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Sample records for hydrogen isotope adsorption

  1. CRYOGENIC ADSORPTION OF HYDROGEN ISOTOPES OVER NANO-STRUCTURED MATERIALS

    SciTech Connect

    Xiao, S.; Heung, L.

    2010-10-07

    Porous materials such as zeolites, activated carbon, silica gels, alumina and a number of industrial catalysts are compared and ranked for hydrogen and deuterium adsorption at liquid nitrogen temperature. All samples show higher D{sub 2} adsorption than that of H{sub 2}, in which a HY sample has the greatest isotopic effect while 13X has the highest hydrogen uptake capacity. Material's moisture content has significant impact to its hydrogen uptake. A material without adequate drying could result in complete loss of its adsorption capacity. Even though some materials present higher H{sub 2} adsorption capacity at full pressure, their adsorption at low vapor pressure may not be as good as others. Adsorption capacity in a dynamic system is much less than in a static system. A sharp desorption is also expected in case of temperature upset.

  2. Breakthrough curve analysis of pressure swing adsorption for hydrogen isotope separation

    SciTech Connect

    Kotoh, K.; Tanaka, M.; Sakamoto, T.; Nakamura, Y.; Asakura, Y.; Uda, T.; Sugiyama, T.

    2008-07-15

    For the purpose of developing an effective system for hydrogen isotope separation, we have been studying the adsorption-desorption dynamic behavior of hydrogen and deuterium in a packed-bed column with synthetic zeolites, aimed at applying the pressure swing adsorption process. The adsorption behavior of molecules in the packed-bed is reflected in the breakthrough curves. To understand the characteristic behaviors of hydrogen isotopes in the packed-bed, we carried out breakthrough experiments in a conventional adsorption process and in a practical process following sequential processes alternating between adsorption and desorption. From the former experiments, the results were obtained that the overall mass transfer was influenced by longitudinal dispersion relating to the superficial velocity and that the process governing the mass transfer within adsorbents was diffusion in the macro-pores of pellets. In the latter experiments, unique profile breakthrough curves were observed. These curves can be described with the numerical simulation assuming the initial distributions in a packed-bed. (authors)

  3. Correlation of adsorption isotherms of hydrogen isotopes on mordenite adsorbents using reactive vacancy solution theory

    SciTech Connect

    Munakata, K.; Nakamura, A.; Kawamura, Y.

    2015-03-15

    The authors have applied the isotherm equations derived from the reactive vacancy solution theory (RVST) to correlation of experimental and highly non-ideal adsorption isotherms of hydrogen and deuterium on a mordenite adsorbent, and have examined the ability of the isotherm equations to match this correlation. Several isotherm equations such as Langmuir, Freundlich, Toth, Vacancy Solution Theory and so forth were also tested, but they did not work. For the Langmuir-Freundlich equation tests have indicated that its 'ability to correlate' of the adsorption isotherms is not satisfactory. For the multi-site Langmuir-Freundlich (MSLF) equation the correlation of the isotherms appears to be somewhat improved but remains unsatisfactory. The results show that the isotherm equations derived from RVST can better correlate the experimental isotherms.

  4. HYDROGEN ISOTOPE TARGETS

    DOEpatents

    Ashley, R.W.

    1958-08-12

    The design of targets for use in the investigation of nuclear reactions of hydrogen isotopes by bombardment with accelerated particles is described. The target con struction eomprises a backing disc of a metal selected from the group consisting of molybdenunn and tungsten, a eoating of condensed titaniunn on the dise, and a hydrogen isotope selected from the group consisting of deuterium and tritium absorbed in the coatiag. The proeess for preparing these hydrogen isotope targets is described.

  5. Chromatographic hydrogen isotope separation

    DOEpatents

    Aldridge, Frederick T.

    1981-01-01

    Intermetallic compounds with the CaCu.sub.5 type of crystal structure, particularly LaNiCo.sub.4 and CaNi.sub.5, exhibit high separation factors and fast equilibrium times and therefore are useful for packing a chromatographic hydrogen isotope separation colum. The addition of an inert metal to dilute the hydride improves performance of the column. A large scale mutli-stage chromatographic separation process run as a secondary process off a hydrogen feedstream from an industrial plant which uses large volumes of hydrogen can produce large quantities of heavy water at an effective cost for use in heavy water reactors.

  6. Chromatographic hydrogen isotope separation

    DOEpatents

    Aldridge, F.T.

    Intermetallic compounds with the CaCu/sub 5/ type of crystal structure, particularly LaNiCo/sub 4/ and CaNi/sub 5/, exhibit high separation factors and fast equilibrium times and therefore are useful for packing a chromatographic hydrogen isotope separation column. The addition of an inert metal to dilute the hydride improves performance of the column. A large scale multi-stage chromatographic separation process run as a secondary process off a hydrogen feedstream from an industrial plant which uses large volumes of hydrogen cn produce large quantities of heavy water at an effective cost for use in heavy water reactors.

  7. Adsorption and coadsorption of molecular hydrogen isotopes in zeolites. II. Infrared analyses of H2, HD, and D2 in NaA

    NASA Astrophysics Data System (ADS)

    Stéphanie-Victoire, Françoise; de Lara, Evelyne Cohen

    1998-10-01

    The infrared analysis of the induced bands of molecular hydrogen isotopes, adsorbed in NaA zeolite, shows several features; (i) when the amount of adsorbed molecules increases, the bands become complex, showing three components, which can be related to different energetic situation of the molecules in the cavity; (ii) the band frequency is lower than the gas frequency; for each species the shifts are proportional to the inverse square root of the mass (same interaction with the crystal); (iii) the absolute intensity increases when the temperature decreases, this is due to the fact that the molecule remains longer in the vicinity of the adsorption site where the electric field is the highest. Its amplitude is deduced from the absolute intensities measured at the lowest temperature (˜1010 V/m, in agreement with other results).

  8. Analysis of hydrogen isotope mixtures

    DOEpatents

    Villa-Aleman, Eliel

    1994-01-01

    An apparatus and method for determining the concentrations of hydrogen isotopes in a sample. Hydrogen in the sample is separated from other elements using a filter selectively permeable to hydrogen. Then the hydrogen is condensed onto a cold finger or cryopump. The cold finger is rotated as pulsed laser energy vaporizes a portion of the condensed hydrogen, forming a packet of molecular hydrogen. The desorbed hydrogen is ionized and admitted into a mass spectrometer for analysis.

  9. Adsorption and isotopic fractionation of Xe

    NASA Technical Reports Server (NTRS)

    Bernatowicz, T. J.; Podosek, F. A.

    1986-01-01

    A theoretical description of the mechanisms of isotopic fractionation arising during adsorption of noble gases in a Henry's Law pressure regime is given. Experimental data on the isotopic composition of Xe adsorbed on activated charcoal in the temperature range 220 K to 350 K are presented. Both theoretical considerations and the experimental data indicate that equilibrium adsorption does not significantly alter the isotopic structure of adsorbed structure of adsorbed noble gases. Therefore, if adsorption is responsible for the elemental noble gas pattern in meteorites and the earth, the heavy noble gas isotopic fractionation between them must have been produced prior to and by a different process than equilibrium adsorption.

  10. Container for hydrogen isotopes

    DOEpatents

    Solomon, David E.

    1977-01-01

    A container for the storage, shipping and dispensing of hydrogen isotopes such as hydrogen, deuterium, tritium, or mixtures of the same which has compactness, which is safe against fracture or accident, and which is reusable. The container consists of an outer housing with suitable inlet and outlet openings and electrical feed elements, the housing containing an activated sorber material in the form, for example, of titanium sponge or an activated zirconium aluminate cartridge. The gas to be stored is introduced into the chamber under conditions of heat and vacuum and will be retained in the sorber material. Subsequently, it may be released by heating the unit to drive off the stored gas at desired rates.

  11. Hydrogen Adsorption in Carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Cabrera, A. L.; Rojas, S.; Dias-Droguett, D. E.; Bhuyan, H.; Aomoa, N.; Kakati, M.

    2013-03-01

    We have studied hydrogen adsorption in carbon nanoparticles using a quartz crystal microbalance. The carbon nanoparticles were synthesized from a thermal plasma jet at different pressure (15 - 263 torr) of the reactants and different current (50 - 250 A) to generate the plasma. The as-prepared carbon nanoparticles were directly deposited on top of the gold electrode of a quartz crystal and we monitored in-situ the changes in resonance frequency while the chamber was pressurized at different hydrogen pressures. These changes enabled determination of absorbed hydrogen mass in order to get H/C mass ratio curves as a function of H2 pressure. Adsorption curves obtained in some carbon nanoparticles indicated the formation of hydrogen monolayer inside the pores of the carbon nanoparticles. Using the value of the jump due to the formation of a H2\\ monolayer, a surface area was estimated between 40-60 m2/g for hydrogen adsorption. In other carbon samples, hydrogen uptake curves indicated that H2 was filling the sample's pores when pore volume was large. These observations will be discussed in detail for several carbon nanoparticles samples. Funds provided by VRI Puente 9/2012 and 10/2012

  12. Cascades for hydrogen isotope separation using metal hydrides

    SciTech Connect

    Hill, F.B.; Grzetic, V.

    1982-01-01

    Designs are presented for continuous countercurrent hydrogen isotope separation cascades based on the use of metal hydrides. The cascades are made up of pressure swing adsorption (PSA) or temperature swing adsorption (TSA) stages. The designs were evolved from consideration of previously conducted studies of the separation performance of four types of PSA and TSA processes.

  13. Apparatus and process for separating hydrogen isotopes

    DOEpatents

    Heung, Leung K; Sessions, Henry T; Xiao, Xin

    2013-06-25

    The apparatus and process for separating hydrogen isotopes is provided using dual columns, each column having an opposite hydrogen isotopic effect such that when a hydrogen isotope mixture feedstock is cycled between the two respective columns, two different hydrogen isotopes are separated from the feedstock.

  14. Hydrogen adsorption on functionalized nanoporous activated carbons.

    PubMed

    Zhao, X B; Xiao, B; Fletcher, A J; Thomas, K M

    2005-05-12

    There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions.

  15. Hydrogen isotope separation

    DOEpatents

    Bartlit, J.R.; Denton, W.H.; Sherman, R.H.

    Disclosed is a system of four cryogenic fractional distillation columns interlinked with two equilibrators for separating a DT and hydrogen feed stream into four product streams, consisting of a stream of high purity D/sub 2/, DT, T/sub 2/, and a tritium-free stream of HD for waste disposal.

  16. Hydrogen isotope separation

    DOEpatents

    Bartlit, John R.; Denton, William H.; Sherman, Robert H.

    1982-01-01

    A system of four cryogenic fractional distillation columns interlinked with two equilibrators for separating a DT and hydrogen feed stream into four product streams, consisting of a stream of high purity D.sub.2, DT, T.sub.2, and a tritium-free stream of HD for waste disposal.

  17. Interactions of Hydrogen Isotopes and Oxides with Metal Tubes

    SciTech Connect

    Glen R. Longhurst

    2008-08-01

    Understanding and accounting for interaction of hydrogen isotopes and their oxides with metal surfaces is important for persons working with tritium systems. Reported data from several investigators have shown that the processes of oxidation, adsorption, absorption, and permeation are all coupled and interactive. A computer model has been developed for predicting the interaction of hydrogen isotopes and their corresponding oxides in a flowing carrier gas stream with the walls of a metallic tube, particularly at low hydrogen concentrations. An experiment has been constructed to validate the predictive model. Predictions from modeling lead to unexpected experiment results.

  18. Process for exchanging hydrogen isotopes between gaseous hydrogen and water

    SciTech Connect

    Hindin, Saul G.; Roberts, George W.

    1980-08-12

    A process for exchanging isotopes of hydrogen, particularly tritium, between gaseous hydrogen and water is provided whereby gaseous hydrogen depeleted in tritium and liquid or gaseous water containing tritium are reacted in the presence of a metallic catalyst.

  19. Hydrogen-isotope permeation barrier

    DOEpatents

    Maroni, Victor A.; Van Deventer, Erven H.

    1977-01-01

    A composite including a plurality of metal layers has a Cu-Al-Fe bronze layer and at least one outer layer of a heat and corrosion resistant metal alloy. The bronze layer is ordinarily intermediate two outer layers of metal such as austenitic stainless steel, nickel alloys or alloys of the refractory metals. The composite provides a barrier to hydrogen isotopes, particularly tritium that can reduce permeation by at least about 30 fold and possibly more below permeation through equal thicknesses of the outer layer material.

  20. Apparatus for storing hydrogen isotopes

    DOEpatents

    McMullen, John W.; Wheeler, Michael G.; Cullingford, Hatice S.; Sherman, Robert H.

    1985-01-01

    An improved method and apparatus for storing isotopes of hydrogen (especially tritium) are provided. The hydrogen gas(es) is (are) stored as hydrides of material (for example uranium) within boreholes in a block of copper. The mass of the block is critically important to the operation, as is the selection of copper, because no cooling pipes are used. Because no cooling pipes are used, there can be no failure due to cooling pipes. And because copper is used instead of stainless steel, a significantly higher temperature can be reached before the eutectic formation of uranium with copper occurs, (the eutectic of uranium with the iron in stainless steel forming at a significantly lower temperature).

  1. Advanced Mass Spectrometers for Hydrogen Isotope Analyses

    SciTech Connect

    Chastagner, P.

    2001-08-01

    This report is a summary of the results of a joint Savannah River Laboratory (SRL) - Savannah River Plant (SRP) ''Hydrogen Isotope Mass Spectrometer Evaluation Program''. The program was undertaken to evaluate two prototype hydrogen isotope mass spectrometers and obtain sufficient data to permit SRP personnel to specify the mass spectrometers to replace obsolete instruments.

  2. Zn isotope fractionation during adsorption on birnessite

    NASA Astrophysics Data System (ADS)

    Bryan, A. L.; Dong, S.; Wasylenki, L. E.

    2013-12-01

    The biogeochemical cycling of zinc (Zn), an important micronutrient in the ocean, may influence primary productivity and species composition within surface waters. The chemical speciation and bioavailability of Zn is governed by diverse abiotic and biotic processes. These processes include adsorption reactions at mineral/water interfaces, as nanoparticles of oxyhydroxide minerals are known to adsorb significant amounts of Zn in surface waters (and during formation of ferromanganese crusts). Investigation of Zn isotope fractionation caused by adsorption onto birnessite, the dominant manganese oxide mineral in ferromanganese crusts, may help to explain the enrichment of heavy Zn isotopes in ferromanganese crusts. This will provide insight into the role of adsorption of Zn to nanoparticulate minerals in surface waters and into the overall biogeochemical cycling of Zn. This work aims to determine the mechanism and magnitude of Zn isotope fractionation during adsorption onto synthetic birnessite (KMn2O4.1.5H2O). Our simple-system experiments involve mixing solutions of 130 ppb Zn with aliquots of birnessite suspension (proportions varied to give a range of surface coverage) and a fixed pH near that of seawater at ~8.5. The mixtures react for 48 hours. The recovered dissolved Zn and adsorbed Zn are then separated, purified, and analyzed isotopically on a Nu Plasma MC-ICP-MS. Preliminary results show enrichment of light Zn isotopes on the mineral surfaces (Δ66/64Znsorbed-aqueous = -0.3‰). A time series will reveal whether this process is governed by equilibrium or Rayleigh fractionation. Contrary to our results, previously published studies led us to hypothesize that isotopically heavy Zn would adsorb compared to co-existing dissolved Zn. Maréchal et al. (2000) recorded ferromanganese crusts that were heavier than seawater with a mean δ66Zn value of 0.90‰. Dissolved Zn is octahedrally coordinated with oxygen atoms, but an EXAFS study by Manceau et al. (2002

  3. Cryogenic adsorption of low-concentration hydrogen on charcoal, 5A molecular sieve, sodalite, ZSM-5 and Wessalith DAY

    SciTech Connect

    Willms, R.S.

    1993-12-01

    The separation of low-concentration hydrogen isotopes from helium is a processing step that is required for ceramic lithium breeding blanket processing. Cryogenic adsorption is one method of effecting this separation. In this study live adsorbents were considered for this purpose: charcoal, 5A molecular sieve, UOP S-115, ZSM-5 and Wessalith DAY. The first two adsorbents exhibit good equilibrium loadings and are shown to be quite effective at adsorbing low-concentration hydrogen isotopes. The latter three adsorbents display considerably lower equilibrium loadings. This study concludes that by using either charcoal or 5A molecular sieve, cryogenic adsorption would be an effective means of separating hydrogen isotopes from helium.

  4. Atomic line emission analyzer for hydrogen isotopes

    DOEpatents

    Kronberg, James W.

    1993-01-01

    Apparatus for isotopic analysis of hydrogen comprises a low pressure chamber into which a sample of hydrogen is introduced and then exposed to an electrical discharge to excite the electrons of the hydrogen atoms to higher energy states and thereby cause the emission of light on the return to lower energy states, a Fresnel prism made at least in part of a material anomalously dispersive to the wavelengths of interest for dispersing the emitted light, and a photodiode array for receiving the dispersed light. The light emitted by the sample is filtered to pass only the desired wavelengths, such as one of the lines of the Balmer series for hydrogen, the wavelengths of which differ slightly from one isotope to another. The output of the photodiode array is processed to determine the relative amounts of each isotope present in the sample. Additionally, the sample itself may be recovered using a metal hydride.

  5. Hydrogen isotope separation installation for tritium facility

    SciTech Connect

    Andreev, B.M.; Perevezentsev, A.N.; Selivanenko, I.L.; Tenyaev, B.N.; Vedeneev, A.I.; Golubkov, A.N.

    1995-10-01

    The separation of hydrogen isotopes in the hydrogen-palladium system in sectioned separation columns with the simulation of counter-current isotopic exchange is described. The separation efficiency of sectioned columns is investigated with the experimental installation as a function of various parameters. The separation of deuterium-tritium mixtures with high tritium concentrations is tested with the pilot installation operating at room temperature and atmospheric hydrogen pressure. Due to very high separation efficiency, flexibility and simplicity of operation separation installations with sectioned columns are ideally suitable for tritium laboratories and facilities dealing with separation of hydrogen isotopes. Estimation of applicability of sectioned columns for regeneration of exhaust gas in a fuel cycle of thermonuclear reactors, such as JET and ITER, shows the number of advantages of separation installations with sectioned columns. 12 refs., 3 figs., 2 tabs.

  6. Kinetic and geometric isotope effects originating from different adsorption potential energy surfaces: cyclohexane on Rh(111).

    PubMed

    Koitaya, Takanori; Shimizu, Sumera; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2012-06-07

    Novel isotope effects were observed in desorption kinetics and adsorption geometry of cyclohexane on Rh(111) by the use of infrared reflection absorption spectroscopy, temperature programmed desorption, photoelectron spectroscopy, and spot-profile-analysis low energy electron diffraction. The desorption energy of deuterated cyclohexane (C(6)D(12)) is lower than that of C(6)H(12). In addition, the work function change by adsorbed C(6)D(12) is smaller than that by adsorbed C(6)H(12). These results indicate that C(6)D(12) has a shallower adsorption potential than C(6)H(12) (vertical geometric isotope effect). The lateral geometric isotope effect was also observed in the two-dimensional cyclohexane superstructures as a result of the different repulsive interaction between interfacial dipoles. The observed isotope effects should be ascribed to the quantum nature of hydrogen involved in the C-H···metal interaction.

  7. Apparatus for separating and recovering hydrogen isotopes

    DOEpatents

    Heung, Leung K.

    1994-01-01

    An apparatus for recovering hydrogen and separating its isotopes. The apparatus includes a housing bearing at least a fluid inlet and a fluid outlet. A baffle is disposed within the housing, attached thereto by a bracket. A hollow conduit is coiled about the baffle, in spaced relation to the baffle and the housing. The coiled conduit is at least partially filled with a hydride. The hydride can be heated to a high temperature and cooled to a low temperature quickly by circulating a heat transfer fluid in the housing. The spacing between the baffle and the housing maximizes the heat exchange rate between the fluid in the housing and the hydride in the conduit. The apparatus can be used to recover hydrogen isotopes (protium, deuterium and tritium) from gaseous mixtures, or to separate hydrogen isotopes from each other.

  8. Review of Hydrogen Isotope Permeability Through Materials

    SciTech Connect

    Steward, S. A.

    1983-08-15

    This report is the first part of a comprehensive summary of the literature on hydrogen isotope permeability through materials that do not readily form hydrides. While we mainly focus on pure metals with low permeabilities because of their importance to tritium containment, we also give data on higher-permeability materials such as iron, nickel, steels, and glasses.

  9. Hydrogen adsorption in metal-decorated silicon carbide nanotubes

    NASA Astrophysics Data System (ADS)

    Singh, Ram Sevak; Solanki, Ankit

    2016-09-01

    Hydrogen storage for fuel cell is an active area of research and appropriate materials with excellent hydrogen adsorption properties are highly demanded. Nanotubes, having high surface to volume ratio, are promising storage materials for hydrogen. Recently, silicon carbide nanotubes have been predicted as potential materials for future hydrogen storage application, and studies in this area are ongoing. Here, we report a systematic study on hydrogen adsorption properties in metal (Pt, Ni and Al) decorated silicon carbide nanotubes (SiCNTs) using first principles calculations based on density functional theory. The hydrogen adsorption properties are investigated by calculations of adsorption energy, electronic band structure, density of states (DOS) and Mulliken charge population analysis. Our findings show that hydrogen adsorptions on Pt, Ni and Al-decorated SiCNTs undergo spontaneous exothermic reactions with significant modulation of electronic structure of SiCNTs in all cases. Importantly, according to the Mulliken charge population analysis, dipole-dipole interaction causes chemisorptions of hydrogen in Pt, Ni and Al decorated SiCNTs with formation of chemical bonds. The study is a platform for the development of metal decorated SiCNTs for hydrogen adsorption or hydrogen storage application.

  10. METHOD OF SEPARATING HYDROGEN ISOTOPES

    DOEpatents

    Salmon, O.N.

    1958-12-01

    The process of separating a gaseous mixture of hydrogen and tritium by contacting finely dlvided palladium with the mixture in order to adsorb the gases, then gradually heating the palladium and collecting the evolved fractlons, is described. The fraction first given off is richer in trltium than later fractions.

  11. Isotope effects of hydrogen and atom tunnelling

    NASA Astrophysics Data System (ADS)

    Buchachenko, A. L.; Pliss, E. M.

    2016-06-01

    The abnormally high mass-dependent isotope effects in liquid-phase hydrogen (deuterium) atom transfer reactions, which are customarily regarded as quantum effects, are actually the products of two classical effects, namely, kinetic and thermodynamic ones. The former is determined by the rate constants for atom transfer and the latter is caused by nonbonded (or noncovalent) isotope effects in the solvation of protiated and deuterated reacting molecules. This product can mimic the large isotope effects that are usually attributed to tunnelling. In enzymatic reactions, tunnelling is of particular interest; its existence characterizes an enzyme as a rigid molecular machine in which the residence time of reactants on the reaction coordinate exceeds the waiting time for the tunnelling event. The magnitude of isotope effect becomes a characteristic parameter of the internal dynamics of the enzyme catalytic site. The bibliography includes 61 references.

  12. Isotope tracer study of hydrogen spillover on carbon-based adsorbents for hydrogen storage.

    PubMed

    Lachawiec, Anthony J; Yang, Ralph T

    2008-06-17

    A composite material comprising platinum nanoparticles supported on molecular sieve templated carbon was synthesized and found to adsorb 1.35 wt % hydrogen at 298 K and 100 atm. The isosteric heat of adsorption for the material at low coverage was approximately 14 kJ/mol, and it approached a value of 10.6 kJ/mol as coverage increased for pressures at and above 1 atm. The increase in capacity is attributed to spillover, which is observed with the use of isotopic tracer TPD. IRMOF-8 bridged to Pt/C, a material known to exhibit hydrogen spillover at room temperature, was also studied with the hydrogen-deuterium scrambling reaction for comparison. The isotherms were reversible. For desorption, sequential doses of H2 and D2 at room temperature and subsequent TPD yield product distributions that are strong indicators of the surface diffusion controlled reverse spillover process.

  13. Collision integrals for isotopic hydrogen molecules.

    NASA Technical Reports Server (NTRS)

    Brown, N. J.; Munn, R. J.

    1972-01-01

    The study was undertaken to determine the effects of reduced mass and differences in asymmetry on the collision integrals and thermal diffusion factors of isotopic hydrogen systems. Each system selected for study consisted of two diatoms, one in the j = 0 rotation state and the other in the j = 1 state. The molecules interacted with a Lennard-Jones type potential modified to include angular terms. A set of cross sections and collision integrals were obtained for each system.

  14. Oxygen and hydrogen isotope geochemistry of zeolites

    NASA Technical Reports Server (NTRS)

    Karlsson, Haraldur R.; Clayton, Robert N.

    1990-01-01

    Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

  15. Biogeochemistry of the stable hydrogen isotopes

    NASA Astrophysics Data System (ADS)

    Estep, Marilyn F.; Hoering, Thomas C.

    1980-08-01

    The fractionation of H isotopes between the water in the growth medium and the organically bonded H from microalgae cultured under conditions, where light intensity and wavelength, temperature, nutrient availability, and the H isotope ratio of the water were controlled, is reproducible and light dependant. All studies were based either on the H isotope ratios of the total organic H or on the lipids, where most of the H is firmly bonded to C. H bonded into other macromolecules, proteins, carbohydrates and nucleic acids, does not exchange with water, when algae are incubated in water enriched with deuterium. Only after the destruction of quaternary H bonds are labile hydrogens in macromolecules free to exchange with water. By growing algae (18 strains), including blue-green algae, green algae and diatoms, in continuous light, the isotope fractionations in photosynthesis were reproducibly -93 to -178 %. depending on the organism tested. This fractionation was not temperature dependent. Microalgae grown in total darkness with an organic substrate did not show the isotope fractionation seen in cells grown in light. In both light- and dark-grown algae, however, additional depletion of deuterium (-30 to -60%.) in cellular organic matter occurs during the metabolism of carbohydrates to form lipids. Plants from several natural populations also fractionated isotopes during photosynthesis by an average of -90 to -110%. In addition, the organically bonded H in nonsaponifiable lipids was further fractionated by -80%. from that in saponifiable lipids, isolated from two geographically distinct populations of marsh plants. This difference between H isotope ratios of these two groups of lipids provides an endogenous isotopic marker.

  16. Hydrogen adsorption on sulphur-doped SiC nanotubes

    NASA Astrophysics Data System (ADS)

    Sevak Singh, Ram

    2016-07-01

    Hydrogen (H2) is an energy carrier and clean fuel that can be used for a broad range of applications that include fuel cell vehicles. Therefore, development of materials for hydrogen storage is demanded. Nanotubes, in this context, are appropriate materials. Recently, silicon carbide nanotube (SiCNTs) have been predicted as potential nanomaterials for hydrogen storage, and atomic doping into the nanotubes improves the H2 adsorption. Here, we report H2 adsorption properties of sulphur-doped (S-doped) SiCNTs using first-principles calculations based on density functional theory. The H2 adsorption properties are investigated by calculations of energy band structures, density of states (DOS), adsorption energy and Mulliken charge population analysis. Our findings show that, compared to the intrinsic SiCNT, S-doped SiCNT is more sensitive to H2 adsorption. H2 gas adsorption on S-doped C-sites of SiCNT brings about significant modulation of the electronic structure of the nanotube, which results in charge transfer from the nanotube to the gas, and dipole-dipole interactions cause chemisorptions of hydrogen. However, in the case of H2 gas adsorption on S-doped Si-sites of the nanotube, lesser charge transfer from the nanotube to the gas results in physisorptions of the gas. The efficient hydrogen sensing properties of S-doped SiCNTs, studied here, may have potential for its practical realization for hydrogen storage application.

  17. Challenges in hydrogen adsorptions: from physisorption to chemisorption

    NASA Astrophysics Data System (ADS)

    Ding, Feng; Yakobson, Boris I.

    2011-06-01

    In this short review, we will briefly discuss the story of hydrogen storage, its impact on clean energy application, especially the challenges of using hydrogen adsorption for onboard application. After a short comparison of the main methods of hydrogen storage (high pressure tank, metal hydride and adsorption), we will focus our discussion on adsorption of hydrogen in graphitic carbon based large surface area adsorbents including carbon nanotubes, graphene and metal organic frameworks. The mechanisms, advantages, disadvantages and recent progresses will be discussed and reviewed for physisorption, metal-assisted storage and chemisorption. In the last section, we will discuss hydrogen spillover chemisorption in detail for the mechanism, status, challenges and perspectives. We hope to present a clear picture of the present technologies, challenges and the perspectives of hydrogen storage for the future studies.

  18. Hydrogen Desorption and Adsorption Measurements on Graphite Nanofibers

    NASA Technical Reports Server (NTRS)

    Ahn, C. C.; Ye, Y.; Ratnakumar, B. V.; Witham, C. K.; Bowman, R. C., Jr.; Fultz, B.

    1998-01-01

    Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying and gas condensation.

  19. Hydrogen isotope separation utilizing bulk getters

    SciTech Connect

    Knize, R.J.; Cecchi, J.L.

    1990-12-11

    This patent describes hydrogen isotope separation utilizing bulk getters. Tritium and deuterium are separated from a gaseous mixture thereof, derived from a nuclear fusion reactor or some other source, by providing a casing with a bulk getter therein for absorbing the gaseous mixture to produce an initial loading of the getter, partially desorbing the getter to produce a desorbed mixture which is tritium-enriched, pumping the desorbed mixture into a separate container, the remaining gaseous loading in the getter being deuterium-enriched, desorbing the getter to a substantially greater extent to produce a deuterium-enriched gaseous mixture, and removing the deuterium-enriched mixture into another container. The bulk getter may comprise a zirconium-aluminum alloy, or a zirconium-vanadium-iron alloy. The partial desorption may reduce the loading by approximately fifty percent. The basic procedure may be extended to produce a multistage isotope separator, including at least one additional bulk getter into which the tritium-enriched mixture is absorbed. The second getter is then partially desorbed to produce a desorbed mixture which is further tritium-enriched. The last mentioned mixture is then removed from the container for the second getter, which is then desorbed to a substantially greater extent to produce a desorbed mixture which is deuterium-enriched. The last-mentioned mixture is then removed so that the cycle can be continued and repeated. The method of isotope separation is also applicable to other hydrogen isotopes, in that the method can be employed for separating either deuterium or tritium from normal hydrogen.

  20. Hydrogen isotope fractionation in methane plasma.

    PubMed

    Robert, François; Derenne, Sylvie; Lombardi, Guillaume; Hassouni, Khaled; Michau, Armelle; Reinhardt, Peter; Duhamel, Rémi; Gonzalez, Adriana; Biron, Kasia

    2017-01-31

    The hydrogen isotope ratio (D/H) is commonly used to reconstruct the chemical processes at the origin of water and organic compounds in the early solar system. On the one hand, the large enrichments in deuterium of the insoluble organic matter (IOM) isolated from the carbonaceous meteorites are interpreted as a heritage of the interstellar medium or resulting from ion-molecule reactions taking place in the diffuse part of the protosolar nebula. On the other hand, the molecular structure of this IOM suggests that organic radicals have played a central role in a gas-phase organosynthesis. So as to reproduce this type of chemistry between organic radicals, experiments based on a microwave plasma of CH4 have been performed. They yielded a black organic residue in which ion microprobe analyses revealed hydrogen isotopic anomalies at a submicrometric spatial resolution. They likely reflect differences in the D/H ratios between the various CHx radicals whose polymerization is at the origin of the IOM. These isotopic heterogeneities, usually referred to as hot and cold spots, are commensurable with those observed in meteorite IOM. As a consequence, the appearance of organic radicals in the ionized regions of the disk surrounding the Sun during its formation may have triggered the formation of organic compounds.

  1. Hydrogen isotope fractionation in methane plasma

    PubMed Central

    Robert, François; Derenne, Sylvie; Lombardi, Guillaume; Hassouni, Khaled; Michau, Armelle; Reinhardt, Peter; Duhamel, Rémi; Gonzalez, Adriana; Biron, Kasia

    2017-01-01

    The hydrogen isotope ratio (D/H) is commonly used to reconstruct the chemical processes at the origin of water and organic compounds in the early solar system. On the one hand, the large enrichments in deuterium of the insoluble organic matter (IOM) isolated from the carbonaceous meteorites are interpreted as a heritage of the interstellar medium or resulting from ion−molecule reactions taking place in the diffuse part of the protosolar nebula. On the other hand, the molecular structure of this IOM suggests that organic radicals have played a central role in a gas-phase organosynthesis. So as to reproduce this type of chemistry between organic radicals, experiments based on a microwave plasma of CH4 have been performed. They yielded a black organic residue in which ion microprobe analyses revealed hydrogen isotopic anomalies at a submicrometric spatial resolution. They likely reflect differences in the D/H ratios between the various CHx radicals whose polymerization is at the origin of the IOM. These isotopic heterogeneities, usually referred to as hot and cold spots, are commensurable with those observed in meteorite IOM. As a consequence, the appearance of organic radicals in the ionized regions of the disk surrounding the Sun during its formation may have triggered the formation of organic compounds. PMID:28096422

  2. Hydrogen isotope separation utilizing bulk getters

    DOEpatents

    Knize, R.J.; Cecchi, J.L.

    1991-08-20

    Tritium and deuterium are separated from a gaseous mixture thereof, derived from a nuclear fusion reactor or some other source, by providing a casing with a bulk getter therein for absorbing the gaseous mixture to produce an initial loading of the getter, partially desorbing the getter to produce a desorbed mixture which is tritium-enriched, pumping the desorbed mixture into a separate container, the remaining gaseous loading in the getter being deuterium-enriched, desorbing the getter to a substantially greater extent to produce a deuterium-enriched gaseous mixture, and removing the deuterium-enriched mixture into another container. The bulk getter may comprise a zirconium-aluminum alloy, or a zirconium-vanadium-iron alloy. The partial desorption may reduce the loading by approximately fifty percent. The basic procedure may be extended to produce a multistage isotope separator, including at least one additional bulk getter into which the tritium-enriched mixture is absorbed. The second getter is then partially desorbed to produce a desorbed mixture which is further tritium-enriched. The last-mentioned mixture is then removed from the container for the second getter, which is then desorbed to a substantially greater extent to produce a desorbed mixture which is deuterium-enriched. The last-mentioned mixture is then removed so that the cycle can be continued and repeated. The method of isotope separation is also applicable to other hydrogen isotopes, in that the method can be employed for separating either deuterium or tritium from normal hydrogen. 4 figures.

  3. Hydrogen isotope separation utilizing bulk getters

    DOEpatents

    Knize, Randall J.; Cecchi, Joseph L.

    1990-01-01

    Tritium and deuterium are separated from a gaseous mixture thereof, derived from a nuclear fusion reactor or some other source, by providing a casing with a bulk getter therein for absorbing the gaseous mixture to produce an initial loading of the getter, partially desorbing the getter to produce a desorbed mixture which is tritium-enriched, pumping the desorbed mixture into a separate container, the remaining gaseous loading in the getter being deuterium-enriched, desorbing the getter to a substantially greater extent to produce a deuterium-enriched gaseous mixture, and removing the deuterium-enriched mixture into another container. The bulk getter may comprise a zirconium-aluminum alloy, or a zirconium-vanadium-iron alloy. The partial desorption may reduce the loading by approximately fifty percent. The basic procedure may be extended to produce a multistage isotope separator, including at least one additional bulk getter into which the tritium-enriched mixture is absorbed. The second getter is then partially desorbed to produce a desorbed mixture which is further tritium-enriched. The last-mentioned mixture is then removed from the container for the second getter, which is then desorbed to a substantially greater extent to produce a desorbed mixture which is deuterium-enriched. The last-mentioned mixture is then removed so that the cycle can be continued and repeated. The method of isotope separation is also applicable to other hydrogen isotopes, in that the method can be employed for separating either deuterium or tritium from normal hydrogen.

  4. Hydrogen isotope separation utilizing bulk getters

    DOEpatents

    Knize, Randall J.; Cecchi, Joseph L.

    1991-01-01

    Tritium and deuterium are separated from a gaseous mixture thereof, derived from a nuclear fusion reactor or some other source, by providing a casing with a bulk getter therein for absorbing the gaseous mixture to produce an initial loading of the getter, partially desorbing the getter to produce a desorbed mixture which is tritium-enriched, pumping the desorbed mixture into a separate container, the remaining gaseous loading in the getter being deuterium-enriched, desorbing the getter to a substantially greater extent to produce a deuterium-enriched gaseous mixture, and removing the deuterium-enriched mixture into another container. The bulk getter may comprise a zirconium-aluminum alloy, or a zirconium-vanadium-iron alloy. The partial desorption may reduce the loading by approximately fifty percent. The basic procedure may be extended to produce a multistage isotope separator, including at least one additional bulk getter into which the tritium-enriched mixture is absorbed. The second getter is then partially desorbed to produce a desorbed mixture which is further tritium-enriched. The last-mentioned mixture is then removed from the container for the second getter, which is then desorbed to a substantially greater extent to produce a desorbed mixture which is deuterium-enriched. The last-mentioned mixture is then removed so that the cycle can be continued and repeated. The method of isotope separation is also applicable to other hydrogen isotopes, in that the method can be employed for separating either deuterium or tritium from normal hydrogen.

  5. Hydrogen isotope fractionation in methane plasma

    NASA Astrophysics Data System (ADS)

    Robert, François; Derenne, Sylvie; Lombardi, Guillaume; Hassouni, Khaled; Michau, Armelle; Reinhardt, Peter; Duhamel, Rémi; Gonzalez, Adriana; Biron, Kasia

    2017-01-01

    The hydrogen isotope ratio (D/H) is commonly used to reconstruct the chemical processes at the origin of water and organic compounds in the early solar system. On the one hand, the large enrichments in deuterium of the insoluble organic matter (IOM) isolated from the carbonaceous meteorites are interpreted as a heritage of the interstellar medium or resulting from ion‑molecule reactions taking place in the diffuse part of the protosolar nebula. On the other hand, the molecular structure of this IOM suggests that organic radicals have played a central role in a gas-phase organosynthesis. So as to reproduce this type of chemistry between organic radicals, experiments based on a microwave plasma of CH4 have been performed. They yielded a black organic residue in which ion microprobe analyses revealed hydrogen isotopic anomalies at a submicrometric spatial resolution. They likely reflect differences in the D/H ratios between the various CHx radicals whose polymerization is at the origin of the IOM. These isotopic heterogeneities, usually referred to as hot and cold spots, are commensurable with those observed in meteorite IOM. As a consequence, the appearance of organic radicals in the ionized regions of the disk surrounding the Sun during its formation may have triggered the formation of organic compounds.

  6. Isotope microscopy visualization of the adsorption profile of 2-methylisoborneol and geosmin in powdered activated carbon.

    PubMed

    Matsui, Yoshihiko; Sakamoto, Asuka; Nakao, Soichi; Taniguchi, Takuma; Matsushita, Taku; Shirasaki, Nobutaka; Sakamoto, Naoya; Yurimoto, Hisayoshi

    2014-09-16

    Decreasing the particle size of powdered activated carbon may enhance its equilibrium adsorption capacity for small molecules and micropollutants, such as 2-methylisoborneol (MIB) and geosmin, as well as for macromolecules and natural organic matter. Shell adsorption, in which adsorbates do not completely penetrate the adsorbent but instead preferentially adsorb near the outer surface of the adsorbent, may explain this enhancement in equilibrium adsorption capacity. Here, we used isotope microscopy and deuterium-doped MIB and geosmin to directly visualize the solid-phase adsorbate concentration profiles of MIB and geosmin in carbon particles. The deuterium/hydrogen ratio, which we used as an index of the solid-phase concentration of MIB and geosmin, was higher in the shell region than in the inner region of carbon particles. Solid-phase concentrations of MIB and geosmin obtained from the deuterium/hydrogen ratio roughly agreed with those predicted by shell adsorption model analyses of isotherm data. The direct visualization of the localization of micropollutant adsorbates in activated carbon particles provided direct evidence of shell adsorption.

  7. Compact hydrogen/helium isotope mass spectrometer

    DOEpatents

    Funsten, Herbert O.; McComas, David J.; Scime, Earl E.

    1996-01-01

    The compact hydrogen and helium isotope mass spectrometer of the present invention combines low mass-resolution ion mass spectrometry and beam-foil interaction technology to unambiguously detect and quantify deuterium (D), tritium (T), hydrogen molecule (H.sub.2, HD, D.sub.2, HT, DT, and T.sub.2), .sup.3 He, and .sup.4 He concentrations and concentration variations. The spectrometer provides real-time, high sensitivity, and high accuracy measurements. Currently, no fieldable D or molecular speciation detectors exist. Furthermore, the present spectrometer has a significant advantage over traditional T detectors: no confusion of the measurements by other beta-emitters, and complete separation of atomic and molecular species of equivalent atomic mass (e.g., HD and .sup.3 He).

  8. Zinc isotope fractionation during surface adsorption by bacteria

    NASA Astrophysics Data System (ADS)

    Kafantaris, F. A.; Borrok, D. M.

    2011-12-01

    The cycling and transport of zinc (Zn) in natural waters is partly controlled by its adsorption and uptake by bacterial communities. These reactions are reflected in changes in the ratios of stable Zn isotopes; however, the magnitudes and directions of these changes are largely unconstrained. In the current work, we attempt to define Zn isotope fractionation factors for bacteria-Zn interactions by performing adsorption experiments with representative Gram-positive (Bacillus subtilis) and Gram-negative (Pseudomonas mendocina) bacteria. Experiments included, (1) pH-dependent adsorption using differing bacteria:Zn ratios, (2) Zn loading at constant pH, and (3) kinetics and reversibility experiments. Results indicate that Zn adsorption is fully reversible for both bacterial species. Moreover, under the same experimental conditions both bacterial species adsorbed Zn to similar extents. Initial isotopic analysis (using a Nu Instruments MC-ICP-MS) demonstrates that, as the extent of adsorption increases, the heavier Zn isotopes are preferentially incorporated as bacterial-surface complexes. Under conditions of low bacteria:Zn ratio, the Δ66Znbacteria-solution was about 0.3% for both bacterial species. This separation factor is similar to that found in other studies involving the complexation of Zn with biologic or organic components. For example, the complexation of Zn with Purified Humic Acid (PHA) resulted in a Δ66ZnPHA-solution of +0.24% [1], and sorption of Zn onto two separate diatom species resulted in Δ66Znsolid-solution of +0.43% and +0.27%, respectively [2]. These results suggest that Zn complexation with functional groups common to bacteria and natural organic matter may be a process that universally incorporates the heavier Zn isotopes. Our current work is focused on quantifying Zn isotope fractionation during metabolic incorporation by separating this effect from surface adsorption reactions. [1] Jouvin et al., (2009) Environ. Sci. Technol., 43(15) 5747

  9. Hydrogen Adsorption in Zeolite Studied with Sievert and Thermogravimetric Methods

    NASA Astrophysics Data System (ADS)

    Lesnicenoks, P.; Sivars, A.; Grinberga, L.; Kleperis, J.

    2012-08-01

    Natural clinoptilolite (mixture from clinoptilolite, quartz and muscovite) is activated with palladium and tested for hydrogen adsorption capability at temperatures RT - 200°C. Thermogravimetric and volumetric methods showed that zeolite activated with palladium (1.25%wt) shows markedly high hydrogen adsorption capacity - up to 3 wt%. Lower amount of adsorbed hydrogen (~1.5 wt%) was found for raw zeolite and activated with higher amount of palladium sample. Hypothesis is proposed that the heating of zeolite in argon atmosphere forms and activates the pore structure in zeolite material, where hydrogen encapsulation (trapping) is believed to occur when cooling down to room temperature. An effect of catalyst (Pd) on hydrogen sorption capability is explained by spillover phenomena were less-porous fractions of natural clinoptilolite sample (quartz and muscovite) are involved.

  10. Tritium Isotope Separation Using Adsorption-Distillation Column

    SciTech Connect

    Fukada, Satoshi

    2005-07-15

    In order to miniaturize the height of a distillation tower for the detritiation of waste water from fusion reactors, two experiments were conducted: (1) liquid frontal chromatography of tritium water eluting through an adsorption column and (2) water distillation using a column packed with adsorbent particles. The height of the distillation tower depends on the height equivalent to a theoretical plate, HETP, and the equilibrium isotope separation factor, {alpha}{sub H-T}{sup equi}. The adsorption action improved not only HETP but also {alpha}{sub H-T}{sup equi}. Since the adsorption-distillation method proposed here can shorten the tower height with keeping advantages of the distillation, it may bring an excellent way for miniaturizing the distillation tower to detritiate a large amount of waste water from fusion reactors.

  11. Enthalpy and entropy effects in hydrogen adsorption on carbon nanotubes.

    PubMed

    Efremenko, Irena; Sheintuch, Moshe

    2005-07-05

    Interaction energies and entropies associated with hydrogen adsorption on the inner and outer surfaces of zigzag single-wall carbon nanotubes (SWCNT) of various diameters are analyzed by means of molecular mechanics, density functional theory, and ab initio calculations. For a single molecule the strongest interaction, which is 3.5 greater than that with the planar graphite sheet, is found inside a (8,0) nanotube. Adsorption on the outer surfaces is weaker than that on graphite. Due to the steric considerations, both processes are accompanied by an extremely strong decline in entropy. Absence of specific adsorption sites and weak attractive interaction between hydrogen molecules within carbon nanotubes results in their close packing at low temperatures. Using the calculated geometric and thermodynamic parameters in Langmuir isotherms we predict the adsorption capacity of SWCNTs at room temperature to be smaller than 1 wt % even at 100 bar.

  12. Temperature-dependent adsorption of hydrogen, deuterium, and neon on porous Vycor glass

    NASA Astrophysics Data System (ADS)

    Huber, T. E.; Scardino, D.; Tsou, H. L.

    1995-10-01

    Adsorption isotherms of H2, D2, and Ne have been measured in the temperature range from 15 K to the corresponding critical points in samples of porous Vycor glass. From the Brunauer-Emmett-Teller theory the surface layer coverages are determined. These are found to be temperature dependent. A model-independent approach allows us to fit the data for coverages ranging from submonolayer to thin film, below capillary condensation, for each adsorbate at all temperatures with a temperature-independent curve. This characteristic curve represents the distribution of adsorption sites versus the adsorption potential. In the intermediate coverage range, the isotherms exhibit the modified Frenkel-Halsey-Hill (FHH) behavior. The adsorption saturates for low-adsorption potentials. The characteristic curve is a useful universal curve since it is roughly the same for the three species investigated. We examine the relative strengths of the surface potentials and densities of the two isotopic modifications of hydrogen and of the more classical Ne adsorbed on porous Vycor glass. The characteristic adsorption curve is compared with results from two models for the adsorbate: Dubinin's isotherm for microporous solids and its extension to rough surfaces which places importance on the porosity of the surface, and Halsey's model, which is an extension of the FHH isotherm that takes into account the long-range variations of substrate adsorption potential.

  13. Ultrafiltration by a compacted clay membrane-I. Oxygen and hydrogen isotopic fractionation

    USGS Publications Warehouse

    Coplen, T.B.; Hanshaw, B.B.

    1973-01-01

    Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5%. and in O18 by 0.8%. relative to the residual solution. No additional isotopic fractionation due to a salt filtering mechanism was observed at NaCl concentrations up to 0.01 N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. ?? 1973.

  14. Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 1. Amphibolite experiments

    NASA Astrophysics Data System (ADS)

    Minitti, Michelle E.; Rutherford, Malcolm J.; Taylor, Bruce E.; Dyar, M. Darby; Schultz, Peter H.

    2008-02-01

    Kaersutitic amphiboles found within a subset of the Martian meteorites have low water contents and variably heavy hydrogen isotope compositions. In order to assess if impact shock-induced devolatilization and hydrogen isotope fractionation were determining factors in these water and isotopic characteristics of the Martian kaersutites, we conducted impact shock experiments on samples of Gore Mountain amphibolite in the Ames Vertical Gun Range (AVGR). A parallel shock experiment conducted on an anorthosite sample indicated that contamination of shocked samples by the AVGR hydrogen propellant was unlikely. Petrographic study of the experimental amphibolite shock products indicates that only ˜ 10% of the shock products experienced levels of damage equivalent to those found in the most highly shocked kaersutite-bearing Martian meteorites (30-35 GPa). Ion microprobe studies of highly shocked hornblende from the amphibolite exhibited elevated water contents (ΔH 2O ˜ 0.1 wt.%) and enriched hydrogen isotope compositions (Δ D ˜ + 10‰) relative to unshocked hornblende. Water and hydrogen isotope analyses of tens of milligrams of unshocked, moderately shocked, and highly shocked hornblende samples by vacuum extraction/uranium reduction and isotope ratio mass spectrometry (IRMS), respectively, are largely consistent with analyses of single grains from the ion microprobe. The mechanisms thought to have produced the excess water in most of the shocked hornblendes are shock-induced reduction of hornblende Fe and/or irreversible adsorption of hydrogen. Addition of the isotopically enriched Martian atmosphere to the Martian meteorite kaersutites via these mechanisms could explain their enriched and variable isotopic compositions. Alternatively, regrouping the water extraction and IRMS analyses on the basis of isotopic composition reveals a small, but consistent, degree of impact-induced devolatilization (˜ 0.1 wt.% H 2O) and H isotope enrichment (Δ D ˜ + 10

  15. Isotope effects on desorption kinetics of hydrogen isotopes implanted into stainless steel by glow discharge

    SciTech Connect

    Matsuyama, M.; Kondo, M.; Noda, N.; Tanaka, M.; Nishimura, K.

    2015-03-15

    In a fusion device the control of fuel particles implies to know the desorption rate of hydrogen isotopes by the plasma-facing materials. In this paper desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by experiment and numerical calculation. The temperature of a maximum desorption rate depends on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions have been successfully reproduced by numerical simulations that are based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel is limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms. (authors)

  16. Investigation of Hydrogen Adsorption on Single Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Nam, Sang-Hun; Jeong, Seong Hun; Lee, Soon-Bo; Boo, Jin-Hyo

    We have investigated adsorption and desorption condition of atomic hydrogen on single-walled nanotubes (SWCNTs) using ultraviolet photoelectron spectroscopy (UPS) and thermal desorption spectroscopy (TDS). The SWCNTs were made by the high pressure carbon monoxide (HiPCO) method. In our results, we observe from UPS data absorptive states reduce with increasing hydrogen doses and a new peak is developed near 8.6 eV and other points. But this peak is gradually diminished with pumping time. The TDS data show two characteristic peaks at 640 and 790K. By comparing with density functional calculations, we propose these peaks to be related to the presence of atomic hydrogen. Therefore, we can know that there are two adsorption sites on SWCNTs. Also we observed physisorption and chemisorption site by pumping time. We note that the UPS data are fully recoverable after hydrogen desorption at 1200K.

  17. [Fractionation of hydrogen stable isotopes in the human body].

    PubMed

    Siniak, Iu E; Grigor'ev, A I; Skuratov, V M; Ivanova, S M; Pokrovskiĭ, B G

    2006-01-01

    Fractionation of hydrogen stable isotopes was studied in 9 human subjects in a chamber with normal air pressure imitating a space cabin. Mass-spectrometry of isotopes in blood, urine, saliva, and potable water evidenced increases in the contents of heavy H isotope (deuterium) in the body liquids as compared with water. These results support one of the theories according to which the human organism eliminates heavy stable isotopes of biogenous chemical elements.

  18. Cadmium isotope fractionation during adsorption to Mn-oxyhydroxide

    NASA Astrophysics Data System (ADS)

    Wasylenki, L. E.; Swihart, J. W.

    2013-12-01

    The heavy metal cadmium is of interest both as a toxic contaminant in groundwater and as a critical nutrient for some marine diatoms [1], yet little is known about the biogeochemistry of this element. Horner et al. [2] suggested that Cd stable isotopes could potentially enable reconstruction of biological use of Cd in the marine realm: since cultured diatoms fractionate Cd isotopes [3], and ferromanganese crusts appear to incorporate a faithful record of deepwater Cd isotopes [2], depth profiles in such crusts may yield information about the extent of Cd assimilation of isotopically light Cd by diatoms over time. Although no work has yet been published regarding the use of stable isotopes to track reactive transport of Cd in contaminated aquifers, others have recently demonstrated the potential of isotopes to track reactions affecting the mobility of other toxic metals (e.g., [4]). With both of these potential applications in mind, we conducted two sets of experiments, at low and high ionic strength, in which Cd partially adsorbed to potassium birnessite. Our goals are to quantify the fractionations and to constrain the mechanisms governing Cd isotope behavior during adsorption to an environmentally abundant scavenger of Cd. Suspensions of synthetic birnessite were doped with various amounts of dissolved Cd2+ at pH ~8.3. Following reaction, the dissolved and adsorbed pools of Cd were separated by filtration, purified by anion exchange chromatography, and analyzed by multicollector ICP-MS using a double-spike routine. In all cases, lighter isotopes preferentially adsorbed to the birnessite particles. At low ionic strength (I<0.01m), we observed a small fractionation of 0.15‰×0.05 (Δ114/112) that was constant as a function of the fraction of Cd adsorbed. This indicates a small equilibrium isotope effect, likely driven by a subtle shift in coordination geometry for Cd during adsorption. In a groundwater system with continuous flow of dissolved Cd, this

  19. Equations of state and phase diagrams of hydrogen isotopes

    SciTech Connect

    Urlin, V. D.

    2013-11-15

    A new form of the semiempirical equation of state proposed for the liquid phase of hydrogen isotopes is based on the assumption that its structure is formed by cells some of which contain hydrogen molecules and others contain hydrogen atoms. The values of parameters in the equations of state of the solid (molecular and atomic) phases as well as of the liquid phase of hydrogen isotopes (protium and deuterium) are determined. Phase diagrams, shock adiabats, isentropes, isotherms, and the electrical conductivity of compressed hydrogen are calculated. Comparison of the results of calculations with available experimental data in a wide pressure range demonstrates satisfactory coincidence.

  20. Adsorption process to recover hydrogen from feed gas mixtures having low hydrogen concentration

    DOEpatents

    Golden, Timothy Christopher; Weist, Jr., Edward Landis; Hufton, Jeffrey Raymond; Novosat, Paul Anthony

    2010-04-13

    A process for selectively separating hydrogen from at least one more strongly adsorbable component in a plurality of adsorption beds to produce a hydrogen-rich product gas from a low hydrogen concentration feed with a high recovery rate. Each of the plurality of adsorption beds subjected to a repetitive cycle. The process comprises an adsorption step for producing the hydrogen-rich product from a feed gas mixture comprising 5% to 50% hydrogen, at least two pressure equalization by void space gas withdrawal steps, a provide purge step resulting in a first pressure decrease, a blowdown step resulting in a second pressure decrease, a purge step, at least two pressure equalization by void space gas introduction steps, and a repressurization step. The second pressure decrease is at least 2 times greater than the first pressure decrease.

  1. Hydrogen isotope systematics of submarine basalts

    USGS Publications Warehouse

    Kyser, T.K.; O'Neil, J.R.

    1984-01-01

    The D/H ratios and water contents in fresh submarine basalts from the Mid-Atlantic Ridge, the East Pacific Rise, and Hawaii indicate that the primary D/H ratios of many submarine lavas have been altered by processes including (1) outgassing, (2) addition of seawater at magmatic temperature, and (3) low-temperature hydration of glass. Decreases in ??D and H2O+ from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between ??D and H2O+ in basalts from the Galapagos Rise and the FAMOUS Area are attributed to outgassing of CH4 and H2. A good correlation between ??D values and H2O is observed in a suite of submarine tholeiites dredged from the Kilauea East Rift Zone where seawater (added directly to the magma), affected only the isotopic compositions of hydrogen and argon. Analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having ??D values as low as -100. ??D values vary with H2O contents of subaerial transitional basalts from Molokai, Hawaii, and subaerial alkali basalts from the Society Islands, indicating that the primary ??D values were similar to those of submarine lavas. Extrapolations to possible unaltered ??D values and H2O contents indicate that the primary ??D values of most thoteiite and alkali basalts are near -80 ?? 5: the weight percentages of water are variable, 0.15-0.35 for MOR tholeiites, about 0.25 for Hawaiian tholeiites, and up to 1.1 for alkali basalts. The primary ??D values of -80 for most basalts are comparable to those measured for deep-seated phlogopites. These results indicate that hydrogen, in marked contrast to other elements such as Sr, Nd, Pb, and O, has a uniform isotopic composition in the mantle. This uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the Earth. ?? 1984.

  2. Isotopic inferences of ancient biochemistries - Carbon, sulfur, hydrogen, and nitrogen

    NASA Technical Reports Server (NTRS)

    Schidlowski, M.; Hayes, J. M.; Kaplan, I. R.

    1983-01-01

    In processes of biological incorporation and subsequent biochemical processing sizable isotope effects occur as a result of both thermodynamic and kinetic fractionations which take place during metabolic and biosynthetic reactions. In this chapter a review is provided of earlier work and recent studies on isotope fractionations in the biogeochemical cycles of carbon, sulfur, hydrogen, and nitrogen. Attention is given to the biochemistry of carbon isotope fractionation, carbon isotope fractionation in extant plants and microorganisms, isotope fractionation in the terrestrial carbon cycle, the effects of diagenesis and metamorphism on the isotopic composition of sedimentary carbon, the isotopic composition of sedimentary carbon through time, implications of the sedimentary carbon isotope record, the biochemistry of sulfur isotope fractionation, pathways of the biogeochemical cycle of nitrogen, and the D/H ratio in naturally occurring materials.

  3. Detection of Hydrogen Spillover in Palladium-Modified Activated Carbon Fibers During Hydrogen Adsorption

    SciTech Connect

    Contescu, Cristian I; Brown, Craig; Liu, Yun; Bhat, Vinay V; Gallego, Nidia C

    2009-01-01

    Palladium-modified activated carbon fibers (Pd-ACF) are being evaluated for adsorptive hydrogen storage at near-ambient conditions because of their enhanced hydrogen uptake in comparison to Pd-free activated carbon fibers (ACF). The net uptake enhancement (at room temperature and 20 bar) is in excess of the amount corresponding to formation of Pd hydride, and is usually attributed to hydrogen spillover. In this paper, inelastic neutron scattering was used to demonstrate the formation of new C-H bonds in Pd-containing activated carbon fibers after exposure to hydrogen at 20 oC and 1.6 MPa, at the expense of physisorbed H2. This finding is a post-factum proof of the atomic nature of H species formed in presence of a Pd catalyst, and of their subsequent spillover and binding to the carbon support. Chemisorption of hydrogen may explain the reduction in hydrogen uptake from first to second adsorption cycle.

  4. Hydrogen isotope type-curves of very hot crude oils.

    PubMed

    Fekete, József; Sajgó, Csanád; Demény, Attila

    2011-01-15

    Several crude oil accumulations in the Pannonian Basin are trapped in uncommonly hot (>170°C) reservoirs. Their maturities range from mature to very mature on the basis of cracking parameters of their biological marker homologous series (ratio of products to reactants). A stable carbon isotopic study of these oils, poor in biological markers commonly used for correlation purposes, did not provide a reliable oil-to-oil correlation. As an alternative tool, the hydrogen isotope compositions of oil fractions separated on the basis of different polarities were measured, and hydrogen isotope type-curves were generated for a set of mature to very mature crude oil samples. This method of presenting hydrogen isotope composition of fractions as type-curves is novel. Nineteen samples (17 crude oils from SE-Hungary, 1 oil condensate and 1 artificial oil) were chosen for the present study. The aim was to examine the applicability of hydrogen isotope type-curves in oil-to-oil correlation and to test the simultaneous application of carbon and hydrogen isotope type-curves in the field of petroleum geochemistry. We have shown that, although the conventionally used co-variation plots proved to be inadequate for the correlation of these hot and mature oils, the simultaneous use of carbon and the newly introduced hydrogen isotope type-curves allows us to group and distinguish oils of different origins.

  5. Cd Isotope Fractionation During Adsorption Varies with Salinity

    NASA Astrophysics Data System (ADS)

    Wasylenki, L. E.; Montanez, G.; Anbar, A. D.

    2009-12-01

    Because its marine concentration profile is very similar to that of phosphate [1], Cd is considered to have potential as a paleophosphate or paleonutrient proxy in the geologic record. Previous work [2,3] has established that lighter isotopes of Cd are preferentially assimilated by phytoplankton, leaving surface waters isotopically heavy. Another recent study [4] suggests that analysis of Cd isotope variations in transects of ferromanganese crusts could reveal past variations in the extent to which Cd, and thus phosphate, has been depleted over time. This idea presumes that the extent of consumption of Cd by phytoplankton is reflected in the isotopic composition of seawater and that the Cd isotopic composition of seawater is in turn faithfully recorded in ferromanganese crusts. To test the latter assumption, Rehkämper et al. [4] measured the Cd isotopic composition of 15 Fe-Mn crusts from various ocean basins and found that 13 of those samples were within analytical error of the Cd isotopic composition of deep seawater from [3], indicating that Cd often does not fractionate appreciably during incorporation into ferromanganese crusts. Other studies [5,6] have likewise revealed little or no variation in Cd isotopic compositions among various terrestrial rocks and carbonaceous chondrites, suggesting that few earth processes significantly fractionate Cd isotopes. To test this conclusion experimentally, we performed adsorption experiments in which aqueous Cd was allowed to adsorb to synthetic birnessite (Mn oxyhydroxide). Stock solutions of dissolved Cd and birnessite suspension were mixed and agitated from 1 to 48 hours at room temperature. Some experiments had 0.1m KNO3 as background electrolyte, while others had 0.3m NaCl + 0.1m KNO3. After filtration, both the fluid with remaining dissolved Cd and solids with adsorbed Cd were purified with anion exchange chemistry. Column yields and proportions of dissolved and adsorbed Cd were determined by ICP-MS, and isotope

  6. A superior process for forming titanium hydrogen isotopic films

    NASA Technical Reports Server (NTRS)

    Steinberg, R.; Alger, D. L.; Cooper, D. W.

    1975-01-01

    Process forms stoichiometric, continuous, strongly bonded titanium hydrogen isotopic films. Films have thermal and electrical conductivities approximately the same as bulk pure titanium, ten times greater than those of usual thin films.

  7. Longitudinal dispersion coefficient depending on superficial velocity of hydrogen isotopes flowing in column packed with zeolite pellets at 77.4 K

    SciTech Connect

    Kotoh, K.; Kubo, K.; Takashima, S.; Moriyama, S.T.; Tanaka, M.; Sugiyama, T.

    2015-03-15

    Authors have been developing a cryogenic pressure swing adsorption system for hydrogen isotope separation. In the problem of its design and operation, it is necessary to predict the concentration profiles developing in packed beds of adsorbent pellets. The profiling is affected by the longitudinal dispersion of gas flowing in packed beds, in addition to the mass transfer resistance in porous media of adsorbent pellets. In this work, an equation is derived for estimating the packed-bed dispersion coefficient of hydrogen isotopes, by analyzing the breakthrough curves of trace D{sub 2} or HD replacing H{sub 2} adsorbed in synthetic zeolite particles packed columns at the liquefied nitrogen temperature 77.4 K. Since specialized for hydrogen isotopes, this equation can be considered to estimate the dispersion coefficients more reliable for the cryogenic hydrogen isotope adsorption process, than the existing equations. (authors)

  8. Production of negative ions of hydrogen isotopes. [Patent application

    SciTech Connect

    Garscadden, A.

    1981-05-14

    A process for generating negative ions of hydrogen isotopes is described which comprises cooling the hydrogen gas below 300K, and preferably to about 200K, vibrationally exciting the molecules of the gas, and then dissociating the molecules by electron impact into neutral hydrogen atoms and negative hydrogen ions. Alternatively, the gas may first be vibrationally excited by heating or the like, and then cooled translationally, for example, by rapid expansion prior to dissociation by electron impact. The processes of this invention are characterized by control of non-equilibrium conditions to obtain large increases in dissociative attachment rates by increasing the population of hydrogen gas molecules having a higher vibrational energy state.

  9. Gas chromatographic separation of hydrogen isotopes using metal hydrides

    SciTech Connect

    Aldridge, F.T.

    1984-05-09

    A study was made of the properties of metal hydrides which may be suitable for use in chromatographic separation of hydrogen isotopes. Sixty-five alloys were measured, with the best having a hydrogen-deuterium separation factor of 1.35 at 60/sup 0/C. Chromatographic columns using these alloys produced deuterium enrichments of up to 3.6 in a single pass, using natural abundance hydrogen as starting material. 25 references, 16 figures, 4 tables.

  10. Adsorption of hydrogen on stable and metastable Ir(100) surfaces

    NASA Astrophysics Data System (ADS)

    Arman, Mohammad Alif; Klein, Andreas; Ferstl, Pascal; Valookaran, Abhilash; Gustafson, Johan; Schulte, Karina; Lundgren, Edvin; Heinz, Klaus; Schneider, Alexander; Mittendorfer, Florian; Hammer, Lutz; Knudsen, Jan

    2017-02-01

    Using the combination of high resolution core level spectroscopy and density functional theory we present a detailed spectroscopic study for all clean and hydrogen covered phases of Ir(100). The results are complemented by an investigation of the hydrogen desorption process from various phases using temperature programmed desorption spectroscopy and scanning tunneling microscopy. In total, all experimentally determined core level shifts match very well with those predicted by density functional theory based on established structural models. In particular, we find for the (bridge site) adsorption on the unreconstructed 1×1 phase that the initial core level shift of surface Ir atoms is altered by +0.17 eV for each Ir-H bond formed. In the submonolayer regime we find evidence for island formation at low temperatures. For the H-induced deconstructed 5×1-H phase we identify four different surface core level shifts with two of them being degenerate. Finally, for the reconstructed 5×1-hex phase also four surface components are identified, which undergo a rather rigid core level shift of +0.15 eV upon hydrogen adsorption suggesting a similarly homogeneous charge transfer to all Ir surface atoms. Thermodesorption experiments for the 5×1-H phase reveal two different binding states for hydrogen independent of the total coverage. We conclude that the surface always separates into patches of fully covered deconstructed and uncovered reconstructed phases. We could also show by tunneling microscopy that with the desorption of the last hydrogen atom from the deconstructed unit cell the surface instantaneously reverts into the reconstructed state. Eventually, we could determine the saturation coverage upon molecular adsorption for all phases to be θmax1 × 1 - H = 1.0 ML , θmax5 × 1 - H = 0.8 ML , and θmax5 × 1 - hex - H ≥ 1.0 ML .

  11. Process for recovering evolved hydrogen enriched with at least one heavy hydrogen isotope

    DOEpatents

    Tanaka, John; Reilly, Jr., James J.

    1978-01-01

    This invention relates to a separation means and method for enriching a hydrogen atmosphere with at least one heavy hydrogen isotope by using a solid titaniun alloy hydride. To this end, the titanium alloy hydride containing at least one metal selected from the group consisting of vanadium, chromium, manganese, molybdenum, iron, cobalt and nickel is contacted with a circulating gaseous flow of hydrogen containing at least one heavy hydrogen isotope at a temperature in the range of -20.degree. to +40.degree. C and at a pressure above the dissociation pressure of the hydrided alloy selectively to concentrate at least one of the isotopes of hydrogen in the hydrided metal alloy. The contacting is continued until equilibrium is reached, and then the gaseous flow is isolated while the temperature and pressure of the enriched hydride remain undisturbed selectively to isolate the hydride. Thereafter, the enriched hydrogen is selectively recovered in accordance with the separation factor (S.F.) of the alloy hydride employed.

  12. Investigation of Morphology and Hydrogen Adsorption Capacity of Disordered Carbons

    NASA Astrophysics Data System (ADS)

    He, Lilin; Melnichenko, Yuri; Gallego, Nidia; Contescu, Cristian

    2014-03-01

    We have applied small angle neutron scattering (SANS) technique to study the morphologies and hydrogen adsorption capabilities of wood-based ultramicroporous carbon and poly(furfuryl alcohol) derived carbon. The Polydispersed Spherical model and chord length analysis of the scattering profiles were performed to obtain morphological parameters such as average pore size and pore size distribution of the dry carbons, which agreed reasonably well with the independent gas sorption measurements. The hydrogen physisorbed in these two carbons at room temperature and moderate pressures was investigated by In-situ SANS measurements. The experimental data analyzed using a modified Kalliat model for decoupling scattering contributions from pores with different sizes indicates that the molecular hydrogen condenses preferentially in narrow micropores at all measured pressures, which supports the theoretical prediction by quantum mechanical and thermodynamical models.

  13. Carbon and Hydrogen Isotopic Fractionation during Anaerobic Biodegradation of Benzene

    PubMed Central

    Mancini, Silvia A.; Ulrich, Ania C.; Lacrampe-Couloume, Georges; Sleep, Brent; Edwards, Elizabeth A.; Sherwood Lollar, Barbara

    2003-01-01

    Compound-specific isotope analysis has the potential to distinguish physical from biological attenuation processes in the subsurface. In this study, carbon and hydrogen isotopic fractionation effects during biodegradation of benzene under anaerobic conditions with different terminal-electron-accepting processes are reported for the first time. Different enrichment factors (ɛ) for carbon (range of −1.9 to −3.6‰) and hydrogen (range of −29 to −79‰) fractionation were observed during biodegradation of benzene under nitrate-reducing, sulfate-reducing, and methanogenic conditions. These differences are not related to differences in initial biomass or in rates of biodegradation. Carbon isotopic enrichment factors for anaerobic benzene biodegradation in this study are comparable to those previously published for aerobic benzene biodegradation. In contrast, hydrogen enrichment factors determined for anaerobic benzene biodegradation are significantly larger than those previously published for benzene biodegradation under aerobic conditions. A fundamental difference in the previously proposed initial step of aerobic versus proposed anaerobic biodegradation pathways may account for these differences in hydrogen isotopic fractionation. Potentially, C-H bond breakage in the initial step of the anaerobic benzene biodegradation pathway may account for the large fractionation observed compared to that in aerobic benzene biodegradation. Despite some differences in reported enrichment factors between cultures with different terminal-electron-accepting processes, carbon and hydrogen isotope analysis has the potential to provide direct evidence of anaerobic biodegradation of benzene in the field. PMID:12513995

  14. Capture of heavy hydrogen isotopes in a metal-organic framework with active Cu(I) sites

    NASA Astrophysics Data System (ADS)

    Weinrauch, I.; Savchenko, I.; Denysenko, D.; Souliou, S. M.; Kim, H.-H.; Le Tacon, M.; Daemen, L. L.; Cheng, Y.; Mavrandonakis, A.; Ramirez-Cuesta, A. J.; Volkmer, D.; Schütz, G.; Hirscher, M.; Heine, T.

    2017-03-01

    The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol-1) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol-1 between D2 and H2 results in D2-over-H2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H2/D2 mixtures allows the prediction of selectivities for tritium-containing isotopologues.

