, and contains building blocks that are structurally. identical to the Bergman-type clusters as well as fused icosahedral units known with active metals, triels and late transition elements. II also contains a polycationic network with elements of the clathrate V type structure. Tight-binding electronic structure calculations using linear muffin-tin-orbital (LMTO) methods on idealized models of I and II indicate that both compounds are metallic with evident pseudogaps at the corresponding Fermi levels. The overall Hamilton bond populations are generally dominated by Au-Ga and Au-Au bonds in I and by Ga-Ga bonds in II; moreover, the Na-Au and Na-Ga contributions in I are unexpectedly large, 20% of the total. A similar involvement of sodium in covalent bonding has also been found in the electron-richer i-Nai(3)Aui(2)Gai(5) quasicrystal approximant. (C) 2013 Elsevier Inc. All rights reserved.

  6. Lithiation-induced zinc clustering of Zn3, Zn12, and Zn18 units in Zintl-like Ca~30Li3+xZn60-x (x=0.44-1.38)

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Qisheng [Ames Laboratory

    2014-11-14

    Zinc clusters are not common for binary intermetallics with relatively low zinc content, but this work shows that zinc clustering can be triggered by lithiation, as exemplified by Ca~30Li3+xZn60-x, P6/mmm, Z = 1, which can be directly converted from CaZn2. Two end members of the solid solution (x = 0.44 and 1.38) were established and structurally characterized by single-crystal X-ray diffraction analyses: Ca30Li3.44(6)Zn59.56(6), a = 15.4651(9) Å, c = 9.3898(3) Å; Ca30.45(2)Li4.38(6)Zn58.62(6), a = 15.524(3) Å, c = 9.413(2) Å. The structures of Ca~30Li3+xZn60-x feature a condensed anionic network of Zn3 triangles, lithium-centered Zn12 icosahedra, and arachno-(Zn,Li)18 tubular clusters that are surrounded respectively by Ca14, Ca20, and Ca30 polyhedra. These polyhedra share faces and form a clathrate-like cationic framework. The specific occupation of lithium in the structure is consistent with theoretical “coloring” analyses. Analysis by the linear muffin-tin orbital (LMTO) method within the atomic sphere approximation reveals that Ca~30Li3+xZn60-x is a metallic, Zintl-like phase with an open-shell electronic structure. The contribution of Ca–Zn polar covalent interactions is about 41%.

  7. Un fusible de méthane pour l'explosion cambrienne : les cycles du carbone et dérive des pôles

    Science.gov (United States)

    Kirschvink, Joseph L.; Raub, Timothy D.

    2003-01-01

    The dramatic diversification of animal groups known as the Cambrian Explosion (evolution's 'Big Bang') remains an unsolved puzzle in Earth Science. The Vendian-Cambrian interval is characterized by anomalously high rates of apparent plate motion, interpreted as True Polar Wander (TPW), and by more than a dozen large, high-frequency perturbations in carbon isotopes that dwarf all others observed through the past 65 million years. We suggest that these biological, tectonic, and geochemical events are intimately related in the following fashion. First, tropical continental margins and shelf-slopes which formed during fragmentation of the supercontinent Rodinia accumulated massive quantities of isotopically-light organic carbon during Late Neoproterozoic time, as indicated by strikingly heavy isotope ratios in inorganic carbon during interglacial intervals. Second, an initial phase of Vendian TPW moved these organic-rich deposits to high latitude, where conditions favored trapping biogenic methane in layers of gas hydrate and perhaps permafrost. Continued sedimentation during Late Vendian time added additional hydrate/gas storage volume and stabilized underlying units until the geothermal gradient moved them out of the clathrate stability field, building up deep reservoirs of highly pressurized methane. Finally, a burst of TPW brought these deposits back to the Tropics, where they gradually warmed and were subjected to regional-scale thermohaline eddy variation and related sedimentation regime changes. Responding to the stochastic character of such changes, each reservoir reached a critical failure point independently at times throughout the Cambrian. By analogy with the Late Paleocene Thermal Maximum event, these methane deposits yield transient, greenhouse-induced pulses of global warming when they erupt. Temperature correlates powerfully with biodiversity; the biochemical kinetics of metabolism at higher temperature decrease generation time and maintain relatively

  8. Abundance, viability and diversity of the indigenous microbial populations at different depths of the NEEM Greenland ice core

    Directory of Open Access Journals (Sweden)

    Vanya Miteva

    2015-02-01

    Full Text Available The 2537-m-deep North Greenland Eemian Ice Drilling (NEEM core provided a first-time opportunity to perform extensive microbiological analyses on selected, recently drilled ice core samples representing different depths, ages, ice structures, deposition climates and ionic compositions. Here, we applied cultivation, small subunit (SSU rRNA gene clone library construction and Illumina next-generation sequencing (NGS targeting the V4–V5 region, to examine the microbial abundance, viability and diversity in five decontaminated NEEM samples from selected depths (101.2, 633.05, 643.5, 1729.75 and 2051.5 m deposited 300–80 000 years ago. These comparisons of the indigenous glacial microbial populations in the ice samples detected significant spatial and temporal variations. Major findings include: (a different phylogenetic diversity of isolates, dominated by Actinobacteria and fungi, compared to the culture-independent diversity, in which Proteobacteria and Firmicutes were more frequent; (b cultivation of a novel alphaproteobacterium; (c dominance of Cyanobacteria among the SSU rRNA gene clones from the 1729.75-m ice; (d identification of Archaea by NGS that are rarely detected in glacial ice; (e detection of one or two dominant but different genera among the NGS sequences from each sample; (f finding dominance of Planococcaceae over Bacillaceae among Firmicutes in the brittle and the 2051.5-m ice. The overall beta diversity between the studied ice core samples examined at the phylum/class level for each approach showed that the population structure of the brittle ice was significantly different from the two deep clathrated ice samples and the shallow ice core.

  9. Thermodynamic stability and crystallization behavior of molecular complexes with TEP host

    Science.gov (United States)

    Fijiwara, Atsushi; Kitamura, Mitsutaka

    2013-06-01

    In the crystallization of molecular complex (co-crystal, clathrate complex), polymorphism in regard to the host structure frequently appears. Previously, we studied the release process of the biocide, CMI (5-chloro-2-methyl-4-isothiazolin-3-one) from the molecular complex with TEP (1,1,2,2-tetrakis(4-hydroxyphenyl)ethane) (TEP·2CMI) in methanol-water mixed solvents. It was clear that the release process of the biocide (CMI) is composed of the transformation from the TEP·2CMI crystal to a more stable molecular complex crystal with solvent. In this work, the crystallization was performed in the methanol solutions including TEP and CMI at constant temperature (298 K and 308 K). It appeared that two kinds of TEP molecular complexes (TEP·2CMI and TEP·2MeOH) crystallize competitively. The crystallization zone of each molecular complex was shown in the map using the coordinates of initial concentrations of TEP and CMI. In the boundary zone both molecular complexes appeared and the transformation from TEP·2CMI to TEP·2MeOH was observed, indicating that the stable form is TEP·2MeOH. Without the boundary zone the corresponding stable form crystallized in each zone. The value of the initial concentration ratio of CMI/TEP for the selective crystallization of TEP·2CMI was higher at 298 K (1.54) than that (1.36) at 308 K. The equilibrium concentrations of TEP and CMI in the presence of two molecular complexes were expressed using the dissociation constants of the molecular complexes and it was indicated that the dissociation of TEP·2CMI highly increases with temperature

  10. An atmosphere-ocean GCM modelling study of the climate response to changing Arctic seaways in the early Cenozoic.

    Science.gov (United States)

    Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

    2008-12-01

    previous findings on the potential influence of Arctic gateways on ocean overturning and also suggests that Northern Hemisphere climate, particularly in the North Atlantic, was very sensitive to changes in Arctic seaways. This result is of particular significance when considered in the context of the Paleocene Eocene Thermal Maximum (PETM). Volcanic activity prior to the PETM may have been responsible for the formation of a sub-aerial barrier in the North Atlantic, and consequently may have driven warming of intermediate waters sufficient to destabilize methane clathrates. Evidence for freshening of Arctic ocean waters prior to the PETM would support this hypothesis.

  11. Tracking the MSL-SAM methane detection source location Through Mars Regional Atmospheric Modeling System (MRAMS)

    Science.gov (United States)

    Pla-García, Jorge

    2016-04-01

    1. Introduction: The putative in situ detection of methane by Sample Analysis at Mars (SAM) instrument suite on Curiosi-ty at Gale crater has garnered significant attention because of the potential implications for the presence of geological methane sources or indigenous Martian organisms [1, 2]. SAM reported detection of back-ground levels of atmospheric methane of mean value 0.69±0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). Additionally, in four sequential measurements spanning a 60-sol period, SAM observed elevated levels of methane of 7.2±2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source. There are many major unresolved questions regard-ing this detection: 1) What are the potential sources of the methane release? 2) What causes the rapid decrease in concentration? and 3) Where is the re-lease location? 4) How spatially extensive is the re-lease? 5) For how long is CH4 released? Regarding the first question, the source of methane, is so far not identified. It could be related with geo-logical process like methane release from clathrates [3], serpentinisation [4] and volcanism [5]; or due to biological activity from methanogenesis [6]. To answer the second question, the rapid decrease in concentration, it is important to note that the photo-chemical lifetime of methane is of order 100 years, much longer than the atmospheric mixing time scale, and thus the gas should tend to be well mixed except near a source or shortly after an episodic release. The observed spike of 7 ppb from the background of LPI contributions, 1719: 1366; [2] Webster et al. (2015), Science, vol. 347, no. 6220, 415-417; [3] Chastain and Chevrier (2007). Planet. Space Science, 55, 1246-1256; [4] Oze and Sharma (2005). Geophys. Res. Lett., 32, L10203; [5] Etiope et al. (2007), J. Volcanol. Geo-therm. Res., 165, 76-86; [6] Reid et al. (2006), Int. J. Astrobiol., 5, 89-97; [7] Jensen et al. (2014), Icarus

  12. 河豚鱼肝油中EPA、DHA的纯化与含量测定%Purification and Content Determination of EPA and DHA in Puffer Fish Liver Oil

    Institute of Scientific and Technical Information of China (English)

    郭斌; 孟磊; 彭宏伟; 李智

    2011-01-01

    OBJECTIVE: To study purification method of EPA and DHA in the puffer fish liver oil and to establish the methods for the content determination of EPA and DHA. METHODS: Unsaturated fatty acid was purified by refinement, salt fractionation,hypothermy-sylvite method and urea clathration method. After activated by methyl ester, the content of EPA and DHA were detected by GC chromatography. RESULTS: Highly purified unsaturated fatty acids were purified from puffer fish liver oil and the content of EPA and DHA was 0.261 9 g· g-1 and 0.452 7 g· g-1, respectively. The calibration curves were linear in the ranges of 0.05-0.25 mg· mL-1 for EPA methyl ester and DHA methyl ester. CONCLUSION: It is a feasible method for purification of EPA and DHA in puffer fish liver oil. The method is simple, accurate and reproducible for the content determination.%目的:研究河豚鱼肝油中二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)的纯化方法,并建立EPA和DHA的含量测定方法.方法:河豚鱼肝油经精炼、盐析、低温-钾盐乙醇法和尿素包合法相结合纯化得不饱和脂肪酸;不饱和脂肪酸经甲脂化后,采用气相色谱法测定EPA和DHA的含量.结果:河豚鱼肝油经纯化可获得高纯度的不饱和脂肪酸;EPA和DHA的含量分别为0.261 9g·g-1和0.4527 g·g-1.EPA甲酯和DHA甲酯标准品浓度均在0.05~0.25mg·mL-1范围内同其与内标的峰面积比值呈良好的线性关系(r分别为0.999 7、0.999 8).结论:河豚鱼肝油中EPA和DHA的纯化方法可行;检测方法操作简单、结果准确、重复性良好,是一种可行的含量测定方法.

