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Sample records for hydrogen desorption kinetics

  1. Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Carter, Richard J.; Schneider, Thomas P.; Nemanich, Robert J.

    2015-09-15

    The desorption kinetics of molecular hydrogen (H{sub 2}) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H{sub 2} desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH{sub 2/3}), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H{sub 2} desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H{sub 2} evolved from subsurface states and 450 °C exposure leading to more H{sub 2} desorption from surface SiH{sub x} species. Additional surface desorption states were observed, which were attributed to H{sub 2} desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H{sub 2} desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.

  2. 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)

  3. Kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys

    SciTech Connect

    Sharp, J.W. ); Eres, G. )

    1993-05-31

    The kinetics of hydrogen desorption in surface-limited thin-film growth of SiGe alloys from binary mixtures of disilane and digermane was investigated by surface differential reflectance. The hydrogen desorption process from the alloy surface was found to consist of two components. Both components are thermally activated, but the activation energies appear to equal neither the hydrogen desorption energy from pure silicon nor that from pure germanium surfaces. We suggest that the two components represent Ge- and Si-mediated hydrogen desorption, with the former being more rapid than the latter.

  4. Tunneling effects in the kinetics of helium and hydrogen isotopes desorption from single-walled carbon nanotube bundles

    SciTech Connect

    Danilchenko, B. A. Yaskovets, I. I.; Uvarova, I. Y.; Dolbin, A. V.; Esel'son, V. B.; Basnukaeva, R. M.; Vinnikov, N. A.

    2014-04-28

    The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent with theoretical prediction.

  5. Desorption kinetics of {H}/{Mo(211) }

    NASA Astrophysics Data System (ADS)

    Lopinski, G. P.; Prybyla, J. A.; Estrup, P. J.

    1994-08-01

    The desorption kinetics of the {H}/{Mo(211) } chemisorption system were studied by thermal desorption and measurement of adsorption isobars. Analysis of the steady-state measurements permits the independent determination of the desorption energy ( Ed) and prefactor ( v). These quantities are found to depend strongly on coverage, with ( Ed) varying continuously from 145 {kJ}/{mol} at low coverage to 65 {kJ}/{mol} near saturation. Three regions of hydrogen adsorption are clearly indicated by the isobars as well as the thermal desorption traces. These regions can be correlated with structural changes observed previously with HREELS and LEED. The coverage dependence of the kinetic parameters is attributed to hydrogen-induced local distortions of the substrate structure. By relating the desorption energy to the isosteric heat the partial molar entropy is also extracted from the data and indicates localized adsorption as well as significant adsorbate-induced changes in the substrate degrees of freedom.

  6. Gas Diffusion in Metals: Fundamental Study of Helium-Point Defect Interactions in Iron and Kinetics of Hydrogen Desorption from Zirconium Hydride

    NASA Astrophysics Data System (ADS)

    Hu, Xunxiang

    The behavior of gaseous foreign species (e.g., helium and hydrogen), which are either generated, adsorbed or implanted within the structural materials (e.g., iron and zirconium) exposed to irradiation environments, is an important and largely unsolved topic, as they intensively interact with the irradiation-induced defects, or bond with the lattice atoms to form new compounds, and impose significant effects on their microstructural and mechanical properties in fission and fusion reactors. This research investigates two cases of gas diffusion in metals (i.e., the helium-point defect interactions in iron and kinetics of hydrogen desorption from zirconium hydride) through extensive experimental and modeling studies, with the objective of improving the understanding of helium effects on the microstructures of iron under irradiation and demonstrating the kinetics of hydrogen diffusion and precipitation behavior in zirconium that are crucial to predict cladding failures and hydride fuel performance. The study of helium effects in structural materials aims to develop a self-consistent, experimentally validated model of helium---point defect, defect cluster and intrinsic defects through detailed inter-comparisons between experimental measurements on helium ion implanted iron single crystals and computational models. The combination of thermal helium desorption spectrometry (THDS) experiment with the cluster dynamic model helps to reveal the influence of impurities on the energetics and kinetics of the He-defect interactions and to realize the identification of possible mechanisms governing helium desorption peaks. Positron annihilation spectroscopy is employed to acquire additional information on He-vacancy cluster evolution, which provides an opportunity to validate the model qualitatively. The inclusion of He---self-interstitial clusters extends the cluster dynamic model while MD simulations explore the effects of dislocation loops on helium clustering. In addition, the

  7. Erbium hydride thermal desorption : controlling kinetics.

    SciTech Connect

    Ferrizz, Robert Matthew

    2007-08-01

    Thermal desorption spectroscopy (TDS) is used to study the decomposition kinetics of erbium hydride thin films. The TDS results presented in this report show that hydride film processing parameters directly impact thermal stability. Issues to be addressed include desorption kinetics for dihydrides and trihydrides, and the effect of film growth parameters, loading parameters, and substrate selection on desorption kinetics.

  8. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    SciTech Connect

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-21

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53–75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  9. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    NASA Astrophysics Data System (ADS)

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-01

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53-75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  10. Molecular beam-thermal hydrogen desorption from palladium

    SciTech Connect

    Lobo, R. F. M.; Berardo, F. M. V.; Ribeiro, J. H. F.

    2010-04-15

    Among the most efficient techniques for hydrogen desorption monitoring, thermal desorption mass spectrometry is a very sensitive one, but in certain cases can give rise to uptake misleading results due to residual hydrogen partial pressure background variations. In this work one develops a novel thermal desorption variant based on the effusive molecular beam technique that represents a significant improvement in the accurate determination of hydrogen mass absorbed on a solid sample. The enhancement in the signal-to-noise ratio for trace hydrogen is on the order of 20%, and no previous calibration with a chemical standard is required. The kinetic information obtained from the hydrogen desorption mass spectra (at a constant heating rate of 1 deg. C/min) accounts for the consistency of the technique.

  11. Superior hydrogen desorption kinetics of Mg(NH{sub 2}){sub 2} hollow nanospheres mixed with MgH{sub 2} nanoparticles

    SciTech Connect

    Xie Lei; Li Yaoqi; Yang Rong; Liu Yang; Li Xingguo

    2008-06-09

    Mg{sub 3}N{sub 2} nanocubes were prepared by vaporized bulk magnesium in ammonia atmosphere associated with plasma metal reaction. Then the product transformed to Mg(NH{sub 2}){sub 2} hollow nanospheres after it was reacted with NH{sub 3} based on the Kirkendall effect. The electron microscopy results suggested that the obtained hollow nanospheres were around 100 nm and the shell thickness was about 10 nm. Because of its short distance for Mg{sup 2+} diffusion and large specific surface area for interaction between Mg(NH{sub 2}){sub 2} and MgH{sub 2}, the structure dramatically enhanced the hydrogen desorption kinetics of Mg(NH{sub 2}){sub 2}-2MgH{sub 2}.

  12. Thermal desorption of hydrogen from the diamond C(100) surface

    NASA Astrophysics Data System (ADS)

    Su, C.; Lin, J.-C.

    1998-05-01

    Temperature-programmed desorption (TPD) is used to measure the kinetics of hydrogen desorption from the C(100) surface. Two major desorption channels, attributed to hydrogen desorption from (2×1) domains ( α sites) and disordered domain boundaries sites ( β sites) were observed. The change in the morphology of the C(100) surface upon hydrogen adsorption/desorption leads to a variation in the intensity ratio between the two hydrogen desorption peaks. The degradation results in smaller (2×1) domains, as evidenced by deteriorated LEED patterns in which the characteristic (2×1) half-order spots disappear. The (2×1) LEED pattern can be restored on the degraded C(100) surface by repeated hydrogenation-annealing cycles in the temperature range 300-1100 K. Fitting the experimental TPD data with simulated curves from the two-site model shows that desorption from the α site obeys first-order kinetics with a prefactor of 1.4±0.9×10 13 s -1 and an activation energy of 80.3±1.3 kcal mol -1, whereas the process giving rise to the β peak follows second-order kinetics with a prefactor of 2.3±0.9×10 13 s -1 (expressed in first-order units) and an activation energy of 75.1±0.5 kcal mol -1. Possible mechanisms for first-order recombinative hydrogen desorption from the C(100)-(2×1) surface are also discussed.

  13. Desorption kinetics of cesium from Fukushima soils.

    PubMed

    Murota, Kento; Saito, Takumi; Tanaka, Satoru

    2016-03-01

    Understanding the behaviors of Cs(+) in soils is crucial for evaluation of the impacts of disposal of soils contaminated by radiocesium, (137)Cs. The desorption rate of Cs(+) evaluated in relatively short periods of time may not be adequate for such a purpose. In this study, we investigated long-term desorption kinetics of (137)Cs and (133)Cs from soils collected in Fukushima Prefecture by batch desorption experiments in the presence of cation exchange resin as a sorbent. The sorbent can keep the concentration of Cs(+) in the aqueous phase low and prevent re-sorption of desorbed Cs(+). Up to 60% of (137)Cs was desorbed after 139 d in dilute KCl media, which was larger than the desorption by conventional short-term extraction with 1 M ammonium acetate. Desorption of (137)Cs continued even after this period. It was also found that high concentration of K(+) prevented desorption of Cs(+) in the initial stage of desorption, but the effect was alleviated with time. The desorbed fraction of stable Cs was smaller than that of (137)Cs. This indicated that (137)Cs may gradually move to more stable states in soils. The half-life of (137)Cs desorption from the slowest sorption site was estimated to be at least two years by a three-site desorption model. PMID:26773507

  14. Diffusion Analysis Of Hydrogen-Desorption Measurements

    NASA Technical Reports Server (NTRS)

    Danford, Merlin D.

    1988-01-01

    Distribution of hydrogen in metal explains observed desorption rate. Report describes application of diffusion theory to anaylsis of experimental data on uptake and elimination of hydrogen in high-strength alloys of 25 degree C. Study part of program aimed at understanding embrittlement of metals by hydrogen. Two nickel-base alloys, Rene 41 and Waspaloy, and one ferrous alloy, 4340 steel, studied. Desorption of hydrogen explained by distribution of hydrogen in metal. "Fast" hydrogen apparently not due to formation of hydrides on and below surface as proposed.

  15. Adsorption-Desorption Kinetics of Soft Particles

    NASA Astrophysics Data System (ADS)

    Osberg, Brendan; Nuebler, Johannes; Gerland, Ulrich

    2015-08-01

    Adsorption-desorption processes are ubiquitous in physics, chemistry, and biology. Models usually assume hard particles, but within the realm of soft matter physics the adsorbing particles are compressible. A minimal 1D model reveals that softness fundamentally changes the kinetics: Below the desorption time scale, a logarithmic increase of the particle density replaces the usual Rényi jamming plateau, and the subsequent relaxation to equilibrium can be nonmonotonic and much faster than for hard particles. These effects will impact the kinetics of self-assembly and reaction-diffusion processes.

  16. A continuous hydrogen desorption model from zirconium hydride and subsequent metal in Vacuum

    SciTech Connect

    Hu, X.; Terrani, K. A.; Wirth, B. D.

    2013-07-01

    Predictions of a one-dimensional, moving boundary model coupled with a kinetic description of hydrogen desorption from a two-phase region of {delta}-ZrH{sub 1.6{+-}}n and {alpha}-Zr have been compared with the hydrogen flux obtained in a thermal desorption spectroscopy experiment. The model accurately reproduces the major features of the hydrogen desorption flux on the sample surface after executing a parameter optimization. (authors)

  17. Superior hydrogen absorption and desorption behavior of Mg thin films

    NASA Astrophysics Data System (ADS)

    Qu, Jianglan; Wang, Yuntao; Xie, Lei; Zheng, Jie; Liu, Yang; Li, Xingguo

    Pd-capped Mg films prepared by magnetron sputtering achieved complete dehydrogenation in air at room temperature and behaved as favorable gasochromic switchable mirrors. Their cyclic hydrogen absorption and desorption kinetics in air were investigated by using the Bruggeman effective medium approximation. The overall activation energy was 80 kJ mol -1, while the reaction orders controlling desorption were deduced to be n = 2 at 328 K and n = 1 at lower temperatures by analyzing the transmittance data. The hydrogen diffusion coefficient and the corresponding activation energy were calculated by electrochemical measurements. Mg thin films exhibited the smaller activation energy and remarkable diffusion kinetics at room temperature which implied potential applications in smart windows.

  18. Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Nemanich, Robert J.