  15. Capture of heavy hydrogen isotopes in a metal-organic framework with active Cu(I) sites

    PubMed Central

    Weinrauch, I.; Savchenko, I.; Denysenko, D.; Souliou, S. M.; Kim, H-H; Le Tacon, M.; Daemen, L. L.; Cheng, Y.; Mavrandonakis, A.; Ramirez-Cuesta, A. J.; Volkmer, D.; Schütz, G.; Hirscher, M.; Heine, T.

    2017-01-01

    The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol−1) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol−1 between D2 and H2 results in D2-over-H2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H2/D2 mixtures allows the prediction of selectivities for tritium-containing isotopologues. PMID:28262794

  16. Hydrogen adsorption in thin films of Prussian blue analogue

    SciTech Connect

    Yang, Dali; Ding, Vivian; Luo, Junhua; Currier, Robert P; Obrey, Steve; Zhao, Yusheng

    2008-01-01

    Quartz crystal microbalance with dissipation (QCM-D) measurement was used to investigate the kinetics of the molecular hydrogen adsorption into thin films of prussian blue analogues - Cu{sub 3}[Co(CN){sub 6}]{sub 2} at ambient conditions. Although the equilibrium adsorption seems to be independent of the thickness, the adsorption rate substantially decreases with the thickness of the films. In addition, the reversibility of H{sub 2} adsorption into the Cu{sub 3}[Co(CN){sub 6}]{sub 2} films was investigated. The results indicate that the Cu{sub 3}[Co(CN){sub 6}]{sub 2} maily interacts with H{sub 2} molecules physically. The highest H{sub 2} uptake by the Cu{sub 3}[Co(CN){sub 6}]{sub 2} films is obtained when the gas phase is stagnant inside the testing cell. However, the unusual high H{sub 2} uptake obtained from the QCM-D measurement makes us question how reliable this analytic methodology is.

  17. Evaluation of the isosteric heat of adsorption at zero coverage for hydrogen on activated carbons

    NASA Astrophysics Data System (ADS)

    Dohnke, E.; Beckner, M.; Romanos, J.; Olsen, R.; Wexler, C.; Pfeifer, P.

    2011-03-01

    Activated carbons made from corn cob show promise as materials for high-capacity hydrogen storage. As part of our characterization of these materials, we are interested in learning how different production methods affect the adsorption energies. In this talk, we will show how hydrogen adsorption isotherms may be used to calculate these adsorption energies at zero coverage using Henry's law. We will additionally discuss differences between the binding energy and the isosteric heat of adsorption by applying this analysis at different temperatures.

  18. Hydrogen isotope separation in carbon nanotubes: calculation of coupled rotational and translational States at high densities.

    PubMed

    Garberoglio, Giovanni; Johnson, J Karl

    2010-03-23

    The effect of the quantized rotational degrees of freedom of hydrogen on the adsorption and sieving properties in carbon nanotubes is studied using computer simulations. We have developed a highly efficient multiple timestep algorithm for hybrid Monte Carlo sampling of quantized rotor configurations and extended the grand canonical Boltzmann bias method to rigid linear molecules. These new computational tools allow us to calculate accurately the quantum sieving selectivities for cases of extreme two-dimensional confinement as a function of pressure. The para-T2/para-H2 selectivity at 20 K is analyzed as a function of the tube diameter and the density of adsorbed hydrogen. Extraordinarily high selectivities, up to 2.6 x 10(8), are observed in the narrowest nanotube. The quantized nature of the rotational degrees of freedom is found to dramatically affect adsorption and selectivity for hydrogen isotopes adsorbed in very narrow nanotubes. The T2/H2 zero-pressure selectivity increases from 2.4 x 10(4) to 1.7 x 10(8) in the (3,6) nanotube at 20 K when quantum rotations are accounted for. The isotopic selectivity is found to increase with pressure, tending to a constant value at saturation. A simplified mean-field model is used to discuss the origin of this behavior.

  19. Sulfur and Hydrogen Isotope Anomalies in Meteorite Sulfonic Acids

    NASA Technical Reports Server (NTRS)

    Cooper, George W.; Thiemens, Mark H.; Jackson, Teresa L.; Chang, Sherwood

    1997-01-01

    Intramolecular carbon, hydrogen, and sulfur isotope ratios were measured on a homologous series of organic sulfonic acids discovered in the Murchison meteorite. Mass-independent sulfur isotope fractionations were observed along with high deuterium/hydrogen ratios. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low-temperature environment that is consistent with that of interstellar clouds. Sulfur-33 enrichments observed in methanesulfonic acid could have resulted from gas-phase ultraviolet irradiation of a precursor, carbon disulfide. The source of the sulfonic acid precursors may have been the reactive interstellar molecule carbon monosulfide.

  20. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    NASA Astrophysics Data System (ADS)

    Ni, Yunyan; Ma, Qisheng; Ellis, Geoffrey S.; Dai, Jinxing; Katz, Barry; Zhang, Shuichang; Tang, Yongchun

    2011-05-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2 cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using δD values in ethane from several basins in the world are in close agreement with similar predictions based on the δ 13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that δD values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that δD values in ethane might be more suitable for modeling than comparable values in methane and propane.

  1. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    USGS Publications Warehouse

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  2. Thermal effects in dynamic storage of hydrogen by adsorption

    SciTech Connect

    Lamari, M.; Aoufi, A.; Malbrunot, P.

    2000-03-01

    Thermal effects in dynamic hydrogen storage by adsorption at room temperature and high pressure are studied theoretically and experimentally. The system of adsorbate-adsorbent used was hydrogen in granular activated carbon. The theoretical analysis was based on heat- and mass-transfer modeling in a packed-bed adsorber, with particular emphasis on the thermal effects occurring during charge and discharge steps. The influence of gas flow rate and storage pressure (up to 15 MPa) on the total amount stored or delivered was investigated. Operating conditions were compatible with practical application for onboard vehicle storage. The experimental study was carried out in cylindrical 2-L reservoirs filled with granular activated carbon in which the bed temperature was measured at various positions. The temperature changes during both charge and discharge agreed well with the model predictions.

  3. Local doping of graphene devices by selective hydrogen adsorption

    SciTech Connect

    Park, Min; Park, Yung Woo E-mail: kbh37@incheon.ac.kr; Yun, Yong Ju; Jun, Yongseok; Lee, Minwoo; Jeong, Dae Hong; Kim, Byung Hoon E-mail: kbh37@incheon.ac.kr

    2015-01-15

    N-type graphene fabricated by exposure to hydrogen gas has been previously studied. Based on this property of graphene, herein, we demonstrate local doping in single-layer graphene using selective adsorption of dissociative hydrogen at 350 K. A graphene field effect transistor was produced covered with PMMA on half of the graphene region. The charge neutrality point of the PMMA-window region shifted to a negative gate voltage (V{sub G}) region prominently compared with that of the PMMA-covered region. Consequently, a single graphene p-n junction was obtained by measuring the V{sub G}-dependent resistance of the whole graphene region. This method presents opportunities for developing and controlling the electronic structure of graphene and device applications.

  4. Hydrogen recycle and isotope exchange from dense carbon films

    SciTech Connect

    Clausing, R.E.; Heatherly, L.

    1987-03-01

    Dense carbon films were prepared by deposition from hydrogen plasmas to which methane was added. The initial hydrogen recycle coefficient from the films ranges from more than two to less than one. The films contain large amounts of hydrogen (up to 50 at. %). They adjust themselves to provide recycling coefficients near unity. Isotope changeover times tend to be long. The reservoir of hydrogen instantly available to the plasma to maintain or stabilize the recycle coefficient and isotopic composition of the plasma is 10/sup 15/ cm/sup -2/ or greater depending on film preparation, temperature, and prior plasma exposure conditions. Simulator observations tend to support and improve the understanding of the observations in TEXTOR and JET; however, they also point out the need for control of film deposition and operating parameters to provide desirable and reproducible properties. The films and the hydrogen isotopes they contain can be removed easily by plasma processes. Since the hydrogen in these films is relatively immobile except in the zone reached by energetic particles, or at temperatures above 400/sup 0/C, dense carbon films may be useful in managing the tritium recovery from near-term fusion experiments.

  5. Hydrogen Adsorption by Alkali Metal Graphite Intercalation Compounds

    NASA Astrophysics Data System (ADS)

    Purewal, Justin

    Adsorption occurs whenever a solid surface is exposed to a gas or liquid, and is characterized by an increase in fluid density near the interface. Adsorbents have drawn attention in the current effort to engineer materials that store hydrogen at high densities within moderate temperature and pressure regimes. Carbon adsorbents are a logical choice as a storage material due to their low costs and large surface areas. Unfortunately, carbon adsorbents suffer from a low binding enthalpy for H2 (about 5 kJ mol-1), well below the 15 to 18 kJ mol-1) that is considered optimal for hydrogen storage systems. Binding interactions can be increased by the following methods: (1) adjusting the graphite interplanar separation with a pillared structure, and (2) introducing dopant species that interact with H2 molecules by strong electrostatic forces. Graphite intercalation compounds are a class of materials that contain both pillared structures and chemical dopants, making them an excellent model system for studying the fundamentals of hydrogen adsorption in nanostructured carbons. Pressure-composition-temperature diagrams of the MC24(H 2)x graphite intercalation compounds were measured for M = (K, Rb, Cs). Adsorption enthalpies were measured as a function of H2 concentration. Notably, CsC24 had an average adsorption enthalpy of 14.9 kJ mol-1), nearly three times larger than that of pristine graphite. The adsorption enthalpies were found to be positively correlated with the alkali metal size. Adsorption capacities were negatively correlated with the size of the alkali metal. The rate of adsorption is reduced at large H2 compositions, due to the effects of site-blocking and correlation on the H2 diffusion. The strong binding interaction and pronounced molecular-sieving behavior of KC24 is likely to obstruct the translational diffusion of adsorbed H2 molecules. In this work, the diffusion of H2 adsorbed in KC24 was studied by quasielastic neutron scattering measurements and molecular

  6. RECTIFIED ABSORPTION METHOD FOR THE SEPARATION OF HYDROGEN ISOTOPES

    DOEpatents

    Hunt, C.D.; Hanson, D.N.

    1961-10-17

    A method is described for separating and recovering heavy hydrogen isotopes from gaseous mixtures by multiple stage cyclic absorption and rectification from an approximate solvent. In particular, it is useful for recovering such isoteoes from ammonia feedstock streams containing nitrogen solvent. Modifications of the process ranging from isobaric to isothermal are provided. Certain impurities are tolerated, giving advantages over conventional fractional distillation processes. (AEC)

  7. Hydrogen Isotopic Systematics of Nominally Anhydrous Phases in Martian Meteorites

    NASA Astrophysics Data System (ADS)

    Tucker, Kera

    Hydrogen isotope compositions of the martian atmosphere and crustal materials can provide unique insights into the hydrological and geological evolution of Mars. While the present-day deuterium-to-hydrogen ratio (D/H) of the Mars atmosphere is well constrained (~6 times that of terrestrial ocean water), that of its deep silicate interior (specifically, the mantle) is less so. In fact, the hydrogen isotope composition of the primordial martian mantle is of great interest since it has implications for the origin and abundance of water on that planet. Martian meteorites could provide key constraints in this regard, since they crystallized from melts originating from the martian mantle and contain phases that potentially record the evolution of the H 2O content and isotopic composition of the interior of the planet over time. Examined here are the hydrogen isotopic compositions of Nominally Anhydrous Phases (NAPs) in eight martian meteorites (five shergottites and three nakhlites) using Secondary Ion Mass Spectrometry (SIMS). This study presents a total of 113 individual analyses of H2O contents and hydrogen isotopic compositions of NAPs in the shergottites Zagami, Los Angeles, QUE 94201, SaU 005, and Tissint, and the nakhlites Nakhla, Lafayette, and Yamato 000593. The hydrogen isotopic variation between and within meteorites may be due to one or more processes including: interaction with the martian atmosphere, magmatic degassing, subsolidus alteration (including shock), and/or terrestrial contamination. Taking into consideration the effects of these processes, the hydrogen isotope composition of the martian mantle may be similar to that of the Earth. Additionally, this study calculated upper limits on the H2O contents of the shergottite and nakhlite parent melts based on the measured minimum H2O abundances in their maskelynites and pyroxenes, respectively. These calculations, along with some petrogenetic assumptions based on previous studies, were subsequently used

  8. Isotopic composition of atmospheric hydrogen and methane

    USGS Publications Warehouse

    Bainbridge, A.E.; Suess, H.E.; Friedman, I.

    1961-01-01

    IN a recent communication, Bishop and Taylor1 express the opinion that the tritium concentration of free hydrogen in the atmosphere has been rising over the past ten years, with a doubling time of approximately 18 months. The authors suspect that artificial tritium was released into the atmosphere several years before the Castle test series in 1954, which is commonly assumed to have led to the first pronounced rise in the tritium concentration of terrestrial surface water. Bishop and Taylor's communication includes a diagram of the logarithms of all the experimentally determined tritium values in free atmospheric hydrogen plotted against time. The plot shows that the values follow a straight line that includes the first value obtained by Faltings and Harteck2 on atmospheric hydrogen collected in 1948. ?? 1961 Nature Publishing Group.

  9. A hydrogen gas-water equilibration method produces accurate and precise stable hydrogen isotope ratio measurements in nutrition studies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable hydrogen isotope methodology is used in nutrition studies to measure growth, breast milk intake, and energy requirement. Isotope ratio MS is the best instrumentation to measure the stable hydrogen isotope ratios in physiological fluids. Conventional methods to convert physiological fluids to ...

  10. Lignin methoxyl hydrogen isotope ratios in a coastal ecosystem

    NASA Astrophysics Data System (ADS)

    Feakins, Sarah J.; Ellsworth, Patricia V.; Sternberg, Leonel da Silveira Lobo

    2013-11-01

    Stable hydrogen isotope ratios of plant lignin methoxyl groups have recently been shown to record the hydrogen isotopic composition of meteoric water. Here we extend this technique towards tracing water source variations across a saltwater to freshwater gradient in a coastal, subtropical forest ecosystem. We measure the hydrogen isotopic composition of xylem water (δDxw) and methoxyl hydrogen (δDmethoxyl) to calculate fractionations for coastal mangrove, buttonwood and hammock tree species in Sugarloaf Key, as well as buttonwoods from Miami, both in Florida, USA. Prior studies of the isotopic composition of cellulose and plant leaf waxes in coastal ecosystems have yielded only a weak correlation to source waters, attributed to leaf water effects. Here we find δDmethoxyl values range from -230‰ to -130‰, across a 40‰ range in δDxw with a regression equation of δDmethoxyl ‰ = 1.8 * δDxw - 178‰ (R2 = 0.48, p < 0.0001, n = 74). This is comparable within error to the earlier published relationship for terrestrial trees which was defined across a much larger 125‰ isotopic range in precipitation. Analytical precision for measurements of δD values of pure CH3I by gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-P-IRMS) is σ = 6‰ (n = 31), which is considerably better than for CH3I liberated through cleavage with HI from lignin with σ = 18‰ (n = 26). Our results establish that δDmethoxyl can record water sources and salinity incursion in coastal ecosystems, where variations sufficiently exceed method uncertainties (i.e., applications with δD excursions >50‰). For the first time, we also report yields of propyl iodide, which may indicate lignin synthesis of propoxyl groups under salt-stress.

  11. Hydrogen isotope MicroChemLab FY15.

    SciTech Connect

    Robinson, David; Luo, Weifang; Stewart, Kenneth D.

    2015-09-01

    We have developed a new method to measure the composition of gaseous mixtures of any two hydrogen isotopes, as well as an inert gas component. When tritium is one of those hydrogen isotopes, there is usually some helium present, because the tritium decays to form helium at a rate of about 1% every 2 months. The usual way of measuring composition of these mixtures involves mass spectrometry, which involves bulky, energy-intensive, expensive instruments, including vacuum pumps that can quite undesirably disperse tritium. Our approach uses calorimetry of a small quantity of hydrogen-absorbing material to determine gas composition without consuming or dispersing the analytes. Our work was a proof of principle using a rather large and slow benchtop calorimeter. Incorporation of microfabricated calorimeters, such as those that have been developed in Sandia’s MicroChemLab program or that are now commercially available, would allow for faster measurements and a smaller instrument footprint.

  12. Uranium Isotopic Fractionation Induced by U(VI) Adsorption onto Common Aquifer Minerals.

    PubMed

    Jemison, N E; Johnson, T M; Shiel, A E; Lundstrom, C C

    2016-11-15

    Uranium groundwater contamination due to U mining and processing affects numerous sites globally. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is potentially a very effective remediation strategy. Uranium isotopes ((238)U/(235)U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ∼1‰ isotopic fractionation, with the U(IV) product enriched in (238)U. However, the isotopic fractionation produced by adsorption may complicate the use of (238)U/(235)U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn oxides produced a -0.2‰ fractionation with the adsorbed U(VI) depleted in (238)U. In this study, adsorption to quartz, goethite, birnessite, illite, and aquifer sediments induced an average isotopic fractionation of -0.15‰ with the adsorbed U(VI) isotopically lighter than coexisting aqueous U(VI). In bicarbonate-bearing matrices, the fractionation depended little on the nature of the sorbent, with only birnessite producing an atypically large fractionation. In the case of solutions with ionic strengths much lower than those of typical groundwater, less isotopic fractionation was produced than U(VI) solutions with greater ionic strength. Studies using U isotope data to assess U(VI) reduction must consider adsorption as a lesser, but significant isotope fractionation process.

  13. Poisoning effect on solubility of hydrogen isotopes in getter materials

    NASA Astrophysics Data System (ADS)

    Yamanaka, Shinsuke; Sato, Yuichi; Ogawa, Hidenori; Shirasu, Yoshirou; Miyake, Masanobu

    1991-03-01

    Hydrogen and deuterium solubilities in Ti-C and Zr-N alloys with various compositions have been measured at pressures below 100 Pa. All of the solubility data were found to follow Sieverts' law. The presence of carbon in Ti increased the solubilities of hydrogen isotopes and reduced the enthalpies of solution. The solubility increased and the enthalpy of solution decreased with addition of nitrogen into Zr. The hydrogen solubility in Ti-C and Zr-N alloys was larger than the deuterium solubility. Partial thermodynamic functions of hydrogen and deuterium in Ti-C and Zr-N alloys were obtained by a dilute solution model and compared with those in Ti-(O, N) and Zr-O alloys. The isotope effect of hydrogen and deuterium solubilities in the Ti-(O, N, C) and Zr-(O, N) alloys was discussed, and the tritium solubility in Ti-C and Zr-N alloys was evaluated from hydrogen and deuterium data.

  14. Laser-induced separation of hydrogen isotopes in the liquid phase

    DOEpatents

    Freund, Samuel M.; Maier, II, William B.; Beattie, Willard H.; Holland, Redus F.

    1980-01-01

    Hydrogen isotope separation is achieved by either (a) dissolving a hydrogen-bearing feedstock compound in a liquid solvent, or (b) liquefying a hydrogen-bearing feedstock compound, the liquid phase thus resulting being kept at a temperature at which spectral features of the feedstock relating to a particular hydrogen isotope are resolved, i.e., a clear-cut isotope shift is delineated, irradiating the liquid phase with monochromatic radiation of a wavelength which at least preferentially excites those molecules of the feedstock containing a first hydrogen isotope, inducing photochemical reaction in the excited molecules, and separating the reaction product containing the first isotope from the liquid phase.

  15. Process for hydrogen isotope concentration between liquid water and hydrogen gas

    DOEpatents

    Stevens, William H.

    1976-09-21

    A process for hydrogen isotope exchange and concentration between liquid water and hydrogen gas, wherein liquid water and hydrogen gas are contacted, in an exchange section, with one another and with at least one catalyst body comprising at least one metal selected from Group VIII of the Periodic Table and preferably a support therefor, the catalyst body has a liquid-water-repellent, gas permeable polymer or organic resin coating, preferably a fluorinated olefin polymer or silicone coating, so that the isotope concentration takes place by two simultaneously occurring steps, namely, ##EQU1## WHILE THE HYDROGEN GAS FED TO THE EXCHANGE SECTION IS DERIVED IN A REACTOR VESSEL FROM LIQUID WATER THAT HAS PASSED THROUGH THE EXCHANGE SECTION.

  16. Isotopic disproportionation during hydrogen isotopic analysis of nitrogen-bearing organic compounds

    USGS Publications Warehouse

    Nair, Sreejesh; Geilmann, Heike; Coplen, Tyler B.; Qi, Haiping; Gehre, Matthias; Schimmelmann, Arndt; Brand, Willi A.

    2015-01-01

    Rationale High-precision hydrogen isotope ratio analysis of nitrogen-bearing organic materials using high-temperature conversion (HTC) techniques has proven troublesome in the past. Formation of reaction products other than molecular hydrogen (H2) has been suspected as a possible cause of incomplete H2 yield and hydrogen isotopic fractionation. Methods The classical HTC reactor setup and a modified version including elemental chromium, both operated at temperatures in excess of 1400 °C, have been compared using a selection of nitrogen-bearing organic compounds, including caffeine. A focus of the experiments was to avoid or suppress hydrogen cyanide (HCN) formation and to reach quantitative H2 yields. The technique also was optimized to provide acceptable sample throughput. Results The classical HTC reaction of a number of selected compounds exhibited H2 yields from 60 to 90 %. Yields close to 100 % were measured for the experiments with the chromium-enhanced reactor. The δ2H values also were substantially different between the two types of experiments. For the majority of the compounds studied, a highly significant relationship was observed between the amount of missing H2and the number of nitrogen atoms in the molecules, suggesting the pyrolytic formation of HCN as a byproduct. A similar linear relationship was found between the amount of missing H2 and the observed hydrogen isotopic result, reflecting isotopic fractionation. Conclusions The classical HTC technique to produce H2 from organic materials using high temperatures in the presence of glassy carbon is not suitable for nitrogen-bearing compounds. Adding chromium to the reaction zone improves the yield to 100 % in most cases. The initial formation of HCN is accompanied by a strong hydrogen isotope effect, with the observed hydrogen isotope results on H2 being substantially shifted to more negative δ2H values. The reaction can be understood as an initial disproportionation leading to H2 and HCN

  17. Hydrogen Isotopic Composition of Hornblendes From Active Volcanoes of Mexico

    NASA Astrophysics Data System (ADS)

    Taran, Y.; Kusakabe, M.; Valdez, G.; Mora, J. C.

    2002-12-01

    Horblendes (Hb) crystallize in water-rich magmas in magma chambers or in deeper zones. Isotopic composition of hydrogen in OH-groups of Hb represents the water isotopic composition of magmatic fluid or dissolved magmatic volatiles and therefore, is an isotopic characteristics of magmatic water. At lower vapor pressure in conduits and shallower magma chambers, Hb can decompose and loose water with significant isotopic effects. We measured hydrogen isotopic composition of hornblendes from modern lavas and pyroclastics of El Chichon, Colima and Popocatepetl volcanoes. Hornblendes from the last and previous pyroclastic flows of El Chichon are the more abundant mineral phases (after plagioclase), showing pleochroism from green to brown. They are relatively uniform in composition (close to magnesian hastingsite hornblende), without chemical variations between cores and rims. Using the Johnson and Rutherford (1989) calibration of the Al-in-hornblende geobarometer, the hornblendes show equilibrium with the melt at pressure of 4 kb that correspond to 12 km of depth. These pressure conditions likely represent the location of the magma chamber below El Chichon volcano, however, these pressure estimates need to be confirmed. The water content of all analyzed Hbs is 1.5-1.8 wt%, but may be higher due to a minor amount of impurities of pyroxenes which sometimes are difficult to separate from Hb. Hydrogen isotopic composition in 10 samples of Hb from El Chichon of different age and facies (pumice, lithic fragments in pyroclastics) was in a narrow range -40 to -37 permil V-SMOW. Such isotopic signature corresponds to so-called "andesitic" waters, i.e. waters from subduction-related magmas, The origin of these waters is suggested to be the recycled water from subducted oceanic sediments. The data for El Chichon volcano are in the range of the already known values for subduction-related magmas though the tectonic setting of El Chichon is more complicated. The measured isotopic

  18. Adsorption properties of polyvinyl-alcohol-grafted particles toward genistein driven by hydrogen-bond interaction.

    PubMed

    Zhang, Yanyan; Gao, Baojiao; Xu, Zeqing

    2013-05-09

    The adsorption properties of polyvinyl alcohol (PVA)-grafted silica gel particles PVA/SiO2 toward genistein are researched in this paper. The effects of the main factors on the adsorption properties are investigated, the adsorption mechanism is explored in depth, and the adsorption thermodynamics is researched. The experimental results show that the conventional hydrogen bond is formed between the hydroxyl groups with high density on the surfaces of PVA/SiO2 and the phenolic hydroxyl groups in genistein, while π-type hydrogen bond is formed between the hydroxyl groups of PVA/SiO2 and the conjugated aromatic rings. It is the two types of hydrogen bond that make the functional composite particles PVA/SiO2 produce very strong physical adsorption toward genistein. The competitive adsorption of the solvent can have severe negative impact on the adsorption capacity of genistein. Increasing temperature will weaken the hydrogen-bond interaction between PVA/SiO2 particles and genistein. The existence of electrolytes in the protic solvent will affect the adsorption negatively. The adsorption process of PVA/SiO2 particles toward genistein is exothermic and driven by enthalpy. The adsorption isotherm data matches the Langmuir model.

  19. Adsorption of hydrogen on Pt(111) and Pt(100) surfaces and its role in the HOR.

    SciTech Connect

    Strmcnik, D.; Tripkovic, D.; van der Vliet, D.; Stamenkovic, V.; Markovic, N. M.; Materials Science Division

    2008-10-01

    Hydrogen adsorption isotherms, evaluated by combination of cyclic voltammetry and chronoamperometry, are reported on Pt(1 1 1) and Pt(1 0 0) surfaces in 0.1 M HClO{sub 4}. We found that at E > 0.05 V Pt(1 1 1) and Pt(1 0 0) are only partially covered by the adsorbed hydrogen (H{sub ad}). On both surfaces, a full monolayer of the adsorbed hydrogen is completed at -0.1 V, i.e. the adsorption of atomic hydrogen is observed in the hydrogen evolution potential region. We also found, that the activity of the hydrogen oxidation reaction is mirrored by the shape of the hydrogen adsorption isotherms, implying that H{sub ad} is in fact a spectator in the HOR.

  20. Comparison of methods for separating small quantities of hydrogen isotopes from an inert gas

    SciTech Connect

    Willms, R.S.; Tuggle, D.; Birdsell, S.; Parkinson, J.; Price, B.; Lohmeir, D.

    1998-03-01

    It is frequent within tritium processing systems that a small amount of hydrogen isotopes (Q{sub 2}) must be separated from an inert gas such as He, Ar and N{sub 2}. Thus, a study of presently available technologies for effecting such a separation was performed. A base case and seven technology alternatives were identified and a simple design of each was prepared. These technologies included oxidation-adsorption-metal bed reduction, oxidation-adsorption-palladium membrane reactor, cryogenic adsorption, cryogenic trapping, cryogenic distillation, hollow fiber membranes, gettering and permeators. It was found that all but the last two methods were unattractive for recovering Q{sub 2} from N{sub 2}. Reasons for technology rejection included (1) the method unnecessarily turns the hydrogen isotopes into water, resulting in a cumbersome and more hazardous operation, (2) the method would not work without further processing, and (3) while the method would work, it would only do so in an impractical way. On the other hand, getters and permeators were found to be attractive methods for this application. Both of these methods would perform the separation in a straightforward, essentially zero-waste, single step operation. The only drawback for permeators was that limited low-partial Q{sub 2} pressure data is available. The drawbacks for getters are their susceptibility to irreversible and exothermic reaction with common species such as oxygen and water, and the lack of long-term operation of such beds. More research is envisioned for both of these methods to mature these attractive technologies.

  1. Effect of nitrogen doping of graphene oxide on hydrogen and hydroxyl adsorption

    NASA Astrophysics Data System (ADS)

    Min, Byeong June; Jeong, Hae Kyung

    2014-05-01

    We investigate how nitrogen-doping affects the hydrogen (H) and the hydroxyl (OH) adsorption on graphene oxide (GO) and on nitrogen-doped GO (NGO) via pseudopotential plane wave density functional calculations within the local spin density approximation. We find that the nitrogendoping brings about drastic changes in the hydrogen and the hydroxyl adsorption energetics, but its effects depend sensitively on the nitrogen configuration in NGO. The H and the OH adsorption energies are comparable only for pyrrolic NGO. In GO and quarternary NGO, the H adsorption energy is greater than the OH adsorption energy while the trend is reversed in pyridinic NGO. Also, the OH adsorption process is less affected by nitrogen-doping than the H adsorption is.

  2. First-principles investigation of vanadium isotope fractionation in solution and during adsorption

    NASA Astrophysics Data System (ADS)

    Wu, Fei; Qin, Tian; Li, Xuefang; Liu, Yun; Huang, Jen-How; Wu, Zhongqing; Huang, Fang

    2015-09-01

    Equilibrium fractionation factors of vanadium (V) isotopes among tri- (V(III)), tetra- (V(IV)) and penta-valent (V(V)) inorganic V species in aqueous system and during adsorption of V(V) to goethite are estimated using first-principles calculation. Our results highlight the dependence of V isotope fractionation on valence states and the chemical binding environment. The heavy V isotope (51V) is enriched in the main V species following a sequence of V(III) < V(IV) < V(V). According to our calculations, at 25 °C, the equilibrium isotope fractionation factor between [V5+O2(OH)2]- and [V4+O(H2O)5]2+ (ln ⁡α V (V)- V (IV)) is 3.9‰, and the equilibrium isotope fractionation factor between [V5+O2(OH)2]- and [V3+(OH)3(H2O)3] (ln ⁡α V (V)- V (III)) is 6.4‰. In addition, isotope fractionation between +5 valence species [V5+O2(OH)2]- and [V5+O2(H2O)4]+ is 1.5‰ at 25 °C, which is caused by their different bond lengths and coordination numbers (CN). Theoretical calculations also show that light V isotope (50V) is preferentially adsorbed on the surface of goethite. Our work reveals that V isotopes can be significantly fractionated in the Earth's surface environments due to redox reaction and mineral adsorption, indicating that V isotope data can be used to monitor toxic V(V) attenuation processes through reduction or adsorption in natural water systems. In addition, a simple mass balance model suggests that V isotope composition of seawater might vary with change of ambient oxygen levels. Thus our theoretical investigations imply a promising future for V isotopes as a potential new paleo-redox tracer.

  3. Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures

    NASA Astrophysics Data System (ADS)

    van Zuilen, Kirsten; Müller, Thomas; Nägler, Thomas F.; Dietzel, Martin; Küsters, Tim

    2016-08-01

    Variations in barium (Ba) stable isotope abundances measured in low and high temperature environments have recently received increasing attention. The actual processes controlling Ba isotope fractionation, however, remain mostly elusive. In this study, we present the first experimental approach to quantify the contribution of diffusion and adsorption on mass-dependent Ba isotope fractionation during transport of aqueous Ba2+ ions through a porous medium. Experiments have been carried out in which a BaCl2 solution of known isotopic composition diffused through u-shaped glass tubes filled with silica hydrogel at 10 °C and 25 °C for up to 201 days. The diffused Ba was highly fractionated by up to -2.15‰ in δ137/134Ba, despite the low relative difference in atomic mass. The time-dependent isotope fractionation can be successfully reproduced by a diffusive transport model accounting for mass-dependent differences in the effective diffusivities of the Ba isotope species (D137Ba /D134Ba =(m134 /m137) β). Values of β extracted from the transport model were in the range of 0.010-0.011. Independently conducted batch experiments revealed that adsorption of Ba onto the surface of silica hydrogel favoured the heavier Ba isotopes (α = 1.00015 ± 0.00008). The contribution of adsorption on the overall isotope fractionation in the diffusion experiments, however, was found to be small. Our results contribute to the understanding of Ba isotope fractionation processes, which is crucial for interpreting natural isotope variations and the assessment of Ba isotope ratios as geochemical proxies.

  4. Installations for separation of hydrogen isotopes by the method of chemical isotopic exchange in the `water-hydrogen` system

    SciTech Connect

    Andreev, B.M.; Sakharovsky, Y.A.; Rozenkevich, M.B.; Magomedbekov, E.P.; Park, Y.S.; Uborskiy, V.V.; Trenin, V.D.; Alekseev, I.A.; Fedorchenko, O.A.; Karpov, S.P.; Konoplev, K.A.

    1995-10-01

    The paper presents the results of more than a year of running a pilot setup for separation of hydrogen isotopes using catalytic isotopic exchange between hydrogen and liquid water. The setup is 5 m high, has the inner diameter of 28 mm, and is equipped with upper and lower reflux devices. The experimental values of HETP vary from 15 cm at T=333 K to 38 cm at T=293 K. The setup is capable of upgrading diluted heavy water with 85-90% deuterium content up to [D{sub 2}O] > 99.95 at.%, yielding daily 4 kg of the product. We also report on the progress in constructing a similar setup for eliminating tritium and an industrial setup, for which the one reported is a prototype. 10 refs., 1 fig., 3 tabs.

  5. Impact of hydrogen isotope species on microinstabilities in helical plasmas

    NASA Astrophysics Data System (ADS)

    Nakata, Motoki; Nunami, Masanori; Sugama, Hideo; Watanabe, Tomo-Hiko

    2016-07-01

    The impact of isotope ion mass on ion-scale and electron-scale microinstabilities such as ion temperature gradient (ITG) mode, trapped electron mode (TEM), and electron temperature gradient (ETG) mode in helical plasmas are investigated by using gyrokinetic Vlasov simulations with a hydrogen isotope and real-mass kinetic electrons. Comprehensive scans for the equilibrium parameters and magnetic configurations clarify the transition from ITG mode to TEM instability, where a significant TEM enhancement is revealed in the case of inward-shifted plasma compared to that in the standard configuration. It is elucidated that the ion-mass dependence on the ratio of the electron-ion collision frequency to the ion transit one, i.e. {ν\\text{ei}}/{ω\\text{ti}}\\propto {{≤ft({{m}\\text{i}}/{{m}\\text{e}}\\right)}1/2} , leads to a stabilization of the TEM for heavier isotope ions. The ITG growth rate indicates a gyro-Bohm-like ion-mass dependence, where the mixing-length estimate of diffusivity yields γ /k\\bot2\\propto m\\text{i}1/2 . On the other hand, a weak isotope dependence of the ETG growth rate is identified. A collisionality scan also reveals that the TEM stabilization by the isotope ions becomes more significant for relatively higher collisionality in a banana regime.

  6. Isotope separation by photochromatography

    DOEpatents

    Suslick, K.S.

    1975-10-03

    A photochromatographic method for isotope separation is described. An isotopically mixed molecular species is adsorbed on an adsorptive surface, and the adsorbed molecules are irradiated with radiation of a predetermined wavelength which will selectively excite desired isotopic species. Sufficient energy is transferred to the excited molecules to desorb them from the surface and thus separate them from the undesired isotopic species. The method is particularly applicable to the separation of hydrogen isotopes. (BLM)

  7. Isotope separation by photochromatography

    DOEpatents

    Suslick, Kenneth S.

    1977-01-01

    An isotope separation method which comprises physically adsorbing an isotopically mixed molecular species on an adsorptive surface and irradiating the adsorbed molecules with radiation of a predetermined wavelength which will selectively excite a desired isotopic species. Sufficient energy is transferred to the excited molecules to desorb them from the surface and thereby separate them from the unexcited undesired isotopic species. The method is particularly applicable to the separation of hydrogen isotopes.

  8. Unexpected hydrogen isotope variation in oceanic pelagic seabirds.

    PubMed

    Ostrom, Peggy H; Wiley, Anne E; Rossman, Sam; Stricker, Craig A; James, Helen F

    2014-08-01

    Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. The basis for this methodology lies in predictable, continental patterns of precipitation δD values that are often reflected in an organism's tissues. δD variation is not expected for oceanic pelagic organisms whose dietary hydrogen (water and organic hydrogen in prey) is transferred up the food web from an isotopically homogeneous water source. We report a 142‰ range in the δD values of flight feathers from the Hawaiian petrel (Pterodroma sandwichensis), an oceanic pelagic North Pacific species, and inquire about the source of that variation. We show δD variation between and within four other oceanic pelagic species: Newell's shearwater (Puffinus auricularis newellii), Black-footed albatross (Phoebastria nigripes), Laysan albatross (Phoebastria immutabilis) and Buller's shearwater (Puffinus bulleri). The similarity between muscle δD values of hatch-year Hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. Salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.

  9. Unexpected hydrogen isotope variation in oceanic pelagic seabirds

    USGS Publications Warehouse

    Ostrom, Peggy H.; Wiley, Anne E.; Rossman, Sam; Stricker, Craig A.; James, Helen F.

    2014-01-01

    Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. The basis for this methodology lies in predictable, continental patterns of precipitation δD values that are often reflected in an organism's tissues. δD variation is not expected for oceanic pelagic organisms whose dietary hydrogen (water and organic hydrogen in prey) is transferred up the food web from an isotopically homogeneous water source. We report a 142% range in the δD values of flight feathers from the Hawaiian petrel (Pterodroma sandwichensis), an oceanic pelagic North Pacific species, and inquire about the source of that variation. We show δD variation between and within four other oceanic pelagic species: Newell's shearwater (Puffinus auricularis newellii), Black-footed albatross (Phoebastria nigripes), Laysan albatross (Phoebastria immutabilis) and Buller's shearwater (Puffinus bulleri). The similarity between muscle δD values of hatch-year Hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. Salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.

  10. Structure and hydrogen adsorption properties in low density nanoporous carbons from simulations

    SciTech Connect

    Peng, L.; Morris, James R

    2012-01-01

    We systematically model the hydrogen adsorption in nanoporous carbons over a wide range of carbon bulk densities (0.6 - 2.4 g/cm3) by using tight binding molecular dynamics simulations for the carbon structures and thermodynamics calculations of the hydrogen adsorption. The resulting structures are in good agreement with the experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by comparisons of the microstructure at atomic level, pair distribution function, and pore size distribution. The hydrogen adsorption calculations in carbon structures demonstrate both a promising hydrogen storage capacity (excess uptake of 1.33 wt% at 298K and 5 MPa, for carbon structures at the lower range of densities) and a reasonable heat of adsorption (12-22 kJ/mol). This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons.

  11. The molecular mechanism of Mo isotope fractionation during adsorption to birnessite

    USGS Publications Warehouse

    Wasylenki, L.E.; Weeks, C.L.; Bargar, J.R.; Spiro, T.G.; Hein, J.R.; Anbar, A.D.

    2011-01-01

    Fractionation of Mo isotopes during adsorption to manganese oxides is a primary control on the global ocean Mo isotope budget. Previous attempts to explain what drives the surprisingly large isotope effect ??97/95Modissolved-??97/95Moadsorbed=1.8??? have not successfully resolved the fractionation mechanism. New evidence from extended X-ray absorption fine structure analysis and density functional theory suggests that Mo forms a polymolybdate complex on the surfaces of experimental and natural samples. Mo in this polynuclear structure is in distorted octahedral coordination, while Mo remaining in solution is predominantly in tetrahedral coordination as MoO42- Our results indicate that the difference in coordination environment between dissolved Mo and adsorbed Mo is the cause of isotope fractionation. The molecular mechanism of metal isotope fractionation in this system should enable us to explain and possibly predict metal isotope effects in other systems where transition metals adsorb to mineral surfaces. ?? 2011 Elsevier Ltd.

  12. Evidence From Hydrogen Isotopes in Meteorites for a Martian Permafrost

    NASA Technical Reports Server (NTRS)

    Usui, T.; Alexander, C. M. O'D.; Wang, J.; Simon, J. I.; Jones, J. H.

    2014-01-01

    Fluvial landforms on Mars suggest that it was once warm enough to maintain persistent liquid water on its surface. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. We have investigated the evolution of surface water/ ice and its interaction with the atmosphere by measurements of hydrogen isotope ratios (D/H: deuterium/ hydrogen) of martian meteorites. Hydrogen is a major component of water (H2O) and its isotopes fractionate significantly during hydrological cycling between the atmosphere, surface waters, ground ice, and polar cap ice. Based on in situ ion microprobe analyses of three geochemically different shergottites, we reported that there is a water/ice reservoir with an intermediate D/H ratio (delta D = 1,000?2500 %) on Mars. Here we present the possibility that this water/ice reservoir represents a ground-ice/permafrost that has existed relatively intact over geologic time.

  13. Raman spectroscopic and mass spectrometric investigations of the hydrogen isotopes and isotopically labelled methane

    SciTech Connect

    Jewett, J.R., Fluor Daniel Hanford

    1997-02-24

    Suitable analytical methods must be tested and developed for monitoring the individual process steps within the fuel cycle of a fusion reactor and for tritium accountability. The utility of laser-Raman spectroscopy accompanied by mass spectrometry with an Omegatron was investigated using the analysis of all hydrogen isotopes and isotopically labeled methanes as an example. The Omegatron is useful for analyzing all hydrogen isotopes mixed with the stable helium isotopes. The application of this mass spectrometer were demonstrated by analyzing mixtures of deuterated methanes. In addition, it was employed to study the radiochemical Witzbach exchange reaction between tritium and methanes. A laser-Raman spectrometer was designed for analysis of tritium-containing gases and was built from individual components. A tritium-compatible, metal-sealed Raman cuvette having windows with good optical properties and additional means for measuring the stray light was first used successfully in this work. The Raman spectra of the hydrogen isotopes were acquired in the pure rotation mode and in the rotation-vibration mode and were used for on. The deuterated methanes were measured by Raman spectroscopy, the wavenumbers determined were assigned to the corresponding vibrations, and the wavenumbers for the rotational fine-structure were summarized in tables. The fundamental Vibrations of the deuterated methanes produced Witzbach reactions were detected and assigned. The fundamental vibrations of the molecules were obtained with Raman spectroscopy for the first time in this work. The @-Raman spectrometer assembled is well suited for the analysis of tritium- containing gases and is practical in combination with mass spectrometry using an Omegatron, for studying gases used in fusion.

  14. Finite-Temperature Hydrogen Adsorption/Desorption Thermodynamics Driven by Soft Vibration Modes

    SciTech Connect

    Woo, Sung-Jae; Lee, Eui-Sup; Yoon, Mina; Yong-Hyun, Kim

    2013-01-01

    It is widely accepted that room-temperature hydrogen storage on nanostructured or porous materials requires enhanced dihydrogen adsorption. In this work we reveal that room-temperature hydrogen storage is possible not only by the enhanced adsorption, but also by making use of the vibrational free energy from soft vibration modes. These modes exist for example in the case of metallo-porphyrin-incorporated graphenes (M-PIGs) with out-of-plane ( buckled ) metal centers. There, the in-plane potential surfaces are flat because of multiple-orbital-coupling between hydrogen molecules and the buckled-metal centers. This study investigates the finite-temperature adsorption/desorption thermodynamics of hydrogen molecules adsorbed on M-PIGs by employing first-principles total energy and vibrational spectrum calculations. Our results suggest that the current design strategy for room-temperature hydrogen storage materials should be modified by explicitly taking finite-temperature vibration thermodynamics into account.

  15. Equilibrium carbon and hydrogen isotope fractionation in iron

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2009-12-01

    Recent theoretical and experimental studies (e.g., [1-3]) have suggested that Si- and Fe-isotopic signatures can be used to characterize the compositions and conditions of segregation of metallic cores in planetary interiors. This study expands the theoretical framework to include carbon and hydrogen, which may also be alloying elements. Hydrogen (D/H) and carbon (13C/12C) fractionations in iron-rich metallic melts are estimated by modeling analogous iron-rich crystals, i.e., dhcp-FeH and η-Fe2C. C- and H-atoms in these crystals are completely coordinated by iron. The driving energy for equilibrium fractionation is assumed to come from the reduction of vibrational frequencies when heavy isotopes are substituted for light ones; vibrations are assumed to be harmonic. This treatment is crude at high temperature, and for the relatively anharmonic vibrations typical of hydrogen-bearing substances, but may provide a reasonably accurate, semi-quantitative approximation of real fractionation behavior. Vibrational frequencies of all crystals are modeled with density functional theory, using gradient-corrected functionals and ultrasoft pseudopotentials. For both carbon and hydrogen, the models suggest that the metal phase will be strongly depleted in heavy isotopes. At 2000 K, 1 atm, η-Fe2C will have 3‰ lower 13C/12C than coexisting diamond. Combining this result with previous high-temperature theoretical and experimental studies (e.g., [4]), metal-graphite fractionation is expected to be very similar, while metal-CO2 fractionation will be almost twice as large, ca. -5‰. Deuterium/hydrogen fractionations are expected to be an order of magnitude larger, with 50-70‰ lower D/H in dhcp-FeH than in coexisting H2 gas at 2000 K, and approximately 100‰ lower D/H than water vapor. These fractionations are much larger than those inferred for silicon and iron, as expected given the differences in atomic mass. References: 1. Georg et al. (2007) Nature 447:1102; 2. Rustad & Yin

  16. Practical-scale tests of cryogenic molecular sieve for separating low-concentration hydrogen isotopes from helium

    NASA Astrophysics Data System (ADS)

    Willms, R. S.; Taylor, D. J.; Enoeda, Mikio; Okuno, Kenji

    1994-04-01

    Earlier bench-scale work at the Tritium Systems Test Assembly (TSTA) at Los Alamos National Laboratory examined a number of adsorbents for their suitability for separating low-concentration hydrogen (no tritium) from helium. One of the effective adsorbents was Linde 5A molecular sieve. Recently, experiments including tritium were conducted using practical-scale adsorbers. These tests used existing cryogenic molecular sieve beds (CMSB's) which each contain about 1.6 kg of Linde 5A molecular sieve. They are part of the TSTA integrated tritium processing system. Gas was fed to each CMSB at about 13 SLPM with a nominal composition of 99% He, 0.98% H2, and 0.02% HT. In all cases, for an extended period of time, the beds allowed no detectable (via Raman spectroscopy) hydrogen isotopes to escape in the bed effluent. Thereafter, the hydrogen isotopes appeared in the bed exit with a relatively sharp breakthrough curve. This work concludes that cryogenic molecular sieve adsorption is a practical and effective means of separating low-concentration hydrogen isotopes from a helium carrier.

  17. First-principles study on hydrogen adsorption on nitrogen doped graphene

    NASA Astrophysics Data System (ADS)

    Muhammad, Rafique; Shuai, Yong; Tan, He-Ping

    2017-04-01

    In this paper we have investigated the adsorption of Hydrogen on Nitrogen doped graphene in detail by means of first-principles calculations. A comprehensive study is performed of the structural, electronic and optical properties of hydrogen atoms adsorbed on dopant atoms sites and on carbon atoms neighboring dopant atoms. The effect of doping has been investigated by varying the concentration of doping atoms from 3.125%(one atom of nitrogen in 32 host atoms) to 6.25% (two nitrogen atoms in 32 host atoms). Similarly the effect of adsorption has been investigated by varying the concentration of hydrogen atoms and also varying the adsorption sites. Band structure, partial density of states (PDOS) and optical properties of pure, nitrogen doped and hydrogen adsorbed graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with nitrogen doped graphene and Hydrogen adsorbed graphene sheet. It is found that upon nitrogen doping the Dirac point in the graphene band structure shifts below the Fermi Energy level and energy gap appears at the high symmetric K-point. On the other hand, by adsorption of Hydrogen atom, there is further change in the band structure near the Fermi level and also the energy gap at the high symmetric K-point is increased. There is change in the dielectric function and refractive index of the graphene after H atoms adsorption on N-doped graphene. The overall absorption spectra is decreased in case of nitrogen doping and after adsorption process of Hydrogen atoms. However a significant red shift in absorption towards visible range of radiation is found to occur for hydrogen atoms adsorbed on nitrogen doped graphene sheet. The reflectivity peak of graphene increases in low energy region after H adsorption on N-doped graphene. The results can be used to tune the Fermi Energy level and to tailor the optical properties of graphene sheet in visible region.

  18. Uranium Isotope Fractionation during Adsorption, (Co)precipitation, and Biotic Reduction.

    PubMed

    Dang, Duc Huy; Novotnik, Breda; Wang, Wei; Georg, R Bastian; Evans, R Douglas

    2016-12-06

    Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth's oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope ((235)U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ(238)U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ(238)U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope ((238)U) is accumulated in reduced species (δ(238)U up to -1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications.

  19. Application of computational fluid dynamics for the simulation of cryogenic molecular sieve bed absorber of hydrogen isotopes recovery system for Indian LLCB-TBM

    SciTech Connect

    Gayathri Devi, V.; Sircar, A.; Sarkar, B.

    2015-03-15

    One of the most challenging tasks in the design of the fuel cycle system lies in the effective design of Tritium Extraction System (TES) which involves proper extraction and purification of tritium in the fuel cycle of the fusion reactor. Indian Lead Lithium cooled Ceramic Breeder Test Blanket Module (LLCB-TBM) would extract hydrogen isotopes through Cryogenic Molecular Sieve Bed (CMSB) adsorber system. A prototype Hydrogen Isotopes Recovery System (HIRS) is being developed to validate the concepts for tritium extraction by adsorption mass transfer mechanism. In this study, a design model has been developed and analyzed to simulate the adsorption mass transfer kinetics in a fixed bed adsorption column. The simulation leads primarily to effective design of HIRS, which is a state-of-the-art technology. The paper describes the process simulation approach and the results of Computational Fluid Dynamics (CFD) analysis. The effects of different operating conditions are studied to investigate their influence on the hydrogen isotopes adsorption capacity. The results of the present simulation study would be used to understand the best optimized transport phenomenon before realizing the TES as a system for LLCB-TBM. (authors)

  20. Enhanced hydrogen adsorption on graphene by manganese and manganese vanadium alloy decoration.

    PubMed

    Pei, P; Whitwick, M B; Sun, W L; Quan, G; Cannon, M; Kjeang, E

    2017-03-23

    In this work, two kinds of novel manganese decorated (G + Mn) and manganese-vanadium co-decorated (G + MnV) graphene composites are synthesized by in situ wet chemical reduction, and their hydrogen storage properties and microstructures are characterized by Sievert-type adsorption apparatus, BET, SEM, TEM/STEM, EDX and EELS. Compared with pristine graphene, Mn decoration marginally increases the hydrogen adsorption capacity of graphene at room temperature and 4 MPa hydrogen pressure from 0.25 wt% to 0.36 wt%. On the other hand, the co-decoration of Mn and V increases the room temperature hydrogen storage capacity of graphene significantly to 1.81 wt% under 4 MPa hydrogen pressure, which is 1.56 wt% higher than the capacity of pristine graphene. The microstructures and valence states of the decorated Mn and Mn-V nanoparticles are investigated by TEM, EDX and EELS analyses, and strong interactions between the decorated nanoparticles and graphene are observed. Based on the results from structural analyses, potential enhancement mechanisms are suggested in terms of the catalytic effects of nanoparticles on graphene hydrogen adsorption. Given the relatively low cost of Mn and V metals compared to noble metals such as Pd, Pt and Au, these results demonstrate a low cost and effective way to significantly enhance the room temperature hydrogen adsorption properties of graphene for potential hydrogen storage applications.

  1. Demonstration of compound-specific isotope analysis of hydrogen isotope ratios in chlorinated ethenes.

    PubMed

    Kuder, Tomasz; Philp, Paul

    2013-02-05

    High-temperature pyrolysis conversion of organic analytes to H(2) in hydrogen isotope ratio compound-specific isotope analysis (CSIA) is unsuitable for chlorinated compounds such as trichloroethene (TCE) and cis-1,2-dichloroethene (DCE), due to competition from HCl formation. For this reason, the information potential of hydrogen isotope ratios of chlorinated ethenes remains untapped. We present a demonstration of an alternative approach where chlorinated analytes reacted with chromium metal to form H(2) and minor amounts of HCl. The values of δ(2)H were obtained at satisfactory precision (± 10 to 15 per thousand), however the raw data required daily calibration by TCE and/or DCE standards to correct for analytical bias that varies over time. The chromium reactor has been incorporated into a purge and trap-CSIA method that is suitable for CSIA of aqueous environmental samples. A sample data set was obtained for six specimens of commercial product TCE. The resulting values of δ(2)H were between -184 and +682 ‰, which significantly widened the range of manufactured TCE δ(2)H signatures identified by past work. The implications of this finding to the assessment of TCE contamination are discussed.

  2. Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition

    NASA Astrophysics Data System (ADS)

    Szynkiewicz, Anna; Borrok, David M.

    2016-01-01

    In order to better understand the factors influencing zinc (Zn) isotope composition in hydrological systems, we analyzed the δ66Zn of dissolved Zn in the streams and groundwater of the Upper and Middle Rio Grande watershed in Colorado and New Mexico, United States. The stream water samples have a wider variation of δ66Zn (-0.57 to + 0.41 ‰ relative to the JMC 3-0749-Lyon standard) than groundwater samples (-0.13 to + 0.12 ‰) and than samples from streams that are in close proximity to abandoned mining sites (+0.24 to + 0.40 ‰). Regional changes of bedrock geology, from primarily igneous rocks to primarily sedimentary rocks, have no resolvable effect on the δ66Zn of aqueous samples. Instead, an increase in water pH from 7.5 to 8.5 corresponds to a considerable decrease in the δ66Zn of dissolved Zn (R2 = - 0.37, p = 0.003, n = 22). Consequently, we link the observed Zn isotope variations to the process of adsorption of Zn onto suspended sediment and bedrock minerals (average Δ66Znadsorbed-dissolved = + 0.31 ‰). Our results are in good agreement with previous experimental and empirical studies suggesting that Zn adsorption leads to a residual dissolved pool enriched in light Zn isotopes. Given that anthropogenic Zn sources can also be responsible for lowering of δ66Zn, and may overlap with the pH/adsorption effect on δ66Zn, the latter needs to be carefully considered in future studies to differentiate between natural and anthropogenic factors influencing Zn isotopes in this and other aquatic systems.

  3. Adsorption of hydrogen chloride on microcrystalline silica. [solid rocket propellant exhaust

    NASA Technical Reports Server (NTRS)

    Kang, Y.; Wightman, J. P.

    1979-01-01

    The interaction of hydrogen chloride with quartz was studied to determine the extent to which silica can irreversibly remove hydrogen chloride from the atmosphere. Adsorption isotherms were measured at 30 C for hydrogen chloride on silica outgassed between 100 C and 400 C. Readsorption isotherms were also measured. The silica surface was characterized further by infrared spectroscopy, electron spectroscopy for chemical analysis, scanning electron microscopy, and immersional calorimetry. Ground debris samples obtained from the Kennedy Space Center, were likewise examined.

  4. Hydrogen-graphite interaction: Experimental evidences of an adsorption barrier

    NASA Astrophysics Data System (ADS)

    Aréou, E.; Cartry, G.; Layet, J.-M.; Angot, T.

    2011-01-01

    The interaction of H atoms having relatively low average kinetic energy (˜0.025 eV) with both perfectly clean and D-covered HOPG surfaces is investigated using high resolution electron energy loss spectroscopy. From this study we confirm, in a controlled fashion, the presence of the theoretically predicted adsorption barrier since no adsorption is detected for such H atoms on HOPG. Moreover, we demonstrate that the exposure of a D saturated HOPG surface to these H atoms results in the complete removal of adatoms, with no further adsorption despite the prediction of the adsorption barrier to vanish for H dimers in para configuration. Therefore, the recombinative abstraction mechanism which competes with the adsorption process is more efficient.

  5. Intracrystalline site preference of hydrogen isotopes in borax

    SciTech Connect

    Pradhananga, T.M.; Matsuo, S.

    1985-01-03

    The total hydrogen involved in borax synthesized at 25/sup 0/C in aqueous solution is enriched in deuterium by 5.3% compared with the mother liquor. There is no change in the value of the D/H fractionation factor between the hydrogen in borax and those in the mother liquor with changes in the degree of supersaturation. The fractionation factor changes slightly with a change in the crystallization temperature of borax in the range from 5 to 25/sup 0/C. The D/H ratio in the different sites of borax was estimated by a fractional dehydration technique. The results show that hydrogen atoms of the polyanionic group (B/sub 4/O/sub 5/(OH)/sub 4/) are much more enriched in deuterium than those of the cationic group (Na/sub 2/ x 8H/sub 2/O). The delta D values, referred to the mother liquor from which the borax was crystallized, for the cationic group (site A) and the polyanionic group (site B) are -35 +/- 3 and 167 +/- 13%, respectively based on the fractional dehydration results obtained at -21/sup 0/C. At -21/sup 0/C, isotopic exchange between different sites during dehydration is assumed not to occur. The mechanism for dehydration of borax is discussed. 48 references, 8 figures, 3 tables.

  6. A DFT study of hydrogen adsorption on Be, Mg and Ca frameworks in erionite zeolite

    NASA Astrophysics Data System (ADS)

    Fellah, Mehmet Ferdi

    2017-02-01

    The molecular hydrogen adsorption was investigated on additional frameworks with earth alkaline metal atoms (Be, Mg and Ca) in 24T ERI zeolite cluster model by means of Density Functional Theory study. HOMO and LUMO energy values, chemical potential, chemical hardness, electronegativity, adsorption energy and adsorption enthalpy values have been calculated in this study. Mg-ERI and Ca-ERI clusters have much lower chemical potentials with much lower adsorption energy values when compared to the value of Be-ERI cluster. Additionally, they are softer than Be-ERI cluster with respect to their lower chemical hardness values. Hydrogen adsorption enthalpy values were computed as -3.6 and -3.9 kJ/mol on Mg-ERI and Ca-ERI clusters, respectively. These adsorption enthalpy values are significantly larger than the enthalpy value of liquefaction for hydrogen molecule. This consequently specifies that Mg-ERI and Ca-ERI zeolite structures which have higher chemical reactivity appear to be a promising candidate cryoadsorbent for hydrogen storage.

  7. Analysis of Hydrogen Isotopic Exchange: Lava Creek Tuff Ash and Isotopically Labeled Water

    NASA Astrophysics Data System (ADS)

    Ross, A. M.; Seligman, A. N.; Bindeman, I. N.; Nolan, G. S.

    2015-12-01

    Nolan and Bindeman (2013) placed secondarily hydrated ash from the 7.7 ka eruption of Mt. Mazama (δD=-149‰, 2.3wt% H2Ot) in isotopically labeled water (+650 ‰ δD, +56 ‰ δ18O) and observed that the H2Ot and δ18O values remained constant, but the δD values of ash increased with the surrounding water at 20, 40 and 70 °C. We expand on this work by conducting a similar experiment with ash from the 640 ka Lava Creek Tuff (LCT, δD of -128 ‰; 2.1 wt.% H2Ot) eruption of Yellowstone to see if significantly older glass (with a hypothesized gel layer on the surface shielding the interior from alteration) produces the same results. We have experiments running at 70, 24, and 5 °C, and periodically remove ~1.5 mg of glass to measure the δD (‰) and H2Ot (wt.%) of water extracted from the glass on a TC/EA MAT 253 continuous flow system. After 600 hours, the δD of the samples left at 5 and 24 °C remains at -128 ‰, but increased 8‰ for the 70 °C run series. However, there is no measurable change in wt.% of H2Ot, indicating that hydrogen exchange is not dictated by the addition of water. We are measuring and will report further progress of isotope exchange. We also plan to analyze the water in the LCT glass for δ18O (‰) to see if, as is the case for the Mt. Mazama glass, the δ18O (‰) remains constant. We also analyzed Mt. Mazama glass from the Nolan and Bindeman (2013) experiments that have now been sitting in isotopically labeled water at room temperature for ~5 years. The water concentration is still unchanged (2.3 wt.% H2Ot), and the δD of the water in the glass is now -111 ‰, causing an increase of 38 ‰. Our preliminary results show that exchange of hydrogen isotopes of hydrated glass is not limited by the age of the glass, and that the testing of hydrogen isotopes of secondarily hydrated glass, regardless of age, may not be a reliable paleoclimate indicator.

  8. Modeling experimental stable isotope results from CO2 adsorption and diffusion experiments

    NASA Astrophysics Data System (ADS)

    Larson, T. E.

    2012-12-01

    Transport of carbon dioxide through porous media can be affected by diffusion, advection and adsorption processes. Developing new tools to understand which of these processes dominates migration of CO2 or other gases in the subsurface is important to a wide range of applications including CO2 storage. Whereas advection rates are not affected by isotope substitution in CO2, adsorption and diffusion constants are. For example, differences in the binary diffusion constant calculated between C12O2-He and C13O2-He results in a carbon isotope fractionation whereby the front of the chromatographic peak is enriched in carbon-12 and the tail of the peak is enriched in carbon-13. Interestingly, adsorption is shown to have an opposite, apparent inverse affect whereby the lighter isotopologues of CO2 are preferentially retained by the chromatographic column and the heavier isotopologues are eluted first. This apparent inverse chromatographic effect has been ascribed to Van der Waals dispersion forces. Smaller molar volumes of the heavier isotopologues resulting from increased bond strength (shorter bond length) effectively decreases Van der Waals forces in heavier isotopologues compared to lighter isotopologues. Here we discuss the possible application of stable isotope values measured across chromatographic peaks to differentiate diffusion-dominated from adsorption-dominated transport processes for CO2. Separate 1-dimensional flow-through columns were packed with quartz and illite, and one remained empty. Dry helium was used as a carrier gas. Constant flow rate, temperature and column pressure were maintained. After background CO2 concentrations were minimized and constant, a sustained pulse of CO2 was injected at the head of the column and the effluent was sampled at 4 minute intervals for CO2 concentration, and carbon and oxygen isotope ratios. The quartz-sand packed and empty columns resulted in similar trends in concentration and isotope ratios whereby CO2 concentrations

  9. Hydrogen Adsorption on Activated Carbon an Carbon Nanotubes Using Volumetric Differential Pressure Technique

    NASA Astrophysics Data System (ADS)

    Sanip, S. M.; Saidin, M. A. R.; Aziz, M.; Ismail, A. F.

    2010-03-01

    A simple hydrogen adsorption measurement system utilizing the volumetri differential pressure technique has been designed, fabricated and calibrated. Hydroge adsorption measurements have been carried out at temperatures 298 K and 77 K on activate carbon and carbon nanotubes with different surface areas. The adsorption data obtained will b helpful in understanding the adsorption property of the studied carbon materials using th fundamentals of adsorption theory. The principle of the system follows the Sievert-type metho The system measures a change in pressure between the reference cell, R1 and the sample cell S1, S2, S3 over a certain temperature range. R1, S1, S2, and S3 having known fixed volume The sample temperatures will be monitored by thermocouple TC while the pressures in R1 an S1, S2, S3 will be measured using a digital pressure transducer. The maximum operatin pressure of the pressure transducer is 20 bar and calibrated with an accuracy of ±0.01 bar. Hig purity hydrogen is being used in the system and the amount of samples for the study is betwee 1.0-2.0 grams. The system was calibrated using helium gas without any samples in S1, S2 an S3. This will provide a correction factor during the adsorption process providing an adsorption free reference point when using hydrogen gas resulting in a more accurate reading of th adsorption process by eliminating the errors caused by temperature expansion effects and oth non-adsorption related phenomena. The ideal gas equation of state is applied to calculate th hydrogen adsorption capacity based on the differential pressure measurements. Activated carbo with a surface area of 644.87 m2/g showed a larger amount of adsorption as compared to multiwalled nanotubes (commercial) with a surface area of 119.68 m2/g. This study als indicated that there is a direct correlation between the amounts of hydrogen adsorbed an surface area of the carbon materials under the conditions studied and that the adsorption significant at 77

  10. Isotope Effect in Tunneling Ionization of Neutral Hydrogen Molecules

    NASA Astrophysics Data System (ADS)

    Wang, X.; Xu, H.; Atia-Tul-Noor, A.; Hu, B. T.; Kielpinski, D.; Sang, R. T.; Litvinyuk, I. V.

    2016-08-01

    It has been recently predicted theoretically that due to nuclear motion light and heavy hydrogen molecules exposed to strong electric field should exhibit substantially different tunneling ionization rates [O. I. Tolstikhin, H. J. Worner, and T. Morishita, Phys. Rev. A 87, 041401(R) (2013)]. We studied that isotope effect experimentally by measuring relative ionization yields for each species in a mixed H2/D2 gas jet interacting with intense femtosecond laser pulses. In a reaction microscope apparatus, we detected ionic fragments from all contributing channels (single ionization, dissociation, and sequential double ionization) and determined the ratio of total single ionization yields for H2 and D2 . The measured ratio agrees quantitatively with the prediction of the generalized weak-field asymptotic theory in an apparent failure of the frozen-nuclei approximation.

  11. Adsorption dynamics for the system hydrogen/palladium and its relation to the surface electronic structure

    NASA Astrophysics Data System (ADS)

    Resch, Ch.; Berger, H. F.; Rendulic, K. D.; Bertel, E.

    1994-09-01

    We have determined differential sticking coefficients for a monoenergetic nozzle beam of hydrogen on Pd(111) and Pd(110). In particular the energy dependence and the angular variation of the initial sticking coefficient were measured. The results indicate that adsorption of hydrogen on palladium occurs in parallel processes through a direct path with an activation barrier of perhaps 50 meV or less and a precursor path. There is relatively little difference in the adsorption properties of the (111) and the (110) plane. The appearance of a molecular precursor on the (111) plane can be related to the electronic structure of palladium, in particular to the absence of occupied Shockley surface states, as compared to Ni (111) and Pt (111). Pre-adsorbed potassium on a (110) plane acts as an inhibitor to adsorption. Different inhibiting mechanisms are observed for the direct adsorption path and the precursor path. At high potassium coverage the precursor path is completely suppressed.

  12. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption.

    PubMed

    Strmcnik, Dusan; Uchimura, Masanobu; Wang, Chao; Subbaraman, Ram; Danilovic, Nemanja; van der Vliet, Dennis; Paulikas, Arvydas P; Stamenkovic, Vojislav R; Markovic, Nenad M

    2013-04-01

    The development of hydrogen-based energy sources as viable alternatives to fossil-fuel technologies has revolutionized clean energy production using fuel cells. However, to date, the slow rate of the hydrogen oxidation reaction (HOR) in alkaline environments has hindered advances in alkaline fuel cell systems. Here, we address this by studying the trends in the activity of the HOR in alkaline environments. We demonstrate that it can be enhanced more than fivefold compared to state-of-the-art platinum catalysts. The maximum activity is found for materials (Ir and Pt₀.₁Ru₀.₉) with an optimal balance between the active sites that are required for the adsorption/dissociation of H₂ and for the adsorption of hydroxyl species (OHad). We propose that the more oxophilic sites on Ir (defects) and PtRu material (Ru atoms) electrodes facilitate the adsorption of OHad species. Those then react with the hydrogen intermediates (Had) that are adsorbed on more noble surface sites.

  13. Copper isotope fractionation during surface adsorption and intracellular incorporation by bacteria

    NASA Astrophysics Data System (ADS)

    Navarrete, Jesica U.; Borrok, David M.; Viveros, Marian; Ellzey, Joanne T.

    2011-02-01

    Copper isotopes may prove to be a useful tool for investigating bacteria-metal interactions recorded in natural waters, soils, and rocks. However, experimental data which attempt to constrain Cu isotope fractionation in biologic systems are limited and unclear. In this study, we utilized Cu isotopes (δ 65Cu) to investigate Cu-bacteria interactions, including surface adsorption and intracellular incorporation. Experiments were conducted with individual representative species of Gram-positive ( Bacillus subtilis) and Gram-negative ( Escherichia coli) bacteria, as well as with wild-type consortia of microorganisms from several natural environments. Ph-dependent adsorption experiments were conducted with live and dead cells over the pH range 2.5-6. Surface adsorption experiments of Cu onto live bacterial cells resulted in apparent separation factors (Δ 65Cu solution-solid = δ 65Cu solution - δ 65Cu solid) ranging from +0.3‰ to +1.4‰ for B. subtilis and +0.2‰ to +2.6‰ for E. coli. However, because heat-killed bacterial cells did not exhibit this behavior, the preference of the lighter Cu isotope by the cells is probably not related to reversible surface adsorption, but instead is a metabolically-driven phenomenon. Adsorption experiments with heat-killed cells yielded apparent separation factors ranging from +0.3‰ to -0.69‰ which likely reflects fractionation from complexation with organic acid surface functional group sites. For intracellular incorporation experiments the lab strains and natural consortia preferentially incorporated the lighter Cu isotope with an apparent Δ 65Cu solution-solid ranging from ˜+1.0‰ to +4.4‰. Our results indicate that live bacterial cells preferentially sequester the lighter Cu isotope regardless of the experimental conditions. The fractionation mechanisms involved are likely related to active cellular transport and regulation, including the reduction of Cu(II) to Cu(I). Because similar intracellular Cu machinery is

  14. Copper isotope fractionation during surface adsorption and intracellular incorporation by bacteria

    PubMed Central

    Navarrete, Jesica U.; Borrok, David M.; Viveros, Marian; Ellzey, Joanne T.

    2011-01-01

    Copper isotopes may prove to be a useful tool for investigating bacteria–metal interactions recorded in natural waters, soils, and rocks. However, experimental data which attempt to constrain Cu isotope fractionation in biologic systems are limited and unclear. In this study, we utilized Cu isotopes (δ65Cu) to investigate Cu–bacteria interactions, including surface adsorption and intracellular incorporation. Experiments were conducted with individual representative species of Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, as well as with wild-type consortia of microorganisms from several natural environments. Ph-dependent adsorption experiments were conducted with live and dead cells over the pH range 2.5–6. Surface adsorption experiments of Cu onto live bacterial cells resulted in apparent separation factors (Δ65Cusolution–solid = δ65Cusolution – δ65Cusolid) ranging from +0.3‰ to +1.4‰ for B. subtilis and +0.2‰ to +2.6‰ for E. coli. However, because heat-killed bacterial cells did not exhibit this behavior, the preference of the lighter Cu isotope by the cells is probably not related to reversible surface adsorption, but instead is a metabolically-driven phenomenon. Adsorption experiments with heat-killed cells yielded apparent separation factors ranging from +0.3‰ to –0.69‰ which likely reflects fractionation from complexation with organic acid surface functional group sites. For intracellular incorporation experiments the lab strains and natural consortia preferentially incorporated the lighter Cu isotope with an apparent Δ65Cusolution–solid ranging from ~+1.0‰ to +4.4‰. Our results indicate that live bacterial cells preferentially sequester the lighter Cu isotope regardless of the experimental conditions. The fractionation mechanisms involved are likely related to active cellular transport and regulation, including the reduction of Cu(II) to Cu(I). Because similar intracellular Cu machinery is

  15. Stable hydrogen isotopic analysis of nanomolar molecular hydrogen by automatic multi-step gas chromatographic separation.