  13. Study on gas hydrate as a new energy resource in the 21th century

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Byeong-Jae; Kwak Young-Hoon; Kim, Won-Sik [Korea Institute of Geology Mining and Materials, Taejon (KR)] (and others)

    1999-12-01

    Natural gas hydrate, a special type of clathrate hydrates, is a metastable solid compound which mainly consists of methane and water, and generally called as gas hydrate. It is stable in the specific low-temperature/high-pressure conditions. Gas hydrates play an important role as major reservoir of methane on the earth. On the other hand, the formation and dissociation of gas hydrates could cause the plugging in pipeline, gas kick during production, atmospheric pollution and geohazard. To understand the formation and dissociation of the gas hydrate, the experimental equilibrium conditions of methane hydrate were measured in pure water, 3 wt.% NaCl and MgCl{sub 2} solutions. The equilibrium conditions of propane hydrates were also measured in pure water. The relationship between methane hydrate formation time and overpressure was also analyzed through the laboratory work. The geophysical surveys using air-gun system and multibeam echo sounder were implemented to develop exploration techniques and to evaluate the gas hydrate potential in the East Sea, Korea. General indicators of submarine gas hydrates on seismic data is commonly inferred from the BSR developed parallel to the see floor, amplitude blanking at the upper part of the BSR, and phase reversal and decrease of the interval velocity at BSR. The field data were processed using Geobit 2.9.5 developed by KIGAM to detect the gas hydrate indicators. The accurate velocity analysis was performed by XVA (X-window based Velocity Analysis). Processing results show that the strong reflector occurred parallel to the sea floor were shown at about 1800 ms two way travel time. The interval velocity decrease at this strong reflector and at the reflection phase reversal corresponding to the reflection at the sea floor. Gas hydrate stability field in the study area was determined using the data of measured hydrate equilibrium condition, hydrothermal gradient and geothermal gradient. The depth of BSR detected in the seismic

  14. Synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early Aptian oceanic anoxic event 1a: Evidence for the release of 13C-depleted carbon into the atmosphere

    Science.gov (United States)

    van Breugel, Yvonne; Schouten, Stefan; Tsikos, Harilaos; Erba, Elisabetta; Price, Gregory D.; Sinninghe Damsté, Jaap S.

    2007-03-01

    A common feature of records of the early Aptian oceanic anoxic event (OAE) 1a is the sharp negative δ13C excursion displayed in both carbonate and organic matter at the onset of this event. A synchronous negative δ13C excursion has also been noted for terrestrial organic matter. This negative excursion has been attributed to either an injection of 13C-depleted light carbon into the atmosphere or, in case of marine sediments, recycling of 13C-depleted CO2. However, most studies were done on separate cores, and no information on the relative timing of the negative spikes in terrestrial versus marine records has been obtained. Here we examine early Aptian core sections from two geographically distal sites (Italy and the mid-Pacific) to elucidate the causes and relative timing of this negative "spike." At both sites, increased organic carbon (Corg) and decreased bulk carbonate contents characterize the interval recording OAE 1a (variously referred to as the "Selli event"). The organic material within the "Selli level" is immature and of autochthonous origin. Measured δ13C values of marine and terrestrial biomarkers largely covary with those of bulk organic carbon, with lowest values recorded at the base of the organic-rich section. By contrast, sediments enveloping the "Selli level" exhibit very low Corg contents, and their extractable Corg is predominantly of allochthonous origin. Hydrous pyrolysis techniques used to obtain an autochthonous, pre-Selli δ13C value for algal-derived pristane from corresponding sample material yielded a negative δ13C shift of up to 4‰. A negative δ13C shift of similar magnitude was also measured for the terrigenous n-alkanes. The results are collectively best explained by means of a massive, syndepositional, rapid input of 13C-depleted carbon into the atmosphere and surface oceans, likely delivered either via methane produced from the dissociation of sedimentary clathrates or perhaps by widespread thermal metamorphism of Corg

  15. Carbon Isotopic Constraints on Arctic Methane Sources, 2008-2010

    Science.gov (United States)

    Fisher, R. E.; Lowry, D.; Lanoiselle, M.; Sriskantharajah, S.; Nisbet, E. G.

    2010-12-01

    Arctic methane source strengths are particularly vulnerable to large changes with year-to year meteorological variations and with climatic change. A global increase in methane seen in 2007 (Dlugokencky et al., 2009) may have been in part be due to elevated wetland emissions caused by a warm, wet summer over large parts of Siberia. In 2010 wildfires over large areas of Russia will have added methane to the Arctic atmosphere. Carbon isotopic composition of methane in air from the Arctic arriving at a measurement station can be used to identify sources of the gas. Measurement of methane δ13C in air close to sources, including wetlands, permafrost, pine forest and submarine methane clathrate has extended the available data of source signatures of methane from northern sources. Keeling plot analysis of diurnal records from field campaigns in Arctic wetlands show that bulk wetland methane emissions are typically close to δ13CCH4 -69±1 ‰. Air samples from Zeppelin (Spitsbergen, Norway), Pallas (Finland) and Barra (Outer Hebrides, Scotland) have been regularly analysed for methane δ13C. Summer campaigns at Zeppelin point to a 13C depleted bulk Arctic source of dominantly biogenic origin, at -67‰. In spring, while the wetlands are still frozen, the source signature is more enriched, -53‰, with trajectory analysis implying a large contribution from onshore gas fields. Arctic methane emissions respond rapidly to warming with strong positive feedbacks. With rapid warming there is the potential to release large stores of carbon from permafrost and methane hydrates. Isotopic data are powerful discriminants of sources. High frequency, ideally continuous, monitoring of methane δ13C from a number of Arctic sites, onshore and offshore, coupled with back-trajectory analysis and regional modelling, will be important if future changes in Arctic source strengths are to be quantified. Reference: Dlugokencky, E. J., et al. (2009), Observational constraints on recent increases

  16. Hydrates in the California Borderlands Revisited: Results from a Controlled-Source Electromagnetic Survey of the Santa Cruz Basin.

    Science.gov (United States)

    Kannberg, P. K.; Constable, S.

    2014-12-01

    Methane hydrate, an ice-like clathrate of water and methane, forms in shallow continental slope sediments, and is both a potential energy source and geologic hazard. Hydrates presence is traditionally inferred from the presence of the bottom simulating reflector (BSR), a seismic velocity inversion resulting from free gas pooling at the base of the hydrate stability field. The BSR is not a measure of hydrate, but rather a proxy for free gas presence. Whereas seismic methods are sensitive to velocity anomalies, controlled-source electromagnetic (CSEM) methods are sensitive to conductivity anomalies. The electrically resistive methane hydrate makes a favorable target for CSEM surveys, which are capable of detecting and potentially quantifying the presence of methane hydrate directly. Building on previous work 100km to the south in the San Nicolas Basin, we present initial results from a 6-day June 2014 survey in the Santa Cruz Basin, located 100km west of Los Angeles. CSEM surveys are performed by deep-towing an EM source that is transmitting a known signal; this signal is detected by towed and seafloor receivers. The initial EM source signal is altered by the electrical properties of the surrounding environment. Conductors such as brine and seawater are attenuating mediums, while resistors such as methane hydrate, gas, and oil are preservative of the original signal. Twenty-one seafloor receivers, as well as a 4 receiver towed array were deployed to image the resistivity structure of the Santa Cruz Basin. Using 30-year-old 2D seismic profiles as a guide, potential hydrate targets were identified, and the transmitter and array were towed over 150 km on 6 lines with 5 seafloor receivers each. The 6 towed lines were coincident with legacy seismic lines. The towed array is sensitive to sediment depths less than 1km, allowing for high data density through the hydrate stability field. The larger transmitter-receiver offsets of the seafloor receivers allow sensitivity to at

  17. Guest Molecule Exchange Kinetics for the 2012 Ignik Sikumi Gas Hydrate Field Trial

    Energy Technology Data Exchange (ETDEWEB)

    White, Mark D.; Lee, Won Suk

    2014-05-14

    A commercially viable technology for producing methane from natural gas hydrate reservoirs remains elusive. Short-term depressurization field tests have demonstrated the potential for producing natural gas via dissociation of the clathrate structure, but the long-term performance of the depressurization technology ultimately requires a heat source to sustain the dissociation. A decade of laboratory experiments and theoretical studies have demonstrated the exchange of pure CO2 and N2-CO2 mixtures with CH4 in sI gas hydrates, yielding critical information about molecular mechanisms, recoveries, and exchange kinetics. Findings indicated the potential for producing natural gas with little to no production of water and rapid exchange kinetics, generating sufficient interest in the guest-molecule exchange technology for a field test. In 2012 the U.S. DOE/NETL, ConocoPhillips Company, and Japan Oil, Gas and Metals National Corporation jointly sponsored the first field trial of injecting a mixture of N2-CO2 into a CH4-hydrate bearing formation beneath the permafrost on the Alaska North Slope. Known as the Ignik Sikumi #1 Gas Hydrate Field Trial, this experiment involved three stages: 1) the injection of a N2-CO2 mixture into a targeted hydrate-bearing layer, 2) a 4-day pressurized soaking period, and 3) a sustained depressurization and fluid production period. Data collected during the three stages of the field trial were made available after an extensive quality check. These data included continuous temperature and pressure logs, injected and recovered fluid compositions and volumes. The Ignik Sikumi #1 data set is extensive, but contains no direct evidence of the guest-molecule exchange process. This investigation is directed at using numerical simulation to provide an interpretation of the collected data. A numerical simulator, STOMP-HYDT-KE, was recently completed that solves conservation equations for energy, water, mobile fluid guest molecules, and hydrate guest