    2014-09-01

    The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H{sub 2}O), fluorine (F{sub 2}), hydrogen (H{sub 2}), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) diluted in methanol (CH{sub 3}OH). Pre-TPD XPS measurements of the CH{sub 3}OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H{sub 2}, H{sub 2}O, HF, F{sub 2}, and CH{sub 3}OH with some evidence for nitrogen (N{sub 2}) and ammonia (NH{sub 3}) desorption as well. For H{sub 2}O, two desorption peaks with second order kinetics were observed at 195 and 460 °C with activation energies (E{sub d}) of 51 ± 3 and 87 ± 5 kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475 °C and E{sub d} of 110 ± 5 kJ/mol. The TPD spectra for F{sub 2} exhibited two peaks at 485 and 585 °C with second order kinetics and E{sub d} of 62 ± 3 and 270 ± 10 kJ/mol, respectively. These values are in excellent agreement with previous E{sub d} measurements for desorption of H{sub 2}O from SiO{sub 2} and AlF{sub x} from AlN surfaces, respectively. The F{sub 2} desorption is therefore attributed to fragmentation of AlF{sub x} species in the mass spectrometer ionizer. H{sub 2} desorption exhibited

  19. HYDROGEN AND ITS DESORPTION IN RHIC.

    SciTech Connect

    HSEUH,H.C.

    2002-11-11

    Hydrogen is the dominating gas specie in room temperature, ultrahigh vacuum systems of particle accelerators and storage rings, such as the Relativistic Heavy Ion Collider (RHIC) at Brookhaven. Rapid pressure increase of a few decades in hydrogen and other residual gases was observed during RHIC's recent high intensity gold and proton runs. The type and magnitude of the pressure increase were analyzed and compared with vacuum conditioning, beam intensity, number of bunches and bunch spacing. Most of these pressure increases were found to be consistent with those induced by beam loss and/or electron stimulated desorption from electron multipacting.

  20. Extremely fast hydrogen absorption/desorption through platinum overlayers

    NASA Astrophysics Data System (ADS)

    Połczyński, Piotr; Jurczakowski, Rafał

    2016-02-01

    The hydrogen electrosorption in thin palladium films (50-1000 nm) was investigated at palladium electrodes covered with platinum overlayers. The results for this model system show that the rates of the hydrogen sorption/desorption are orders of magnitude higher for platinized samples with respect to pure palladium. The highest absorption kinetics have been observed for Pd electrodes fully covered with 1-3 platinum monolayers. By means of electrochemical impedance spectroscopy (EIS) we have shown that the process is diffusion limited at platinized Pd layers. Diffusion coefficient, DH, determined in EIS, is two orders of magnitude higher than that previously reported for thin palladium films and approaches DH for bulk palladium. The system stability after hydrogen absorption was assessed and the sorption mechanism was discussed. Surprisingly high durability of the platinized palladium enables its use in a variety of applications where fast and selective response in the presence of hydrogen is required.

  1. Desorption Kinetics of Methanol, Ethanol, and Water from Graphene

    SciTech Connect

    Smith, R. Scott; Matthiesen, Jesper; Kay, Bruce D.

    2014-09-18

    The desorption kinetics of methanol, ethanol, and water from graphene covered Pt(111) are investigated. The temperature programmed desorption (TPD) spectra for both methanol and ethanol have well-resolved first, second, third, and multilayer layer desorption peaks. The alignment of the leading edges is consistent with zero-order desorption kinetics from all layers. In contrast, for water the first and second layers are not resolved. At low water coverages (< 1 ML) the initial desorption leading edges are aligned but then fall out of alignment at higher temperatures. For thicker water layers (10 to 100 ML), the desorption leading edges are in alignment throughout the desorption of the film. The coverage dependence of the desorption behavoir suggests that at low water coverages the non-alignment of the desorption leading edges is due to water dewetting from the graphene substrate. Kinetic simulations reveal that the experimental results are consistent with zero-order desorption. The simulations also show that fractional order desorption kinetics would be readily apparent in the experimental TPD spectra.

  2. Hydrogen chemisorption and thermal desorption on the diamond C(111) surface

    NASA Astrophysics Data System (ADS)

    Su, C.; Song, K.-J.; Wang, Y. L.; Lu, H.-L.; Chuang, T. J.; Lin, J.-C.

    1997-11-01

    Temperature programmed desorption (TPD) and low energy electron diffraction (LEED) were utilized to study the interaction of atomic hydrogen with single crystal diamond C(111) surface. From isotherm and isostere analysis of TPD spectra acquired at various sample heating rates ranging from 0.6 K/s to 30 K/s, the kinetic parameters were extracted. It is found that molecular hydrogen desorption from the C(111) surface exhibits the first-order kinetics. This result is confirmed by no apparent shift in peak temperatures of TPD spectra for hydrogen coverage above 0.2 ML. At lower coverage regime, the isothermal desorption experiment also indicates the first-order desorption kinetics. A nearly coverage-independent activation energy of (3.7±0.1) eV and a prefactor of (9.5±4.0)×1013s-1 are obtained except at relatively low coverages (below ˜0.2 ML). In addition, the half-order LEED spots intensity decreases linearly with increase of the hydrogen coverage and drops to zero at ˜0.5 ML. These results are interpreted with a model that during adsorption hydrogen atoms segregate to form metastable, highly hydrogenated domains from where hydrogen atoms recombine and desorb concertedly as the substrate surface is heated up. The comparison of this work with the hydrogen adsorption and desorption on silicon surfaces is also discussed.

  3. Hydrogen desorption properties of hydrogenated UThZr alloys

    NASA Astrophysics Data System (ADS)

    Suwarno, Hadi; Yamamoto, Takuya; Ono, Futaba; Yamaguchi, Kenji; Yamawaki, Michio

    1997-08-01

    Hydrogen desorption properties of hydrogenated UThZr alloys of varied compositions were investigated using a hydrogen absorption-desorption experimental system, TG-DTA and DSC analyzers. Isothermal desorption at 900°C of elemental ratio U:Th:Zr:H = 1:1:4:9.5 exhibited that there were two distinct plateau regions identified as ZrH 1.4-ZrH and ThZr 2H 7- x - ThZr 2 systems. TG-DTA and DSC measurements under the temperature range from room temperature to 1000°C have shown that there were three endothermic peaks identified as dehydrogenation reactions of ZrH 2 - x - ZrH and ThZr 2H 7-x. The DTA curve identified the first peak area as the ZrH 1.4-ZrH system, while the DSC curves identified that the second peak is the decomposition of ZrH and the third peak is the decomposition of ThZr 2H 7 - x. It was also shown that both ZrH 2 - x and ThZr 2H 7 - x are more stable in the alloy than the pure ones. Measured enthalpy changes during decomposition of the hydrogenated UThZr alloy are similar to the theoretical calculation. Oxidation during measurement of the U:Th:Zr:H = 2:1:6:13.1 resulted in a different measured enthalpy change and calculation. Isothermal decomposition of the U:Th:Zr:H = 1:1:4:9.5 without any disintegration indicates stability of the alloy against powdering on hydriding-dehydriding cycles. Stability of the samples at high temperature similar to that of UZrH 1.6 for TRIGA fuel can be maintained after the decomposition.

  4. Kinetics of desorption of organic compounds from dissolved organic matter.

    PubMed

    Kopinke, Frank-Dieter; Ramus, Ksenia; Poerschmann, Juergen; Georgi, Anett

    2011-12-01

    This study presents a new experimental technique for measuring rates of desorption of organic compounds from dissolved organic matter (DOM) such as humic substances. The method is based on a fast solid-phase extraction of the freely dissolved fraction of a solute when the solution is flushed through a polymer-coated capillary. The extraction interferes with the solute-DOM sorption equilibrium and drives the desorption process. Solutes which remain sorbed to DOM pass through the extraction capillary and can be analyzed afterward. This technique allows a time resolution for the desorption kinetics from subseconds up to minutes. It is applicable to the study of interaction kinetics between a wide variety of hydrophobic solutes and polyelectrolytes. Due to its simplicity it is accessible for many environmental laboratories. The time-resolved in-tube solid-phase microextraction (TR-IT-SPME) was applied to two humic acids and a surfactant as sorbents together with pyrene, phenanthrene and 1,2-dimethylcyclohexane as solutes. The results give evidence for a two-phase desorption kinetics: a fast desorption step with a half-life of less than 1 s and a slow desorption step with a half-life of more than 1 min. For aliphatic solutes, the fast-desorbing fraction largely dominates, whereas for polycyclic aromatic hydrocarbons such as pyrene, the slowly desorbing, stronger-bound fraction is also important. PMID:22035249

  5. Current-Driven Hydrogen Desorption from Graphene: Experiment and Theory.

    PubMed

    Gao, Li; Pal, Partha Pratim; Seideman, Tamar; Guisinger, Nathan P; Guest, Jeffrey R

    2016-02-01

    Electron-stimulated desorption of hydrogen from the graphene/SiC(0001) surface at room temperature was investigated with ultrahigh vacuum scanning tunneling microscopy and ab initio calculations in order to elucidate the desorption mechanisms and pathways. Two different desorption processes were observed. In the high electron energy regime (4-8 eV), the desorption yield is independent of both voltage and current, which is attributed to the direct electronic excitation of the C-H bond. In the low electron energy regime (2-4 eV), however, the desorption yield exhibits a threshold dependence on voltage, which is explained by the vibrational excitation of the C-H bond via transient ionization induced by inelastic tunneling electrons. The observed current independence of the desorption yield suggests that the vibrational excitation is a single-electron process. We also observed that the curvature of graphene dramatically affects hydrogen desorption. Desorption from concave regions was measured to be much more probable than desorption from convex regions in the low electron energy regime (∼2 eV), as would be expected from the identified desorption mechanism. PMID:26787160

  6. Sequential desorption energy of hydrogen from nickel clusters

    SciTech Connect

    Deepika,; Kumar, Rakesh; R, Kamal Raj.; Kumar, T. J. Dhilip

    2015-06-24

    We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage and regeneration of Hydrogen as a clean energy carrier.

  7. Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces

    SciTech Connect

    King, Sean W. Tanaka, Satoru; Davis, Robert F.; Nemanich, Robert J.

    2015-09-15

    Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H{sub 2}) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700–1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H{sub 2} desorption at both lower temperatures (200–550 °C) as well as higher temperatures (>700 °C). The low temperature H{sub 2} desorption was deconvoluted into multiple desorption states that, based on similarities to H{sub 2} desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H{sub 2} desorption was similarly attributed to H{sub 2} evolved from surface O-H groups at ∼750 °C as well as the liberation of H{sub 2} during Si-O desorption at temperatures >800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at <700 °C remain terminated by some surface C–O and

  8. Modelling of discrete TDS-spectrum of hydrogen desorption

    NASA Astrophysics Data System (ADS)

    Rodchenkova, Natalia I.; Zaika, Yury V.

    2015-12-01

    High concentration of hydrogen in metal leads to hydrogen embrittlement. One of the methods to evaluate the hydrogen content is the method of thermal desorption spectroscopy (TDS). As the sample is heated under vacuumization, atomic hydrogen diffuses inside the bulk and is desorbed from the surface in the molecular form. The extraction curve (measured by a mass-spectrometric analyzer) is recorded. In experiments with monotonous external heating it is observed that background hydrogen fluxes from the extractor walls and fluxes from the sample cannot be reliably distinguished. Thus, the extraction curve is doubtful. Therefore, in this case experimenters use discrete TDS-spectrum: the sample is removed from the analytical part of the device for the specified time interval, and external temperature is then increased stepwise. The paper is devoted to the mathematical modelling and simulation of experimental studies. In the corresponding boundary-value problem with nonlinear dynamic boundary conditions physical- chemical processes in the bulk and on the surface are taken into account: heating of the sample, diffusion in the bulk, hydrogen capture by defects, penetration from the bulk to the surface and desorption. The model aimed to analyze the dynamics of hydrogen concentrations without preliminary artificial sample saturation. Numerical modelling allows to choose the point on the extraction curve that corresponds to the initial quantity of the surface hydrogen, to estimate the values of the activation energies of diffusion, desorption, parameters of reversible capture and hydride phase decomposition.