    PubMed

    Komatsu, Daisuke D; Tsunogai, Urumu; Kamimura, Kanae; Konno, Uta; Ishimura, Toyoho; Nakagawa, Fumiko

    2011-11-15

    We have developed a new automated analytical system that employs a continuous flow isotope ratio mass spectrometer to determine the stable hydrogen isotopic composition (δD) of nanomolar quantities of molecular hydrogen (H(2)) in an air sample. This method improves previous methods to attain simpler and lower-cost analyses, especially by avoiding the use of expensive or special devices, such as a Toepler pump, a cryogenic refrigerator, and a special evacuation system to keep the temperature of a coolant under reduced pressure. Instead, the system allows H(2) purification from the air matrix via automatic multi-step gas chromatographic separation using the coolants of both liquid nitrogen (77 K) and liquid nitrogen + ethanol (158 K) under 1 atm pressure. The analytical precision of the δD determination using the developed method was better than 4‰ for >5 nmol injections (250 mL STP for 500 ppbv air sample) and better than 15‰ for 1 nmol injections, regardless of the δD value, within 1 h for one sample analysis. Using the developed system, the δD values of H(2) can be quantified for atmospheric samples as well as samples of representative sources and sinks including those containing small quantities of H(2) , such as H(2) in soil pores or aqueous environments, for which there is currently little δD data available. As an example of such trace H(2) analyses, we report here the isotope fractionations during H(2) uptake by soils in a static chamber. The δD values of H(2) in these H(2)-depleted environments can be useful in constraining the budgets of atmospheric H(2) by applying an isotope mass balance model.

  16. Round robin analyses of hydrogen isotope thin films standards.

    SciTech Connect

    Browning, James Frederick; Doyle, Barney Lee; Wampler, William R.; Wetteland, C. J.; LaDuca, Carol A.; Banks, James Clifford; Wang, Y. Q.; Tesmer, Joseph R.

    2003-06-01

    Hydrogen isotope thin film standards have been manufactured at Sandia National Laboratories for use by the materials characterization community. Several considerations were taken into account during the manufacture of the ErHD standards, with accuracy and stability being the most important. The standards were fabricated by e-beam deposition of Er onto a Mo substrate and the film stoichiometrically loaded with hydrogen and deuterium. To determine the loading accuracy of the standards two random samples were measured by thermal desorption mass spectrometry and atomic absorption spectrometry techniques with a stated combined accuracy of {approx}1.6% (1{sigma}). All the standards were then measured by high energy RBS/ERD and RBS/NRA with the accuracy of the techniques {approx}5% (1{sigma}). The standards were then distributed to the IBA materials characterization community for analysis. This paper will discuss the suitability of the standards for use by the IBA community and compare measurement results to highlight the accuracy of the techniques used.

  17. Isotope Effects in Collisional VT Relaxation of Molecular Hydrogen

    NASA Technical Reports Server (NTRS)

    Bieniek, R. J.

    2006-01-01

    A simple exponential-potential model of molecular collisions leads to a two-parameter analytic expression for rates of collisionally induced vibrational-translation (VT) energy exchange that has been shown to be accurate over variations of orders of magnitude as a function of temperature in a variety of systems. This includes excellent agreement with reported experimental and theoretical results for the fundamental self-relaxation rate of molecular hydrogen H2(v = 1) + H2 yields H2(v = 0) + H2. The analytic rate successfully follows the five-orders-of-magnitude change in experimental values for the temperature range 50-2000 K. This approach is now applied to isotope effects in the vibrational relaxation rates of excited HD and D2 in collision with H2: HD(v = 1)+H2 yields HD(v = 0)+H2 and D2(v = 1)+H2 yields D2(v = 0)+H2. The simplicity of the analytic expression for the thermal rate lends itself to convenient application in modeling the evolving vibrational populations of molecular hydrogen in shocked astrophysical environments.

  18. Ultrafiltration by a compacted clay membrane. I - Oxygen and hydrogen isotopic fractionation. II - Sodium ion exclusion at various ionic strengths.

    NASA Technical Reports Server (NTRS)

    Coplen, T. B.; Hanshaw, B. B.

    1973-01-01

    Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disk compacted to a porosity of 35% by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5% and in O-18 by 0.8% relative to the residual solution. No additional isotopic fractionation due to a salt-filtering mechanism was observed at NaCl concentrations up to 0.01N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. It is shown how it is possible to proceed from the ion exchange capacity of clay minerals and, by means of the Donnan membrane equilibrium concept and the Teorell-Meyer-Siever theory, develop a theory to explain why and to what extent ultrafiltration occurs when solutions of known concentration are forced to flow through a clay membrane.

  19. Significance of Isotopically Labile Organic Hydrogen in Thermal Maturation of Organic Matter

    SciTech Connect

    Arndt Schimmelmann; Maria Mastalerz

    2010-03-30

    Isotopically labile organic hydrogen in fossil fuels occupies chemical positions that participate in isotopic exchange and in chemical reactions during thermal maturation from kerogen to bitumen, oil and gas. Carbon-bound organic hydrogen is isotopically far less exchangeable than hydrogen bound to nitrogen, oxygen, or sulfur. We explore why organic hydrogen isotope ratios express a relationship with organic nitrogen isotope ratios in kerogen at low to moderate maturity. We develop and apply new techniques to utilize organic D/H ratios in organic matter fractions and on a molecular level as tools for exploration for fossil fuels and for paleoenvironmental research. The scope of our samples includes naturally and artificially matured substrates, such as coal, shale, oil and gas.

  20. Surface morphology of orthorhombic Mo2C catalyst and high coverage hydrogen adsorption

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tian, Xinxin; Yang, Yong; Li, Yong-Wang; Wang, Jianguo; Beller, Matthias; Jiao, Haijun

    2016-09-01

    High coverage hydrogen adsorption on twenty two terminations of orthorhombic Mo2C has been systematically studied by using density functional theory and ab initio thermodynamics. Hydrogen stable coverage on the surfaces highly depends on temperatures and H2 partial pressure. The estimated hydrogen desorption temperatures under ultra-high vacuum condition on Mo2C are in reasonable agreement with the available temperature-programmed desorption data. Obviously, hydrogen adsorption can affect the surface stability and therefore modify the surface morphology of Mo2C. Upon increasing the chemical potential of hydrogen which can be achieved by increasing the H2 partial pressure and/or decreasing the temperature, the proportions of the (001), (010), (011) and (100) surfaces increase, while those of the (101), (110) and (111) surfaces decrease. Among these surfaces, the (100) surface is most sensitive upon hydrogen adsorption and the (111) surface is most exposed under a wide range of conditions. Our study clearly reveals the role of hydrogen on the morphology of orthorhombic Mo2C catalyst in conjugation with hydro-treating activity.

  1. Carbon, Hydrogen, and Oxygen Isotope Ratios of Cellulose from Plants Having Intermediary Photosynthetic Modes 1

    PubMed Central

    Sternberg, Leonel O'Reilly; Deniro, Michael J.; Ting, Irwin P.

    1984-01-01

    Carbon and hydrogen isotope ratios of cellulose nitrate and oxygen isotope ratios of cellulose from species of greenhouse plants having different photosynthetic modes were determined. When hydrogen isotope ratios are plotted against carbon isotope ratios, four clusters of points are discernible, each representing different photosynthetic modes: C3 plants, C4 plants, CAM plants, and C3 plants that can shift to CAM or show the phenomenon referred to as CAM-cycling. The combination of oxygen and carbon isotope ratios does not distinguish among the different photosynthetic modes. Analysis of the carbon and hydrogen isotope ratios of cellulose nitrate should prove useful for screening different photosynthetic modes in field specimens that grew near one another. This method will be particularly useful for detection of plants which show CAM-cycling. PMID:16663360

  2. Hydrogen and oxygen adsorption stoichiometries on silica supported ruthenium nanoparticles

    SciTech Connect

    Berthoud, Romain; Delichere, Pierre; Gajan, David; Lukens, Wayne; Pelzer, Katrin; Basset, Jean-Marie; Candy, Jean-Pierre; Coperet, Christophe

    2008-12-01

    Treatment under H{sub 2} at 300 C of Ru(COD)(COT) dispersed on silica yields 2 nm ruthenium nanoparticles, [Ru{sub p}/SiO{sub 2}], according to EXAFS, HRTEM and XPS. H{sub 2} adsorption measurements on [Ru{sub p}/SiO{sub 2}] in the absence of O{sub 2} show that Ru particles adsorb up to ca. 2 H per surface ruthenium atoms (2H/Ru{sub s}) on various samples; this technique can therefore be used to measure the dispersion of Ru particles. In contrast, O{sub 2} adsorption on [Ru{sub p}/SiO{sub 2}] leads to a partial oxidation of the bulk at 25 C, to RuO{sub 2} at 200 C and to sintering upon further reduction under H{sub 2}, showing that O{sub 2} adsorption cannot be used to measure the dispersion of Ru particles.

  3. Understanding H isotope adsorption and absorption of Al-alloys using modeling and experiments (LDRD: #165724)

    SciTech Connect

    Ward, Donald K.; Zhou, Xiaowang; Karnesky, Richard A.; Kolasinski, Robert; Foster, Michael E.; Thurmer, Konrad; Chao, Paul; Epperly, Ethan Nicholas; Zimmerman, Jonathan A.; Wong, Bryan M.; Sills, Ryan B.

    2015-09-01

    Current austenitic stainless steel storage reservoirs for hydrogen isotopes (e.g. deuterium and tritium) have performance and operational life-limiting interactions (e.g. embrittlement) with H-isotopes. Aluminum alloys (e.g.AA2219), alternatively, have very low H-isotope solubilities, suggesting high resistance towards aging vulnerabilities. This report summarizes the work performed during the life of the Lab Directed Research and Development in the Nuclear Weapons investment area (165724), and provides invaluable modeling and experimental insights into the interactions of H isotopes with surfaces and bulk AlCu-alloys. The modeling work establishes and builds a multi-scale framework which includes: a density functional theory informed bond-order potential for classical molecular dynamics (MD), and subsequent use of MD simulations to inform defect level dislocation dynamics models. Furthermore, low energy ion scattering and thermal desorption spectroscopy experiments are performed to validate these models and add greater physical understanding to them.

  4. Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: a density-functional theory study.

    PubMed

    Li, Yanfang; Zhang, Ping; Sun, Bo; Yang, Yu; Wei, Yinghui

    2009-07-21

    We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage Theta [from 0.11 to 2.0 monolayers (ML)] and adsorption sites. In the coverage range 0 < Theta < 1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendency to the formation of H islands (clusters) when increasing the coverage within the region 0 < Theta < 1.0. The on-surface diffusion path energetics of atomic hydrogen as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites are also presented at low coverage. At high coverage of 1.0 < Theta < or = 2.0, it is found that the coadsorption configuration with 1.0 monolayer of H residing on the surface fcc sites and the remaining (Theta-1.0) monolayer of H occupying the subsurface tetra-I sites is most energetically favorable. The resultant H-Mg-H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH(2) in the density of states. The other properties of the H/Mg(0001) system including the charge distribution, the lattice relaxation, the work function, and the electronic density of states are also studied and discussed in detail. It is pointed out that the H-Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.

  5. Hydrogen adsorption in the NaA zeolite: A comparison between numerical simulations and experiments

    NASA Astrophysics Data System (ADS)

    Darkrim, Farida; Aoufi, Asdin; Malbrunot, Pierre; Levesque, Dominique

    2000-04-01

    At room temperature and high pressures between 10 MPa and 140 MPa, hydrogen adsorption in the NaA zeolite was studied by grand canonical Monte Carlo simulation. The computed values of the average number of hydrogen molecules adsorbed in a crystal unit were compared to those measured at the same temperature and pressures between 10 MPa and 70 MPa. A quantitative agreement between the two sets of values was obtained by using, in the simulations, a model of zeolite crystal where the Al, Si, O, and Na atoms, disposed in accordance with the crystallographic structure of the NaA zeolite determined by x-ray diffraction, had effective electric charges and were sources of a van der Waals interaction. The adsorption of hydrogen molecules in the NaA zeolite resulted from the combined effects of van der Waals interactions and polarization of hydrogen molecules induced by the electric field of the effective charges.

  6. Quantifying residual hydrogen adsorption in low-temperature STMs

    NASA Astrophysics Data System (ADS)

    Natterer, F. D.; Patthey, F.; Brune, H.

    2013-09-01

    We report on low-temperature scanning tunneling microscopy observations demonstrating that individual Ti atoms on hexagonal boron nitride dissociate and adsorb hydrogen without measurable reaction barrier. The clean and hydrogenated states of the adatoms are clearly discerned by their apparent height and their differential conductance revealing the Kondo effect upon hydrogenation. Measurements at 50 K and 5 × 10- 11 mbar indicate a sizable hydrogenation within only 1 h originating from the residual gas pressure, whereas measurements at 4.7 K can be carried out for days without H2 contamination problems. However, heating up a low-T STM to operate it at variable temperature results in very sudden hydrogenation at around 17 K that correlates with a sharp peak in the total chamber pressure. From a quantitative analysis we derive the desorption energies of H2 on the cryostat walls. We find evidence for hydrogen contamination also during Ti evaporation and propose a strategy on how to dose transition metal atoms in the cleanliest fashion. The present contribution raises awareness of hydrogenation under seemingly ideal ultra-high vacuum conditions, it quantifies the H2 uptake by isolated transition metal atoms and its thermal desorption from the gold plated cryostat walls.

  7. Study of hydrogen isotopes super permeation through vanadium membrane on 'Prometheus' setup

    SciTech Connect

    Musyaev, R. K.; Yukhimchuk, A. A.; Lebedev, B. S.; Busnyuk, A. O.; Notkin, M. E.; Samartsev, A. A.; Livshits, A. I.

    2008-07-15

    To develop the membrane pumping technology by means of superpermeable membranes at RFNC-VNIIEF in the 'Prometheus' setup, the experiments on superpermeation of hydrogen isotopes through metal membranes were carried out. The experimental results on superpermeation of thermal atoms of hydrogen isotopes including tritium through a cylindrical vanadium membrane are presented. The possibility of effective pumping, compression and recuperation of hydrogen isotopes by means of superpermeable membrane was demonstrated. The evaluation of membrane pumping rates and asymmetry degree of pure vanadium membrane was given. The work was performed under the ISTC-2854 project. (authors)

  8. A new isotopic reference material for stable hydrogen and oxygen isotope-ratio measurements of water—USGS50 Lake Kyoga Water

    USGS Publications Warehouse

    Coplen, Tyler B.; Wassenaar, Leonard I; Mukwaya, Christine; Qi, Haiping; Lorenz, Jennifer M.

    2015-01-01

    This isotopic reference material, designated as USGS50, is intended as one of two reference waters for daily normalization of stable hydrogen and oxygen isotopic analysis of water with an isotope-ratio mass spectrometer or a laser absorption spectrometer, of use especially for isotope-hydrology laboratories analyzing freshwater samples from equatorial and tropical regions.

  9. High-capacity hydrogen and nitric oxide adsorption and storage in a metal-organic framework.

    PubMed

    Xiao, Bo; Wheatley, Paul S; Zhao, Xuebo; Fletcher, Ashleigh J; Fox, Sarah; Rossi, Adriano G; Megson, Ian L; Bordiga, S; Regli, L; Thomas, K Mark; Morris, Russell E

    2007-02-07

    Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H2 per g of HKUST-1 (22.7 mg g(-)1, 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-)1, 3.6 wt %) at 10 bar. Adsorption of D2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at <100 mbar) times the H2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of approximately 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.

  10. An enhanced hydrogen adsorption enthalpy for fluoride intercalated graphite compounds.

    PubMed

    Cheng, Hansong; Sha, Xianwei; Chen, Liang; Cooper, Alan C; Foo, Maw-Lin; Lau, Garret C; Bailey, Wade H; Pez, Guido P

    2009-12-16

    We present a combined theoretical and experimental study on H(2) physisorption in partially fluorinated graphite. This material, first predicted computationally using ab initio molecular dynamics simulation and subsequently synthesized and characterized experimentally, represents a novel class of "acceptor type" graphite intercalated compounds that exhibit significantly higher isosteric heat of adsorption for H(2) at near ambient temperatures than previously demonstrated for commonly available porous carbon-based materials. The unusually strong interaction arises from the semi-ionic nature of the C-F bonds. Although a high H(2) storage capacity (>4 wt %) at room temperature is predicted not to be feasible due to the low heat of adsorption, enhanced storage properties can be envisaged by doping the graphitic host with appropriate species to promote higher levels of charge transfer from graphene to F(-) anions.

  11. Experimental Evidence for Hydrogen Tunneling when the Isotopic Arrhenius Prefactor (AH/AD) is Unity

    PubMed Central

    Sharma, Sudhir C.; Klinman, Judith P.

    2009-01-01

    The temperature dependence of the kinetic isotope effect (KIE) is one of the major tools used for the investigation of hydrogen tunneling in condensed phase. Hydrogen transfer reactions displaying isotopic Arrhenius prefactor ratios (AH/AD) of unity are generally ascribed to a semi-classical mechanism. Here, we have identified a double mutant of soybean lipoxygenase (SLO-1, an enzyme previously shown to follow quantum mechanical hydrogen tunneling), that displays an AH/AD of unity and highly elevated (non-classical) KIEs. This observation highlights the shortcoming of assigning a hydrogen transfer reaction to a semi-classical model based solely on an Arrhenius prefactor ratio. PMID:19061319

  12. Hydrogen adsorption in the series of carbon nanostructures: Graphenes-graphene nanotubes-nanocrystallites

    NASA Astrophysics Data System (ADS)

    Soldatov, A. P.; Kirichenko, A. N.; Tat'yanin, E. V.

    2016-07-01

    A comparative analysis of hydrogen absorption capability is performed for the first time for three types of carbon nanostructures: graphenes, oriented carbon nanotubes with graphene walls (OCNTGs), and pyrocarbon nanocrystallites (PCNs) synthesized in the pores of TRUMEM ultrafiltration membranes with mean diameters ( D m) of 50 and 90 nm, using methane as the pyrolized gas. The morphology of the carbon nanostructures is studied by means of powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). Hydrogen adsorption is investigated via thermogravimetric analysis (TGA) in combination with mass-spectrometry. It is shown that only OCNTGs can adsorb and store hydrogen, the desorption of which under atmospheric pressure occurs at a temperature of around 175°C. Hydrogen adsorption by OCNTGs is quantitatively determined and found to be about 1.5% of their mass. Applying certain assumptions, the relationship between the mass of carbon required for the formation of single-wall OCNTGs in membrane pores and the surface area of pores is established. Numerical factor Ψ = m dep/ m calc, where m dep is the actual mass of carbon deposited upon the formation of OCNTGs and mcalc is the calculated mass of carbon necessary for the formation of OCNTGs is introduced. It is found that the dependence of specific hydrogen adsorption on the magnitude of the factor has a maximum at Ψ = 1.2, and OCNTGs can adsorb and store hydrogen in the interval 0.4 to 0.6 < Ψ < 1.5 to 1.7. Possible mechanisms of hydrogen adsorption and its relationship to the structure of carbon nanoformations are examined.

  13. Carbon and hydrogen isotope fractionation of benzene and toluene during hydrophobic sorption in multistep batch experiments.

    PubMed

    Imfeld, G; Kopinke, F-D; Fischer, A; Richnow, H-H

    2014-07-01

    The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (Δδ(13)C=1.6 ± 0.3‰ and Δδ(2)H=88 ± 3‰), yielding isotope fractionation factors of αC=1.0030 ± 0.0005 and αH=1.195 ± 0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with π-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation.

  14. A model predicting hydrogen and oxygen isotopes of mammalian hair at the landscape scale

    NASA Astrophysics Data System (ADS)

    Ehleringer, J.; Podlesak, D.; Cerling, T.; Chesson, L.; Bowen, G.

    2006-12-01

    A model has been developed to predict hydrogen and oxygen isotope ratios of keratin in hair of mammalian herbivores and omnivores, incorporating the influences of drinking water and dietary input. The isotopic composition of carbohydrates in food sources and the water in blood and tissues are predicted as intermediate components linking drinking water and dietary sources (environment) with hair (environmental recorder). This model is scaled to landscape and regional levels using geographic information system map predictions of the hydrogen and oxygen isotope ratios of drinking waters and anticipated hydrogen and oxygen isotope ratios of carbohydrate food sources. The model was tested using isotope ratios of human hair (an omnivore) from across the USA. We discuss the application of this model as a tool for providing spatially integrated information about the quality of primary productivity relevant to mammalian herbivores over time, through the effects of varying primary productivity on protein nitrogen balance of the herbivore.

  15. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds.

    PubMed

    Hansen, Poul Erik

    2015-01-30

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between "static" and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N-. The paper will be deal with both secondary and primary isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles.

  16. Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: implications for planetary accretion.

    PubMed

    Tyburczy, J A; Krishnamurthy, R V; Epstein, S; Ahrens, T J

    1990-05-01

    The degree of impact-induced devolatilization of nonporous serpentine, porous serpentine, and deuterium-enriched serpentine was investigated using two independent experimental methods, the gas recovery method and the solid recovery method, yielding consistent results. The gas recovery method enables determination of the chemical and hydrogen isotopic composition of the recovered gases. Experiments on deuterium-enriched serpentine unambiguously identify the samples as the source of the recovered gases, as opposed to other possible contaminants. For shock pressures near incipient devolatilization (Pinitial = 5.0 GPa), the hydrogen isotopic composition of the evolved gas is similar to that of the starting material. For higher shock pressures the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H2O to H2 in gases recovered at higher shock pressures, probably caused by reaction of evolved H2O with the metal gas recovery fixture. The hydrogen isotopic fractionation between the evolved gas and the residual solid indicates nonequilibrium, kinetic control of gas-solid isotopic ratios. In contrast, gaseous H2O-H2 isotopic fractionation suggests high temperature (800-1300 K) isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition (i.e., shear bands). Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can affect the distribution of hydrogen isotopes of planetary bodies during accretion, leaving the interiors enriched in deuterium. The significance of this process for planetary development depends on the models used for extrapolation of the observed isotopic fractionation to devolatilizations greater than those investigated experimentally and assumptions about timing and rates of protoatmosphere loss, frequency of multiple impacts, and rates of gas-solid or gas-melt isotopic re

  17. SAMPEX observations of energetic hydrogen isotopes in the inner zone

    NASA Technical Reports Server (NTRS)

    Looper, M. D.; Blake, J. B.; Cummings, J. R.; Mewaldt, R. A.

    1996-01-01

    We report observations of geomagnetically-trapped hydrogen isotopes at low altitudes, near the feet of field lines in the inner zone, made with the PET instrument aboard the SAMPEX satellite. We have mapped protons from 19 to 500 MeV, and have discovered a collocated belt of deuterons, which we have mapped from 18 to 58 MeV/nucleon. We found deuterium at about 1% of the level of the proton flux at the same energy per nucleon, and no tritium at energies of tens of MeV/nucleon with an upper limit of about 0.1% of the proton flux. Protons and deuterons showed similar time dependence, with fluxes approximately tripling from July 1992 to March 1996, and similar pitch-angle dependence. The high-L limits of the proton and deuteron belts as functions of energy were organized by rigidity, as was to be expected if these limits were set for both species by inability of particles to sustain adiabatic motion and stable trapping.

  18. Relation between hydrogen isotopic ratios of bone collagen and rain

    SciTech Connect

    Cormie, A.B.; Schwarcz, H.P. ); Gray, J. )

    1994-01-01

    The hydrogen isotopic value ([delta]D) of deer bone collagen is related to both [delta]D of rain during the growing season and growing season relative humidity (RH). With correction for the effects of RH, bone [delta]D is related to growing season rain [delta]D in a simple manner with a slope of 1.0. This indicates that, with RH correction, there are no additional sources of bias in the [delta]D of bone due to unaccounted for biologic or climatic effects. Due to a low sensitivity of bone [delta]D to RH effects, both yearly and growing season rain [delta]D can be estimated with considerable accuracy (R = 0.97 and R = 0.96) from bone collagen [delta]D and [delta][sup 15]N. Here, [delta][sup 15]N is used to correct bone [delta]D for the effects of RH. From these estimates of rain [delta]D, it may then be possible to evaluate temperature since the [delta]D of rain primarily reflects local temperature. Therefore, the measurement of bone collagen [delta]D has good potential for evaluating paleoclimates.

  19. In situ monitoring hydrogen isotope retention in ITER first wall

    NASA Astrophysics Data System (ADS)

    Mukhin, E. E.; Andrew, P.; Anthoine, A. D.; Bazhenov, A. N.; Barnsley, R.; Bukreev, I. M.; Bukhovets, V. L.; Chernakov, A. P.; Gorodetsky, A. E.; Kochergin, M. M.; Koval, A. N.; Kukushkin, A. B.; Kukushkin, A. S.; Kurskiev, G. S.; Levashova, M. G.; Litvinov, A. E.; Litunovsky, V. N.; Markin, A. V.; Mazul, I. V.; Masyukevich, S. V.; Miroshnikov, I. V.; Nemov, A. S.; Novokhatsky, A. N.; Razdobarin, A. G.; Sherstnev, E. V.; Samsonov, D. S.; Semenov, V. V.; Smirnov, A. S.; De Temmerman, G.; Tolstyakov, S. Yu.; Zalavutdinov, R. Kh.; Walsh, M. J.

    2016-03-01

    Tritium retention inside the vacuum vessel is a potentially serious constraint in the operation of large-scale fusion machines like ITER. An in situ diagnostics for first wall H/D/T retention by laser induced desorption spectroscopy (LIDS) is proposed for use between plasma discharges. The technique is based on local baking of the first wall by laser irradiation and subsequent analysis of the in-vessel gas by optical emission spectroscopy of plasma radiation. The local heating implementation, kinetics of H/D/T thermal extraction and the accuracy of optical emission spectroscopy measurements are analysed. To resolve the H/D/T lines spectroscopically, their thermal broadening should be minimized to prevent overlapping of the line shapes. A comparative performance analysis of several types of plasma sources with relatively cold ions is made including the following types of discharges: Penning, RF multipactor, laser torch and ECR. All these radiation sources require rather low power and could be used for remote in situ measurements of relative densities of the thermally extracted hydrogen isotopes.

  20. Hydrogen isotope trapping in Al-Cu binary alloys

    DOE PAGES

    Chao, Paul; Karnesky, Richard A.

    2016-01-01

    In this study, the trapping mechanisms for hydrogen isotopes in Al–X Cu (0.0 at. % < X < 3.5 at. %) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al–Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is (18 ± 3) kJ•mol–1 (0.19 ± 0.03 eV). Typical occupancy of this trap is high;more » for Al–2.6 at. % Cu (a Cu composition comparable to that in AA2219) charged at 200 °C with 130 MPa D2 for 68 days, there is ca. there is 3.15×10–7 mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample.« less

  1. Hydrogen isotope trapping in Al-Cu binary alloys

    SciTech Connect

    Chao, Paul; Karnesky, Richard A.

    2016-01-01

    In this study, the trapping mechanisms for hydrogen isotopes in Al–X Cu (0.0 at. % < X < 3.5 at. %) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al–Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is (18 ± 3) kJ•mol–1 (0.19 ± 0.03 eV). Typical occupancy of this trap is high; for Al–2.6 at. % Cu (a Cu composition comparable to that in AA2219) charged at 200 °C with 130 MPa D2 for 68 days, there is ca. there is 3.15×10–7 mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample.

  2. Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

    NASA Astrophysics Data System (ADS)

    Nielson, Kristine E.; Bowen, Gabriel J.

    2010-03-01

    Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

  3. Hydrogen adsorption on Ru(001) studied by Scanning TunnelingMicroscopy

    SciTech Connect

    Tatarkhanov, Mous; Rose, Franck; Fomin, Evgeny; Ogletree, D.Frank; Salmeron, Miquel

    2008-01-18

    The adsorption of hydrogen on Ru(001) was studied by scanning tunneling microscopy at temperatures around 50 K. Hydrogen was found to adsorb dissociatively forming different ordered structures as a function of coverage. In order of increasing coverage {theta} in monolayers (ML) these were ({radical}3 x {radical}3)r30{sup o} at {theta} = 0.3 ML; (2 x 1) at {theta} = 0.50 ML, (2 x 2)-3H at {theta} = 0.75, and (1 x 1) at {theta} = 1.00. Some of these structures were observed to coexist at intermediate coverage values. Close to saturation of 1 ML, H-vacancies (unoccupied three fold fcc hollow Ru sites) were observed either as single entities or forming transient aggregations. These vacancies diffuse and aggregate to form active sites for the dissociative adsorption of hydrogen.

  4. Caution on the use of liquid nitrogen traps in stable hydrogen isotope-ratio mass spectrometry

    USGS Publications Warehouse

    Coplen, T.B.; Qi, H.

    2010-01-01

    An anomalous stable hydrogen isotopic fractionation of 4 ??? in gaseous hydrogen has been correlated with the process of adding liquid nitrogen (LN2) to top off the dewar of a stainless-steel water trap on a gaseous hydrogen-water platinum equilibration system. Although the cause of this isotopic fractionation is unknown, its effect can be mitigated by (1) increasing the capacity of any dewars so that they do not need to be filled during a daily analytic run, (2) interspersing isotopic reference waters among unknowns, and (3) applying a linear drift correction and linear normalization to isotopic results with a program such as Laboratory Information Management System (LIMS) for Light Stable Isotopes. With adoption of the above guidelines, measurement uncertainty can be substantially improved. For example, the long-term (months to years) ??2H reproducibility (1?? standard deviation) of nine local isotopic reference waters analyzed daily improved substantially from about 1 ??? to 0.58 ???. This isotopically fractionating mechanism might affect other isotope-ratio mass spectrometers in which LN2 is used as a moisture trap for gaseous hydrogen. ?? This article not subject to U.S. Copyright. Published 2010 by the American Chemical Society.

  5. Caution on the use of liquid nitrogen traps in stable hydrogen isotope-ratio mass spectrometry

    USGS Publications Warehouse

    Coplen, Tyler B.; Qi, Haiping

    2010-01-01

    An anomalous stable hydrogen isotopic fractionation of 4 ‰ in gaseous hydrogen has been correlated with the process of adding liquid nitrogen (LN2) to top off the dewar of a stainless-steel water trap on a gaseous hydrogen-water platinum equilibration system. Although the cause of this isotopic fractionation is unknown, its effect can be mitigated by (1) increasing the capacity of any dewars so that they do not need to be filled during a daily analytic run, (2) interspersing isotopic reference waters among unknowns, and (3) applying a linear drift correction and linear normalization to isotopic results with a program such as Laboratory Information Management System (LIMS) for Light Stable Isotopes. With adoption of the above guidelines, measurement uncertainty can be substantially improved. For example, the long-term (months to years) δ2H reproducibility (1& sigma; standard deviation) of nine local isotopic reference waters analyzed daily improved substantially from about 1‰ to 0.58 ‰. This isotopically fractionating mechanism might affect other isotope-ratio mass spectrometers in which LN2 is used as a moisture trap for gaseous hydrogen

  6. Hydrogen Isotope Measurements of Organic Acids and Alcohols by Pyrolysis-GC-MS-TC-IRMS

    NASA Technical Reports Server (NTRS)

    Socki, Richard A.; Fu, Qi; Niles, Paul B.

    2011-01-01

    One possible process responsible for methane generation on Mars is abiotic formation by Fischer-Tropsch-type (FTT) synthesis during serpentinization reactions. Measurement of carbon and hydrogen isotopes of intermediary organic compounds can help constrain the origin of this methane by tracing the geochemical pathway during formation. Of particular interest within the context of this work is the isotopic composition of organic intermediaries produced on the surfaces of mineral catalysts (i.e. magnetite) during hydrothermal experiments, and the ability to make meaningful and reproducible hydrogen isotope measurements. Reported here are results of experiments to characterize the hydrogen isotope composition of low molecular weight organic acids and alcohols. The presence of these organic compounds has been suggested by others as intermeadiary products made during mineral surface catalyzed reactions. This work compliments our previous study characterizing the carbon isotope composition of similar low molecular weight intermediary organic compounds (Socki, et al, American Geophysical Union Fall meeting, Abstr. #V51B-2189, Dec., 2010). Our hydrogen isotope measurements utilize a unique analytical technique combining Pyrolysis-Gas Chromatograph-Mass Spectrometry-High Temperature Conversion-Isotope Ratio Mass Spectrometry (Py-GC-MS-TC-IRMS). Our technique is unique in that it carries a split of the pyrolyzed GC-separated product to a Thermo DSQ-II? quadrupole mass spectrometer as a means of making qualitative and semi-quantitative compositional measurements of separated organic compounds, therefore both chemical and isotopic measurements can be carried out simultaneously on the same sample.

  7. The dissociative adsorption of hydrogen on defect-'free' Pt(111)

    NASA Astrophysics Data System (ADS)

    Poelsema, Bene; Lenz, Klaus; Comsa, George

    2010-08-01

    The interaction of hydrogen with an (almost) defect-free Pt(111) surface (step density ~ 0.1%) is revisited in a combined thermal energy atom scattering/thermal desorption spectroscopy (TEAS/TDS) study. We propose a novel kinetic precursor-mediated adsorption/desorption model for hydrogen/Pt(111) to reconcile seemingly conflicting results, such as extremely different dissociative adsorption kinetics at 25 and 155 K. Up to a perpendicular energy of (at least) 60 meV, highly relevant for hydrogenation reactions, the initial sticking probability scales with perpendicular energy to the power 1.9. This atypical behaviour is attributed to probing larger corrugation amplitudes at higher normal energy, leading to scattering of hydrogen into a dynamic precursor prior to dissociation and thus to increased trapping. Scrutiny of the data demonstrates that only a small minority of the surface sites (most probably steps) is active in dissociation. The observed decay of the heat of adsorption with coverage indicates strong repulsion between hydrogen atoms. The TDS-spectra of hydrogen from the defect-'free' Pt(111) consist definitively of a single (β2-)peak in contrast to the frequently measured double (β1, β2-)peak structure and at variance with the yet widely accepted conjecture that repulsive interactions lead to double (β1, β2-)peak structures in TDS-spectra. TDS-spectra simulated by applying the micro-reversibility principle and using TEAS-data are in agreement with the experimental ones. The TEAS-data, probing hydrogen whilst on the surface, are thus consistent with TDS-data, probing hydrogen after leaving the surface.

  8. A comparative analysis of the cryo-compression and cryo-adsorption hydrogen storage methods

    SciTech Connect

    Petitpas, G; Benard, P; Klebanoff, L E; Xiao, J; Aceves, S M

    2014-07-01

    While conventional low-pressure LH₂ dewars have existed for decades, advanced methods of cryogenic hydrogen storage have recently been developed. These advanced methods are cryo-compression and cryo-adsorption hydrogen storage, which operate best in the temperature range 30–100 K. We present a comparative analysis of both approaches for cryogenic hydrogen storage, examining how pressure and/or sorbent materials are used to effectively increase onboard H₂ density and dormancy. We start by reviewing some basic aspects of LH₂ properties and conventional means of storing it. From there we describe the cryo-compression and cryo-adsorption hydrogen storage methods, and then explore the relationship between them, clarifying the materials science and physics of the two approaches in trying to solve the same hydrogen storage task (~5–8 kg H₂, typical of light duty vehicles). Assuming that the balance of plant and the available volume for the storage system in the vehicle are identical for both approaches, the comparison focuses on how the respective storage capacities, vessel weight and dormancy vary as a function of temperature, pressure and type of cryo-adsorption material (especially, powder MOF-5 and MIL-101). By performing a comparative analysis, we clarify the science of each approach individually, identify the regimes where the attributes of each can be maximized, elucidate the properties of these systems during refueling, and probe the possible benefits of a combined “hybrid” system with both cryo-adsorption and cryo-compression phenomena operating at the same time. In addition the relationships found between onboard H₂ capacity, pressure vessel and/or sorbent mass and dormancy as a function of rated pressure, type of sorbent material and fueling conditions are useful as general designing guidelines in future engineering efforts using these two hydrogen storage approaches.

  9. Adsorption of Silica on Synthetic Iron Oxides Fractionates Stable Silicon Isotopes

    NASA Astrophysics Data System (ADS)

    Delstanche, S.; Opfergelt, S.; Cardinal, D.; André, L.; Delvaux, B.

    2006-12-01

    Recent advances show that the quantification of silicon isotopic fractionation by biotic and abiotic processes readily contributes to the understanding of the continental cycle of silicon, involving a.o. Si transfers between aqueous solutions, living organisms and soil minerals. Si uptake by biota, silicate weathering and clay formation all fractionate Si isotopes. Yet, silica may also be quantitatively retrieved from aqueous solutions through specific adsorption of uncharged monosilicic acid (H4SiO4) on oxide surfaces. Iron oxides are ubiquitous in sediments, weathered rocks and soils, where they appear as crystalline and/or short-range ordered (sro) minerals. Here, we report on silicon mass fractionation by H4SiO4 adsorption on two iron oxides: goethite and ferrihydrite. The respective crystalline and sro oxides were synthesized silicon-free and characterized through elementary analysis, selective dissolution, X-ray diffraction and Transmission Electronic Microscopy (TEM). The surface area, as determined by ethylene glycol monoethyl ether (EGME), is 147 m2.g-1 for goethite and 338 m2.g-1 for ferrihydrite. The adsorption of H4SiO4 was measured in batch experiment series designed as function of time (0-504 h) and initial Si concentration in solution (0.2-1.8 mM), at 20°C, constant pH (5.5) and ionic force. The solid:solution ratio was 5g:1000ml. After equilibration, isotopic compositions of 20 selected solution samples were measured on a Nu Plasma Multicollector Mass Spectrometer (MC-ICP-MS) operating in dry plasma mode with external Mg doping. The results were expressed as δ^{29}Si relatively to the NBS28- standard, with an average precision of ± 0.08‰ (± 2σM). With respect to oxide mass but not to EGME-surface area, ferrihydrite (74%) adsorbed more Si than goethite (46%) relatively to initial Si input (at 1.1 mM Si initial concentration after 504 h of contact). Measured against its initial composition (0.00 ± 0.09‰), the equilibrium solution was

  10. Evidence from Hydrogen Isotopes in Meteorites for a Subsurface Hydrogen Reservoir on Mars

    NASA Technical Reports Server (NTRS)

    Usui, Tomohiro; Alexander, Conel M. O'D.; Wang, Jianhua; Simon, Justin I.; Jones, John H.

    2015-01-01

    The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. We have conducted in situ hydrogen isotope (D/H) analyses of quenched and impact glasses in three Martian meteorites (Yamato 980459, EETA79001, LAR 06319) by Cameca ims-6f at Digital Terrain Models (DTM) following the methods of [1]. The hydrogen isotope analyses provide evidence for the existence of a distinct but ubiquitous water/ice reservoir (D/H = 2-3 times Earth's ocean water: Standard Mean Ocean Water (SMOW)) that lasted from at least the time when the meteorites crystallized (173-472 Ma) to the time they were ejected by impacts (0.7-3.3 Ma), but possibly much longer [2]. The origin of this reservoir appears to predate the current Martian atmospheric water (D/H equals approximately 5-6 times SMOW) and is unlikely to be a simple mixture of atmospheric and primordial water retained in the Martian mantle (D/H is approximately equal to SMOW [1]). Given the fact that this intermediate-D/H reservoir (2-3 times SMOW) is observed in a diverse range of Martian materials with different ages (e.g., SNC (Shergottites, Nakhlites, Chassignites) meteorites, including shergottites such as ALH 84001; and Curiosity surface data [3]), we conclude that this intermediate-D/H reservoir is likely a global surficial feature that has remained relatively intact over geologic time. We propose that this reservoir represents either hydrated crust and/or ground ice interbedded within sediments. Our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of Mars.

  11. EXAFS Reveals the Mechanism of U Isotope Fractionation During Adsorption to Mn Oxyhydroxide

    NASA Astrophysics Data System (ADS)

    Wasylenki, L. E.; Brennecka, G.; Bargar, J.; Weyer, S.; Anbar, A. D.

    2010-12-01

    Natural variations in the ratio of 238U/235U due to “stable” isotope fractionation have now been reported for a range of geological samples [1-3]. Among the observed variations are a small difference in 238U/235U between seawater and ferromanganese sediments (seawater slightly heavier) and a larger difference, with opposite sense, between seawater and black shales (seawater lighter). These variations suggest that long-term changes in the proportions of oxic and anoxic/sulfidic sinks for U in the ocean over Earth’s history may be recorded as shifts in the isotopic compositions of marine sediments. Thus U isotopes are a potential paleoredox proxy for the oceans, as suggested by [4]. In order to investigate the mechanism behind fractionation of U isotopes in oxidizing marine environments, we previously conducted simple adsorption experiments in which an isotopically known pool of dissolved U partly adsorbed onto synthetic birnessite, a common Mn oxyhydroxide in hydrogenetic ferromanganese crusts. Our experimental result agreed very well with that observed between seawater and natural ferromanganese sediments: δ238U/235U of adsorbed U was 0.2‰ lighter than δ238U/235U of dissolved U [5]. The magnitude of fractionation is constant as a function of experimental duration and fraction of U adsorbed, suggesting an equilibrium isotope effect. Many metal isotope effects are driven by changes in oxidation state for the metal of interest. Because both dissolved and adsorbed U are hexavalent in this system, a redox reaction cannot be causing isotope fractionation. We therefore hypothesized that a difference in uranium’s coordination environment between dissolved and adsorbed U is likely responsible for the isotope effect. We analyzed a sample from our experimental study with extended X-ray absorption fine structure (EXAFS) spectroscopy. Comparison of the EXAFS spectrum of U adsorbed on birnessite with the spectra of aqueous U species (UO22+ and UO2(CO3)34-) reveals

  12. Adsorption of ammonia on hydrogen covered GaN(0001) surface - Density Functional Theory study

    NASA Astrophysics Data System (ADS)

    Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad; Krukowski, Stanisław

    2014-09-01

    Density Functional Theory (DFT) simulations of ammonia adsorption at clean and H-covered surface confirmed that ammonia may dissociate into NH2 radical and H adatom or remain in the molecular form. The remaining hydrogen atoms are attached to Ga atoms where the charge transfer to the surface is possible. The calculations show that for the molecular process, the ammonia adsorption energy is close to 2.0 eV, independent of hydrogen coverage. The dissociative process is strongly H-coverage dependent, for low H-coverage the adsorption energy is close to 2.8 eV, for high coverage changes by more than 4 eV reaching negative values. Thus for low coverage the energetically preferred adsorption is dissociative, for high is molecular. The dissociation energy and preferred mode change are related to the change of the Fermi level pinning from Ga broken bond state to valence band maximum (VBM), confirming the decisive role of charge transfer in the adsorption processes.

  13. Adsorption of iodine on hydrogen-reduced silver-exchanged mordenite: Experiments and modeling

    SciTech Connect

    Nan, Yue; Tavlarides, Lawrence L.; DePaoli, David W.

    2016-08-03

    The adsorption process of iodine, a major volatile radionuclide in the off-gas streams of spent nuclear fuel reprocessing, on hydrogen-reduced silver-exchanged mordenite (Ag0Z) was studied at the micro-scale. The gas-solid mass transfer and reaction involved in the adsorption process were investigated and evaluated with appropriate models. Optimal conditions for reducing the silver-exchanged mordenite (AgZ) in a hydrogen stream were determined. Kinetic and equilibrium data of iodine adsorption on Ag0Z were obtained by performing single-layer adsorption experiments with experimental systems of high precision at 373–473 K over various iodine concentrations. Results indicate approximately 91% to 97% of the iodine adsorption was through the silver-iodine reaction. The effect of temperature on the iodine loading capacity of Ag0Z was discussed. In conclusion, the Shrinking Core model describes the data well, and the primary rate controlling mechanisms were macro-pore diffusion and silver-iodine reaction. © 2016 American Institute of Chemical Engineers AIChE J, 2016

  14. Adsorption of iodine on hydrogen-reduced silver-exchanged mordenite: Experiments and modeling

    DOE PAGES

    Nan, Yue; Tavlarides, Lawrence L.; DePaoli, David W.

    2016-08-03

    The adsorption process of iodine, a major volatile radionuclide in the off-gas streams of spent nuclear fuel reprocessing, on hydrogen-reduced silver-exchanged mordenite (Ag0Z) was studied at the micro-scale. The gas-solid mass transfer and reaction involved in the adsorption process were investigated and evaluated with appropriate models. Optimal conditions for reducing the silver-exchanged mordenite (AgZ) in a hydrogen stream were determined. Kinetic and equilibrium data of iodine adsorption on Ag0Z were obtained by performing single-layer adsorption experiments with experimental systems of high precision at 373–473 K over various iodine concentrations. Results indicate approximately 91% to 97% of the iodine adsorption wasmore » through the silver-iodine reaction. The effect of temperature on the iodine loading capacity of Ag0Z was discussed. In conclusion, the Shrinking Core model describes the data well, and the primary rate controlling mechanisms were macro-pore diffusion and silver-iodine reaction. © 2016 American Institute of Chemical Engineers AIChE J, 2016« less

  15. High precision quantum-chemical treatment of adsorption: Benchmarking physisorption of molecular hydrogen on graphane

    NASA Astrophysics Data System (ADS)

    Usvyat, Denis

    2015-09-01

    A multilevel hierarchical ab initio protocol for calculating adsorption on non-conducting surfaces is presented. It employs fully periodic treatment, which reaches local Møller-Plesset perturbation theory of second order (MP2) with correction for the basis set incompleteness via the local F12 technique. Post-MP2 corrections are calculated using finite clusters. That includes the coupled cluster treatment in the local and canonical frameworks (up to perturbative quadruples) and correlated core (with MP2). Using this protocol, the potential surface of hydrogen molecules adsorbed on graphane was computed. According to the calculations, hydrogen molecules are adsorbed on graphane in a perpendicular to the surface orientation with the minimum of the potential surface of around -3.6 kJ/mol located at the distance of 3.85 Å between the bond center of the hydrogen molecule and the mid-plane of graphane. The adsorption sites along the path from the downward-pointing carbon to the ring center of the graphane are energetically virtually equally preferable, which can enable nearly free translations of hydrogen molecules along these paths. Consequently, the hydrogen molecules on graphane most likely form a non-commensurate monolayer. The analysis of the remaining errors reveals a very high accuracy of the computed potential surface with an error bar of a few tenths of a kJ/mol. The obtained results are a high-precision benchmark for further theoretical and experimental studies of hydrogen molecules interacting with graphane.

  16. Predicting hydrogen and methane adsorption in carbon nanopores for energy storage

    NASA Astrophysics Data System (ADS)

    Ihm, Yungok; Morris, James; Cooper, Valentino; Morris Lab, U. tennessee Collaboration; Advanced material Group, ORNL Collaboration

    2013-03-01

    There are increasing demands for alternate fuels for transportation, which requires safe, high energy density, lightweight storage materials. Experimental measurements and theoretical predictions show relatively low hydrogen storage capacities in various porous materials, limiting hydrogen as a viable alternative for automobiles. In this work, we use a continuum model based on van der Waals density functional (vdW-DF) calculations to elucidate the role that long-range interactions play in the hydrogen adsorption properties of model slit nanopores in carbon. The proper treatment of long-range interactions gives an optimal pore size for hydrogen storage of 8-9 Å (larger than previously predicted). Remarkably, we find a peak hydrogen density close to that of liquid H2 at ambient temperatures, in agreement with recent experimental results on pore-size dependent adsorption in nanoporous carbon. We then show that such nanopores would be better suited to storing methane, possibly providing an alternative to fill the gap between the capacity required by DOE goals and that attainable with current hydrogen storage technology. Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

  17. High precision quantum-chemical treatment of adsorption: Benchmarking physisorption of molecular hydrogen on graphane

    SciTech Connect

    Usvyat, Denis

    2015-09-14

    A multilevel hierarchical ab initio protocol for calculating adsorption on non-conducting surfaces is presented. It employs fully periodic treatment, which reaches local Møller-Plesset perturbation theory of second order (MP2) with correction for the basis set incompleteness via the local F12 technique. Post-MP2 corrections are calculated using finite clusters. That includes the coupled cluster treatment in the local and canonical frameworks (up to perturbative quadruples) and correlated core (with MP2). Using this protocol, the potential surface of hydrogen molecules adsorbed on graphane was computed. According to the calculations, hydrogen molecules are adsorbed on graphane in a perpendicular to the surface orientation with the minimum of the potential surface of around −3.6 kJ/mol located at the distance of 3.85 Å between the bond center of the hydrogen molecule and the mid-plane of graphane. The adsorption sites along the path from the downward-pointing carbon to the ring center of the graphane are energetically virtually equally preferable, which can enable nearly free translations of hydrogen molecules along these paths. Consequently, the hydrogen molecules on graphane most likely form a non-commensurate monolayer. The analysis of the remaining errors reveals a very high accuracy of the computed potential surface with an error bar of a few tenths of a kJ/mol. The obtained results are a high-precision benchmark for further theoretical and experimental studies of hydrogen molecules interacting with graphane.

  18. Biochemical Hydrogen Isotope Fractionation during Lipid Biosynthesis in Higher Plants

    NASA Astrophysics Data System (ADS)

    Kahmen, A.; Gamarra, B.; Cormier, M. A.

    2014-12-01

    Although hydrogen isotopes (δ2H) of leaf wax lipids are increasingly being applied as (paleo-) hydrological proxies, we still do not understand some of the basic processes that shape the δ2H values of these compounds. In general, it is believed that three variables shape the δ2H values of leaf wax lipids: source water δ2H values, evaporative deuterium (2H) enrichment of leaf water and the biosynthetic fractionation (ɛbio) during the synthesis of organic compounds. While the influences of source water δ2H values and leaf water evaporative 2H enrichment have been well documented, very little is known how ɛbio shapes the δ2H values of plant-derived lipids. I will present the results from recent experiments, where we show that the magnitude of ɛbio, and thus the δ2H value of plant-derived lipids, strongly depends on the carbon (C) metabolism of a plant. Specifically, I will show that plants that rely for their tissue formation on recently assimilated C have δ2H values in their n-alkanes that are up to 60‰ more negative than plants that depend for their tissue formation on stored carbohydrates. Our findings can be explained by the fact that NADPH is the primary source of hydrogen in plant lipids and that the δ2H value of NADPH differs whether NADPH was generated directly in the light reaction of photosynthesis or whether it was generated by processing stored carbohydrates. As such, the δ2H values of plant-derived lipids will directly depend on whether the tissue containing these lipids was synthesized using recent assimilates, e.g. in a C autonomous state or, if it was synthesized from stored or otherwise aquired C sources, e.g. in a not C autonomous state. Given the magnidude of this effect, our results have important implications for interpretation of plant-derived lipid δ2H values when used as (paleo-) hydrological proxies. In addition, our results suggest, that δ2H values of plant-derived lipids could be employed as a new tools to assess the C

  19. Effects of hydrogen isotopes in the irradiation damage of CLAM steel

    NASA Astrophysics Data System (ADS)

    Zhao, M. Z.; Liu, P. P.; Zhu, Y. M.; Wan, F. R.; He, Z. B.; Zhan, Q.

    2015-11-01

    The isotope effect of hydrogen in irradiation damage plays an important role in the development of reduced activation Ferritic/Martensitic steels in nuclear reactors. The evolutions of microstructures and mechanical properties of China low active martensitic (CLAM) steel subjected to hydrogen and deuterium ions irradiation are studied comparatively. Under the same irradiation conditions, larger size and smaller density of dislocation loops are generated by deuterium ion than by hydrogen ion. Irradiation hardening occurs under the ion irradiation and the hardening induced by hydrogen ion is higher than by deuterium ion. Moreover, the coarsening of M23C6 precipitates is observed, which can be explained by the solute drag mechanisms. It turns out that the coarsening induced by deuterium ion irradiation is more distinct than by hydrogen ion irradiation. No distinct variations for the compositions of M23C6 precipitates are found by a large number of statistical data after hydrogen isotopes irradiation.

  20. Hydrogen Isotope Fractionation As a Tool to Identify Aerobic and Anaerobic PAH Biodegradation.

    PubMed

    Kümmel, Steffen; Starke, Robert; Chen, Gao; Musat, Florin; Richnow, Hans H; Vogt, Carsten

    2016-03-15

    Aerobic and anaerobic polycyclic aromatic hydrocarbon (PAH) biodegradation was characterized by compound specific stable isotope analysis (CSIA) of the carbon and hydrogen isotope effects of the enzymatic reactions initiating specific degradation pathways, using naphthalene and 2-methylnaphtalene as model compounds. Aerobic activation of naphthalene and 2-methylnaphthalene by Pseudomonas putida NCIB 9816 and Pseudomonas fluorescens ATCC 17483 containing naphthalene dioxygenases was associated with moderate carbon isotope fractionation (εC = -0.8 ± 0.1‰ to -1.6 ± 0.2‰). In contrast, anaerobic activation of naphthalene by a carboxylation-like mechanism by strain NaphS6 was linked to negligible carbon isotope fractionation (εC = -0.2 ± 0.2‰ to -0.4 ± 0.3‰). Notably, anaerobic activation of naphthalene by strain NaphS6 exhibited a normal hydrogen isotope fractionation (εH = -11 ± 2‰ to -47 ± 4‰), whereas an inverse hydrogen isotope fractionation was observed for the aerobic strains (εH = +15 ± 2‰ to +71 ± 6‰). Additionally, isotope fractionation of NaphS6 was determined in an overlaying hydrophobic carrier phase, resulting in more reliable enrichment factors compared to immobilizing the PAHs on the bottle walls without carrier phase. The observed differences especially in hydrogen fractionation might be used to differentiate between aerobic and anaerobic naphthalene and 2-methylnaphthalene biodegradation pathways at PAH-contaminated field sites.

  1. Hydrogen and oxygen isotope exchange reactions between clay minerals and water

    USGS Publications Warehouse

    O'Neil, J.R.; Kharaka, Y.K.

    1976-01-01

    The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100-350?? for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100??. Exchange rates were 3-5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure. Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O18 exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O18 exchange. At 350?? kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O18 exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor. ?? 1976.

  2. Quest for Inexpensive Hydrogen Isotopic Fractionation: Do We Need 2D Quantum Confining in Porous Materials or Are Rough Surfaces Enough? The Case of Ammonia Nanoclusters.

    PubMed

    Mella, Massimo; Curotto, E

    2016-10-05

    We study the adsorption energetics and quantum properties of the molecular hydrogen isotopes H2, D2, and T2 onto the surface of rigid ammonia nanoclusters with quantum simulations and accurate model potential energy surfaces (PES). A highly efficient diffusion Monte Carlo (DMC) algorithm for rigid rotors allowed us to accurately define zero-point adsorption energies for the three isotopes, as well as the degree of translational and rotational delocalization that each affords on the surface. From the data emerges that the quantum adsorption energy (Eads) of T2 can be up to twice the one of H2 at 0 K, suggesting the possibility of exploiting some form of solid ammonia to selectivity separate hydrogen isotopes at low temperatures (≃20 K). This is discussed by focusing on the structural motif that may be more effective for the task. The analysis of the contributions to Eads, however, surprisingly indicates that the average kinetic energy (E(kin)) and rotation energy (Erot(kin)) of T2 can also be, respectively, 2 times and 20 times higher than those of H2; this finding markedly deviates from what is predicted for hydrogen molecules inside carbon nanotubes (CNT) or metallic-organic frameworks (MOF), where E(kin) and Erot(kin) is higher for H2 due to the unavoidable effects of confinement and hindrance to its rotational motion. The rationale for these differences is provided by the geometrical distributions for the rigid rotors, which reveal an increasingly stronger coupling between rotational and translational degrees of freedom upon increasing the isotopic mass. This effect has never been observed before on adsorbing surfaces (e.g., graphite) and is induced by a strongly anisotropic and anharmonic bowl-like potential experienced by the rotors.

  3. Isotopic Studies of Hydrogen and Deuterium Phase IV at Multi-Megabar Pressures

    NASA Astrophysics Data System (ADS)

    Gregoryanz, Eugene; Guillaume, Christophe; Scheler, Thomas; Howie, Ross

    2013-06-01

    The recent discovery of the mixed atomic and molecular phase IV of hydrogen (deuterium) is exemplary of how the studies of hydrogen at multi-megabar pressures is constitutive to the understanding of simple systems at extreme compressions. Through a series of high pressure Raman spectroscopic experiments we have conducted an isotopic comparison between hydrogen and deuterium in phase I. Isotopic studies not only reveal differences in phase stability, imposing constraints on the P-T phase diagram, but also provide strong evidence for structural phenomena, such as proton (deuteron) tunnelling. New data will be presented over a wide temperature range.

  4. Design and synthesis of vanadium hydrazide gels for Kubas-type hydrogen adsorption: a new class of hydrogen storage materials.

    PubMed

    Hoang, Tuan K A; Webb, Michael I; Mai, Hung V; Hamaed, Ahmad; Walsby, Charles J; Trudeau, Michel; Antonelli, David M

    2010-08-25

    In this paper we demonstrate that the Kubas interaction, a nondissociative form of weak hydrogen chemisorption with binding enthalpies in the ideal 20-30 kJ/mol range for room-temperature hydrogen storage, can be exploited in the design of a new class of hydrogen storage materials which avoid the shortcomings of hydrides and physisorpion materials. This was accomplished through the synthesis of novel vanadium hydrazide gels that use low-coordinate V centers as the principal Kubas H(2) binding sites with only a negligible contribution from physisorption. Materials were synthesized at vanadium-to-hydrazine ratios of 4:3, 1:1, 1:1.5, and 1:2 and characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption, elemental analysis, infrared spectroscopy, and electron paramagnetic resonance spectroscopy. The material with the highest capacity possesses an excess reversible storage of 4.04 wt % at 77 K and 85 bar, corresponding to a true volumetric adsorption of 80 kg H(2)/m(3) and an excess volumetric adsorption of 60.01 kg/m(3). These values are in the range of the ultimate U.S. Department of Energy goal for volumetric density (70 kg/m(3)) as well as the best physisorption material studied to date (49 kg H(2)/m(3) for MOF-177). This material also displays a surprisingly high volumetric density of 23.2 kg H(2)/m(3) at room temperature and 85 bar--roughly 3 times higher than that of compressed gas and approaching the DOE 2010 goal of 28 kg H(2)/m(3). These materials possess linear isotherms and enthalpies that rise on coverage and have little or no kinetic barrier to adsorption or desorption. In a practical system these materials would use pressure instead of temperature as a toggle and can thus be used in compressed gas tanks, currently employed in many hydrogen test vehicles, to dramatically increase the amount of hydrogen stored and therefore the range of any vehicle.

  5. On the hydrogen adsorption and dissociation on Cu surfaces and nanorows

    NASA Astrophysics Data System (ADS)

    Álvarez-Falcón, Leny; Viñes, Francesc; Notario-Estévez, Almudena; Illas, Francesc

    2016-04-01

    Here we present a thorough density functional theory study, including and excluding dispersive forces interaction description, on the adsorption and dissociation of H2 molecule on the low-index Miller Cu (111), (100), and (110) surfaces and two different surface Cu nanorows, all displaying a different number of surface nearest neighbors, nn. The computational setup has been optimized granting an accuracy below 0.04 eV. Surface and nanorow energies-for which a new methodology to extract them is presented- are found to follow the nn number. However, the adsorption strength is found not to. Thus, the adsorption energies seem to be governed by a particular orbital ↔ band interaction rather than by the simple nn surface saturation. The van der Waals (vdW) forces are found to play a key role in the adsorption of H2, and merely an energetic adjustment on chemisorbed H adatoms. Neither clear trends are observed for H2 and H adsorption energies, and H2 dissociation energy with respect nn, and nor Brønsted-Evans-Polanyi, making H2 adsorption and dissociation a trend outlier compared to other cases. H2 is found to adsorb and dissociate on Cu(100) surface. On the Cu(111) surface, the rather small H2 adsorption energy would prevent H2 dissociation, regardless if it is thermodynamically driven. On Cu(110) surface, the H2 dissociation process would be endothermic and achievable if adsorption energy is released on surpassing the dissociation energy barrier. On low-coordinated sites on Cu nanorows, vdW plays a key role in the H2 dissociation process, which otherwise is found to be endothermic. Indeed, dispersive forces turn the process markedly exothermic. Nanoparticle Cu systems must display Cu(100) surfaces or facets in order to dissociate H2, vital in many hydrogenation processes.

  6. Molecular Paleohydrology: Interpreting the Hydrogen-Isotopic Composition of Lipid Biomarkers from Photosynthesizing Organisms

    NASA Astrophysics Data System (ADS)

    Sachse, Dirk; Billault, Isabelle; Bowen, Gabriel J.; Chikaraishi, Yoshito; Dawson, Todd E.; Feakins, Sarah J.; Freeman, Katherine H.; Magill, Clayton R.; McInerney, Francesca A.; van der Meer, Marcel T. J.; Polissar, Pratigya; Robins, Richard J.; Sachs, Julian P.; Schmidt, Hanns-Ludwig; Sessions, Alex L.; White, James W. C.; West, Jason B.; Kahmen, Ansgar

    2012-05-01

    Hydrogen-isotopic abundances of lipid biomarkers are emerging as important proxies in the study of ancient environments and ecosystems. A decade ago, pioneering studies made use of new analytical methods and demonstrated that the hydrogen-isotopic composition of individual lipids from aquatic and terrestrial organisms can be related to the composition of their growth (i.e., environmental) water. Subsequently, compound-specific deuterium/hydrogen (D/H) ratios of sedimentary biomarkers have been increasingly used as paleohydrological proxies over a range of geological timescales. Isotopic fractionation observed between hydrogen in environmental water and hydrogen in lipids, however, is sensitive to biochemical, physiological, and environmental influences on the composition of hydrogen available for biosynthesis in cells. Here we review the factors and processes that are known to influence the hydrogen-isotopic compositions of lipids—especially n-alkanes—from photosynthesizing organisms, and we provide a framework for interpreting their D/H ratios from ancient sediments and identify future research opportunities.

  7. Insights into hydrogen atom adsorption on and the electrochemical properties of nitrogen-substituted carbon materials.

    PubMed

    Zhu, Z H; Hatori, H; Wang, S B; Lu, G Q

    2005-09-08

    The nitrogen substitution in carbon materials is investigated theoretically using the density functional theory method. Our calculations show that nitrogen substitution decreases the hydrogen adsorption energy if hydrogen atoms are adsorbed on both nitrogen atoms and the neighboring carbon atoms. On the contrary, the hydrogen adsorption energy can be increased if hydrogen atoms are adsorbed only on the neighboring carbon atoms. The reason can be explained by the electronic structures analysis of N-substituted graphene sheets. Nitrogen substitution reduces the pi electron conjugation and increases the HOMO energy of a graphene sheet, and the nitrogen atom is not stable due to its 3-valent character. This raises an interesting research topic on the optimization of the N-substitution degree, and is important to many applications such as hydrogen storage and the tokamaks device. The electronic structure studies also explain well why nitrogen substitution increases the capacitance but decreases the electron conductivity of carbon electrodes as was experimentally observed in our experiments on the supercapacitor.

  8. Carbon and hydrogen isotopic effects of stomatal density in Arabidopsis thaliana

    NASA Astrophysics Data System (ADS)

    Lee, Hyejung; Feakins, Sarah J.; Sternberg, Leonel da S. L.

    2016-04-01

    Stomata are key gateways mediating carbon uptake and water loss from plants. Varied stomatal densities in fossil leaves raise the possibility that isotope effects associated with the openness of exchange may have mediated plant wax biomarker isotopic proxies for paleovegetation and paleoclimate in the geological record. Here we use Arabidopsis thaliana, a widely used model organism, to provide the first controlled tests of stomatal density on carbon and hydrogen isotopic compositions of cuticular waxes. Laboratory grown wildtype and mutants with suppressed and overexpressed stomatal densities allow us to directly test the isotope effects of stomatal densities independent of most other environmental or biological variables. Hydrogen isotope (D/H) measurements of both plant waters and plant wax n-alkanes allow us to directly constrain the isotopic effects of leaf water isotopic enrichment via transpiration and biosynthetic fractionations, which together determine the net fractionation between irrigation water and n-alkane hydrogen isotopic composition. We also measure carbon isotopic fractionations of n-alkanes and bulk leaf tissue associated with different stomatal densities. We find offsets of +15‰ for δD and -3‰ for δ13C for the overexpressed mutant compared to the suppressed mutant. Since the range of stomatal densities expressed is comparable to that found in extant plants and the Cenozoic fossil record, the results allow us to consider the magnitude of isotope effects that may be incurred by these plant adaptive responses. This study highlights the potential of genetic mutants to isolate individual isotope effects and add to our fundamental understanding of how genetics and physiology influence plant biochemicals including plant wax biomarkers.

  9. Multiscale Study of Hydrogen Adsorption on Six Designed Covalent Organic Frameworks Based on Porphyrazine, Cyclobutane and Scandium

    NASA Astrophysics Data System (ADS)

    Li, Le-Le; Gao, Teng-Fei; Zhang, Ruan-Yu; Zhang, Hong

    2014-09-01

    The first-principles method of hydrogen adsorption is used to investigate the interaction of H2 with the scandium-porphyrazine (Sc-Pz) and porphyrazine (Pz) clusters. The result shows that the interaction of H2 with Sc-Pz is stronger than with Pz. Then grand canonical Monte Carlo simulations are used to investigate hydrogen adsorption in six designed covalent organic frameworks (COFs), which are designed based on porphyrazine, cyclobutane and scandium. When the pressure is from 0.1 to 100 bar and the temperature is 298 K and 77 K, the hydrogen adsorption capacities of the six COFs are calculated. We further study the importance of Sc and fillers to improve the H2 uptake in the modified COFs by analyzing the isosteric heat of hydrogen adsorption.

  10. Strain effect on the adsorption, diffusion, and molecular dissociation of hydrogen on Mg (0001) surface

    SciTech Connect

    Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Hupalo, Myron; Wang, Yangang; McDougall, Dan; Tringides, Michael; Ho, Kaiming

    2013-12-14

    The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H{sub 2} molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H{sub 2} molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.

  11. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption

    NASA Astrophysics Data System (ADS)

    Strmcnik, Dusan; Uchimura, Masanobu; Wang, Chao; Subbaraman, Ram; Danilovic, Nemanja; van der Vliet, Dennis; Paulikas, Arvydas P.; Stamenkovic, Vojislav R.; Markovic, Nenad M.

    2013-04-01

    The development of hydrogen-based energy sources as viable alternatives to fossil-fuel technologies has revolutionized clean energy production using fuel cells. However, to date, the slow rate of the hydrogen oxidation reaction (HOR) in alkaline environments has hindered advances in alkaline fuel cell systems. Here, we address this by studying the trends in the activity of the HOR in alkaline environments. We demonstrate that it can be enhanced more than fivefold compared to state-of-the-art platinum catalysts. The maximum activity is found for materials (Ir and Pt0.1Ru0.9) with an optimal balance between the active sites that are required for the adsorption/dissociation of H2 and for the adsorption of hydroxyl species (OHad). We propose that the more oxophilic sites on Ir (defects) and PtRu material (Ru atoms) electrodes facilitate the adsorption of OHad species. Those then react with the hydrogen intermediates (Had) that are adsorbed on more noble surface sites.

  12. American woodcock migratory connectivity as indicated by hydrogen isotopes

    USGS Publications Warehouse

    Sullins, Daniel S.; Conway, Warren C.; Haukos, David A.; Hobson, Keith A.; Wassenaar, Leonard I; Comer, Christopher E.; Hung, I-Kuai

    2016-01-01

    To identify factors contributing to the long-term decline of American woodcock, a holistic understanding of range-wide population connectivity throughout the annual cycle is needed. We used band recovery data and isotopic composition of primary (P1) and secondary (S13) feathers to estimate population sources and connectivity among natal, early fall, and winter ranges of hunter-harvested juvenile American woodcock. We used P1 feathers from known-origin pre-fledged woodcock (n = 43) to create a hydrogenδ2Hf isoscape by regressing δ2Hf against expected growing-season precipitation (δ2Hp). Modeled δ2Hp values explained 79% of the variance in P1 δ2Hf values, indicating good model fit for estimating woodcock natal origins. However, a poor relationship (r2 = 0.23) between known-origin, S13 δ2Hf values, and expected δ2Hp values precluded assignment of early fall origins. We applied the δ2Hfisoscape to assign natal origins using P1 feathers from 494 hunter-harvested juvenile woodcock in the United States and Canada during 2010–2011 and 2011–2012 hunting seasons. Overall, 64% of all woodcock origins were assigned to the northernmost (>44°N) portion of both the Central and Eastern Management Regions. In the Eastern Region, assignments were more uniformly distributed along the Atlantic coast, whereas in the Central Region, most woodcock were assigned to origins within and north of the Great Lakes region. We compared our origin assignments to spatial coverage of the annual American woodcock Singing Ground Survey (SGS) and evaluated whether the survey effectively encompasses the entire breeding range. When we removed the inadequately surveyed Softwood shield Bird Conservation Region (BCR) from the northern portion of the SGS area, only 48% of juvenile woodcock originated in areas currently surveyed by the SGS. Of the individuals assigned to the northernmost portions of the breeding range, several were harvested in the southern extent of the

  13. Hydrogen isotope fractionation by Methanothermobacter thermoautotrophicus in coculture and pure culture conditions

    NASA Astrophysics Data System (ADS)

    Yoshioka, Hideyoshi; Sakata, Susumu; Kamagata, Yoichi

    2008-06-01

    We grew a hydrogen-utilizing methanogen, Methanothermobacter thermoautotrophicus strain ΔH, in coculture and pure culture conditions to evaluate the hydrogen isotope fractionation associated with carbonate reduction under low (< several tens of μM; coculture) and high (>6 mM; pure culture) concentrations of H 2 in the headspace. In the cocultures, which were grown at 55 °C with a thermophilic butyrate-oxidizing syntroph, the hydrogen isotopic relationship between methane and water was well represented by the following equation: δD=0.725(±0.003)·δDO-275(±3), in which the hydrogen isotope fractionation factor ( αH) was 0.725 ± 0.003. The relationship was consistent with the isotopic data on methane and water from terrestrial fields (a peat bog in Washington State, USA, and a sandy aquifer in Denmark), where carbonate reduction was reported to be the dominant pathway of methanogenesis. In the pure cultures, grown at 55 and 65 °C, the αH values were 0.755 ± 0.014 and 0.749 ± 0.014, respectively. Dependence of αH on growth temperature was not observed. The αH value at 55 °C in the pure culture was slightly higher than that in the coculture, a finding that disagrees with a hypothesis proposed by Burke [Burke, Jr. R. A. (1993) Possible influence of hydrogen concentration on microbial methane stable hydrogen isotopic composition. Chemosphere26, 55-67] that hydrogen isotope fractionation between methane and water increases (and αH decreases) with increasing H 2 concentration.