  18. Gas hydrates: past and future geohazard?

    Science.gov (United States)

    Maslin, Mark; Owen, Matthew; Betts, Richard; Day, Simon; Dunkley Jones, Tom; Ridgwell, Andrew

    2010-05-28

    Gas hydrates are ice-like deposits containing a mixture of water and gas; the most common gas is methane. Gas hydrates are stable under high pressures and relatively low temperatures and are found underneath the oceans and in permafrost regions. Estimates range from 500 to 10,000 giga tonnes of carbon (best current estimate 1600-2000 GtC) stored in ocean sediments and 400 GtC in Arctic permafrost. Gas hydrates may pose a serious geohazard in the near future owing to the adverse effects of global warming on the stability of gas hydrate deposits both in ocean sediments and in permafrost. It is still unknown whether future ocean warming could lead to significant methane release, as thermal penetration of marine sediments to the clathrate-gas interface could be slow enough to allow a new equilibrium to occur without any gas escaping. Even if methane gas does escape, it is still unclear how much of this could be oxidized in the overlying ocean. Models of the global inventory of hydrates and trapped methane bubbles suggest that a global 3( degrees )C warming could release between 35 and 940 GtC, which could add up to an additional 0.5( degrees )C to global warming. The destabilization of gas hydrate reserves in permafrost areas is more certain as climate models predict that high-latitude regions will be disproportionately affected by global warming with temperature increases of over 12( degrees )C predicted for much of North America and Northern Asia. Our current estimates of gas hydrate storage in the Arctic region are, however, extremely poor and non-existent for Antarctica. The shrinking of both the Greenland and Antarctic ice sheets in response to regional warming may also lead to destabilization of gas hydrates. As ice sheets shrink, the weight removed allows the coastal region and adjacent continental slope to rise through isostacy. This removal of hydrostatic pressure could destabilize gas hydrates, leading to massive slope failure, and may increase the risk of

  19. Water interactions with hydrophobic groups: Assessment and recalibration of semiempirical molecular orbital methods

    International Nuclear Information System (INIS)

    In this work, we present a study of the ability of different semiempirical methods to describe intermolecular interactions in water solution. In particular, we focus on methods based on the Neglect of Diatomic Differential Overlap approximation. Significant improvements of these methods have been reported in the literature in the past years regarding the description of non-covalent interactions. In particular, a broad range of methodologies has been developed to deal with the properties of hydrogen-bonded systems, with varying degrees of success. In contrast, the interactions between water and a molecule containing hydrophobic groups have been little analyzed. Indeed, by considering the potential energy surfaces obtained using different semiempirical Hamiltonians for the intermolecular interactions of model systems, we found that none of the available methods provides an entirely satisfactory description of both hydrophobic and hydrophilic interactions in water. In addition, a vibrational analysis carried out in a model system for these interactions, a methane clathrate cluster, showed that some recent methods cannot be used to carry out studies of vibrational properties. Following a procedure established in our group [M. I. Bernal-Uruchurtu, M. T. C. Martins-Costa, C. Millot, and M. F. Ruiz-López, J. Comput. Chem. 21, 572 (2000); W. Harb, M. I. Bernal-Uruchurtu, and M. F. Ruiz-López, Theor. Chem. Acc. 112, 204 (2004)], we developed new parameters for the core-core interaction terms based on fitting potential energy curves obtained at the MP2 level for our model system. We investigated the transferability of the new parameters to describe a system, having both hydrophilic and hydrophobic groups, interacting with water. We found that only by introducing two different sets of parameters for hydrophilic and hydrophobic hydrogen atom types we are able to match the features of the ab initio calculated properties. Once this assumption is made, a good agreement with the

  20. Organic synthesis in the outer Solar System: Recent laboratory simulations for Titan, the Jovian planets, Triton and comets

    Science.gov (United States)

    Sagan, C.; Thompson, W. R.; Khare, B. N.; Chyba, C. F.

    1991-01-01

    We tabulate the most abundant gases and their radiation yields, for two experimental pressures: 0.24 mb, more relevant to upper atmosphere excitation, and 17 mb, more relevant to tropospheric, cosmic ray excitation. The yields computed in the 0.24 mb experiment combined with measured electronic fluxes and a simple, eddy diffusion model of Titan's atmosphere predict abundances of detected molecules in agreement with those found by Voyager and for heavier products, in somewhat better agreement with observation than photochemical absolute reaction rate kinetics models. All Voyager organics are accounted for and no detectable products are found that Voyager did not detect. A striking increase of products with multiple bonds is found with decreasing pressure. Hydrocarbon abundances decline slowly with increasing carbon number. Additionally, we list preliminary estimates for the yield of the heteropolymer, which seems to be produced in a quantity comparable (in moles of C+N consumed) to the total amount of gaseous product. The production rate required to sustain Titan's haze against sedimentation also indicates yields of this order. As can be seen from the table, over 10(exp 9) years substantial amounts of these products can accumulate on the surface -- ranging from cm thickness for the (C+N equals 4) species to a meter or more for HCN and C2H2; we also expect a meter or more of tholins. Similar analyses have been or are being done for the Jovian planets and Triton. Charged particle irradiation of hydrocarbon clathrates or mixed hydrocarbon/water ices produces a range of organic products, reddening and darkening of the ices and characteristic infrared spectra. From such spectra, the predicted emission by fine particles in cometary comae well-matches the observed 3.4 micron emission spectra of Comet Halley and other recent comets. Heliocentric evolution of organic emission features in comets is predicted. Organic products of such ice irradiation may account for colors and

  1. Modelling the carbon cycle though Neoproterozoic Earth system changes

    Science.gov (United States)

    Bjerrum, C. J.; Canfield, D. E.

    2011-12-01

    The Neoproterozoic-Cambrian records major changes in geochemical proxies as a result of a profound reorganization of the Earth system. Extensive glaciations and the first oxygenation of the deep ocean with a shift from sulfidic/ferruginous conditions to more oxic conditions was accompanied by the radiation of the first animals. The reorganization was also recorded in enigmatic large-amplitude fluctuations in the isotopic composition of marine carbonate carbon (δ13CIC ), were only some are associated with major known glaciations. The carbon isotope events seem to grow in amplitude through the Neoproterozoic culminating in the Shuram anomaly - the largest in Earth history. The δ13CIC events are also accompanied by changes in the isotope composition of marine organic carbon (δ13COC), where the co-variation of δ13CIC and δ13COC seems to evolve from markedly positive relationship over a subdued δ13COC variation and an almost inverse pattern. There is limited understanding as to why or how the structure of these isotope events evolved over time and how these events may tie to the reorganization of the Earth system. We use our published quantitative model of the Shuram anomaly to explore carbon cycle dynamics during the Neoproterozoic. By changing in pre-event atmosphere-ocean chemistry we explore which factors contribute to the observed patterns of the large Neoproterozoic carbon isotope events. In particular, decreasing atmospheric CO2 and a slight increase of oxygen together with an increasing CO source from rising DOC concentrations results in progressively larger event amplitudes with changing co-variation between δ13CIC and δ13COC , culminating with the structure observed for the Shurum-Wonaka anomaly in the Ediacaran. In our model, the carbon isotope excursions were driven by methane from sediment-hosted clathrate hydrate deposits. Being a powerful greenhouse gas, methane increased temperature and melted icecaps. These combined to produce a negative 18O

  2. Constraining the cause of the end-Guadalupian extinction with coupled records of carbon and calcium isotopes

    Science.gov (United States)

    Jost, A. B.; Mundil, R.; He, B.; Brown, S. T.; Altiner, D.; Sun, Y.; DePaolo, D. J.; Payne, J.

    2013-12-01

    A negative δ13C excursion in carbonate sediments from Guadalupian (Middle Permian) and Lopingian (Late Permian) stratigraphic sections has been interpreted to result from a large carbon cycle disturbance during end-Guadalupian extinction event (ca. 260 Ma). However, the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbations to the global carbon cycle. The carbon and calcium cycles are coupled via CaCO3 burial, so changes in calcium isotopes can be used to constrain the cause of a carbon isotope excursion. In this study, we present coupled carbon and calcium isotope records from three Guadalupian-Lopingian (G/L) sections in China and Turkey. Isotope records among our studied sections are inconsistent in both their δ13C and δ44/40Ca records. Similar inconsistencies in δ13C among sections occur across previously published datasets. Sections with large (>3‰) changes in δ13C either show evidence for diagenetic alteration or do not show δ13C and δ44/40Ca changes consistent with severe volcanic degassing from Emeishan or methane clathrate destabilization. We conclude that the large isotopic changes are more likely the result of local burial conditions or diagenetic effects, rather than a large carbon cycle disturbance. Perturbations to the global carbon and calcium cycles appear to have been much smaller across the G/L transition than across the subsequent Permian-Triassic boundary. This finding is consistent with recent paleobiological data showing that the end-Guadalupian extinction was much less severe than previously believed, and was indistinguishable in magnitude from background intervals. However, selective extinction of marine animals with passive respiratory physiology indicates that the G/L extinction cannot simply be due to background extinction or sampling failure, and that it was triggered by some environmental event. Therefore, any environmental event must have been small enough to not generate large

  3. Ocean storage, including costs and risks

    International Nuclear Information System (INIS)

    The long-term effectiveness of ocean storage will have to be based on theoretical understanding and models as there is no way to perform experiments on the required time and space scales for outgassing estimation. Based on observations of tracer behavior, the ventilation time of deep water has been revealed. Calibrated and constrained by these results, most of the OGCMs tell us that CO2 injected into the thermohaline circulation would not come back to the atmosphere in more than several hundred years. There are two types of concepts of ocean storage: one is a lake type concept to keep the CO2 at the ocean floor or a depression site as long as possible, and the other is to inject CO2 into the deep waters so that it is dispersed as quickly as possible. The technological concepts so far for implementation with minimum environmental impacts are much elaborated based on laboratory and computer experiments incorporating the key understanding of the CO2 clathrate properties attained in this decade. The frequently addressed concern of this technology includes the ecological modification of the ocean system. But even in the business-as-usual release of CO2 into the atmosphere, some modification might be foreseen in the deep ocean environment and could be inevitable not caused by the climate change but by the direct influence of the increase in the CO2 concentration in deep waters in future. We cannot stop the CO2 invasion into the deep ocean due to the existing of the excess CO2 in the atmosphere. Whichever release method is used, carbon dioxide we are releasing to the atmosphere now will find its way into the deep oceans. Hence, the right scientific question is whether there exist additional risks to the deep sea environment associated with this technology. If we accept the target of a stabilization level of the atmospheric concentration of CO2, our generation's commitment to the CO2 futures anyway extends to the modification of the deep sea environment induced by the

  4. Constraining the cause of the end-Guadalupian extinction with coupled records of carbon and calcium isotopes

    Science.gov (United States)

    Jost, Adam B.; Mundil, Roland; He, Bin; Brown, Shaun T.; Altiner, Demir; Sun, Yadong; DePaolo, Donald J.; Payne, Jonathan L.