  9. Hydrogen formation in PDRs: Laboratory stuides on recombinative hydrogen desorption from graphite

    NASA Astrophysics Data System (ADS)

    Baouche, Saoud; Hornekær, Liv; Petrunin, V. V.; Luntz, Alan C.; Zecho, T.; Baurichter, Arnd

    Recent laboratory studies have shown that hydrogen atoms with temperatures exceeding 2000K, corresponding to velocities higher than 0.6 Km/s, adsorb into the chemisorption state on graphite surfaces [Zecho (2002)], at conditions similar to those occuring near dissociation fronts in photo dissociation regions (PDRs) [Hollenbach, & Tielens (1999)]. In the same study it was found by thermal desorption spectroscopy that hydrogen desorbs recombinatively with first order kinetics at temperatures around 450 K on a laboratory time scale [Zecho (2002)]. The corresponding desorption energy is compatible with 1.3eV, a value derived from an elaborate density functional analysis [Sha, & Jackson (2002)]. We present and discuss results of laboratory investigations on the dynamics of the molecular hydrogen formation reaction. In our ultra high vacuum surface science apparatus, we first cover a highly oriented pyrolitically grown graphite (0001) surface (HOPG) at room temperature with hydrogen atoms from a thermal cracker type atom source (T(H)= 2000K). We then apply pulsed laser assisted associative desorption (LAAD)[Diekhoner (2001)] to measure time-of-flight distributions of hydrogen and deuterium molecules released from the surface. We find that the molecules are ejected with high translational energies into the gas phase. The translational energy distribution peaks at around 1.3eV and is about 1.0eV wide, indicating that in the extreme up to 1/2 of the recombination energy is going into the translational co-ordinate. Molecules desorbing from step edges desorb at higher temperatures but exhibit a lower translational energy component, compatible with a surface temperature Maxwell Boltzmann distribution. Angular resolved measurements show that the desorption is sharply peaked into the direction of the surface normal, the width of the distribution depending on the surface temperature and the nature of the 'launch site' (basal plane sites/ edge site). An isotope effect could not be

  10. Patterning graphene at the nanometer scale via hydrogen desorption.

    SciTech Connect

    Sessi, P.; Guest, J. R.; Bode, M.; Guisinger, N.; Center for Nanoscale Materials; Politecnico di Milano

    2009-12-01

    We have demonstrated the reversible and local modification of the electronic properties of graphene by hydrogen passivation and subsequent electron-stimulated hydrogen desorption with an scanning tunneling microscope tip. In addition to changing the morphology, we show that the hydrogen passivation is stable at room temperature and modifies the electronic properties of graphene, opening a gap in the local density of states. This insulating state is reversed by local desorption of the hydrogen, and the unaltered electronic properties of graphene are recovered. Using this mechanism, we have 'written' graphene patterns on nanometer length scales. For patterned regions that are roughly 20 nm or greater, the inherent electronic properties of graphene are completely recovered. Below 20 nm we observe dramatic variations in the electronic properties of the graphene as a function of pattern size. This reversible and local mechanism for modifying the electronic properties of graphene has far-reaching implications for nanoscale circuitry fabricated from this revolutionary material.

  11. Role of deuterium desorption kinetics on the thermionic emission properties of polycrystalline diamond films with respect to kinetic isotope effects

    SciTech Connect

    Paxton, W. F. Howell, M.; Kang, W. P.; Davidson, J. L.; Brooks, M. M.; Tolk, N.

    2014-06-21

    The desorption kinetics of deuterium from polycrystalline chemical vapor deposited diamond films were characterized by monitoring the isothermal thermionic emission current behavior. The reaction was observed to follow a first-order trend as evidenced by the decay rate of the thermionic emission current over time which is in agreement with previously reported studies. However, an Arrhenius plot of the reaction rates at each tested temperature did not exhibit the typical linear behavior which appears to contradict past observations of the hydrogen (or deuterium) desorption reaction from diamond. This observed deviation from linearity, specifically at lower temperatures, has been attributed to non-classical processes. Though no known previous studies reported similar deviations, a reanalysis of the data obtained in the present study was performed to account for tunneling which appeared to add merit to this hypothesis. Additional investigations were performed by reevaluating previously reported data involving the desorption of hydrogen (as opposed to deuterium) from diamond which further indicated this reaction to be dominated by tunneling at the temperatures tested in this study (<775 °C). An activation energy of 3.19 eV and a pre-exponential constant of 2.3 × 10{sup 12} s{sup −1} were determined for the desorption reaction of deuterium from diamond which is in agreement with previously reported studies.

  12. Adsorption-desorption kinetics of soft particles onto surfaces

    NASA Astrophysics Data System (ADS)

    Osberg, Brendan; Gerland, Ulrich

    A broad range of physical, chemical, and biological systems feature processes in which particles randomly adsorb on a substrate. Theoretical models usually assume ``hard'' (mutually impenetrable) particles, but in soft matter physics the adsorbing particles can be effectively compressible, implying ``soft'' interaction potentials. We recently studied the kinetics of such soft particles adsorbing onto one-dimensional substrates, identifying three novel phenomena: (i) a gradual density increase, or ''cramming'', replaces the usual jamming behavior of hard particles, (ii) a density overshoot, can occur (only for soft particles) on a time scale set by the desorption rate, and (iii) relaxation rates of soft particles increase with particle size (on a lattice), while hard particles show the opposite trend. The latter occurs since unjamming requires desorption and many-bodied reorganization to equilibrate -a process that is generally very slow. Here we extend this analysis to a two-dimensional substrate, focusing on the question of whether the adsorption-desorption kinetics of particles in two dimensions is similarly enriched by the introduction of soft interactions. Application to experiments, for example the adsorption of fibrinogen on two-dimensional surfaces, will be discussed.

  13. Chemisorption kinetics of hydrogen on evaporated iron films

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1975-01-01

    Measurements were made of the isothermal adsorption-desorption kinetics for H2 chemisorbed onto Fe films. The chemisorption process is observed to proceed via a precursor state of adsorbed molecular hydrogen similar to the H2-Ni system. The first measurements of the activation energy for desorption, and estimates of the values of the fast kinetic rates between the precursor and chemisorbed states are reported. Adsorption into the precursor state does not appear to be activated, but the process connecting the precursor state with the chemisorbed state will, under certain circumstances, be a rate limiting step for adsorption. The effects of contamination of the surface are evidenced in the measurements.

  14. Chemisorption kinetics of hydrogen on evaporated iron films

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1975-01-01

    An investigation is conducted of the kinetics of isothermal adsorption-desorption processes involving molecular hydrogen which is chemisorbed onto thin (20 to 50 A) polycrystalline Fe films at temperatures near 300 K. The results of the investigation indicate that chemisorption in the H2-Fe system occurs via a precursor state of molecularly adsorbed hydrogen. Contamination of the surface from unknown impurities in the gas phase is found to affect the number of available adsorption sites and to modify the prefactor for the absolute desorption rate constant for the precursor state.

  15. Kinetics of ethylene oxide desorption from sterilized materials.

    PubMed

    Mendes, Gisela C; Brandão, Teresa R S; Silva, Cristina L M

    2013-01-01

    Ethylene oxide gas is commonly used to sterilize medical devices, and concerns about using this agent on biological systems are well-established. Medical devices sterilized by ethylene oxide must be properly aerated to remove residual gas and by-products. In this work, kinetics of ethylene oxide desorption from different sterilized materials were studied in a range of aeration temperatures. The experimental data were well-described by a Fickian diffusion mass transfer behavior, and diffusivities were estimated for two textile and two polymeric materials within the temperature range of 1.5 to 59.0 degrees C. The results will allow predictions of ethylene oxide desorption, which is a key step for the design of sterilization/aeration processes, contributing to an efficient removal of residual ethylene oxide content. PMID:23513954

  16. Thermal Desorption Kinetics of Volatiles on Silicate ``Smokes:'' Analog to Micrometeoric Impact Vapor Condensates

    NASA Astrophysics Data System (ADS)

    McLain, J. L.; Sarantos, M.; Johnson, N. M.; Keller, J. W.; Nuth, J. A.; Farrell, W. M.

    2015-11-01

    Laboratory measurements of the thermal desorption kinetics of Ar, H2O and other common lunar volatiles on silicate smokes will be presented, with a focus on comparing the desorption energies and surface chemistry with other regolith analogs.

  17. A thermal desorption spectroscopy study of hydrogen trapping in polycrystalline α-uranium

    SciTech Connect

    Lillard, R. S.; Forsyth, R. T.

    2015-03-14

    The kinetics of hydrogen desorption from polycrystalline α-uranium (α-U) was examined using thermal desorption spectroscopy (TDS). The goal was to identify the major trap sites for hydrogen and their associated trap energies. In polycrystalline α-U six TDS adsorption peaks were observed at temperatures of 521 K, 556 K, 607 K, 681 K, 793 K and 905 K. In addition, the desorption was determined to be second order based on peak shape. The position of the first three peaks was consistent with desorption from UH3. To identify the trap site corresponding to the high temperature peaks the data were compared to a plastically deformed sample and a high purity single crystal sample. The plastically deformed sample allowed the identification of trapping at dislocations while the single crystal sample allow for the identification of high angle boundaries and impurities. Thus, with respect to the desorption energy associated with each peak, values between 12.9 and 26.5 kJ/mole were measured.

  18. A thermal desorption spectroscopy study of hydrogen trapping in polycrystalline α-uranium

    DOE PAGESBeta

    Lillard, R. S.; Forsyth, R. T.

    2015-03-14

    The kinetics of hydrogen desorption from polycrystalline α-uranium (α-U) was examined using thermal desorption spectroscopy (TDS). The goal was to identify the major trap sites for hydrogen and their associated trap energies. In polycrystalline α-U six TDS adsorption peaks were observed at temperatures of 521 K, 556 K, 607 K, 681 K, 793 K and 905 K. In addition, the desorption was determined to be second order based on peak shape. The position of the first three peaks was consistent with desorption from UH3. To identify the trap site corresponding to the high temperature peaks the data were compared tomore » a plastically deformed sample and a high purity single crystal sample. The plastically deformed sample allowed the identification of trapping at dislocations while the single crystal sample allow for the identification of high angle boundaries and impurities. Thus, with respect to the desorption energy associated with each peak, values between 12.9 and 26.5 kJ/mole were measured.« less

  19. Hydrogen retention in tungsten materials studied by Laser Induced Desorption

    NASA Astrophysics Data System (ADS)

    Zlobinski, M.; Philipps, V.; Schweer, B.; Huber, A.; Reinhart, M.; Möller, S.; Sergienko, G.; Samm, U.; 't Hoen, M. H. J.; Manhard, A.; Schmid, K.; Textor Team

    2013-07-01

    Development of methods to characterise the first wall in ITER and future fusion devices without removal of wall tiles is important to support safety assessments for tritium retention and dust production and to understand plasma wall processes in general. Laser based techniques are presently under investigation to provide these requirements, among which Laser Induced Desorption Spectroscopy (LIDS) is proposed to measure the deuterium and tritium load of the plasma facing surfaces by thermal desorption and spectroscopic detection of the desorbed fuel in the edge of the fusion plasma. The method relies on its capability to desorb the hydrogen isotopes in a laser heated spot. The application of LID on bulk tungsten targets exposed to a wide range of deuterium fluxes, fluences and impact energies under different surface temperatures is investigated in this paper. The results are compared with Thermal Desorption Spectrometry (TDS), Nuclear Reaction Analysis (NRA) and a diffusion model.

  20. Electrochemical desorption of hydrogen atoms adsorbed on liquid gallium

    SciTech Connect

    Krivenko, A.G.; Vekin, A.B.; Benderskii, V.A.

    1987-12-01

    Laser-pulse electron photoemission was used to measure absolute values of the rate constants, W/sub 3/, of electrochemical desorption (ECD) of hydrogen atoms from liquid gallium. The W/sub 3/ were shown to be a linear function of hydrogen concentration, in accord with the fact that both hydrogen ions and water molecules are involved in desorption. The components of W/sub 3/ arising from the two reaction channels are exponential functions of electrode potential, and in their order of magnitude (approx. 10/sup 8/ liter/mole x sec and approx. 10/sup 6/ sec/sup -1/) are close to the corresponding constants for mercury and bismuth. In the desorption involving hydrogen ions, the H/D isotope effect decreases from 5 to 3 as the overpotential is raised from 0.75 to 1.15 V. It was suggested that isotope effects which are higher than those found for Hg and Bi electrodes arise from longer proton tunneling distance.

  1. Desorption of hydrogen trapped in carbon and graphite

    NASA Astrophysics Data System (ADS)

    Atsumi, H.; Takemura, Y.; Miyabe, T.; Konishi, T.; Tanabe, T.; Shikama, T.