  14. Surface and subsurface hydrogen: adsorption properties on transition metals and near-surface alloys.

    PubMed

    Greeley, Jeff; Mavrikakis, Manos

    2005-03-03

    Periodic, self-consistent DFT-GGA calculations are used to study the thermochemical properties of both surface and subsurface atomic hydrogen on a variety of pure metals and near-surface alloys (NSAs). For surface hydrogen on pure metals, calculated site preferences, adsorption geometries, vibrational frequencies, and binding energies are reported and are found to be in good agreement with available experimental data. On NSAs, defined as alloys wherein a solute is present near the surface of a host metal in a composition different from the bulk composition, surface hydrogen generally binds more weakly than it binds to the pure-metal components composing the alloys. Some of the NSAs even possess the unusual property of binding hydrogen as weakly as the noble metals while, at the same time, dissociating H(2) much more easily. On both NSAs and pure metals, formation of surface hydrogen is generally exothermic with respect to H(2)(g). In contrast, formation of subsurface hydrogen is typically endothermic with respect to gas-phase H(2) (the only exception to this general statement is found for pure Pd). As with surface H, subsurface H typically binds more weakly to NSAs than to the corresponding pure-metal components of the alloys. The diffusion barrier for hydrogen from surface to subsurface sites, however, is usually lower on NSAs compared to the pure-metal components, suggesting that population of subsurface sites may occur more rapidly on NSAs.

  15. Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Li, Ming; Huang, Xiaobo; Kang, Zhan

    2015-08-01

    Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

  16. Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

    SciTech Connect

    Li, Ming; Kang, Zhan; Huang, Xiaobo

    2015-08-28

    Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

  17. Stable Isotope Measurements of Carbon Dioxide, Methane, and Hydrogen Sulfide Gas Using Frequency Modulation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Nowak-Lovato, K.

    2014-12-01

    Seepage from enhanced oil recovery, carbon storage, and natural gas sites can emit trace gases such as carbon dioxide, methane, and hydrogen sulfide. Trace gas emission at these locations demonstrate unique light stable isotope signatures that provide information to enable source identification of the material. Light stable isotope detection through surface monitoring, offers the ability to distinguish between trace gases emitted from sources such as, biological (fertilizers and wastes), mineral (coal or seams), or liquid organic systems (oil and gas reservoirs). To make light stable isotope measurements, we employ the ultra-sensitive technique, frequency modulation spectroscopy (FMS). FMS is an absorption technique with sensitivity enhancements approximately 100-1000x more than standard absorption spectroscopy with the advantage of providing stable isotope signature information. We have developed an integrated in situ (point source) system that measures carbon dioxide, methane and hydrogen sulfide with isotopic resolution and enhanced sensitivity. The in situ instrument involves the continuous collection of air and records the stable isotope ratio for the gas being detected. We have included in-line flask collection points to obtain gas samples for validation of isotopic concentrations using our in-house isotope ratio mass spectroscopy (IRMS). We present calibration curves for each species addressed above to demonstrate the sensitivity and accuracy of the system. We also show field deployment data demonstrating the capabilities of the system in making live dynamic measurements from an active source.

  18. Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: Implications for planetary accretion

    NASA Technical Reports Server (NTRS)

    Tyburczy, James A.; Krishnamurthy, R. V.; Epstein, Samuel; Ahrens, Thomas J.

    1988-01-01

    Impact-induced devolatilization of porous serpentine was investigated using two independent experimental methods, the gas recovery and the solid recovery method, each yielding nearly identical results. For shock pressures near incipient devolatilization, the hydrogen isotopic composition of the evolved H2O is very close to that of the starting material. For shock pressures at which up to 12 percent impact-induced devolatilization occurs, the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H2O to H2 in gases recovered at these higher shock pressures, probably caused by reaction of evolved H2O with the metal gas recovery fixture. Gaseous H2O-H2 isotopic fractionation suggests high temperature isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition. Bulk gas-residual solid isotopic fractionations indicate nonequilibrium, kinetic control of gas-solid isotopic ratios. Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can strongly affect the long-term planetary isotopic ratios of planetary bodies, leaving the interiors enriched in deuterium. Depending on the model used for extrapolation of the isotopic fractionation to devolatilization fractions greater than those investigated experimentally can result from this process.

  19. New Carbon-Based Porous Materials with Increased Heats of Adsorption for Hydrogen Storage

    SciTech Connect

    Snurr, Randall Q.; Hupp, Joseph T.; Kanatzidis, Mercouri G.; Nguyen, SonBinh T.

    2014-11-03

    . Only after modeling suggested record-breaking hydrogen uptake at 77 K did we proceed to synthesize, characterize, and test the material, ultimately yielding experimental results that agreed closely with predictions that were made before the material was synthesized. We also synthesized, characterized, and computationally simulated the behavior of two new materials displaying the highest experimental Brunauer$-$Emmett$-$Teller (BET) surface areas of any porous materials reported to date (~7000 m2/g). Key to evacuating the initially solvent-filled materials without pore collapse, and thereby accessing the ultrahigh areas, was the use of a supercritical CO2 activation technique developed by our team. In our efforts to increase the hydrogen binding energy, we developed the first examples of “zwitterionic” metal-organic frameworks (MOFs). The two structures feature zwitterionic characteristics arising from N-heterocyclic azolium groups in the linkers and negatively charged Zn2(CO2)5 nodes. These groups interact strongly with the H2 quadrupole. High initial isosteric heats of adsorption for hydrogen were measured at low H2 loading. Simulations were used to determine the H2 binding sites, and results were compared with inelastic neutron scattering. In addition to MOFs, the project produced a variety of related materials known as porous organic frameworks (POFs), including robust catechol-functionalized POFs with tunable porosities and degrees of functionalization. Post-synthesis metalation was readily carried out with a wide range of metal precursors (CuII, MgII, and MnII salts and complexes), resulting in metalated POFs with enhanced heats of hydrogen adsorption compared to the starting nonmetalated materials. Isosteric heats of adsorption as high as 9.6 kJ/mol were observed, compared to typical values around 5 kJ/mol in unfunctionalized MOFs and POFs

  20. Measurements of Cosmic-Ray Hydrogen and Helium Isotopes with the PAMELA Experiment

    NASA Astrophysics Data System (ADS)

    Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergè, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.

    2016-02-01

    The cosmic-ray hydrogen and helium (1H, 2H, 3He, 4He) isotopic composition has been measured with the satellite-borne experiment PAMELA, which was launched into low-Earth orbit on board the Resurs-DK1 satellite on 2006 June 15. The rare isotopes 2H and 3He in cosmic rays are believed to originate mainly from the interaction of high-energy protons and helium with the galactic interstellar medium. The isotopic composition was measured between 100 and 1100 MeV/n for hydrogen and between 100 and 1400 MeV/n for helium isotopes using two different detector systems over the 23rd solar minimum from 2006 July to 2007 December.

  1. MEASUREMENTS OF COSMIC-RAY HYDROGEN AND HELIUM ISOTOPES WITH THE PAMELA EXPERIMENT

    SciTech Connect

    Adriani, O.; Bongi, M.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Bruno, A.; Boezio, M.; Bonvicini, V.; Formato, V.; Bogomolov, E. A.; Bottai, S.; Cafagna, F.; Campana, D.; Carlson, P.; Casolino, M.; Santis, C. De; Castellini, G.; Donato, C. De; Simone, N. De; Felice, V. Di; and others

    2016-02-10

    The cosmic-ray hydrogen and helium ({sup 1}H, {sup 2}H, {sup 3}He, {sup 4}He) isotopic composition has been measured with the satellite-borne experiment PAMELA, which was launched into low-Earth orbit on board the Resurs-DK1 satellite on 2006 June 15. The rare isotopes {sup 2}H and {sup 3}He in cosmic rays are believed to originate mainly from the interaction of high-energy protons and helium with the galactic interstellar medium. The isotopic composition was measured between 100 and 1100 MeV/n for hydrogen and between 100 and 1400 MeV/n for helium isotopes using two different detector systems over the 23rd solar minimum from 2006 July to 2007 December.

  2. Carbon and hydrogen isotopic composition of bacterial methane in a shallow freshwater lake

    SciTech Connect

    Woltemate, I.; Whiticar, M.J.; Schoell, M.

    1984-09-01

    Anoxic sediments from freshwater environments such as bogs, swamps, and lakes undergoing early diagenesis are frequently characterized by the formation of biogenic methane. Freshwater biogenic methanes exhibit carbon and hydrogen isotopic values strongly depleted in C-13 and deuterium relative to the respective values for carbon dioxide and formation water. The percentages of methane generated by fermentation and carbon dioxide reduction can be estimated by comparison of hydrogen isotopes in the formation water and methane. On the basis of these hydrogen isotope data, about 75% of the methane formation in Wurmsee comes from acetate reduction. Fermentation is thus the dominant although not exclusive process. Carbon dioxide reduction contributed the balance of the bacterial methane generated. 35 references, 5 figures, 1 table.

  3. Thermal management of the adsorption-based vessel for hydrogeneous gas storage

    NASA Astrophysics Data System (ADS)

    Vasiliev, L. L.; Kanonchik, L. E.; Babenko, V. A.

    2012-09-01

    Thermal management is a design bottleneck in the creation of rational gas storage sorption systems. Inefficient heat transfer in a sorption bed is connected with a relatively low thermal conductivity (0.1-0.5 W/(mṡK)) and an appreciable sorption heat of activated gas storage materials. This work is devoted to the development of a thermally regulated onboard system of hydrogenous gas (methane and hydrogen) storage with the use of novel carbon sorbents. A hydrogenous gas storage system based on combined gas adsorption and compression at moderate pressures (3-6 MPa) and low temperatures (from the temperature of liquid nitrogen of about 77 K to a temperature of 273 K) is suggested.

  4. Plant leaf wax biomarkers capture gradients in hydrogen isotopes of precipitation from the Andes and Amazon

    NASA Astrophysics Data System (ADS)

    Feakins, Sarah J.; Bentley, Lisa Patrick; Salinas, Norma; Shenkin, Alexander; Blonder, Benjamin; Goldsmith, Gregory R.; Ponton, Camilo; Arvin, Lindsay J.; Wu, Mong Sin; Peters, Tom; West, A. Joshua; Martin, Roberta E.; Enquist, Brian J.; Asner, Gregory P.; Malhi, Yadvinder

    2016-06-01

    Plant leaf waxes have been found to record the hydrogen isotopic composition of precipitation and are thus used to reconstruct past climate. To assess how faithfully they record hydrological signals, we characterize leaf wax hydrogen isotopic compositions in forest canopy trees across a highly biodiverse, 3 km elevation range on the eastern flank of the Andes. We sampled the dominant tree species and assessed their relative abundance in the tree community. For each tree we collected xylem and leaf samples for analysis of plant water and plant leaf wax hydrogen isotopic compositions. In total, 176 individuals were sampled across 32 species and 5 forest plots that span the gradient. We find both xylem water and leaf wax δD values of individuals correlate (R2 = 0.8 and R2 = 0.3 respectively) with the isotopic composition of precipitation (with an elevation gradient of -21‰ km-1). Minimal leaf water enrichment means that leaf waxes are straightforward recorders of the isotopic composition of precipitation in wet climates. For these tropical forests we find the average fractionation between source water and leaf wax for C29n-alkanes, -129 ± 2‰ (s.e.m., n = 136), to be indistinguishable from that of temperate moist forests. For C28n-alkanoic acids the average fractionation is -121 ± 3‰ (s.e.m., n = 102). Sampling guided by community assembly within forest plots shows that integrated plant leaf wax hydrogen isotopic compositions faithfully record the gradient of isotopes in precipitation with elevation (R2 = 0.97 for n-alkanes and 0.60 for n-alkanoic acids). This calibration study supports the use of leaf waxes as recorders of the isotopic composition of precipitation in lowland tropical rainforest, tropical montane cloud forests and their sedimentary archives.

  5. Adsorption as a cause for iron isotope fractionation in reduced groundwater

    NASA Astrophysics Data System (ADS)

    Teutsch, Nadya; von Gunten, Urs; Porcelli, Don; Cirpka, Olaf A.; Halliday, Alex N.

    2005-09-01

    Iron isotopes were used to investigate iron transformation processes during an in situ field experiment for removal of dissolved Fe from reduced groundwater. This experiment provided a unique setting for exploring Fe isotope fractionation in a natural system. Oxygen-containing water was injected at a test well into an aquifer containing Fe(II)-rich reduced water, leading to oxidation of Fe(II) and precipitation of Fe(III)(hydr)oxides. Subsequently, groundwater was extracted from the same well over a time period much longer than the injection time. Since the surrounding water is rich in Fe(II), the Fe(II) concentration in the extracted water increased over time. The increase was strongly retarded in comparison to a conservative tracer added to the injected solution, indicating that adsorption of Fe(II) onto the newly formed Fe(III)(hydr)oxides occurred. A series of injection-extraction (push-pull) cycles were performed at the same well. The δ 57Fe/ 54Fe of pre-experiment background groundwater (-0.57 ± 0.17 ‰) was lighter than the sediment leach of Fe(III) (-0.24 ± 0.08 ‰), probably due to slight fractionation (only ˜0.3 ‰) during microbial mediated reductive dissolution of Fe(III)(hydr)oxides present in the aquifer. During the experiment, Fe(II) was adsorbed from native groundwater drawn into the oxidized zone and onto Fe(III)(hydr)oxides producing a very light groundwater component with δ 57Fe/ 54Fe as low as -4 ‰, indicating that heavier Fe(II) is preferentially adsorbed to the newly formed Fe(III)(hydr)oxides surfaces. Iron concentrations increased with time of extraction, and δ 57Fe/ 54Fe linearly correlated with Fe concentrations (R 2 = 0.95). This pattern was reproducible over five individual cycles, indicating that the same process occurs during repeated injection/extraction cycles. We present a reactive transport model to explain the observed abiotic fractionation due to adsorption of Fe(II) on Fe(III)(hydr)oxides. The fractionation is

  6. A Biomimetic Approach to New Adsorptive Hydrogen Storage Metal-Organic Frameworks

    SciTech Connect

    Zhou, Hongcai J

    2015-08-12

    In the past decades, there has been an escalation of interest in the study of MOFs due to their fascinating structures and intriguing application potentials. Their exceptionally high surface areas, uniform yet tunable pore sizes, and well-defined adsorbate-MOF interaction sites make them suitable for hydrogen storage. Various strategies to increase the hydrogen capacity of MOFs, such as constructing pore sizes comparable to hydrogen molecules, increasing surface area and pore volume, utilizing catenation, and introducing coordinatively unsaturated metal centers (UMCs) have been widely explored to increase the hydrogen uptake of the MOFs. MOFs with hydrogen uptake approaching the DOE gravimetric storage goal under reasonable pressure but cryo- temperature (typically 77 K) were achieved. However, the weak interaction between hydrogen molecules and MOFs has been the major hurdle limiting the hydrogen uptake of MOFs at ambient temperature. Along the road, we have realized both high surface area and strong interaction between framework and hydrogen are equally essential for porous materials to be practically applicable in Hydrogen storage. Increasing the isosteric heats of adsorption for hydrogen through the introduction of active centers into the framework could have great potential on rendering the framework with strong interaction toward hydrogen. Approaches on increasing the surface areas and improving hydrogen affinity by optimizing size and structure of the pores and the alignment of active centers around the pores in frameworks have been pursued, for example: (a) the introduction of coordinatively UMC (represents a metal center missing multiple ligands) with potential capability of multiple dihydrogen-binding (Kubas type, non-dissociative) per UMC, (b) the design and synthesis of proton-rich MOFs in which a + H3 binds dihydrogen just like a metal ion does, and (c) the preparation of MOFs and PPNs with well aligned internal electric fields. We believe the

  7. Lake Louise Water (USGS47): A new isotopic reference water for stable hydrogen and oxygen isotope measurements

    USGS Publications Warehouse

    Qi, Haiping; Lorenz, Jennifer M.; Coplen, Tyler B.; Tarbox, Lauren V.; Mayer, Bernhard; Taylor, Steve

    2014-01-01

    RESULTS: The δ2H and δ18O values of this reference water are –150.2 ± 0.5 ‰ and –19.80 ± 0.02 ‰, respectively, relative to VSMOW on scales normalized such that the δ2H and δ18O values of SLAP reference water are, respectively, –428 and –55.5 ‰. Each uncertainty is an estimated expanded uncertainty (U = 2uc) about the reference value that provides an interval that has about a 95-percent probability of encompassing the true value. CONCLUSION: This isotopic reference material, designated as USGS47, is intended as one of two isotopic reference waters for daily normalization of stable hydrogen and stable oxygen isotopic analysis of water with a mass spectrometer or a laser absorption spectrometer. "

  8. Major evolutionary trends in hydrogen isotope fractionation of vascular plant leaf waxes.

    PubMed

    Gao, Li; Edwards, Erika J; Zeng, Yongbo; Huang, Yongsong

    2014-01-01

    Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences.

  9. Major Evolutionary Trends in Hydrogen Isotope Fractionation of Vascular Plant Leaf Waxes

    PubMed Central

    Gao, Li; Edwards, Erika J.; Zeng, Yongbo; Huang, Yongsong

    2014-01-01

    Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences. PMID:25402476

  10. Selected bibliography on heavy water, tritiated water and hydrogen isotopes (1981-1992)

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, V. T.; Sutawane, U. B.; Rathi, B. N.

    A selected bibliography on heavy water, tritiated water and hydrogen isotopes is presented. This bibliography covers the period 1981-1992 and is in continuation to Division's earlier report BARC-1192 (1983). The sources of information for this compilation are Chemical Abstracts, INIS Atom Index and also some scattered search through journals and reports available in our library. No claim is made towards exhaustiveness of this bibliography even though sincere attempts have been made for a wide coverage. The bibliography is arranged under the headings: (1) production, purification, recovery, reprocessing and storage; (2) isotope exchange; (3) isotope analysis; (4) properties; and (5) miscellaneous. Total number of references in the bibliography are 1762.

  11. Hydrogen adsorption in metal-organic frameworks: the role of nuclear quantum effects.

    PubMed

    Wahiduzzaman, Mohammad; Walther, Christian F J; Heine, Thomas

    2014-08-14

    The role of nuclear quantum effects on the adsorption of molecular hydrogen in metal-organic frameworks (MOFs) has been investigated on grounds of Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT) calculations. For this purpose, we have carefully validated classical H2-host interaction potentials that are obtained by fitting Born-Oppenheimer ab initio reference data. The hydrogen adsorption has first been assessed classically using Liquid Density-Functional Theory and the Grand-Canonical Monte Carlo methods. The results have been compared against the semi-classical treatment of quantum effects by applying the Feynman-Hibbs correction to the Born-Oppenheimer-derived potentials, and by explicit treatment within the GC-QLDFT. The results are compared with experimental data and indicate pronounced quantum and possibly many-particle effects. After validation calculations have been carried out for IRMOF-1 (MOF-5), GC-QLDFT is applied to study the adsorption of H2 in a series of MOFs, including IRMOF-4, -6, -8, -9, -10, -12, -14, -16, -18, and MOF-177. Finally, we discuss the evolution of the H2 quantum fluid with increasing pressure and lowering temperature.

  12. Hydrogen adsorption in metal-organic frameworks: The role of nuclear quantum effects

    SciTech Connect

    Wahiduzzaman, Mohammad; Walther, Christian F. J.; Heine, Thomas

    2014-08-14

    The role of nuclear quantum effects on the adsorption of molecular hydrogen in metal-organic frameworks (MOFs) has been investigated on grounds of Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT) calculations. For this purpose, we have carefully validated classical H{sub 2}-host interaction potentials that are obtained by fitting Born-Oppenheimer ab initio reference data. The hydrogen adsorption has first been assessed classically using Liquid Density-Functional Theory and the Grand-Canonical Monte Carlo methods. The results have been compared against the semi-classical treatment of quantum effects by applying the Feynman-Hibbs correction to the Born-Oppenheimer-derived potentials, and by explicit treatment within the GC-QLDFT. The results are compared with experimental data and indicate pronounced quantum and possibly many-particle effects. After validation calculations have been carried out for IRMOF-1 (MOF-5), GC-QLDFT is applied to study the adsorption of H{sub 2} in a series of MOFs, including IRMOF-4, -6, -8, -9, -10, -12, -14, -16, -18, and MOF-177. Finally, we discuss the evolution of the H{sub 2} quantum fluid with increasing pressure and lowering temperature.

  13. Molecular and dissociative adsorption of water and hydrogen sulfide at perfect and defective Cu(110) surfaces.

    PubMed

    Lousada, Cláudio M; Johansson, Adam Johannes; Korzhavyi, Pavel A

    2017-03-07

    We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of H2O and H2S at perfect and defective Cu(110) surfaces described using supercells with c(6 × 6) periodicity. The defective surface consists of a terrace surrounded by pits. We found considerable differences in adsorption modes and energies for H2O and H2S. At the defective Cu(110) surface, monomers of H2O and H2S preferentially adsorb at the terrace site and molecular adsorption of H2O is significantly more favorable than that of H2S. For dissociative adsorption however, the sulfur species are considerably more stable than the oxygen species. For monolayer (ML) coverages, there are small differences in the molecular adsorption energies for H2O and H2S. However, for the formation of 1 ML of HO and 1 ML of HS from 1 ML of H2O and 1 ML of H2S, respectively, with the release of H2(g), the differences are very large. The formation of 1 ML HO at the perfect Cu(110) surface is endoergic, while at the defective Cu(110) surface it is exoergic by -0.6 eV. For high coverages, H2S forms stacked half-monolayers that interact with each other via a complex hydrogen bond network with a strength per H2S molecule of -0.140 eV per H2S and -0.120 eV per H2S for H2S located in the underlayer and overlayer, respectively. The large distances between hydrogen bonded H2S molecules explain the preference for the formation of the two stacked half-monolayers of H2S instead of a single monolayer as it happens with H2O. Additionally, the formation of 1 ML of HS does not occur because of the spontaneous splitting of some H-S bonds resulting in surface bound HS and S and H2S molecules. Extensive surface reconstruction and relaxation accompanies adsorption of the sulfur adsorbates. Such reconstructions with outwards pull of Cu atoms can be at the origin of the weak adhesion of sulfide films that explains the release of CuS particles from copper sulfide films at copper surfaces. Overall, the

  14. Holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at Steel Lake, Minnesota

    NASA Astrophysics Data System (ADS)

    Henderson, Anna K.; Nelson, David M.; Hu, Feng Sheng; Huang, Yongsong; Shuman, Bryan N.; Williams, John W.

    2010-12-01

    Middle-Holocene (8 to 4 ka BP) warmth and aridity are well recorded in sediment archives from midcontinental North America. However, neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators. For example, an important challenge is to distinguish among the interacting effects of evaporation, temperature, or precipitation seasonality in existing δ 18O records from the region. Here we combine hydrogen isotopes of palmitic acid and oxygen isotopes of carbonate to derive lake-water isotopic values during the Holocene at Steel Lake in north-central Minnesota. In combination, these data enable us to separate variations in evaporation from variations in the isotopic composition of input-waters to lake. Variations in evaporation are used as a proxy for aridity and lake-water input isotopic values are used as a proxy for the isotopic values of meteoric precipitation. Our results suggest that lake-water input isotopic values were more negative during the middle Holocene than at present. To test whether these more negative values are related to temperature or precipitation seasonality, we compare pollen-inferred temperatures and the expected isotopic value of precipitation resulting from these temperatures to the reconstructed precipitation isotopic values. Results suggest that middle Holocene warmth and aridity were associated with increased evaporation rates and decreased summer precipitation. These inferences are consistent with climate simulations that highlight the role of seasonal insolation and sea surface temperatures in driving variations in precipitation seasonality during the Holocene. Results also suggest that changes in Holocene precipitation seasonality may have influenced the expansion of the prairie-forest border in Minnesota as well as regional variations in grassland community composition. This study demonstrates the efficacy of the dual hydrogen and

  15. Spin-polarized hydrogen and its isotopes: A rich class of quantum phases (Review Article)

    NASA Astrophysics Data System (ADS)

    Bešlić, I.; Vranješ Markić, L.; Boronat, J.

    2013-10-01

    We review the recent activity in the theoretical description of spin-polarized atomic hydrogen and its isotopes at very low temperatures. Spin-polarized hydrogen is the only system in nature that remains stable in the gas phase even in the zero temperature limit due to its small mass and weak interatomic interaction. Hydrogen and its heavier isotope tritium are bosons, the heavier mass of tritium producing a self-bound (liquid) system at zero temperature. The other isotope, deuterium, is a fermion with nuclear spin one making possible the study of three different quantum systems depending on the population of the three degenerate spin states. From the theoretical point of view, spin-polarized hydrogen is specially appealing because its interatomic potential is very accurately known making possible its precise quantum many-body study. The experimental study of atomic hydrogen has been very difficult due to its high recombination rate, but it finally led to its Bose-Einstein condensate state in 1998. Degeneracy has also been observed in thin films of hydrogen adsorbed on the 4He surface allowing for the possibility of observing the Berezinskii-Kosterlitz-Thouless superfluid transition.

  16. Isotopes and analogs of hydrogen--from fundamental investigations to practical applications.

    PubMed

    Macrae, Roderick M

    2013-01-01

    Hydrogen has a central role in the story of the universe itself and also in the story of our efforts to understand it. This paper retells the story of the part played by hydrogen and its stable isotope deuterium in the primordial synthesis of the elements, then goes on to describe how the spectrum of atomic hydrogen led to insights into the laws governing matter at the most fundamental level, from the quantum mechanics of Schrödinger and Heisenberg, through quantum electrodynamics, to the most recent work investigating the underlying structure of the proton itself. Atomic hydrogen is unique among the elements in that the concept of isotopy--atoms having the same nuclear charge but different masses--is stretched to its limit in the isotopes of hydrogen, ranging from the well-known isotopes deuterium and tritium to exotic species such as muonium, muonic helium, and positronium. These atoms, or atom-like objects, have much to tell us about fundamental aspects of the universe. In recent years the idea of utilizing hydrogen either as an energy source (through nuclear fusion) or as an energy storage medium (bound in hydrides or other materials) has attracted much attention as a possible avenue to a post-oil energy future. Some of the more interesting recent developments are described here. Dedicated to the memory of Brian C. Webster (1939-2008).

  17. Adsorption and hydrogenation of simple alkenes at Pt-group metal electrodes studied by DEMS: influence of the crystal orientation

    NASA Astrophysics Data System (ADS)

    Müller, Ulrich; Schmiemann, Udo; Dülberg, Andreas; Baltruschat, Helmut

    1995-07-01

    The adsorption of ethene and cyclohexene on mono-and polycrystalline Pt and on polycrystalline Pd electrodes was studied using differential electrochemical mass spectrometry (DEMS). Both molecules are partially hydrated to an oxygen containing species upon adsorption on Pt. In the case of ethene, this species dissociated to methane and adsorbed CO at negative potentials. Another part of the adsorbed ethene can be cathodically desorbed as ethane and butane. The ratio of the various species formed strongly depends on crystal orientation and adsorption potential. Contrary to heterogenous gas phase hydrogenation (and also contrary to some earlier reports on electrochemical hydrogenation), the rate of the Faradaic hydrogenation reaction is also strongly dependent on the crystallographic orientation, being faster on Pt(110) or roughened surfaces. During hydrogenation, H/D exchange occurs to an appreciable degree, suggesting the participation of adsorbed intermediates.

  18. Simulation of hydrogen adsorption systems adopting the flow through cooling concept

    SciTech Connect

    Corgnale, Claudio; Hardy, Bruce; Chahine, Richard; Cossement, Daniel; Tamburello, David; Anton, Donald

    2014-10-13

    Hydrogen storage systems based on adsorbent materials have the potential of achieving the U.S. Department of Energy (DOE) targets, especially in terms of gravimetric capacity. This paper deals with analysis of adsorption storage systems adopting the flow through cooling concept. By this approach the feeding hydrogen provides the needed cold to maintain the tank at low temperatures. Two adsorption systems have been examined and modeled adopting the Dubinin-Astakhov model, to see their performance under selected operating conditions. A first case has been analyzed, modeling a storage tank filled with carbon based material (namely MaxSorb®) and comparing the numerical outcomes with the available experimental results for a 2.5 L tank. Under selected operating conditions (minimum inlet hydrogen temperature of approximately 100 K and maximum pressure on the order of 8.5 MPa) and adopting the flow through cooling concept the material shows a gravimetric capacity of about 5.7 %. A second case has been modeled, examining the same tank filled with metal organic framework material (MOF5®) under approximately the same conditions. The model shows that the latter material can achieve a (material) gravimetric capacity on the order of 11%, making the system potentially able to achieve the DOE 2017 target.

  19. Simulation of hydrogen adsorption systems adopting the flow through cooling concept

    DOE PAGES

    Corgnale, Claudio; Hardy, Bruce; Chahine, Richard; ...

    2014-10-13

    Hydrogen storage systems based on adsorbent materials have the potential of achieving the U.S. Department of Energy (DOE) targets, especially in terms of gravimetric capacity. This paper deals with analysis of adsorption storage systems adopting the flow through cooling concept. By this approach the feeding hydrogen provides the needed cold to maintain the tank at low temperatures. Two adsorption systems have been examined and modeled adopting the Dubinin-Astakhov model, to see their performance under selected operating conditions. A first case has been analyzed, modeling a storage tank filled with carbon based material (namely MaxSorb®) and comparing the numerical outcomes withmore » the available experimental results for a 2.5 L tank. Under selected operating conditions (minimum inlet hydrogen temperature of approximately 100 K and maximum pressure on the order of 8.5 MPa) and adopting the flow through cooling concept the material shows a gravimetric capacity of about 5.7 %. A second case has been modeled, examining the same tank filled with metal organic framework material (MOF5®) under approximately the same conditions. The model shows that the latter material can achieve a (material) gravimetric capacity on the order of 11%, making the system potentially able to achieve the DOE 2017 target.« less

  20. Hydrogen isotope analysis of amino acids and whole cells reflects biosynthetic processing of nutrient- and water-derived hydrogen

    NASA Astrophysics Data System (ADS)

    Griffin, P.; Newsome, S.; Steele, A.; Fogel, M. L.

    2011-12-01

    Hydrogen (H) isotopes serve as sensitive tracers of biochemical processes that can be exploited to answer critical questions in biogeochemistry, ecology, and microbiology. Despite this apparent utility, relatively little is known about the specific mechanisms of H isotope fractionation involved in biosynthesis. In order to understand how organisms incorporate hydrogen from their chemical milieu into biomass, we have cultured the model bacterium E. coli MG1655 in a variety of media composed of deuterium-labeled nutrients and waters. Isotopic analysis of bulk cell mass reveals that the H fractionation between media water and cell material varies as a function of the nutrient source, with commonly used organic food sources (glucose and tryptone) leading to far smaller fractionation signals than non-standard ones (such as formamide, adenine, and urea). In addition, we have completed compound specific isotope analysis of amino acids using combined GC-IRMS. Amino acids harvested from E. coli cultured on glucose in water of varied D/H composition posses an extraordinary range of isotopic compositions (400-600 %). Furthermore, these amino acids follow a systematic distribution of D/H where proline is always heaviest and glycine is always lightest. However, when the short-chain peptide tryptone is used in place of glucose, only the non-essential amino acids reflect media water D/H values, suggesting the direct incorporation of some media-borne amino acids into cellular protein. These observations provide a foundation for understanding the cellular routing of hydrogen obtained from food and water sources and indicate that D/H analysis can serve as a powerful probe of biological function.

  1. Final Report: Characterization of Hydrogen Adsorption in Carbon-Based Materials by NMR

    SciTech Connect

    Wu, Yue; Kleinhammes, Alfred

    2011-07-11

    In support of DOE/EERE's Fuel Cell Technologies Program Hydrogen Sorption Center of Excellence (HSCoE), UNC conducted Nuclear Magnetic Resonance (NMR) measurements that contributed spectroscopic information as well as quantitative analysis of adsorption processes. While NMR based Langmuir isotherms produce reliable H2 capacity measurements, the most astute contribution to the center is provided by information on dihydrogen adsorption on the scale of nanometers, including the molecular dynamics of hydrogen in micropores, and the diffusion of dihydrogen between macro and micro pores. A new method to assess the pore width using H2 as probe of the pore geometry was developed and is based on the variation of the observed chemical shift of adsorbed dihydrogen as function of H2 pressure. Adsorbents designed and synthesized by the Center were assessed for their H2 capacity, the binding energy of the adsorption site, their pore structure and their ability to release H2. Feedback to the materials groups was provided to improve the materials’ properties. To enable in situ NMR measurements as a function of H2 pressure and temperature, a unique, specialized NMR system was designed and built. Pressure can be varied between 10-4 and 107 Pa while the temperature can be controlled between 77K and room temperature. In addition to the 1H investigation of the H2 adsorption process, NMR was implemented to measure the atomic content of substituted elements, e.g. boron in boron substituted graphitic material as well as to determine the local environment and symmetry of these substituted nuclei. The primary findings by UNC are the following: • Boron substituted for carbon in graphitic material in the planar BC3 configuration enhances the binding energy for adsorbed hydrogen. • Arrested kinetics of H2 was observed below 130K in the same boron substituted carbon samples that combine enhanced binding energy with micropore structure. • Hydrogen storage material made from activated

  2. Hydrogen and carbon isotope fractionation during degradation of chloromethane by methylotrophic bacteria

    PubMed Central

    Nadalig, Thierry; Greule, Markus; Bringel, Françoise; Vuilleumier, Stéphane; Keppler, Frank

    2013-01-01

    Chloromethane (CH3Cl) is a widely studied volatile halocarbon involved in the destruction of ozone in the stratosphere. Nevertheless, its global budget still remains debated. Stable isotope analysis is a powerful tool to constrain fluxes of chloromethane between various environmental compartments which involve a multiplicity of sources and sinks, and both biotic and abiotic processes. In this study, we measured hydrogen and carbon isotope fractionation of the remaining untransformed chloromethane following its degradation by methylotrophic bacterial strains Methylobacterium extorquens CM4 and Hyphomicrobium sp. MC1, which belong to different genera but both use the cmu pathway, the only pathway for bacterial degradation of chloromethane characterized so far. Hydrogen isotope fractionation for degradation of chloromethane was determined for the first time, and yielded enrichment factors (ε) of −29‰ and −27‰ for strains CM4 and MC1, respectively. In agreement with previous studies, enrichment in 13C of untransformed CH3Cl was also observed, and similar isotope enrichment factors (ε) of −41‰ and −38‰ were obtained for degradation of chloromethane by strains CM4 and MC1, respectively. These combined hydrogen and carbon isotopic data for bacterial degradation of chloromethane will contribute to refine models of the global atmospheric budget of chloromethane. PMID:24019296

  3. Application of Hydrogen Isotope Geochemistry to Volcanology: Recent Perspective on Eruption Dynamics

    SciTech Connect

    Nakamura, M.; Kasai, Y.; Sato, N.; Yoshimura, S.

    2008-02-25

    Degassing of magma is central to understand the dynamics of volcanic eruption. Hydrogen isotopic composition of volcanic rocks reflects degassing processes. The natural obsidian samples in some eruptions typically show a gently and then rapidly decreasing {delta}D trends with decreasing water content; this led to the two-stage degassing model, with closed-system volatile exsolution (batch fractionation of hydrogen isotope) during the explosive phase followed by open-system degassing (Rayleigh fractionation) to produce the low {delta}D value of the dome and flow lavas. However, the relationship between pattern of degassing (and fractionation) and mode of eruption is controversial. Based on the CO{sub 2}/H{sub 2}O ratio of the obsidians, Rust et al. suggested that the analyzed samples with relatively constant {delta}D value and high water content were buffered (re-equilibrated) with vapor of relatively constant isotopic composition, assuming that silicic magma along conduit wall is fragmented and highly permeable. However, the timing and mechanism of the shift to open system degassing (Rayleigh fractionation) has not been clarified. To further constrain the eruption dynamics, experimental study on the hydrogen isotope fractionation during degassing would be helpful, although common noble metals used as sample capsules, including Au, are permeable to hydrogen at magmatic temperature, and even to water molecule in the prolonged run, probably due to the change of grain boundary properties such as thermal grooving.

  4. Multi-saline sample distillation apparatus for hydrogen isotope analyses : design and accuracy

    USGS Publications Warehouse

    Hassan, Afifa Afifi

    1981-01-01

    A distillation apparatus for saline water samples was designed and tested. Six samples may be distilled simultaneously. The temperature was maintained at 400 C to ensure complete dehydration of the precipitating salts. Consequently, the error in the measured ratio of stable hydrogen isotopes resulting from incomplete dehydration of hydrated salts during distillation was eliminated. (USGS)

  5. Electronic and optical properties of BxNyCz monolayers with adsorption of hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Leite, L.; Azevedo, S.; de Lima Bernardo, B.

    2017-03-01

    We apply first-principles calculations, using density functional theory, to analyze the electronic and optical properties of monolayers of graphene with a nanodomain of 2D hexagonal boron nitrite (h-BN). It also investigated the effects of the adsorption of hydrogen atoms in different atoms at the edge of the h-BN nanodomain. We calculate the electronic band structure, the complex dielectric function and the optical conductivity. For such systems, the calculations demonstrate that the compounds exhibit a prominent excitement in the visible and near-infrared regions. In this form, the present study provides physical basis for potential applications of the considered materials in optoelectronic devices at the nanoscale.

  6. Assessing carbon and hydrogen isotopic fractionation of diesel fuel n-alkanes during progressive evaporation.

    PubMed

    Muhammad, Syahidah A; Hayman, Alan R; Van Hale, Robert; Frew, Russell D

    2015-01-01

    Compound-specific isotope analysis offers potential for fingerprinting of diesel fuels, however, possible confounding effects of isotopic fractionation due to evaporation need to be assessed. This study measured the fractionation of the stable carbon and hydrogen isotopes in n-alkane compounds in neat diesel fuel during evaporation. Isotope ratios were measured using a continuous flow gas chromatograph/isotope ratio mass spectrometer. Diesel samples were progressively evaporated at 24 ± 2°C for 21 days. Increasing depletion of deuterium in nC12-nC17 alkanes in the remaining liquid with increasing carbon chain length was observed. Negligible carbon isotope fractionation was observed. Preferential vaporization was measured for the shorter chain n-alkanes and the trend decreased with increasing chain length. The decrease in δ(2) H values indicates the preferential vaporization of the isotopically heavier species consistent with available quantitative data for hydrocarbons. These results are most important in the application of stable isotope technology to forensic analysis of diesel.

  7. Adsorption Behavior of Metasilicate on N-Methyl d-Glucamine Functional Groups and Associated Silicon Isotope Fractionation.

    PubMed

    Wang, Wei; Wei, Hai-Zhen; Jiang, Shao-Yong; Eastoe, Christopher J; Guo, Qi; Lin, Yi-Bo

    2016-09-06

    Significant isotope fractionation of silicon provides a powerful geochemical tracer for biological and physicochemical processes in terrestrial and marine environments. The exact mechanism involved in silicon uptake as part of the biological process is not well known. The silicon uptake in biological processes is investigated using silicate adsorption onto the N-methylglucamine functional group (sugarlike structure, abbreviated as L) of Amberlite IRA-743 resin as an analogue of the formation of silicate-sugar complexes in plants. This study provides new evidence that certain sugars can react readily with basic silicic acid to form sugar-silicate chelating complexes, and the equilibrium adsorption behavior of silicate can be well described by the Langmuir isotherm with a Gibbs free energy (ΔG) of -11.94 ± 0.21 kJ·mol(-1) at 293 K. The adsorption kinetics corresponds well to a first-order kinetic model in which the adsorption rate constant ka of 1.25 × 10(-4) s(-1) and the desorption rate constant kd of 4.00 × 10(-6) s(-1) are obtained at 293 K. Both ka and kd increase with increasing temperature. The bonding configurations of silicate-sugar complexes imply the principal coordination complex of hexacoordinated silicon (silicon/L = 1:3) in the liquid phase and the dominant tetracoordinated silicon in the solid phase. Similar to those of many natural processes, the biological uptake via the sugar-silicate chelating complexes favors the preferential enrichment of light Si isotopes into solids, and the Rayleigh model controls the dynamic isotope fractionation with an estimated silicon isotope fractionation factor (i.e., αsolid-solution = [Formula: see text]) of 0.9971. This study advanced the fundamental understanding of the dynamic isotope fractionation of silicon during silicon cycling from the lithosphere to the biosphere and hydrosphere in surficial processes.

  8. Hydrogen isotope separation installation for the regeneration of tritium from gas mixtures in tritium facilities

    SciTech Connect

    Andrew, B.M.; Perevezentsev, A.N.; Selivanenko, I.L.

    1994-12-31

    The advantages and disadvantages of different methods for hydrogen isotope separation are considered in terms of their applicability for tritium regeneration in a tritium facility. Due to low inventory, simplicity of operation, flexibility, and safety the methods of separation using solid phases are preferable for tritium facility. The detail consideration of the separation processes with a solid phase reveals that highest efficiency of separation should be achieved in a counter-current separation column, which allow multiplying the thermodynamic isotopic effect. Because of difficulties of the organization of a solid phase motion in a separation column this method did not found practical application for separation of hydrogen isotopic mixtures. The main efforts of a few researches groups were devoted to improve the chromatographic separation process and equipment. The detail comparison of the separation in sectioned column with that in chromatographic as well as in cryodistillation columns show that counter-current separation in a sectioned column is more effective and has other advantages when middle throughput is required. Complete regeneration of an isotopic mixture with separation into three practically pure isotopes independently from isotopic composition of feed can be provided using two sectioned separation columns. Separation installation can operate continuously as well as periodically.

  9. Use of H/D isotope effects to gather information about hydrogen bonding and hydrogen exchange rates.

    PubMed

    Takeda, Mitsuhiro; Miyanoiri, Yohei; Terauchi, Tsutomu; Yang, Chun-Jiun; Kainosho, Masatsune

    2014-04-01

    Polar side-chains in proteins play important roles in forming and maintaining three-dimensional structures, and thus participate in various biological functions. Until recently, most protein NMR studies have focused on the non-exchangeable protons of amino acid residues. The exchangeable protons attached to polar groups, such as hydroxyl (OH), sulfhydryl (SH), and amino (NH2) groups, have mostly been ignored, because in many cases these hydrogen atoms exchange too quickly with water protons, making NMR observations impractical. However, in certain environments, such as deep within the hydrophobic interior of a protein, or in a strong hydrogen bond to other polar groups or interacting ligands, the protons attached to polar groups may exhibit slow hydrogen exchange rates and thus become NMR accessible. To explore the structural and biological implications of the interactions involving polar side-chains, we have developed versatile NMR methods to detect such cases by observing the line shapes of (13)C NMR signals near the polar groups, which are affected by deuterium-proton isotope shifts in a mixture of H2O and D2O. These methods allow the detection of polar side-chains with slow hydrogen-deuterium exchange rates, and therefore provide opportunities to retrieve information about the polar side-chains, which might otherwise be overlooked by conventional NMR experiments. Future prospects of applications using deuterium-proton isotope shifts to retrieve missing structural and dynamic information of proteins are discussed.

  10. Hydrogen and Oxygen Isotope Ratios in Body Water and Hair: Modeling Isotope Dynamics in Nonhuman Primates

    PubMed Central

    O’Grady, Shannon P.; Valenzuela, Luciano O.; Remien, Christopher H.; Enright, Lindsey E.; Jorgensen, Matthew J.; Kaplan, Jay R.; Wagner, Janice D.; Cerling, Thure E.; Ehleringer, James R.

    2012-01-01

    The stable isotopic composition of drinking water, diet, and atmospheric oxygen influence the isotopic composition of body water (2H/1H, 18O/16O expressed as δ2H and δ18O). In turn, body water influences the isotopic composition of organic matter in tissues, such as hair and teeth, which are often used to reconstruct historical dietary and movement patterns of animals and humans. Here, we used a nonhuman primate system (Macaca fascicularis) to test the robustness of two different mechanistic stable isotope models: a model to predict the δ2H and δ18O values of body water and a second model to predict the δ2H and δ18O values of hair. In contrast to previous human-based studies, use of nonhuman primates fed controlled diets allowed us to further constrain model parameter values and evaluate model predictions. Both models reliably predicted the δ2H and δ18O values of body water and of hair. Moreover, the isotope data allowed us to better quantify values for two critical variables in the models: the δ2H and δ18O values of gut water and the 18O isotope fractionation associated with a carbonyl oxygen-water interaction in the gut (αow). Our modeling efforts indicated that better predictions for body water and hair isotope values were achieved by making the isotopic composition of gut water approached that of body water. Additionally, the value of αow was 1.0164, in close agreement with the only other previously measured observation (microbial spore cell walls), suggesting robustness of this fractionation factor across different biological systems. PMID:22553163

  11. Hydrogen and oxygen isotope ratios in body water and hair: modeling isotope dynamics in nonhuman primates.

    PubMed

    O'Grady, Shannon P; Valenzuela, Luciano O; Remien, Christopher H; Enright, Lindsey E; Jorgensen, Matthew J; Kaplan, Jay R; Wagner, Janice D; Cerling, Thure E; Ehleringer, James R

    2012-07-01

    The stable isotopic composition of drinking water, diet, and atmospheric oxygen influence the isotopic composition of body water ((2)H/(1)H, (18)O/(16)O expressed as δ(2) H and δ(18)O). In turn, body water influences the isotopic composition of organic matter in tissues, such as hair and teeth, which are often used to reconstruct historical dietary and movement patterns of animals and humans. Here, we used a nonhuman primate system (Macaca fascicularis) to test the robustness of two different mechanistic stable isotope models: a model to predict the δ(2)H and δ(18)O values of body water and a second model to predict the δ(2)H and δ(18)O values of hair. In contrast to previous human-based studies, use of nonhuman primates fed controlled diets allowed us to further constrain model parameter values and evaluate model predictions. Both models reliably predicted the δ(2)H and δ(18)O values of body water and of hair. Moreover, the isotope data allowed us to better quantify values for two critical variables in the models: the δ(2)H and δ(18)O values of gut water and the (18)O isotope fractionation associated with a carbonyl oxygen-water interaction in the gut (α(ow)). Our modeling efforts indicated that better predictions for body water and hair isotope values were achieved by making the isotopic composition of gut water approached that of body water. Additionally, the value of α(ow) was 1.0164, in close agreement with the only other previously measured observation (microbial spore cell walls), suggesting robustness of this fractionation factor across different biological systems.

  12. Hydrogen isotopic composition of the water in CR chondrites

    NASA Astrophysics Data System (ADS)

    Bonal, L.; Alexander, C. M. O.'D.; Huss, G. R.; Nagashima, K.; Quirico, E.; Beck, P.

    2013-04-01

    The thermal and aqueous alteration experienced by QUE 99177, MET 00426, EET 92042, GRA 95229, Renazzo and Al Rais CR chondrites was assessed through multi-technique characterization of their the carbonaceous matter and hydrated mineral phases. Each of the chondrites escaped long duration thermal metamorphism as reflected by the low structural order of the polyaromatic carbonaceous matter assessed by Raman spectroscopy. The infrared spectra of the matrix grains clearly reveal the presence of hydrated minerals in each of the CR chondrites. In particular, the extent of aqueous alteration experienced by QUE 99177 and MET 00426 may have been previously underestimated. The H isotopic compositions of the altering fluids were measured in situ in fine-grained phyllosilicates and individual coarse-grained hydrated silicates. In the analyzed CR chondrites, the main observations are that (i) the water is systematically enriched in D, and the enrichments (δDwater up to 1600‰) can be even higher than the highest D-enrichments reported for cometary water; (ii) the isotopic composition of the water is highly variable at the micrometer scale; (iii) there is no clear trend observed in the isotopic composition of the water (maximum D-enrichment, range of variation) along the aqueous alteration sequence. The D-enrichments and spatial variability are easier to explain as secondary signatures acquired through parent body processes, rather than as being due to the accretion of at least two ices with distinct isotopic compositions and sources that did not fully mix when they melted at the start of the aqueous alteration process.

  13. Adsorption of hydrogen on neutral and charged fullerene: experiment and theory.

    PubMed

    Kaiser, A; Leidlmair, C; Bartl, P; Zöttl, S; Denifl, S; Mauracher, A; Probst, M; Scheier, P; Echt, O

    2013-02-21

    Helium droplets are doped with fullerenes (either C60 or C70) and hydrogen (H2 or D2) and investigated by high-resolution mass spectrometry. In addition to pure helium and hydrogen cluster ions, hydrogen-fullerene complexes are observed upon electron ionization. The composition of the main ion series is (H2)(n)HC(m)(+) where m = 60 or 70. Another series of even-numbered ions, (H2)(n)C(m)(+), is slightly weaker in stark contrast to pure hydrogen cluster ions for which the even-numbered series (H2)(n)(+) is barely detectable. The ion series (H2)(n)HC(m)(+) and (H2)(n)C(m)(+) exhibit abrupt drops in ion abundance at n = 32 for C60 and 37 for C70, indicating formation of an energetically favorable commensurate phase, with each face of the fullerene ion being covered by one adsorbate molecule. However, the first solvation layer is not complete until a total of 49 H2 are adsorbed on C60(+); the corresponding value for C70(+) is 51. Surprisingly, these values do not exhibit a hydrogen-deuterium isotope effect even though the isotope effect for H2/D2 adsorbates on graphite exceeds 6%. We also observe doubly charged fullerene-deuterium clusters; they, too, exhibit abrupt drops in ion abundance at n = 32 and 37 for C60 and C70, respectively. The findings imply that the charge is localized on the fullerene, stabilizing the system against charge separation. Density functional calculations for C60-hydrogen complexes with up to five hydrogen atoms provide insight into the experimental findings and the structure of the ions. The binding energy of physisorbed H2 is 57 meV for H2C60(+) and (H2)2C60(+), and slightly above 70 meV for H2HC60(+) and (H2)2HC60(+). The lone hydrogen in the odd-numbered complexes is covalently bound atop a carbon atom but a large barrier of 1.69 eV impedes chemisorption of the H2 molecules. Calculations for neutral and doubly charged complexes are presented as well.

  14. Large effect of irradiance on hydrogen isotope fractionation of alkenones in Emiliania huxleyi

    NASA Astrophysics Data System (ADS)

    van der Meer, Marcel T. J.; Benthien, Albert; French, Katherine L.; Epping, Eric; Zondervan, Ingrid; Reichart, Gert-Jan; Bijma, Jelle; Sinninghe Damsté, Jaap S.; Schouten, Stefan

    2015-07-01

    The hydrogen isotopic (δD) composition of long-chain alkenones produced by certain haptophyte algae has been suggested as a potential proxy for reconstructing paleo sea surface salinity. However, environmental parameters other than salinity may also affect the δD of alkenones. We investigated the impact of the level of irradiance on hydrogen isotopic fractionation of alkenones versus growth water by cultivating two strains of the cosmopolitan haptophyte Emiliania huxleyi at different light intensities. The hydrogen isotope fractionation decreased by approximately 40‰ when irradiance was increased from 15 to 200 μmol photons m-2 s-1 above which it was relatively constant. The response is likely a direct effect of photosystem I and II activity as the relationship of the fractionation factor α versus light intensity can be described by an Eilers-Peeters photosynthesis model. This irradiance effect is in agreement with published δD data of alkenones derived from suspended particulate matter collected from different depths in the photic zone of the Gulf of California and the eastern tropical North Pacific. However, haptophyte algae tend to bloom at relatively high light intensities (>500 μmol photons m-2 s-1) occurring at the sea surface, at which hydrogen isotope fractionation is relatively constant and not affected by changes in light intensity. Alkenones accumulating in the sediment are likely mostly derived from these surface water haptophyte blooms, when the largest amount of biomass is produced. Therefore, the observed irradiance effect is unlikely to affect the applicability of the hydrogen isotopic composition of sedimentary long chain alkenones as a proxy for paleosalinity.

  15. The effect of amorphous silicon surface hydrogenation on morphology, wettability and its implication on the adsorption of proteins

    NASA Astrophysics Data System (ADS)

    Filali, Larbi; Brahmi, Yamina; Sib, Jamal Dine; Bouhekka, Ahmed; Benlakehal, Djamel; Bouizem, Yahya; Kebab, Aissa; Chahed, Larbi

    2016-10-01

    We study the effect of amorphous silicon (a-Si) surface hydrogenation on Bovine Serum Albumin (BSA) adsorption. A set of (a-Si) films was prepared by radio frequency magnetron sputtering (RFMS) and after deposition; they were treated in molecular hydrogen ambient at different pressures (1-3 Pa). Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and spectroscopic ellipsometry (SE) were used to study the hydrogenation effect and BSA adsorption. Atomic force microscopy (AFM) was used to evaluate morphological changes caused by hydrogenation. The wettability of the films was measured using contact angle measurement, and in the case of the hydrogenated surfaces, it was found to be driven by surface roughness. FTIR-ATR spectroscopy and SE measurements show that proteins had the strongest affinity toward the surfaces with the highest hydrogen content and their secondary structure was affected by a significant decrease of the α-helix component (-27%) compared with the proteins adsorbed on the un-treated surface, which had a predominantly α-helix (45%) structure. The adsorbed protein layer was found to be densely packed with a large thickness (30.9 nm) on the hydrogen-rich surfaces. The most important result is that the surface hydrogen content was the dominant factor, compared to wettability and morphology, for protein adsorption.

  16. Hydrogen adsorption and diffusion, and subcritical-crack growth in high strength steels and nickel base alloys

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Klier, K.; Simmons, G. W.; Chornet, E.

    1973-01-01

    Embrittlement, or the enhancement of crack growth by gaseous hydrogen in high strength alloys, is of primary interest in selecting alloys for various components in the space shuttle. Embrittlement is known to occur at hydrogen gas pressures ranging from fractions to several hundred atmospheres, and is most severe in the case of martensitic high strength steels. Kinetic information on subcritical crack growth in gaseous hydrogen is sparse at this time. Corroborative information on hydrogen adsorption and diffusion is inadequate to permit a clear determination of the rate controlling process and possible mechanism in hydrogen enhanced crack growth, and for estimating behavior over a range of temperatures and pressures. Therefore, coordinated studies of the kinetics of crack growth, and adsorption and diffusion of hydrogen, using identical materials, have been initiated. Comparable conditions of temperature and pressure will be used in the chemical and mechanical experiments. Inconel 718 alloy and 18Ni(200) maraging steel have been selected for these studies. Results from these studies are expected to provide not only a better understanding of the gaseous hydrogen embrittlement phenomenon itself, but also fundamental information on hydrogen adsorption and diffusion, and crack growth information that can be used directly for design.

  17. Observations of hydrogen and helium isotopes in solar cosmic rays. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Hurford, G. J.

    1974-01-01

    The isotopic composition of hydrogen and helium in solar cosmic rays provides a means of studying solar flare particle acceleration mechanisms since the enhanced relative abundance of rare isotopes, such as H-2, H-3, and He-3, is due to their production by inelastic nuclear collisions in the solar atmosphere during the flare. Electron isotope spectrometer on an IMP spacecraft was used to measure this isotopic composition. The response of the dE/dx-E particle telescope is discussed, and alpha particle channeling in thin detectors is identified as an important background source affecting measurement of low values of (He-3/He-4). The flare-averaged results obtained for the period October, 1972 November, 1973 are given.

  18. Structure and Hydrogen Adsorption Properties of SBA-15 Doped with Pd Nanoparticles.

    PubMed

    Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong

    2015-11-01

    Hydrogen adsorption properties of Pd-doped Santa Barbara amorphous No. 15 (Pd-SBA-15) were investigated and the results were compared with pure SBA-15 ones in terms of change of its structure and Pd concentration. Pd-SBA-15 samples were prepared by a hydrothermal reaction, using mixture of PEO20PPO70PEO20 (P123) and tetraethyl orthosilicate (TEOS). For the doping of Pd on SBA-15, PdC2 solution was added into the mixture of P123 and TEOS, and the solution was annealed at 80 degrees C for 2 hours under 800 Torr of hydrogen atmosphere. According to the X-ray diffraction and transmission electron microscope data, Pd-doped SBA-15 samples form a hexagonal array of mesoporous structure with 20-30 nm size of Pd particles. Values of specific surface area decreased from 630 to 414 m2/g as increasing the Pd doping level due to the increasing of the volume density. In fact, the volume density increased from 0.103 to 0.276 g/cc as increasing the mass ratio of PdCl2 to TEOS from 0 to 0.5. For the Pd-doped SBA-15, the amount of adsorbed hydrogen significantly increased from 0.49 to 0.99 wt% as increasing the Pd doping level from 0 to 0.5 demonstrating that Pd doping is an effect method for SBA-1 5 as a potential use of hydrogen storage application.

  19. Hydrogen adsorption and storage on Palladium - functionalized graphene with NH-dopant: A first principles calculation

    NASA Astrophysics Data System (ADS)

    Faye, Omar; Szpunar, Jerzy A.; Szpunar, Barbara; Beye, Aboubaker Chedikh

    2017-01-01

    We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315-0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H2 molecules, which helps also to avoid the desorption of Pd(H2)n (n = 1-5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

  20. Enhanced hydrogen adsorption on Li-coated B12C6N6.

    PubMed

    Jin, Xueling; Qi, Pengtang; Yang, Huihui; Zhang, Yan; Li, Jinyun; Chen, Hongshan

    2016-10-28

    The hydrogen storage property of Li-coated B12C6N6 is investigated by density functional theory calculations. B12C6N6 is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li(+) ions. The computation shows that each Li atom coated on B12C6N6 can hold 2-3 H2 molecules with adsorption energies in the range of 0.21-0.24 eV/H2. The B12C6N6Li8 can adsorb 16 H2 and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity.

  1. Enhanced hydrogen adsorption on Li-coated B12C6N6

    NASA Astrophysics Data System (ADS)

    Jin, Xueling; Qi, Pengtang; Yang, Huihui; Zhang, Yan; Li, Jinyun; Chen, Hongshan

    2016-10-01

    The hydrogen storage property of Li-coated B12C6N6 is investigated by density functional theory calculations. B12C6N6 is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li+ ions. The computation shows that each Li atom coated on B12C6N6 can hold 2-3 H2 molecules with adsorption energies in the range of 0.21-0.24 eV/H2. The B12C6N6Li8 can adsorb 16 H2 and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity.

  2. Adsorption and recombination of hydrogen atoms on a model graphite surface. [in interstellar space

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.; Chang, S.

    1985-01-01

    The adsorption and recombination of atomic hydrogen on a model graphite grain have been examined in a series of calculations in which a modified, iterative, extended Hueckel program was used. The hydrogen atom is found to be chemisorbed at a site with a zero-point binding energy of 0.7 eV and at an equilibrium distance of 2.25 A above the site. Despite a barrier of about 0.4 eV between adjacent sites, calculations suggest that at temperatures as low as 10 K, an H atom will tunnel through to adjacent sites in less than one nanosecond. However, a potential barrier to the recombination of two hydrogen atoms has been found which displays high sensitivity to the mutual arrangement of the two hydrogen atoms with respect to the graphite surface. Results show that at very low temperatures, recombinations can occur only by tunneling. Consistent with experiment, the region in which H2 begins to form exhibits a repulsive potential with respect to possible chemisorption of the incipient H2 entity.

  3. Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

    DOE PAGES

    Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; ...

    2013-06-03

    Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H2 peak is seen from planar Ir(210) at all coverages whereas a single H2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity in recombination and desorptionmore » of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H2 from faceted Ir(210): F1 from desorption of H2 on {311} facets while F2 from desorption of H2 on (110) facets.« less

  4. Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

    NASA Astrophysics Data System (ADS)

    Okumura, Tomoyo; Kawagucci, Shinsuke; Saito, Yayoi; Matsui, Yohei; Takai, Ken; Imachi, Hiroyuki

    2016-12-01

    Hydrogen and carbon isotope systematics of H2O-H2-CO2-CH4 in hydrogenotrophic methanogenesis and their relation to H2 availability were investigated. Two H2-syntrophic cocultures of fermentatively hydrogenogenic bacteria and hydrogenotrophic methanogens under conditions of <102 Pa-H2 and two pure cultures of hydrogenotrophic methanogens under conditions of 105 Pa-H2 were tested. Carbon isotope fractionation between CH4 and CO2 during hydrogenotrophic methanogenesis was correlated with pH2, as indicated in previous studies. The hydrogen isotope ratio of CH4 produced during rapid growth of the thermophilic methanogen Methanothermococcus okinawensis under high pH2 conditions ( 105 Pa) was affected by the isotopic composition of H2, as concluded in a previous study of Methanothermobacter thermautotrophicus. This " {δ D}_{{H}_2} effect" is a possible cause of the diversity of previously reported values for hydrogen isotope fractionation between CH4 and H2O examined in H2-enriched culture experiments. Hydrogen isotope fractionation between CH4 and H2O, defined by (1000 + {δ D}_{{CH}_4} )/(1000 + {δ D}_{{H}_2O} ), during hydrogenotrophic methanogenesis of the H2-syntrophic cocultures was in the range 0.67-0.69. The hydrogen isotope fractionation of our H2-syntrophic dataset overlaps with those obtained not only from low- pH2 experiments reported so far but also from natural samples of "young" methane reservoirs (0.66-0.74). Conversely, such hydrogen isotope fractionation is not consistent with that of "aged" methane in geological samples (≥0.79), which has been regarded as methane produced via hydrogenotrophic methanogenesis from the carbon isotope fractionation. As a possible process inducing the inconsistency in hydrogen isotope signatures between experiments and geological samples, we hypothesize that the hydrogen isotope signature of CH4 imprinted at the time of methanogenesis, as in the experiments and natural young methane, may be altered by diagenetic hydrogen

  5. Genesis and evolution of water in a two-mica pluton: A hydrogen isotope study

    USGS Publications Warehouse

    Brigham, R.H.; O'Neil, J.R.

    1985-01-01

    Measurements were made of the hydrogen isotope composition of 74 samples of muscovite, biotite, vein quartz and whole rocks from the Papoose Flat pluton, eastern California, U.S.A., and adjacent metamorphic and sedimentary rocks in order to elucidate the genesis and evolution of water and hydrous minerals in a two-mica granodiorite. Electron microprobe analyses were made of all micas so that the Suzuoki-Epstein equation could be used in evaluating the data. Based on experimental, theoretical and textural evidence of mica paragenesis, a model of hydrogen isotope fractionation between an aqueous vapor and a magma during crystallization has been constructed. This model accounts for the observed hydrogen isotope relations and implies that primary hydrogen isotope compositions have been preserved in a large portion of the pluton. The ?? D-values of biotites vary widely over the range -103 to -66% with most values lying between -90 and -70??? Muscovites, on the other hand, are isotopically more uniform and have ?? D-values of -61 to -41??? with most values lying between -50 and -46??? These data are consistent with the interpretation that biotite formed over a long period of crystallization whereas muscovite formed in a narrow interval, presumably during the final stages of crystallization when alumina and water contents were at their highest. Only 8 of the 21 muscovite-biotite pairs analyzed are in hydrogen isotope equilibrium as calculated from the Suzuoki-Epstein equation. Biotites in the western half of the pluton have relatively low ?? D-values of around -85???, whereas those in the eastern half have higher values of up to -66??? This pattern is a consequence of a loss of permeability associated with the syn-intrusive deformation of the western margin of the pluton. This loss of permeability enhanced the preservation of primary hydrogen isotope relations there by diverting water evolved from the magma out through the eastern half of the pluton where some deuteric

  6. Hydrogen isotopes from source water to leaf lipid in a continental-scale sample network

    NASA Astrophysics Data System (ADS)

    Nelson, Daniel; Kahmen, Ansgar

    2015-04-01

    Sedimentary plant waxes are useful paleoclimate proxies because they are preserved in depositional settings on geologic timescales and the isotopic composition of the hydrogen in these molecules reflects that of the source water available during biosynthesis. This application is based largely on empirical calibrations that have demonstrated continental-scale correlations between source water and lipid hydrogen isotope values. However, the importance of variable net isotopic fractionation between source water and lipid for different species and environmental conditions is increasingly recognized. Isotopic enrichment of leaf water during transpiration is key among these secondary factors, and is itself sensitive to changes in hydroclimate. Leaf water enrichment also occurs prior to photosynthetic water uptake, and is therefore independent from cellular-level biomarker synthesis. Mechanistic models can predict the mean leaf water hydrogen isotope composition from readily available meteorological variables. This permits global-scale isoscape maps of leaf water isotopic composition and enrichment above source water to be generated, but these models have not been widely validated at continental spatial scales. We have established a network of twenty-one sites across Europe where we are sampling for leaf-, xylem-, and soil-water isotopes (H and O) at approximately 5-week intervals over the summer growing season. We augment the sample set with weekly to monthly precipitation samples and early- and late-season plant wax lipid samples. Collaborators at each site are conducting the sampling, and most sites are members of the FLUXNET tower network that also record high-resolution meteorological data. We present information on the implementation of the network and preliminary results from the 2014 summer season. The complete dataset will be used to track the evolution of water isotopes from source to leaf water and from leaf water to lipid hydrogen across diverse environments

  7. Hydrogen adsorption on Be, Mg, Ca and Sr doped graphenes: The role of the dopant in the IIA main group

    NASA Astrophysics Data System (ADS)

    Luo, Huijuan; Li, Hejun; Fu, Qiangang

    2017-02-01

    Hydrogen (H2) adsorption on the IIA elements doped double-vacancy graphenes (BeG, MgG, CaG and SrG) was studied by using dispersion-corrected density functional theory calculations. Through investigation of different numbers of hydrogen dockings from two directions, it is found that 1H2/BeG, 1H2/MgG, 8H2/CaG and 8H2/SrG are the most stable adsorption configurations for Be, Mg, Ca and Sr doped graphenes, respectively. Atomic radius, electronegativity and ionization potential of the IIA dopant contribute to the dominating adsorption mechanism under specific H2 concentration. The study would facilitate exploration of high performance graphene-related supports for hydrogen storage.

  8. Doubly labeled water method: in vivo oxygen and hydrogen isotope fractionation

    SciTech Connect

    Schoeller, D.A.; Leitch, C.A.; Brown, C.

    1986-12-01

    The accuracy and precision of the doubly labeled water method for measuring energy expenditure are influenced by isotope fractionation during evaporative water loss and CO/sub 2/ excretion. To characterize in vivo isotope fractionation, we collected and isotopically analyzed physiological fluids and gases. Breath and transcutaneous water vapor were isotopically fractionated. The degree of fractionation indicated that the former was fractionated under equilibrium control at 37/sup 0/C, and the latter was kinetically fractionated. Sweat and urine were unfractionated. By use of isotopic balance models, the fraction of water lost via fractionating routes was estimated from the isotopic abundances of body water, local drinking water, and dietary solids. Fractionated water loss averaged 23% (SD = 10%) of water turnover, which agreed with our previous estimates based on metabolic rate, but there was a systematic difference between the results based on O/sub 2/ and hydrogen. Corrections for isotopic fractionation of water lost in breath and (nonsweat) transcutaneous loss should be made when using labeled water to measure water turnover or CO/sub 2/ production.

  9. Hydrogen and oxygen isotope ratios in human hair are related to geography

    PubMed Central

    Ehleringer, James R.; Bowen, Gabriel J.; Chesson, Lesley A.; West, Adam G.; Podlesak, David W.; Cerling, Thure E.

    2008-01-01

    We develop and test a model to predict the geographic region-of-origin of humans based on the stable isotope composition of their scalp hair. This model incorporates exchangeable and nonexchangeable hydrogen and oxygen atoms in amino acids to predict the δ2H and δ18O values of scalp hair (primarily keratin). We evaluated model predictions with stable isotope analyses of human hair from 65 cities across the United States. The model, which predicts hair isotopic composition as a function of drinking water, bulk diet, and dietary protein isotope ratios, explains >85% of the observed variation and reproduces the observed slopes relating the isotopic composition of hair samples to that of local drinking water. Based on the geographical distributions of the isotope ratios of tap waters and the assumption of a “continental supermarket” dietary input, we constructed maps of the expected average H and O isotope ratios in human hair across the contiguous 48 states. Applications of this model and these observations are extensive and include detection of dietary information, reconstruction of historic movements of individuals, and provision of region-of-origin information for unidentified human remains. PMID:18299562

  10. Hydrogen and oxygen isotope ratios in human hair are related to geography.

    PubMed

    Ehleringer, James R; Bowen, Gabriel J; Chesson, Lesley A; West, Adam G; Podlesak, David W; Cerling, Thure E

    2008-02-26

    We develop and test a model to predict the geographic region-of-origin of humans based on the stable isotope composition of their scalp hair. This model incorporates exchangeable and nonexchangeable hydrogen and oxygen atoms in amino acids to predict the delta(2)H and delta(18)O values of scalp hair (primarily keratin). We evaluated model predictions with stable isotope analyses of human hair from 65 cities across the United States. The model, which predicts hair isotopic composition as a function of drinking water, bulk diet, and dietary protein isotope ratios, explains >85% of the observed variation and reproduces the observed slopes relating the isotopic composition of hair samples to that of local drinking water. Based on the geographical distributions of the isotope ratios of tap waters and the assumption of a "continental supermarket" dietary input, we constructed maps of the expected average H and O isotope ratios in human hair across the contiguous 48 states. Applications of this model and these observations are extensive and include detection of dietary information, reconstruction of historic movements of individuals, and provision of region-of-origin information for unidentified human remains.

  11. Capture and isotopic exchange method for water and hydrogen isotopes on zeolite catalysts up to technical scale for pre-study of processing highly tritiated water

    SciTech Connect

    Michling, R.; Braun, A.; Cristescu, I.; Dittrich, H.; Gramlich, N.; Lohr, N.; Glugla, M.; Shu, W.; Willms, S.

    2015-03-15

    Highly tritiated water (HTW) may be generated at ITER by various processes and, due to the excessive radio toxicity, the self-radiolysis and the exceedingly corrosive property of HTW, a potential hazard is associated with its storage and process. Therefore, the capture and exchange method for HTW utilizing Molecular Sieve Beds (MSB) was investigated in view of adsorption capacity, isotopic exchange performance and process parameters. For the MSB, different types of zeolite were selected. All zeolite materials were additionally coated with platinum. The following work comprised the selection of the most efficient zeolite candidate based on detailed parametric studies during the H{sub 2}/D{sub 2}O laboratory scale exchange experiments (about 25 g zeolite per bed) at the Tritium Laboratory Karlsruhe (TLK). For the zeolite, characterization analytical techniques such as Infrared Spectroscopy, Thermogravimetry and online mass spectrometry were implemented. Followed by further investigation of the selected zeolite catalyst under full technical operation, a MSB (about 22 kg zeolite) was processed with hydrogen flow rates up to 60 mol*h{sup -1} and deuterated water loads up to 1.6 kg in view of later ITER processing of arising HTW. (authors)

  12. Kinetic isotope effect for H2 and D2 quantum molecular sieving in adsorption/desorption on porous carbon materials.

    PubMed

    Zhao, Xuebo; Villar-Rodil, Silvia; Fletcher, Ashleigh J; Thomas, K Mark

    2006-05-25

    Adsorption and desorption of H(2) and D(2) from porous carbon materials, such as activated carbon at 77 K, are usually fully reversible with very rapid adsorption/desorption kinetics. The adsorption and desorption of H(2) and D(2) at 77 K on a carbon molecular sieve (Takeda 3A), where the kinetic selectivity was incorporated by carbon deposition, and a carbon, where the pore structure was modified by thermal annealing to give similar pore structure characteristics to the carbon molecular sieve substrate, were studied. The D(2) adsorption and desorption kinetics were significantly faster (up to x1.9) than the corresponding H(2) kinetics for specific pressure increments/decrements. This represents the first experimental observation of kinetic isotope quantum molecular sieving in porous materials due to the larger zero-point energy for the lighter H(2), resulting in slower adsorption/desorption kinetics compared with the heavier D(2). The results are discussed in terms of the adsorption mechanism.