    2014-06-01

    A negative δC13 excursion in carbonate sediments near the Guadalupian/Lopingian (Middle/Late Permian) boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end-Guadalupian extinction event (ca. 260 Ma). However, the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle. Calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via CaCO3 burial. In this study, we present coupled carbon and calcium isotope records from three Guadalupian-Lopingian (G/L) sections in China (Penglaitan and Chaotian) and Turkey (Köserelik Tepe). The δC13 and δCa44/40 records differ among our studied sections and do not co-vary in the same manner. No section shows δC13 and δCa44/40 changes consistent with massive, rapid volcanic CO2 emissions or methane clathrate destabilization. Additionally, many sections with large (>3‰) changes in δC13 exhibit δO18 evidence for diagenetic alteration. Only one section exhibits a large excursion in the δCa44/40 of limestone but the absence of a similar excursion in the δCa44/40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle. Hence, we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects, rather than from a large carbon and calcium cycle disturbance. Perturbations to the global carbon and calcium cycles across the G/L transition were much less intense than the disturbances that occurred across the subsequent Permian-Triassic boundary. This finding is consistent with the much smaller magnitude of the end-Guadalupian extinction relative to the end-Permian.

  5. Martian Polar Caps: Folding, Faulting, Flowing Glaciers of Multiple Interbedded Ices

    Science.gov (United States)

    Kargel, J. S.

    2001-12-01

    The Martian south polar cap (permanent CO2 cap and polar layered deposits), exhibit abundant, varied, and widespread deformational phenomena. Folding and boudinage are very common. Strike-slip or normal faults are rarer. Common in the vicinity of major troughs and scarps are signs of convergent flow tectonics manifested as wrinkle-ridge-like surface folds, thrust faults, and viscous forebulges with thin-skinned extensional crevasses and wrinkle-ridge folds. Such flow convergence is predicted by theory. Boudinage and folding at the 300-m wavelength scale, indicating rheologically contrasting materials, is widely exposed at deep levels along erosional scarps. Independent morphologic evidence indicates south polar materials of contrasting volatility. Hence, the south polar cap appears to be a multiphase structure of interbedded ices. The north polar cap locally also exhibits flow indicators, though they are neither as common nor as varied as in the south. The large-scale quasi-spiral structure of the polar caps could be a manifestation of large-scale boudinage. According to this scenario, deep-level boudinage continuously originates under the glacial divide (the polar cap summit). Rod-like boudin structures are oriented transverse to flow and migrate outward with the large-scale flow field. Troughs develop over areas between major boudins. A dynamic competition, and possibly a rough balance, develops between the local flow field in the vicinity of a trough (which tends to close the trough by lateral closure and upwelling flow) and sublimation erosion (which tends to widen and deepen them). Over time, the troughs flow to the margins of the polar cap where they, along with other polar structures, are destroyed by sublimation. Major ice types contributing to rheological and volatility layering may include, in order of highest to lowest mechanical strength, CO2 clathrate hydrate, water ice containing inert/insoluble dust, pure water ice, water ice containing traces of

  6. Magnetofossils as tracers of oxygenation change: a case study from the stratified Pettaquamscutt River Estuary

    Science.gov (United States)

    Chen, A. P.; Berounsky, V. M.; Chan, M. K.; Moskowitz, B. M.; Andrade Lima, E.; Kopp, R. E.; Cady, C.; Weiss, B. P.; Hesse, P. P.

    2013-12-01

    Magnetotactic bacteria (MB) are motile organisms commonly found around the oxic-anoxic-interface (OAI) in sediments and stratified water columns. Magnetite and greigite crystals synthesized by MB intracellularly, termed magnetosomes, can be preserved in sediments as magnetofossils. Changes in OAI thickness (due to changes in temperature, clathrate dissociation & methane oxidation, organic carbon supply/oxidation, or sedimentation rate) would produce proportional changes in MB population and sedimentary magnetofossil concentration. While potentially useful as an oxygenation proxy, magnetofossil quantification techniques and variables controlling their preservation in sediments need to be better understood. Most prior work focused on cultured magnetite-MB and sediment mixtures while studies of greigite-MB (found just below the OAI in the sulfidic hypolimnion) is lacking because axenic cultures do not exist. To address these issues, we study wild magnetite- and greigite-MB from the seasonally stratified Pettaquamscutt River Estuary Upper Basin (RI, USA) as a function of water depth, d. Transmission electron microscope imaging of 21 MB (377 magnetosomes) revealed a complexity in wild MB not found in cultures. From d=3.9 m-7.0 m, live-cell assays confirmed the presence of multiple MB morphotypes, both north- (majority) and south-seeking (minority), and a few magnetic protists. Based on a previous microscopy study just 1.4 km south of Upper Basin (Bazylinski et al., 1995), magnetite-MB are expected for dgreigite-MB for 5.0 mgreigite-MB for d>6.0 m. Coercivity distributions for all depths are characterized by a small variance, reflecting uniformity in magnetosome size. Interestingly, despite changing from dominant magnetite to greigite-MB with increasing depth, the median coercivity remained largely unchanged. Median coercivity is therefore not diagnostic of magnetosome mineralogy. We also report ferromagnetic resonance spectroscopy (FMR) results. The first derivative of

  7. H{sub 2} storage in microporous materials: a comparison between zeolites and Mos

    Energy Technology Data Exchange (ETDEWEB)

    Ricchiardi, G.; Regli, L.; Vitillo, J. G.; Cocina, D.; Bordiga, S.; Lamberti, C.; Spoto, G.; Zecchina, A.; Bjorgen, M.; Lillerud, K. P.

    2005-07-01

    One of the main concerns about a hydrogen-based energy economy is the efficient storage and transport of this highly flammable gas. Many strategies have been followed or suggested in recent years to solve this problem. The most important ones are: 1) storage in metals and alloys; 2) storage in complex hydrides (alanates, borides); 3) storage by trapping in clathrates (ice and others); 4) storage in microporous materials (carbons, zeolitic materials, metal-organic frameworks, polymers). [1, 2] In this work we have focused our attention on microporous materials, where the crucial point is the strength of the interaction between the molecular hydrogen and the internal surfaces of micropores and/ or of cages of entrapping materials. It is known from fundamental studies that H2 strongly interacts with ions in the gas but that the presence of counterions decreases the interaction energy substantially. The most prominent class of microporous materials, which contains isolated and exposed cations, are zeolites and zeotypes: ideal systems to investigate the interaction of H2 with both dispersive and electrostatic forces [3]. So, even if they are not sufficiently light to represent the final solution to H2 storage, the availability of a large variety of frameworks and chemical compositions combined with low cost and superior mechanical and thermal stabilities increases the interest in these materials. In this work we have studied in detail, by means of volumetric and spectroscopic measurements, zeolites with CHA topology (as they are characterized by a strong acidity and by a big surface area). H-SSZ-13 zeolite, characterized by a low Al content (Si/Al = 11), has shown the best properties in hydrogen storage in respect to all the other zeolites and zeotypes with different compositions and topologies [4]. The results have been compared with those obtained for MOF-5 [5], a well known Metal-Organic Framework, indicated as a very good material for molecular hydrogen storage [6

  8. Pressure laboratories for parameter controlled experimentation of deep sea environments

    Science.gov (United States)

    Steffen, H.; Holscher, B.; Gust, G.; Thomsen, L.

    2003-04-01

    the measurement of pressure effects on bacterial respiration rates and the trapping and observation of deep sea zooplankton. Gas hydrate related experiments address the decomposition of core sampled natural clathrates as well as growth and dissolution of artificial, homogenous gas hydrates under varying environmental parameters such as pressure, temperature and boundary layer stress (see Drews et al.). Drews, M. et al.: Simulating the dissolution of gas hydrates at the deep sea floor in the pressure chamber under controlled P/T and shear stress conditions, this volume.

  9. Pcw/phemos for Arctic Weather, Climate and Air Quality: a Quasi-Geostationary View of the Arctic and Environs

    Science.gov (United States)

    McConnell, J. C.; O'Neill, N. T.; McElroy, C. T.; Solheim, B.; Buijs, H.; Rahnama, P.; Walker, K. A.; Martin, R. V.; Sioris, C.; Garand, L.; Trichtchenko, A.; Nassar, R.

    2011-12-01

    abundance data on methane and possibly CO2 to assess perturbations due to their increasing release from the permafrost and from shallowly buried clathrates. We will outline the scientific objectives and the status of the current instrument design and challenges.

  10. Polyclusters and Substitution Effects in the Na–Au–Ga System: Remarkable Sodium Bonding Characteristics in Polar Intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Smetana, Volodymyr [Ames Laboratory; Miller, Gordon J. [Ames Laboratory; Corbett, John D. [Ames Laboratory

    2013-10-18

    A systematic exploration of Na- and Au-poor parts of the Na–Au–Ga system (less than 15 at. % Na or Au) uncovered several compounds with novel structural features that are unusual for the rest of the system. Four ternary compounds Na1.00(3)Au0.18Ga1.82(1) (I), NaAu2Ga4 (II), Na5Au10Ga16 (III), and NaAu4Ga2 (IV) have been synthesized and structurally characterized by single crystal X-ray diffraction: Na1.00(3)Au0.18Ga1.82(1)(I, P6/mmm, a = 15.181(2), c =9.129(2)Å, Z = 30); NaAu2Ga4 (II, Pnma, a = 16.733(3), b = 4.3330(9), c =7.358(3) Å, Z = 4); Na5Au10Ga16 (III, P63/m, a = 10.754(2), c =11.457(2) Å, Z = 2); and NaAu4Ga2 (IV, P21/c, a = 8.292(2), b = 7.361(1), c =9.220(2)Å, β = 116.15(3), Z = 4). Compound I lies between the large family of Bergman-related compounds and Na-poor Zintl-type compounds and exhibits a clathrate-like structure containing icosahedral clusters similar to those in cubic 1/1 approximants, as well as tunnels with highly disordered cation positions and fused Na-centered clusters. Structures II, III, and IV are built of polyanionic networks and clusters that generate novel tunnels in each that contain isolated, ordered Na atoms. Tight-binding electronic structure calculations using linear muffin-tin-orbital (LMTO) methods on II, III, IV and an idealized model of I show that all are metallic with evident pseudogaps at the Fermi levels. The integrated crystal orbital Hamilton populations for II–IV are typically dominated by Au–Ga, Ga–Ga, and Au–Au bonding, although Na–Au and Na–Ga contributions are also significant. Sodium’s involvement into such covalency is consistent with that recently reported in Na–Au–M (M = Ga, Ge, Sn, Zn, and Cd) phases.