    2013-11-01

    Thermal desorption behavior of deuterium (D2) from isotropic graphites and a carbon fiber carbon composite (CFC) charged with D2 gas has been investigated to obtain information concerning hydrogen recycling and tritium inventory in fusion experimental devices as well as a futuristic fusion reactor. After thermal desorption experiments were conducted at temperatures up to 1740 K, a desorption peak at approximately 1600 K (peak 4) was discovered. This is in addition to the previously known peak at approximately 1300 K (peak 3). Peak 3 can be attributed to the release of deuterium controlled by the diffusion process in a graphite filler grain and peak 4 can be attributed to the detrapping of deuterium released from an interstitial cluster loop edge site. Activation energies of peaks 3 and 4 are estimated to be 3.48 and 6.93 eV, respectively. TDS spectra of D2 from graphite and CFCs had previously not been thoroughly investigated. A desorption peak at approximately 1600 K was discovered in the TDS spectra for all samples heated with a linear ramp rate of 0.1 K/s. For an isotropic graphite, ISO-880U, four desorption peaks were recognized in the TDS spectra at approximately 660 K, 900 K, 1300 K, and 1600 K. These peaks were named as peaks 1, 2, 3, and 4 in order of increasing temperature. Major desorption peaks (i.e., peaks 3 and 4) were analyzed and discussed in detail. The temperature of peak 3 was dependent on the size of a graphite filler grain. The desorption process is suggested to be controlled by deuterium diffusion within the filler grain with a strong influence of trapping sites, where the migration takes place as a sequence of detrapping and retrapping. The desorption for peak 4 can be ascribed to the detrapping reaction from an interstitial cluster loop edge site. Activation energies were estimated from the peak shift by varying the heating rate of TDS to be 3.48 and 6.93 eV for peaks 3 and 4, respectively. Theoretical desorption curves for peaks 3 and 4 with

  2. Tunneling Desorption of Single Hydrogen on the Surface of Titanium Dioxide.

    PubMed

    Minato, Taketoshi; Kajita, Seiji; Pang, Chi-Lun; Asao, Naoki; Yamamoto, Yoshinori; Nakayama, Takashi; Kawai, Maki; Kim, Yousoo

    2015-07-28

    We investigated the reaction mechanism of the desorption of single hydrogen from a titanium dioxide surface excited by the tip of a scanning tunneling microscope (STM). Analysis of the desorption yield, in combination with theoretical calculations, indicates the crucial role played by the applied electric field. Instead of facilitating desorption by reducing the barrier height, the applied electric field causes a reduction in the barrier width, which, when coupled with the electron excitation induced by the STM tip, leads to the tunneling desorption of the hydrogen. A significant reduction in the desorption yield was observed when deuterium was used instead of hydrogen, providing further support for the tunneling-desorption mechanism. PMID:26158720

  3. Measurement of hydrogen solubility and desorption rate in V-4Cr-4Ti and liquid lithium-calcium alloys

    SciTech Connect

    Park, J.H.; Erck, R.; Park, E.T.

    1997-04-01

    Hydrogen solubility in V-4Cr-4Ti and liquid lithium-calcium was measured at a hydrogen pressure of 9.09 x 10{sup {minus}4} torr at temperatures between 250 and 700{degrees}C. Hydrogen solubility in V-4Cr-4Ti and liquid lithium decreased with temperature. The measured desorption rate of hydrogen in V-4Cr-4Ti is a thermally activated process; the activation energy is 0.067 eV. Oxygen-charged V-4Cr-4Ti specimens were also investigated to determine the effect of oxygen impurity on hydrogen solubility and desorption in the alloy. Oxygen in V-4Cr-4Ti increases hydrogen solubility and desorption kinetics. To determine the effect of a calcium oxide insulator coating on V-4Cr-4Ti, hydrogen solubility in lithium-calcium alloys that contained 0-8.0 percent calcium was also measured. The distribution ratio R of hydrogen between liquid lithium or lithium-calcium and V-4Cr-4Ti increased as temperature decreased (R {approx} 10 and 100 at 700 and 250{degrees}C, respectively). However at <267{degrees}C, solubility data could not be obtained by this method because of the slow kinetics of hydrogen permeation through the vanadium alloy.

  4. Thermal Desorption Analysis of Hydrogen in High Strength Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Enomoto, M.; Hirakami, D.; Tarui, T.

    2012-02-01

    Thermal desorption analyses (TDA) were conducted in high strength martensitic steels containing carbon from 0.33 to 1.0 mass pct, which were charged with hydrogen at 1223 K (950 °C) under hydrogen of one atmospheric pressure and quenched to room temperature. In 0.33C steel, which had the highest M s temperature, only one desorption peak was observed around 373 K (100 °C), whereas two peaks, one at a similar temperature and the other around and above 573 K (300 °C), were observed in the other steels, the height of the second peak increasing with carbon content. In 0.82C steel, both peaks disappeared during exposure at room temperature in 1 week, whereas the peak heights decreased gradually over 2 weeks in specimens electrolytically charged with hydrogen and aged for varying times at room temperature. From computer simulation, by means of the McNabb-Foster theory coupled with theories of carbon segregation, these peaks are likely to be due to trapping of hydrogen in the strain fields and cores of dislocations, and presumably to a lesser extent in prior austenite grain boundaries. The results also indicate that carbon atoms prevent and even expel hydrogen from trapping sites during quenching and aging in these steels.

  5. Reduction Kinetics of Graphene Oxide Determined by Temperature Programmed Desorption

    NASA Astrophysics Data System (ADS)

    Ventrice, Carl; Clark, Nicholas; Field, Daniel; Geisler, Heike; Jung, Inhwa; Yang, Dongxing; Piner, Richard; Ruoff, Rodney

    2009-10-01

    Graphene oxide, which is an electrical insulator, shows promise for use in several technological applications such as dielectric layers in nanoscale electronic devices or as the active region of chemical sensors. In principle, graphene oxide films could also be used as a precursor for the formation of large-scale graphene films by either thermal or chemical reduction of the graphene oxide. In order to determine the thermal stability and reduction kinetics of graphene oxide, temperature program desorption (TPD) measurements have been performed on multilayer films of graphene oxide deposited on SiO2/Si(100) substrates. The graphene oxide was exfoliated from the graphite oxide source material by slow-stirring in aqueous solution, which produces single-layer platelets with an average lateral size of ˜10 μm. From the TPD measurements, it was determined that the decomposition process begins at ˜80 ^oC. The primary desorption products of the graphene oxide films for temperatures up to 300 ^oC are H2O, CO2, and CO, with only trace amounts of O2 being detected. An activation energy of 1.4 eV/molecule was determined by assuming an Arrhenius dependence for the decomposition process.

  6. Adsorption and Desorption of Hydrogen by Gas-Phase Palladium Clusters Revealed by In Situ Thermal Desorption Spectroscopy.

    PubMed

    Takenouchi, Masato; Kudoh, Satoshi; Miyajima, Ken; Mafuné, Fumitaka

    2015-07-01

    Adsorption and desorption of hydrogen by gas-phase Pd clusters, Pdn(+), were investigated by thermal desorption spectroscopy (TDS) experiments and density functional theory (DFT) calculations. The desorption processes were examined by heating the clusters that had adsorbed hydrogen at room temperature. The clusters remaining after heating were monitored by mass spectrometry as a function of temperature up to 1000 K, and the temperature-programmed desorption (TPD) curve was obtained for each Pdn(+). It was found that hydrogen molecules were released from the clusters into the gas phase with increasing temperature until bare Pdn(+) was formed. The threshold energy for desorption, estimated from the TPD curve, was compared to the desorption energy calculated by using DFT, indicating that smaller Pdn(+) clusters (n ≤ 6) tended to have weakly adsorbed hydrogen molecules, whereas larger Pdn(+) clusters (n ≥ 7) had dissociatively adsorbed hydrogen atoms on the surface. Highly likely, the nonmetallic nature of the small Pd clusters prevents hydrogen molecule from adsorbing dissociatively on the surface. PMID:26043808

  7. Effect of Synthesized MgNi4Y Catalyst on Hydrogen Desorption Properties of Milled MgH2

    NASA Astrophysics Data System (ADS)

    ChitsazKhoyi, Leila; Raygan, Shahram; Pourabdoli, Mehdi

    2015-03-01

    It has been reported that ball milling and adding catalyst can improve hydrogen desorption properties of MgH2. In this study, simultaneous effect of adding catalyst and ball milling on hydrogen desorption properties of MgH2 was studied. Mechanical alloying and heat treatment methods were used to synthesize MgNi4Y intermetallic as a catalyst. In this regard, pure Mg, Ni, and Y elemental powders were ball milled in different conditions and then heat treated at 1073 K (800 °C) for 4 hours. XRD and FESEM methods were used to investigate properties of the samples. It was found that, after 10 hours of ball milling and then heat treating at 1073 K (800 °C), MgNi4Y intermetallic was formed almost completely. The results of Sievert tests showed that as-received MgH2 did not release any significant amount of hydrogen at 623 K (350 °C). But, after ball milling for 10 hours, 0.8 wt pct hydrogen was released from MgH2 at 623 K (350 °C) in 40 minutes. Adding 10 wt pct catalyst via ball milling to MgH2 led to releasing 3.5 wt pct hydrogen in the same conditions. In addition, increasing ball milling time from 10 to 65 hours increased the amount of released hydrogen from 51 to 85 pct of theoretical hydrogen desorption value and improved kinetic of desorption process.

  8. Revisited reaction-diffusion model of thermal desorption spectroscopy experiments on hydrogen retention in material

    SciTech Connect

    Guterl, Jerome Smirnov, R. D.; Krasheninnikov, S. I.

    2015-07-28

    Desorption phase of thermal desorption spectroscopy (TDS) experiments performed on tungsten samples exposed to flux of hydrogen isotopes in fusion relevant conditions is analyzed using a reaction-diffusion model describing hydrogen retention in material bulk. Two regimes of hydrogen desorption are identified depending on whether hydrogen trapping rate is faster than hydrogen diffusion rate in material during TDS experiments. In both regimes, a majority of hydrogen released from material defects is immediately outgassed instead of diffusing deeply in material bulk when the evolution of hydrogen concentration in material is quasi-static, which is the case during TDS experiments performed with tungsten samples exposed to flux of hydrogen isotopes in fusion related conditions. In this context, analytical expressions of the hydrogen outgassing flux as a function of the material temperature are obtained with sufficient accuracy to describe main features of thermal desorption spectra (TDSP). These expressions are then used to highlight how characteristic temperatures of TDSP depend on hydrogen retention parameters, such as trap concentration or activation energy of detrapping processes. The use of Arrhenius plots to characterize retention processes is then revisited when hydrogen trapping takes place during TDS experiments. Retention processes are also characterized using the shape of desorption peaks in TDSP, and it is shown that diffusion of hydrogen in material during TDS experiment can induce long desorption tails visible aside desorption peaks at high temperature in TDSP. These desorption tails can be used to estimate activation energy of diffusion of hydrogen in material.

  9. Removal of semivolatiles from soils by steam stripping. IV. Effects of adsorption/desorption kinetics

    SciTech Connect

    Rodriguez-Maroto, J.M.; Gomez-Lahoz, C.; Wilson, D.J.

    1995-07-01

    A mathematical model is developed for in-situ steam stripping of semivolatile organic compounds (SVOCs) in which the adsorption isotherm of the SVOCs on the soil is nonlinear and in which desorption kinetics may be rate limiting. Severe tailing, similar to that found with diffusion-limited steam stripping, is readily produced by the model, even under situations in which adsorption-desorption kinetics are rapid. The results also indicate that field experiments alone are not likely to be able to distinguish between limitations imposed on the rate of steam-stripping remediation by diffusion kinetics and those imposed by desorption kinetics.

  10. A study of the kinetics of isothermal nicotine desorption from silicon dioxide

    NASA Astrophysics Data System (ADS)

    Adnadjevic, Borivoj; Lazarevic, Natasa; Jovanovic, Jelena

    2010-12-01

    The isothermal kinetics of nicotine desorption from silicon dioxide (SiO 2) was investigated. The isothermal thermogravimetric curves of nicotine at temperatures of 115 °C, 130 °C and 152 °C were recorded. The kinetic parameters ( Ea, ln A) of desorption of nicotine were calculated using various methods (stationary point, model constants and differential isoconversion method). By applying the "model-fitting" method, it was found that the kinetic model of nicotine desorption from silicon dioxide was a phase boundary controlled reaction (contracting volume). The values of the kinetic parameters, Ea,α and ln Aα, complexly change with changing degree of desorption and a compensation effect exists. A new mechanism of activation for the desorption of the absorbed molecules of nicotine was suggested in agreement with model of selective energy transfer.

  11. Effect of carbon on hydrogen desorption and absorption of mechanically milled MgH 2

    NASA Astrophysics Data System (ADS)

    Shang, C. X.; Guo, Z. X.

    The use of MgH 2, instead of pure Mg, in the mechanical synthesis of Mg-based hydrogen storage materials offers added benefit to powder size refinement and reduced oxygen contamination. Alloying additions can further improve the sorption kinetics at a relatively low temperature. This paper examines the effect of graphitic carbon on the desorption and absorption of MgH 2. Graphite powder of different concentrations were mechanically milled with MgH 2 particles. The milled powder was characterised by XRD, SEM and simultaneous TG and DSC techniques. The results show that graphite poses little influence on the desorption properties of MgH 2. However, it does benefit the absorption process, leading to rapid hydrogen uptake in the re-hydrogenated sample. After dehydrogenation, 5 wt.% of hydrogen was re-absorbed within 30 min at 250 °C for the ( MgH 2+10 G) mixture prior-milled for 8 h, while only 0.8 wt.% for the pure MgH 2 milled for 8 h, the effect may be attributed to the interaction between crystalline graphite with H 2 disassociation close to the MgH 2 or Mg surface. Moreover, graphite can also inhibit the formation of a new oxide layer on the surface of Mg particles.