  13. Automotive hydrogen storage system using cryo-adsorption on activated carbon.

    SciTech Connect

    Ahluwalia, R. K.; Peng, J. K.; Nuclear Engineering Division

    2009-07-01

    An integrated model of a sorbent-based cryogenic compressed hydrogen system is used to assess the prospect of meeting the near-term targets of 36 kg-H{sub 2}/m{sup 3} volumetric and 4.5 wt% gravimetric capacity for hydrogen-fueled vehicles. The model includes the thermodynamics of H{sub 2} sorption, heat transfer during adsorption and desorption, sorption dynamics, energetics of cryogenic tank cooling, and containment of H{sub 2} in geodesically wound carbon fiber tanks. The results from the model show that recoverable hydrogen, rather than excess or absolute adsorption, is a determining measure of whether a sorbent is a good candidate material for on-board storage of H{sub 2}. A temperature swing is needed to recover >80% of the sorption capacity of the superactivated carbon sorbent at 100 K and 100 bar as the tank is depressurized to 3-8 bar. The storage pressure at which the system needs to operate in order to approach the system capacity targets has been determined and compared with the breakeven pressure above which the storage tank is more compact if H{sub 2} is stored only as a cryo-compressed gas. The amount of liquid N{sub 2} needed to cool the hydrogen dispensed to the vehicle to 100 K and to remove the heat of adsorption during refueling has been estimated. The electrical energy needed to produce the requisite liquid N{sub 2} by air liquefaction is compared with the electrical energy needed to liquefy the same amount of H{sub 2} at a central plant. The alternate option of adiabatically refueling the sorbent tank with liquid H{sub 2} has been evaluated to determine the relationship between the storage temperature and the sustainable temperature swing. Finally, simulations have been run to estimate the increase in specific surface area and bulk density of medium needed to satisfy the system capacity targets with H{sub 2} storage at 100 bar.

  14. Hydrogen isotope systematics of H2-H2O-CH4 during hydrogenotrophic methanogenesis

    NASA Astrophysics Data System (ADS)

    Kobayashi, M.; Kawagucci, S.; Hattori, S.; Yamada, K.; Ueno, Y.; Takai, K.; Yoshida, N.

    2011-12-01

    Hydrogen and carbon isotopes of CH4 have been utilized to trace microbial processes. The isotope fractionations during hydrogenotrophic methanogenesis, one of the major processes of environmental CH4, have been studied by several laboratory incubations. For the carbon isotope, H2 concentration is thought to be the major parameter controlling the carbon isotope fractionation by hydrogenotrophic methanogenesis. For the hydrogen, on the other hand, factors controlling isotope fractionation remain poorly understood, although H2 concentration is suggested to be important. This uncertainty prevents us to utilize δD-CH4 value as the tracer. The most important and principal question is whether all hydrogen atoms in microbially-generated CH4 come from environmental H2O or not. To answer the question, we investigated the D/H systematics of H2-H2O-CH4 during hydrogenotrophic methanogenesis by pure culture incubation with softly deuterium-enriched H2 and/or H2O. Our results demonstrate that δD-CH4 value produced by hydrogenotrophic methanogens depends not only on δD-H2O value but also on δD-H2 value. We observed constant correlation between δD-H2 and δD-CH4 values as well as between δD-H2O and δD-CH4 values, which suggests that hydrogen (/deuterium) atom of substrate H2 is also transferred to the product CH4. This implies that the range of δD-CH4 value produced by hydrogenotrophic methanogenesis should be re-evaluated considering the distribution of δD-H2 and δD-H2O values in natural environments.

  15. Fractionation of Hydrogen Isotopes by Sulfate- and Nitrate-Reducing Bacteria

    PubMed Central

    Osburn, Magdalena R.; Dawson, Katherine S.; Fogel, Marilyn L.; Sessions, Alex L.

    2016-01-01

    Hydrogen atoms from water and food are incorporated into biomass during cellular metabolism and biosynthesis, fractionating the isotopes of hydrogen—protium and deuterium—that are recorded in biomolecules. While these fractionations are often relatively constant in plants, large variations in the magnitude of fractionation are observed for many heterotrophic microbes utilizing different central metabolic pathways. The correlation between metabolism and lipid δ2H provides a potential basis for reconstructing environmental and ecological parameters, but the calibration dataset has thus far been limited mainly to aerobes. Here we report on the hydrogen isotopic fractionations of lipids produced by nitrate-respiring and sulfate-reducing bacteria. We observe only small differences in fractionation between oxygen- and nitrate-respiring growth conditions, with a typical pattern of variation between substrates that is broadly consistent with previously described trends. In contrast, fractionation by sulfate-reducing bacteria does not vary significantly between different substrates, even when autotrophic and heterotrophic growth conditions are compared. This result is in marked contrast to previously published observations and has significant implications for the interpretation of environmental hydrogen isotope data. We evaluate these trends in light of metabolic gene content of each strain, growth rate, and potential flux and reservoir-size effects of cellular hydrogen, but find no single variable that can account for the differences between nitrate- and sulfate-respiring bacteria. The emerging picture of bacterial hydrogen isotope fractionation is therefore more complex than the simple correspondence between δ2H and metabolic pathway previously understood from aerobes. Despite the complexity, the large signals and rich variability of observed lipid δ2H suggest much potential as an environmental recorder of metabolism. PMID:27531993

  16. Mica Mountain Muscovite: A New Silicate Hydrogen Isotope Standard Reference Material

    NASA Astrophysics Data System (ADS)

    Lonero, A.; Larson, P. B.; Neill, O. K.

    2015-12-01

    A new standard reference material consisting of finely ground muscovite flakes has been developed and utilized at Washington State University to calibrate hydrogen isotope ratio (D/H) measurements to the VSMOW scale. This standard was prepared from a single crystal 'book' of a muscovite-bearing pegmatite near Deary, ID. The value we obtained for this muscovite standard (MMM) is: δD VSMOW = -79.1 ± 2.0‰ relative to NBS-30 biotite at -65.7‰ compared to a VSMOW value of 0.00‰. This mean value was determined for the muscovite and has been used as our working standard. There have been many recent geological applications to continuous flow isotope ratio mass spectroscopy. When hydrogen isotope ratios are of interest, a suitable standard for hydrogen in silicate systems often is not available. With supplies of the older NBS-30 biotite standard exhausted, much D/H data measured on silicate minerals have been linked to the VSMOW scale via non-silicate reference materials which may not behave similarly to minerals under study. Some recent studies have shown the NBS-30 standard to have poor intra-laboratory agreement with that material's measured and accepted isotopic values (Qi et al., 2014). Many laboratories which would measure D/H in silicate minerals would benefit from using a silicate-based standard for hydrogen. With further characterization, this muscovite may also be useful as a standard for silicate oxygen ratios as well as for some major element cations. This muscovite standard gives consistent values and it is easy to work with and does not leave much combustion residue. Also, because muscovite contains little iron, metal-hydride formation and associated fractionation factors is greatly reduced during the sample combustion. A new silicate-hydrogen standard is needed by the community, and this work represents an example of what a replacement standard material could look like.

  17. Hydrogen isotopes in Eocene river gravels and paleoelevation of the Sierra Nevada.

    PubMed

    Mulch, Andreas; Graham, Stephan A; Chamberlain, C Page

    2006-07-07

    We determine paleoelevation of the Sierra Nevada, California, by tracking the effect of topography on precipitation, as recorded in hydrogen isotopes of kaolinite exposed in gold-bearing river deposits from the Eocene Yuba River. The data, compared with the modern isotopic composition of precipitation, show that about 40 to 50 million years ago the Sierra Nevada stood tall (>/=2200 meters), a result in conflict with proposed young surface uplift by tectonic and climatic forcing but consistent with the Sierra Nevada representing the edge of a pre-Eocene continental plateau.

  18. Systematics of isotopic production cross sections from interactions of relativistic 40Ca in hydrogen

    NASA Astrophysics Data System (ADS)

    Chen, C.-X.; Albergo, S.; Caccia, Z.; Costa, S.; Crawford, H. J.; Cronqvist, M.; Engelage, J.; Greiner, L.; Guzik, T. G.; Insolia, A.; Knott, C. N.; Lindstrom, P. J.; McMahon, M.; Mitchell, J. W.; Potenza, R.; Russo, G. V.; Soutoul, A.; Testard, O.; Tull, C. E.; Tuvé, C.; Waddington, C. J.; Webber, W. R.; Wefel, J. P.

    1997-09-01

    The isotopic production cross sections for 40Ca projectiles at 357, 565, and 763 MeV/nucleon interacting in a liquid hydrogen target have been measured by the Transport Collaboration at the LBL HISS facility. The systematics of these cross sections are studied, and the results indicate that nuclear structure effects are present in the isotope production process during the relativistic collisions. The newly measured cross sections are also compared with those predicted by semiempirical and parametric formulas, but the predictions do not fully describe the systematics such as the energy dependence. The consequences of the cross section systematics in galactic cosmic ray studies are also discussed.

  19. Microscopic observation of kinetic molecular sieving of hydrogen isotopes in a nanoporous material.

    PubMed

    Nguyen, T X; Jobic, H; Bhatia, S K

    2010-08-20

    We report quasielastic neutron scattering studies of H2-D2 diffusion in a carbon molecular sieve, demonstrating remarkable quantum effects, with the heavier isotope diffusing faster below 100 K, confirming our recent predictions. Our transition state theory and molecular dynamics calculations show that while it is critical for this effect to have narrow windows of size comparable to the de Broglie wavelength, high flux requires that the energy barrier be reduced through small cages. Such materials will enable novel processes for kinetic molecular sieving of hydrogen isotopes.

  20. Microscopic Observation of Kinetic Molecular Sieving of Hydrogen Isotopes in a Nanoporous Material

    NASA Astrophysics Data System (ADS)

    Nguyen, T. X.; Jobic, H.; Bhatia, S. K.

    2010-08-01

    We report quasielastic neutron scattering studies of H2-D2 diffusion in a carbon molecular sieve, demonstrating remarkable quantum effects, with the heavier isotope diffusing faster below 100 K, confirming our recent predictions. Our transition state theory and molecular dynamics calculations show that while it is critical for this effect to have narrow windows of size comparable to the de Broglie wavelength, high flux requires that the energy barrier be reduced through small cages. Such materials will enable novel processes for kinetic molecular sieving of hydrogen isotopes.

  1. Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water

    USGS Publications Warehouse

    Balistrieri, L.S.; Borrok, D.M.; Wanty, R.B.; Ridley, W.I.

    2008-01-01

    Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (??soln-solid) are 0.99927 ?? 0.00008 for Cu and 0.99948 ?? 0.00004 for Zn or, alternately, the separation factors (??soln-solid) are -0.73 ?? 0.08??? for Cu and -0.52 ?? 0.04??? for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal-oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu > Zn > Fe(II).

  2. Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water

    NASA Astrophysics Data System (ADS)

    Balistrieri, Laurie S.; Borrok, David M.; Wanty, Richard B.; Ridley, W. Ian

    2008-01-01

    Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (αsoln-solid) are 0.99927 ± 0.00008 for Cu and 0.99948 ± 0.00004 for Zn or, alternately, the separation factors (Δsoln-solid) are -0.73 ± 0.08‰ for Cu and -0.52 ± 0.04‰ for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal-oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu > Zn > Fe(II).

  3. HYDROGEN ISOTOPE RECOVERY USING PROTON EXCHANGE MEMBRANE ELECTROLYSIS OF WATER

    SciTech Connect

    Fox, E; Scott Greenway, S; Amy Ekechukwu, A

    2007-08-27

    A critical component of tritium glovebox operations is the recovery of high value tritium from the water vapor in the glove box atmosphere. One proposed method to improve existing tritium recovery systems is to replace the disposable hot magnesium beds used to separate the hydrogen and oxygen in water with continuous use Proton Exchange Membrane Electrolyzers (PEMEs). This study examines radiation exposure to the membrane of a PEME and examines the sizing difference that would be needed if the electrolyzer were operated with a cathode water vapor feed instead of an anode liquid water feed.

  4. Oxygen and hydrogen isotope systematics of Lake Baikal, Siberia: Implications for paleoclimate studies

    USGS Publications Warehouse

    Seal, R.R.; Shanks, Wayne C.

    1998-01-01

    We interpret oxygen and hydrogen isotope data for water samples from Lake Baikal, Siberia, its tributaries and other local rivers, and local precipitation in terms of the known water budget for the modem lake in order to gain insight into past limnological and climatic processes that influenced the lake. Lake Baikal is remarkably uniform in its isotopic composition (??18O = -15.8 ?? 0.2???; ??D = -123 ?? 2???) and lies slightly to the right of the global meteoric water line, which suggests significant evaporation. Water is supplied to the lake by over 300 rivers and streams. The oxygen isotope values (??18O) of the rivers in the Baikal catchment range from -13.4 to -21.2???. The hydrogen isotope values (??D) for the same area range from -103 to -156???. Both these ranges generally conform to the global meteoric water line. The weighted average isotopic composition of input to the lake (rivers plus precipitation) is -15.2??? for ??18O and -116??? for ??D, values higher than those of the modem lake. Therefore, the isotopic composition of the modem lake cannot be related to the modem input through simple evaporation. Instead, modeling of the isotopic mass balance of the lake suggests that inputs (precipitation and influx from rivers) and outputs (evaporation and outflow) are not at a steady-state equilibrium under current climate conditions. We found previous input to the lake had lower ??18O and ??D values than modem input, which reflects cooler climates in the past compared with modern conditions. Under constant climate conditions, steady-state conditions are not expected to be reached by the lake for at least 700 yr because of its large size and the long residence time of water in the lake.

  5. [Solid state isotope hydrogen exchange for deuterium and tritium in human gene-engineered insulin].

    PubMed

    Zolotarev, Yu A; Dadayan, A K; Kozik, V S; Gasanov, E V; Nazimov, I V; Ziganshin, R Kh; Vaskovsky, B V; Murashov, A N; Ksenofontov, A L; Haribin, O N; Nikolaev, E N; Myasoedov, N F

    2014-01-01

    The reaction of high temperature solid state catalytic isotope exchange in peptides and proteins under the action of catalyst-activated spillover hydrogen was studied. The reaction of human gene-engineered insulin with deuterium and tritium was conducted at 120-140° C to produce insulin samples containing 2-6 hydrogen isotope atoms. To determine the distribution of the isotope label over tritium-labeled insulin's amino acid residues, oxidation of the S-S bonds of insulin by performic acid was performed and polypeptide chains isolated; then their acid hydrolysis, amino acid analysis and liquid scintillation counts of tritium in the amino acids were conducted. The isotope label was shown to be incorporated in all amino acids of the protein, with the peptide fragment FVNQHLCGSHLVE of the insulin β-chain showing the largest incorporation. About 45% of the total protein isotope label was incorporated in His5 and His10 of this fragment. For the analysis of isotope label distribution in labeled insulin's peptide fragments, the recovery of the S-S bonds by mercaptoethanol, the enzymatic hydrolysis by glutamyl endopeptidase from Bacillus intermedius and HPLC division of the resulting peptides were carried out. Attribution of the peptide fragments formed due to hydrolysis at the Glu-X bond in the β-chain was accomplished by mass spectrometry. Mass spectrometry analysis data of the deuterium-labeled insulin samples' isotopomeric composition showed that the studied solid state isotope exchange reaction equally involved all the protein molecules. Biological studying of tritium-labeled insulin showed its physiological activity to be completely retained.

  6. Hydrogen Isotope Biogeochemistry of Plant Biomarkers in Tropical Trees from the Andes to Amazon

    NASA Astrophysics Data System (ADS)

    Feakins, S. J.; Ponton, C.; West, A. J.; Malhi, Y.; Goldsmith, G.; Salinas, N.; Bentley, L. P.

    2014-12-01

    Plant leaf waxes are well known biomarkers for terrestrial vegetation. Generally, their hydrogen isotopic composition (D/H) records the isotopic composition of precipitation, modulated by leaf water processes and a large biosynthetic fractionation. In addition, the D/H of methoxyl groups on tree wood lignin is an emerging technique thought to record the D/H of source waters, without leaf water complications. Using each of these biomarkers as proxies requires understanding D/H fractionations in plant systems, but few studies have directly studied hydrogen isotope biogeochemistry in tropical plants. An approach that has proven helpful is the paired analysis of plant waters and plant biomarkers: in order that fractionations can be directly computed rather than assumed. This presents logistical challenges in remote tropical forest environments. We report on a unique dataset collected by tree-climbers from 6 well-studied vegetation plots across a 4km elevation transect in the Peruvian Andes and Amazonia. We have measured the D/H of stem water and leaf water, and we compare these to precipitation isotopes and stream waters. The goal of the plant water studies is to understand plant water uptake and stem-leaf water isotopic offsets which can vary due to both transpiration and foliar uptake of water in tropical montane forests. We are in the process of measuring the D/H of plant biomarkers (n-alkanoic acids, n-alkanes and lignin methoxyl) in order to assess how these water isotopic signals are encoded in plant biomarkers. We compare the species-specific modern plant insights to the plant leaf wax n-alkanoic acid D/H that we have recently reported from soils and river sediments from the same region, in order to understand how signals of plant biogeochemistry are integrated into geological sedimentary archives. Progress and open questions in tropical isotope biogeochemistry will be discussed at the meeting.

  7. Isotopically exchangeable organic hydrogen in coal relates to thermal maturity and maceral composition

    USGS Publications Warehouse

    Mastalerz, Maria; Schimmelmann, A.

    2002-01-01

    Hydrogen isotopic exchangeability (Hex) and ??Dn values of non-exchangeable organic hydrogen were investigated in coal kerogens ranging in rank from lignite to graphite. The relative abundance of Hex is highest in lignite with about 18% of total hydrogen being exchangeable, and decreases to around 2.5% in coals with Ro of 1.7 to ca. 5.7%. At Still higher rank (Ro > 6%), Hex increases slightly, although the abundance of total hydrogen decreases. ??Dn is influenced by original biochemical D/H ratios and by thermal maturation in contact with water. Therefore, ??Dn does not show an overall consistent trend with maturity. ?? 2002 Elsevier Science Ltd. All rights reserved.

  8. Thermochemical sulphate reduction (TSR) versus maturation and their effects on hydrogen stable isotopes of very dry alkane gases

    NASA Astrophysics Data System (ADS)

    Liu, Q. Y.; Worden, R. H.; Jin, Z. J.; Liu, W. H.; Li, J.; Gao, B.; Zhang, D. W.; Hu, A. P.; Yang, C.

    2014-07-01

    Here we report the first study of the effect of thermochemical sulphate reduction (TSR) on the hydrogen isotopes of natural gas. Variably sour (H2S-bearing) and very dry (>97% methane) gas samples from Lower Triassic, Permian and Carboniferous marine carbonate reservoirs in the Sichuan Basin, China, have been analysed. All gases seem to have been sourced from mature marine kerogen and contain H2S that resulted from TSR. The Carboniferous samples are largely unaffected by TSR and were used to assess the effects of normal thermal maturation processes on the carbon and hydrogen isotopes of methane and ethane as a function of gas dryness (a proxy for thermal maturity). Maturation led to heavier carbon isotopes of methane and ethane and hydrogen isotopes of ethane; in contrast methane hydrogen isotopes seem to have little systematic variation with increasing maturity. TSR did not have a systematic effect on the hydrogen isotopes of methane, although the spread of values diminished (ending up at a constant -120‰) as TSR proceeded. This was possibly due to the partial thermochemical sulphate reduction of ethane adding isotopically light methane and thus offsetting the Rayleigh fractionation effects of TSR of methane. In contrast, hydrogen isotopes of ethane became much heavier as TSR proceeded, to values greater than those for samples only influenced by maturation. Under some circumstances, the effects of TSR can be identified and discerned from the effects of normal thermal maturation by plotting the difference between the carbon isotope compositions of methane and ethane and the difference between the hydrogen isotope compositions of methane and ethane. Do the hydrogen isotope ratios of alkane gases systematically vary as a function of dryness or sourness? Do the hydrogen isotope ratios of alkane gases from the Carboniferous, Permian and Lower Triassic dry gas reservoirs help reveal the maturity and/or extent of TSR in the Sichuan Basin? Is it possible to separate and

  9. FI-STM study of hydrogen adsorption on Si(100) surface

    NASA Astrophysics Data System (ADS)

    Hua, Lu; Xiang-dong, Wang; Motai, K.; Hashizume, T.; Sakurai, T.

    1992-11-01

    Chemisorption of atomic hydrogen on the Si(100)2 × 1 surface has been investigated in detail by using a field ion-scanning tunneling microscope (FI-STM). The results showed that the adsorption geometry changed from the 2 × 1 monohydride phase to the 1 × 1 dihydride phase with increasing exposure of hydrogen. The data of desorption of the hydrogen-saturated Si surface showed that on annealing at 670 K the surface becomes highly disordered: the 1 × 1 dihydride structure is eliminated and the 2 × 1 reconstructed monohydride is also hardly to identify. When the temperature rises to as high as 730 K, the surface is dominated by the 2 × 1 structure with missing dimer rows, and some adatom chains occur on the Si substrate terraces. We attribute the formation of these atomic chains to an epitaxial growth of Si atoms which are formed by the dissociation of SiHx (x = 1, 2, 3 or 4) compounds on the Si surface.

  10. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Adsorption Mechanism of Hydrogen on Boron-Doped Fullerenes

    NASA Astrophysics Data System (ADS)

    Yu, Liu-Min; Shi, Guo-Sheng; Wang, Zhi-Gang; Ji, Guang-Fu; Lu, Zhi-Peng

    2009-08-01

    The C35BH-H2 complex and two other possible isomers, C34BCaH-H2 and C34BCbH-H2, are investigated using the local-spin-density approximation (LSDA) method. The results indicate that a single hydrogen molecule could be strongly adsorbed on two isomers, C34BCaH and C34BCbH, with binding energies of 0.42 and 0.47 eV, respectively, and that these calculated binding energies are suitable for reversible hydrogen adsorption/desorption near room temperature. However, it is difficult for the H2 molecule to be firmly adsorbed on C35BH. We analyze the interaction between C34BCxH (x = a, b) and the H2 molecule using dipole moments and molecular orbitals. The charge analysis showed there was a partial charge (about 0.32e) transfer from H2 to the doped fullerenes. These calculation results should broaden our understanding of the mechanisms of hydrogen storage using boron-doped fullerenes.

  11. Direct observation and modelling of ordered hydrogen adsorption and catalyzed ortho-para conversion on ETS-10 titanosilicate material.

    PubMed

    Ricchiardi, Gabriele; Vitillo, Jenny G; Cocina, Donato; Gribov, Evgueni N; Zecchina, Adriano

    2007-06-07

    Hydrogen physisorption on porous high surface materials is investigated for the purpose of hydrogen storage and hydrogen separation, because of its simplicity and intrinsic reversibility. For these purposes, the understanding of the binding of dihydrogen to materials, of the structure of the adsorbed phase and of the ortho-para conversion during thermal and pressure cycles are crucial for the development of new hydrogen adsorbents. We report the direct observation by IR spectroscopic methods of structured hydrogen adsorption on a porous titanosilicate (ETS-10), with resolution of the kinetics of the ortho-para transition, and an interpretation of the structure of the adsorbed phase based on classical atomistic simulations. Distinct infrared signals of o- and p-H2 in different adsorbed states are measured, and the conversion of o- to p-H2 is monitored over a timescale of hours, indicating the presence of a catalyzed reaction. Hydrogen adsorption occurs in three different regimes characterized by well separated IR manifestations: at low pressures ordered 1:1 adducts with Na and K ions exposed in the channels of the material are formed, which gradually convert into ordered 2:1 adducts. Further addition of H2 occurs only through the formation of a disordered condensed phase. The binding enthalpy of the Na+-H2 1:1 adduct is of -8.7+/-0.1 kJ mol(-1), as measured spectroscopically. Modeling of the weak interaction of H2 with the materials requires an accurate force field with a precise description of both dispersion and electrostatics. A novel three body force field for molecular hydrogen is presented, based on the fitting of an accurate PES for the H2-H2 interaction to the experimental dipole polarizability and quadrupole moment. Molecular mechanics simulations of hydrogen adsorption at different coverages confirm the three regimes of adsorption and the structure of the adsorbed phase.

  12. Vibrational Spectroscopic Studies of Hydrogen, Carbon-Monoxide and Thiophene Adsorption on Ruthenium-Sulfide and Sulfided Ruthenium Catalysts.

    NASA Astrophysics Data System (ADS)

    Heise, William Herbert

    The "working surface" of ruthenium hydrodesulfurization (HDS) catalysts has been modeled by preadsorption of sulfur, carbon and carbon plus sulfur on Ru(0001). Adsorption and decomposition of thiophene over these surfaces have been investigated using TDS/TPRS, XPS and EELS. Thiophene is proposed to decompose via a three-step mechanism involving: (i) initial thiophene cracking at 120 K yielding surface sulfur and hydrocarbon species, (ii) hydrogen desorption near 230 K providing additional decomposition ensembles and (iii) continued decomposition to form "metallocycle -like" intermediates which retain EELS features similar to thiophene. Preadsorbed carbon or carbon plus sulfur are not as effective for passivation of the surface toward metallocycle formation as preadsorbed sulfur alone. This result is attributed to the fact that carbon deposited from butadiene annealed and decomposed at 700 K forms islands, while sulfur establishes a well-ordered superlattice on the surface. The decrease in metallocycle formation with increasing poison levels appears to explain HDS selectivity and specific activity trends observed in our laboratory from mildly sulfided (10% H_2S/H_2 , 673 K, 2h) ruthenium catalysts retaining submonolayers of sulfur. Incoherent inelastic neutron scattering (IINS) has been used to characterize hydrogen adsorption sites on ruthenium sulfide. Hydrogen resides on sulfur anions to form SH groups, yielding two non-degenerate bending modes at 600 and 710 cm^{-1}. Complementary hydrogen adsorption and H_2/D _2 exchange data suggest that the active sites for hydrogen adsorption may be coordinatively unsaturated S-S anion pairs. Comparison of CO adsorption on sulfided Ru/Al _2O_3 to sulfur precovered Ru(0001) reveals an adsorption site related to edge/corner atoms directly perturbed by sulfur, consistent with previous kinetic studies demonstrating higher specific activity for thiophene HDS over smaller ruthenium crystallites.

  13. A revision in hydrogen isotopic composition of USGS42 and USGS43 human-hair stable isotopic reference materials for forensic science

    USGS Publications Warehouse

    Coplen, Tyler B.; Qi, Haiping

    2016-01-01

    The hydrogen isotopic composition (δ2HVSMOW-SLAP) of USGS42 and USGS43 human hair stable isotopic reference materials, normalized to the VSMOW (Vienna-Standard Mean Ocean Water)–SLAP (Standard Light Antarctic Precipitation) scale, was originally determined with a high temperature conversion technique using an elemental analyzer (TC/EA) with a glassy carbon tube and glassy carbon filling and analysis by isotope-ratio mass spectrometer (IRMS). However, the TC/EA IRMS method can produce inaccurate δ2HVSMOW-SLAPresults when analyzing nitrogen-bearing organic substances owing to the formation of hydrogen cyanide (HCN), leading to non-quantitative conversion of a sample into molecular hydrogen (H2) for IRMS analysis. A single-oven, chromium-filled, elemental analyzer (Cr-EA) coupled to an IRMS substantially improves the measurement quality and reliability of hydrogen isotopic analysis of hydrogen- and nitrogen-bearing organic material because hot chromium scavenges all reactive elements except hydrogen. USGS42 and USGS43 human hair isotopic reference materials have been analyzed with the Cr-EA IRMS method, and the δ2HVSMOW-SLAP values of their non-exchangeable hydrogen fractions have been revised:where mUr = 0.001 = ‰. On average, these revised δ2HVSMOW-SLAP values are 5.7 mUr more positive than those previously measured. It is critical that readers pay attention to the δ2HVSMOW-SLAP of isotopic reference materials in publications as they may need to adjust the δ2HVSMOW–SLAP measurement results of human hair in previous publications to ensure all results are on the same isotope-delta scale.

  14. Precision Measurement of the Hydrogen-Deuterium 1S-2S Isotope Shift

    SciTech Connect

    Parthey, Christian G.; Matveev, Arthur; Alnis, Janis; Pohl, Randolf; Udem, Thomas; Kolachevsky, Nikolai; Haensch, Theodor W.; Jentschura, Ulrich D.

    2010-06-11

    Measuring the hydrogen-deuterium isotope shift via two-photon spectroscopy of the 1S-2S transition, we obtain 670 994 334 606(15) Hz. This is a 10-times improvement over the previous best measurement [A. Huber et al., Phys. Rev. Lett. 80, 468 (1998)] confirming its frequency value. A calculation of the difference of the mean square charge radii of deuterium and hydrogen results in {sub d}-{sub p}=3.820 07(65) fm{sup 2}, a more than twofold improvement compared to the former value.

  15. Method and apparatus for storing hydrogen isotopes. [stored as uranium hydride in a block of copper

    DOEpatents

    McMullen, J.W.; Wheeler, M.G.; Cullingford, H.S.; Sherman, R.H.

    1982-08-10

    An improved method and apparatus for storing isotopes of hydrogen (especially tritium) are provided. The hydrogen gas is stored as hydrides of material (for example uranium) within boreholes in a block of copper. The mass of the block is critically important to the operation, as is the selection of copper, because no cooling pipes are used. Because no cooling pipes are used, there can be no failure due to cooling pipes. And because copper is used instead of stainless steel, a significantly higher temperature can be reached before the eutectic formation of uranium with copper occurs, (the eutectic of uranium with the iron in stainless steel forms at a significantly lower temperature).

  16. Hydrogen bonding and vapor pressure isotope effect of deuterioisomeric methanethiols

    SciTech Connect

    Wolff, H.; Szydlowski, J.; Dill-Staffenberger, L.

    1981-04-16

    Wilson parameters, activity coefficients, association constants, and other thermodynamic functions which are derived from isothermal vapor pressure measurements between 223 and 293 K for binary mixtures of CH/sub 3/SH, CH/sub 3/SD, CS/sub 3/SH, and CD/sub 3/SD with n-hexane show the weakness of the hydrogen and the deuterium bonds of methanethiol. As far as these functions depend on the association model used for the calculation, the relation of their values to those obtained for the corresponding amines and alcohols under the same conditions attests the weak methanethiol association. While for the more strongly associated methylamines and methanols a greater energy of the deuterium bond compared to the hydrogen bond has clearly been observed, the differences between the thermodynamic functions of the systems with the SH compounds and of those with the SD compounds are insignificant. This observation as well as the fact that the vapor pressure ratios P-(CH/sub 3/SD)/P(CH/sub 3/SH) are only slightly greater than unity, that the ratios P(CD/sub 3/SD)/P(CH/sub 3/SH) are even greater than P(CD/sub 3/SH)/P(CH/sub 3/SH), and that the changes of these ratios with temperature and dilution are small in comparison to the strong increase of the corresponding quotients of the methylamines and the methanols are the consequence of the weak methanethiol association. P(CH/sub 3/SD)/P(CH/sub 3/SH), P(CD/sub 3/SH)/P(CH/sub 3/SH), and P(CD/sub 3/SD)/P(CH/sub 3/SH) are represented by equations of the type ln P/sub D/ P/sub H/ = -A/T/sup 2/ + B/T where A and B are nearly additive. The low values of A and B for CH/sub 3/SD/CH/sub 3/SH in comparison to the high values for CH/sub 3/ND/sub 2//CH/sub 3/NH/sub 2/ and CH/sub 3/OD/CH/sub 3/OH reflect the weakness of the methanethiol hydrogen bonds. The constants can be related to the thermochemical and the spectroscopic data reported in the literature.

  17. INSTRUMENTS AND METHODS OF INVESTIGATION: Dynamic compression of hydrogen isotopes at megabar pressures

    NASA Astrophysics Data System (ADS)

    Trunin, Ryurik F.; Urlin, Vitalii D.; Medvedev, Aleksandr B.

    2010-09-01

    We review the results of shock compression of solid protium to the pressure 66 GPa, of liquid deuterium to 110 GPa, and of solid deuterium to 123 GPa in explosive devices of spherical geometry. The results are compared with data obtained by US scientists using traditional energy sources (explosives and light-gas guns), striker acceleration in a strong magnetic field (Z facility at Sandia), and powerful lasers (Nova at Lawrence Livermore National Laboratory (LLNL) and Omega at the Laboratory for Laser Energetics, University of Rochester). Results of density measurements of hydrogen isotopes under quasi-isentropic compression are analyzed. The absence of an anomalous increase in density under shock and quasi-isentropic compression of hydrogen isotopes is demonstrated. On the other hand, both processes exhibit a sharp change in the compression curve slopes, at the respective pressures 45 and 300 GPa.

  18. Effects of hydrogen adsorption on the properties of double wall BN and (BN)xCy nanotubes

    NASA Astrophysics Data System (ADS)

    Freitas, A.; Azevedo, S.; Kaschny, J. R.

    2016-01-01

    In the present contribution, we apply first-principles calculations, based on the density functional theory, to study the effects of hydrogen adsorption on the structural and electronic properties of boron nitride and hybrid carbon-boron nitride double wall nanotubes. The results demonstrate that the hydrogen decoration induces significant structural deformation and an appreciable reduction in the gap energy. When the number of hydrogen atoms introduced on the outer wall is increased, desorption of hydrogen pairs are observed. The calculations indicate that each adsorbed hydrogen atom induces a structural deformation with an energetic cost of about 68 meV/atom. It is also found that the introduction of hydrogen atoms can be applied as an efficient tool for tuning the electronic properties of such structures.

  19. Multi-purpose hydrogen isotopes separation plant design

    SciTech Connect

    Boniface, H.A.; Gnanapragasam, N.V.; Ryland, D.K.; Suppiah, S.; Castillo, I.

    2015-03-15

    There is a potential interest at AECL's Chalk River Laboratories to remove tritium from moderately tritiated light water and to reclaim tritiated, downgraded heavy water. With only a few limitations, a single CECE (Combined Electrolysis and Catalytic Exchange) process configuration can be designed to remove tritium from heavy water or light water and upgrade heavy water. Such a design would have some restrictions on the nature of the feed-stock and tritium product, but could produce essentially tritium-free light or heavy water that is chemically pure. The extracted tritium is produced as a small quantity of tritiated heavy water. The overall plant capacity is fixed by the total amount of electrolysis and volume of catalyst. In this proposal, with 60 kA of electrolysis a throughput of 15 kg*h{sup -1} light water for detritiation, about 4 kg*h{sup -1} of heavy water for detritiation and about 27 kg*h{sup -1} of 98% heavy water for upgrading can be processed. Such a plant requires about 1,000 liters of AECL isotope exchange catalyst. The general design features and details of this multi-purpose CECE process are described in this paper, based on some practical choices of design criteria. In addition, we outline the small differences that must be accommodated and some compromises that must be made to make the plant capable of such flexible operation. (authors)

  20. Hydrogen Isotopes Record the History of the Martian Hydrosphere and Atmosphere

    NASA Technical Reports Server (NTRS)

    Usui, T.; Simon, J. I.; Jones, J. H.; Kurokawa, H.; Sato, M.; Alexander, C. M. O'D; Wang, J.

    2015-01-01

    The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. This study presents insights from hydrogen isotopes for the origin and evolution of Martian water reservoirs.

  1. 35Cl NQR study of geometric isotope effect in hydrogen bonded chlorooctanes

    NASA Astrophysics Data System (ADS)

    Zdanowska-Fraçzek, M.

    1994-05-01

    35Cl NQR spectroscopy was applied to study the geometric isotope effect in a wide range of 2 : 1 salts of chloroacetic, trichloroacetic and difluorochloroacetic acids. The NQR results were correlated with IR spectroscopic studies, which provided information on the potential shape for proton motion. The NQR results were discussed on the basis of a variational correlated ground state wave function theory of a single hydrogen bond.

  2. Jarosite-water oxygen and hydrogen isotope fractionations: preliminary experimental data

    USGS Publications Warehouse

    Rye, R.O.; Stoffregen, R.E.

    1995-01-01

    Stable isotope studies of alunite have added a powerful tool for understanding geochemical processes in the surficial environment. Jarosite [KFe3(SO4)2(OH)6], like alunite, is a common mineral in the weathered portions of many sulfide-bearing ore deposits and mine drainages where its formation reflects acidic conditions produced by the oxidation of sulfides. This paper describes oxygen and hydrogen isotope fractionations in jarosite-water experiments over a temperature range of 100?? to 250??C and the extrapolation of the results to surface conditions. It also includes some general observations on the exchange reaction mechanism that are important for evaluating how well natural samples of jarosite retain primary isotopic compositions. -from Authors

  3. Extreme changes in stable hydrogen isotopes and precipitation characteristics in a landfalling Pacific storm

    USGS Publications Warehouse

    Coplen, T.B.; Neiman, P.J.; White, A.B.; Landwehr, J.M.; Ralph, F.M.; Dettinger, M.D.

    2008-01-01

    With a new automated precipitation collector we measured a remarkable decrease of 51??? in the hydrogen isotope ratio (?? 2H) of precipitation over a 60-minute period during the landfall of an extratropical cyclone along the California coast on 21 March 2005. The rapid drop in ??2H occurred as precipitation generation transitioned from a shallow to a much deeper cloud layer, in accord with synoptic-scale ascent and deep "seeder-feeder" precipitation. Such unexpected ?? 2H variations can substantially impact widely used isotope-hydrograph methods. From extreme ??2H values of -26 and -78???, we calculate precipitation temperatures of 9.7 and -4.2??C using an adiabatic condensation isotope model, in good agreement with temperatures estimated from surface observations and radar data. This model indicates that 60 percent of the moisture was precipitated during ascent as temperature decreased from 15??C at the ocean surface to -4??C above the measurement site.

  4. Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces

    SciTech Connect

    Kaghazchi, Payam; Jacob, Timo; Chen, Wenhua; Bartynski, Robert A.

    2013-06-03

    Here, we report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H2 peak is seen from planar Ir(210) at all coverages whereas a single H2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity in recombination and desorption of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H2 from faceted Ir(210): F1 from desorption of H2 on {311} facets while F2 from desorption of H2 on (110) facets.

  5. Carbon and hydrogen isotopic compositions of algae and bacteria from hydrothermal environments, Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Estep, Marilyn L. F.

    1984-03-01

    Stromatolites forming today on a small scale in hydrothermal environments are chemical and biological analogues of much larger Precambrian formations. Carbon isotopic composition varied as a function of CO 2 concentration, pH, and species composition. Stratiform, layered stromatolites grew in silica-depositing springs at 55° to 70°C; they consisted mainly of a unicellular alga, Synechococcus, and a filamentous, photosynthetic bacterium, Chloroflexus. These thermophiles become enriched in 12C as the concentration of carbon dioxide in the effluent waters increases. At a concentration of 40 ppm total inorganic C, and δ 13C of organic carbon was ˜ -12%., whereas at 900 ppm total inorganic C, the δ 13C of similar species was ˜ -25%.. Conical stromatolites or conophytons (principally a filamentous, blue-green alga Phormidium and Chloroflexus) grew at 40°-55°C. In older, broader conophytons, Chloroflexus was the dominant organism. Their δ 13C values were ˜ -18%. in a variety of hot springs. In carbonate-depositing springs, i.e., carbon dioxide saturated, conophytons and stromatolites consisting of a variety of blue-green algae and photosynthetic bacteria had the most negative δ 13C values (to -30%.). These carbon isotope ratios are directly comparable to carbon isotope ratios of kerogen from Precambrian stromatolites. The presence and activity of methanogenic bacteria or heterotrophic, aerobic and anaerobic bacteria did not alter significantly the δ 13C of the original organic matter. The hydrogen isotopic fractionation between thermophilic organisms and water is 0 to -74 for temperatures of 85° to 46°C, respectively. Acidophilic algae fractionated hydrogen isotopes to a lesser extent than did the photosynthetic organisms inhabiting neutral pH springs. Because organic matter retains some of its original isotopic signature, relationships of CO 2 levels, pH, temperature, and species composition between modern stromatolites and their environment and those of

  6. Hydrogen production from food wastes and gas post-treatment by CO2 adsorption.

    PubMed

    Redondas, V; Gómez, X; García, S; Pevida, C; Rubiera, F; Morán, A; Pis, J J

    2012-01-01

    The production of H(2) by biological means, although still far from being a commercially viable proposition, offers great promise for the future. Purification of the biogas obtained may lead to the production of highly concentrated H(2) streams appropriate for industrial application. This research work evaluates the dark fermentation of food wastes and assesses the possibility of adsorbing CO(2) from the gas stream by means of a low cost biomass-based adsorbent. The reactor used was a completely stirred tank reactor run at different hydraulic retention times (HRTs) while the concentration of solids of the feeding stream was kept constant. The results obtained demonstrate that the H(2) yields from the fermentation of food wastes were affected by modifications in the hydraulic retention time (HRT) due to incomplete hydrolysis. The decrease in the duration of fermentation had a negative effect on the conversion of the substrate into soluble products. This resulted in a lower amount of soluble substrate being available for metabolisation by H(2) producing microflora leading to a reduction in specific H(2) production. Adsorption of CO(2) from a gas stream generated from the dark fermentation process was successfully carried out. The data obtained demonstrate that the column filled with biomass-derived activated carbon resulted in a high degree of hydrogen purification. Co-adsorption of H(2)S onto the activated carbon also took place, there being no evidence of H(2)S present in the bio-H(2) exiting the column. Nevertheless, the concentration of H(2)S was very low, and this co-adsorption did not affect the CO(2) capture capacity of the activated carbon.

  7. Hydrogen adsorption at the graphene surface: A vdW-DF perspective

    SciTech Connect

    Cooper, Valentino R; Ihm, Yungok; Morris, James R

    2012-01-01

    We use the recently developed van der Waals density functional (vdW-DF) along with the C09x exchange functional to explore the interactions of molecular hydrogen with a single sheet of graphene. Our calculations demonstrate the importance of the inclusion of dispersion interactions for evaluating the adsorption capacity of graphitic, sparsely packed materials. In particular we show that, although the commonly used local density approximation (LDA) exchange-correlation functional gives reasonable H$_2$-graphene separation distances, these interactions are in fact too strong and decrease too rapidly as the H$_2$-graphene distance increases. On the other hand, calculations employing the generalized gradient approximation (GGA) for exchange and correlation exhibit very little binding. The vdW-DF$^{\\rm C09x}$ functional, however, gives binding very similar to benchmark second-order M$\\o$ller-Plesset (MP2) theory results for the H$_2$-coronene interaction and has an appropriate long range interaction with the graphene sheet. This shortcoming of the LDA and GGA functionals is shown to have significant consequences on the overall adsorption densities of H$_2$ near the graphene, thus emphasizing the fundamental importance of properly characterizing the interactions of adsorbed molecules in porous media.

  8. Adsorption of hydrogen sulphide from aqueous solutions using modified nano/micro fibrillated cellulose.

    PubMed

    Hokkanen, Sanna; Repo, Eveliina; Bhatnagar, Amit; Tang, Walter Zhonghong; Sillanpää, Mika

    2014-01-01

    In the present study, microfibrillated cellulose (MFC) was modified by aminopropyltriethoxysilane (APS), hydroxy-carbonated apatite (HAP), or epoxy in order to produce novel nanostructured adsorbents for the removal of hydrogen sulphide (H2S) from the aqueous solutions. Structural properties of the modified MFC materials were examined using a scanning electron microscope, Fourier transform infrared spectroscopy and acid/base titration. These methods were used to verify the presence of nanostructures on the adsorbents surfaces as well as functionalities suitable for H2S adsorption. Adsorption of H2S by prepared adsorbents was investigated in batch mode under different experimental conditions, i.e., varying pH and H2S concentrations. H2S uptake was found to be 103.95, 13.38 and 12.73 mg/g by APS/MFC, HAP/MFC and epoxy/MFC, respectively from 80 mg/L H2S solution. The equilibrium data were best described by the Langmuir isotherm for HAP/MFC and APS/MFC and the Sips isotherm for epoxy/MFC.

  9. Investigations of intramolecular hydrogen bonding in three types of Schiff bases by 2H and 3H NMR isotope effects.

    PubMed

    Schilf, Wojciech; Bloxsidge, James P; Jones, John R; Lu, Shui-Yu

    2004-06-01

    Hydrogen bonding within the structures of three Schiff bases (1-3), obtained by condensation of 4-methoxy-, 5-methoxy- and 4,6-dimethoxysalicylaldehyde with methylamine, was investigated by measuring deuterium and tritium NMR isotope effects. The primary deuterium and tritium isotope effects (delta(XH)-delta(XD/T)) and secondary one-bond nitrogen deuterium effect appear to be very useful parameters for defining the character of intramolecular hydrogen bonds. The tritium isotope effects were also determined for nitrogen-hydrogen one-bond coupling constants for both 4-methoxy and 4,6-dimethoxy derivatives. These parameters are seen to be highly sensitive to hydrogen bond characteristics and can be used to distinguish localized and tautomeric hydrogen bonds.

  10. Investigation related to hydrogen isotopes separation by cryogenic distillation

    SciTech Connect

    Bornea, A.; Zamfirache, M.; Stefanescu, I.; Preda, A.; Balteanu, O.; Stefan, I.

    2008-07-15

    Research conducted in the last fifty years has shown that one of the most efficient techniques of removing tritium from the heavy water used as moderator and coolant in CANDU reactors (as that operated at Cernavoda (Romania)) is hydrogen cryogenic distillation. Designing and implementing the concept of cryogenic distillation columns require experiments to be conducted as well as computer simulations. Particularly, computer simulations are of great importance when designing and evaluating the performances of a column or a series of columns. Experimental data collected from laboratory work will be used as input for computer simulations run at larger scale (for The Pilot Plant for Tritium and Deuterium Separation) in order to increase the confidence in the simulated results. Studies carried out were focused on the following: - Quantitative analyses of important parameters such as the number of theoretical plates, inlet area, reflux flow, flow-rates extraction, working pressure, etc. - Columns connected in series in such a way to fulfil the separation requirements. Experiments were carried out on a laboratory-scale installation to investigate the performance of contact elements with continuous packing. The packing was manufactured in our institute. (authors)

  11. Absorption/desorption of hydrogen isotopes and isotopic waters by Zr-alloy getters

    SciTech Connect

    Ichimura, K.; Matsuyama, M.; Watanabe, K.; Takeuchi, T.

    1988-07-01

    Zr-alloy getters have been applied to tritium handling and vacuum conditioning for fusion devices. Some of their properties, however, should be improved to apply them in future devices. From this viewpoint, we have studied the effects of alloying on the getter properties of Zr alloys. We found that the activation energy of absorption and desorption of hydrogen varied considerably with alloying. The activation energy for hydrogen absorption was 0.74 for Zr/sub 61/Al/sub 39/, 0.01 for Zr/sub 57/V/sub 36/Fe/sub 7/, 0.63 for Zr/sub 67/Ni/sub 33/, and 2.8 kcal/mol for Zr/sub 85/Ni/sub 15/, whereas that for Zr was 2.6 kcal/mol. The heat of hydrogen absorption was 27.8 kcal/mol for Zr: it changed with alloying as 32.0--33.4 (Zr/sub 61/Al/sub 39/), 27.8--28.4 (Zr/sub 57/V/sub 36/Fe/sub 7/), 29.0 (Zr/sub 67/Ni/sub 33/), and 28.0 (Zr/sub 85/Ni/sub 15/). In addition, the ratio of the pumping speed of water vapor to that of hydrogen at room temperature varied with alloying element: for example, 1/40 for Zr/sub 57/V/sub 36/Fe/sub 7/ and 1/4 for Zr/sub 67/Ni/sub 33/. The alloying effects mentioned above are considered due to modification of the electronic and/or geometric structure of Zr with alloying.

  12. Hydrogen isotope composition of leaf wax n-alkanes in Arabidopsis lines with different transpiration rates

    NASA Astrophysics Data System (ADS)

    Pedentchouk, N.; Lawson, T.; Eley, Y.; McAusland, L.

    2012-04-01

    Stable isotopic compositions of oxygen and hydrogen are used widely to investigate modern and ancient water cycles. The D/H composition of organic compounds derived from terrestrial plants has recently attracted significant attention as a proxy for palaeohydrology. However, the role of various plant physiological and biochemical factors in controlling the D/H signature of leaf wax lipids in extant plants remains unclear. The focus of this study is to investigate the effect of plant transpiration on the D/H composition of n-alkanes in terrestrial plants. This experiment includes 4 varieties of Arabidopsis thaliana that differ with respect to stomatal density and stomatal geometry. All 4 varieties were grown indoors under identical temperature, relative humidity, light and watering regimes and then sampled for leaf wax and leaf water stable isotopic measurements. During growth, stomatal conductance to carbon dioxide and water vapour were also determined. We found that the plants varied significantly in terms of their transpiration rates. Transpiration rates were significantly higher in Arabidopsis ost1 and ost1-1 varieties (2.4 and 3.2 mmol m-2 s-1, respectively) than in Arabidopsis RbohD and Col-0 (1.5 and 1.4). However, hydrogen isotope measurements of n-alkanes extracted from leaf waxes revealed a very different pattern. Varieties ost1, ost1-1, and RbohD have very similar deltaD values of n-C29 alkane (-125, -128, and -127 per mil), whereas the deltaD value of Col-0 is more negative (-137 per mil). The initial results of this work suggest that plant transpiration is decoupled from the D/H composition of n-alkanes. In other words, physical processes that affect water vapour movement between the plant and its environment apparently cannot account for the stable hydrogen isotope composition of organic compounds that comprise leaf waxes. Additional, perhaps biochemical, processes that affect hydrogen isotope fractionation during photosynthesis might need to be invoked

  13. Hydrogen isotopic composition of individual n-alkanes as an intrinsic tracer for bioremediation and source identification of petroleum contamination.

    PubMed

    Pond, Kristy L; Huang, Yongsong; Wang, Yi; Kulpa, Charles F

    2002-02-15

    The isotopic signatures of crude oil hydrocarbons are potentially powerful intrinsic tracers to their origins and the processes by which the oils are modified in the environment. Stable carbon isotopic data are of limited use for studying petroleum contaminants because of the relatively small amount of isotopic fractionation that occurs during natural processes. Hydrogen isotopes, in contrast, are commonly fractionated to a much greater extent and as a result display larger variations in delta values. We studied the effect of in vitro aerobic biodegradation on the hydrogen isotopic composition of individual n-alkanes from crude oil. The isotopic analysis was conducted using gas chromatography-thermal conversion-isotope ratio mass spectrometry. In general, biodegradation rates decreased with increasing hydrocarbon chain length, consistent with previous studies. More importantly the n-alkanes that were degraded at the fastest rates (n-C15 to n-C18) also showed the largest overall isotopic fractionation (approximately 12-25 per thousand deuterium enrichment), suggesting that the lower molecular weight n-alkanes can be used to monitor in-situ bioremediation of crude oil contamination. The hydrogen isotopic compositions of the longer chain alkanes (n-C19 to n-C27) were relatively stable during biodegradation (<5%o overall deuterium enrichment), indicating that these compounds are effective tracers for oil-source identification studies.

  14. Hydrogen isotopic composition of the Martian mantle inferred from the newest Martian meteorite fall, Tissint

    NASA Astrophysics Data System (ADS)

    Mane, P.; Hervig, R.; Wadhwa, M.; Garvie, L. A. J.; Balta, J. B.; McSween, H. Y.

    2016-11-01

    The hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets. The sources of water and the hydrological evolution of Mars may be inferred from the hydrogen isotopic compositions of mineral phases in Martian meteorites, which are currently the only samples of Mars available for Earth-based laboratory investigations. Previous studies have shown that δD values in minerals in the Martian meteorites span a large range of -250 to +6000‰. The highest hydrogen isotope ratios likely represent a Martian atmospheric component: either interaction with a reservoir in equilibrium with the Martian atmosphere (such as crustal water), or direct incorporation of the Martian atmosphere due to shock processes. The lowest δD values may represent those of the Martian mantle, but it has also been suggested that these values may represent terrestrial contamination in Martian meteorites. Here we report the hydrogen isotopic compositions and water contents of a variety of phases (merrillites, maskelynites, olivines, and an olivine-hosted melt inclusion) in Tissint, the latest Martian meteorite fall that was minimally exposed to the terrestrial environment. We compared traditional sample preparation techniques with anhydrous sample preparation methods, to evaluate their effects on hydrogen isotopes, and find that for severely shocked meteorites like Tissint, the traditional sample preparation techniques increase water content and alter the D/H ratios toward more terrestrial-like values. In the anhydrously prepared Tissint sample, we see a large range of δD values, most likely resulting from a combination of processes including magmatic degassing, secondary alteration by crustal fluids, shock-related fractionation, and implantation of Martian atmosphere. Based on these data, our best estimate of the δD value for the Martian depleted mantle is -116 ± 94‰, which is the lowest value measured in a phase in the

  15. Fractionation of sulfur and hydrogen isotopes in Desulfovibrio vulgaris with perturbed DsrC expression.

    PubMed

    Leavitt, William D; Venceslau, Sofia S; Pereira, Inês A C; Johnston, David T; Bradley, Alexander S

    2016-10-01

    Dissimilatory sulfate reduction is the central microbial metabolism in global sulfur cycling. Understanding the importance of sulfate reduction to Earth's biogeochemical S cycle requires aggregating single-cell processes with geochemical signals. For sulfate reduction, these signals include the ratio of stable sulfur isotopes preserved in minerals, as well as the hydrogen isotope ratios and structures of microbial membrane lipids preserved in organic matter. In this study, we cultivated the model sulfate reducer, Desulfovibrio vulgaris DSM 644(T), to investigate how these parameters were perturbed by changes in expression of the protein DsrC. DsrC is critical to the final metabolic step in sulfate reduction to sulfide. S and H isotopic fractionation imposed by the wild type was compared to three mutants. Discrimination against (34)S in sulfate, as calculated from the residual reactant, did not discernibly differ among all strains. However, a closed-system sulfur isotope distillation model, based on accumulated sulfide, produced inconsistent results in one mutant strain IPFG09. Lipids produced by IPFG09 were also slightly enriched in (2)H. These results suggest that DsrC alone does not have a major impact on sulfate-S, though may influence sulfide-S and lipid-H isotopic compositions. While intriguing, a mechanistic explanation requires further study under continuous culture conditions.

  16. Sulfur and Hydrogen Isotope Anomalies in Organic Compounds from the Murchison Meteorite

    NASA Technical Reports Server (NTRS)

    Cooper, G. W.; Thiemens, M. H.; Jackson, T.; Chang, Sherwood

    1996-01-01

    Isotopic measurements have been made on organic sulfur and phosphorus compounds recently discovered in the Murchison meteorite. Carbon, hydrogen and sulfur measurements were performed on individual members of the organic sulfur compounds, alkyl sulfonates; and carbon and hydrogen measurements were made on bulk alkyl phosphonates. Cooper and Chang reported the first carbon isotopic measurements of Murchison organic sulfonates, providing insight into the potential synthetic mechanisms of these and, possibly, other organic species. Hydrogen isotopic measurements of the sulforiates now reveal deuterium excesses ranging from +660 to +2730 %. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low temperature astrophysical environment consistent with that of dense molecular clouds. Measurements of the sulfur isotopes provide further constraints on the origin and mechanism of formation of these organic molecules. Recently, there has been growing documentation of sulfur isotopic anomalies in meteoritic material. Thiemens and Jackson have shown that some bulk ureilites possess excess S-33 and Thiemens et al. have reported excess S-33 in an oldhamite separate from the Norton County meteorite. Rees and Thode reported a large S-33 excess in an Allende acid residue, however, attempts to verify this measurements have been unsuccessful, possibly due to the heterogeneous nature of the carrier phase. With the recognition that sulfur isotopes may reflect chemistry in the protosolar nebula or the precursor molecular cloud, identification of potential carriers is of considerable interest. In the present study, the stable isotopes of sulfur were measured in methane sulfonic acid extracted from the Murchison meteorite. The isotopic composition was found to be: (delta)S-33 = 2.48 %, (delta)S-34 = 2.49 % and (delta)S-36 = 6.76 %. Based upon analysis of more than 60 meteoritic and numerous terrestrial samples, the mass fractionation lines are

  17. Trends in the adsorption and reactivity of hydrogen on magnesium silicate nanoclusters.

    PubMed

    Oueslati, Ichraf; Kerkeni, Boutheïna; Bromley, Stefan T

    2015-04-14

    We study nanoclusters of Mg-rich olivine and pyroxene (having (MgO)6(SiO2)3 and (MgO)4(SiO2)4 compositions) with respect to their reactivity towards hydrogen atoms, using density functional calculations. Ultrasmall silicate particles are fundamental intermediates in cosmic dust grain formation and processing, and are thought to make up a significant mass fraction of the grain population. Due to their nanoscale dimensions and high surface area to bulk ratios, they are likely to also have a disproportionately large influence on surface chemistry in the interstellar medium. This work investigates the potential role of silicate nanoclusters in vital interstellar hydrogen-based chemistry by studying atomic H adsorption and H2 formation. Our extensive set of calculations confirm the generality of a Brønsted-Evans-Polanyi (BEP) relation between the H2 reaction barrier and the 2Hchem binding energy, suggesting it to be independent of silicate dust grain shape, size, crystallinity and composition. Our results also suggest that amorphous/porous grains with forsteritic composition would tend to dissociate H2, but relatively Mg-poor silicate grains (e.g. enstatite composition) and/or more crystalline/compact silicate grains would tend to catalyse H2 formation. The high structural thermostability of silicate nanoclusters with respect to the heat released during exothermic H2 formation reactions is also verified.

  18. Adsorption isotherms for hydrogen chloride (HCl) on ice surfaces between 190 and 220 K.

    PubMed

    Zimmermann, S; Kippenberger, M; Schuster, G; Crowley, J N

    2016-05-18

    The interaction of hydrogen chloride (HCl) with ice surfaces at temperatures between 190 and 220 K was investigated using a coated-wall flow-tube connected to a chemical ionization mass spectrometer. Equilibrium surface coverages of HCl were determined at gas phase concentrations as low as 2 × 10(9) molecules cm(-3) (∼4 × 10(-8) Torr at 200 K) to derive Langmuir adsorption isotherms. The data are described by a temperature independent partition coefficient: KLang = (3.7 ± 0.2) × 10(-11) cm(3) molecule(-1) with a saturation surface coverage Nmax = (2.0 ± 0.2) × 10(14) molecules cm(-2). The lack of a systematic dependence of KLang on temperature contrasts the behaviour of numerous trace gases which adsorb onto ice via hydrogen bonding and is most likely related to the ionization of HCl at the surface. The results are compared to previous laboratory studies, and the equilibrium partitioning of HCl to ice surfaces under conditions relevant to the atmosphere is evaluated.

  19. Hydrogen isotope exchange between n-alkanes and water under hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Reeves, Eoghan P.; Seewald, Jeffrey S.; Sylva, Sean P.

    2012-01-01

    To investigate the extent of hydrogen isotope (2H and 1H) exchange between hydrocarbons and water under hydrothermal conditions, we performed experiments heating C1-C5n-alkanes in aqueous solutions of varying initial 2H/1H ratios in the presence of a pyrite-pyrrhotite-magnetite redox buffer at 323 °C and 35-36 MPa. Extensive and reversible incorporation of water-derived hydrogen into C2-C5n-alkanes was observed on timescales of months. In contrast, comparatively minor exchange was observed for CH4. Isotopic exchange is facilitated by reversible equilibration of n-alkanes and their corresponding n-alkenes with H2 derived from the disproportionation of water. Rates of δ2H variation in C3+n-alkanes decreased with time, a trend that is consistent with an asymptotic approach to steady state isotopic compositions regulated by alkane-water isotopic equilibrium. Substantially slower δ2H variation was observed for ethane relative to C3-C5n-alkanes, suggesting that the greater stability of C3+ alkenes and isomerization reactions may dramatically enhance rates of 2H/1H exchange in C3+n-alkanes. Thus, in reducing aqueous environments, reversible reaction of alkanes and their corresponding alkenes facilitates rapid 2H/1H exchange between water and alkyl-bound hydrogen on relatively short geological timescales at elevated temperatures and pressures. The proximity of some thermogenic and purported abiogenic alkane δ2H values to those predicted for equilibrium 2H/1H fractionation with ambient water suggests that this process may regulate the δ2H signatures of some naturally occurring hydrocarbons.

  20. Suppression of hydrogenated carbon film deposition and hydrogen isotope retention by nitrogen addition into cold remote H/D and CH4 mixture plasmas

    NASA Astrophysics Data System (ADS)

    Iida, K.; Notani, M.; Uesugi, Y.; Tanaka, Y.; Ishijima, T.

    2015-08-01

    Control of tritium retention and its removal from the first wall of future fusion devices are one of the most crucial issues for safety and effective use for fuel. Nitrogen addition into remote edge plasmas has been considered and tested as an effective method for suppression of carbon film deposition and reduction of hydrogen isotope absorption in the deposited films. In this paper we have investigated the scavenger effects of nitrogen injected into low temperature D2/CH4 plasmas on hydrogenated carbon film growth using a small helical device. The result of the deposition shows that the key reactive particles with CN and ND(H) bonds to suppression of hydrogenated carbon film growth and hydrogen isotope absorption are much slowly generated compared with hydrocarbon particles such as CD(H)x and C2D(H)x. This may be due to the slow atomic nitrogen diffusion into hydrogenated carbon layer and the chemical equilibrium between nitrogen absorption.

  1. Sims Analysis of Water Abundance and Hydrogen Isotope in Lunar Highland Plagioclase

    NASA Technical Reports Server (NTRS)

    Hui, Hejiu; Guan, Yunbin; Chen, Yang; Peslier, Anne H.; Zhang, Youxue; Liu, Yang; Rossman, George R.; Eiler, John M.; Neal, Clive R.

    2015-01-01

    The detection of indigenous water in mare basaltic glass beads has challenged the view established since the Apollo era of a "dry" Moon. Since this discovery, measurements of water in lunar apatite, olivine-hosted melt inclusions, agglutinates, and nominally anhydrous minerals have confirmed that lunar igneous materials contain water, implying that some parts of lunar mantle may have as much water as Earth's upper mantle. The interpretation of hydrogen (H) isotopes in lunar samples, however, is controversial. The large variation of H isotope ratios in lunar apatite (delta Deuterium = -202 to +1010 per mille) has been taken as evidence that water in the lunar interior comes from the lunar mantle, solar wind protons, and/or comets. The very low deuterium/H ratios in lunar agglutinates indicate that solar wind protons have contributed to their hydrogen content. Conversely, H isotopes in lunar volcanic glass beads and olivine-hosted melt inclusions being similar to those of common terrestrial igneous rocks, suggest a common origin for water in both Earth and Moon. Lunar water could be inherited from carbonaceous chondrites, consistent with the model of late accretion of chondrite-type materials to the Moon as proposed by. One complication about the sources of lunar water, is that geologic processes (e.g., late accretion and magmatic degassing) may have modified the H isotope signatures of lunar materials. Recent FTIR analyses have shown that plagioclases in lunar ferroan anorthosite contain approximately 6 ppm H2O. So far, ferroan anorthosite is the only available lithology that is believed to be a primary product of the lunar magma ocean (LMO). A possible consequence is that the LMO could have contained up to approximately 320 ppm H2O. Here we examine the possible sources of water in the LMO through measurements of water abundances and H isotopes in plagioclase of two ferroan anorthosites and one troctolite from lunar highlands.

  2. Experimental Investigation of Irradiation-driven Hydrogen Isotope Fractionation in Analogs of Protoplanetary Hydrous Silicate Dust

    NASA Astrophysics Data System (ADS)

    Roskosz, Mathieu; Laurent, Boris; Leroux, Hugues; Remusat, Laurent

    2016-11-01

    The origin of hydrogen in chondritic components is poorly understood. Their isotopic composition is heavier than the solar nebula gas. In addition, in most meteorites, hydrous silicates are found to be lighter than the coexisting organic matter. Ionizing irradiation recently emerged as an efficient hydrogen fractionating process in organics, but its effect on H-bearing silicates remains essentially unknown. We report the evolution of the D/H of hydrous silicates experimentally irradiated by electrons. Thin films of amorphous silica, amorphous “serpentine,” and pellets of crystalline muscovite were irradiated at 4 and 30 keV. For all samples, irradiation leads to a large hydrogen loss correlated with a moderate deuterium enrichment of the solid residue. The entire data set can be described by a Rayleigh distillation. The calculated fractionation factor is consistent with a kinetically controlled fractionation during the loss of hydrogen. Furthermore, for a given ionizing condition, the deuteration of the silicate residues is much lower than the deuteration measured on irradiated organic macromolecules. These results provide firm evidence of the limitations of ionizing irradiation as a driving mechanism for D-enrichment of silicate materials. The isotopic composition of the silicate dust cannot rise from a protosolar to a chondritic signature during solar irradiations. More importantly, these results imply that irradiation of the disk naturally induces a strong decoupling of the isotopic signatures of coexisting organics and silicates. This decoupling is consistent with the systematic difference observed between the heavy organic matter and the lighter water typically associated with minerals in the matrix of most carbonaceous chondrites.

  3. The Use of Stable Hydrogen Isotopes as a Geothermometer in Hydrothermal Systems

    NASA Astrophysics Data System (ADS)

    Proskurowski, G.; Lilley, M. D.; Früh-Green, G. L.; Olson, E. J.; Kelley, D. S.

    2004-12-01

    Terrestrial geothermal work by Arnason in the 1970's demonstrated the utility of stable hydrogen isotopes as a geothermometer[1]. However, with the exception of two data points from 9°N in a study by Horibe and Craig[2], the value of this geothermometer in hydrothermal systems has never been rigorously assessed. Equilibrium fractionation factors for H2-H2O and H2-CH4 have previously been determined experimentally and theoretically over a range of temperatures and provide an expression relating alpha (fractionation) and temperature. We have measured the dD of H2(g), CH4(g) and H2O from a diverse selection of hydrothermal vent localities including Lost City, Middle Valley, Endeavour, Guaymas, Logatchev, Broken Spur, and SWIR. These samples were chosen to represent a wide range of fluid temperatures and a variety of environmental settings. We see a strong correlation between measured vent temperature and predicted vent temperature using both the hydrogen-water and the methane-hydrogen geothermometers over a temperature range of 25-400°C. In the case of the H2-H2O geothermometer, the predicted temperatures are slightly elevated with respect to the measured temperatures at the low temperature Lost City site, and are in good agreement at high temperature vent sites. The H2-CH4 geothermometer predicts temperatures that are 40-80°C elevated with respect to the measured temperature in both the low and high temperature sites. These measurements demonstrate that the hydrogen isotope geothermometer in the hydrogen-methane-water system is robust in hydrothermal systems and may be a useful tool in determining the temperature of the root zone. 1. Arnason, B., The Hydrogen-Water Isotope Thermometer Applied to Geothermal Areas In Iceland. Geothermics, 1977. 5: p. 75-80. 2. Horibe, Y. and H. Craig, D/ H fractionation in the system methane-hydrogen-water. Geochimica et Cosmochimica Acta, 1995. 59(24): p. 5209-5217.

  4. Evaluating the role of re-adsorption of dissolved Hg(2+) during cinnabar dissolution using isotope tracer technique.

    PubMed

    Jiang, Ping; Li, Yanbin; Liu, Guangliang; Yang, Guidi; Lagos, Leonel; Yin, Yongguang; Gu, Baohua; Jiang, Guibin; Cai, Yong

    2016-11-05

    Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbed Hg on cinnabar surface via the reduction in spiked (202)Hg(2+). By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred μgL(-1), while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. These results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.

  5. Evaluating the role of re-adsorption of dissolved Hg2+ during cinnabar dissolution using isotope tracer technique

    DOE PAGES

    Jiang, Ping; Li, Yanbin; Liu, Guangliang; ...

    2016-06-02

    Cinnabar dissolution is an important factor controlling mercury (Hg) cycling. Recent studies have suggested the co-occurrence of re-adsorption of the released Hg during the course of cinnabar dissolution. However, there is a lack of feasible techniques that can quantitatively assess the amount of Hg re-adsorbed on cinnabar when investigating cinnabar dissolution. In this study, a new method, based on isotope tracing and dilution techniques, was developed to study the role of Hg re-adsorption in cinnabar dissolution. The developed method includes two key components: (1) accurate measurement of both released and spiked Hg in aqueous phase and (2) estimation of re-adsorbedmore » Hg on cinnabar surface via the reduction in spiked 202Hg2+. By adopting the developed method, it was found that the released Hg for trials purged with oxygen could reach several hundred g L–1, while no significant cinnabar dissolution was detected under anaerobic condition. Cinnabar dissolution rate when considering Hg re-adsorption was approximately 2 times the value calculated solely with the Hg detected in the aqueous phase. Lastly, these results suggest that ignoring the Hg re-adsorption process can significantly underestimate the importance of cinnabar dissolution, highlighting the necessity of applying the developed method in future cinnabar dissolution studies.« less

  6. An instrumental and numerical method to determine the hydrogenic ratio in isotopic experiments in the TJ-II stellarator

    SciTech Connect

    Baciero, A. Zurro, B.; Martínez, M.

    2014-11-15

    The isotope effect is an important topic that is relevant for future D-T fusion reactors, where the use of deuterium, rather than hydrogen, may lean to improved plasma confinement. An evaluation of the ratio of hydrogen/deuterium is needed for isotope effect studies in current isotopic experiments. Here, the spectral range around H{sub α} and D{sub α} lines, obtained with an intensified multi-channel detector mounted to a 1-m focal length spectrometer, is analyzed using a fit function that includes several Gaussian components. The isotopic ratio evolution for a single operational day of the TJ-II stellarator is presented. The role of injected hydrogen by Neutral Beam Injection heating is also studied.