  11. Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63}: The diversity of pseudo 5-fold symmetries in the Na–Au–Ga system

    Energy Technology Data Exchange (ETDEWEB)

    Smetana, Volodymyr; Corbett, John D., E-mail: jcorbett@iastate.edu; Miller, Gordon J.

    2013-11-15

    The Na-rich part (∼30% Na) of the Na–Au–Ga system between NaAu{sub 2}, NaGa{sub 4}, and Na{sub 22}Ga{sub 39} has been found to contain the ternary phases Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} (I) and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} (II), according to the results of single crystal X-ray diffraction measurements. I is orthorhombic, Cmcm, a=5.3040(1), b=24.519(5), c=14.573(3) Å, and contains a network of clusters with local 5-fold symmetry along the a-axis. Such clusters are frequent building units in decagonal quasicrystals and their approximants. II is rhombohedral, R3{sup ¯}m, a=16.325(2), c=35.242(7) Å, and contains building blocks that are structurally identical to the Bergman-type clusters as well as fused icosahedral units known with active metals, triels and late transition elements. II also contains a polycationic network with elements of the clathrate V type structure. Tight-binding electronic structure calculations using linear muffin–tin-orbital (LMTO) methods on idealized models of I and II indicate that both compounds are metallic with evident pseudogaps at the corresponding Fermi levels. The overall Hamilton bond populations are generally dominated by Au–Ga and Au–Au bonds in I and by Ga–Ga bonds in II; moreover, the Na–Au and Na–Ga contributions in I are unexpectedly large, ∼20% of the total. A similar involvement of sodium in covalent bonding has also been found in the electron-richer i-Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal approximant. - Graphical abstract: Multiply-endohedral Bergman-related clusters in the structure of Na{sub 17}Au{sub 5.9(1)}Ga{sub 46.6.} Display Omitted - Highlights: • Two new compounds with the local 5-fold symmetry have been investigated. • Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} is an orthorhombic approximant of the Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal. • Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} represents a rhombohedral distortion of the Bergman-type phases.

  12. Liquid Carbon Dioxide Venting at the Champagne Hydrothermal Site, NW Eifuku Volcano, Mariana Arc

    Science.gov (United States)

    Lupton, J.; Lilley, M.; Butterfield, D.; Evans, L.; Embley, R.; Olson, E.; Proskurowski, G.; Resing, J.; Roe, K.; Greene, R.; Lebon, G.

    2004-12-01

    In March/April 2004, submersible dives with the remotely-operated vehicle ROPOS discovered an unusual CO2-rich hydrothermal system near the summit of NW Eifuku, a submarine volcano located at 21.49° N, 144.04° E in the northern Mariana Arc. Although several sites of hydrothermal discharge were located on NW Eifuku, the most intense venting was found at 1600-m depth at the Champagne site, slightly west of the volcano summit. The Champagne site was found to be discharging two distinct fluids into the ocean: a) several small white chimneys were emitting milky 103° C gas-rich hydrothermal fluid with at least millimolar levels of H2S and b) cold (grapes. The film coating the droplets was assumed to be CO2 hydrate (or clathrate) which is known to form whenever liquid CO2 contacts water under these P,T conditions. Samples of the 103° C hydrothermal fluids were collected in special gas-tight titanium sampling bottles that were able to withstand the high internal pressures created by the dissolved gases. The Champagne hydrothermal fluids contained a surprising 2.3 moles/kg of CO2, an order of magnitude higher than any CO2 values previously reported for submarine hydrothermal fluids. The overall gas composition was 87% CO2, yielded δ 13C = -1.75 ‰ , much heavier than the -6.0 ‰ typical for carbon in MOR vent fluids. The C/3He ratio was ~2.2 x 1010, an order of magnitude higher than the average value of 2 x 109 found in MOR vent fluids. The δ 13C and C/3He values suggest a substantial contribution to the carbon from subducted carbonates rather than mantle carbon. The Champagne site is only the second locality where liquid CO2 has been observed venting into the deep sea (the other reported location is in the Okinawa Trough, see Sakai et al., 1990). Because of the presence of liquid CO2 in proximity to hydrothermal organisms, the Champagne site may prove to be a valuable natural laboratory for studying the effects of high CO2 concentrations on marine ecosystems.

  13. Hydro-geochemical and isotopic fluid evolution of the Los Azufres geothermal field, Central Mexico

    International Nuclear Information System (INIS)

    Hydrothermal alteration at Los Azufres geothermal field is mostly propylitic with a progressive dehydration with depth and temperature increase. Argillic and advanced argillic zones overlie the propylitic zone owing to the activity of gases in the system. The deepest fluid inclusions (proto-fluid) are liquid-rich with low salinity, with NaCl dominant fluid type and ice melting temperatures (Tmi) near zero (0 deg C), and salinities of 0.8 wt% NaCl equivalent. The homogenization temperature (Th) = 325 ± 5 deg C. The boiling zone shows Th = ±300 deg C and apparent salinities between 1 and 4.9 wt% NaCl equivalent, implying a vaporization process and a very important participation of non-condensable gases (NCGs), mostly CO2. Positive clathrate melting temperatures (fusion) with Th = 150 deg C are observed in the upper part of the geothermal reservoir (from 0 to 700 m depth). These could well be the evidence of a high gas concentration. The current water produced at the geothermal wells is NaCl rich (geothermal brine) and is fully equilibrated with the host rock at temperatures between T = 300 and 340 deg C. The hot spring waters are acid-sulfate, indicating that they are derived from meteoric water heated by geothermal steam. The NCGs related to the steam dominant zone are composed mostly of CO2 (80-98% of all the gases). The gases represent between 2 and 9 wt% of the total mass of the fluid of the reservoir. The authors interpret the evolution of this system as deep liquid water boiling when ascending through fractures connected to the surface. Boiling is caused by a drop of pressure, which favors an increase in the steam phase within the brine ascending towards the surface. During this ascent, the fluid becomes steam-dominant in the shallowest zone, and mixes with meteoric water in perched aquifers. Stable isotope compositions (δ18O-δD) of the geothermal brine indicate mixing between meteoric water and a minor magmatic component. The enrichment in δ18O is due to

  14. 盐湖丰产元素与Zintl化合物(续完)%The Correlation of Abundant Elements and Zintl Phases

    Institute of Scientific and Technical Information of China (English)

    贾永忠; 景燕; 马军; 岳都元; Claude Belin; Monique Tillard

    2011-01-01

    Zintl化合物是以Edward Zintl命名的化合物,是一类由电正性的碱金属或碱土金属与电负性的13族或14族元素形成的特殊金属间化合物.其价键模式可以是离子键、金属键和共价键共存,其中的准金属可以共价键的形式形成各种形式的离子簇,因而其结构复杂多样.这类化合物的部分阴离子簇不仅具有稳定的笼状、层状和链状结构,并且具有特殊的光、电、磁等性能,使得在半导体、催化、电极材料等方面都有应用的前景和发展潜力.介绍了几个特殊Zintl化合物体系,盐湖丰产元素在Zinfi化合物中的作用,指出了含有盐湖丰产元素的Zintl化合物的应用前景和方向.%The term Zintl phase has been coined in honour of Edward Zintl,a German chemist. Zintl phases are formed by combinations of moderately electronegative post-transition elements, such as main group 13 and 14 elements with electropositive alkaline or alkaline-earth metals. In these combinations, owing to electron transfers ( total or partial) from the electropositive to the electronegative elements, anionic frameworks are formed in solid state that range from isolated anionic clusters, rings. cages and 1,2 or 3-D extended structures of which clathrates are among the most remarkable.The authors discuss the correlation of salt lake resources and Zintl phases. The potential applications of Zintl phases in salt lake resources are briefly discussed. This strategy for the synthesis of solid state compounds, which comprised light elements of salt lake resources, main group 13 and 14 elements and transition metal, have unique magnetic, electronic, thermoelectric, colossal magnetoresistance and ferromagnetic properties.

  15. 天然气水合物形成与生长影响因素综述%Review of influence factors of natural gas hydrate formation and growth

    Institute of Scientific and Technical Information of China (English)

    丁麟; 史博会; 吕晓方; 柳扬; 宫敬

    2016-01-01

    Natural gas hydrate is a kind of complex clathrate crystal formed by water and natural gas molecules,which has an important significance for research and utilization in industries of oil/gas pipeline transportation,natural gas storage and refrigeration. While the formation and growth of natural gas hydrate is a complex process involving multi-components and multistages,and the influence of different factors on hydrate formation and growth still needs to be understood. This paper introduces the physical process of natural gas formation and three hypotheses of natural gas nucleation. Then,the influences of substrate amphipathy,additives,porous media environment and impurities,liquid composition,temperature,pressure and flow conditions on hydrate formation and growth are discussed. At last,this paper points out that quantification of inhibition of hydrate caused by different crude oil compositions,influence of wax on mass transfer and heat transfer during hydrate growth,and a microscopic mechanism of kinetic hydrate inhibition should be further studied in the future.%天然气水合物(NGH)是水分子和天然气分子形成的一种复杂的笼型晶体,其在油气管道输送、天然气储存和制冷等行业中都具有重要的研究意义和利用价值,但天然气水合物的形成是一个多组分、多阶段的复杂过程,不同因素对于天然气水合物形成和生长的影响尚有待明确。本文介绍了天然气水合物形成的物理过程以及水合物成核的3种机理假说;详细梳理了基质两亲性、添加剂、多孔介质环境和杂质、液体组成、温度压力以及流动条件等因素对于天然气水合物形成和生长的影响,并对其作了简要分析。同时指出,原油组成对于水合物抑制效果的定量化、蜡晶结构对于水合物形成过程中传质和传热的影响以及微观化的动力学抑制剂抑制机理等都是水合物相关研究中需要进一步深入探究和明确的问题。

  16. Storage of Nitrogen in the Cyclosilicates Beryl and Cordierite: Nitrogen Cycling, Isotope Fractionation, and Fluid-Rock Interactions

    Science.gov (United States)

    Lazzeri, K. E.; Bebout, G. E.; Idleman, B. D.; Geiger, C. A.; Li, L.