  12. Kinetics of surfactant desorption at an air-solution interface.

    PubMed

    Morgan, C E; Breward, C J W; Griffiths, I M; Howell, P D; Penfold, J; Thomas, R K; Tucker, I; Petkov, J T; Webster, J R P

    2012-12-18

    The kinetics of re-equilibration of the anionic surfactant sodium dodecylbenzene sulfonate at the air-solution interface have been studied using neutron reflectivity. The experimental arrangement incorporates a novel flow cell in which the subphase can be exchanged (diluted) using a laminar flow while the surface region remains unaltered. The rate of the re-equilibration is relatively slow and occurs over many tens of minutes, which is comparable with the dilution time scale of approximately 10-30 min. A detailed mathematical model, in which the rate of the desorption is determined by transport through a near-surface diffusion layer into a diluted bulk solution below, is developed and provides a good description of the time-dependent adsorption data. A key parameter of the model is the ratio of the depth of the diffusion layer, H(c), to the depth of the fluid, H(f), and we find that this is related to the reduced Péclet number, Pe*, for the system, via H(c)/H(f) = C/Pe*(1/2). Although from a highly idealized experimental arrangement, the results provide an important insight into the "rinse mechanism", which is applicable to a wide variety of domestic and industrial circumstances. PMID:23167573

  13. Discovery of spontaneous deformation of Pd metal during hydrogen absorption/desorption cycles

    PubMed Central

    Yamazaki, Toshimitsu; Sato, Masaharu; Itoh, Satoshi

    2009-01-01

    A drastic deformation was observed in Pd metal of various shapes after hydrogen absorption and desorption cycles at 150 °C at a gas pressure of 1–5 MPa. All of the phenomena observed indicate that some strong internal force is induced spontaneously during hydrogen absorption/desorption cycles to produce a collective deformation so as to minimize the surface. PMID:19444010

  14. An investigation of the desorption of hydrogen from lithium oxide using temperature programmed desorption and diffuse reflectance infrared spectroscopy

    SciTech Connect

    Kopasz, J.P.; Johnson, C.E.; Ortiz-Villafuerte, J.

    1994-09-01

    The addition of hydrogen to the purge stream has been shown to enhance tritium release from ceramic breeder materials. In an attempt to determine the mechanism for this enhancement the authors have investigated the adsorption and desorption of hydrogen and water from lithium oxide (a leading candidate for the breeder material) by temperature programmed desorption and diffuse reflectance infrared spectroscopy. The results from these studies indicate that several different types of hydroxide groups are formed on the lithium oxide surface. They also suggest that under certain conditions hydride species form on the surface. The role of these species in tritium release from lithium oxide is discussed.

  15. Synergy on catalytic effect of Fe-Zr additives mixed in different proportions on the hydrogen desorption from MgH{sub 2}

    SciTech Connect

    Kale, A.; Bazzanella, N.; Checchetto, R.; Miotello, A.

    2009-05-18

    Mg films with mixed Fe and Zr metallic additives were prepared by rf magnetron sputtering keeping the total metal content constant, about 7 at. %, and changing the [Fe]/[Zr] ratio. Isothermal hydrogen desorption curves showed that the kinetics depends on [Fe]/[Zr] ratio and is fastest when the [Fe]/[Zr] ratio is {approx}1.8. X-ray diffraction analysis revealed formation of Fe nanoclusters and Mg grain refinement. The improvement of the hydrogen desorption kinetics can be explained by the presence of atomically dispersed Zr and Fe nanoclusters acting as nucleation centers, as well as Mg grain refinement.

  16. Kinetics of uranium(VI) desorption from contaminated sediments: effect of geochemical conditions and model evaluation.

    PubMed

    Liu, Chongxuan; Shi, Zhenqing; Zachara, John M

    2009-09-01

    Stirred-flow cell experiments were performed to investigate the kinetics of uranyl [U(VI)] desorption from a contaminated sedimentcollected from the Hanford 300 Area at the U.S. Department of Energy Hanford Site, Washington. Three influent solutions of variable pH, Ca and carbonate concentrations that affected U(VI) aqueous and surface speciation were used under dynamic flow conditions to evaluate the effect of geochemical conditions on the rate of U(Vl) desorption. The measured rate of U(VI) desorption varied with solution chemical composition that evolved as a result of thermodynamic and kinetic interactions between the solutions and sediment The solution chemical composition that led to a larger disequilibrium between adsorbed U(VI) and equilibrium adsorption state yielded a faster desorption rate. The experimental results were used to evaluate a multirate, surface complexation model (SCM) that has been proposed to describe U(VI) desorption kinetics in the Hanford sedimentthat contained complex adsorbed U(VI) in mass transfer limited domains (Lui et al. Water Resour. Res. 2008, 44, W08413). The model was modified and supplemented by including multirate, ion exchange reactions to describe the geochemical interactions between the solutions and sediment With the same setof model parameters, the modified model reasonably well described the evolution of major ions and the rates of U(VI) desorption under variable geochemical and flow conditions, implying that the multirate SCM is an effective way to describe U(VI) desorption kinetics in subsurface sediments. PMID:19764217

  17. Selective photon-stimulated desorption of hydrogen from GaAs surfaces.

    PubMed

    Petravic, M; Deenapanray, P N; Comtet, G; Hellner, L; Dujardin, G; Usher, B F

    2000-03-01

    Photon-stimulated desorption of H(+) from hydrogenated GaAs (110) and (100) surfaces was studied as a function of photon energy. Distinct peaks, observed around As 3d core-level binding energy for desorption from the GaAs (100) surface and in the As 3d and Ga 3p region for desorption from the GaAs (110) surface, show a striking similarity with the fine structure (spin-orbit splitting) measured in the photoemission from As 3d and Ga 3p levels. These results provide clear evidence for direct desorption processes and represent a basis for selective modification of hydrogenated GaAs surfaces. PMID:11017257

  18. A New Approach to Simulate the Kinetics of Metal Desorption from Mineral Surfaces

    NASA Astrophysics Data System (ADS)

    Tinnacher, R. M.; Powell, B. A.; Kersting, A. B.; Zavarin, M.

    2010-12-01

    The relevance of colloid-facilitated metal transport is largely dependent on metal sorption/desorption kinetics and the degree of reversibility of metal surface binding. Thus, transport predictions need to incorporate modeling concepts that can simulate time- and history-dependent surface processes on the microscale. In this study, we characterized the sorption and desorption kinetics of neptunium(V) reactions on goethite in a flow-cell experiment. Modeling was used to evaluate differences between sorption and desorption kinetics in terms of aging, hysteresis, and ‘irreversible’ sorption. First, aging represents a series of surface-chemical processes on the microscale that lead to changes in contaminant surface speciation over time. Second, hysteresis effects indicate fundamental, chemical differences in the microscopic pathways of reactions for net sorption and desorption processes. Both phenomena may result in a sorbed contaminant fraction that is not readily available for exchange with the solution phase (apparent irreversible sorption). Most currently available kinetic sorption/desorption models incorporate fundamental changes in adsorption and desorption behavior indirectly, e.g., by postulating surface sites with different kinetic rates or ‘irreversible’ sorption behavior. We propose a new approach that allows for the specific incorporation of changes in overall reaction pathways for (ad)sorption and desorption processes. Based on experimental results, observed rates for Np(V) desorption from goethite are substantially slower than for (ad)sorption processes. Differences in metal sorption and desorption kinetics can be simulated with a minimum number of fitting parameters by combining isotherm-based sorption rate laws with a modeling concept related to transition state theory (TST). This concept is based on the assumption that changes in reaction pathways for (ad)sorption and desorption processes lead to differences in overall driving forces and

  19. The effect of stress on hydrogen uptake and desorption by A-286

    NASA Technical Reports Server (NTRS)

    Danford, Merlin D.

    1991-01-01

    The uptake and desorption of hydrogen by A-286 as a function of stress was studied using electrochemical methods. It was found that the apparent surface hydrogen concentration, the mean hydrogen concentration, and the hydrogen distribution uniformity all increased up to a stress level 50 percent of yield and decreased thereafter. The value of the hydrogen diffusion coefficient was relatively unaffected by stress while the percent of trapped hydrogen appeared to decrease with increasing stress.

  20. Long-term kinetics of uranyl desorption from sediments under advective conditions

    NASA Astrophysics Data System (ADS)

    Shang, Jianying; Liu, Chongxuan; Wang, Zheming; Zachara, John

    2014-02-01

    Long-term (>4 months) column experiments were performed to investigate the kinetics of uranyl (U(VI)) desorption in sediments collected from the Integrated Field Research Challenge site at the U.S. Department of Energy Hanford 300 Area. The experimental results were used to evaluate alternative multirate surface complexation reaction (MRSCR) approaches to describe the short and long-term kinetics of U(VI) desorption under flow conditions. The surface complexation reaction (SCR) stoichiometry and equilibrium constants and multirate parameters in the MRSCR models were independently characterized in batch and stirred flow-cell reactors. MRSCR models that were either additively constructed using the MRSCRs for individual size fractions, or composite in nature, could effectively describe short-term U(VI) desorption under flow conditions. The long-term desorption results, however, revealed that using the labile U concentration measured by carbonate extraction underestimated desorbable U(VI) and the long-term rate of U(VI) desorption. This study also found that the gravel size fraction (2-8 mm), which is typically treated as nonreactive in modeling U(VI) reactive transport because of low external surface area, can have an important effect on the U(VI) desorption in the sediment. This study demonstrates an approach to effectively extrapolate U(VI) desorption kinetics for field-scale application and identifies important parameters and uncertainties affecting model predictions.

  1. Optimization and kinetic modeling of cadmium desorption from citrus peels: a process for biosorbent regeneration.

    PubMed

    Njikam, Eloh; Schiewer, Silke

    2012-04-30

    Citrus peel biosorbents are efficient in removing heavy metals from wastewater. Heavy metal recovery and sorbent regeneration are important for the financial competitiveness of biosorption with other processes. The desorbing agents HNO(3), NaNO(3), Ca(NO(3))(2), EDTA, S, S-EDDS, and Na-Citrate were studied at different concentrations to optimize cadmium elution from orange or grapefruit peels. In most cases, desorption was fast, being over 90% complete within 50 min. However sodium nitrate and 0.001 M nitric acid were less efficient. Several new models for desorption kinetics were developed. While zero-, first- and second-order kinetics are commonly applied for modeling adsorption kinetics, the present study adapts these models to describe desorption kinetics. The proposed models relate to the number of metal-filled binding sites as the rate-determining reactant concentration. A model based on first order kinetics with respect to the remaining metal bound performed best. Cd bound in subsequent adsorption after desorption was similar to the original amount bound for desorption by nitric acid, but considerably lower for calcium nitrate as the desorbent. While complexing agents were effective desorbents, their cost is higher than that of common mineral acids. Thus 0.01-0.1 M acids are the most promising desorbing agents for efficient sorbent regeneration. PMID:22342899

  2. Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

    NASA Astrophysics Data System (ADS)

    Tinnacher, Ruth M.; Zavarin, Mavrik; Powell, Brian A.; Kersting, Annie B.

    2011-11-01

    Various sorption phenomena, such as aging, hysteresis and irreversible sorption, can cause differences between contaminant (ad)sorption and desorption behavior and lead to apparent sorption 'asymmetry'. We evaluate the relevance of these characteristics for neptunium(V) (Np(V)) sorption/desorption on goethite using a 34-day flow-cell experiment and kinetic modeling. Based on experimental results, the Np(V) desorption rate is much slower than the (ad)sorption rate, and appears to decrease over the course of the experiment. The best model fit with a minimum number of fitting parameters was achieved with a multi-reaction model including (1) an equilibrium Freundlich site (site 1), (2) a kinetically-controlled, consecutive, first-order site (site 2), and (3) a parameter ψ, which characterizes the desorption rate on site 2 based on a concept related to transition state theory (TST). This approach allows us to link differences in adsorption and desorption kinetics to changes in overall reaction pathways, without assuming different adsorption and desorption affinities (hysteresis) or irreversible sorption behavior a priori. Using modeling as a heuristic tool, we determined that aging processes are relevant. However, hysteresis and irreversible sorption behavior can be neglected within the time-frame (desorption over 32 days) and chemical solution conditions evaluated in the flow-cell experiment. In this system, desorption reactions are very slow, but they are not irreversible. Hence, our data do not justify an assumption of irreversible Np(V) sorption to goethite in transport models, which effectively limits the relevance of colloid-facilitated Np(V) transport to near-field environments. However, slow Np(V) desorption behavior may also lead to a continuous contaminant source term when metals are sorbed to bulk mineral phases. Additional long-term experiments are recommended to definitely rule out irreversible Np(V) sorption behavior at very low surface loadings and

  3. Kinetic desorption and sorption of U(VI) during reactive transport in a contaminated Hanford sediment.

    PubMed

    Qafoku, Nikolla P; Zachara, John M; Liu, Chongxuan; Gassman, Paul L; Qafoku, Odeta S; Smith, Steven C

    2005-05-01

    Column experiments were conducted to investigate U(VI) desorption and sorption kinetics in a sand-textured, U(VI)-contaminated (22.7 micromol kg(-1)) capillary fringe sediment from the U.S. Department of Energy (DOE) Hanford site. Saturated column experiments were performed under mildly alkaline conditions representative of the Hanford site where uranyl-carbonate and calcium-uranyl-carbonate complexes dominate aqueous speciation. A U(VI)-free solution was used to study contaminant U(VI) desorption in columns where different flow rates were applied. Sorbed, contaminant U(VI) was partially labile (11.8%), and extended leaching times and water volumes were required for complete desorption of the labile fraction. Uranium-(VI) sorption was studied after the desorption of labile, contaminant U(VI) using different U(VI) concentrations in the leaching solution. Strong kinetic effects were observed for both U(VI) sorption and desorption, with half-life ranging from 8.5 to 48.5 h for sorption and from 39.3 to 150 h for desorption. Although U(VI) is semi-mobile in mildly alkaline, subsurface environments, we observed substantial U(VI) adsorption, significant retardation during transport, and atypical breakthrough curves with extended tailing. A distributed rate model was applied to describe the effluent data and to allow comparisons between the desorption rate of contaminant U(VI) with the rate of shortterm U(VI) sorption. Desorption was the slower process. We speculate that the kinetic behavior results from transport or chemical phenomena within the phyllosilicate-dominated fine fraction present in the sediment. Our results suggest that U(VI) release and transport in the vadose zone and aquifer system from which the sediment was obtained are kinetically controlled. PMID:15926566

  4. Liquefaction chemistry and kinetics: Hydrogen utilization studies

    SciTech Connect

    Rothenberger, K.S.; Warzinski, R.P.; Cugini, A.V.