  7. Dye-adsorption capacity of high surface-area hydrogen titanate nanosheets processed via modified hydrothermal method.

    PubMed

    Padinhattayil, Hareesh; Augustine, Rimesh; Shukla, Satyajit

    2013-04-01

    High surface-area (380 m2 x g(-1)) hydrogen titanate nanosheets (HTNS) processed via the modified hydrothermal method have been utilized for the removal of methylene blue (MB) dye from an aqueous solution via the surface-adsorption process involving the electrostatic attraction mechanism. The HTNS have been characterized using the transmission electron microscope (TEM), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) specific surface-area measurement techniques. The amount of MB dye adsorbed on the surface of HTNS at equilibrium (q(e)) has been examined as a function of contact time, initial dye-concentration, and initial solution-pH. Within the investigated range of initial solution-pH (2.5-11), the MB dye adsorption on the surface of HTNS has been observed to follow the pseudo-second-order kinetics with the dye-adsorption capacity of 119 mg x g(-1) at the initial solution-pH of - 10. The adsorption equilibrium follows the Langmuir isotherm within the initial solution-pH range of 2.5-10. However, in a highly basic solution (initial solution-pH -11), the adsorption equilibrium has been observed to follow the Langmuir, Freundlich, and Dubinin-Kaganer-Radushkevich (DKR) models in the different ranges of initial MB dye concentration. The mere dependence on the DKR model has not been observed within the investigated range of initial solution-pH. The differences in the dye-adsorption characteristics and capacity of HTNS, compared with those of hydrogen titanate nanotubes, have been attributed to the difference in their specific surface-area. Irrespective of the morphology, the maximum coverage of MB dye on the surface of hydrogen titanate has been noted to be the same (52%).

  8. Effects of volatilization on carbon and hydrogen isotope ratios of MTBE.

    PubMed

    Kuder, Tomasz; Philp, Paul; Allen, Jon

    2009-03-15

    Contaminant attenuation studies utilizing CSIA (compound-specific isotope analysis) routinely assume that isotope effects (IEs) result only from degradation. Experimental results on MTBE behavior in diffusive volatilization and dynamic vapor extraction show measurable changes in the isotope ratios of the MTBE remaining in the aqueous or nonaqueous phase liquid (NAPL) matrix. A conceptual model for interpretation of those IEs is proposed, based on the physics of liquid-air partitioning. Normal or inverse IEs were observed for different volatilization scenarios. The range of carbon enrichment factors (epsilon) was from +0.7 per thousand (gasoline vapor extraction) to -1 per thousand (diffusive volatilization of MTBE from gasoline), the range of hydrogen epsilon was from +7 per thousand (gasoline vapor extraction) to -12 per thousand (air sparging of aqueous MTBE). The observed IEs are lower than those associated with MTBE degradation. However, under a realistic scenario for MTBE vapor removal, their magnitude is within the detection limits of CSIA. The potential for interference of those IEs is primarily in confusing the interpretation of samples with a small extent of fractionation and where only carbon CSIA data are available. The IEs resulting from volatilization and biodegradation, respectively, can be separated by combined carbon and hydrogen 2D-CSIA.

  9. Measurements of Hydrogen and Helium Isotopes with the BESS-Polar II Instrument

    NASA Astrophysics Data System (ADS)

    Picot-Clemente, Nicolas; BESS-Polar Collaboration

    2015-04-01

    The Balloon-Borne Experiment with a Superconducting Spectrometer (BESS-Polar II) flew successfully over Antarctica for 24.5 days in December 2007 through January 2008 during a period of minimum Solar activity. BESS-Polar II is configured with a solenoidal superconducting magnet and a suite of precision particle detectors. It can accurately identify hydrogen and helium isotopes among the incoming cosmic-ray nuclei with energies from 0.2 up to about 1.5 GeV/n. The long duration of the flight, and the good stability of the detectors increased the number of cosmic-ray events previously recorded with BESS-Polar I by a factor of 5, reaching about 4.7 billion collected particles. This allows to study and measure energy spectrum of hydrogen and helium isotope fluxes with unprecedented precision. The isotope flux and ratio measurements with BESS-Polar II will be presented and compared to previous measurements and theoretical predictions. They provide essential information to constrain cosmic-ray propagation models.

  10. Carbon and Hydrogen Stable Isotope Fractionation Associated with the Aerobic and Anaerobic Degradation of Saturated and Alkylated Aromatic Hydrocarbons.

    PubMed

    Musat, Florin; Vogt, Carsten; Richnow, Hans H

    2016-01-01

    Saturated hydrocarbons (alkanes) and alkylated aromatic hydrocarbons are abundant environmental compounds. Hydrocarbons are primarily removed from the environment by biodegradation, a process usually associated with moderate carbon and significant hydrogen isotope fractionation allowing monitoring of biodegradation processes in the environment. Here, we review the carbon and hydrogen stable isotope fractionation associated with the cleavage of C-H bonds at alkyl chains of hydrocarbons. Propane, n-butane and ethylbenzene were used as model components for alkyl moieties of aliphatic and aromatic hydrocarbons with emphasis on the cleavage of the C-H bond without the involvement of molecular oxygen. The carbon and hydrogen isotope fractionation factors were further used to explore the diagnostic potential for characterizing the mode of bond cleavage under oxic and anoxic conditions. x039B; factors, calculated to correlate carbon and hydrogen fractionation, allowed to distinguish between aerobic and anaerobic biodegradation processes in the environment.

  11. Dissociative Adsorption of Hydrogen and Oxygen on Palladium Clusters:  A Comparison with the (111) Infinite Surface.

    PubMed

    Roques, Jérôme; Lacaze-Dufaure, Corinne; Mijoule, Claude

    2007-05-01

    We report a density-functional study of some properties of the dissociative interaction of hydrogen and oxygen molecules on small palladium clusters (n = 5, 7, and 10). The calculated physisorption and chemisorption energies are compared with those of the infinite (111) palladium surface. First, adsorption of atomic hydrogen and oxygen is investigated on the Pd5, Pd7, and Pd10 clusters. Second, the interaction between H2 (O2) and the small Pd5 cluster is examined and compared to the process occurring on an infinite (111) surface. Finally, the simultaneous adsorption of two hydrogen (oxygen) atoms is analyzed in detail. As shown in a previous work, the binding energy of the first hydrogen (oxygen) atom does not depend significantly on the cluster size, and small two-layer clusters (n ≤ 10) can be used to determine with accuracy the interaction of atomic adsorbates with an infinite (111) palladium surface. In this study, we show that the dissociative chemisorption of H2 and more especially of O2 on a small palladium cluster may lead to erroneous binding energy:  the cluster's size may prevent an accurate description of the adsorbate-adsorbate interaction as a function of their distance. It is demonstrated that a good choice of both the size and the shape of the cluster is preponderant for a good description of the dissociative adsorption of H2 and O2 on an infinite (111) surface.

  12. Collective vibrational effects in hydrogen bonded liquid amides and proteins studied by isotopic substitution

    NASA Astrophysics Data System (ADS)

    Nielsen, O. F.; Johansson, C.; Christensen, D. H.; Hvidt, S.; Flink, J.; Høime Hansen, S.; Poulsen, F.

    2000-09-01

    Raman spectroscopy is used to study the fast dynamics of simple liquid amides and proteins. Raman spectra in the visible region of liquid amides are obtained with a triple additive scanning monochromator, whereas FT-Raman technique is used in the near-IR region in order to avoid fluorescence from impurities in the proteins. Raman spectra are shown in the amide-I region of HCONHCH 3 ( N-methylformamide with all isotopes in their natural abundance), H 13CONHCH 3, HC 18ONHCH 3, human growth hormone, frog tropomyosin and chymotrypsin inhibitor 2 including C-13 and N-15 enriched samples of the latter. Resonance energy transfer (RET) between amide molecules gives rise to a non-coincidence effect of the anisotropic and the isotropic components of the amide-I band. This effect influences the band position in mixtures of liquid amide isotopomers. A further spectral feature caused by collective vibrational modes in the hydrogen bonded liquid amides is named coalescence of bands in mixtures of isotopomers (CBMI). The result of this effect is that only one band is found in mixtures of isotopomers where bands at different frequencies are observed for each of the isotopomers. A similar effect may account for the observation of protein amide-I bands with frequencies dependent only on the secondary structure of the protein and not on the amino acid residues. RET and CBMI are due to a collectivity of vibrational modes in different amide molecules. This collectivity may be related to a cooperativity of hydrogen bonds. A low-frequency band around 100 cm -1 is observed in hydrogen bonded liquid amides and proteins. Isotopic substitution shows that the mode corresponding to this band involves displacements of atoms in hydrogen bonds. This mode may drive a breaking of the hydrogen bond.

  13. Isotopic evidence for biogenic molecular hydrogen production in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Walter, S.; Kock, A.; Steinhoff, T.; Fiedler, B.; Fietzek, P.; Kaiser, J.; Krol, M. C.; Popa, M. E.; Chen, Q.; Tanhua, T.; Röckmann, T.

    2015-10-01

    Oceans are a net source of molecular hydrogen (H2) to the atmosphere. The production of marine H2 is assumed to be mainly biological by N2 fixation, but photochemical pathways are also discussed. We present measurements of mole fraction and isotopic composition of dissolved and atmospheric H2 from the southern and northern Atlantic between 2008 and 2010. In total almost 400 samples were taken during five cruises along a transect between Punta Arenas (Chile) and Bremerhaven (Germany), as well as at the coast of Mauretania. The isotopic source signatures of dissolved H2 extracted from surface water are highly deuterium-depleted and correlate negatively with temperature, showing δD values of (-629 ± 54) ‰ for water temperatures at (27 ± 3) °C and (-249 ± 88) ‰ below (19 ± 1) °C. The results for warmer water masses are consistent with biological production of H2. This is the first time that marine H2 excess has been directly attributed to biological production by isotope measurements. However, the isotope values obtained in the colder water masses indicate that beside possible biological production a significant different source should be considered. The atmospheric measurements show distinct differences between both hemispheres as well as between seasons. Results from the global chemistry transport model TM5 reproduce the measured H2 mole fractions and isotopic composition well. The climatological global oceanic emissions from the GEMS database are in line with our data and previously published flux calculations. The good agreement between measurements and model results demonstrates that both the magnitude and the isotopic signature of the main components of the marine H2 cycle are in general adequately represented in current atmospheric models despite a proposed source different from biological production or a substantial underestimation of nitrogen fixation by several authors.

  14. Isotopic evidence for biogenic molecular hydrogen production in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Walter, S.; Kock, A.; Steinhoff, T.; Fiedler, B.; Fietzek, P.; Kaiser, J.; Krol, M.; Popa, M. E.; Chen, Q.; Tanhua, T.; Röckmann, T.

    2016-01-01

    Oceans are a net source of molecular hydrogen (H2) to the atmosphere. The production of marine H2 is assumed to be mainly biological by N2 fixation, but photochemical pathways are also discussed. We present measurements of mole fraction and isotopic composition of dissolved and atmospheric H2 from the southern and northern Atlantic between 2008 and 2010. In total almost 400 samples were taken during 5 cruises along a transect between Punta Arenas (Chile) and Bremerhaven (Germany), as well as at the coast of Mauritania.

    The isotopic source signatures of dissolved H2 extracted from surface water are highly deuterium-depleted and correlate negatively with temperature, showing δD values of (-629 ± 54) ‰ for water temperatures at (27 ± 3) °C and (-249 ± 88) ‰ below (19 ± 1) °C. The results for warmer water masses are consistent with the biological production of H2. This is the first time that marine H2 excess has been directly attributed to biological production by isotope measurements. However, the isotope values obtained in the colder water masses indicate that beside possible biological production, a significant different source should be considered.

    The atmospheric measurements show distinct differences between both hemispheres as well as between seasons. Results from the global chemistry transport model TM5 reproduce the measured H2 mole fractions and isotopic composition well. The climatological global oceanic emissions from the GEMS database are in line with our data and previously published flux calculations. The good agreement between measurements and model results demonstrates that both the magnitude and the isotopic signature of the main components of the marine H2 cycle are in general adequately represented in current atmospheric models despite a proposed source different from biological production or a substantial underestimation of nitrogen fixation by several authors.

  15. Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal

    PubMed Central

    Sellick, Megan J.; Kyser, T. Kurt; Wunder, Michael B.; Chipley, Don; Norris, D. Ryan

    2009-01-01

    Background Isotopes can provide unique solutions to fundamental problems related to the ecology and evolution of migration and dispersal because prior movements of individuals can theoretically be tracked from tissues collected from a single capture. However, there is still remarkably little information available about how and why isotopes vary in wild animal tissues, especially over large spatial scales. Methodology/Principal Findings Here, we describe variation in both stable-hydrogen (δDF) and strontium (87Sr/86SrF) isotopic compositions in the feathers of a migratory songbird, the Tree Swallow (Tachycineta bicolor), across 18 sampling sites in North America and then examine potential mechanisms driving this variation. We found that δDF was correlated with latitude of the sampling site, whereas 87Sr/86SrF was correlated with longitude. δDF was related to δD of meteoric waters where molting occurred and 87Sr/86SrF was influenced primarily by the geology in the area where feathers were grown. Using simulation models, we then assessed the utility of combining both markers to estimate the origin of individuals. Using 13 geographic regions, we found that the number of individuals correctly assigned to their site of origin increased from less than 40% using either δD or 87Sr/86Sr alone to 74% using both isotopes. Conclusions/Significance Our results suggest that these isotopes have the potential to provide predictable and complementary markers for estimating long-distance animal movements. Combining isotopes influenced by different global-scale processes may allow researchers to link the population dynamics of animals across large geographic ranges. PMID:19266102

  16. Isotopic fractionation in proteins as a measure of hydrogen bond length

    SciTech Connect

    McKenzie, Ross H.; Athokpam, Bijyalaxmi; Ramesh, Sai G.

    2015-07-28

    If a deuterated molecule containing strong intramolecular hydrogen bonds is placed in a hydrogenated solvent, it may preferentially exchange deuterium for hydrogen. This preference is due to the difference between the vibrational zero-point energy for hydrogen and deuterium. It is found that the associated fractionation factor Φ is correlated with the strength of the intramolecular hydrogen bonds. This correlation has been used to determine the length of the H-bonds (donor-acceptor separation) in a diverse range of enzymes and has been argued to support the existence of short low-barrier H-bonds. Starting with a potential energy surface based on a simple diabatic state model for H-bonds, we calculate Φ as a function of the proton donor-acceptor distance R. For numerical results, we use a parameterization of the model for symmetric O–H⋯O bonds [R. H. McKenzie, Chem. Phys. Lett. 535, 196 (2012)]. We consider the relative contributions of the O–H stretch vibration, O–H bend vibrations (both in plane and out of plane), tunneling splitting effects at finite temperature, and the secondary geometric isotope effect. We compare our total Φ as a function of R with NMR experimental results for enzymes, and in particular with an earlier model parametrization Φ(R), used previously to determine bond lengths.

  17. Sulfur, carbon, hydrogen, and oxygen isotope geochemistry of the Idaho cobalt belt

    USGS Publications Warehouse

    Johnson, Craig A.; Bookstrom, Arthur A.; Slack, John F.

    2012-01-01

    Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ34S values are nearly uniform throughout the Blackbird dis- trict, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ (n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore for- mation as H2S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form vol- canogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit

  18. Dynamic behavior of hydrogen isotopes in tungsten-carbon composite materials

    NASA Astrophysics Data System (ADS)

    Horikawa, T.; Tsuchiya, B.; Morita, K.

    The thermal re-emission of hydrogen isotopes from WC layers on graphite, implanted with 5 keV H +2 and D +2 ion beams up to saturation at room temperature, has been studied by means of the elastic recoil detection (ERD) technique. It is found on isochronal annealing for 10 min that the re-emission takes place in three stages: the first stage occurs for retained fraction of 1.0-0.6, the second stage for retained fractions of 0.6-0.2 and the third stage below the retained fraction of 0.2, which is ascribed to re-emission from carbon segregated in the grain boundaries of the WC layers. It is also found on isothermal annealing that the concentration of retained hydrogen decreases rapidly in the beginning and hereafter very gradually with increasing the annealing time. The isothermal re-emission curves have been analyzed by taking into account the two trapping sites and the mass balance equations with two kinds of thermal detrapping ( Σd 1, Σd 2), retrapping (Σ t) and local molecular recombination ( K1) between free hydrogen atoms. The isotope difference of the rate constants for elementary processes determined by best fitting of the solution to the experimental re-emission profiles is discussed with relevance to the nature of two trapping sites.

  19. The setup of an extraction system coupled to a hydrogen isotopes distillation column

    SciTech Connect

    Zamfirache, M.; Bornea, A.; Stefanescu, I.; Bidica, N.; Balteanu, O.; Bucur, C.

    2008-07-15

    Among the most difficult problems of cryogenic distillation one stands apart: the extraction of the heavy fraction. By an optimal design of the cycle scheme, this problem could be avoided. A 'worst case scenario' is usually occurring when the extracted fraction consists of one prevalent isotope such as hydrogen and small amounts of the other two hydrogen isotopes (deuterium and/or tritium). This situation is further complicated by two parameters of the distillation column: the extraction flow rate and the hold-up. The present work proposes the conceptual design of an extraction system associated to the cryogenic distillation column used in hydrogen separation processes. During this process, the heavy fraction (DT, T{sub 2}) is separated, its concentration being the highest at the bottom of the distillation column. From this place the extraction of the gaseous phase can now begin. Being filled with adsorbent, the extraction system is used to temporarily store the heavy fraction. Also the extraction system provides samples for the gas Chromatograph. The research work is focused on the existent pilot plant for tritium and deuterium separation from our institute to validate the experiments carried out until now. (authors)

  20. Hydrogen isotopes in individual amino acids reflect differentiated pools of hydrogen from food and water in Escherichia coli

    PubMed Central

    Fogel, Marilyn L.; Griffin, Patrick L.; Newsome, Seth D.

    2016-01-01

    Hydrogen isotope (δ2H) analysis is widely used in animal ecology to study continental-scale movement because δ2H can trace precipitation and climate. To understand the biochemical underpinnings of how hydrogen is incorporated into biomolecules, we measured the δ2H of individual amino acids (AAs) in Escherichia coli cultured in glucose-based or complex tryptone-based media in waters with δ2H values ranging from −55‰ to +1,070‰. The δ2H values of AAs in tryptone spanned a range of ∼250‰. In E. coli grown on glucose, the range of δ2H among AAs was nearly 200‰. The relative distributions of δ2H of AAs were upheld in cultures grown in enriched waters. In E. coli grown on tryptone, the δ2H of nonessential AAs varied linearly with the δ2H of media water, whereas δ2H of essential AAs was nearly identical to δ2H in diet. Model calculations determined that as much as 46% of hydrogen in some nonessential AAs originated from water, whereas no more than 12% of hydrogen in essential AAs originated from water. These findings demonstrate that δ2H can route directly at the molecular level. We conclude that the patterns and distributions in δ2H of AAs are determined through biosynthetic reactions, suggesting that δ2H could become a new biosignature for studying novel microbial pathways. Our results also show that δ2H of AAs in an organism’s tissues provides a dual tracer for food and environmental (e.g., drinking) water. PMID:27444017

  1. Solubility of, and hydrogen ion adsorption on, some metal oxides in aqueous solutions to high temperatures

    SciTech Connect

    Palmer, D.A.; Benezeth, P.; Wesolowski, D.J.; Anovitz, L.M.; Machesky, M.L.; Hayashi, Ken-ichiro; Hyde, K.E.

    1997-08-01

    Solubility of boehmite (AlOOH), ferrous hydroxide (Fe(OH)2)/magnetite (Fe3O4), zincite (ZnO), and brucite (Mg(OH)2) were measured over a range of temperatures (AlOOH, 100-290 C; Fe(OH)2/Fe3O4, 100-250 C; ZnO, 50-290 C; Mg(OH)2, 60-200 C) using in situ pH measurements. A hydrogen-electrode concentration cell was used; the pH range depended on the oxide. The solubility results for boehmite mainly demonstrate the method viability, while those for zincite are mainly restricted to mildly acidic to neutral pH where Zn{sup 2+} predominates in solution. The magnetite (presumably coated with Fe(OH)2) solubilities extend from pHs > 5 and, because of relevance to water/steam cycles of power plants, are compared in detail with previous studies. The same cell was used to investigate the surface adsorption-desorption thermodynamics of H ions on rutile (TiO2) and zincite to 290 C. Behavior of pH at zero-point-of-charge as function of temperature and application of the Stern-3-layer model were determined for this solid. The zincite study is still incomplete; preliminary results show trends that can be rationalized only qualitatively now with the zero- point-of-charge being apparently affected by hydration of the surface in basic solutions and specific adsorption of Na ions under the same conditions.

  2. Hydrogen Isotopic Composition of Water in the Martian Atmosphere and Released from Rocknest Fines

    NASA Technical Reports Server (NTRS)

    Leshin, L. A.; Webster, C. R.; Mahaffy, P. R.; Flesh, G. J.; Christensen, L. E.; Stern, J. C.; Franz, H. B.; McAdam, A. C.; Niles, P. B.; Archer, P. B., Jr.; Sutter, B.; Jones, J. H.; Ming, D. W.; Atreya, S. K.; Owen, T. C.; Conrad, P.

    2013-01-01

    The Mars Science Laboratory Curiosity rover sampled the aeolian bedform called Rocknest as its first solid samples to be analyzed by the analytical instruments CheMin and SAM. The instruments ingested aliquots from a sieved sample of less than 150 micrometer grains. As discussed in other reports at this conference [e.g., 1], CheMin discovered many crystalline phases, almost all of which are igneous minerals, plus some 10s of percent of x-ray amorphous material. The SAM instrument is focused on understanding volatiles and possible organics in the fines, performing evolved gas analysis (EGA) with the SAM quadrapole mass spectrometer (QMS), isotope measurements using both the QMS and the tunable laser spectrometer (TLS), which is sensitive to CO2, water and methane, and organics with the gas chromatograph mass spectrometer (GCMS). As discussed in the abstract by Franz et al. [2] and others, EGA of Rocknest fines revealed the presence of significant amounts of H2O as well as O-, C- and S-bearing materials. SAM has also tasted the martian atmosphere several times, analyzing the volatiles in both the TLS and QMS [e.g., 3,4]. This abstract will focus on presentation of initial hydrogen isotopic data from the TLS for Rocknest soils and the atmosphere, and their interpretation. Data for CO2 isotopes and O isotopes in water are still being reduced, but should be available by at the conference.

  3. Carbon, hydrogen and nitrogen isotopes in solvent-extractable organic matter from carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Becker, R. H.; Epstein, S.

    1982-01-01

    CCl4 and CH3OH solvent extractions were performed on the Murray, Murchison, Orgueil and Renazzo carbonaceous chondrites. Delta-D values of +300-+500% are found in the case of the CH3OH-soluble organic matter. The combined C, H and N isotope data makes it unlikely that the CH3OH-soluble components are derivable from, or simply related to, the insoluble organic polymer found in the same meteorites. A relation between the event that formed hydrous minerals in CI1 and CM2 meteorites and the introduction of water- and methanol-soluble organic compounds is suggested. Organic matter soluble in CCl4 has no N, and delta-C-13 values are lower than for CH3OH-soluble phases. It is concluded that there either are large isotopic fractionations for carbon and hydrogen between different soluble organic phases, or the less polar components are partially of terrestrial origin.

  4. Stable-isotope ratios of hydrogen and oxygen in precipitation at Norman, Oklahoma, 1996-2008

    USGS Publications Warehouse

    Jaeschke, Jeanne B.; Scholl, Martha A.; Cozzarelli, Isabelle M.; Masoner, Jason R.; Christenson, Scott; Qi, Haiping

    2011-01-01

    Precipitation samples for measurement of stable-isotope ratios of hydrogen (delta2H) and oxygen (delta18O) were collected at the Norman Landfill Research Site in Norman, Oklahoma, from May 1996 to October 2008. Rainfall amounts also were measured at the site (U.S. Geological Survey gaging station 07229053) during the collection period. The delta2H of precipitation samples ranged from -121.9 to +8.3 per mil, and the delta18O of precipitation ranged from -16.96 to +0.50 per mil. The volume-weighted average values for delta2H and delta18O of precipitation over the 12-year measurement period were -31.13 per mil for delta2H and -5.57 per mil for delta18O. Average summer-season delta2H and delta18O values of precipitation usually were more positive (enriched in the heavier isotopes) than winter values.

  5. Systematics of isotopic production cross sections from interactions of relativistic {sup 40}Ca in hydrogen

    SciTech Connect

    Chen, C.; Guzik, T.G.; McMahon, M.; Wefel, J.P.; Albergo, S.; Caccia, Z.; Costa, S.; Insolia, A.; Potenza, R.; Russo, G.V.; Tuve, C.; Crawford, H.J.; Cronqvist, M.; Engelage, J.; Greiner, L.; Knott, C.N.; Waddington, C.J.; Lindstrom, P.J.; Tull, C.E.; Mitchell, J.W.; Webber, W.R.

    1997-09-01

    The isotopic production cross sections for {sup 40} Ca projectiles at 357, 565, and 763 MeV/nucleon interacting in a liquid hydrogen target have been measured by the Transport Collaboration at the LBL HISS facility. The systematics of these cross sections are studied, and the results indicate that nuclear structure effects are present in the isotope production process during the relativistic collisions. The newly measured cross sections are also compared with those predicted by semiempirical and parametric formulas, but the predictions do not fully describe the systematics such as the energy dependence. The consequences of the cross section systematics in galactic cosmic ray studies are also discussed. {copyright} {ital 1997} {ital The American Physical Society}

  6. BESS-Polar II Hydrogen and Helium Isotope Measurements to Constrain Cosmic-Ray Propagation Models

    NASA Astrophysics Data System (ADS)

    Picot-Clemente, Nicolas; BESS-Polar Collaboration

    2017-01-01

    The Balloon-borne Experiment with Superconducting Spectrometer BESS-Polar II flew over Antarctica for 24.5 days from December 2007 through January 2008, during the 23rd solar cycle minimum. The instrument is made of complementary particle detectors which allow to precisely measure the charge, velocity and rigidity of incoming cosmic rays. It can accurately separate cosmic-ray hydrogen and helium isotopes from 0.2 to 1.5 GeV/nucleon. Flux and secondary-to-primary ratios of these particles can bring important information to better understand the cosmic-ray propagation history in the Galaxy. BESS-Polar II provides the most precise isotope measurements to date between 0.2 and 1.5 GeV/nucleon. These data will be reported and constraints on cosmic-ray propagation models, using the GALPROP program, will be discussed.

  7. Hydrogen-isotope evidence for extrusion mechanisms of the Mount St Helens lava dome

    NASA Technical Reports Server (NTRS)

    Anderson, Steven W.; Fink, Jonathan H.

    1989-01-01

    Hydrogen isotope analyses were used to determine water content and deuterium content for 18 samples of the Mount St Helens dome dacite in an attempt to identify the triggering mechanisms for periodic dome-building eruptions of lava. These isotope data, the first ever collected from an active lava dome, suggest a steady-state process of magma evolution combining crystallization-induced volatile production in the chamber with three different degassing mechanisms: closed-system volatile loss in the magma chamber, open-system volatile release during ascent, and kinetically controlled degassing upon eruption at the surface. The data suggest the future dome-building eruptions may require a new influx of volatile-rich magma into the chamber.

  8. Hydrogen isotope measurement of bird feather keratin, one laboratory's response to evolving methodologies.

    PubMed

    Fan, Majie; Dettman, David L

    2015-01-01

    Hydrogen in organic tissue resides in a complex mixture of molecular contexts. Some hydrogen, called non-exchangeable (H(non)), is strongly bound, and its isotopic ratio is fixed when the tissue is synthesized. Other pools of hydrogen, called exchangeable hydrogen (H(ex)), constantly exchange with ambient water vapor. The measurement of the δ(2)H(non) in organic tissues such as hair or feather therefore requires an analytical process that accounts for exchangeable hydrogen. In this study, swan feather and sheep wool keratin were used to test the effects of sample drying and capsule closure on the measurement of δ(2)H(non) values, and the rate of back-reaction with ambient water vapor. Homogenous feather or wool keratins were also calibrated at room temperature for use as control standards to correct for the effects of exchangeable hydrogen on feathers. Total δ(2)H values of both feather and wool samples showed large changes throughout the first ∼6 h of drying. Desiccant plus low vacuum seems to be more effective than room temperature vacuum pumping for drying samples. The degree of capsule closure affects exchangeable hydrogen equilibration and drying, with closed capsules responding more slowly. Using one control keratin standard to correct for the δ(2)H(ex) value for a batch of samples leads to internally consistent δ(2)H(non) values for other calibrated keratins run as unknowns. When placed in the context of other recent improvements in the measurement of keratin δ(2)H(non) values, we make recommendations for sample handing, data calibration and the reporting of results.

  9. Sulfur and Hydrogen Isotope Anomalies in Organic Compounds from the Murchison Meteorite

    NASA Astrophysics Data System (ADS)

    Cooper, G. W.; Thiemens, M. H.; Jackson, T.; Chang, S.

    1995-09-01

    Carbon, hydrogen and sulfur isotopic measurements have been made on individual members of a recently discovered class of organic sulfur compounds, alkyl sulfonates, in the Murchison meteorite. Cooper and Chang (1) reported the first carbon isotopic measurements of Murchison organic sulfonates, providing insight into potential synthetic mechanisms of these, and possibly other, organic species. Hydrogen isotopic measurements of the sulfonates now reveal deuterium excesses ranging from +660 to +2730 per mil. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low temperature astrophysical environment consistent with that of dense molecular clouds. Measurement of the sulfur isotopes provide further constraints on the origin and mechanism of formation of these organic molecules. Recently, there has been growing documentation of sulfur isotopic anomalies in meteoritic material. Thiemens and Jackson (2) have shown that some bulk ureilites possess excess 33S and Thiemens et al. (3) have reported excess 33S in an oldhamite separate from Norton County. Rees and Thode (4) reported a large 33S excess in an Allende acid residue, however, attempts to verify this measurement have been unsuccessful, possibly due to the heterogeneous nature of the carrier phase. With the recognition that sulfur isotopes may reflect nebular chemistry, identification of potential carriers is of considerable interest. In the present study the three stable isotopes of sulfur were measured in methane sulfonate extracted from the Murchison meteorite. The isotopic composition was found to be delta 33S=2.48, delta 34S=2.49 and delta 36S = 6.76 per mil. Based upon analysis of more than 60 meteoritic, and numerous terrestrial samples, the mass fractionation lines are defined by 33Delta = delta 33S-0.50 delta 34S and 36Delta = delta 36S -1.97 delta 34S. From these relations a 33Delta = 1.24 per mil and 36Delta = 0.89 per mil is observed. These anomalies

  10. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, Mickey R.

    1991-01-01

    The goal was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of the degradation process. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. Modern advanced aerospace applications often require the use of structural materials in high pressure hydrogen environments at temperatures which range from low cryogenic temperatures to very high temperatures (1300 K and greater). Materials proposed for these applications, such as the titanium aluminides, beta-titanium alloys, nickel- and cobalt-based superalloys, molybdenum-rhenium alloys, beryllium, and various beryllides, need to possess a high degree of immunity from hydrogen induced degradation of mechanical properties. In the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak, in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in

  11. Carbon and hydrogen isotope fractionation by microbial methane oxidation: Improved determination

    SciTech Connect

    Mahieu, Koenraad . E-mail: Koenraad.Mahieu@Ugent.be; Visscher, Alex De; Vanrolleghem, Peter A.; Cleemput, Oswald Van

    2006-07-01

    Isotope fractionation is a promising tool for quantifying methane oxidation in landfill cover soils. For good quantification an accurate determination of the isotope fractionation factor ({alpha}) of methane oxidation based on independent batch experiments with soil samples from the landfill cover is required. Most studies so far used data analysis methods based on approximations of the Rayleigh model to determine {alpha}. In this study, the two most common approximations were tested, the simplified Rayleigh approach and the Coleman method. To do this, the original model of Rayleigh was described in measurable variables, methane concentration and isotopic abundances, and fitted to batch oxidation data by means of a weighted non-linear errors-in-variables regression technique. The results of this technique were used as a benchmark to which the results of the two conventional approximations were compared. Three types of batch data were used: simulated data, data obtained from the literature, and data obtained from new batch experiments conducted in our laboratory. The Coleman approximation was shown to be acceptable but not recommended for carbon fractionation (error on {alpha} - 1 up to 5%) and unacceptable for hydrogen fractionation (error up to 20%). The difference between the simplified Rayleigh approach and the exact Rayleigh model is much smaller for both carbon and hydrogen fractionation (error on {alpha} - 1 < 0.05%). There is also a small difference when errors in both variables (methane concentration and isotope abundance) are accounted for instead of assuming an error-free independent variable. By means of theoretical calculations general criteria, not limited to methane, {sup 13}C, or D, were developed for the validity of the simplified Rayleigh approach when using labelled compounds.

  12. Hydrogen isotope systematics of phase separation in submarine hydrothermal systems: Experimental calibration and theoretical models

    USGS Publications Warehouse

    Berndt, M.E.; Seal, R.R.; Shanks, Wayne C.; Seyfried, W.E.

    1996-01-01

    Hydrogen isotope fractionation factors were measured for coexisting brines and vapors formed by phase separation of NaCl/H2O fluids at temperatures ranging from 399-450??C and pressures from 277-397 bars. It was found that brines are depleted in D compared to coexisting vapors at all conditions studied. The magnitude of hydrogen isotope fractionation is dependent on the relative amounts of Cl in the two phases and can be empirically correlated to pressure using the following relationship: 1000 ln ??(vap-brine) = 2.54(??0.83) + 2.87(??0.69) x log (??P), where ??(vap-brine) is the fractionation factor and ??P is a pressure term representing distance from the critical curve in the NaCl/H2O system. The effect of phase separation on hydrogen isotope distribution in subseafloor hydrothermal systems depends on a number of factors, including whether phase separation is induced by heating at depth or by decompression of hydrothermal fluids ascending to the seafloor. Phase separation in most subseafloor systems appears to be a simple process driven by heating of seawater to conditions within the two-phase region, followed by segregation and entrainment of brine or vapor into a seawater dominated system. Resulting vent fluids exhibit large ranges in Cl concentration with no measurable effect on ??D. Possible exceptions to this include hydrothermal fluids venting at Axial and 9??N on the East Pacific Rise. High ??D values of low Cl fluids venting at Axial are consistent with phase separation taking place at relatively shallow levels in the oceanic crust while negative ??D values in some low Cl fluids venting at 9??N suggest involvement of a magmatic fluid component or phase separation of D-depleted brines derived during previous hydrothermal activity.

  13. Influence of thermal maturity on the hydrogen isotope content of extractable hydrocarbons

    NASA Astrophysics Data System (ADS)

    Radke, J.; Bechtel, A.; Püttmann, W.; Gleixner, G.

    2003-04-01

    Based on hydrogen isotope analysis of hydrocarbons from recent sediments it is suggested that compound specific hydrogen isotope ratios are a new proxy to reconstruct the palaeoclimate (Sauer et al., 2001). However, it remains unclear if transformation of carbon bound hydrogen with environmental water during maturation or thermal methanogenesis might influence the observed values. Short-term experiments excluded exchange reactions of deuterium from alkanes (Schimmelmann et al., 1999), however, thermally stressed kerogens are enriched in deuterium (Schoell, 1984). Therefore, we investigated the influence of maturity on the deltaD-values of alkanes and acyclic isoprenoids. In the Kupferschiefer horizon from the Polish Zechstein Basin thermal maturity of organic matter is correlated to burial depth yielding a natural long-term exchange experiment. The deltaD-values of extracted hydrocarbons linearly correlated with thermal maturity. These results enable the correction of deltaD values from biomarkers with known maturity and therefore expanding palaeoclimatic reconstructions using deltaD values to the geological past. References: SAUER, P.E., EGLINTON, T.I., HAYES, J.M., SCHIMMELMANN, A. &SESSIONS, A.L. (2001) Compound specific D/H ratios of lipid biomarkers from sediments as a proxy for environmental and climatic conditions. Geochimica et Cosmochimica Acta, 65(2), 213-222. SCHIMMELMANN, A., LEWAN, M.D. &WINTSCH, R.P. (1999) D/H isotope ratios of kerogen, bitumen, oil, and water in hydrous pyrolysis of source rocks containing kerogen types I, II, IIS, and III. Geochimica et Cosmochimica Acta, 63(22), 3751-3766. SCHOELL, M. (1984) Wasserstoff- und Kohlenstoffisotope in organischen Substanzen, Erdölen und Erdgasen. Schweitzerbart'sche Verlagsbuchhandlung, Stuttgart. Reihe D (67), 161pp.

  14. Hydrogen isotopic compositions of organic compounds in plants reflect the plant's carbon metabolism

    NASA Astrophysics Data System (ADS)

    Cormier, M. A.; Kahmen, A.; Werner, R. A.

    2015-12-01

    The main factors controlling δ2H of plant organic compounds are generally assumed to be the plant's source water and the evaporative deuterium enrichment of leaf water. Hydrogen isotope analyses of plant compounds from sediments or tree rings are therefore mainly applied to assess hydrological conditions at different spatial and temporal scales. However, the biochemical hydrogen isotope fractionation occurring during biosynthesis of plant organic compounds (ɛbio) also accounts for a large part of the variability observed in the δ2H values. Nevertheless, only few studies have directly addressed the physiological basis of this variability and even fewer studies have thus explored possible applications of hydrogen isotope variability in plant organic compounds for plant physiological research. Here we show two datasets indicating that the plant's carbon metabolism can have a substantial influence on δ2H values of n-alkanes and cellulose. First, we performed a controlled experiment where we forced plants into heterotrophic and autotrophic C-metabolism by growing them under four different light treatments. Second, we assessed the δ2H values of different parasitic heterotrophic plants and their autotrophic host plants. Our two datasets show a systematic shift in ɛbio of up to 80 ‰ depending on the plant's carbon metabolism (heterotrophic or autotrophic). Differences in n-alkane and cellulose δ2H values in plants with autotrophic vs. heterotrophic metabolisms can be explained by different NADPH pools that are used by the plants to build their compounds either with assimilates that originate directly from photosynthesis or from stored carbohydrates. Our results have significant implications for the calibration and interpretation of geological records. More importantly, as the δ2H values reflect the plant's carbon metabolism involved during the tissue formation, our findings highlight the potential of δ2H values as new tool for studying plant and ecosystem carbon

  15. Water masses along the OVIDE 2010 section as identified by oxygen and hydrogen stable isotope values

    NASA Astrophysics Data System (ADS)

    Voelker, Antje; Salgueiro, Emilia; Thierry, Virginie

    2016-04-01

    The OVIDE transect between the western Iberian Peninsula and the southern tip of Greenland is one of the hydrographic sections in the North Atlantic that is measured regularly to identify changes in water mass formation and transport and thus to evaluate the state of the Atlantic Meridional Overturning Circulation (Mercier et al., 2015; García-Ibáñez et al., 2015; both in Progr. in Oceanography). During the OVIDE 2010 campaign seawater samples covering the complete water column were collected on the section between Portugal and the Reykjanes ridge for stable isotope analyses. Oxygen (δ18O) and hydrogen (δD) stable isotope values were measured simultaneously by cavity ring-down laser spectroscopy using a L1102-i Picarro water isotope analyser at the Godwin Laboratory for Paleoclimate Research (Univ. Cambridge, UK). Within the upper water column the stable isotope values clearly mark the positions of the Portugal Current (40.3°N 11°W), the North Atlantic Drift (46.2°N 19.4°W) and of the subarctic front (51°N 23.5°W). Up to Station 36 (47.7°N 20.6°W) an upper (around 600 m) and lower (around 1000 m) branch of the Mediterranean Outflow water (MOW) can clearly be distinguished by high oxygen (0.5-0.7‰) and hydrogen (3-5‰) values. At Station 28 (42.3°N 15.1°W) strong MOW influence is also indicated between 1400 and 1600 m. In the west European Basin, lower oxygen isotope values reveal the presence of Labrador Sea Water (LSW) below the MOW (down to 2200 m). Close to and west of the subarctic front this water mass shallows and occupies the complete interval between 1000 and 2000 m water depth. In the Iceland basin, two additional levels with lower oxygen isotope values are observed. The deeper level (2200-3500 m) marks Iceland Scotland Overflow Water (ISOW) that based on its distinct isotopic signature (δ18O ≤ 0.25‰) can be traced as far east as 18.5°W (down to at least 3500 m). Close to the Reykjanes ridge both, the ISOW and LSW, are also

  16. The relationship between microstructure and hydrogen isotopes in the Wildhorse detachment, Pioneer Mountains, Idaho

    NASA Astrophysics Data System (ADS)

    McFadden, R. R.; Mulch, A.; Teyssier, C.; Seaton, N. C.; Tokle, L.

    2010-12-01

    The Pioneer migmatite-cored metamorphic core complex in south-central Idaho is bounded by the N-dipping Wildhorse Detachment fault, a low-angle normal fault that separates low-grade metasediments and volcanics from amphibolite facies metasediments, migmatites, and granites. The complex developed during the Eocene owing to extensional deformation and emplacement of magma and partially molten rocks. The core rocks were subsequently exhumed along the Wildhorse detachment in Eocene time. Within the detachment, a 100 m thick section of mica- and K-feldspar-bearing mylonitic quartzite contains NW-trending stretching lineations indicating top-to-the-NW sense of shear. We present combined microstructure and stable isotope data from a transect across the quartzite section to evaluate the relationship among microstructure development, strain localization, and fluid-rock interaction. Microstructure and EBSD data from quartz in conjunction with hydrogen stable isotope data and electron microprobe data on biotite and white mica suggest a systematic relationship between fluid flow and strain. EBSD analyses indicate a significant component of simple shear deformation, with prominent asymmetry of c- and a-axes patterns consistent with top-to-the-NW sense of shear. Synkinematic white mica and biotite deltaD values from the quartzite samples form two groups with highly negative deltaD values of ca. -145 per mil and -120 per mil, respectively. Microstructural observations show distinct differences between the two groups delineated by the hydrogen isotope analyses. The more negative group is characterized by intensely deformed and recrystallized quartz with very small recrystallized grains. The less negative group generally shows microstructures consistent with regime 2 deformation (quartz ribbons and large quartz grains flattened in the foliation). Micas are coarser in the less negative group than in the more negative group. Hydrogen stable isotope ratios of syntectonic hydrous

  17. Practically convenient and industrially-aligned methods for iridium-catalysed hydrogen isotope exchange processes.

    PubMed

    Cochrane, A R; Idziak, C; Kerr, W J; Mondal, B; Paterson, L C; Tuttle, T; Andersson, S; Nilsson, G N

    2014-06-14

    The use of alternative solvents in the iridium-catalysed hydrogen isotope exchange reaction with developing phosphine/NHC Ir(I) complexes has identified reaction media which are more widely applicable and industrially acceptable than the commonly employed chlorinated solvent, dichloromethane. Deuterium incorporation into a variety of substrates has proceeded to deliver high levels of labelling (and regioselectivity) in the presence of low catalyst loadings and over short reaction times. The preparative outputs have been complemented by DFT studies to explore ligand orientation, as well as solvent and substrate binding energies within the catalyst system.

  18. Gas Feeding System Supplying the U-400M Cyclotron Ion Source with Hydrogen Isotopes

    NASA Astrophysics Data System (ADS)

    Yukhimchuk, A. A.; Antilopov, V. V.; Apasov, V. A.; Vinogradov, Yu. I.; Golubkov, A. N.; Gornostaev, Ye. V.; Grishechkin, S. K.; Demin, A. M.; Zlatoustovski, S. V.; Klevtsov, V. G.; Kuryakin, A. V.; Malkov, I. N.; Musyaev, R. K.; Pustovoi, V. I.; Bekhterev, V. V.; Bogomolov, S. L.; Gulbekian, G. G.; Yefremov, A. A.; Zelenak, A.; Leporis, M.; Loginov, V. N.; Oganessian, Yu. Ts.; Pashchenko, S. V.; Rodin, A. M.; Smirnov, Yu. I.; Ter-Akopian, G. M.; Yazvitski, N. Yu.

    2005-09-01

    Automated system feeding into ion source hydrogen isotopes as molecules with preset ratio of the fluxes is described. The control system automatically maintained the working parameters and provided graphic and digital representation of the controlled processes. The radiofrequency (RF) ion source installed at the axial injection line of the cyclotron produced ion beams of HD+, HT+, DT+, D2H+, etc. At a several months DT+ beam acceleration the tritium consumption was less than 108 Bq/hr. The intensity of a 58.2 MeV triton beam (T+ ions) extracted from the cyclotron chamber was about 10 nA.

  19. Multiple Uses of Hydrogen Isotopes as a Tracer of Rehydration Processes in Glassy Lavas

    NASA Astrophysics Data System (ADS)

    Cameron, B. I.; Fink, J. H.; Guan, Y.; Leshin, L. A.

    2001-12-01

    Silicic lava flows contain zones of enhanced vesicularity with high total H2O contents. This relationship between volatile content and vesicularity has promoted the monitoring of active lava domes using remote sensing techniques in an effort to forecast explosive activity. A persistent complication in attempts to relate surface texture to H2O content and explosivity was the confounding effect of meteoric H2O. Glassy and vesicular lavas exposed at the surface of the Earth for prolonged periods readily interact with meteoric H2O. Rehydration is a time-, temperature-, and porosity-dependent process governed by the slow diffusion of molecular H2O into the glass. This inevitable addition of secondary H2O obscures the spatial distribution of juvenile H2O in lava flows. The ability to distinguish magmatic from meteoric H2O in glassy lavas would help identify regions of overpressure on active domes and thereby improve hazard assessment. Three types of hydrogen isotopic studies of glassy lavas have been utilized to disentangle rehydration processes from primary magmatic ones. First, bulk hydrogen isotopic data on variably textured lava flows reveal enrichments in both δ D and total H2O as vesicularity increases. Mixing between a degassed magmatic and a partially evaporated meteoric H2O best explains the observed trend from lower δ D values in the interior massive obsidian samples to higher δ D in the most surficial vesicular pumice. Second, step-heated hydrogen isotopic analyses further prove that the vesicular samples contain a high percentage of meteoric H2O. Whereas dense massive obsidian samples release a large fraction of deuterium-depleted H2O at temperatures above 600° C, the bubble-rich pumiceous samples lose a majority of their H2O at temperatures below 400° C. Lastly, the Cameca 6f ion microprobe at ASU was used to measure hydrogen isotope transects into the vesicle-melt interface. The gradation from depleted δ D values in the glassy interstices to more

  20. Hydrogen isotope exchange in tungsten: Discussion as removal method for tritium

    NASA Astrophysics Data System (ADS)

    Roth, J.; Schwarz-Selinger, T.; Alimov, V. Kh.; Markina, E.

    2013-01-01

    Hydrogen isotope exchange in re-crystallized polycrystalline tungsten was investigated at 320 and 450 K. In a first step the tungsten samples were loaded with deuterium to a fluence of 1024 D/m2 from a low-temperature plasma at 200 eV/D particle energy. In a second step, H was implanted at the same particle energy and similar target temperature with a mass-separated ion beam at different ion fluences ranging from 2 × 1020 to 7.5 × 1023 H/m2. The analytic methods used were nuclear reaction analysis with D(3He,p)α reaction and elastic recoil detection analysis with 4He. In order to determine the D concentration at depths of up to 7.4 μm the 3He energy was varied from 0.5 to 4.5 MeV. It was found that already at an H fluence of 2 × 1020 H/m2, i.e. at 1/5000 of the initial D fluence, about 30% of the retained D was released. Depth profiling of D without and with subsequent H implantation shows strong replacement close to the surface at 320 K, but extending to all analyzable depths at 450 K especially at high fluences, leading to higher release efficiency. The reverse sequence of hydrogen isotopes allowed the analysis of the replacing isotope and showed that the release of D is balanced by the uptake of H. It also shows that hydrogen does not diffuse through a region of filled traps into a region were unfilled traps can be encounter but transport is rather a dynamic process of trapping and de-trapping even at 320 K. Initial D retention in H loaded W is an order of magnitude higher than in pristine W, indicating that every H-containing trap is a potential trap for D. In consequence, hydrogen isotope exchange is not a viable method to significantly enhance the operation time before the tritium inventory limit is reached but should be considered an option to reduce the tritium inventory in ITER before major interventions at the end of an operation period.

  1. Climatic implications of an 8000-year hydrogen isotope time series from bristlecone pine trees

    SciTech Connect

    Feng, X.; Epstein, S. )

    1994-08-19

    Tree rings from three dendrochronologically dated bristlecone pines were analyzed for stable hydrogen isotopic composition. These trees give a continuous time series from 8000 years ago to the present that indicates the presence of a postglacial climate optimum 6800 years ago and a continuous cooling since then. The qualitative agreement between this record and records from other sources, such as ice cores, pollen, and treeline fluctuations, indicates that these climate changes were global. This record can serve as a reference for other climate indicators throughout the past 8000 years.

  2. About Tagish Lake as a Potential Parent Body for Polar Micrometeorites; Clues from their Hydrogen Isotopic Compositions

    NASA Technical Reports Server (NTRS)

    Engrand, C.; Gounelle, M.; Zolensky, M. E.; Duprat, J.

    2003-01-01

    The origin of the Antarctic micrometeorites (AMMs) is still a matter of debate. Their closest meteoritic counterparts are the C2 chondrites, but the match is not perfect, and the parent body(ies) of the AMMs is(are) still to be identified. Tagish Lake is a new meteorite fall which bears similarity with CI1 and CM2 chondrites, but is distinct from both. Based on the mineralogy of phyllosilicates, Noguchi et al. proposed that the phyllosilicate-rich AMMs and the Tagish Lake meteorites could derive from similar asteroids. The hydrogen isotopic compositions of extra-terrestrial samples can be used to get some insight on their origin. The D/H ratios of AMMs and of Tagish Lake have been measured, but using different analytical techniques. They are therefore not directly comparable. We performed additional hydrogen isotopic analyses of fragments of Tagish Lake using the same experimental setup previously used for the measurement of the hydrogen isotopic composition of AMMs. In this work, we could also analyze separately both lithologies of Tagish Lake (carbonate-poor and -rich). The distributions of delta D values measured in the two lithologies of Tagish Lake are very similar, indicating that fluids with similar hydrogen isotopic compositions altered the meteorite on the parent body for the two lithologies. Yet, the hydrogen isotopic composition of Tagish Lake is different from that of AMMs, suggesting that they do not derive from the same parent body.

  3. Low-temperature adsorption/storage of hydrogen on FAU, MFI, and MOR zeolites with various Si/Al ratios: effect of electrostatic fields and pore structures.

    PubMed

    Jhung, Sung Hwa; Yoon, Ji Woong; Lee, Ji Sun; Chang, Jong-San

    2007-01-01

    Several zeolites, such as faujasite, mordenite, and ZSM-5, with various aluminum contents have been used to analyze the effect of aluminum or cation concentration (strength of electrostatic field) on hydrogen adsorption at low temperature. Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (-DeltaHads), surface coverage, and micropore occupancy increase with increasing aluminum content of a zeolite. Zeolites with a higher amount of aluminum favorably adsorb hydrogen at relatively low pressures. For zeolites with similar aluminum contents, the adsorption capacity, isosteric heat of adsorption, surface coverage, and micropore occupancy are in the order of mordenite>ZSM-5>faujasite, probably due to differing pore sizes and the presence or absence of pore intersections. This work demonstrates that zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.

  4. Solar flare accelerated isotopes of hydrogen and helium. [observed by IMP-4 and IMP-5

    NASA Technical Reports Server (NTRS)

    Anglin, J. D.; Dietrich, W. F.; Simpson, J. A.

    1973-01-01

    Measurements of solar flare hydrogen, deuterium, tritium, helium-3, and helium-4 in the energy range approximately 10 to 50 MeV per nucleon obtained with instrumentation on the IMP-4 and IMP-5 satellites are reported and studies based on these results which place several constraints on theories of solar flare particle acceleration are discussed. A brief review of previous work and the difficulties in studying the rare isotopes of hydrogen and helium is also included. Particular emphasis is placed on the fact that the information to be obtained from the solar flare products of high energy interactions is not available through either solar wind observations where both the acceleration mechanism and the coronal source of the nuclear species are different, or optical measurements of solar active regions.

  5. Multisample conversion of water to hydrogen by zinc for stable isotope determination

    USGS Publications Warehouse

    Kendall, C.; Coplen, T.B.

    1985-01-01

    Two techniques for the conversion of water to hydrogen for stable isotope ratio determination have been developed that are especially suited for automated multisample analysis. Both procedures involve reaction of zinc shot with a water sample at 450 ??C. in one method designed for water samples in bottles, the water is put in capillaries and is reduced by zinc in reaction vessels; overall savings in sample preparation labor of 75% have been realized over the standard uranium reduction technique. The second technique is for waters evolved under vacuum and is a sealed-tube method employing 9 mm o.d. quartz tubing. Problems inherent with zinc reduction include surface inhomogeneity of the zinc and exchange of hydrogen both with the zinc and with the glass walls of the vessels. For best results, water/zinc and water/glass surface area ratios of vessels should be kept as large as possible.

  6. Insight into chemoselectivity of nitroarene hydrogenation: A DFT-D3 study of nitroarene adsorption on metal surfaces under the realistic reaction conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Lidong; Cao, Xiao-Ming; Hu, P.

    2017-01-01

    The adsorption of nitrobenzene and 4-nitrostyrene on the Pt(111) and the Au(111) surfaces under the general reaction condition of nitroarene catalytic hydrogenation is investigated utilizing periodic density functional theory calculations with the Grimme's empirical three-body dispersion correction to understand the influence of adsorption configurations on chemoselectivity of nitroarene compound hydrogenation. It is found that at the low coverage both nitrobenzene and 4-nitrostyrene tend to adsorb paralleling to the Pt(111) and the Au(111) surfaces. Based on the crystal orbital Hamilton population analysis, it is found that the chemical bonding between nitro group and Pt(111) surface is weak. The adsorption configurations of nitrobenzene and 4-nitrostyrene are determined by the chemisorption strength of phenyl group and vinyl group. Under the reaction condition, the 1/9 ML nitrobenzene and 4/9 ML hydrogen atom can be coadsorbed while the 1/6 ML 4-nitrostyrene and 1/3 ML hydrogen atom can be coadsorbed on Pt(111). With the increase of the coverage, nitrobenzene still remains its paralleled adsorption configuration while the adsorption configuration of 4-nitrostyrene is switched to the tilted adsorption configuration through vinyl group without the chemisorption of phenyl and nitro group on Pt(111). In addition, the competitive adsorption with hydrogen will not change the adsorption configuration of nitrobenzene and 4-nitrostyrene under the reaction condition. On Au(111), the physical adsorption strength determines the adsorption configuration. The paralleled adsorption with the shortest average distance between the adsorbate and Au(111) surface is preferred. At the paralleled adsorption configuration, the chemoselectivities of the hydrogenation on these functional groups are similar if only in terms of geometric configuration. However, the hydrogenation on nitro group encounters the problem of steric hindrance at the tilted adsorption configuration through vinyl

  7. Does transpiration matter to the hydrogen isotope ratios of leaf wax n-alkanes? (Invited)

    NASA Astrophysics Data System (ADS)

    McInerney, F. A.; Helliker, B. R.; Freeman, K. H.

    2010-12-01

    Transpiration and evaporation from soils both affect he hydrogen isotope composition of leaf water, but the extent to which they effect the hydrogen isotope ratio of leaf wax lipids is still under debate. To address this question, we analyzed hydrogen isotope ratios of high-molecular weight n-alkanes (δDl) and oxygen isotope ratios of α-cellulose (δ18OC) for C3 and C4 grasses grown in the field and in controlled-environment growth chambers. The relatively firm understanding of 18O-enrichment in leaf water and α-cellulose was used to elucidate fractionation patterns of δDl signatures. In the different relative humidity environments of the growth chambers, we observed clear and predictable effects of leaf-water enrichment on δ18OC values. Using a Craig-Gordon model, we demonstrate that leaf water in the growth chamber grasses should have experienced significant D-enriched due to transpiration. Nonetheless, we found no effect of transpirational D-enrichment on the δDl values. In field samples, we saw clear evidence of enrichment (correlating with relative humidity of the field sites) in both δ18OC and δDl. These seemingly contrasting results can be explained if leaf waxes are synthesized in an environment that is isotopically similar to water entering plant roots due to either temporal or spatial isolation from evaporatively enriched leaf waters. For grasses in the controlled environment, there was no enrichment of source water, whereas enrichment of grass source water via evaporation from soils and/or stems was likely for grass samples grown in the field. Based on these results, evaporation from soils and/or stems appears to affect δDl, but transpiration from leaves does not. Further evidence for this conclusion is found in modeling expected net evapotranspirational enrichment. A Craig-Gordon model applied to each of the field sites yields leaf water oxygen isotope ratios that can be used to accurately predict the observed δ18OC values. In contrast, the

  8. Expanded porous MOF-505 analogue exhibiting large hydrogen storage capacity and selective carbon dioxide adsorption.

    PubMed

    Zheng, Baishu; Yun, Ruirui; Bai, Junfeng; Lu, Zhiyong; Du, Liting; Li, Yizhi

    2013-03-18

    An expanded 4,4-paddlewheel-connected porous MOF-505-type metal-organic framework (MOF), [Cu2(PDEB)(H2O)2]·xS (NJU-Bai12; NJU-Bai represents the Nanjing University Bai group and S represents noncoordinated solvent molecules) has been designed from a nanosized rectangular diisophthalate linker containing alkyne groups 5,5'-(1,4-phenylenedi-2,1-ethynediyl)bis(1,3-benzenecarboxylic acid). This MOF material possesses permanent microporosity with the highest Brunauer-Emmett-Teller surface area of 3038 m(2)·g(-1) and the largest unsaturated total hydrogen storage capacity of 62.7 mg·g(-1) at 77 K and 20 bar among reported MOF-505 analogues. Additionally, NJU-Bai12 also exhibits excellent carbon dioxide (CO2) uptake capacity (23.83 and 19.85 mmol·g(-1) at 20 bar for 273 and 298 K, respectively) and selective gas adsorption properties with CO2/CH4 selectivity of 5.0 and CO2/N2 selectivity of 24.6 at room temperature.

  9. Isotopic effect of parametric instabilities during lower hybrid waves injection into hydrogen/deuterium plasmas

    NASA Astrophysics Data System (ADS)

    Zhao, Aihui; Gao, Zhe

    2017-01-01

    Based on the local dispersion relation, the parametric instability (PI) was numerically investigated for the injection of lower hybrid waves (LHWs) into hydrogen and deuterium plasmas separately. Numerical calculations under typical scrape-off layer parameters in tokamak plasmas show that both the unstable regions of the PI and the values of growth rates are close for two cases, in spite of the decaying channel of the ion sound quasimode or ion cyclotron quasimode (ICQM). These numerical results could be understood by the analyses based on the fluid model. Parameter dependences are also similar for hydrogen and deuterium plasmas. For example, the ICQM growth rate increases with an increasing density, a decreasing temperature, and a decreasing magnetic field in deuterium plasmas as it does in hydrogen plasmas. The isotopic effect of the PI during the LHW injection is weak. As a result, the lower hybrid current drive efficiency at a high density in deuterium plasmas cannot be much improved over hydrogen plasmas if the PI process dominates the behavior of LHWs at the plasma edge.

  10. 3d-transition metal induced enhancement of molecular hydrogen adsorption on Mg(0001) surface: An Ab-initio study

    NASA Astrophysics Data System (ADS)

    Banerjee, Paramita; Das, G. P.

    2016-05-01

    In our effort to do first principles design of suitable materials for hydrogen storage, we have explored the interaction characteristics of a hydrogen molecule with pure as well as a 3d-transition metal (TM) atom doped Mg(0001) surface using density functional theory (DFT) based approach. Doping of a 3d-TM atom by creating a vacancy on the top most layer of Mg(0001) surface, enhances the molecular hydrogen adsorption efficiency of this surface by ~ 6 times. The TM atom gains some charge from the defected site of the Mg(0001) surface, becomes anionic and adsorbs the hydrogen molecule via Anti Kubas-type interaction. The interaction energy of this H2 molecule, including van der Waals dispersion correction, turns out to be ~ 0.4 eV, which falls in the right energy window between physisorption and chemisorption. On full coverage of this 3d-TM atom doped Mg(0001) surface with hydrogen molecules, the gravimetric density of hydrogen has been estimated to be ~ 5.6 wt %, thereby satisfying the criteria set by the department of energy (DOE) for efficient hydrogen storage.

  11. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, Mickey R.

    1994-01-01

    The goal of this program has been to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. During the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak. Weak in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in hydrogen while gamma titanium aluminide exhibits less degradation and beryllium essentially no degradation. The interaction of oxygen with the surface of several of these materials was studied. More recently, preliminary hydrogen permeation studies were completed for three high temperature alloys, Incoloy 909, Mo-47.5Re (wt. %), and this past year, Haynes 188.

  12. Stable hydrogen-isotope ratios in beetle chitin: preliminary European data and re-interpretation of North American data

    NASA Astrophysics Data System (ADS)

    Gröcke, Darren R.; Schimmelmann, Arndt; Elias, Scott; Miller, Randall F.

    2006-08-01

    Beetle exoskeletons contain chitin, a poly amino-sugar that is biosynthesized incorporating hydrogen isotopes from diet and water. As the stable isotope ratios D/H (or 2H/ 1H, expressed as δ D values) of precipitation and diet are jointly influenced by climate, the biochemically recorded hydrogen-isotope ratio in fossil beetle exoskeleton has the potential to be used for paleoclimatic reconstruction. New δ D data from modern beetles are presented as a preliminary database for Europe, with a re-evaluation of earlier North American data. We present correlated matrices of δ D values in modern beetle chitin and modern precipitation to demonstrate the concept. We review the pertinent literature to highlight the history, utility, and likely future research directions for the use of chitin's stable isotopes in entomological paleoclimatology.

  13. The fractionation factors of stable carbon and hydrogen isotope ratios for VOCs

    NASA Astrophysics Data System (ADS)

    Kawashima, H.

    2014-12-01

    Volatile organic compounds (VOCs) are important precursors of ozone and secondary organic aerosols in the atmosphere, some of which are carcinogenic, teratogenic, or mutagenic. VOCs in ambient air originate from many sources, including vehicle exhausts, gasoline evaporation, solvent use, natural gas emissions, and industrial processes, and undergo intricate chemical reactions in the atmosphere. To develop efficient air pollution remediation strategies, it is important to clearly identify the emission sources and elucidate the reaction mechanisms in the atmosphere. Recently, stable carbon isotope ratios (δ13C) of VOCs in some sources and ambient air have been measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). In this study, we measured δ13C and stable hydrogen isotope ratios (δD) of atmospheric VOCs by using the gas chromatography/thermal conversion/isotope ratio mass spectrometry coupled with a thermal desorption instrument (TD-GC/TC/IRMS). The wider δD differences between sources were found in comparison with the δ13C studies. Therefore, determining δD values of VOCs in ambient air is potentially useful in identifying VOC sources and their reactive behavior in the atmosphere. However, to elucidate the sources and behavior of atmospheric VOCs more accurately, isotopic fractionation during atmospheric reaction must be considered. In this study, we determined isotopic fractionation of the δ13C and δD values for the atmospheric some VOCs under irradiation conditions. As the results, δ13C for target all VOCs and δD for most VOCs were increasing after irradiation. But, the δD values for both benzene and toluene tended to decrease as irradiation time increased. We also estimated the fractionation factors for benzene and toluene, 1.27 and 1.05, respectively, which differed from values determined in previous studies. In summary, we were able to identify an inverse isotope effect for the δD values of benzene and toluene

  14. Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Spruijt, Evan; Biesheuvel, P. M.; de Vos, Wiebe M.

    2015-01-01

    We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N -vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3 kBT per PVP segment at low p H . As the p H increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical p H . Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O2 plasma, we find that the former have a significantly higher density of silanol groups.

  15. Analysis of hydrogen adsorption and surface binding configuration on tungsten using direct recoil spectrometry

    DOE PAGES

    Kolasinski, R. D.; Hammond, K. D.; Whaley, J. A.; ...

    2014-12-03

    In our work, we apply low energy ion beam analysis to examine directly how the adsorbed hydrogen concentration and binding configuration on W(1 0 0) depend on temperature. We exposed the tungsten surface to fluxes of both atomic and molecular H and D. We then probed the H isotopes adsorbed along different crystal directions using 1–2 keV Ne+ ions. At saturation coverage, H occupies two-fold bridge sites on W(1 0 0) at 25 °C. Moreover, the H coverage dramatically changes the behavior of channeled ions, as does reconstruction of the surface W atoms. For the exposure conditions examined here, wemore » find that surface sites remain populated with H until the surface temperature reaches 200 °C. Then, we observe H rapidly desorbing until only a residual concentration remains at 450 °C. Development of an efficient atomistic model that accurately reproduces the experimental ion energy spectra and azimuthal variation of recoiled H is underway.« less

  16. Analysis of hydrogen adsorption and surface binding configuration on tungsten using direct recoil spectrometry

    NASA Astrophysics Data System (ADS)

    Kolasinski, R. D.; Hammond, K. D.; Whaley, J. A.; Buchenauer, D. A.; Wirth, B. D.

    2015-08-01

    In this work, we apply low energy ion beam analysis to examine directly how the adsorbed hydrogen concentration and binding configuration on W(1 0 0) depend on temperature. We exposed the tungsten surface to fluxes of both atomic and molecular H and D. We then probed the H isotopes adsorbed along different crystal directions using 1-2 keV Ne+ ions. At saturation coverage, H occupies two-fold bridge sites on W(1 0 0) at 25 °C. The H coverage dramatically changes the behavior of channeled ions, as does reconstruction of the surface W atoms. For the exposure conditions examined here, we find that surface sites remain populated with H until the surface temperature reaches 200 °C. After this point, we observe H rapidly desorbing until only a residual concentration remains at 450 °C. Development of an efficient atomistic model that accurately reproduces the experimental ion energy spectra and azimuthal variation of recoiled H is underway.

  17. Turnover of oxygen and hydrogen isotopes in the body water, CO 2, hair, and enamel of a small mammal

    NASA Astrophysics Data System (ADS)

    Podlesak, David W.; Torregrossa, Ann-Marie; Ehleringer, James R.; Dearing, M. Denise; Passey, Benjamin H.; Cerling, Thure E.

    2008-01-01

    Oxygen and hydrogen isotope signatures of animal tissues are strongly correlated with the isotope signature of local precipitation and as a result, isotope signatures of tissues are commonly used to study resource utilization and migration in animals and to reconstruct climate. To better understand the mechanisms behind these correlations, we manipulated the isotope composition of the drinking water and food supplied to captive woodrats to quantify the relationships between drinking water ( δdw), body water ( δbw), and tissue ( δt). Woodrats were fed an isotopically constant food but were supplied with isotopically depleted or enriched water. Some animals were switched between these waters, allowing simultaneous determination of body water turnover, isotope change recorded in teeth and hair, and fractional contributions of atmospheric O 2, drinking water, and food to the oxygen and hydrogen budgets of the animals. The half-life of the body water turnover was 3-6 days. A mass balance model estimated that drinking water, atmospheric O 2, and food were responsible for 56%, 30%, and 15% of the oxygen in the body water, respectively. Drinking water and food were responsible for 71% and 29% of the hydrogen in the body water, respectively. Published generalized models for lab rats and humans accurately estimated δbw, as did an updated version of a specific model for woodrats. The change in drinking water was clearly recorded in hair and tooth enamel, and multiple-pool and tooth enamel forward models closely predicted these changes in hair and enamel, respectively. Oxygen and hydrogen atoms in the drinking water strongly influence the composition of the body water and tissues such as hair and tooth enamel; however, food and atmospheric O 2 also contribute oxygen and/or hydrogen atoms to tissue. Controlled experiments allow researchers to validate models that estimate δt based on δdw and so will increase the reliability of estimates of resource utilization and climate

  18. Comparable hydrogen isotopic fractionation of plant leaf wax n-alkanoic acids in arid and humid subtropical ecosystems

    NASA Astrophysics Data System (ADS)

    Gao, Li; Zheng, Mei; Fraser, Matthew; Huang, Yongsong

    2014-02-01

    Leaf wax hydrogen isotope proxies have been widely used to reconstruct past hydrological changes. However, published reconstructions have given little consideration for the potentially variable hydrogen isotopic fractionation relative to precipitation (ɛwax-p) under different climate and environmental settings. Chief among various potential factors controlling fractionation is relative humidity, which is known to strongly affect oxygen isotopic ratios of plant cellulose, but its effect on hydrogen isotopic fractionation of leaf waxes is still ambiguous. Analyses of lake surface sediments and individual modern plants have provided valuable information on the variability of ɛwax-p, but both approaches have significant limitations. Here, we present an alternative method to obtain the integrated, time-resolved ecosystem-level ɛwax-p values, by analyzing modern aerosol samples collected weekly from arid (Arizona lowlands) and humid subtropical (Atlanta, Georgia) environments during the main growth season. Because aerosol samples mainly reflect regional leaf wax resources, the extreme contrast in the hydroclimate and associated vegetation assemblages between our study sites allows us to rigorously assess the impact of relative humidity and associated vegetation assemblages on leaf wax hydrogen isotopic fractionation. We show there is only minor difference (mostly <10‰) in the mean ɛwax-p values in the two end-member environments. One possible explanation is that the positive isotopic effects of low relative humidity are offset by progressive replacement of trees with grasses that have a more negative apparent fractionation. Our results represent an important step toward quantitative interpretation of leaf wax hydrogen isotopic records.

  19. Long-term stability of hydrogen isotope ratios in hydrated volcanic glass

    NASA Astrophysics Data System (ADS)

    Cassel, Elizabeth J.; Breecker, Daniel O.

    2017-03-01

    The advancement of conceptual and numerical geodynamic models necessitates quantitative, orogen-scale paleoelevation data. Felsic volcanic glasses, which record the hydrogen isotope compositions (δD) of meteoric water shortly after deposition, provide several advantages as a paleoelevation proxy. Questions remain, however, about the reliability of this relatively new proxy, including the effect of hydrofluoric (HF) acid abrasion in the preparation of glass shards for hydrogen isotope analysis and the stability of hydrogen isotope ratios in hydrated glass shards over geologic time (106-107 years). HF acid abrasion of natural ancient glass shards results in systematic shifts in glass δD values away from modern water δD values. To evaluate the effectiveness of HF acid abrasion, we treated 70-150 μm glass shards separated from various natural tephras with deuterium-labeled water (DLW; δD = +18,205‰) for up to 400 days. For all glasses, this treatment resulted in elevated δD values in comparison to untreated samples. HF acid abrasion after DLW exposure, however, removed this effect and restored glass shards to their original untreated δD values in samples older than 104 years. HF acid abrasion removes hydrous alteration precipitates at the glass surface without measurably changing the δD values of the underlying hydrated glass, regardless of abrasion duration or glass composition. Additionally, 45-34 Ma glasses record δD values that directly reflect their depositional environments as determined by stratigraphy: glasses from tuffs deposited in demonstrably evaporative lacustrine environments have relatively high δD values compared to glasses from contemporaneous tuffs deposited in nearby fluvial environments, which have much lower δD values. The preservation of δD values that systematically vary with original depositional environment, despite >30 Myr of post-hydration exposure to the same meteoric water, indicates that these volcanic glasses resisted

  20. Hydrogen-isotopic variability in fatty acids from Yellowstone National Park hot spring microbial communities

    NASA Astrophysics Data System (ADS)

    Osburn, Magdalena R.; Sessions, Alex L.; Pepe-Ranney, Charles; Spear, John R.