    2011-12-01

    granulite-facies metasedimentary migmatites at Mt. Stafford, Australia, contain up to 350 ppm N with δ15N similar to that of the whole-rocks. Ongoing work is also being directed at analyzing a suite of pure cordierite separates from different petrologic enviironments, for which Geiger et al. (in revision for GCA) conducted degassing experiments and noted the presence of N2. In a related study, we are examining the N concentrations and isotopic compositions of silicate phases crystalized in various low-T hydrothermal settings. Some low-temperature silicates, such as zeolites and melanophlogite (silica clathrate), as well as palagonitized volcanic glasses, can preserve records of low-temperature biogeochemical processes on Earth and potentially on early Mars as well (Bebout et al., 2011, abstract LPSC).

  17. The science of the lunar poles

    Science.gov (United States)

    Lucey, P. G.

    2011-12-01

    It was the great geochemist Harold Urey who first called attention to peculiar conditions at the poles of the Moon where the very small inclination of the lunar spin axis with respect to the sun causes craters and other depressions to be permanently shaded from sunlight allowing very low temperatures. Urey suggested that the expected low temperature surfaces could cold trap and collect any vapors that might transiently pass through the lunar environment. Urey's notion has led to studies of the poles as a new research area in lunar science. The conditions and science of the poles are utterly unlike those of the familiar Moon of Neil Armstrong, and the study of the poles is similar to our understanding of the Moon itself at the dawn of the space age, with possibilities outweighing current understanding. Broadly, we can treat the poles as a dynamic system of input, transport, trapping, and loss. Volatile sources range from continuous, including solar wind, the Earth's polar fountain and micrometeorites, to episodic, including comets and wet asteroids, to nearly unique events including late lunar outgassing and passage through giant molecular clouds. The lunar exosphere transports volatiles to the poles, complicated by major perturbances to the atmosphere by volatile-rich sources. Trapping includes cold trapping, but also in situ creation of more refractory species such as organics, clathrates and water-bearing minerals, as well as sequester by regolith overturn or burial by larger impacts. Finally, volatiles are lost to space by ionization and sweeping. Spacecraft results have greatly added to the understanding of the polar system. Temperatures have been precisely measured by LRO, and thermal models now allow determination of temperature over the long evolution of the lunar orbit, and show very significant changes in temperature and temperature distribution with time and depth. Polar topography is revealed in detail by Selene and LRO laser altimeters while direct

  18. Impact of Atmosphere-sea Exchange on the Isotopic Expression of Carbon Excursions: Observations and Modeling of OAE-1a

    Science.gov (United States)

    Finkelstein, D. B.; Pratt, L. M.; Brassell, S. C.; Montañez, I. P.

    2005-12-01

    Negative carbon isotope excursions are a recurring phenomenon in earth history (e.g., Permo-Triassic boundary, Jurassic and Cretaceous oceanic anoxic events, and the Paleocene-Eocene Thermal Maximum) variously attributed to destabilization of methane clathrates, a decrease in primary productivity, intensified volcanism, and more recently to widespread peat fires. Each forcing mechanism invoked accounts for both the magnitude of the negative isotopic shift and the reservoir required to drive the shift as observed at one to several locales. Studies rarely consider the effect of latitudinal temperature changes on the excursion. Here, we explore the early Aptian oceanic anoxic event as an example of a negative isotopic shift whose magnitude varies with paleolatitude in terrestrial settings. It increases (from -2.0 to -8.2 ‰) with paleolatitude (5° to 33°N) and is greater than that expected for changes in plant C isotope discrimination driven by environmental stresses (~3 ‰). Conceptually, an isotopic shift of terrestrial vegetation across paleolatitudes represents a response to its forcing mechanism and temperature. A closed system carbon cycle model constructed of five reservoirs (atmosphere, vegetation, soil, and shallow and deep oceans), and five fluxes (productivity, respiration, litter fall, atmosphere-ocean exchange, and surface-deep ocean exchange) was employed is assessment of a negative isotopic shift at 2x pre-industrial atmospheric levels (P.A.L.) for pCO2 keeping all variables constant with the exception of temperature. The model was run at 5°C increments from 5° to 40°C to simulate the effect of temperature gradients on isotopic shifts at variable latitudes, with the appropriate temperature dependent fractionations for atmosphere - sea exchange. The magnitude of the negative isotopic shift at each temperature was calculated for both terrestrial and marine organic matter. In terrestrial vegetation it changed from -4 to -5.8 ‰ with decreasing

  19. Natural Gas Hydrates as CH4 Source and CO2 Sink - What do SO2 Impurities do?

    Science.gov (United States)

    Beeskow-Strauch, B.; Schicks, J. M.; Spangenberg, E.; Erzinger, J.

    2009-04-01

    The large amounts of gas hydrates stored in natural reservoirs are thought to be a promising future energy source. The recently discussed idea of methane extraction from these formations, together with the subsequent storage of CO2 in form of gas hydrates is an elegant approach to bring forward. A number of experiments have been performed on lab scale showing the replacement of CH4 by CO2 and vice versa. For instance, Graue and Kvamme (2006) demonstrated with Magnetic Resonance Images of core plug experiments the possibility of CH4 extraction by using liquid CO2. Laser Raman investigations of Schicks et al. (2007) showed, on the other hand, the ineffectiveness and slowness of the CH4 exchange reaction with gaseous CO2. After 120 hours, only 20% CH4 were exchanged for CO2. Natural methane hydrates which include often higher hydrocarbons tend to be even more stable than pure methane hydrates (Schicks et al., 2006). Contrary to lab conditions, industrial emitted CO2 contains - despite much effort to clean it - traces of impurities. For instance, CO2 emitted from the state-of-the-art Vattenfall Oxyfuel pilot plant in Schwarze Pumpe should reach a quality of >99.7% CO2 but still contains small amounts of N2, Ar, O2, SOx and NOx (pers. comm. Dr. Rolland). Here we present a microscopic and laser Raman study in a p-T range of 1 to 4 MPa and 271 to 280K focussing on CO2 hydrate formation and CH4-exchange reaction in the presence of 1% SO2. The experiments have been performed in a small-scale cryocell. The Raman spectra show that CO2 and SO2 occupy both large and small cages of the hydrate lattice. SO2 occurs strongly enriched in the hydrate clathrate, compared to its concentration in the feed gas which causes a strong acidification of the liquid phase after hydrate dissociation. Our study reveals that the hydrate formation rate from impure CO2 is similar to that of pure CO2 hydrate but that the stability of the CO2-SO2-hydrate exceeds that of pure CO2 hydrate. The improved

  20. Study on the stability of anthocyanin in purple sweet potato beverage%紫甘薯饮料中花青素的稳定性研究

    Institute of Scientific and Technical Information of China (English)

    孙鹏尧; 周芳宁; 李喜层; 曹燕华; 袁素辉; 牟德华

    2014-01-01

    The spectrum characteristics of anthocyanins in purple sweet potato beverage with different pH was analyzed, besides, the effect of pH, temperature, Vc, sugar, and light on the stability of anthocyanin from purple sweet potato beverage were studied. The results showed that the anthocyanins had better stability at the pH of 2.2, 3.0, 4.0. The stability gradually decreased along with the pH increased. High temperature had obvious effect on the stability of purple sweet potato antho-cyanins and the higher the temperature was, the lower retention of anthocyanin had. Vc could accelerate the degradation of anthocyanins. Glucose and lactose had no effect on the stability of anthocyanins. Clathrate which formed of Fe3+and antho-cyan might reduce the stability of anthocyanins, however, other metal ions had no influence almost. The stability of antho-cyanins decreased under the light. Natural light had no obvious impact in a short period of time. Incandescent light and ul-traviolet lamp could speed up decomposition of anthocyanin.%研究了不同pH值紫甘薯饮料中花青素的色泽光谱特性以及pH值、温度、抗坏血酸、糖、光照等因素对紫甘薯饮料中花青素稳定性的影响。结果表明, pH值为2.2、3.0、4.0时花青素较稳定,随着pH值的升高,稳定性逐渐降低;高温处理对紫甘薯花青素的稳定性的影响较显著,温度越高,花青素的保留率越低;抗坏血酸的加入会加速花色苷的降解;葡萄糖和乳糖的加入对花色苷的稳定性无影响; Fe3+与花青素类物质形成络合物,降低了花青素的稳定性,其他的金属离子对花色苷的稳定性影响不大;光照使花青素稳定性降低,自然光在短时间内影响较小,花色苷在白炽灯和紫外灯照射下降解速度加快。

  1. Hydrate pingoes at Nyegga - natural small-scale carbon capture laboratories?

    Science.gov (United States)

    Hovland, M. T.; Rueslaatten, H.