    1995-12-31

    The objectives of this project are to investigate the chemistry and kinetics that occur in the initial stages of coal liquefaction and to determine the effects of hydrogen pressure, catalyst activity, and solvent type on the quantity and quality of the products produced. The project comprises three tasks: (1) preconversion chemistry and kinetics, (2) hydrogen utilization studies, and (3) assessment of kinetic models for liquefaction. The hydrogen utilization studies work will be the main topic of this report. However, the other tasks are briefly described.

  5. Kinetic Desorption and Sorption of U(VI) During Reactive Transport in a Contaminated Hanford Sediment

    SciTech Connect

    Qafoku, Nik; Zachara, John M.; Liu, Chongxuan; Gassman, Paul L.; Qafoku, Odeta; Smith, Steven C.

    2005-05-12

    Column experiments were conducted to investigate U(VI) desorption and sorption kinetics in a sand-textured, contaminated (22.7 µmol kg-1) capillary fringe sediment that had experienced long-term exposure to U(VI). The clay fraction mineralogy of the sediment was dominated by montmorillonite, muscovite, vermiculite, and chlorite. Saturated column experiments were performed under mildly alkaline/calcareous conditions representative of the Hanford site where uranyl–carbonate and calcium–uranyl–carbonate complexes dominate aqueous speciation. A U(VI) free solution was used to study U(VI) desorption in columns where different flow rates were applied. Uranium(VI) sorption was studied after the desorption of labile contaminant U(VI) using different U(VI) concentrations in the leaching solution. Strong kinetic behavior was observed for both U(VI) desorption and sorption. Although U(VI) is semi–mobile in mildly alkaline, calcareous subsurface environments, our results showed substantial U(VI) sorption, significant retardation during transport, and atypical breakthrough curves with extended tailing. A distributed rate model was applied to describe the effluent data and to allow comparisons between the desorption rate of contaminant U(VI) with the rate of short-term U(VI) sorption. Desorption was the slower process. Our results suggest that U(VI) release and transport in the vadose zone and aquifer system from which the sediment was obtained are kinetically controlled.

  6. Change in soft magnetic properties of Fe-based metallic glasses during hydrogen absorption and desorption

    SciTech Connect

    Novak, L.; Lovas, A.; Kiss, L.F.

    2005-08-15

    The stress level can be altered in soft magnetic amorphous alloys by hydrogen absorption. The resulting changes in the soft magnetic parameters are reversible or irreversible, depending on the chemical composition. Some of these effects are demonstrated in Fe-B, Fe-W-B, and Fe-V-B glassy ribbons, in which various magnetic parameters are measured mainly during hydrogen desorption. The rate of hydrogen desorption is also monitored by measuring the pressure change in a hermetically closed bomb. The observed phenomena are interpreted on the basis of induced stresses and chemical interactions between the solute metal and hydrogen.

  7. Kinetics of tetracycline, oxytetracycline, and chlortetracycline adsorption and desorption on two acid soils.

    PubMed

    Fernández-Calviño, David; Bermúdez-Couso, Alipio; Arias-Estévez, Manuel; Nóvoa-Muñoz, Juan Carlos; Fernández-Sanjurjo, Maria J; Álvarez-Rodríguez, Esperanza; Núñez-Delgado, Avelino

    2015-01-01

    The purpose of this work was to quantify retention/release of tetracycline, oxytetracycline, and chlortetracycline on two soils, paying attention to sorption kinetics and to implications of the adsorption/desorption processes on transfer of these pollutants to the various environmental compartments. We used the stirred flow chamber (SFC) procedure to achieve this goal. All three antibiotics showed high affinity for both soils, with greater adsorption intensity for soil 1, the one with the highest organic matter and Al and Fe oxides contents. Desorption was always <15%, exhibiting strong hysteresis in the adsorption/desorption processes. Adsorption was adequately modeled using a pseudo first-order equation with just one type of adsorption sites, whereas desorption was better adjusted considering both fast and slow sorption sites. The adsorption maximum (qmax) followed the sequence tetracycline > oxytetracycline > chlortetracycline in soil 1, with similar values for the three antibiotics and the sequence tetracycline > chlortetracycline > oxytetracycline in soil 2. The desorption sequences were oxytetracycline > tetracycline > chlortetracycline in soil 1 and oxytetracycline > chlortetracycline > tetracycline in soil 2. In conclusion, the SFC technique has yielded new kinetic data regarding tetracycline, oxytetracycline, and chlortetracycline adsorption/desorption on soils, indicating that it can be used to shed further light on the retention and transport processes affecting antibiotics on soils and other media, thus increasing knowledge on the behavior and evolution of these pharmaceutical residues in the environment. PMID:25081007

  8. Progress in improving thermodynamics and kinetics of new hydrogen storage materials

    NASA Astrophysics Data System (ADS)

    Song, Li-fang; Jiang, Chun-hong; Liu, Shu-sheng; Jiao, Cheng-li; Si, Xiao-liang; Wang, Shuang; Li, Fen; Zhang, Jian; Sun, Li-xian; Xu, Fen; Huang, Feng-lei

    2011-06-01

    Hydrogen storage material has been much developed recently because of its potential for proton exchange membrane (PEM) fuel cell applications. A successful solid-state reversible storage material should meet the requirements of high storage capacity, suitable thermodynamic properties, and fast adsorption and desorption kinetics. Complex hydrides, including boron hydride and alanate, ammonia borane, metal organic frameworks (MOFs), covalent organic frameworks (COFs) and zeolitic imidazolate frameworks (ZIFs), are remarkable hydrogen storage materials because of their advantages of high energy density and safety. This feature article focuses mainly on the thermodynamics and kinetics of these hydrogen storage materials in the past few years.

  9. Long-term Kinetics of Uranyl Desorption from Sediments Under Advective Conditions

    SciTech Connect

    Shang, Jianying; Liu, Chongxuan; Wang, Zheming; Zachara, John M.

    2014-02-15

    Long-term (> 4 months) column experiments were performed to investigate the kinetics of uranyl (U(VI)) desorption in sediments collected from the Integrated Field Research Challenge (IFRC) site at the US Department of Energy (DOE) Hanford 300 Area. The experimental results were used to evaluate alternative multi-rate surface complexation reaction (SCR) approaches to describe the short- and long-term kinetics of U(VI) desorption under flow conditions. The SCR stoichiometry, equilibrium constants, and multi-rate parameters were independently characterized in batch and stirred flow-cell reactors. Multi-rate SCR models that were either additively constructed using the SCRs for individual size fractions (e.g., Shang et al., 2011), or composite in nature could effectively describe short-term U(VI) desorption under flow conditions. The long-term desorption results, however, revealed that using a labile U concentration measured by carbonate extraction under-estimated desorbable U(VI) and the long-term rate of U(VI) desorption. An alternative modeling approach using total U as the desorbable U(VI) concentration was proposed to overcome this difficulty. This study also found that the gravel size fraction (2-8 mm), which is typically treated as non-reactive in modeling U(VI) reactive transport because of low external surface area, can have an important effect on the U(VI) desorption in the sediment. This study demonstrates an approach to effectively extrapolate U(VI) desorption kinetics for field-scale application, and identifies important parameters and uncertainties affecting model predictions.

  10. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    SciTech Connect

    Bartram, Michael E.; Creighton, J. Randall

    1999-05-26

    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

  11. Electron-stimulated desorption of hydrogen from the Si(111) surface by scanning tunneling microscopy

    SciTech Connect

    Schwartzkopff, M.; Radojkovic, P.; Enachescu, M.; Hartmann, E.; Koch, F.

    1996-03-01

    Preparation of suitable silicon (111) wafers in weakly alkaline HF solutions results in the formation of atomically flat, hydrogen-terminated surfaces. Under high-vacuum conditions, the scanning tunneling microscope has been employed to selectively desorb the passivating hydrogen from nanometer-sized surface regions. The hydrogen depassivation process is studied as a function of current and applied bias voltage, voltage polarity, and exposure time to incident electrons either on individual surface locations or by varying the speed of tip motion to control the electron dose. The experimental findings are interpreted in terms of two distinct desorption mechanisms and the respective desorption yields are specified. {copyright} {ital 1996 American Vacuum Society}

  12. Chemical Kinetic Modeling of Hydrogen Combustion Limits

    SciTech Connect

    Pitz, W J; Westbrook, C K

    2008-04-02

    A detailed chemical kinetic model is used to explore the flammability and detonability of hydrogen mixtures. In the case of flammability, a detailed chemical kinetic mechanism for hydrogen is coupled to the CHEMKIN Premix code to compute premixed, laminar flame speeds. The detailed chemical kinetic model reproduces flame speeds in the literature over a range of equivalence ratios, pressures and reactant temperatures. A series of calculation were performed to assess the key parameters determining the flammability of hydrogen mixtures. Increased reactant temperature was found to greatly increase the flame speed and the flammability of the mixture. The effect of added diluents was assessed. Addition of water and carbon dioxide were found to reduce the flame speed and thus the flammability of a hydrogen mixture approximately equally well and much more than the addition of nitrogen. The detailed chemical kinetic model was used to explore the detonability of hydrogen mixtures. A Zeldovich-von Neumann-Doring (ZND) detonation model coupled with detailed chemical kinetics was used to model the detonation. The effectiveness on different diluents was assessed in reducing the detonability of a hydrogen mixture. Carbon dioxide was found to be most effective in reducing the detonability followed by water and nitrogen. The chemical action of chemical inhibitors on reducing the flammability of hydrogen mixtures is discussed. Bromine and organophosphorus inhibitors act through catalytic cycles that recombine H and OH radicals in the flame. The reduction in H and OH radicals reduces chain branching in the flame through the H + O{sub 2} = OH + O chain branching reaction. The reduction in chain branching and radical production reduces the flame speed and thus the flammability of the hydrogen mixture.

  13. Surface diffusion and desorption kinetics for perfluoro-n-butane on Ru(001)

    NASA Astrophysics Data System (ADS)

    Arena, M. V.; Westre, E. D.; George, S. M.

    1991-03-01

    The surface diffusion and desorption kinetics for perfluoro-n-butane on Ru(001) were examined using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The surface diffusion displayed Arrhenius behavior and was coverage independent. The surface diffusion parameters for perfluoro-n-butane on Ru(001) were Edif=2.9±0.3 kcal/mol and D0=5.9×10-2±0.2 cm2/s. The desorption parameters for perfluoro-n-butane on Ru(001) were Edes=13.8±0.6 kcal/mol and νdes=2.8×1021±0.1 s-1. In comparison, the surface diffusion parameters for n-butane on Ru(001) were Edif=3.5±0.2 kcal/mol and D0=1.4×10-1±0.2 cm2/s. The desorption parameters for n-butane on Ru(001) were Edes=11.9±0.5 kcal/mol and νdes=3.6×1015±0.1 s-1. The corrugation ratio, defined as Ω≡Edif/Edes, was determined to be Ω=0.21 for perfluoro-n-butane on Ru(001). This corrugation ratio was substantially different than the corrugation ratio of Ω≊0.30 measured for n-butane and various other n-alkanes, cycloalkanes and branched alkanes on Ru(001). The comparison between perfluoro-n-butane and the other alkanes indicates that fluorination lowers the surface corrugation ratio on Ru(001). Likewise, fluorination significantly increases the preexponential for desorption from Ru(001). This study illustrates the magnitude of substituent effects on surface diffusion and desorption kinetics for a physisorbed molecule on a single-crystal metal surface.