    2011-09-01

    We report the abundances and hydrogen-isotopic compositions (D/H ratios) of fatty acids extracted from hot-spring microbial mats in Yellowstone National Park. The terrestrial hydrothermal environment provides a useful system for studying D/H fractionations because the numerous microbial communities in and around the springs are visually distinct, separable, and less complex than those in many other aquatic environments. D/H fractionations between lipids and water ranged from -374‰ to +41‰ and showed systematic variations between different types of microbial communities. Lipids produced by chemoautotrophic hyperthermophilic bacteria, such as icosenoic acid (20:1), generally exhibited the largest and most variable fractionations from water (-374‰ to -165‰). This was in contrast to lipids characteristic of heterotrophs, such as branched, odd chain-length fatty acids, which had the smallest fractionations (-163‰ to +41‰). Mats dominated by photoautotrophs exhibited intermediate fractionations similar in magnitude to those expressed by higher plants. These data support the hypothesis that variations in lipid D/H are strongly influenced by central metabolic pathways. Shifts in the isotopic compositions of individual fatty acids across known ecological boundaries show that the isotopic signature of specific metabolisms can be recognized in modern environmental samples, and potentially recorded in ancient ones. Considering all sampled springs, the total range in D/H ratios is similar to that observed in marine sediments, suggesting that the trends observed here are not exclusive to the hydrothermal environment.

  1. Isotope Dependence and Quantum Effects on Atomic Hydrogen Diffusion in Liquid Water.

    PubMed

    Walker, J A; Mezyk, S P; Roduner, E; Bartels, D M

    2016-03-03

    Relative diffusion coefficients were determined in water for the D, H, and Mu isotopes of atomic hydrogen by measuring their diffusion-limited spin-exchange rate constants with Ni(2+) as a function of temperature. H and D atoms were generated by pulse radiolysis of water and measured by time-resolved pulsed EPR. Mu atoms are detected by muonium spin resonance. To isolate the atomic mass effect from solvent isotope effect, we measured all three spin-exchange rates in 90% D2O. The diffusion depends on the atomic mass, demonstrating breakdown of Stokes-Einstein behavior. The diffusion can be understood using a combination of water "cavity diffusion" and "hopping" mechanisms, as has been proposed in the literature. The H/D isotope effect agrees with previous modeling using ring polymer molecular dynamics. The "quantum swelling" effect on muonium due to its larger de Broglie wavelength does not seem to slow its "hopping" diffusion as much as predicted in previous work. Quantum effects of both the atom mass and the water librations have been modeled using RPMD and a qTIP4P/f quantized flexible water model. These results suggest that the muonium diffusion is very sensitive to the Mu versus water potential used.

  2. Hydrogen isotope ratios of leaf wax n-alkanes in grasses are insensitive to transpiration

    NASA Astrophysics Data System (ADS)

    McInerney, Francesca A.; Helliker, Brent R.; Freeman, Katherine H.

    2011-01-01

    We analyzed hydrogen isotope ratios of high-molecular weight n-alkanes ( δD l) and oxygen isotope ratios of α-cellulose ( δ18O C) for C 3 and C 4 grasses grown in the field and in controlled-environment growth chambers. The relatively firm understanding of 18O-enrichment in leaf water and α-cellulose was used to elucidate fractionation patterns of δD l signatures. In the different relative humidity environments of the growth chambers, we observed clear and predictable effects of leaf-water enrichment on δ18O C values. Using a Craig-Gordon model, we demonstrate that leaf water in the growth chamber grasses should have experienced significant D-enriched due to transpiration. Nonetheless, we found no effect of transpirational D-enrichment on the δD l values. In field samples, we saw clear evidence of enrichment (correlating with relative humidity of the field sites) in both δ18O C and δD l. These seemingly contrasting results could be explained if leaf waxes are synthesized in an environment that is isotopically similar to water entering plant roots due to either temporal or spatial isolation from evaporatively enriched leaf waters. For grasses in the controlled environment, there was no enrichment of source water, whereas enrichment of grass source water via evaporation from soils and/or stems was likely for grass samples grown in the field. Based on these results, evaporation from soils and/or stems appears to affect δD l, but transpiration from leaves does not. Further evidence for this conclusion is found in modeling expected net evapotranspirational enrichment. A Craig-Gordon model applied to each of the field sites yields leaf water oxygen isotope ratios that can be used to accurately predict the observed δ18O C values. In contrast, the calculated leaf water hydrogen isotope ratios are more enriched than what is required to predict observed δD l values. These calculations lend support to the conclusion that while δ18O C reflects both soil

  3. Biochemical hydrogen isotope fractionation during biosynthesis in higher plants reflects carbon metabolism of the plant

    NASA Astrophysics Data System (ADS)

    Cormier, Marc-André; Kahmen, Ansgar

    2015-04-01

    Compound-specific isotope analyses of plant material are frequently applied to understand the response of plants to the environmental changes. As it is generally assume that the main factors controlling δ2H values in plants are the plant's source water and evaporative deuterium enrichment of leaf water, hydrogen isotope analyses of plant material are mainly applied regarding hydrological conditions at different time scales. However, only few studies have directly addressed the variability of the biochemical hydrogen isotope fractionation occurring during biosynthesis of organic compounds (ɛbio), accounting also for a large part in the δ2H values of plants but generally assumed to be constant. Here we present the results from a climate-controlled growth chambers experiment where tested the sensitivity of ɛbio to different light treatments. The different light treatments were applied to induce different metabolic status (autotrophic vs. heterotrophic) in 9 different plant species that we grew from large storage organs (e.g. tubers or roots). The results show a systematic ɛbio shift (up to 80 ) between the different light treatments for different compounds (i.e. long chain n-alkanes and cellulose). We suggest that this shift is due to the different NADPH pools used by the plants to build up the compounds from stored carbohydrates in heterotrophic or autotrophic conditions. Our results have important implications for the calibration and interpretation of sedimentary and tree rings records in geological studies. In addition, as the δ2H values reflect also strongly the carbon metabolism of the plant, our findings support the idea of δ2H values as an interesting proxy for plant physiological studies.

  4. Carbon and hydrogen isotope fractionation during nitrite-dependent anaerobic methane oxidation by Methylomirabilis oxyfera

    NASA Astrophysics Data System (ADS)

    Rasigraf, Olivia; Vogt, Carsten; Richnow, Hans-Hermann; Jetten, Mike S. M.; Ettwig, Katharina F.

    2012-07-01

    Anaerobic oxidation of methane coupled to nitrite reduction is a recently discovered methane sink of as yet unknown global significance. The bacteria that have been identified to carry out this process, Candidatus Methylomirabilis oxyfera, oxidize methane via the known aerobic pathway involving the monooxygenase reaction. In contrast to aerobic methanotrophs, oxygen is produced intracellularly and used for the activation of methane by a phylogenetically distinct particulate methane monooxygenase (pMMO). Here we report the fractionation factors for carbon and hydrogen during methane oxidation by an enrichment culture of M. oxyfera bacteria. In two separate batch incubation experiments with different absolute biomass and methane contents, the specific methanotrophic activity was similar and the progressive isotope enrichment identical. Headspace methane was consumed up to 98% with rates showing typical first order reaction kinetics. The enrichment factors determined by Rayleigh equations were -29.2 ± 2.6‰ for δ13C (εC) and -227.6 ± 13.5‰ for δ2H (εH), respectively. These enrichment factors were in the upper range of values reported so far for aerobic methanotrophs. In addition, two-dimensional specific isotope analysis (Λ = ( α H - 1 - 1)/( α C - 1 - 1)) was performed and also the determined Λ value of 9.8 was within the range determined for other aerobic and anaerobic methanotrophs. The results showed that in contrast to abiotic processes biological methane oxidation exhibits a narrow range of fractionation factors for carbon and hydrogen irrespective of the underlying biochemical mechanisms. This work will therefore facilitate the correct interpretation of isotopic composition of atmospheric methane with implications for modeling of global carbon fluxes.

  5. [Hydrogen and Oxygen Isotopic Compositions of Precipitation and Its Water Vapor Sources in Eastern Qaidam Basin].

    PubMed

    Zhu, Jian-jia; Chen, Hui; Gong, Guo-li

    2015-08-01

    Stable hydrogen and oxygen isotopes can be used as a tracer to analyze water vapor sources of atmospheric precipitation. We choose Golmud and Delingha as our study areas, Golmud locates in the south of Qaidam basin, and Delingha locates in the northeast. Based on the analysis of monthly change of hydrogen and oxygen isotopic compositions of precipitation during June to September of 2010, and the relationship between deltaD and delta18O in precipitation, we investigated the water vapor sources of precipitation in eastern Qaidam basin. The results show that: (1) meteoric water line between June to September in Golmud is: deltaD = 7.840 delta18O - 4.566 (R2 = 0.918, P < 0.001), and in Delingha is: deltaD = 7.833 delta18O + 8.606 (R2 = 0.986, P < 0.001). The slopes and intercepts of meteoric water line between June to September in both Golmud and Delingha are lower than the global average, and the intercept in Golmud is only -4.566, which indicates the extremely arid climate condition. (2) the delta18O content of precipitation is much higher in Golmud in early July, it shows the enrichment of some heavier isotopes. However, the delta18O content of precipitation becomes lower from late July to early September, especially for the late September. The 8180 content of precipitation in Delingha is higher in June to August than that in late September. (3) the water vapor sources of precipitation in Golmud and Delingha are different, Golmud area is the northern border of Qinghai-Tibet Plateau where the southwest monsoon can reach, and the southwest monsoon brings water vapors of precipitation, but the water vapors of precipitation in Delingha are mainly from local evaporation.

  6. Geochemistry and origin of formation waters in the western Canada sedimentary basin-I. Stable isotopes of hydrogen and oxygen

    USGS Publications Warehouse

    Hitchon, B.; Friedman, I.

    1969-01-01

    Stable isotopes of hydrogen and oxygen, together with chemical analyses, were determined for 20 surface waters, 8 shallow potable formation waters, and 79 formation waters from oil fields and gas fields. The observed isotope ratios can be explained by mixing of surface water and diagenetically modified sea water, accompanied by a process which enriches the heavy oxygen isotope. Mass balances for deuterium and total dissolved solids in the western Canada sedimentary basin demonstrate that the present distribution of deuterium in formation waters of the basin can be derived through mixing of the diagenetically modified sea water with not more than 2.9 times as much fresh water at the same latitude, and that the movement of fresh water through the basin has redistributed the dissolved solids of the modified sea water into the observed salinity variations. Statistical analysis of the isotope data indicates that although exchange of deuterium between water and hydrogen sulphide takes place within the basin, the effect is minimized because of an insignificant mass of hydrogen sulphide compared to the mass of formation water. Conversely, exchange of oxygen isotopes between water and carbonate minerals causes a major oxygen-18 enrichment of formation waters, depending on the relative masses of water and carbonate. Qualitative evidence confirms the isotopic fractionation of deuterium on passage of water through micropores in shales. ?? 1969.

  7. Hydrogen bonding at the water surface revealed by isotopic dilution spectroscopy.

    PubMed

    Stiopkin, Igor V; Weeraman, Champika; Pieniazek, Piotr A; Shalhout, Fadel Y; Skinner, James L; Benderskii, Alexander V

    2011-06-08

    The air-water interface is perhaps the most common liquid interface. It covers more than 70 per cent of the Earth's surface and strongly affects atmospheric, aerosol and environmental chemistry. The air-water interface has also attracted much interest as a model system that allows rigorous tests of theory, with one fundamental question being just how thin it is. Theoretical studies have suggested a surprisingly short 'healing length' of about 3 ångströms (1 Å = 0.1 nm), with the bulk-phase properties of water recovered within the top few monolayers. However, direct experimental evidence has been elusive owing to the difficulty of depth-profiling the liquid surface on the ångström scale. Most physical, chemical and biological properties of water, such as viscosity, solvation, wetting and the hydrophobic effect, are determined by its hydrogen-bond network. This can be probed by observing the lineshape of the OH-stretch mode, the frequency shift of which is related to the hydrogen-bond strength. Here we report a combined experimental and theoretical study of the air-water interface using surface-selective heterodyne-detected vibrational sum frequency spectroscopy to focus on the 'free OD' transition found only in the topmost water layer. By using deuterated water and isotopic dilution to reveal the vibrational coupling mechanism, we find that the free OD stretch is affected only by intramolecular coupling to the stretching of the other OD group on the same molecule. The other OD stretch frequency indicates the strength of one of the first hydrogen bonds encountered at the surface; this is the donor hydrogen bond of the water molecule straddling the interface, which we find to be only slightly weaker than bulk-phase water hydrogen bonds. We infer from this observation a remarkably fast onset of bulk-phase behaviour on crossing from the air into the water phase.

  8. Hydrogen isotope fractionation between C-H-O species in magmatic fluids

    NASA Astrophysics Data System (ADS)

    Foustoukos, D. I.; Mysen, B. O.

    2012-12-01

    Constraining the hydrogen isotope fractionation between H-bearing volatiles (e.g. H2, CH4, hydrocarbons, H2O) as function of temperature and pressure helps to promote our understanding of the isotopic composition of evolved magmatic fluids and the overall mantle-cycling of water and reduced C-O-H volatiles. To describe the thermodynamics of the exchange reactions between the different H/D isotopologues of H2 and CH4 under supercritical water conditions, a novel experimental technique has been developed by combining vibrational Raman spectroscopy with hydrothermal diamond anvil cell designs (HDAC), which offers a method to monitor the in-situ evolution of H/D containing species. To this end, the equilibrium relationship between H2-D2-HD in supercritical fluid was investigated at temperatures ranging from 300 - 800 oC and pressures ~ 0.3 - 1.3 GPa [1]. Experimental results obtained in-situ and ex-situ show a significant deviation from the theoretical values of the equilibrium constant predicted for ideal-gas reference state, and with an apparent negative temperature effect triggered by the enthalpy contributions due to mixing in supercritical water. Here, we present a series of HDAC experiments conducted to evaluate the role of supercritical water on the isotopic equilibrium between H/D methane isotopologues at 600 - 800 oC and 409 - 1622 MPa. In detail, tetrakis-silane (Si5C12H36) was reacted with H2O-D2O aqueous solution in the presence of either Ni or Pt metal catalyst, resulting to the formation of deuterated methane species such as CH3D, CHD3, CH2D2 and CD4. Two distinctly different set of experiments ("gas phase"; "liquid phase") were performed by adjusting the silane/water proportions. By measuring the relative intensities of Raman vibrational modes of species, experimental results demonstrate distinctly different thermodynamic properties for the CH4-CH3D-CHD3-CH2D2 equilibrium in gas and liquid-water-bearing systems. In addition, the D/H molar ratio of

  9. Emissions of molecular hydrogen (H2) and its isotopic signature from residential heaters and waste incinerators

    NASA Astrophysics Data System (ADS)

    Vollmer, M. K.; Walter, S.; Mohn, J.; Steinbacher, M.; Bond, S. W.; Roeckmann, T.; Reimann, S.

    2011-12-01

    Atmospheric molecular hydrogen (H2) has recently received increased interest in the scientific community because of a potential shift to a global hydrogen energy economy which could potentially alter the atmospheric budget of H2 due to substantial leakage. This calls for an improved understanding of the present day's atmospheric H2 budget. One of the major sources of H2 are emissions from incomplete combustion of fossil fuel. While emissions of H2 from car exhaust have been studied extensively, those from fossil fuel based heating systems have remained a matter of speculation. Here we present results from measurements of a variety of residential heating systems covering oil, gas, and wood heating with various burner capacities. For oil and gas heating systems we surprisingly find no net H2 emissions, i.e. the exhaust air contains H2 at or below the mole fractions of the intake air (approx. 0.5 ppm). While H2 emissions are virtually absent, those of carbon monoxide (CO) are not. As a consequence, caution has to be exercised when modeling H2 emissions based on assumed H2/CO ratios and using CO emission inventories. We also find that the molecular hydrogen in the approx. 0.5 ppm exhaust air is isotopically strongly depleted (-20 permil to -200 permil) compared to the ambient air (+130 permil). This suggests that H2 is involved in the combustion processes, and therefore the H2 of the intake air is not the same H2 in the exhaust air. Exhausts from waste incinerator plants are generally also depleted in H2 mole fractions and in their H/D isotopic composition.

  10. MEASUREMENT OF THE ISOTOPIC COMPOSITION OF HYDROGEN AND HELIUM NUCLEI IN COSMIC RAYS WITH THE PAMELA EXPERIMENT

    SciTech Connect

    Adriani, O.; Bongi, M.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Bruno, A.; Boezio, M.; Bonvicini, V.; Carbone, R.; Bogomolov, E. A.; Borisov, S.; Casolino, M.; De Pascale, M. P.; Bottai, S.; Cafagna, F.; Campana, D.; Carlson, P.; Castellini, G.; Danilchenko, I. A.; De Santis, C.; and others

    2013-06-10

    The satellite-borne experiment PAMELA has been used to make new measurements of cosmic ray H and He isotopes. The isotopic composition was measured between 100 and 600 MeV/n for hydrogen and between 100 and 900 MeV/n for helium isotopes over the 23rd solar minimum from 2006 July to 2007 December. The energy spectrum of these components carries fundamental information regarding the propagation of cosmic rays in the galaxy which are competitive with those obtained from other secondary to primary measurements such as B/C.

  11. Hydrogen and oxygen isotope constraints on hydrothermal alteration of the Trinity peridotite, Klamath Mountains, California

    USGS Publications Warehouse

    Liakhovitch, V.; Quick, J.E.; Gregory, R.T.

    2005-01-01

    The Trinity peridotite represents a rare opportunity to examine a relatively fertile plagioclase peridotite that was exhumed and later subjected to intrusive events in a seafloor environment, followed by its emplacement and incorporation into a continent. Over 250 stable isotopic determinations on whole rocks and minerals elucidate the hydrothermal evolution of the Trinity complex. All three serpentine polymorphs are present in the Trinity peridotite; these separate on the basis of their ??D values: antigorite, -46 < ??D < -82??? and lizardite and chrysotile, -90 < ??D < -106 and -110 < ??D < -136???, respectively. Antigorite coexists with chlorite, talc, and tremolite in contact aureole assemblages associated with Silurian/Devonian gabbroic plutons. Lizardite and chrysotile alteration carries a meteoric signature, which suggests association with post-emplacement serpentinization, or overprinting of earlier low-temperature seafloor serpentinization. Regionally, contours of ??D values exhibit bull's-eye patterns associated with the gabbroic plutons, with ??D maxima coinciding with the blackwall alteration at the margins on the plutons. In contrast to the hydrogen isotope behavior, oxygen isotope values of the three polymorphs are indistinguishable, spanning the range 5.3 < ??18O< 7.5, and suggesting low integrated fluid fluxes and strongly 18O-shifted fluids. Inferred primary ?? 18O values for peridotite, gabbro, and late Mesozoic granodiorite indicate a progressive 18O enrichment with time for the source regions of the rocks. These isotopic signatures are consistent with the geology, petrochemistry, and geochronology of the Trinity massif, which indicate the following history: (1) lithospheric emplacement and cooling of the peridotite in an oceanic environment ??? 472 Ma; (2) intrusion of gabbroic plutons into cold peridotite in an arc environment between 435 and 404 Ma; and finally (3) intrusion of felsic plutons between 171 and 127 Ma, long after the peridotite

  12. Effect of hydrogen adsorption on the electronic and optical properties of the Mg-doped O-terminated ZnO surface

    NASA Astrophysics Data System (ADS)

    Lahmer, Mohammed Ali; Guergouri, Kamel

    2015-03-01

    The effect of hydrogen adsorption on the electronic structures and optical properties of undoped and Mg-doped ZnO (000 1 bar) polar surface was investigated using the first principles method. The obtained results show that hydrogen adsorption is more favored on Mg doped-ZnO (000 1 bar) surface than onto the clean surface, and this makes Mg-doped ZnO and MgxZn1 - xO more efficient for H storage or gas sensing applications than undoped ZnO. On the other hand, our results show that the hydrogen adsorption on the Mg doped surface is energetically very preferable when the surface was prepared under O-rich conditions. We have also examined the effect of H adsorption on the optical properties of the surface.

  13. Enhanced reactive adsorption of hydrogen sulfide on the composites of graphene/graphite oxide with copper (hydr)oxychlorides.

    PubMed

    Mabayoje, Oluwaniyi; Seredych, Mykola; Bandosz, Teresa J

    2012-06-27

    Composites of copper (hydr)oxychlorides with graphite oxide or graphene were synthesized and used as adsorbents of hydrogen sulfide at dynamic conditions at ambient temperatures. The materials were extensively characterized before and after adsorption in order to link their performance to the surface features. X-ray diffraction, FTIR, thermal analysis, TEM, SEM/EDX, and adsorption of nitrogen were used. It was found that the composite with graphene has the most favorable surface features enhancing reactive adsorption of hydrogen sulfide. The presence of moisture in the H2S stream has a positive effect on the removal process owing to the dissociation process. H2S is retained on the surface via a direct replacement of OH groups and via acid-base reactions with the copper (hydr)oxide. Highly dispersed reduced copper species on the surface of the composite with graphene enhance activation of oxygen and cause formation of sulfites and sulfates. Higher conductivity of the graphene phase than that of graphite oxide helps in electron transfer in redox reactions.

  14. Stable hydrogen isotope composition of n-alkanes in urban atmospheric aerosols in Taiyuan, China

    NASA Astrophysics Data System (ADS)

    Bai, Huiling; Li, Yinghui; Peng, Lin; Liu, Xiangkai; Liu, Xiaofeng; Song, Chongfang; Mu, Ling

    2017-03-01

    The hydrogen isotope compositions (δD) of n-alkanes associated with particulate matter with a diameter of ≤10 μm from Taiyuan, China, during heating and non-heating periods were measured via gas chromatography-isotope ratio mass spectrometry to reveal the spatial and temporal characteristics of five functional zones and to provide another constraint on atmospheric pollutants. The δD values of n-C16 to n-C31 during the heating and non-heating periods ranged from -235.9‰ to -119.8‰ and from -231.3‰ to -129.2‰, respectively, but these similar spans had different distribution features. During the heating period, the δD distributions between non-central heating and commercial districts were consistent, as were those between residential and industrial districts; the n-alkanes came from two or more types of emission sources. Coal soot might be the primary local emission source, but not the only source. During the non-heating period, the n-alkanes of n-C16 to n-C20 were more depleted in D with the increasing carbon number in all functional zones, but there was no rule for n-C21 to n-C31. Specifically, coal soot and vehicle exhaust might be the primary sources of n-alkanes for non-central heating districts in the heating and non-heating periods, respectively, according to the δD distribution of n-C18 to n-C22; gasoline vehicle exhaust might be an n-alkane source, and the hydrogen isotope fractionation effect during the condensation process should be a pollution mechanism for the commercial district during the heating period; the δD distribution difference of n-C16 to n-C18 between the two periods in the residential and industrial districts was consistent, which indicates a similar source of fossil fuel combustion and a similar isotope fractionation effect during the non-heating period.

  15. Hydrogen adsorption induced antiferrodistortive distortion and metallization at the (001) surface of SrTiO{sub 3}

    SciTech Connect

    Yang, Yi; Lin, Chen-Sheng; Cheng, Wen-Dan

    2015-09-14

    SrTiO{sub 3} (STO) is attracting lots of research interests due to the rich physics and properties presented at its surfaces and the interfaces of STO with other transition metal oxides. Based on density functional theory methods, we have investigated the influence of hydrogen (H) atoms adsorption at the (001) surface of STO on the geometrical and electronic structures of the surface. We find that H adsorption induces significant antiferrodistortive (AFD) distortion of TiO{sub 6} octahedra at the surface. By calculating H adsorption energy, we show that AFD distortion makes a significant contribution to the stability of H adsorbed STO surfaces. The calculated energy position of O-H bond states by hybrid functional method is 9.9 eV below Fermi level, in agreement with experimental value of 10 eV. The electrons donated by H atoms first occupy several d{sub xy} bands and then start to fill in degenerate d{sub yz}/d{sub xz} bands, indicating the metallization of initially insulating STO. The band splitting and occupy sequence calculated here are consistent with recent angle-resolved photoemission spectroscopy experiments. Our results reveal that H adsorption changes the atomic and electronic structures and thus induce fascinating properties at the surface of STO.

  16. Hydrogen Isotope Fractation Between Water and Algal Lipids of Three Strains of Botryococcus braunii Under Controlled Conidtions

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Sachs, J. P.

    2004-12-01

    Understanding of precipitation anomaly variations is essential to the reconstruction of paleo-El Nino at the low latitudes. In enclosed lakes, where lake level is affected by the balance between precipitation and evaporation only, water δ D reflects precipitation patterns. Freshwater algae, which utilize lake water for photosynthesis, should incorporate such signal in the hydrogen isotopes of their tissues. However, a fundamental question still exits: do algal lipid biomarkers truly record lake water hydrogen isotopic ratios? We have measured hydrogen isotope fractionation by freshwater algae Botryococcus braunii (3 strains) grown under controlled conditions in the lab. In order to establish a good relationship between lipid δ D and water δ D, for each strain we set up cultures in five waters with different δ D. δ D of alkadienes and botryococcenes of Botryococcus brauni measured on GCIRMS showed strong positive linear relation with water δ D (R2=0.99). Hydrogen isotopic ratios in the algal hydrocarbons are about 165 ‰ more negative compared to the water at the start while they are 270 ‰ more negative compared to water δ D at harvest. Such linear relationships establish a foundation for reconstructing lake water level and thus precipitation anomaly by analyzing δ D of algal lipids preserved in lake sediments.

  17. Method and means of reducing erosion of components of plasma devices exposed to helium and hydrogen isotope radiation

    DOEpatents

    Kaminsky, Manfred S.; Das, Santosh K.; Rossing, Thomas D.

    1977-01-25

    Surfaces of components of plasma devices exposed to radiation by atoms or ions of helium or isotopes of hydrogen can be protected from damage due to blistering by shielding the surfaces with a structure formed by sintering a powder of aluminum or beryllium and its oxide or by coating the surfaces with such a sintered metal powder.

  18. Seasonal Variations in the Biochemical Fractionation of Hydrogen Isotopes by Spartina alterniflora.

    NASA Astrophysics Data System (ADS)

    Sessions, A. L.

    2005-12-01

    Hydrogen isotope ratios (D/H) of lipids are being intensively explored as a paleoenvironmental proxy, particularly for continental regimes where organic preservation in lakes is generally high. Several studies have already shown good correlations between δD values of lake water and sedimentary (core-top) lipids, but the fractionations indicated by those correlations do not agree well between studies. Moreover, the data cannot be adequately described by a single biochemical fractionation. These difficulties suggest that the relationship between environmental water and plant lipid δD is controlled by multiple environmental and biochemical factors. Understanding these factors will lead to a more robust interpretation of D/H as a paleoclimate proxy. Here we examine seasonal changes in biochemical H-isotopic fractionation by the salt marsh grass Spartina alterniflora. Because S. alterniflora grows partially submerged in a tidal estuary, it has an unlimited and isotopically unvarying source of water for growth. Thus environmental influences on fractionation should be negligible, allowing us to examine seasonal changes in biochemical fractionations. C27 and C29 n-alkanes, β-sitosterol, phytol, and C16 and C18 fatty acids were extracted and analyzed from 35 samples of S. alterniflora harvested from the same location over a period of 18 months. All lipids except β-sitosterol exhibit statistically significant depletions of D during summer months relative to the rest of the year. The magnitude of the isotopic shift is up to 36‰ in the fatty acids (δD values from -130 to -166‰), 31‰ in n-alkanes (-161 to -192‰), and 24‰ in phytol (-252 to -276‰). The shift in D/H ratio is in the opposite direction from that expected due to increased evapotranspiration during the summer months. The largest D-depletions coincide with periods of maximal growth. The observed pattern is interpreted as resulting from increased use of stored carbohydrates as substrates for lipid

  19. Photoinduced adsorption of hydrogen and methane on gamma-alumina. the photoinduced chesorluminescence (PhICL) effect.

    PubMed

    Andreev, N S; Emeline, A V; Polikhova, S V; Ryabchuk, V K; Serpone, N

    2004-01-06

    Adsorption of hydrogen and methane on a preirradiated surface of gamma-Al2O3 produces an afterglow, which has been described as a photoinduced chesorluminescence (PhICL), whose spectral features identify with the intrinsic photoluminescence of alumina. The emission spectrum consists of at least four overlapping single emission bands. For methane adsorption, the PhICL phenomenon is seen only if the solid is preirradiated in the presence of oxygen. Emission decay kinetics of the PhICL effect for gamma-Al2O3 reveal two wavelength regimes: a short wavelength regime at lambda = 300-370 nm (decay time tau = 1.1 +/- 0.2 s; signal width = 2.8 s), and a longer wavelength regime at lambda = 380-700 nm (decay time tau = 2.1 +/- 0.1 s; signal width = 4.3 s). A model is proposed in which there exist two different emission centers and, thus, two different pathways for emission decay. In the first, emission originates with electron trapping by such deep energy traps as anion vacancies {e- + Va --> F+ + hv1} to yield electron F-type color centers, whereas in the second, emission originates from electron/trapped hole recombination {e- + Os*- --> Os2- + hv2}. The first common step of the pathways is homolytic dissociative chemisorption of hydrogen and methane upon interaction with surface-active hole centers Os*-, produced upon preirradiation of alumina, to give atomic hydrogen H* and methyl radicals CH3*. Thermoprogrammed desorption spectra of photoadsorbed or postsorbed oxygen show that adsorbed oxygen interacts with atomic hydrogen and methyl radicals. The products of thermodesorption were H2O for hydrogen and H2O, CO2, and CH3CH3 for methane. The Solonitsyn memory effect coefficient was also evaluated for oxygen photoadsorption.

  20. Hydrogen and Carbon Vapour Pressure Isotope Effects in Liquid Fluoroform Studied by Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Oi, Takao; Mitome, Ryota; Yanase, Satoshi

    2017-03-01

    H/D and 12C/13C vapour pressure isotope effects (VPIEs) in liquid fluoroform (CHF3) were studied at the MPW1PW91/6-31 ++ G(d) level of theory. The CHF3 monomer and CHF3 molecules surrounded by other CHF3 molecules in every direction in CHF3 clusters were used as model molecules of vapour and liquid CHF3. Although experimental results in which the vapour pressure of liquid 12CHF3 is higher than that of liquid 12CDF3 and the vapour pressure of liquid 13CHF3 is higher than that of liquid 12CHF3 between 125 and 212 K were qualitatively reproduced, the present calculations overestimated the H/D VPIE and underestimated the 12C/13C VPIE. Temperature-dependent intermolecular interactions between hydrogen and fluorine atoms of neighbouring molecules were required to explain the temperature dependences of both H/D and 12C/13C VPIEs.

  1. Gas Feeding System Supplying the U-400M Cyclotron Ion Source with Hydrogen Isotopes

    SciTech Connect

    Yukhimchuk, A.A.; Angilopov, V.V.; Apasov, V.A.

    2005-07-15

    Automated system feeding into ion source hydrogen isotopes as molecules with preset ratio of the fluxes is described. The control system automatically maintained the working parameters and provided graphic and digital representation of the controlled processes. The radiofrequency (RF) ion source installed at the axial injection line of the cyclotron produced ion beams of HD{sup +}, HT{sup +}, DT{sup +}, D{sub 2}H{sup +}, etc. At a several months DT{sup +} beam acceleration the tritium consumption was less than 108 Bq/hr. The intensity of a 58.2 MeV triton beam (T{sup +} ions) extracted from the cyclotron chamber was about 10 nA.

  2. Autoinduced catalysis and inverse equilibrium isotope effect in the frustrated Lewis pair catalyzed hydrogenation of imines.

    PubMed

    Tussing, Sebastian; Greb, Lutz; Tamke, Sergej; Schirmer, Birgitta; Muhle-Goll, Claudia; Luy, Burkhard; Paradies, Jan

    2015-05-26

    The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol(-1)) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect.

  3. DEMONSTRATION OF THE NEXT-GENERATION TCAP HYDROGEN ISOTOPE SEPARATION PROCESS

    SciTech Connect

    Heung, L; Henry Sessions, H; Steve Xiao, S; Heather Mentzer, H

    2009-01-09

    The first generation of TCAP hydrogen isotope separation process has been in service for tritium separation at the Savannah River Site since 1994. To prepare for replacement, a next-generation TCAP process has been developed. This new process simplifies the column design and reduces the equipment requirements of the thermal cycling system. An experimental twelve-meter column was fabricated and installed in the laboratory to demonstrate its performance. This new design and its initial test results were presented at the 8th International Conference on Tritium Science and Technology and published in the proceedings. We have since completed the startup and demonstration the separation of protium and deuterium in the experimental unit. The unit has been operated for more than 200 cycles. A feed of 25% deuterium in protium was separated into two streams each better than 99.7% purity.

  4. Interactions of relativistic 36Ar and 40Ar nuclei in hydrogen: Isotopic production cross sections

    NASA Astrophysics Data System (ADS)

    Knott, C. N.; Albergo, S.; Caccia, Z.; Chen, C.-X.; Costa, S.; Crawford, H. J.; Cronqvist, M.; Engelage, J.; Greiner, L.; Guzik, T. G.; Insolia, A.; Lindstrom, P. J.; Mitchell, J. W.; Potenza, R.; Russo, G. V.; Soutoul, A.; Testard, O.; Tull, C. E.; Tuvé, C.; Waddington, C. J.; Webber, W. R.; Wefel, J. P.

    1997-07-01

    The interactions of 36Ar projectile nuclei with energies of 361, 546, and 765 MeV/nucleon and 40Ar nuclei with 352 MeV/nucleon, have been studied in a liquid-hydrogen target as part of a program to study interactions of relevance to the problem of cosmic-ray propagation in the interstellar medium. We have measured the cross sections for the production of isotopic fragments of the projectile nuclei in these interactions. The variations of these cross sections with mass, charge, and energy, are examined for insights into any systematic features of this type of fragmentation reaction that might aid predictions of other, unmeasured cross sections. These cross sections are also compared with the values derived from the most commonly used prediction techniques. It is suggested that these techniques could be improved by taking account of the systematic features identified here.

  5. Recent advances in SRS on hydrogen isotope separation using thermal cycling absorption process

    SciTech Connect

    Xiao, X.; Kit Heung, L.; Sessions, H.T.

    2015-03-15

    TCAP (Thermal Cycling Absorption Process) is a gas chromatograph in principle using palladium in the column packing, but it is unique in the fact that the carrier gas, hydrogen, is being isotopically separated and the system is operated in a semi-continuous manner. TCAP units are used to purify tritium. The recent TCAP advances at Savannah River Site (SRS) include compressor-free concept for heating/cooling, push and pull separation using an active inverse column, and compact column design. The new developments allow significantly higher throughput and better reliability from 1/10 of the current production system's footprint while consuming 60% less energy. Various versions are derived in the meantime for external customers to be used in fusion energy projects.

  6. Dual Studies on a Hydrogen-Deuterium Exchange of Resorcinol and the Subsequent Kinetic Isotope Effect.

    PubMed

    Giles, Richard; Kim, Iris; Chao, Weyjuin Eric; Moore, Jennifer; Jung, Kyung Woon

    2014-08-12

    An efficient laboratory experiment has been developed for undergraduate students to conduct hydrogen-deuterium (H-D) exchange of resorcinol by electrophilic aromatic substitution using D2O and a catalytic amount of H2SO4. The resulting labeled product is characterized by (1)H NMR. Students also visualize a significant kinetic isotope effect (kH/kD ≈ 3 to 4) by adding iodine tincture to solutions of unlabeled resorcinol and the H-D exchange product. This method is highly adaptable to fit a target audience and has been successfully implemented in a pedagogical capacity with second-year introductory organic chemistry students as part of their laboratory curriculum. It was also adapted for students at the advanced high school level.

  7. Hydrogen adsorption and diffusion, and subcritical-crack growth in high-strength steels and nickel base alloys

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Klier, K.; Simmons, G. W.

    1974-01-01

    Coordinated studies of the kinetics of crack growth and of hydrogen adsorption and diffusion were initiated to develop information that is needed for a clearer determination of the rate controlling process and possible mechanism for hydrogen enhanced crack growth, and for estimating behavior over a range of temperatures and pressures. Inconel 718 alloy and 18Ni(200) maraging steel were selected for these studies. 18Ni(250) maraging steel, 316 stainless steel, and iron single crystal of (111) orientation were also included in the chemistry studies. Crack growth data on 18Ni(250) maraging steel from another program are included for comparison. No sustained-load crack growth was observed for the Inconel 718 alloy in gaseous hydrogen. Gaseous hydrogen assisted crack growth in the 18Ni maraging steels were characterized by K-independent (Stage 2) extension over a wide range of hydrogen pressures (86 to 2000 torr or 12 kN/m2 to 266 kN/m2) and test temperatures (-60 C to +100 C). The higher strength 18Ni(250) maraging steel was more susceptible than the lower strength 200 grade. A transition temperature was observed, above which crack growth rates became diminishingly small.

  8. Leaf waxes in riparian trees: hydrogen isotopes, concentrations, and chain-length patterns

    NASA Astrophysics Data System (ADS)

    Tipple, B. J.; Ehleringer, J.; Doman, C.; Khachaturyan, S.

    2011-12-01

    The stable hydrogen isotope ratios of epicuticular leaf wax n-alkanes record aspects of a plant's ecophysiological conditions. However, it remains unclear as to whether n-alkane hydrogen isotope values (δ2H) directly reflect environmental water (source water or tissue water) or environmental water in combination with a biochemical fractionation. Furthermore, it is uncertain if leaf n-alkane δ2H values reflect a single time interval during leaf expansion or if n-alkane δ2H values record the combination of inputs throughout the entire lifespan of a leaf. These different possibilities will influence how leaf wax biomarkers are interpreted in both ecological and environmental reconstruction contexts. To address these issues, we sampled leaves/buds, stems, and water sources of five common western U.S. riparian species under natural field conditions throughout the growing season. Riparian species were selected because the input water source is most likely to be nearly constant through the growing season. We found that species in this study demonstrated marked and systematic variations in n-alkane concentration, average chain length, and δ2H values. Intraspecific patterns were consistent: average chain lengths and δ2H values increased from bud opening through full leaf expansion with little variation during the remainder of the sampling interval, while leaf-wax concentration as a fraction of total biomass increased throughout the growing season. These data imply that leaf-wax δ2H values reflect multiple periods of wax growth and that the leaf wax is continually produced throughout a leaf's lifespan.

  9. Hydrogen isotope fractionation and redox-controlled solution mechanisms in silicate-COH melt + fluid systems

    NASA Astrophysics Data System (ADS)

    Mysen, Bjorn

    2015-11-01

    The behavior of volatiles in silicate-COH melts and fluids and hydrogen isotope fractionation between melt and fluid were determined experimentally to advance our understanding of the role of volatiles in magmatic processes. Experiments were conducted in situ while the samples were at the desired temperature and pressure to 825°C and ~1.6 GPa and with variable redox conditions. Under oxidizing conditions, melt and fluid comprised CO2, CO3, HCO3, OH, H2O, and silicate components, whereas under reducing conditions, the species were CH4, H2, H2O, and silicate components. Temperature-dependent hydrogen isotope exchange among structural entities within coexisting fluids and melts yields ΔH values near 14 and 24 kJ/mol and -5 and -1 kJ/mol under oxidizing and reducing conditions, respectively. This temperature (and probably pressure)-dependent D/H fractionation is because of interaction between D and H and silicate and C-bearing species in silicate-saturated fluids and in COH fluid-saturated melts. The temperature- and pressure-dependent D/H fractionation factors suggest that partial melts in the presence of COH volatiles in the upper mantle can have δD values 100% or more lighter relative to coexisting silicate-saturated fluid. This effect is greater under oxidizing than under reducing conditions. It is suggested that δD variations of upper mantle mid-ocean ridge basalt (MORB) sources, inferred from the δD of MORB magmatic rocks, can be explained by variations in redox conditions during melting. Lower δD values of the MORB magma reflect more reducing conditions in the mantle source.

  10. An interlaboratory study to test instrument performance of hydrogen dual-inlet isotope-ratio mass spectrometers

    USGS Publications Warehouse

    Brand, Willi A.; Coplen, T.B.

    2001-01-01

    An interlaboratory comparison of forty isotope-ratio mass spectrometers of different ages from several vendors has been performed to test 2H/1H performance with hydrogen gases of three different isotopic compositions. The isotope-ratio results (unsufficiently corrected for H3+ contribution to the m/z = 3 collector, uncorrected for valve leakage in the change-over valves, etc.) expressed relative to one of these three gases covered a wide range of values: -630??? to -790??? for the second gas and -368??? to -462??? for the third gas. After normalizing the isotopic abundances of these test gases (linearly adjusting the ?? values so that the gases with the lowest and highest 2H content were identical for all laboratories), the standard deviation of the 40 measurements of the intermediate gas was a remarkably low 0.85???. It is concluded that the use of scaling factors is mandatory for providing accurate internationally comparable isotope-abundance values. Linear scaling for the isotope-ratio scales of gaseous hydrogen mass spectrometers is completely adequate. ?? Springer-Verlag 2001.

  11. Oxygen and hydrogen isotope variations in the Pecos River of American Southwest

    NASA Astrophysics Data System (ADS)

    Yuan, F.; Miyamoto, S.

    2006-12-01

    The Pecos River is located in eastern New Mexico and western Texas, and its salinity increases downstream. Oxygen and hydrogen isotopic compositions (δ18O and δD) were measured on surface waters sampled from the Pecos River and its tributaries in March, May, and July of 2005. The measurements show considerably large variations in δ18O and δD, ranging from a δ18O of - 8.9‰ and δD of -64.5‰ in March at Salt Creek to a δ18O of 3.6‰ and δD of 1.6‰ in July at Girvin. Many surface waters except for head and tail waters have negative values of deuterium excess (dexcess=δD-8δ18O). Combined with the existing stable isotopic data from three gaging stations along the Pecos River (Santa Rosa, Red Bluff and Langtry) collected by the U.S. Geological Survey, it appears that evaporative enrichments of heavier isotopic species (O-18 and D) are more evident in the middle section than other parts of the river. δ18O and δD decrease at Langtry due to substantial increases in local runoff. The enhanced evaporation in the middle Pecos River is probably ascribed to a prolonged residence time resulting from anthropogenic perturbations (e.g., multi-cycle irrigation water uses and water impoundments in typically shallow reservoirs). Additionally, natural topographical gradients may have played a role in affecting water residence time and the amount of water evaporated from watersheds. These observations suggest that high dissolved salt contents of the Pecos River can be attributed to intense evaporation besides dissolution of geological salt deposits.

  12. Tracing the geographical origin of early potato tubers using stable hydrogen isotope ratios of methoxyl groups.

    PubMed

    Keppler, Frank; Hamilton, John T G

    2008-12-01

    The application of stable isotope ratio measurements has become an extremely useful tool for tracing the provenance of food products, thus ensuring that consumers receive products which comply with their labelled specifications. Recently, it has been shown that relative stable hydrogen isotope abundances (delta(2)H values) of wood lignin methoxyl groups have a distinct range that reflects the delta(2)H values of their meteoric source water. Furthermore, it has been suggested that the isotope information stored in methoxyl groups in plant matter generally might assist with determining the place of origin of plant material. We now have measured delta(2)H values of methoxyl groups from natural compounds in tubers of early potatoes (Solanum tuberosum) grown in different geographical locations. Tubers of early potatoes were collected from across Europe and regions close to the Mediterranean Sea between April and July 2004. The methoxyl groups from the potatoes were found to be highly depleted in (2)H, relative to both their meteoric water and bulk biomass, and a systematic shift of the delta(2)H values between methoxyl groups and meteoric water was observed. A constant fractionation of-161+/-11 per thousand. between methoxyl groups and modelled meteoric water is shown over a transaction covering the delta(2)H values of meteoric water from-95 per thousand in Northern Sweden to+25 per thousand in Egypt. From this information, early potato tubers from Middle Europe can be clearly distinguished from those of Mediterranean regions and from Northern Europe. Thus, we suggest that delta(2)H values of methoxyl groups have the potential to become an effective tool in assisting with the constraint of the geographical origin of potato tubers and other food stuffs.

  13. Hydrogen Isotopes as a Sentinel of Biological Invasion by the Japanese Beetle, Popillia japonica (Newman).

    PubMed

    Hungate, Bruce A; Kearns, Diana N; Ogle, Kiona; Caron, Melanie; Marks, Jane C; Rogg, Helmuth W

    2016-01-01

    Invasive species alter ecosystems, threaten native and endangered species, and have negative economic impacts. Knowing where invading individuals are from and when they arrive to a new site can guide management. Here, we evaluated how well the stable hydrogen isotope composition (δ2H) records the recent origin and time since arrival of specimens of the invasive Japanese beetle (Popillia japonica Newman) captured near the Portland International Airport (Oregon, U.S.A.). The δ2H of Japanese beetle specimens collected from sites across the contiguous U.S.A. reflected the δ2H of local precipitation, a relationship similar to that documented for other organisms, and one confirming the utility of δ2H as a geographic fingerprint. Within weeks after experimental relocation to a new isotopic environment, the δ2H of beetles changed linearly with time, demonstrating the potential for δ2H to also mark the timing of arrival to a new location. We used a hierarchical Bayesian model to estimate the recent geographical origin and timing of arrival of each specimen based on its δ2H value. The geographic resolution was broad, with values consistent with multiple regions of origin in the eastern U.S.A., slightly favoring the southeastern U.S.A. as the more likely source. Beetles trapped from 2007-2010 had arrived 30 or more days prior to trapping, whereas the median time since arrival declined to 3-7 days for beetles trapped from 2012-2014. This reduction in the time between arrival and trapping at the Portland International Airport supports the efficacy of trapping and spraying to prevent establishment. More generally, our analysis shows how stable isotopes can serve as sentinels of biological invasions, verifying the efficacy of control measures, or, alternatively, indicating when those measures show signs of failure.

  14. Hydrogen Isotopes as a Sentinel of Biological Invasion by the Japanese Beetle, Popillia japonica (Newman)

    PubMed Central

    Ogle, Kiona; Caron, Melanie; Marks, Jane C.; Rogg, Helmuth W.

    2016-01-01

    Invasive species alter ecosystems, threaten native and endangered species, and have negative economic impacts. Knowing where invading individuals are from and when they arrive to a new site can guide management. Here, we evaluated how well the stable hydrogen isotope composition (δ2H) records the recent origin and time since arrival of specimens of the invasive Japanese beetle (Popillia japonica Newman) captured near the Portland International Airport (Oregon, U.S.A.). The δ2H of Japanese beetle specimens collected from sites across the contiguous U.S.A. reflected the δ2H of local precipitation, a relationship similar to that documented for other organisms, and one confirming the utility of δ2H as a geographic fingerprint. Within weeks after experimental relocation to a new isotopic environment, the δ2H of beetles changed linearly with time, demonstrating the potential for δ2H to also mark the timing of arrival to a new location. We used a hierarchical Bayesian model to estimate the recent geographical origin and timing of arrival of each specimen based on its δ2H value. The geographic resolution was broad, with values consistent with multiple regions of origin in the eastern U.S.A., slightly favoring the southeastern U.S.A. as the more likely source. Beetles trapped from 2007–2010 had arrived 30 or more days prior to trapping, whereas the median time since arrival declined to 3–7 days for beetles trapped from 2012–2014. This reduction in the time between arrival and trapping at the Portland International Airport supports the efficacy of trapping and spraying to prevent establishment. More generally, our analysis shows how stable isotopes can serve as sentinels of biological invasions, verifying the efficacy of control measures, or, alternatively, indicating when those measures show signs of failure. PMID:26959686

  15. Compound-specific hydrogen isotope analysis of heteroatom-bearing compounds via gas chromatography-chromium-based high-temperature conversion (Cr/HTC)-isotope ratio mass spectrometry.

    PubMed

    Renpenning, Julian; Kümmel, Steffen; Hitzfeld, Kristina L; Schimmelmann, Arndt; Gehre, Matthias

    2015-09-15

    The traditional high-temperature conversion (HTC) approach toward compound-specific stable isotope analysis (CSIA) of hydrogen for heteroatom-bearing (i.e., N, Cl, S) compounds has been afflicted by fractionation bias due to formation of byproducts HCN, HCl, and H2S. This study presents a chromium-based high-temperature conversion (Cr/HTC) approach for organic compounds containing nitrogen, chlorine, and sulfur. Following peak separation along a gas chromatographic (GC) column, the use of thermally stable ceramic Cr/HTC reactors at 1100-1500 °C and chemical sequestration of N, Cl, and S by chromium result in quantitative conversion of compound-specific organic hydrogen to H2 analyte gas. The overall hydrogen isotope analysis via GC-Cr/HTC-isotope ratio mass spectrometry (IRMS) achieved a precision of better than ± 5 mUr along the VSMOW-SLAP scale. The accuracy of GC-Cr/HTC-IRMS was validated with organic reference materials (RM) in comparison with online EA-Cr/HTC-IRMS and offline dual-inlet IRMS. The utility and reliability of the GC-Cr/HTC-IRMS system were documented during the routine measurement of more than 500 heteroatom-bearing organic samples spanning a δ(2)H range of -181 mUr to 629 mUr.

  16. The effect of hydrogen isotopes and helium on the tensile properties of 21-6-9 stainless steel

    SciTech Connect

    Morgan, M.J.; Lohmeier, D.

    1990-01-01

    High-energy-rate-forged (HERF) stainless steels are used as the materials of construction for pressure vessels designed for the containment of hydrogen and its isotopes. Hydrogen and helium, the decay product of tritium, are known to embrittle these materials. HERF stainless steels have a relatively good resistance to hydrogen-and-helium-induced embrittlement when compared to annealed stainless steels due to their high number density of dislocations, which act as traps for hydrogen and helium. However, the degree of embrittlement in these materials can vary considerably because of microstructure and yield strength variations introduced during the forging process. In this study the effect of hydrogen and tritium on the tensile properties of 21-6-9 stainless steel was measured as a function of HERF yield strength in the range of 660 to 930 MPa. The effect of microstructure was studied also be conducting tensile tests with HERF and annealed samples.

  17. Hydrogen Isotope Ratios of Leaf Waxes in C3 and C4 Grasses Record Meteoric Water and Aridity Signatures

    NASA Astrophysics Data System (ADS)

    Smith, F. A.; Freeman, K. H.; Ehleringer, J. R.; Helliker, B.

    2004-12-01

    Hydrogen isotope ratios of sedimentary n-alkanes (C27-C33) from vascular plants potentially provide a valuable record of past hydrologic conditions. To explore this, we analyzed grasses grown in a greenhouse and calculated fractionation factors (epsilon) between source water and n-alkane for each sample. An average difference of 21 permil is observed between C3 and C4 grasses, which is comparable to that determined for grasses collected from the Great Plains. The more positive isotope values in C4 grasses likely reflects smaller interveinal distance compared to C3 grass leaves, allowing greater back-diffusion of transpirationally enriched water from stomata, as documented with the oxygen isotope ratios of grass leaf water and cellulose by Helliker and Ehleringer (2000). The oxygen isotope difference is magnified at low relative humidity, when transpiration rates are higher. A similar effect is expected in hydrogen isotope ratios of leaf water and plant compounds. However, preliminary results from grasses grown hydroponically at different relative humidities suggest that there may be a decoupling of the hydrogen isotope ratio of leaf-wax n-alkanes and the oxygen isotope ratio of leaf water and cellulose. To examine the effects of source water delta D and climate on n-alkane delta D values, we analyzed grasses collected from the Great Plains. We use river water delta D values as a proxy for source water and the epsilon values determined in the greenhouse experiments, to predict expected values for C3 and C4 grass lipids. Measured values compare well to predicted values, with the exception of two semi-arid sites where evapotranspiration may have led to leaf-waters that are enriched in deuterium. Residual delta D values (measured-expected) correspond strongly with measures of aridity, such as annual precipitation and recipitation/evaporation ratios.

  18. Effects of shock and Martian alteration on Tissint hydrogen isotope ratios and water content

    NASA Astrophysics Data System (ADS)

    Hallis, L. J.; Huss, G. R.; Nagashima, K.; Taylor, G. J.; Stöffler, D.; Smith, C. L.; Lee, M. R.

    2017-03-01

    The Tissint meteorite, a picritic shergottite, fell to Earth in Morocco on the 18th of July 2011, and is only the fifth Martian meteorite witnessed to fall. Hydrogen isotope ratios and water contents are variable within different minerals in Tissint. Ringwoodite and shock melt pockets contain elevated D/H ratios relative to terrestrial values (δD = 761-4224‰). These high ratios in recrystallized phases indicate significant implantation of hydrogen from the D-rich Martian atmosphere during shock. In contrast, although olivine has detectable water abundances (230-485 ppm), it exhibits much lower D/H ratios (δD = +88 to -150‰), suggesting this water was not implanted from the Martian atmosphere. The minimal terrestrial weathering experienced by Tissint gives confidence that the olivine-hosted water has a Martian origin, but its high concentration indicates direct inheritance from the parental melt is improbable, especially given the low pressure of olivine crystallisation. Incorporation of a low δD crustal fluid, or deuteric alteration during crystallisation, could explain the relatively high water contents and low D/H ratios in Tissint olivine.

  19. Cultivation-independent detection of autotrophic hydrogen-oxidizing bacteria by DNA stable-isotope probing.

    PubMed

    Pumphrey, Graham M; Ranchou-Peyruse, Anthony; Spain, Jim C

    2011-07-01

    Knallgas bacteria are a physiologically defined group that is primarily studied using cultivation-dependent techniques. Given that current cultivation techniques fail to grow most bacteria, cultivation-independent techniques that selectively detect and identify knallgas bacteria will improve our ability to study their diversity and distribution. We used stable-isotope probing (SIP) to identify knallgas bacteria in rhizosphere soil of legumes and in a microbial mat from Obsidian Pool in Yellowstone National Park. When samples were incubated in the dark, incorporation of (13)CO(2) was H(2) dependent. SIP enabled the detection of knallgas bacteria that were not detected by cultivation, and the majority of bacteria identified in the rhizosphere soils were betaproteobacteria predominantly related to genera previously known to oxidize hydrogen. Bacteria in soil grew on hydrogen at concentrations as low as 100 ppm. A hydB homolog encoding a putative high-affinity NiFe hydrogenase was amplified from (13)C-labeled DNA from both vetch and clover rhizosphere soil. The results indicate that knallgas bacteria can be detected by SIP and populations that respond to different H(2) concentrations can be distinguished. The methods described here should be applicable to a variety of ecosystems and will enable the discovery of additional knallgas bacteria that are resistant to cultivation.

  20. Hydrogen isotope ratios of recent lacustrine sedimentary n-alkanes record modern climate variability

    NASA Astrophysics Data System (ADS)

    Sachse, D.; Radke, J.; Gleixner, G.

    2004-12-01

    Hydrogen isotope ratios were measured on n-alkanes (n-C 12 to n-C 31) extracted from recent lake surface sediments along a N-S European transect to test if modern climate variability is recorded in these biomarkers. δD values of the n-alkanes are compared to δD values of meteoric water from the IAEA-GNIP database spanning a range from -119‰ in northern Sweden to -41‰ in southern Italy, to lake water δD values, and to mean annual temperatures, varying between -2.0°C in the north and 13.7°C in the south. δD values of the short-chained n-alkanes n-C 12 to n-C 20, excluding algal derived n-C 17 and n-C 19, are higher in the north and lower in the south. The isotopic fractionation ɛ for hydrogen between meteoric water and the short-chained n-alkanes is increasing from N to S by more than 100‰ and is significantly correlated to mean annual temperature for n-C 16 and n-C 18. This suggests that these n-alkanes may originate from a different source in the northern lakes, possibly due to petroleum contamination, or are synthesized using a different biochemical pathway. The n-C 17 and n-C 19 alkanes of algal origin, the n-C 21 and n-C 23 alkanes originating from water plants, and the long-chain n-alkanes n-C 25, n-C 27, n-C 29, and n-C 31 of terrestrial origin, clearly correlate with δD values of meteoric water, lake water, and mean annual temperature, indicating that they excellently record the δD value of meteoric water. The mean hydrogen isotope fractionation ɛ C17/w of -157‰ (SD = 13) between n-C 17 and meteoric water is fairly constant over the wide range of different climates and lake environments, suggesting only minor influence of environmental factors on this biochemical fractionation. This suggests that δD values of n-C 17 are suitable to reconstruct the isotopic composition of source water. The mean fractionation between the long-chain n-alkanes and water is -128‰ (SD = 12). The mean difference of 31‰ between both ɛ values is likely due to

  1. Effect of chloride ions on adsorption and permeation of hydrogen in iron

    SciTech Connect

    Allam, A.M.; Pickering, H.W.; Ateya, B.G.

    1997-04-01

    Effects of chloride ions on hydrogen absorption into iron and on the hydrogen evolution reaction (HER) on an iron surface were studied in acid and alkaline solutions at 23 C using the permeation method of Devanathan and Stachurski. Cl{sup {minus}} ions reduced the overpotential ({eta}) for HER and, in turn, reduced hydrogen coverage and permeation.Effects on hydrogen permeation were more pronounced in alkaline than in acid solutions. Permeation transients at constant electrode potential of he charging surface and subsequent surface analyses of the uppermost atom layers of the hydrogen-charged iron surface indicated a reversible or low coverage with Cl{sup {minus}} ions, a low hydrogen coverage that was not influenced significantly by Cl{sup {minus}} ion concentration at low {eta}, and a marked effect of Cl{sup {minus}} ions in reducing hydrogen coverage of the surface and permeability in alkaline solutions at high cathodic polarizations.

  2. Multidimensional isotope analysis of carbon, hydrogen and oxygen as tool for identification of the origin of ibuprofen.

    PubMed

    Gilevska, Tetyana; Gehre, Matthias; Richnow, Hans Hermann

    2015-11-10

    Multidimensional isotope profiling is a useful tool for the characterization of the provenance of active pharmaceutical ingredients (API). To evaluate this approach, samples of the nonsteroidal anti-inflammatory drug (NSAIDs) ibuprofen were collected from 32 manufactures and 13 countries, and carbon, hydrogen and oxygen isotope ratios were analyzed by elemental analyzer, chromium-filled elemental analyzer and high temperature conversion elemental analyzer (EA, Cr-EA and TC/EA) coupled to an isotope ratio mass spectrometry (IRMS). The range of isotope values of ibuprofen (δ(13)C: -33.2±0.1‰ to -27.4±0.1‰; δ(2)H: -121.4±1.5‰ to -41.2±0.8‰; and δ(18)O: -12.6±0.3‰ to 19.0±0.6‰) allowed characterization and distinction of 5 groups, which reflect synthetic pathways and/or use of different raw materials, as well as possible isotope fractionation during the synthesis reactions. This study highlights that multi isotope fingerprinting has potential for identification of sources, and provides a database of isotope composition of ibuprofen (δ(2)H, δ(13)C, δ(18)O) that might improve the tracing of origin, transport pathways and environmental fate of ibuprofen.

  3. Characterization of adsorption removal of hydrogen sulfide by waste biocover soil, an alternative landfill cover.

    PubMed

    He, Ruo; Xia, Fang-Fang; Wang, Jing; Pan, Chang-Liang; Fang, Cheng-Ran

    2011-02-15

    Landfill is an important anthropogenic source of odorous gases. In this work, the adsorption characteristics of H(2)S on waste biocover soil, an alternative landfill cover, were investigated. The results showed that the adsorption capacity of H(2)S increased with the reduction of particle size, the increase of pH value and water content of waste biocover soil. The optimal composition of waste biocover soil, in regard to operation cost and H(2)S removal performance, was original pH value, water content of 40% (w/w) and particle size of ≤4 mm. A net increase was observed in the adsorption capacity of H(2)S with temperatures in the range of 4-35°C. The adsorption capacity of H(2)S on waste biocover soil with optimal composition reached the maximum value of 60±1 mg/kg at oxygen concentration of 10% (v/v). When H(2)S concentration was about 5% (v/v), the adsorption capacity was near saturation, maintaining at 383±40 mg/kg. Among the four experimental soils, the highest adsorption capacity of H(2)S was observed on waste biocover soil, followed by landfill cover soil, mulberry soil, and sand soil, which was only 9.8% of that of waste biocover soil.

  4. Compound Specific Hydrogen Isotope Composition of Type II and III Kerogen Extracted by Pyrolysis-GC-MS-IRMS

    NASA Technical Reports Server (NTRS)

    Socki, Richard A.; Pernia, Denet; Evans, Michael; Fu, Qi; Bissada, Kadry K.; Curiale, Joseph A.; Niles, Paul B.

    2013-01-01

    The use of Hydrogen (H) isotopes in understanding oil and gas resource plays is in its infancy. Described here is a technique for H isotope analysis of organic compounds pyrolyzed from oil and gas shale-derived kerogen. Application of this technique will progress our understanding. This work complements that of Pernia et al. (2013, this meeting) by providing a novel method for the H isotope analysis of specific compounds in the characterization of kerogen extracted by analytically diverse techniques. Hydrogen isotope analyses were carried out entirely "on-line" utilizing a CDS 5000 Pyroprobe connected to a Thermo Trace GC Ultra interfaced with a Thermo MAT 253 IRMS. Also, a split of GC-separated products was sent to a DSQ II quadrupole MS to make semi-quantitative compositional measurements of the extracted compounds. Kerogen samples from five different basins (type II and III) were dehydrated (heated to 80 C overnight in vacuum) and analyzed for their H isotope compositions by Pyrolysis-GC-MS-TC-IRMS. This technique takes pyrolysis products separated via GC and reacts them in a high temperature conversion furnace (1450 C) which quantitatively forms H2, following a modified method of Burgoyne and Hayes, (1998, Anal. Chem., 70, 5136-5141). Samples ranging from approximately 0.5 to 1.0mg in size, were pyrolyzed at 800 C for 30s. Compounds were separated on a Poraplot Q GC column. Hydrogen isotope data from all kerogen samples typically show enrichment in D from low to high molecular weight compounds. Water (H2O) average deltaD = -215.2 (V-SMOW), ranging from -271.8 for the Marcellus Shale to -51.9 for the Polish Shale. Higher molecular weight compounds like toluene (C7H8) have an average deltaD of -89.7 0/00, ranging from -156.0 for the Barnett Shale to -50.0 for the Monterey Shale. We interpret these data as representative of potential H isotope exchange between hydrocarbons and sediment pore water during formation within each basin. Since hydrocarbon H isotopes

  5. [Hydrogen and oxygen isotopes of lake water and geothermal spring water in arid area of south Tibet].

    PubMed

    Xiao, Ke; Shen, Li-Cheng; Wang, Peng

    2014-08-01

    The condition of water cycles in Tibet Plateau is a complex process, and the hydrogen and oxygen isotopes contain important information of this process. Based on the analysis of isotopic composition of freshwater lake, saltwater lake and geothermal water in the southern Tibetan Plateau, this study investigated water cycling, composition and variation of hydrogen and oxygen isotopes and the influencing factors in the study area. The study found that the mean values of delta18O and deltaD in Daggyaima lake water (-17.0 per thousand for delta18O and -138. 6 per thousand for deltaD), Langcuo lake water (-6.4 per thousand for delta18O and -87.4 per thousand for deltaD) and Dagejia geothermal water (-19.2 per thousand for delta18 and -158.2 per thousand for deltaD) all showed negative delta18O and deltaD values in Tibetan Plateau by the influence of altitude effects. Lake water and geothermal water were influenced by evaporation effects in inland arid area, and the slope of evaporation line was less than 8. Deuterium excess parameters of lake water and geothermal water were all negative. The temperature of geothermal reservoirs in Dagejia geothermal field was high,and oxygen shift existed in the relationship of hydrogen and oxygen isotopes.

  6. Highly effective hydrogen isotope separation in nanoporous metal-organic frameworks with open metal sites: direct measurement and theoretical analysis.

    PubMed

    Oh, Hyunchul; Savchenko, Ievgeniia; Mavrandonakis, Andreas; Heine, Thomas; Hirscher, Michael

    2014-01-28

    Separating gaseous mixtures that consist of very similar size is one of the critical issues in modern separation technology. Especially, the separation of the isotopes hydrogen and deuterium requires special efforts, even though these isotopes show a very large mass ratio. Conventionally, H/D separation can be realized through cryogenic distillation of the molecular species or the Girdler-sulfide process, which are among the most energy-intensive separation techniques in the chemical industry. However, costs can be significantly reduced by using highly mass-selective nanoporous sorbents. Here, we describe a hydrogen isotope separation strategy exploiting the strongly attractive open metal sites present in nanoporous metal-organic frameworks of the CPO-27 family (also referred to as MOF-74). A theoretical analysis predicts an outstanding hydrogen isotopologue separation at open metal sites due to isotopal effects, which has been directly observed through cryogenic thermal desorption spectroscopy. For H2/D2 separation of an equimolar mixture at 60 K, the selectivity of 12 is the highest value ever measured, and this methodology shows extremely high separation efficiencies even above 77 K. Our theoretical results imply also a high selectivity for HD/H2 separation at similar temperatures, and together with catalytically active sites, we propose a mechanism to produce D2 from HD/H2 mixtures with natural or enriched deuterium content.

  7. Hydrogeochemistry and Oxygen and Hydrogen Isotope Compositions of Sea Water Intrusion in Masan-Jinhae Area, Korea

    NASA Astrophysics Data System (ADS)

    Chon, H.; Song, Y.; Jeong, C.; Kim, Y.; Lee, J.

    2006-12-01

    The purpose of this study is to investigate the geochemical characteristics of the sea water intrusion in Masan - Jinhae area that is bounded by the South Sea of the Korean Peninsula. Sampling of precipitation, stream water, groundwater and sea water in the hydrologic cycle, measurement in field, and the analysis of dissolved ions and oxygen and hydrogen stable isotopes were carried out in order to understand hydrogeochemical property, and to analyze the mixing status of sea water with fresh water. The most appropriate parameters for understanding the status of sea water intrusion were also discussed in this study. Electric conductivity value shows outlier over 1000 §Á/§¯ in some groundwater, which suggests the evidence of sea water intrusion around the well. Groundwater is divided into three types; (Ca,Mg)-(HCO3) type, (Ca,Mg)-(Cl,SO4) type, and (Na+K)-(Cl,SO4) type. In particular, the second type could be due to geochemical evolution through reverse ion exchange reaction with sea water, and third type is chemically similar to sea water. Oxygen and hydrogen isotope compositions of precipitation, stream water, groundwater and sea water show that precipitation reflects seasonal variation, and that stream water is more affected by groundwater rather than surface water. The origin of groundwater is also related to the meteoric water. The oxygen and hydrogen isotope compositions of the collected sea water are lower than normal sea water. In order to understand the source of salinity in saline groundwater, hydrogeochemical parameters, and oxygen and hydrogen isotope compositions were introduced in this stduy. All the parameters and isotope composition data indicate that the salinity was originated from sea water intrusion. The mixing ratios of sea water was determined by using Br, Cl concentration and ¥ä18O. Mixing ratio of sea water in saline groundwater shows scarce changes in most of the wells.

  8. 3D-CSIA: carbon, chlorine, and hydrogen isotope fractionation in transformation of TCE to ethene by a Dehalococcoides culture.

    PubMed

    Kuder, Tomasz; van Breukelen, Boris M; Vanderford, Mindy; Philp, Paul

    2013-09-03

    Carbon (C), chlorine (Cl), and hydrogen (H) isotope effects were determined during dechlorination of TCE to ethene by a mixed Dehalococcoides (Dhc) culture. The C isotope effects for the dechlorination steps were consistent with data published in the past for reductive dechlorination (RD) by Dhc. The Cl effects (combined with an inverse H effect in TCE) suggested that dechlorination proceeded through nucleophilic reactions with cobalamin rather than by an electron transfer mechanism. Depletions of (37)Cl in daughter compounds, resulting from fractionation at positions away from the dechlorination center (secondary isotope effects), further support the nucleophilic dechlorination mechanism. Determination of C and Cl isotope ratios of the reactants and products in the reductive dechlorination chain offers a potential tool for differentiation of Dhc activity from alternative transformation mechanisms (e.g., aerobic degradation and reductive dechlorination proceeding via outer sphere mechanisms), in studies of in situ attenuation of chlorinated ethenes. Hydrogenation of the reaction products (DCE, VC, and ethene) showed a major preference for the (1)H isotope. Detection of depleted dechlorination products could provide a line of evidence in discrimination between alternative sources of TCE (e.g., evolution from DNAPL sources or from conversion of PCE).

  9. The influence of the potassium promoter on the kinetics and thermodynamics of CO adsorption on a bulk iron catalyst applied in Fischer-Tropsch synthesis: a quantitative adsorption calorimetry, temperature-programmed desorption, and surface hydrogenation study.

    PubMed

    Graf, Barbara; Muhler, Martin

    2011-03-07

    The adsorption of carbon monoxide on an either unpromoted or potassium-promoted bulk iron catalyst was investigated at 303 K and 613 K by means of pulse chemisorption, adsorption calorimetry, temperature-programmed desorption and temperature-programmed surface reaction in hydrogen. CO was found to adsorb mainly molecularly in the absence of H(2) at 303 K, whereas the presence of H(2) induced CO dissociation at higher temperatures leading to the formation of CH(4) and H(2)O. The hydrogenation of atomic oxygen chemisorbed on metallic iron was found to occur faster than the hydrogenation of atomically adsorbed carbon. At 613 K CO adsorption occurred only dissociatively followed by recombinative CO(2) formation according to C(ads) + 2O(ads)→ CO(2(g)). The presence of the potassium promoter on the catalyst surface led to an increasing strength of the Fe-C bond both at 303 K and 613 K: the initial differential heat of molecular CO adsorption on the pure iron catalyst at 303 K amounted to 102 kJ mol(-1), whereas it increased to 110 kJ mol(-1) on the potassium-promoted sample, and the initial differential heat of dissociative CO adsorption on the unpromoted iron catalyst at 613 K amounted to 165 kJ mol(-1), which increased to 225 kJ mol(-1) in the presence of potassium. The calorimetric CO adsorption experiments also reveal a change of the energetic distribution of the CO adsorption sites present on the catalyst surface induced by the potassium promoter, which was found to block a fraction of the CO adsorption sites.