    2009-12-01

    methane clathrates into CO2 hydrates by segregation. A ‘Chinese hat’ (steel cone) could for example be put over one of the most accessible pingoes, to collect fluids emitting from it. After a year or so of fluid type and flux monitoring, the next research step could for example be to inject a known volume of CO2 into the base of the pingo and monitor what happens to the flux and fluid type emitting from it. Such pioneering experiments will call for a high degree of international cooperation and probably also the involvement of industry partners, especially with respect to offshore multi-purpose vessel support. References Hovland, M., Svensen, H., 2006. Marine Geology 228, 15-23 Ivanov et al., 2007. EOS 88 (19), 209, 212 Westbrook et al., 2008. ICGH Conf. Proc., Vancouver, July 6-10

  2. Global Assessment of Methane Gas Hydrates: Outreach for the public and policy makers

    Science.gov (United States)

    Beaudoin, Yannick

    2010-05-01

    The United Nations Environment Programme (UNEP), via its official collaborating center in Norway, GRID-Arendal, is in the process of implementing a Global Assessment of Methane Gas Hydrates. Global reservoirs of methane gas have long been the topic of scientific discussion both in the realm of environmental issues such as natural forces of climate change and as a potential energy resource for economic development. Of particular interest are the volumes of methane locked away in frozen molecules known as clathrates or hydrates. Our rapidly evolving scientific knowledge and technological development related to methane hydrates makes these formations increasingly prospective to economic development. In addition, global demand for energy continues, and will continue to outpace supply for the foreseeable future, resulting in pressure to expand development activities, with associated concerns about environmental and social impacts. Understanding the intricate links between methane hydrates and 1) natural and anthropogenic contributions to climate change, 2) their role in the carbon cycle (e.g. ocean chemistry) and 3) the environmental and socio-economic impacts of extraction, are key factors in making good decisions that promote sustainable development. As policy makers, environmental organizations and private sector interests seek to forward their respective agendas which tend to be weighted towards applied research, there is a clear and imminent need for a an authoritative source of accessible information on various topics related to methane gas hydrates. The 2008 United Nations Environment Programme Annual Report highlighted methane from the Arctic as an emerging challenge with respect to climate change and other environmental issues. Building upon this foundation, UNEP/GRID-Arendal, in conjunction with experts from national hydrates research groups from Canada, the US, Japan, Germany, Norway, India and Korea, aims to provide a multi-thematic overview of the key

  3. IN-SITU SAMPLING AND CHARACTERIZATION OF NATURALLY OCCURRING MARINE METHANE HYDRATE USING THE D/V JOIDES RESOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Frank R. Rack; Tim Francis; Peter Schultheiss; Philip E. Long; Barry M. Freifeld

    2005-04-01

    The primary activities accomplished during this quarter were continued efforts to develop plans for Phase 2 of this cooperative agreement based on the evolving operational planning for IODP Expedition 311, which will use the JOIDES Resolution to study marine methane hydrates along the Cascadia margin, offshore Vancouver Island. IODP Expedition 311 has been designed to further constrain the models for the formation of marine gas hydrate in subduction zone accretionary prisms. The objectives include characterizing the deep origin of the methane, its upward transport, its incorporation in gas hydrate, and its subsequent loss to the seafloor. The main attention of this expedition is on the widespread seafloor-parallel layer of dispersed gas hydrate located just above the base of the predicted stability field. In a gas hydrate formation model, methane is carried upward through regional sediment or small-scale fracture permeability, driven by the tectonic consolidation of the accretionary prism. The upward moving methane is incorporated into the gas hydrate clathrate as it enters the methane hydrate stability zone. Also important is the focusing of a portion of the upward methane flux into localized plumes or channels to form concentrations of near-seafloor gas hydrate. The amount of gas hydrate in local concentrations near the seafloor is especially important for understanding the response of marine gas hydrate to climate change. The expedition includes coring and downhole measurements at five sites across the Northern Cascadia accretionary prism. The sites will track the history of methane in an accretionary prism from (1) its production by mainly microbiological processes over a thick sediment vertical extent, (2) its upward transport through regional or locally focused fluid flow, (3) its incorporation in the regional hydrate layer above the BSR or in local concentrations at or near the seafloor, (4) methane loss from the hydrate by upward diffusion, and (5) methane

  4. Apparent Km of mitochondria for oxygen computed from Vmax measured in permeabilized muscle fibers is lower in water enriched in oxygen by electrolysis than injection

    Directory of Open Access Journals (Sweden)

    Zoll J

    2015-07-01

    Full Text Available Joffrey Zoll,1 Jamal Bouitbir,1 Pascal Sirvent,2 Alexis Klein,3 Antoine Charton,1,4 Liliana Jimenez,3 François R Péronnet,5 Bernard Geny,1 Ruddy Richard61Physiology Department, Faculty of Medicine and EA3072, Université de Strasbourg, Strasbourg, 2Clermont Université, Université Blaise Pascal, EA 3533, Laboratoire des Adaptations Métaboliques à l’Exercice en Conditions Physiologiques et Pathologiques, Clermont-Ferrand, 3Danone Research, Centre Daniel Carasso, Palaiseau, 4Department of Anesthesia and Critical Care and EA3072, Hôpital de Hautepierre, Université de Strasbourg, France; 5Kinesiology Department, Université de Montréal, Montréal, QC, Canada; 6Department of Sport Medicine and Functional Explorations and INRA UMR 1019, Faculty of Medicine, Université d’Auvergne, Clermont-Ferrand, FranceBackground: It has been suggested that oxygen (O2 diffusion could be favored in water enriched in O2 by a new electrolytic process because of O2 trapping in water superstructures (clathrates, which could reduce the local pressure/content relationships for O2 and facilitate O2 diffusion along PO2 gradients.Materials and methods: Mitochondrial respiration was compared in situ in saponin-skinned fibers isolated from the soleus muscles of Wistar rats, in solution enriched in O2 by injection or the electrolytic process 1 at an O2 concentration decreasing from 240 µmol/L to 10 µmol/L (132 mmHg to 5 mmHg, with glutamate–malate or N, N, N', N'-tetramethyl-p-phenylenediamine dihydrochloride (TMPD–ascorbate (with antimycin A as substrates; and 2 at increasing adenosine diphosphate (ADP concentration with glutamate–malate as substrate.Results: As expected, maximal respiration decreased with O2 concentration and, when compared to glutamate–malate, the apparent Km O2 of mitochondria for O2 was significantly lower with TMPD–ascorbate with both waters. However, when compared to the water enriched in O2 by injection, the Km O2 was

  5. Oceanic ecosystem dynamics during gigantic volcanic episodes: the Ontong Java and Manihiki Plateaus recorded by calcareous nannoplankton. (Invited)

    Science.gov (United States)

    Erba, E.

    2010-12-01

    Earth's volcanic activity introduces environmental stress that biota are forced to survive. There is a general consensus on the role of volcanogenic carbon dioxide increases, and implicit tectonic-igneous events, triggering major climate changes and profound variations in chemical, physical and trophic characteristics of the oceans through the Phanerozoic. Cretaceous geological records indicate conditions of excess atmCO2 (up to 2000-3000 ppm) derived from construction of Large Igneous Provinces (LIPs). In such “high CO2 world” and greenhouse conditions, the deep ocean became depleted of oxygen promoting the accumulation and burial of massive amounts of organic matter; such episodes are recognized as Oceanic Anoxic Events (OAEs) and their geological records merit careful examination of how the Earth system, and Life in particular, can overcome extreme experiments of global change. The Early Aptian (˜ 120 million years ago) OAE1a is a complex example of volcanicCO2-induced environmental stress. There is a general consensus on the causes of this case-history, namely excess CO2 derived from the construction of the Ontong Java-Manihiki LIP. Multi- and inter-disciplinary studies of the OAE1a have pointed out C, O, Os, Sr isotopic anomalies, a biocalcification crisis in pelagic and neritic settings, enhanced fertility and primary productivity, as well as ocean acidification. Available cyclochronology allows high-resolution dating of biotic and environmental fluctuations, providing the precision necessary for understanding the role of volcanogenic CO2 on nannoplankton biocalcification, adaptations, evolutionary innovation and/or extinctions. The reconstructed sequence of volcanogenic CO2 pulses, and perhaps some clathrate melting, triggered a climate change to supergreenhouse conditions, anoxia and ocean acidification. The demise of heavily calcified nannoconids and reduced calcite paleofluxes marks beginning of the pre-OAE1a calcification crisis. Ephemeral coccolith

  6. Comet 67P's Pitted Surface

    Science.gov (United States)

    Kohler, Susanna

    2015-11-01

    High-resolution imagery of comet 67P ChuryumovGerasimenko has revealed that its surface is covered in active pits some measuring hundreds of meters both wide and deep! But what processes caused these pits to form?Pitted LandscapeESAs Rosetta mission arrived at comet 67P in August 2014. As the comet continued its journey around the Sun, Rosetta extensively documented 67Ps surface through high-resolution images taken with the on-board instrument NavCam. These images have revealed that active, circular depressions are a common feature on the comets surface.In an attempt to determine how these pits formed, an international team of scientists led by Olivier Mousis (Laboratory of Astrophysics of Marseille) has run a series of simulations of a region of the comet the Seth region that contains a 200-meter-deep pit. These simulations include the effects of various phase transitions, heat transfer through the matrix of ices and dust, and gas diffusion throughout the porous material.Escaping VolatilesAdditional examples of pitted areas on 67Ps northern-hemisphere surface include the Ash region and the Maat region (both imaged September 2014 by NavCam) [Mousis et al. 2015]Previous studies have already eliminated two potential formation mechanisms for the pits: impacts (the sizes of the pits werent right) and erosion due to sunlight (the pits dont have the right shape). Mousis and collaborators assume that the pits are instead caused by the depletion of volatile materials chemical compounds with low boiling points either via explosive outbursts at the comets surface, or via sinkholes opening from below the surface. But what process causes the volatiles to deplete when the comet heats?The authors simulations demonstrate that volatiles trapped beneath the comets surface either in icy structures called clathrates or within amorphous ice can be suddenly released as the comet warms up. The team shows that the release of volatiles from these two structures can create 200-meter

  7. Geologically recent small-scale surface features in Meridiani Planum and Gale Crater, Mars

    Science.gov (United States)

    Horne, David

    2014-05-01

    contemporary ground-ice thaw and consequent transient surface run-off may occur occasionally under present conditions in low, near-equatorial latitudes on Mars; short-lived (even for just a few minutes) meltwater emission and flow at the surface could erode gutters before evaporating. The decomposition of buried pockets of methane clathrates, which theoretical considerations suggest might be present and stable even in equatorial regions, could give rise to both methane venting (leveed fissures) and transient surface water (gutters). Another possibility is the decomposition, due to local changes in thermal conditions, of hydrated magnesium sulphates in the bedrock, releasing liquid water. Whatever their explanation, these features hint at previously unrecognized, young martian surface processes which may even be active at the present day; in this context, the apparent downslope extension of a discrete dark dust streak on Burns Cliff (inside Endurance Crater), during Opportunity's approach to that locality, is particularly thought-provoking.