  14. A comparison of two techniques for studying sediment desorption kinetics of hydrophobic pollutants.

    PubMed

    Saalfield, Samantha L; Wnuk, Joshua D; Murray, Megan M; Dunnivant, Frank M

    2007-01-01

    A comparison of two techniques (gaseous purge and vial desorption) for studying the kinetics of desorption of hydrophobic pollutants from natural sediments was conducted using identical, pre-equilibrated pollutant-sediment suspensions. Desorption profiles for the two techniques [for Lindane, Aldrin, 2,2'-dichlorobiphenyl (2,2'-DCB), 4,4'-dichlorobiphenyl (4,4'-DCB), and 2,2',6,6'-tetrachlorobiphenyl (TCB)] were then compared, based on the distribution of pollutant mass between the labile (fast) and non-labile (slow) desorption phases and the release rate constants for each phase of release. The vial desorption technique shows many practical advantages over the gaseous purge technique, including its more realistic mixing conditions, the use of an independent sample for each data point (as opposed to a calculation of a cumulative mass purged at each time point), the fact that the vials constitute a closed system and are therefore less subject to ambient contamination, and the relatively low demands of time and money for the vial technique. No consistent trends in labile rate constants or in pollutant distribution between the labile and non-labile phase were observed between the two techniques. A comparison of kinetic parameters shows much faster non-labile rate constants for the gaseous purge technique, attributed to the violent, continuous agitation employed, which likely disrupted sediment aggregates and oxidized the natural organic matter associated with the sediment. Non-labile rate constants have implications for the long-term fate of compounds adsorbed to repetitively disturbed sediments. This study suggests that the traditionally less popular vial desorption technique may yield more realistic non-labile desorption rate constants. PMID:16757013

  15. Film growth, adsorption and desorption kinetics of indigo on SiO{sub 2}

    SciTech Connect

    Scherwitzl, Boris Resel, Roland; Winkler, Adolf

    2014-05-14

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

  16. Film growth, adsorption and desorption kinetics of indigo on SiO2

    NASA Astrophysics Data System (ADS)

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2014-05-01

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

  17. Mechanisms and kinetics of coal hydrogenation

    SciTech Connect

    Baldwin, R M; Furlong, M W

    1981-05-01

    Colorado School of Mines is engaged in an experimental program to develop comprehensive models for the effects of coal composition upon the kinetics and mechanisms of coal hydrogenation, for the effects of mineral matter additives (disposable catalysts) upon kinetics and mechanisms of coal hydrogenation, and for the kinetics and mechanisms of the hydrogenation of coal derived products such as preasphaltenes, and asphaltenes. Experimental work was completed on a suite of bituminous coals, thus completing the initial phase of the coal reactivity study. Eleven of the 14 coals of the suite were successfully run in duplicate. Conversion to THF solubles was correlated well by pseudo-second order kinetics. The resulting kinetic rate constants correlated with H/C ratio, mean-max vitrinite reflectance, and a specially-defined fraction of reactive macerals. The data did not correlate well with O/C ratios of the parent coals. Computer-derived statistical fits of various kinetic models were limited in their effectiveness at fitting the experimental data. Experimental work on the first phase of the disposal catalyst studies was completed. Statistical significance testing of the experimental data showed: fractional conversion and yield of light hydrocarbon products increased with time; and mineral properties of the additives were more significant in increasing overall conversion than the additive surface areas. The relative effects of the additives are given.

  18. The Hydriding Kinetics of Organic Hydrogen Getters

    SciTech Connect

    Powell, G. L.

    2002-02-11

    The aging of hermetically sealed systems is often accompanied by the gradual production of hydrogen gas that is a result of the decay of environmental gases and the degradation of organic materials. In particular, the oxygen, water, hydrogen ''equilibrium'' is affected by the removal of oxygen due the oxidation of metals and organic materials. This shift of the above ''equilibrium'' towards the formation of hydrogen gas, particularly in crevices, may eventually reach an explosive level of hydrogen gas or degrade metals by hydriding them. The latter process is generally delayed until the oxidizing species are significantly reduced. Organic hydrogen getters introduced by Allied Signal Aerospace Company, Kansas City Division have proven to be a very effective means of preventing hydrogen gas accumulation in sealed containers. These getters are relatively unaffected by air and environmental gases. They can be packaged in a variety of ways to fit particular needs such as porous pellets, fine or coarse [gravel] powder, or loaded into silicone rubber. The hydrogen gettering reactions are extremely irreversible since the hydrogen gas is converted into an organic hydrocarbon. These getters are based on the palladium-catalyzed hydrogenation of triple bonds to double and then single bonds in aromatic aryl compounds. DEB (1,4 bis (phenyl ethynyl) benzene) typically mixed with 25% by weight carbon with palladium (1% by weight of carbon) is one of the newest and best of these organic hydrogen getters. The reaction mechanisms are complex involving solid state reaction with a heterogeneous catalyst leading to the many intermediates, including mixed alkyl and aryl hydrocarbons with the possibilities of many isomers. The reaction kinetics mechanisms are also strongly influenced by the form in which they are packaged. For example, the hydriding rates for pellets and gravel have a strong dependence on reaction extent (i.e., DEB reduction) and a kinetic order in pressure of 0

  19. Effects and Mechanisms of Mechanical Activation on Hydrogen Sorption/ Desorption of Nanoscale Lithium Nitrides

    SciTech Connect

    Shaw, Leon, L.; Yang, Gary, Z.; Crosby, Kyle; Wwan, Xufei. Zhong, Yang; Markmaitree, Tippawan; Osborn, William; Hu, Jianzhi; Kwak, Ja Hun

    2012-04-26

    The objective of this project is to investigate and develop novel, mechanically activated, nanoscale Li3N-based and LiBH4-based materials that are able to store and release {approx}10 wt% hydrogen at temperatures near 100 C with a plateau hydrogen pressure of less than 10 bar. Four (4) material systems have been investigated in the course of this project in order to achieve the project objective. These 4 systems are (i) LiNH2+LiH, (ii) LiNH2+MgH2, (iii) LiBH4, and (iv) LiBH4+MgH2. The key findings we have obtained from these 4 systems are summarized below. *The thermodynamic driving forces for LiNH2+LiH and LiBH4 systems are not adequate to enable H2 release at temperatures < 100 C. *Hydrogen release in the solid state for all of the four systems is controlled by diffusion, and thus is a slow process. *LiNH2+MgH2 and LiBH4+MgH2 systems, although possessing proper thermodynamic driving forces to allow for H2 release at temperatures < 100 C, have sluggish reaction kinetics because of their diffusion-controlled rate-limiting steps. *Reducing particles to the nanometer length scale (< 50 nm) can improve the thermodynamic driving force to enable H2 release at near ambient temperature, while simultaneously enhancing the reaction kinetics as well as changing the diffusion-controlled rate-limiting step to gas desorption-controlled rate-limiting step. This phenomenon has been demonstrated with LiBH4 and offers the hope that further work along this direction will make one of the material systems, i.e., LiBH4, LiBH4+MgH2 and LiNH2+MgH2, possess the desired thermodynamic properties and rapid H2 uptake/release kinetics for on-board applications. Many of the findings and knowledge gained from this project have been published in archival refereed journal articles [1-15] and are accessible by general public. Thus, to avoid a bulky final report, the key findings and knowledge gained from this project will be succinctly summarized, particularly for those findings and knowledge

  20. Numerical comparison of hydrogen desorption behaviors of metal hydride beds based on uranium and on zirconium-cobalt

    SciTech Connect

    Kyoung, S.; Yoo, H.; Ju, H.

    2015-03-15

    In this paper, the hydrogen delivery capabilities of uranium (U) and zirconium-cobalt (ZrCo) are compared quantitatively in order to find the optimum getter materials for tritium storage. A three-dimensional hydrogen desorption model is applied to two identically designed cylindrical beds with the different materials, and hydrogen desorption simulations are then conducted. The simulation results show superior hydrogen delivery performance and easier thermal management capability for the U bed. This detailed analysis of the hydrogen desorption behaviors of beds with U and ZrCo will help to identify the optimal bed material, bed design, and operating conditions for the storage and delivery system in ITER. (authors)

  1. Film growth, adsorption and desorption kinetics of indigo on SiO2

    PubMed Central

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2015-01-01

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer des orption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption. PMID:24832297

  2. Plutonium desorption from mineral surfaces at environmental concentrations of hydrogen peroxide.

    PubMed

    Begg, James D; Zavarin, Mavrik; Kersting, Annie B

    2014-06-01

    Knowledge of Pu adsorption and desorption behavior on mineral surfaces is crucial for understanding its environmental mobility. Here we demonstrate that environmental concentrations of H2O2 can affect the stability of Pu adsorbed to goethite, montmorillonite, and quartz across a wide range of pH values. In batch experiments where Pu(IV) was adsorbed to goethite for 21 days at pH 4, 6, and 8, the addition of 5-500 μM H2O2 resulted in significant Pu desorption. At pH 6 and 8 this desorption was transient with readsorption of the Pu to goethite within 30 days. At pH 4, no Pu readsorption was observed. Experiments with both quartz and montmorillonite at 5 μM H2O2 desorbed far less Pu than in the goethite experiments highlighting the contribution of Fe redox couples in controlling Pu desorption at low H2O2 concentrations. Plutonium(IV) adsorbed to quartz and subsequently spiked with 500 μM H2O2 resulted in significant desorption of Pu, demonstrating the complexity of the desorption process. Our results provide the first evidence of H2O2-driven desorption of Pu(IV) from mineral surfaces. We suggest that this reaction pathway coupled with environmental levels of hydrogen peroxide may contribute to Pu mobility in the environment. PMID:24815745

  3. Radionuclide desorption kinetics on synthetic Zn/Ni-labeled montmorillonite nanoparticles

    NASA Astrophysics Data System (ADS)

    Huber, F. M.; Heck, S.; Truche, L.; Bouby, M.; Brendlé, J.; Hoess, P.; Schäfer, T.

    2015-01-01

    Sorption/desorption kinetics for selected radionuclides (99Tc(VII), 232Th(IV), 233U(VI), 237Np(V), 242Pu and 243Am(III)) under Grimsel (Switzerland) ground water conditions (pH 9.7 and ionic strength of ∼1 mM) in the presence of synthetic Zn or Ni containing montmorillonite nanoparticles and granodiorite fracture filling material (FFM) from Grimsel were examined in batch studies. The structurally bound Zn or Ni in the octahedral sheet of the synthetic colloids rendered them suitable as colloid markers. Only a weak interaction of the montmorillonite colloids with the fracture filling material occurs over the experimental duration of 10,000 h (∼13 months). The tri- and tetravalent radionuclides are initially strongly associated with nanoparticles in contrast to 99Tc(VII), 233U(VI) and 237Np(V) which showed no sorption to the montmorillonite colloids. Radionuclide desorption of the nanoparticles followed by sorption to the fracture filling material is observed for 232Th(IV), 242Pu and 243Am(III). Based on the conceptual model that the driving force for the kinetically controlled radionuclide desorption from nanoparticles and subsequent association to the FFM is the excess in surface area offered by the FFM, the observed desorption kinetics are related to the colloid/FFM surface area ratio. The observed decrease in concentration of the redox sensitive elements 99Tc(VII), 233U(VI) and 237Np(V) may be explained by reduction to lower oxidation states in line with Eh-pH conditions prevailing in the experiments and thermodynamic considerations leading to (i) precipitation of a sparingly soluble phase, (ii) sorption to the fracture filling material, (iii) possible formation of eigencolloids and/or (iv) sorption to the montmorillonite colloids. Subsequent to the sorption/desorption kinetics study, an additional experiment was conducted investigating the potential remobilization of radionuclides/colloids attached to the FFM used in the sorption/desorption kinetic

  4. Hydrogen Dissociation, Spillover, and Desorption from Cu-Supported Co Nanoparticles.

    PubMed

    Lewis, Emily A; Marcinkowski, Matthew D; Murphy, Colin J; Liriano, Melissa L; Sykes, E Charles H

    2014-10-01

    Co-Cu nanoparticles have recently been explored for Fischer-Tropsch synthesis (FTS) as a way to combine the long chain selectivity of Co with Cu's activity for alcohol formation in order to synthesize oxygenated transportation fuels. Depending on particle size, hydrogen dissociation can be a rate-determining step in cobalt-catalyzed FTS. To understand the fundamentals of uptake and release of hydrogen from the Co/Cu bimetallic system, we prepared well-defined Co nanoparticles on Cu(111). We demonstrate that hydrogen spills over from dissociation sites on the Co nanoparticles to the Cu(111) surface via the Co-Cu interface and that desorption of H occurs at a temperature that is lower than from Co or Cu alone, which we attribute to the Co-Cu interface sites. From this data, we have constructed an energy landscape for the facile dissociation, spillover, and desorption of hydrogen on the Co-Cu bimetallic system. PMID:26278448

  5. Hydrogen-bond kinetics in liquid water

    NASA Astrophysics Data System (ADS)

    Luzar, Alenka; Chandler, David

    1996-01-01

    HYDROGEN bonds play a crucial role in the behaviour of water1-4 their spatial patterns and fluctuations characterize the structure and dynamics of the liquid5-7. The processes of breaking and making hydrogen bonds in the condensed phase can be probed indirectly by a variety of experimental techniques8, and more quantitative information can be obtained from computer simulations9. In particular, simulations have revealed that on long timescales the relaxation behaviour of hydrogen bonds in liquid water exhibit non-exponential kinetics7,10-13, suggesting that bond making and breaking are not simple processes characterized by well defined rate constants. Here we show that these kinetics can be understood in terms of an interplay between diffusion and hydrogen-bond dynamics. In our model, which can be extended to other hydrogen-bonded liquids, diffusion governs whether a specific pair of water molecules are near neighbours, and hydrogen bonds between such pairs form and persist at random with average lifetimes determined by rate constants for bond making and breaking.