  10. Facile solvent-thermal synthesis of ultrathin MoSe2 nanosheets for hydrogen evolution and organic dyes adsorption

    NASA Astrophysics Data System (ADS)

    Jiang, Qingqing; Lu, Yongfeng; Huang, Zhengxi; Hu, Juncheng

    2017-04-01

    The flower-like MoSe2 nanospheres with average size of 200 nm which composed of ultrathin nanosheets were synthesized by facile solvent-thermal method. AFM analysis indicated that the thickness of the MoSe2 nanosheets could be changed from 3.4 to 6.4 nm by changing the chains of n-alcohol solvent. The as prepared MoSe2 nanosheets in ethanol solvent exhibited the best electrochemical performance and the highest adsorption capability as compared to samples synthesized in other n-alcohol solvent with longer chains. It was due to MoSe2 synthesized in ethanol exhibited higher crystallinity and better wettability than other samples. The maximum adsorption capability of Rhodamine B (RhB) on MoSe2 nanosheets reached 133 mg g-1 in 5 min, while the same adsorption capabilities on activated carbon need 20 min. Electrochemical results exhibited a relatively small onset potential (120 mV), small Tafel slope (71 mV/dec), and long term stability for MoSe2 synthesized in ethanol which making it a promising candidate for hydrogen evolution reaction.

  11. Hydrogen stable isotopic constraints on methane emissions from oil and gas extraction in the Colorado Front Range, USA

    NASA Astrophysics Data System (ADS)

    Townsend-Small, A.; Botner, E. C.; Jimenez, K.; Blake, N. J.; Schroeder, J.; Meinardi, S.; Barletta, B.; Simpson, I. J.; Blake, D. R.; Flocke, F. M.; Pfister, G.; Bon, D.; Crawford, J. H.

    2015-12-01

    The climatic implications of a shift from oil and coal to natural gas depend on the magnitude of fugitive emissions of methane from the natural gas supply chain. Attempts to constrain methane emissions from natural gas production regions can be confounded by other sources of methane. Here we demonstrate the utility of stable isotopes, particularly hydrogen isotopes, for source apportionment of methane emissions. The Denver, Colorado area is home to a large oil and gas field with both conventional oil and gas wells and newer hydraulic fracturing wells. The region also has a large metropolitan area with several landfills and a sizable cattle population. As part of the DISCOVER-AQ and FRAPPE field campaigns in summer 2014, we collected three types of canister samples for analysis of stable isotopic composition of methane: 1), samples from methane sources; 2), samples from two stationary ground sites, one in the Denver foothills, and one in an oil and gas field; and 3), from the NCAR C-130 aircraft in samples upwind and downwind of the region. Our results indicate that hydrogen isotope ratios are excellent tracers of sources of methane in the region, as we have shown previously in California and Texas. Use of carbon isotope ratios is complicated by the similarity of natural gas isotope ratios to that of background methane. Our results indicate that, despite the large amount of natural gas production in the region, biological sources such as cattle feedlots and landfills account for at least 50% of total methane emissions in the Front Range. Future work includes comparison of isotopes and alkane ratios as tracers of methane sources, and calculation of total methane fluxes in the region using continuous measurements of methane concentrations during aircraft flights.

  12. The effect of hydrogen adsorption on the properties of undoped and Cu-doped ZnO (10 1 bar 0) surfaces: A first-principles study

    NASA Astrophysics Data System (ADS)

    Lahmer, M. A.

    2016-02-01

    The effect of hydrogen adsorption on the electronic structure and properties of clean and Cu-doped ZnO (10 1 bar 0) non polar surface was investigated using the first principles method. We found that the Cu-doped surface is more stable than the undoped one, and that high Cu solubility can be achieved in ZnO under O-rich condition with the use of metallic Cu as a Cu doping source. On the other hand, the obtained results show that hydrogen adsorption is more favored on Cu-doped-ZnO (10 1 bar 0) surface than onto the clean surface, and this make Cu-doped ZnO surface and nanostructures more efficient for atomic H sensing applications than clean ZnO surface. We have also examined the effect of H adsorption on the surface work function of both clean and Cu-doped surfaces. We found that the adsorption of hydrogen molecule increases the work function of both surfaces, while, the adsorption of atomic hydrogen decreases significantly the surface work function.

  13. Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia

    NASA Astrophysics Data System (ADS)

    Ladd, S. Nemiah; Sachs, Julian P.

    2015-11-01

    Hydrogen isotope ratios (2H/1H or δ2H) of plant leaf waxes typically covary with those of precipitation, and are therefore used as a proxy for past hydrologic variability. Mangroves present an important exception to this relationship, as salinity can strongly influence 2H fractionation in leaf lipids. To better understand and calibrate this effect, δ2H values of taraxerol and n-alkanes were measured in the leaves of Rhizophora spp. (red mangroves) from three estuaries and four brackish lakes on the Micronesian islands of Pohnpei and Palau, and compared to the δ2H and δ18O values of leaf water, xylem water and surface water. Net 2H discrimination between surface water and taraxerol increased by 0.9 ± 0.2‰ per part per thousand (ppt-1) over a salinity range of 1-34 ppt. Xylem water was always depleted in 2H relative to surface water, and the magnitude of this depletion increased with salinity, which is most likely due to a combination of greater 2H discrimination by roots during water uptake and opportunistic use of freshwater. Changes in the 2H content of xylem water can account for up to 43% of the change in net taraxerol fractionation with salinity. Leaf water isotopes were minimally enriched relative to xylem water and there was not significant variability in leaf water enrichment with salinity, which is consistent with a Péclet-modified Craig-Gordon model of leaf water enrichment. As leaf water enrichment is therefore unlikely to be responsible for increased 2H/1H fractionation in mangrove leaf lipids at elevated salinities, the majority of this signal is most likely explained either by changes in biosynthetic fractionation in response to salt stress or by salinity influenced changes in the timing of water uptake and lipid synthesis.

  14. Transhydrogenase and Growth Substrate Influence Lipid Hydrogen Isotope Ratios in Desulfovibrio alaskensis G20

    PubMed Central

    Leavitt, William D.; Flynn, Theodore M.; Suess, Melanie K.; Bradley, Alexander S.

    2016-01-01

    Microbial fatty acids preserve metabolic and environmental information in their hydrogen isotope ratios (2H/1H). This ratio is influenced by parameters that include the 2H/1H of water in the microbial growth environment, and biosynthetic fractionations between water and lipid. In some microbes, this biosynthetic fractionation has been shown to vary systematically with central energy metabolism, and controls on fatty acid 2H/1H may be linked to the intracellular production of NADPH. We examined the apparent fractionation between media water and the fatty acids produced by Desulfovibrio alaskensis G20. Growth was in batch culture with malate as an electron donor for sulfate respiration, and with pyruvate and fumarate as substrates for fermentation and for sulfate respiration. A larger fractionation was observed as a consequence of respiratory or fermentative growth on pyruvate than growth on fumarate or malate. This difference correlates with opposite apparent flows of electrons through the electron bifurcating/confurcating transhydrogenase NfnAB. When grown on malate or fumarate, mutant strains of D. alaskensis G20 containing transposon disruptions in a copy of nfnAB show different fractionations than the wild type strain. This phenotype is muted during fermentative growth on pyruvate, and it is absent when pyruvate is a substrate for sulfate reduction. All strains and conditions produced similar fatty acid profiles, and the 2H/1H of individual lipids changed in concert with the mass-weighted average. Unsaturated fatty acids were generally depleted in 2H relative to their saturated homologs, and anteiso-branched fatty acids were generally depleted in 2H relative to straight-chain fatty acids. Fractionation correlated with growth rate, a pattern that has also been observed in the fractionation of sulfur isotopes during dissimilatory sulfate reduction by sulfate-reducing bacteria. PMID:27445998

  15. Interaction of hydrogen chloride with alumina. [influence of outgas and temperature conditions on adsorption

    NASA Technical Reports Server (NTRS)

    Bailey, R. R.; Wightman, J. P.

    1975-01-01

    The influence of outgas conditions and temperature on the adsorptive properties of two aluminas Alon-c and Al6sG were studied using adsorption isotherm measurements. Alon-C and Al6SG were characterized using X-ray powder diffraction, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET nitrogen surface areas. Some of these techniques were applied to two other aluminas but no isotherm data was obtained. Isotherm data and techniques applied to each alumina are summarized in tabular form.

  16. The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft

    NASA Astrophysics Data System (ADS)

    Batenburg, A. M.; Schuck, T. J.; Baker, A. K.; Zahn, A.; Brenninkmeijer, C. A. M.; Röckmann, T.

    2012-01-01

    More than 450 air samples that were collected in the upper troposphere - lower stratosphere (UTLS) region around the tropopause (TP) by the CARIBIC aircraft (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) have been analyzed for molecular hydrogen (H2) mixing ratios (m(H2)) and H2 isotopic composition (deuterium content, δD). More than 120 of the analysed samples consisted of air from the lowermost stratosphere (LMS). These show that m(H2) does not vary appreciably with O3-derived height above the thermal TP, whereas δD does increase with height. The isotope enrichment is caused by competing H2 production and destruction processes that enrich the stratospheric H2 reservoir in deuterium (D); the exact shapes of the profiles are mainly determined by mixing of stratospheric with tropospheric air. Tight negative correlations are found between δD and the mixing ratios of methane (CH4) and nitrous oxide (N2O), as a result of the relatively long lifetimes of these three species. The correlations are described by δ D [‰]=-0.35 · m(CH4)[ppb]+768 and δD [‰]=-1.90 · m(N2O)[ppb]+745. These correlations are similar to previously published results and likely hold globally. Samples that were collected from the Indian subcontinent up to 40° N before, during and after the summer monsoon season show no significant seasonal change in m(H2), but δD is up to 15‰ lower in the July, August and September monsoon samples. This δD lowering is correlated with m(CH4) increase. The significant correlation with m(CH4) and the absence of a perceptible m(H2) increase that accompanies the δD lowering indicates that microbial production of very D-depleted H2 in the wet season may contribute to this phenomenon. Some of the samples have very high m(H2) and very low δD values, which indicates a pollution effect. Aircraft engine exhaust plumes are a suspected cause, since the effect mostly occurs in samples collected close to airports

  17. The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft

    NASA Astrophysics Data System (ADS)

    Batenburg, A. M.; Schuck, T. J.; Baker, A. K.; Zahn, A.; Brenninkmeijer, C. A. M.; Röckmann, T.

    2012-05-01

    More than 450 air samples that were collected in the upper troposphere - lower stratosphere (UTLS) region by the CARIBIC aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) have been analyzed for molecular hydrogen (H2) mixing ratios (χ(H2)) and H2 isotopic composition (deuterium content, δD). More than 120 of the analyzed samples contained air from the lowermost stratosphere (LMS). These show that χ(H2) does not vary appreciably with O3-derived height above the thermal tropopause (TP), whereas δD does increase with height. The isotope enrichment is caused by H2 production and destruction processes that enrich the stratospheric H2 reservoir in deuterium (D); the exact shapes of the profiles are mainly determined by mixing of stratospheric with tropospheric air. Tight negative correlations are found between δD and the mixing ratios of methane (χ(CH4)) and nitrous oxide (χ(N2O)), as a result of the relatively long lifetimes of these three species. The correlations are described by δD[‰]=-0.35 · χ(CH4)[ppb]+768 and δD[‰]=-1.90· χ(N2O)[ppb]+745. These correlations are similar to previously published results and likely hold globally for the LMS. Samples that were collected from the Indian subcontinent up to 40° N before, during and after the summer monsoon season show no significant seasonal change in χ(H2), but δD is up to 12.3‰ lower in the July, August and September monsoon samples. This δD decrease is correlated with the χ(CH4) increase in these samples. The significant correlation with χ(CH4) and the absence of a perceptible χ(H2) increase that accompanies the δD decrease indicates that microbial production of very D-depleted H2 in the wet season may contribute to this phenomenon. Some of the samples have very high χ(H2) and very low δD values, which indicates a pollution effect. Aircraft engine exhaust plumes are a suspected cause, since the effect mostly occurs in samples

  18. Hydrogen isotope composition of dry season atmospheric water vapor on Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Samuels-Crow, K. E.; Galewsky, J.; Hardy, D. R.; Braun, C.

    2011-12-01

    In-situ measurements of modern meteorological conditions at Quelccaya Ice Cap's summit, including the isotopic composition of atmospheric water vapor, may aid in the interpretation of the 1500-year, annually resolved ice-core record available from the site (Thompson et al., 2003). Betweeen July 7 and July 9, 2011, we collected 11 samples of atmospheric water vapor from the summit of Quelccaya and analyzed the hydrogen isotopic composition on a Finnegan MAT-252 mass spectrometer using the method of Strong et al 2007. δD values ranged from -134% to -168%, and specific humidity ranged from 1.5 to 3 g/kg. The isotopic composition of tropical Andean ice cores has been variously interpreted in terms of simple Rayleigh distillation models, in which water evaporates from the tropical Atlantic and condenses as it moves upslope (Grootes et al., 1989; Pierrehumbert, 1999), or in terms of the condensation temperature (Thompson et al., 2003). The joint distribution of water vapor concentrations and δD values in our dataset cannot be explained by a simple upslope Rayleigh distillation model. Such a model predicts higher water-vapor concentrations and lower δD values than those measured during the sampling period. We hypothesize that the joint distribution of water vapor mixing ratio and isotopic composition can be explained by large-scale mixing of air parcels that were last saturated in the upper tropical troposphere. Such mixing necessarily leads to parcels that have higher delta values than would be expected for the simple Rayleigh distillation to the observed mixing ratio. Local effects of snow sublimation may exert additional controls over the water-vapor mixing ratio and delta values. Further monitoring during both the wet and dry seasons may clarify the relationship between large-scale water-vapor transport and the snow and ice preserved on Quelccaya. References Friedman, I. (1953) Deuterium content of natural waters and other substances, Geoch. et Cosmochim. Acta, 4

  19. The History of Water on Venus: a Scenario Accounting for Present Neon and Hydrogen Isotopic Ratios

    NASA Astrophysics Data System (ADS)

    Gillmann, C.; Chassefiere, E.; Lognonne, P.

    2009-12-01

    In order to study the evolution of the primitive atmosphere of Venus, we developped a time dependent model of hydrogen hydrodynamic escape powered by solar EUV (Extreme UV) flux and solar wind, and accounting for oxygen frictional escape We study specifically the isotopic fractionation of noble gases resulting from hydrodynamic escape. The fractionation’s primary cause is the effect of diffusive/gravitational separation between the homopause and the base of the escape. Heavy noble gases such as Kr and Xe are not fractionated. Ar is only marginally fractionated whereas Ne is moderately fractionated. We also take into account oxygen dragged off along with hydrogen by hydrodynamic process. In that case, most of the available energy is consumed by oxygen and the amount of energy available for the escape of hydrogen is reduced by one order of magnitude. We find nonetheless scenarios that are compatible with present-day Ne and Ar fractionation in Venus atmosphere. Our model suggests that during the first 100 Myr of the planetary accretion of Venus, no more than the content of five terrestrial oceans (5 TO) of water have been lost to space. Our preferred scenario shows that around 60% of the oxygen contained in this water was left behind in the atmosphere. During the end of the accretion, the atmospheric water vapor pressure could have been maintained at the value required to maintain the surface temperature above the liquidus. We argue that hydrodynamic escape could have controlled the solidification rate of the magma ocean during the end of the accretion period by pumping the water out of the magma, through the atmosphere, remaining at a pressure of around 300 bar. After most of the water in the magma has been extracted, the atmosphere progressively dried up, and the magma ocean crystallized, leading to a final collapse of the hydrodynamic escape. The end of the hydrodynamic escape phase and the crystallization of the primitive magma ocean would thus roughly coincide

  20. Application of carbon and hydrogen stable isotope analyses to detect exogenous citric acid in Japanese apricot liqueur.

    PubMed

    Akamatsu, Fumikazu; Oe, Takaaki; Hashiguchi, Tomokazu; Hisatsune, Yuri; Kawao, Takafumi; Fujii, Tsutomu

    2017-08-01

    Japanese apricot liqueur manufacturers are required to control the quality and authenticity of their liqueur products. Citric acid made from corn is the main acidulant used in commercial liqueurs. In this study, we conducted spiking experiments and carbon and hydrogen stable isotope analyses to detect exogenous citric acid used as an acidulant in Japanese apricot liqueurs. Our results showed that the δ(13)C values detected exogenous citric acid originating from C4 plants but not from C3 plants. The δ(2)H values of citric acid decreased as the amount of citric acid added increased, whether the citric acid originated from C3 or C4 plants. Commercial liqueurs with declared added acidulant provided higher δ(13)C values and lower δ(2)H values than did authentic liqueurs and commercial liqueurs with no declared added acidulant. Carbon and hydrogen stable isotope analyses are suitable as routine methods for detecting exogenous citric acid in Japanese apricot liqueur.

  1. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

    2016-11-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

  2. Characterization of narrow micropores in almond shell biochars by nitrogen, carbon dioxide, and hydrogen adsorption

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Characterization of biochars usually includes surface area and pore volume determination by nitrogen adsorption. In this study, we show that there is a substantial pore volume in biochars created via slow pyrolysis from low- and high-ash almond shells that cannot be characterized in this fashion due...

  3. Towards a palaeosalinity proxy: hydrogen isotopic fractionation between source water and lipids produced via different biosynthetic pathways in haptophyte algae

    NASA Astrophysics Data System (ADS)

    Chivall, David; M'Boule, Daniela; Heinzelmann, Sandra M.; Kasper, Sebastian; Sinke-Schoen, Daniëlle; Sininnghe-Damsté, Jaap S.; Schouten, Stefan; van der Meer, Marcel T. J.

    2014-05-01

    Palaeosalinity is one of the most important oceanographic parameters that cannot currently be quantified with reasonable accuracy from sedimentary records. Hydrogen isotopic fractionation between water and alkenones is dependent, amongst other factors, upon the salinity in which alkenone-producing haptophyte algae grow and is represented by the fractionation factor, α, increasing with salinity.1 As such, the hydrogen isotopic composition of alkenones is emerging as a palaeosalinity proxy. Understanding the mechanism behind the sensitivity of fractionation to salinity is important for the correct application of the proxy, however this mechanism is currently unknown. Here we present hydrogen isotopic compositions of lipids produced via different biosynthetic pathways from batch cultures of Emiliania huxleyi CCMP 1516 and Isochrysis galbana CCMP 1323 grown over a range of salinities and discuss the possible sources of the sensitivity of hydrogen isotope fractionation to salinity. α for C37 alkenones (produced via an unknown biosynthetic pathway but assumed to be acetogenic; e.g.2) and that for C14:0, C16:0, and C18:1 fatty acids (acetogenic) from exponential growth phase I. galbana show a similar sensitivity to salinity, increasing at 0.0013-0.0019 per salinity unit (S-1). Meanwhile, in exponential growth phase E. huxleyi, α for C37 alkenones and α for brassicasterol (mevalonate pathway) increase at 0.0015-0.0022 S-1, but α for phytol (methylerythritol pathway) shows no significant relationship with salinity. These results suggest that fractionation is sensitive to salinity for lipids formed both in the chloroplast and cytosol. They also suggest that the sensitivity may either originate in glyceralde-3-phosphate or pyruvate but is then lost through hydrogen exchange with cell water during sugar rearrangements in the methylerythritol pathway or sensitivity originates with the production and consumption of acetate. References Schouten, S., Ossebaar, J., Schreiber

  4. Iridium(I)-catalyzed regioselective C-H activation and hydrogen-isotope exchange of non-aromatic unsaturated functionality.

    PubMed

    Kerr, William J; Mudd, Richard J; Paterson, Laura C; Brown, Jack A

    2014-11-03

    Isotopic labelling is a key technology of increasing importance for the investigation of new CH activation and functionalization techniques, as well as in the construction of labelled molecules for use within both organic synthesis and drug discovery. Herein, we report for the first time selective iridium-catalyzed CH activation and hydrogen-isotope exchange at the β-position of unsaturated organic compounds. The use of our highly active [Ir(cod)(IMes)(PPh3 )][PF6 ] (cod=1,5-cyclooctadiene) catalyst, under mild reaction conditions, allows the regioselective β-activation and labelling of a range of α,β-unsaturated compounds with differing steric and electronic properties. This new process delivers high levels of isotope incorporation over short reaction times by using low levels of catalyst loading.

  5. Understanding continental-scale variation in plant hydrogen and oxygen isotope ratios - Pseudotsuga menziesii across a 1500 km transect

    NASA Astrophysics Data System (ADS)

    West, J. B.; Wilson, E.; Hyodo, A.

    2013-12-01

    The isotopic composition of plant tissues provides an important recorder of vegetation response to climate. Hydrogen and oxygen isotope ratios have been used to infer precipitation isotope ratios and therefore variability in temperature. While this is the case, important questions remain about the primary drivers of plant tissue hydrogen and oxygen isotope ratio variation, including fundamental questions about the role of plant physiology. Relatively recent work suggests, in some species, an important role of physiology in organic matter d2H, in particular stomatal conductance, while other work suggests a distinct lack of influence of physiology. It is critical that mechanistic models of plant tissue variation in δ2H and δ18O can encompass landscape and larger-scale variability in plant isotope ratios. In particular existing models need to be compared to large-scale observations in order to assess their ability to describe variation in climate and plant physiology driven by such geographic variables as continentality and elevation. We report on ongoing work to better understand the role of climate and other drivers in plant tissue isotopic composition across relatively large spatial scales. An approximately 1500 km-long transect was established from the Continental Divide in North America (at approximately 39° N latitude) to the Coast Range. Leaf, branch, and tree core samples of Pseudotsuga menziesii were collected, along with surface waters. At each location, samples were collected from at least three elevations and on the western and eastern slopes of the target mountain range. Xylem water broadly reflected local precipitation as inferred from a global precipitation isoscape model and local surface water measurements. There was also a clear difference across the transect in apparent access to surface water, with the drier interior showing greater source water evaporative enrichment. In addition, the relationships between leaf water and stem water changed

  6. Hydrogen isotope response to changing salinity and rainfall in Australian mangroves.

    PubMed

    Ladd, S Nemiah; Sachs, Julian P

    2015-12-01

    Hydrogen isotope ratios ((2) H/(1) H, δ(2) H) of leaf waxes covary with those in precipitation and are therefore a useful paleohydrologic proxy. Mangroves are an exception to this relationship because their δ(2) H values are also influenced by salinity. The mechanisms underlying this response were investigated by measuring leaf lipid δ(2) H and leaf and xylem water δ(2) H and δ(18) O values from three mangrove species over 9.5 months in a subtropical Australian estuary. Net (2) H/(1) H fractionation between surface water and leaf lipids decreased by 0.5-1.0‰ ppt(-1) for n-alkanes and 0.4-0.8‰ ppt(-1) for isoprenoids. Xylem water was (2) H depleted relative to surface water, reflecting (2) H discrimination of 4-10‰ during water uptake at all salinities and opportunistic uptake of freshwater at high salinity. However, leaf water (2) H enrichment relative to estuary water was insensitive to salinity and identical for all species. Therefore, variations in leaf and xylem water δ(2) H values cannot explain the salinity-dependent (2) H depletion in leaf lipids, nor the 30‰ range in leaf lipid δ(2) H values among species. Biochemical changes in direct response to salt stress, such as increased compatible solute production or preferential use of stored carbohydrates, and/or the timing of lipid production and subsequent turnover rates, are more likely causes.

  7. Hydrogen Donor-Acceptor Fluctuations from Kinetic Isotope Effects: A Phenomenological Model

    PubMed Central

    Roston, Daniel; Cheatum, Christopher M.; Kohen, Amnon

    2012-01-01

    Kinetic isotope effects (KIEs) and their temperature dependence can probe the structural and dynamic nature of enzyme-catalyzed proton or hydride transfers. The molecular interpretation of their temperature dependence requires expensive and specialized QM/MM calculations to provide a quantitative molecular understanding. Currently available phenomenological models use a non-adiabatic assumption that is not appropriate for most hydride and proton-transfer reactions, while others require more parameters than the experimental data justify. Here we propose a phenomenological interpretation of KIEs based on a simple method to quantitatively link the size and temperature dependence of KIEs to a conformational distribution of the catalyzed reaction. The present model assumes adiabatic hydrogen tunneling, and by fitting experimental KIE data, the model yields a population distribution for fluctuations of the distance between donor and acceptor atoms. Fits to data from a variety of proton and hydride transfers catalyzed by enzymes and their mutants, as well as non-enzymatic reactions, reveal that steeply temperature-dependent KIEs indicate the presence of at least two distinct conformational populations, each with different kinetic behaviors. We present the results of these calculations for several published cases and discuss how the predictions of the calculations might be experimentally tested. The current analysis does not replace molecular quantum mechanics/molecular mechanics (QM/MM) investigations, but it provides a fast and accessible way to quantitatively interpret KIEs in the context of a Marcus-like model. PMID:22857146

  8. Measurement and modeling of oxidation rate of hydrogen isotopic gases by soil.

    PubMed

    Ota, Masakazu; Yamazawa, Hiromi; Moriizumi, Jun; Iida, Takao

    2007-01-01

    Measurements of oxidation rate of hydrogen isotopic gases by soil were made to model HT oxidation rate by soil. Soil was sampled at a cultivated farmland and laboratory measurements of the oxidation rate of H(2) and D(2) gases simulating HT gas were carried out under controlled conditions of soil. The oxidation rate increased with increase of H(2) or D(2) concentration in air and nearly saturated at high concentration. The oxidation rate was low under extremely dry and wet soil conditions and was the highest at soil water content of 8-14 w/w%. The oxidation rate increased exponentially with increasing soil temperature and was the highest at 46 degrees C. Michaelis constant K(m) increased exponentially with increasing soil temperature. Oxidation rate of H(2) was generally higher than that of D(2), while K(m) of H(2) was generally lower than that of D(2). From these results, oxidation rate of HT was modeled as a product of the functions that represent dependency on each soil factor.

  9. Kinetics of hydrogen isotope exchange in β-phase Pd-H-D

    DOE PAGES

    Luo, Weifang; Cowgill, Donald F.

    2015-07-22

    Hydrogen isotope gas exchange within palladium powders is examined using a batch-type reactor coupled to a residual gas analyzer (RGA). Furthermore, the exchange rates in both directions (H2 + PdD and D2 + PdH) are measured in the temperature range 178–323 K for the samples with different particle sizes. The results show this batch-type exchange is closely approximated as a first-order kinetic process with a rate directly proportional to the surface area of the powder particles. An exchange rate constant of 1.40 ± 0.24 μmol H2/atm cm2 s is found for H2 + PdD at 298 K, 1.4 times highermore » than that for D2 + PdH, with an activation energy of 25.0 ± 3.2 kJ/mol H for both exchange directions. Finally, a comparison of exchange measurement techniques shows these coefficients, and the fundamental exchange probabilities are in good agreement with those obtained by NMR and flow techniques.« less

  10. Kinetics of hydrogen isotope exchange in β-phase Pd-H-D

    SciTech Connect

    Luo, Weifang; Cowgill, Donald F.

    2015-07-22

    Hydrogen isotope gas exchange within palladium powders is examined using a batch-type reactor coupled to a residual gas analyzer (RGA). Furthermore, the exchange rates in both directions (H2 + PdD and D2 + PdH) are measured in the temperature range 178–323 K for the samples with different particle sizes. The results show this batch-type exchange is closely approximated as a first-order kinetic process with a rate directly proportional to the surface area of the powder particles. An exchange rate constant of 1.40 ± 0.24 μmol H2/atm cm2 s is found for H2 + PdD at 298 K, 1.4 times higher than that for D2 + PdH, with an activation energy of 25.0 ± 3.2 kJ/mol H for both exchange directions. Finally, a comparison of exchange measurement techniques shows these coefficients, and the fundamental exchange probabilities are in good agreement with those obtained by NMR and flow techniques.

  11. Evolution of water reservoirs on Mars: Constraints from hydrogen isotopes in martian meteorites

    NASA Astrophysics Data System (ADS)

    Kurokawa, H.; Sato, M.; Ushioda, M.; Matsuyama, T.; Moriwaki, R.; Dohm, J. M.; Usui, T.

    2014-05-01

    Martian surface morphology implies that Mars was once warm enough to maintain persistent liquid water on its surface. While the high D/H ratios (˜6 times the Earth's ocean water) of the current martian atmosphere suggest that significant water has been lost from the surface during martian history, the timing, processes, and the amount of the water loss have been poorly constrained. Recent technical developments of ion-microprobe analysis of martian meteorites have provided accurate estimation of hydrogen isotope compositions (D/H) of martian water reservoirs at the time when the meteorites formed. Based on the D/H data from the meteorites, this study demonstrates that the water loss during the pre-Noachian (>41-99 m global equivalent layers, GEL) was more significant than in the rest of martian history (>10-53 m GEL). Combining our results with geological and geomorphological evidence for ancient oceans, we propose that undetected subsurface water/ice (≃100-1000 m GEL) should exist, and it exceeds the observable present water inventory (≃20-30 m GEL) on Mars.

  12. Hydrogen Isotopic Constraints on the Evolution of Surface and Subsurface Water on Mars

    NASA Technical Reports Server (NTRS)

    Usui, T.; Kurokawa, H.; Wang, J.; Alexander, C. M. O’D.; Simon, J. I.; Jones, J. H.

    2017-01-01

    The geology and geomorphology of Mars provide clear evidence for the presence of liquid water on its surface during the Noachian and Hesperien eras (i.e., >3 Ga). In contrast to the ancient watery environment, today the surface of Mars is relatively dry. The current desert-like surface conditions, however, do not necessarily indicate a lack of surface or near-surface water/ice. In fact, massive deposits of ground ice and/or icy sediments have been proposed based on subsurface radar sounder observations. Hence, accurate knowledge of both the evolution of the distribution of water and of the global water inventory is crucial to our understanding of the evolution of the climate and near-surface environments and the potential habitability of Mars. This study presents insights from hydrogen isotopes for the interactive evolution of Martian water reservoirs. In particular, based on our new measurement of the D/H ratio of 4 Ga-old Noachian water, we constrain the atmospheric loss and possible exchange of surface and subsurface water through time.

  13. MECHANICAL ALLOYING AND THERMAL TREATMENT FOR PRODUCTION OF ZIRCONIUM IRON HYDROGEN ISOTOPE GETTERS

    SciTech Connect

    Fox, K.

    2008-02-20

    The objective of this task was to demonstrate that metal hydrides could be produced by mechanical alloying in the quantities needed to support production-scale hydrogen isotope separations. Three starting compositions (ratios of elemental Zr and Fe powders) were selected and attritor milled under argon for times of 8 to 60 hours. In general, milling times of at least 24 hours were required to form the desired Zr{sub 2}Fe and Zr{sub 3}Fe phases, although a considerable amount of unalloyed Zr and Fe remained. Milling in liquid nitrogen does not appear to provide any advantages over milling in hexane, particularly due to the formation of ZrN after longer milling times. Carbides of Zr formed during some of the milling experiments in hexane. Elemental Zr was present in the as-milled material but not detected after annealing for milling times of 48 and 60 hours. It may be that after intimate mixing of the powders in the attritor mill the annealing temperature was sufficient to allow for the formation of a Zr-Fe alloy. Further investigation of this conversion is necessary, and could provide an opportunity for reducing the amount of unreacted metal powder after milling.

  14. Oxygen and hydrogen isotope compositions of eclogites and associated rocks from the Eastern Sesia zone (Western Alps, Italy)

    USGS Publications Warehouse

    Desmons, J.; O'Neil, J.R.

    1978-01-01

    Oxygen and hydrogen isotope analyses have been made of mineral separates from eclogites, glaucophanites and glaucophane schists from the eastern Sesia zone (Italian Western Alps). Regularities in (1) hydrogen isotope compositions, (2) order of 18O enrichment among coexisting minerals, and (3) ?? 18O (quartz-rutile) and ?? 18O (quartz-phengite) imply attainment of a high degree of isotopic equilibrium. However, some scattering of ??18O values of individual minerals indicates that the eclogitic assemblage did not form in the presence of a thoroughly pervasive fluid. Minerals from an eclogitic lens enclosed in marble have ??18O values distinctly different from those measured in the other rocks. The ??18O values are high in comparison with other type C eclogites of the world, and it is proposed that the fluid present during the high pressure metamorphism has to a large extent been inherited from the precursor rocks of amphibolite facies. An average formation temperature of 540 ?? C is inferred from the oxygen isotope fractionations between quartz and rutile and between quartz and white mica. This temperature is in accordance with petrologic considerations and implies subduction of the precursor rocks into the upper mantle to achieve the high pressures required. ?? 1978 Springer-Verlag.

  15. Compound specific carbon and hydrogen stable isotope analyses of volatile organic compounds in various emissions of combustion processes.

    PubMed

    Vitzthum von Eckstaedt, Christiane D; Grice, Kliti; Ioppolo-Armanios, Marisa; Kelly, David; Gibberd, Mark

    2012-11-01

    This study presents carbon (δ(13)C) and hydrogen (δD) isotope values of volatile organic compounds (VOCs) in various emission sources using thermal desorption-gas chromatography-isotope ratio mass spectrometry (TD-GC-irMS). The investigated VOCs ranged from C6 to C10. Samples were taken from (i) car exhaust emissions as well as from plant combustion experiments of (ii) various C3 and (iii) various C4 plants. We found significant differences in δ values of analysed VOCs between these sources, e.g. δ(13)C of benzene ranged between (i) -21.7 ± 0.2 ‰, (ii) -27.6 ± 1.6 ‰ and (iii) -16.3 ± 2.2 ‰, respectively and δD of benzene ranged between (i) -73 ± 13 ‰, (ii) -111 ± 10 ‰ and (iii) -70 ± 24 ‰, respectively. Results of VOCs present in investigated emission sources were compared to values from the literature (aluminium refinery emission). All source groups could be clearly distinguished using the dual approach of δ(13)C and δD analysis. The results of this study indicate that the correlation of compound specific carbon and hydrogen isotope analysis provides the potential for future research to trace the fate and to determine the origin of VOCs in the atmosphere using thermal desorption compound specific isotope analysis.

  16. Determining the Effect of Growth Rate on Hydrogen Isotope Fractionation of Algal Lipids in Two North Pacific Sites

    NASA Astrophysics Data System (ADS)

    Wolfshorndl, M.; Sachs, J. P.

    2015-12-01

    Tropical hydrologic changes have a large effect on global climate, but there does not yet exist a good indicator of rainfall variation in the tropics. Understanding past natural variability of such features as the Intertropical Convergence Zone and El Niño Southern Oscillation provides information about the extent of anthropogenic climate change today. The hydrogen isotopic composition (D/H ratio) of algal lipids has been shown to track the isotopic composition of source water in which the organism grew, providing information about precipitation variability over time. However, culture work has revealed that environmental factors such as salinity, temperature, growth rate, and irradiance also influence algal lipid D/H ratios. Here I present work determining the effect of growth rate and irradiance on the hydrogen isotope composition of alkenone-producing algae in the water column in two North Pacific locations, off the coast of Oregon and near the Hawaii Ocean Time Series site. This work corroborates empirical relationships observed in culture studies and indicates that the effects of growth rate and irradiance should be taken into account when applying the D/H isotope ratio rainfall proxy to reconstruct past climates.

  17. Mechanism of heat generation from loading gaseous hydrogen isotopes into palladium nanoparticles

    NASA Astrophysics Data System (ADS)

    Dmitriyeva, Olga

    I have carried out the study of hydrogen isotope reactions in the presence of palladium nanoparticles impregnated into oxide powder. My goal was to explain the mechanisms of heat generation in those systems as a result of exposure to deuterium gas. Some researchers have associated this heating with a nuclear reaction in the Pd lattice. While some earlier experiments showed a correlation between the generation of excess heat and helium production as possible evidence of a nuclear reaction, the results of that research have not been replicated by the other groups and the search for radiation was unsuccessful. Therefore, the unknown origin of the excess heat produced by these systems is of great interest. I synthesized different types of Pd and Pt-impregnated oxide samples similar to those used by other research groups. I used different characterization techniques to confirm that the fabrication method I used is capable of producing Pd nanoparticles on the surface of alumina support. I used a custom built gas-loading system to pressurize the material with hydrogen and deuterium gas while measuring heat output as a result of these pressurizations. My initial study confirmed the excess heat generation in the presence of deuterium. However, the in-situ radiometry and alpha-particle measurements did not show any abnormal increase in counts above the background level. In the absence of nuclear reaction products, I decided to look for a conventional chemical process that could account for the excess heat generation. It was earlier suggested that Pd in its nanoparticle form catalyzes hydrogen/deuterium (H/D) exchange reactions in the material. To prove the chemical nature of the observed phenomena I demonstrated that the reaction can be either exo- or endothermic based on the water isotope trapped in the material and the type of gas provided to the system. The H/D exchange was confirmed by RGA, NMR and FTIR analysis. I quantified the amount of energy that can be released due

  18. Ab initio calculations for dissociative hydrogen adsorption on lithium oxide surfaces

    SciTech Connect

    Sutjianto, A. |; Tam, S.W.; Curtiss, L.A.; Johnson, C.E.; Pandey, R.

    1994-12-01

    Lithium ceramics are one class of materials being considered as tritium breeders for fusion technology,and hydrogen is known to enhance the release of tritium from lithium ceramic materials. Dissociative hydrogen chemisorption on the Li{sub 2}O surfaces of the (100), (110), and (111) planes has been investigated with ab initio Hartree-Fock calculations. Calculations for unrelaxed crystal Li{sub 2}O structures indicated that except for the (100) surface, the (110) and (111) surfaces are stable. Results on the heterolytic sites of n-layer (110) (where n {ge} 2) slabs and three-layer (111) slabs suggest that dissociative hydrogen chemisorption is endothermic. For a one-layer (110) slab at 100% surface coverage, the dissociative hydrogen chemisorption is exothermic, forming OH{sup {minus}} and Li{sup +}H{sup {minus}}Li{sup +}. The results also indicate that the low coordination environment in surface step structures, such as kinks and ledges, may plan an important role in the hydrogen chemisorption process. On the homolytic sites of the (110) and (111) surfaces, there is no hydrogen chemisorption.

  19. The Carbon and Hydrogen Stable Isotope Composition of Methane Released from Natural Wetlands and Ruminants

    NASA Astrophysics Data System (ADS)

    Lansdown, John Malcolm

    The delta^{13} {rm C} of CH_4 emitted from the tropical Amazon river floodplain, temperate peat bogs in Washington and Minnesota, and the arctic Alaskan tundra was -59, -73, -66, and -65perthous, respectively. The deltaD of CH_4 from these sites was -294, -308, -339, and -391perthous, respectively, and a linear relationship was observed between the deltaD of CH_4 and soil water. A ^{13} C balance between CH_4, CO _2 and soil organic matter indicated a higher percentage of CH_4 production via methyl conversion at the Amazon floodplain than at the other wetland sites and that the anoxic CO _2 flux was 1.5 to 2.0 times the CH _4 flux. The ^{13} C balance provided greater constraint on the anoxic CO_2 flux than calculations based on soil water gradients. An in situ value of 0.774 for the hydrogen kinetic isotope effect during microbial CH _4 oxidation was estimated from the increase in the delta^{13} {rm C} and deltaD of CH_4 in flux samples from the Amazon site. The average delta^{13 }{rm C} of CH_4 released from an acidic peat bog in Washington state (pH = 3.5) was -73perthous, lower than previously measured at freshwater wetland sites. Soil incubations with ^{14 }C-labeled CO_2 and acetate substrates showed that CO_2 reduction accounted for essentially all methane production in the bog. An in situ value of 0.933 for the carbon kinetic isotope effect for CO_2 reduction was calculated from the delta^{13 }{rm C} of the CH_4 flux and soil water CO_2.. The delta^{13} {rm C} and deltaD of CH_4 emitted from ruminants was measured and averaged -63 and -404perthous, respectively. CO _2 reduction accounted for ~70% of rumen CH_4 production based on the change in the delta ^{13}{rm C} and deltaD of rumen CH_4 vs. time during normal conditions and after the addition of deuterated water to the rumen. These results contrast the dogma in the literature that CO_2 reduction accounts for essentially all CH _4 production in the rumen. A global budget for the deltaD of CH_4 was

  20. Analysis of the hydrogen and oxygen stable isotope ratios of beverage waters without prior water extraction using isotope ratio infrared spectroscopy.

    PubMed

    Chesson, Lesley A; Bowen, Gabriel J; Ehleringer, James R

    2010-11-15

    Hydrogen (δ(2)H) and oxygen (δ(18)O) stable isotope analysis is useful when tracing the origin of water in beverages, but traditional analytical techniques are limited to pure or extracted waters. We measured the isotopic composition of extracted beverage water using both isotope ratio infrared spectroscopy (IRIS; specifically, wavelength-scanned cavity ring-down spectroscopy) and isotope ratio mass spectrometry (IRMS). We also analyzed beer, sodas, juices, and milk 'as is' using IRIS. For IRIS analysis, four sequential injections of each sample were measured and data were corrected for sample-to-sample memory using injections (a) 1-4, (b) 2-4, and (c) 3-4. The variation between δ(2)H and δ(18)O values calculated using the three correction methods was larger for unextracted (i.e., complex) beverages than for waters. The memory correction was smallest when using injections 3-4. Beverage water δ(2)H and δ(18)O values generally fit the Global Meteoric Water Line, with the exception of water from fruit juices. The beverage water stable isotope ratios measured using IRIS agreed well with the IRMS data and fit 1:1 lines, with the exception of sodas and juices (δ(2)H values) and beers (δ(18)O values). The δ(2)H and δ(18)O values of waters extracted from beer, soda, juice, and milk were correlated with complex beverage δ(2)H and δ(18)O values (r = 0.998 and 0.997, respectively) and generally fit 1:1 lines. We conclude that it is possible to analyze complex beverages, without water extraction, using IRIS although caution is needed when analyzing beverages containing sugars, which can clog the syringe and increase memory, or alcohol, a known spectral interference.

  1. The influence of intramolecular hydrogen bonds on the adsorption properties of aromatic alcohols and thiols

    NASA Astrophysics Data System (ADS)

    Varfolomeeva, V. V.; Terent'ev, A. V.; Buryak, A. K.

    2008-06-01

    The thermodynamic characteristics of adsorption equilibria of primary aromatic alcohols and thiols on graphitized carbon black at 300 K were determined by the molecular-statistical method. The influence of intramolecular effects under the action of the force field of the sorbent on the conformation of the molecules studied was considered in comparison with n-alkylbenzenes having similar structures. An increase in the chain length by one-CH2 group was shown to influence the formation of intramolecular H-bonds in alcohol and thiol molecules. In adsorption, a considerable fraction of molecules assumed configurations close to planar. An exception was the nonplanar conformation of the 2-phenylethanol molecule stabilized by the intramolecular H-bond.

  2. Metal composition of layered double hydroxides (LDHs) regulating ClO(-)4 adsorption to calcined LDHs via the memory effect and hydrogen bonding.

    PubMed

    Lin, Yajie; Fang, Qile; Chen, Baoliang

    2014-03-01

    A series of calcined carbonate layered double hydroxides (CLDHs) with various metal compositions and different M(2+)/M(3+) ratios were prepared as adsorbents for perchlorate. Adsorption isotherms fit Langmuir model well, and the adsorption amount followed the order of MgAl-CLDHs ≥ MgFe-CLDHs > ZnAl-CLDHs. The isotherms of MgAl-CLDHs and MgFe-CLDHs displayed a two-step shape at low and high concentration ranges and increased with an increase in the M(2+)/M(3+) ratio from 2 to 4. The two-step isotherm was not observed for ZnAl-CLDHs, and the adsorption was minimally affected by the M(2+)/M(3+) ratio. The LDHs, CLDHs and the reconstructed samples were characterized by X-ray diffraction, SEM, FT-IR and Raman spectra to delineate the analysis of perchlorate adsorption mechanisms. The perchlorate adsorption of MgAl-CLDHs and MgFe-CLDHs was dominated by the structural memory effect and the hydrogen bonds between the free hydroxyl groups on the reconstructed-LDHs and the oxygen atoms of the perchlorates. For ZnAl-CLDHs, the perchlorate adsorption was controlled by the structural memory effect only, as the hydroxyl groups on the hydroxide layers preferred to form strong hydrogen bonds with carbonate over perchlorate, which locked the intercalated perchlorate into a more confined nano-interlayer. Several distinct binding mechanisms of perchlorate by CLDHs with unique M(2+) ions were proposed.

  3. Defect formation on the GaSb (001) surface induced by hydrogen atom adsorption

    NASA Astrophysics Data System (ADS)

    Bermudez, V. M.

    2015-06-01

    Density functional theory has been used to characterize the effects of adsorbed H on the electronic structure of the GaSb (001)-α(4×3) surface, which consists of a combination of Ga-Sb and Sb-Sb dimers. Adsorption of two H atoms at a Ga-Sb adatom dimer either has little effect on surface states above the bulk valence band maximum (VBM) or else eliminates them, depending on the mode of adsorption. However, adsorption at the Sb-Sb dimer in the terminating layer produces a state farther into the gap at ~0.10 eV above the clean-surface VBM. Relaxation accompanying the breaking of the Sb-Sb dimer bond leads to increased interactions involving three-fold-coordinated Sb sites in the terminating layer, which in turn raises the energies of the non-bonding lone-pair orbitals. This defect state, which appears to be unique to the reconstructed GaSb (001) surface, could potentially function as a hole trap on the surface of p-type GaSb.

  4. Hydrogen-isotope transport in an ELBRODUR G CuCrZr alloy for nuclear applications in heat sinks

    NASA Astrophysics Data System (ADS)

    Noh, S. J.; Byeon, W. J.; Shin, H. W.; Kim, H. S.; Kim, Jaeyong; Lee, S. K.; Kim, Jaewoo

    2016-05-01

    We present the first complete data set of the transport parameters (permeability, diffusivity, and solubility) of hydrogen and deuterium in an ELBRODUR G precipitation hardened CuCrZr alloy experimentally measured by using the time-dependent gas-phase technique in an elevated temperature range of 300-600 °C for nuclear applications in heat sinks. Using the measured values for hydrogen and deuterium and a quantum mechanical model based on a harmonic approximation, an extrapolation for tritium is also presented. The isotope effect ratios for the transport parameters were also estimated. Furthermore, our hydrogen results for ELBRODUR G were compared with the results for other copper alloys previously reported by other authors.

  5. Theoretical study of hydrogen adsorption on Ca-decorated C{sub 48}B{sub 12} clusters

    SciTech Connect

    Qi, Pengtang; Chen, Hongshan

    2015-09-15

    The hydrogen adsorption on Ca-decorated C{sub 48}B{sub 12} clusters is studied using density functional theory. The favorable binding site for Ca atom is the hexagonal C{sub 4}B{sub 2} rings. The strong interaction between Ca atoms and C{sub 48}B{sub 12} cluster hinders the aggregation of Ca atoms on the cluster surface. C{sub 48}B{sub 12} is an electron deficient system with a large electron affinity of 2.952 eV. The decorated Ca atoms transfer their electrons to the cluster easily. The net charges on the Ca atoms are in the range of 1.101 to 1.563 e. When H{sub 2} molecules approach the Ca atoms, they are moderately polarized and adsorbed around the Ca atoms in molecular form. The adsorption strength can reach up to 0.133 eV/H{sub 2}. Each Ca atom in the Ca-decorated C{sub 48}B{sub 12} complexes can adsorb three H{sub 2} molecules. The fully decorated C{sub 48}B{sub 12}Ca{sub 6} can hold up to 18 H{sub 2} molecules.

  6. Evaluating Changes in Paleo-temperature Gradients using Hydrogen Isotopic Compositions of Leaf-wax Biomarkers

    NASA Astrophysics Data System (ADS)

    Krishnan, S.; Huber, M.; Pagani, M.

    2014-12-01

    A long-standing problem in the paleoclimate modeling community has been the inability of the models to reproduce the shallow meridional temperature gradient (∆T) observed in proxy temperature records for the warm, greenhouse time intervals in Earth's history, such as the early Eocene. It is often stated that this mismatch indicates a missing high-latitude feedback mechanism in the climate models that would cause substantial polar amplification of warming. However, this issue is complicated by the potential biasing of proxy records due to issues related to temperature calibrations and/or diagenesis. In this study, we propose an alternative approach to estimate ∆T for these time intervals using hydrogen isotopic composition of leaf-wax biomarkers (dDleaf-wax) preserved in the sedimentary record. Today, dDleaf-wax is closely related to the hydrological cycle and source vegetation. In the mid- and high-latitudes, dDleaf-wax changes pertaining to the hydrological cycle can be interpreted using a Rayleigh distillation process, where evaporated moisture from the sub-tropics undergoes isotopic fractionation and becomes increasingly D-depleted during poleward transport. We develop a box model based on the Rayleigh distillation process that uses the global mean temperature for the time-period and geological archives of dDleaf-wax to estimate the meridional temperature gradient. We use this box model for the Paleocene-Eocene Thermal Maximum (PETM; ~56Ma), a rapid-warming event in the early Eocene where global warming is accompanied by evidence for increased input of greenhouse gases. We compile existing leaf-wax dDleaf-wax records from the extra-tropics to estimate ∆T before and during the PETM. Preliminary results suggest that the temperature gradient increased during the body of the PETM, contradicting our expectations based on temperature proxies. We also use this approach to estimate ∆T during other intervals in earth's history, such as the early Eocene. Further

  7. Ab initio investigation on hydrogen adsorption capability in Zn and Cu-based metal organic frameworks

    NASA Astrophysics Data System (ADS)

    Tanuwijaya, V. V.; Hidayat, N. N.; Agusta, M. K.; Dipojono, H. K.

    2015-09-01

    One of the biggest challenge in material technology for hydrogen storage application is to increase hydrogen uptake in room temperature and pressure. As a class of highly porous material, Metal-Organic Frameworks (MOF) holds great potential with its tunable structure. However, little is known about the effect of metal cluster to its hydrogen storage capability. Investigation on this matter has been carried out carefully on small cluster of Zn and Cu-based MOF using first principles method. The calculation of two distinct building units of MOFs, namely octahedral and paddle-wheel models, have been done with B3LYP density functional method using 6-31G(d,p) and LANL2DZ basis sets. From geometry optimization of Zn-based MOF linked by benzene-dicarboxylate (MOF-5), it is found that hydrogen tends to keep distance from metal cluster group and stays above benzene ring. In the other hand, hydrogen molecule prefers to stay atop of the exposed Cu atom in Cu-based MOF system linked by the same linker group (Cu-bdc). Calculated hydrogen binding enthalpies for Zn and Cu octahedral cages at ZnO3 sites are 1.64kJ/mol and 2.73kJ/mol respectively, while hydrogen binding enthalpies for Zn and Cu paddle-wheel cages calculated on top of metal atoms are found to be at 6.05kJ/mol and 6.10kJ/mol respectively. Major difference between Zn-MOF-5 and Cu-bdc hydrogen uptake performance might be caused by unsaturated metal sites present in Cu-bdc system and the influence of their geometric structures, although a small difference on binding energy in the type of transition metal used is also observed. The comparison between Zn and Cu-based MOF may contribute to a comprehensive understanding of metal clusters and the importance of selecting best transition metal for design and synthesis of metal-organic frameworks.

  8. Ab initio investigation on hydrogen adsorption capability in Zn and Cu-based metal organic frameworks

    SciTech Connect

    Tanuwijaya, V. V.; Hidayat, N. N. Agusta, M. K. Dipojono, H. K.

    2015-09-30

    One of the biggest challenge in material technology for hydrogen storage application is to increase hydrogen uptake in room temperature and pressure. As a class of highly porous material, Metal-Organic Frameworks (MOF) holds great potential with its tunable structure. However, little is known about the effect of metal cluster to its hydrogen storage capability. Investigation on this matter has been carried out carefully on small cluster of Zn and Cu-based MOF using first principles method. The calculation of two distinct building units of MOFs, namely octahedral and paddle-wheel models, have been done with B3LYP density functional method using 6-31G(d,p) and LANL2DZ basis sets. From geometry optimization of Zn-based MOF linked by benzene-dicarboxylate (MOF-5), it is found that hydrogen tends to keep distance from metal cluster group and stays above benzene ring. In the other hand, hydrogen molecule prefers to stay atop of the exposed Cu atom in Cu-based MOF system linked by the same linker group (Cu-bdc). Calculated hydrogen binding enthalpies for Zn and Cu octahedral cages at ZnO{sub 3} sites are 1.64kJ/mol and 2.73kJ/mol respectively, while hydrogen binding enthalpies for Zn and Cu paddle-wheel cages calculated on top of metal atoms are found to be at 6.05kJ/mol and 6.10kJ/mol respectively. Major difference between Zn-MOF-5 and Cu-bdc hydrogen uptake performance might be caused by unsaturated metal sites present in Cu-bdc system and the influence of their geometric structures, although a small difference on binding energy in the type of transition metal used is also observed. The comparison between Zn and Cu-based MOF may contribute to a comprehensive understanding of metal clusters and the importance of selecting best transition metal for design and synthesis of metal-organic frameworks.

  9. Theoretical Investigation of Hydrogen Adsorption and Dissociation on Iron and Iron Carbide Surfaces Using the ReaxFF Reactive Force Field Method

    SciTech Connect

    Zou, Chenyu; van Duin, Adri C.T.; Sorescu, Dan C.

    2012-06-01

    We have developed a ReaxFF reactive force field to describe hydrogen adsorption and dissociation on iron and iron carbide surfaces relevant for simulation of Fischer–Tropsch (FT) synthesis on iron catalysts. This force field enables large system (>>1000 atoms) simulations of hydrogen related reactions with iron. The ReaxFF force field parameters are trained against a substantial amount of structural and energetic data including the equations of state and heats of formation of iron and iron carbide related materials, as well as hydrogen interaction with iron surfaces and different phases of bulk iron. We have validated the accuracy and applicability of ReaxFF force field by carrying out molecular dynamics simulations of hydrogen adsorption, dissociation and recombination on iron and iron carbide surfaces. The barriers and reaction energies for molecular dissociation on these two types of surfaces have been compared and the effect of subsurface carbon on hydrogen interaction with iron surface is evaluated. We found that existence of carbon atoms at subsurface iron sites tends to increase the hydrogen dissociation energy barrier on the surface, and also makes the corresponding hydrogen dissociative state relatively more stable compared to that on bare iron. These properties of iron carbide will affect the dissociation rate of H{sub 2} and will retain more surface hydride species, thus influencing the dynamics of the FT synthesis process.

  10. Stable hydrogen isotopes record the summering grounds of eastern red bats (Lasiurus borealis).

    PubMed

    Pylant, Cortney L; Nelson, David M; Keller, Stephen R

    2014-01-01

    Bats face numerous threats associated with global environmental change, including the rapid expansion of wind-energy facilities, emerging infectious disease, and habitat loss. An understanding of the movement and migration patterns of these highly dispersive animals would help reveal how spatially localized the impacts from these threats are likely to be on bat populations, thus aiding in their conservation. Stable hydrogen isotope ratios (δ (2)H) can be used to infer regions where bats have foraged during the summer molt season, thus allowing an assessment of summering location and distance of movement of bats sampled during other times of year. However, a major impediment to the application of δ (2)H for inference of bat movements is that the relationship between δ (2)H of bat hair and precipitation tends to be species specific and is still unknown for some key species of conservation concern. We addressed this issue by using geo-referenced museum specimens to calibrate the relationship between δ (2)H of hair (δ (2)Hhair) and long-term δ (2)H of growing-season precipitation (δ (2)HGSprecip) at the site of collection for eastern red bats (Lasiurus borealis), one of the main species of bats experiencing large numbers of fatalities at wind-energy facilities in North America. Based on comparison of δ (2)Hhair and δ (2)HGSprecip values for males we estimated a period of molt of June 14-August 7. Within this period, male and female red bats exhibited a significant positive relationship between δ (2)Hhair and δ (2)HGSprecip. These results establish the relationship between δ (2)Hhair and δ (2)HGSprecip for red bats, which is necessary for the use of δ (2)Hhair to infer the movement and migration patterns of this important species. These results provide a critical resource to conservation biologists working to assess the impacts of environmental change on bat populations.

  11. Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

    NASA Astrophysics Data System (ADS)

    Hinkley, Todd K.; Quick, James E.; Gregory, Robert T.; Gerlach, Terrence M.

    1995-03-01

    Condensate samples were collected in 1992 from a high-temperature (300° C) fumarole on the floor of the Halemaumau Pit Crater at Kilauea. The emergence about two years earlier of such a hot fumarole was unprecedented at such a central location at Kilauea. The condensates have hydrogen and oxygen isotopic compositions which indicate that the waters emitted by the fumarole are composed largely of meteoric water, that any magmatic water component must be minor, and that the precipitation that was the original source to the fumarole fell on a recharge area on the slopes of Mauna Loa Volcano to the west. However, the fumarole has no tritium, indicating that it taps a source of water that has been isolated from atmospheric water for at least 40 years. It is noteworthy, considering the unstable tectonic environment and abundant local rainfall of the Kilauea and Mauna Loa regions, that waters which are sources to the hot fumarole remain uncontaminated from atmospheric sources over such long times and long transport distances. As for the common, boiling point fumaroles of the Kilauea summit region, their 18O, D and tritium concentrations indicate that they are dominated by recycling of present day meteoric water. Though the waters of both hot and boiling point fumaroles have dominantly meteoric sources, they seem to be from separate hydrological regimes. Large concentrations of halogens and sulfur species in the condensates, together with the location at the center of the Kilauea summit region and the high temperature, initially suggested that much of the total mass of the emissions of the hot fumarole, including the H2O, might have come directly from a magma body. The results of the present study indicate that it is unreliable to infer a magmatic origin of volcanic waters based solely on halogen or sulfur contents, or other aspects of chemical composition of total condensates.

  12. Hydrogen isotope detection in metal matrix using double-pulse laser-induced breakdown-spectroscopy

    NASA Astrophysics Data System (ADS)

    Fantoni, Roberta; Almaviva, Salvatore; Caneve, Luisa; Colao, Francesco; Maddaluno, Giorgio; Gasior, Pawel; Kubkowska, Monika

    2017-03-01

    The amount of hydrogen isotopes retained in plasma facing components (PFCs) and the determination of their surface layer composition are among the most critical issues for the next generation fusion device, ITER, under construction in Cadarache (France). Laser Induced Breakdown Spectroscopy (LIBS) is currently under evaluation as a technique suitable for quantitative, in situ, non-invasive measurements of these quantities. In order to detect traces of contaminant in metallic samples and improve its limit of detection (LOD), the Double Pulse LIBS (DP-LIBS) variant can be used instead of the standard Single Pulse LIBS (SP-LIBS), as it has been proven by several authors that DP-LIBS can considerably raise the analytical performances of the technique. In this work Mo samples coated with a 1.5-1.8 μm thick W-Al mixed layer, contaminated with co-deposited deuterium (D) were measured by SP- and DP-LIBS under vacuum (p 5 × 10- 5 mbar), with an experimental set-up simulating conditions that can be found in a real fusion device between plasma discharges. A partial Calibration Free procedure (pCF) was applied to the LIBS data in order to retrieve the relative concentration of W and Al in the mixed layer. The amount of deuterium was then inferred by using tungsten as internal standard, accounting for the intensity ratio between the Dα line and nearby W I lines. The results are in satisfactory agreement with those obtained from preliminary Ion Beam Analysis measurements performed immediately after the specimen's realization.

  13. Hydrogen and oxygen isotopic compositions of waters from fumaroles at Kilauea summit, Hawaii

    USGS Publications Warehouse

    Hinkley, T.K.; Quick, J.E.; Gregory, R.T.; Gerlach, T.M.

    1995-01-01

    Condensate samples were collected in 1992 from a high-temperature (300?? C) fumarole on the floor of the Halemaumau Pit Crater at Kilauea. The emergence about two years earlier of such a hot fumarole was unprecedented at such a central location at Kilauea. The condensates have hydrogen and oxygen isotopic compositions which indicate that the waters emitted by the fumarole are composed largely of meteoric water, that any magmatic water component must be minor, and that the precipitation that was the original source to the fumarole fell on a recharge area on the slopes of Mauna Loa Volcano to the west. However, the fumarole has no tritium, indicating that it taps a source of water that has been isolated from atmospheric water for at least 40 years. It is noteworthy, considering the unstable tectonic environment and abundant local rainfall of the Kilauea and Mauna Loa regions, that waters which are sources to the hot fumarole remain uncontaminated from atmospheric sources over such long times and long transport distances. As for the common, boiling point fumaroles of the Kilauea summit region, their 18O, D and tritium concentrations indicate that they are dominated by recycling of present day meteoric water. Though the waters of both hot and boiling point fumaroles have dominantly meteoric sources, they seem to be from separate hydrological regimes. Large concentrations of halogens and sulfur species in the condensates, together with the location at the center of the Kilauea summit region and the high temperature, initially suggested that much of the total mass of the emissions of the hot fumarole, including the H2O, might have come directly from a magma body. The results of the present study indicate that it is unreliable to infer a magmatic origin of volcanic waters based solely on halogen or sulfur contents, or other aspects of chemical composition of total condensates. ?? 1995 Springer-Verlag.

  14. Stable hydrogen isotopes record the summering grounds of eastern red bats (Lasiurus borealis)

    PubMed Central

    Pylant, Cortney L.; Keller, Stephen R.

    2014-01-01

    Bats face numerous threats associated with global environmental change, including the rapid expansion of wind-energy facilities, emerging infectious disease, and habitat loss. An understanding of the movement and migration patterns of these highly dispersive animals would help reveal how spatially localized the impacts from these threats are likely to be on bat populations, thus aiding in their conservation. Stable hydrogen isotope ratios (δ2H) can be used to infer regions where bats have foraged during the summer molt season, thus allowing an assessment of summering location and distance of movement of bats sampled during other times of year. However, a major impediment to the application of δ2H for inference of bat movements is that the relationship between δ2H of bat hair and precipitation tends to be species specific and is still unknown for some key species of conservation concern. We addressed this issue by using geo-referenced museum specimens to calibrate the relationship between δ2H of hair (δ2Hhair) and long-term δ2H of growing-season precipitation (δ2HGSprecip) at the site of collection for eastern red bats (Lasiurus borealis), one of the main species of bats experiencing large numbers of fatalities at wind-energy facilities in North America. Based on comparison of δ2Hhair and δ2HGSprecip values for males we estimated a period of molt of June 14–August 7. Within this period, male and female red bats exhibited a significant positive relationship between δ2Hhair and δ2HGSprecip. These results establish the relationship between δ2Hhair and δ2HGSprecip for red bats, which is necessary for the use of δ2Hhair to infer the movement and migration patterns of this important species. These results provide a critical resource to conservation biologists working to assess the impacts of environmental change on bat populations. PMID:25337458

  15. Chemical Warfare Agent Surface Adsorption: Hydrogen Bonding of Sarin and Soman to Amorphous Silica.

    PubMed

    Davis, Erin Durke; Gordon, Wesley O; Wilmsmeyer, Amanda R; Troya, Diego; Morris, John R

    2014-04-17

    Sarin and soman are warfare nerve agents that represent some of the most toxic compounds ever synthesized. The extreme risk in handling such molecules has, until now, precluded detailed research into the surface chemistry of agents. We have developed a surface science approach to explore the fundamental nature of hydrogen bonding forces between these agents and a hydroxylated surface. Infrared spectroscopy revealed that both agents adsorb to amorphous silica through the formation of surprisingly strong hydrogen-bonding interactions with primarily isolated silanol groups (SiOH). Comparisons with previous theoretical results reveal that this bonding occurs almost exclusively through the phosphoryl oxygen (P═O) of the agent. Temperature-programmed desorption experiments determined that the activation energy for hydrogen bond rupture and desorption of sarin and soman was 50 ± 2 and 52 ± 2 kJ/mol, respectively. Together with results from previous studies involving other phosphoryl-containing molecules, we have constructed a detailed understanding of the structure-function relationship for nerve agent hydrogen bonding at the gas-surface interface.

  16. Rayleigh-based concept to tackle strong hydrogen fractionation in dual isotope analysis-the example of ethylbenzene degradation by Aromatoleum aromaticum.

    PubMed

    Dorer, Conrad; Höhener, Patrick; Hedwig, Normen; Richnow, Hans-Hermann; Vogt, Carsten

    2014-05-20

    Compound-specific isotope analysis (CSIA) is a state-of-the-art analytical tool that can be used to establish and quantify biodegradation of pollutants such as BTEX compounds at contaminated field sites. Using isotopes of two elements and characteristic Lambda values (Λ) in dual-isotope-plots can provide insight into reaction mechanisms because kinetic isotope effects (KIEs) of both elements are reflected. However, the concept's validity in the case of reactions that show strong isotope fractionation needs to be examined. The anaerobic ethylbenzene degradation pathway of Aromatoleum aromaticum is initiated by the ethylbenzene dehydrogenase-catalyzed monohydroxylation of the benzylic carbon atom. Measurements of stable isotope ratios revealed highly pronounced hydrogen fractionation, which could not be adequately described by the classical Rayleigh approach. This study demonstrates the nonlinear behavior of hydrogen isotope ratios caused by anaerobic ethylbenzene hydroxylation both mathematically and experimentally, develops alternative dual plots to enable the comparison of reactions by considering the reacting atoms, and illustrates the importance of the stereochemical aspects of substrate and product for the quantification of hydrogen fractionation in an enzymatic reaction. With regard to field application, proposals for an improved CSIA evaluation procedure with respect to pronounced hydrogen enrichment are given.

  17. Adsorption and photocatalytic degradation of methylene blue over hydrogen-titanate nanofibres produced by a peroxide method.

    PubMed

    El Saliby, Ibrahim; Erdei, Laszlo; Kim, Jong-Ho; Shon, Ho Kyong

    2013-08-01

    In this study, Degussa P25 TiO2 was partially dissolved in a mixture of hydrogen peroxide and sodium hydroxide at high pH. The fabrication of nanofibres proceeded by the hydrothermal treatment of the solution at 80 °C. This was followed by acid wash in HCl at pH 2 for 60 min, which resulted in the formation of hydrogen-titanate nanofibres. The nanofibres were annealed at 550 °C for 6 h to produce crystalline anatase nanofibres. The nanofibres were characterised for physico-chemical modifications and tested for the adsorption and photocatalytic degradation of methylene blue as a model water pollutant. An average specific surface area of 31.54 m(2)/g, average pore volume of 0.10 cm(3)/g and average pore size of 50 Å were recorded. The nanofibres were effective adsorbents of the model pollutant and adsorbents and good photocatalysts under simulated solar light illumination. No reduction in photocatalytic activity was observed over three complete treatment cycles, and the effective separation of nanofibres was achieved by gravity settling resulting in low residual solution turbidity.

  18. Adsorption and hydrogenation of CO on Pd( 1 1 1 ) and Rh( 1 1 1 ) modified by subsurface vanadium

    NASA Astrophysics Data System (ADS)

    Klötzer, Bernhard; Unterberger, Werner; Hayek, Konrad

    2003-06-01

    On Pd(1 1 1) and Rh(1 1 1) a subsurface alloy of V atoms located mainly in the second metal layer is formed by vapor deposition of V at elevated temperatures. The topmost layer consists exclusively of Pd or Rh atoms in √3×√3 R30° geometry. Neither reversible adsorption of CO under UHV conditions nor hydrogenation of CO at atmospheric pressure lead to surface segregation of V compounds. Numerical simulation and threshold temperature programmed desorption analysis of CO TPD series obtained from the clean and V modified samples showed that the presence of subsurface V significantly reduces the desorption energy of molecular CO over a wide coverage range and changes the coverage-dependence of the desorption energy. The presence of subsurface V atoms promotes CO hydrogenation on both Pd(1 1 1) and Rh(1 1 1). The enhanced catalytic activity is interpreted in view of the reduced CO desorption energies and of surface roughening induced by subsurface alloy growth.

  19. Relative humidity across the Paleocene-Eocene Thermal Maximum via combined hydrogen-oxygen isotope paleohygrometry (Invited)

    NASA Astrophysics Data System (ADS)

    McInerney, F. A.; Bloch, J. I.; Secord, R.; Wing, S. L.; Kraus, M. J.; Boyer, D. M.

    2009-12-01

    The Paleocene-Eocene Thermal Maximum (PETM) presents an opportunity to characterize continental hydrologic changes during rapid and extreme global warming. The Bighorn Basin, Wyoming, USA, has long been recognized for the PETM sequences preserved there and sits in an ideal location for recording hydrologic changes in the interior of North America. The southeast Bighorn Basin is of particular interest because it contains not only alluvial paleosols and vertebrate fossils, but also macrofloral remains from the PETM. The carbon isotope excursion associated with this event is preserved in this part of the Basin in leaf wax lipids, tooth enamel, and bulk organic matter. To characterize the hydrologic changes that occurred during the PETM we are applying a suite of isotopic, paleobotanical and paleopedological approaches to sections in the southeast Bighorn Basin. Reported here are results from the combined hydrogen and oxygen isotope analysis aimed at reconstructing relative humidity. Oxygen isotope ratios (δ18O) of biogenic apatite from mammalian tooth enamel and fish scales vary with environment, physiology and diet. Because mammals are homeothermic, they primarily track surface water values with predictable physiological offsets. Hydrogen isotope ratios (δD) of leaf-wax lipids (long-chain n-alkanes) reflect both meteoric water δD values and additional D-enrichment caused by evapotranspiration. The enrichment factor between water δD and n-alkane δD can therefore be used as a proxy for relative humidity (RH). In this study, δ18O of surface water is estimated using the δ18O of Coryphodon tooth enamel. We use these δ18O values to estimate surface water δD values using the Global Meteoric Water Line (δD = 8δ18O + 10). We then calculate relative humidity from n-alkane δD values using a Craig-Gordon type isotopic model for D-enrichment caused by transpiration from leaves. Results of the combined hydrogen-oxygen isotope paleohygrometer indicate a general rise in

  20. Comparison of two stable hydrogen isotope-ratio measurement techniques on Antarctic surface-water and ice samples

    USGS Publications Warehouse

    Hopple, J.A.; Hannon, J.E.; Coplen, T.B.

    1998-01-01

    A comparison of the new hydrogen isotope-ratio technique of Vaughn et al. ([Vaughn, B.H., White, J.W.C., Delmotte, M., Trolier, M., Cattani, O., Stievenard, M., 1998. An automated system for hydrogen isotope analysis of water. Chem. Geol. (Isot. Geosci. Sect.), 152, 309-319]; the article immediately preceding this article) for the analysis of water samples utilizing automated on-line reduction by elemental uranium showed that 94% of 165 samples of Antarctic snow, ice, and stream water agreed with the ??2H values determined by H2-H2O platinum equilibration, exhibiting a bias of +0.5??? and a 2 - ?? variation of 1.9???. The isotopic results of 10 reduction technique samples, however, gave ??2H values that differed by 3.5??? or more, and were too negative by as much as 5.4??? and too positive by as much as 4.9??? with respect to those determined using the platinum equilibration technique.