  8. The European Research Infrastructure IAGOS - From dedicated field studies to routine observations of the atmosphere by instrumented passenger aircraft

    Science.gov (United States)

    Petzold, Andreas; Volz-Thomas, Andreas; Gerbig, Christoph; Thouret, Valerie; Cammas, Jean-Pierre; Brenninkmeijer, Carl A. M.; Iagos Team

    2013-04-01

    The global distribution of trace species is controlled by a complex interplay between natural and anthropogenic sources and sinks, atmospheric short- to long-range transport, and in future by diverse, largely not yet quantified feedback mechanisms such as enhanced evaporation of water vapour in a warming climate or possibly the release of methane from melting marine clathrates. Improving global trace gas budgets and reducing the uncertainty of climate predictions crucially requires representative data from routine long-term observations as independent constraint for the evaluation and improvement of model parameterizations. IAGOS (In-service Aircraft for a Global Observing System; www.iagos.org) is a new European Research Infrastructure which operates a unique global observing system by deploying autonomous instruments aboard a fleet of passenger aircraft. IAGOS consists of two complementary building blocks: IAGOS-CORE deploys newly developed high-tech instrumentation for regular in-situ measurements of atmospheric chemical species (O3, CO, CO2, NOx, NOy, H2O, CH4), aerosols and cloud particles. Involved airlines ensure global operation of the network. In IAGOS-CARIBIC a cargo container is operated as a flying laboratory aboard one passenger aircraft. IAGOS aims at the provision of long-term, frequent, regular, accurate, and spatially resolved in-situ observations of the atmospheric chemical composition in the UTLS and the extra tropical troposphere and on vertical profiles of greenhouse gases, reactive trace gases and aerosols throughout the troposphere. It builds on almost 20 years of scientific and technological expertise gained in the research projects MOZAIC (Measurement of Ozone and Water Vapour on Airbus In-service Aircraft) and CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container). The European consortium includes research centres, universities, national weather services, airline operators and aviation

  9. Enceladus' Interior: A Liquid Circulation Model

    Science.gov (United States)

    Matson, Dennis L.; Johnson, Torrence; Lunine, Jonathan; Castillo-Rogez, Julie

    We are studying a model for Enceladus' interior in which the water, gas, dust and heat are supplied to the plumes by a relatively deeply circulating brine solution. Data indicates such a source for the erupting material. On the basis of ammonia in the plume gas Waite et al. [1] suggested that the jets might originate from a liquid water region under Enceladus' icy surface. Postberg et al. [2] noted that the presence of ". . . grains that are rich in sodium salts (0.5-2 percent by mass). . . can arise only if the plumes originate from liquid water." Waite et al. [1] also regard the some of the plume chemicals as evidence for interactions with an ice layer presumably overlying the liquid water reservoir. They suggest that this could be in the form of dissociation of clathrate hydrates [3]. Additionally, there is a large heat flow of more than 15 GW [4, 5] coming out of Enceladus' south polar region. We consider a model that brings heat and chemical species up to the surface from a reservoir or "ocean" located below the ice crust that may be many tens of kilometers thick. Water transits to the surface via vertical conduits. The Cassini INMS data suggest that the water has a relatively large gas content of order a few percent. As the water travels upward and the pressure is released, exolving gases form bubbles. Since the bubbly liquid is less dense than the ice, it moves upward. (This part of the model is a variant of the "Perrier Ocean" Europa model of Crawford and Stevenson [6]. A similar model was studied for Ganymede by Murchie and Head [7].) Postberg et al. [2] model the plume eruptions that result from the water, gases, salts, and other chemicals that our circulation model provides. In the near-surface reservoir feeding the plumes, bubbles reaching the surface of the water pop and throw a very fine spray. Some of these very small droplets of brine exit with the plume gas and provide the observed salt-rich dust particles [2]. Much of the water-borne heat is

  10. Highly efficient molecular simulation methods for evaluation of thermodynamic properties of crystalline phases

    Science.gov (United States)

    Moustafa, Sabry Gad Al-Hak Mohammad

    Molecular simulation (MS) methods (e.g. Monte Carlo (MC) and molecular dynamics (MD)) provide a reliable tool (especially at extreme conditions) to measure solid properties. However, measuring them accurately and efficiently (smallest uncertainty for a given time) using MS can be a big challenge especially with ab initio-type models. In addition, comparing with experimental results through extrapolating properties from finite size to the thermodynamic limit can be a critical obstacle. We first estimate the free energy (FE) of crystalline system of simple discontinuous potential, hard-spheres (HS), at its melting condition. Several approaches are explored to determine the most efficient route. The comparison study shows a considerable improvement in efficiency over the standard MS methods that are known for solid phases. In addition, we were able to accurately extrapolate to the thermodynamic limit using relatively small system sizes. Although the method is applied to HS model, it is readily extended to more complex hard-body potentials, such as hard tetrahedra. The harmonic approximation of the potential energy surface is usually an accurate model (especially at low temperature and large density) to describe many realistic solid phases. In addition, since the analysis is done numerically the method is relatively cheap. Here, we apply lattice dynamics (LD) techniques to get the FE of clathrate hydrates structures. Rigid-bonds model is assumed to describe water molecules; this, however, requires additional orientation degree-of-freedom in order to specify each molecule. However, we were able to efficiently avoid using those degrees of freedom through a mathematical transformation that only uses the atomic coordinates of water molecules. In addition, the proton-disorder nature of hydrate water networks adds extra complexity to the problem, especially when extrapolating to the thermodynamic limit is needed. The finite-size effects of the proton disorder contribution is

  11. Global climate change linkage with episodic methane release even in the western north Pacific in the last glacial period

    International Nuclear Information System (INIS)

    The remarkable similarity of late Quaternary atmospheric methane and temperature variations recorded in ice cores suggests that methane has played a significant role in millennial-scale climatic oscillations, especially Dansgaard-Oeschger (D-O) interstadial. Variations in the size and distribution of marine-sedimentary reservoirs of methane on the continental margins throughout the world's oceans are thought to be one of the important factors controlling the global methane cycle. Marine sediments can act as hosts to gas hydrates under appropriate conditions of high pressure and/or low temperature, and sufficient organic carbon; on the other hand, they show a significant sensitivity to small perturbations in the physical and chemical conditions within the reservoir. During the Last Glacial, direct and indirect evidence accumulated from geochemical data suggests that methane episodically released from hydrate trapped in the seafloor sediments. Recently, Kennett and coworkers interpreted δ13C variations of planktonic and benthic foraminifera found in Last Glacial sediments in the Santa Barbara Basin (SBB) as evidence for periodic releases of methane, arising from the dissociation of methane hydrate, and its subsequent oxidation in bottom- and/or surface-water environments. This result provided the basis for the 'Clathrate Gun Hypothesis', which highlights the potential role of methane hydrate in Quaternary variations in atmospheric methane concentrations. According to recent observations of anomalous bottom-simulating reflections(BSR), the northwest Pacific marginal sediments around Japan main islands bear large abundances of methane hydrate. In this study, the piston cores from the continental slope sediments in the Oyashio current region, which recently is found to bear immense amounts of methane hydrate, have been investigated about planktonic and benthic foraminiferal carbon isotope records during the past 34 cal. kyr BP. Moreover, in order to investigate

  12. 基于葫芦[8]脲主-客体作用的温度及pH敏感壳聚糖超分子凝胶制备与性能%Preparation and Properties of Temperature and pH Sensitive Chitosan Supramolecular Gel Based on Host-guest Interaction of Cucurbit[8]uril

    Institute of Scientific and Technical Information of China (English)

    林友文; 李立凡; 李光文

    2012-01-01

    壳聚糖侧链改性合成N-(4-二甲氨基苯甲基)壳聚糖(MBCS),通过葫芦[8]脲(Q[8])与MBCS侧链之间的主客体作用制得Q[8]/MBCS超分子凝胶.利用红外光谱、紫外光谱、1H NMR、X-射线粉末衍射(XRD)、热重分析(TG)和差示扫描量热(DSC)等技术对改性壳聚糖及凝胶进行表征.以5-氟尿嘧啶(5-Fu)为模型药物,研究载药凝胶在不同pH环境下的释药行为.结果表明Q[8]/MBCS体系在酸性条件下,可组装形成超分子凝胶,该凝胶体系具有温敏性和pH敏感性.扫描电镜(SEM)图显示凝胶具有网状交联结构,1H NMR谱显示,在酸性条件下,Q[8]与MBCS含氮侧链基团间发生主客体包合作用是超分子凝胶形成的主要原因.Q[8]/MBCS载药凝胶在酸性介质中对药物具有明显的缓释作用.%Chitosan(CS) which is a non-toxic,biocompatible,and biodegradable material and a good candidate for hydrogel formation was modified.A chitosan derivative,N-(4-dimethylaminobenzyl)chitosan(MBCS),was synthesized by the reaction of 4-(dimethylamino)benzaldehyde and chitosan to fabricate supramolecular gel system.The new family of macrocyclic host molecules,cucurbit[n]urils(Q[n],n=6~8) with its hydrophobic central cavity and negatively charged carbonyl portals,can bind to a variety of cationic organic guest molecules and neutral species to form the clathrate compounds with high affinity,and shows great potential applications in drug delivery system due to its low toxicity and good thermal stability.Cucurbit[8]uril(Q[8]) has a larger hydrophobic cavity volume of 479 3 and can include two aromatic rings.In this paper a novel supramolecular gel was prepared by utilizing the host-guest interaction between Q[8] and MBCS.The physical properties and structure of supramolecular gel and MBCS were characterized via IR,UV,1H NMR,X-ray powder diffraction(XRD),thermogravimetric method(TG) and differential scanning calorimetry(DSC).The morphology of network

  13. EDITORIAL: Van der Waals interactions in advanced materials, in memory of David C Langreth Van der Waals interactions in advanced materials, in memory of David C Langreth

    Science.gov (United States)

    Hyldgaard, Per; Rahman, Talat S.

    2012-10-01

    forces by examining the impact their inclusion has on predictions of material properties. On the other hand, the experimental and theoretical study of Casimir forces also plays a vital role in the exploration of material behavior. vdW forces are related to the Casimir force but lack retardation effects. While the vdW bonding depends on additional effects (for example, the multipole contributions that reflect image-plane effects), the study of Casimir forces provides direct (and not indirect) measurements of the nature of interactions. Klimchitskaya et al note that to reconcile explicit measurements of the Casmir forces between semiconductor fragments within the Lifshitz description, it is relevant to question the Drude-like description of the contributions from free carriers and instead proceed with a formulation based only on optical observations of the permittivity. This optical response can be seen as a reflection of a more plasmon-like behavior. The authors suggest an experiment involving the study of the impact on the Casimir forces by a Mott transition in doped semiconductors. Such an experiment would permit explicit testing of the validity of the present model for Casimir forces and hence provide additional perspectives on the nature of dispersive interactions. There is an effort to store energy, e.g. H2 or CO2, inside a range of open cage-like structures, such as metal organics frameworks (MOF) or clathrates. The fact that the internal molecular adhesion is dominated by vdW forces suggests that the storage and retrieval costs could perhaps be lowered as compared to an approach that involves more traditional chemical compounds. Nijem et al have provided spectroscopic characterization of vdW interactions of both hydrogen molecules and CO in a specific MOF. The study includes a vdW-DF calculation of structure and a theoretical prediction of expected infrared activity. The potential applications to energy materials have motivated more theoretical characterizations