  6. An investigation of the kinetics for hydrogen chemisorption on iron metal surfaces

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1980-01-01

    A quasi-isothermal approach was used to study the kinetics of hydrogen and hydrogen sulfide chemisorption onto iron film in an effort to understand the environmental degradation of steels. The coverage of chemisorbed hydrogen or chemisorbed sulfur was observed as a function of time for fixed conditions of substrate temperature. Auger electron spectroscopy was used to observe the sulfur and chemisorption-induced resistance change was employed to monitor hydrogen coverage. To compare the results obtained from studying the kinetics by two different techniques, the kinetics of oxygen chemisorption onto iron films was also studied. A reaction model utilized to interpret the H2/Fe2 chemisorption kinetics was applied to data from an earlier study on the desorption kinetics for H2 chemisorbed onto nicket films in the vicinity of the Curie temperature of the film. This analysis permitted a separation of the gross desorption process into individual components so that the influence of the magnetic phase transition on the rate constants could be determined.

  7. Application of diffusion theory to the analysis of hydrogen desorption data at 25 deg C

    SciTech Connect

    Danford, M.D.

    1985-10-01

    The application of diffusion theory to the analysis of hydrogen desorption data (coulombs of H/sub 2/ desorbed versus time) has been studied. From these analyses, important information concerning hydrogen solubilities and the nature of the hydrogen distributions in the metal has been obtained. Two nickel base alloys, Rene' 41 and Waspaloy, and one ferrous alloy, 4340 steel, are studied in this work. For the nickel base alloys, it is found that the hydrogen distributions after electrolytic charging conforms closely to those which would be predicted by diffusion theory. For Waspaloy samples charged at 5,000 psi, it is found that the hydrogen distributions are essentially the same as those obtained by electrolytic charging. The hydrogen distributions in electrolytically charged 4340 steel, on the other hand, are essentially uniform in nature, which would not be predicted by diffusion theory. A possible explanation has been proposed. Finally, it is found that the hydrogen desorption is completely explained by the nature of the hydrogen distribution in the metal, and that the fast hydrogen is not due to surface and sub-surface hydride formation, as was originally proposed.

  8. The application of diffusion theory to the analysis of hydrogen desorption data at 25 deg C

    NASA Technical Reports Server (NTRS)

    Danford, M. D.

    1985-01-01

    The application of diffusion theory to the analysis of hydrogen desorption data (coulombs of H2 desorbed versus time) has been studied. From these analyses, important information concerning hydrogen solubilities and the nature of the hydrogen distributions in the metal has been obtained. Two nickel base alloys, Rene' 41 and Waspaloy, and one ferrous alloy, 4340 steel, are studied in this work. For the nickel base alloys, it is found that the hydrogen distributions after electrolytic charging conforms closely to those which would be predicted by diffusion theory. For Waspaloy samples charged at 5,000 psi, it is found that the hydrogen distributions are essentially the same as those obtained by electrolytic charging. The hydrogen distributions in electrolytically charged 4340 steel, on the other hand, are essentially uniform in nature, which would not be predicted by diffusion theory. A possible explanation has been proposed. Finally, it is found that the hydrogen desorption is completely explained by the nature of the hydrogen distribution in the metal, and that the fast hydrogen is not due to surface and sub-surface hydride formation, as was originally proposed.

  9. Effect of carboxylic and thiol ligands (oxalate, cysteine) on the kinetics of desorption of Hg(II) from kaolinite

    SciTech Connect

    Senevirathna, W. U.; Zhang, Hong; Gu, Baohua

    2010-01-01

    Sorption and desorption of Hg(II) on clay minerals can impact the biogeochemical cycle and bio-uptake of Hg in the environment. We studied the kinetics of the desorption of Hg(II) from kaolinite as affected by oxalate and cysteine, representing the ligands with carboxylic and thiol groups of different affinities for Hg(II). The effects of pH (3, 5, and 7), ligand concentration (0.25 and 1.0 mM), and temperature (15 C, 25 C, and 35 C) on the Hg(II) desorption were investigated through desorption kinetics. Our study showed that the Hg(II) desorption was pH dependent. In the absence of any organic ligand, >90% of the previously adsorbed Hg(II) desorbed at pH 3 within 2 h, compared to <10% at pH 7. Similar results were observed in the presence of oxalate, showing that it hardly affected the Hg(II) desorption. Cysteine inhibited the Hg(II) desorption significantly at all the pH tested, especially in the first 80 min with the desorption less than 20%, but the inhibition of the desorption appeared to be less prominent afterwards. The effect of the ligand concentration on the Hg(II) desorption was small, especially in the presence of oxalate. The effect of temperature on the Hg(II) desorption was nearly insignificant. The effect of the organic acids on the Hg(II) sorption and desorption is explained by the formation of the ternary surface complexes involving the mineral, ligand, and Hg(II). The competition for Hg(II) between the cysteine molecules adsorbed on the particle surfaces and in the solution phase probably can also affect the Hg(II) desorption.

  10. Desorption kinetics of radiocesium from subsurface sediments at Hanford Site, USA

    NASA Astrophysics Data System (ADS)

    Liu, Chongxuan; Zachara, John M.; Smith, Steve C.; McKinley, James P.; Ainsworth, Calvin C.

    2003-08-01

    The desorption of 137Cs + was investigated on sediments from the United States Hanford site. Pristine sediments and ones that were contaminated by the accidental release of alkaline 137Cs +-containing high level nuclear wastes (HLW, 2 × 10 6 to 6 × 10 7 pCi 137Cs +/g) were studied. The desorption of 137Cs + was measured in Na +, K +, Rb +, and NH 4+electrolytes of variable concentration and pH, and in presence of a strong Cs +-specific sorbent (self-assembled monolayer on a mesoporous support, SAMMS). 137Cs + desorption from the HLW-contaminated Hanford sediments exhibited two distinct phases: an initial instantaneous release followed by a slow kinetic process. The extent of 137Cs + desorption increased with increasing electrolyte concentration and followed a trend of Rb + ≥ K + > Na + at circumneutral pH. This trend followed the respective selectivities of these cations for the sediment. The extent and rate of 137Cs + desorption was influenced by surface armoring, intraparticle diffusion, and the collapse of edge-interlayer sites in solutions containing K +, Rb +, or NH 4+. Scanning electron microscopic analysis revealed HLW-induced precipitation of secondary aluminosilicates on the edges and basal planes of micaceous minerals that were primary Cs + sorbents. The removal of these precipitates by acidified ammonium oxalate extraction significantly increased the long-term desorption rate and extent. X-ray microprobe analyses of Cs +-sorbed micas showed that the 137Cs + distributed not only on mica edges, but also within internal channels parallel to the basal plane, implying intraparticle diffusive migration of 137Cs +. Controlled desorption experiments using Cs +-spiked pristine sediment indicated that the 137Cs + diffusion rate was fast in Na +-electrolyte, but much slower in the presence of K + or Rb +, suggesting an effect of edge-interlayer collapse. An intraparticle diffusion model coupled with a two-site cation exchange model was used to interpret the

  11. Role of microstructure and heat treatments on the desorption kinetics of tritium from austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Chêne, J.; Brass, A.-M.; Trabuc, P.; Gastaldi, O.

    2007-02-01

    The liquid scintillation counting of solid samples (LSC-SS technique) was successfully used to study the role of microstructure and heat treatments on the behavior of residual tritium in several austenitic stainless steels (as-cast remelted tritiated waste, 316LN and 321 steels). The role of desorption annealing in the 100-600 °C range on the residual amount of tritium in tritiated waste was investigated. The residual tritium concentration computed from surface activity measurements is in good agreement with experimental values measured by liquid scintillation counting after full dissolution of the samples. The kinetics of tritium desorption recorded with the LSC-SS technique shows a significant desorption of residual tritium at room temperature, a strong barrier effect of thermal oxide films on the tritium desorption and a dependance of the tritium release on the steels microstructure. Annealing in the 300-600 °C range allows to desorb a large fraction of the residual tritium. However a significant trapping of tritium is evidenced. The influence of trapping phenomena on the concentration of residual tritium and on its dependance with the annealing temperature was investigated with different recrystallized and sensitized microstructures. Trapping is evidenced mainly below 150 °C and concerns a small fraction of the total amount of tritium introduced in austenitic steels. It presumably occurs preferentially on precipitates such as Ti(CN) or on intermetallic phases.

  12. Kinetics of protein adsorption/desorption mediated by pH-responsive polymer layer

    NASA Astrophysics Data System (ADS)

    Su, Xiao-Hang; Lei, Qun-Li; Ren, Chun-Lai

    2015-11-01

    We propose a new way of regulating protein adsorption by using a pH-responsive polymer. According to the theoretical results obtained from the molecular theory and kinetic approaches, both thermodynamics and kinetics of protein adsorption are verified to be well controlled by the solution pH. The kinetics and the amount of adsorbed proteins at equilibrium are greatly increased when the solution environment changes from acid to neutral. The reason is that the increased pH promotes the dissociation of the weak polyelectrolyte, resulting in more charged monomers and more stretched chains. Thus the steric repulsion within the polymer layer is weakened, which effectively lowers the barrier felt by the protein during the process of adsorption. Interestingly, we also find that the kinetics of protein desorption is almost unchanged with the variation of pH. It is because although the barrier formed by the polymer layer changes along with the change of pH, the potential at contact with the surface varies equally. Our results may provide useful insights into controllable protein adsorption/desorption in practical applications. Project supported by the National Natural Science Foundation of China (Grant Nos. 21274062, 11474155, and 91027040).

  13. Features of hydrogen trapping and desorption during deposition of yttrium coating on zirconium in a gas discharge

    NASA Astrophysics Data System (ADS)

    Evsin, A. E.; Begrambekov, L. B.; Dovganyuk, S. S.

    2016-01-01

    Transport of hydrogen isotopes during the various regimes of deposition of yttrium coating on zirconium in argon plasma with addition of deuterium is studied. The influence of oxygen contamination in plasma-generating gas on the processes of trapping and desorption of hydrogen isotopes is also investigated. It is shown that deposition of yttrium coating on zirconium in Ar+5%D2 plasma enhances both hydrogen desorption from zirconium and deuterium trapping into zirconium in comparison to those under plasma exposure without deposition. Yttrium deposition in Ar+25%O2+5%D2 plasma, conversely, mitigates both hydrogen desorption and deuterium trapping. Hydrogen desorption from zirconium increases with the increase of energy of ions, bombarding the sample during deposition of the coating in oxygen-free plasma, but it, on the contrary, decreases in oxygen-containing plasma.

  14. Diffusion barriers in the kinetics of water vapor adsorption/desorption on activated carbons

    SciTech Connect

    Harding, A.W.; Foley, N.J.; Thomas, K.M.; Norman, P.R.; Francis, D.C.

    1998-07-07

    The adsorption of water vapor on a highly microporous coconut-shell-derived carbon and a mesoporous wood-derived carbon was studied. These carbons were chosen as they had markedly different porous structures. The adsorption and desorption characteristics of water vapor on the activated carbons were investigated over the relative pressure range p/p{degree} = 0--0.9 for temperatures in the range 285--313 K in a static water vapor system. The adsorption isotherms were analyzed using the Dubinin-Serpinski equation, and this provided an assessment of the polarity of the carbons. The kinetics of water vapor adsorption and desorption were studied with different amounts of preadsorbed water for set changes in pressure relative to the saturated vapor pressure (p/p{degree}). The adsorption kinetics for each relative pressure step were compared and used to calculate the activation energies for the vapor pressure increments. The kinetic results are discussed in relation to their relative position on the equilibrium isotherm and the adsorption mechanism of water vapor on activated carbons.

  15. 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.

  16. 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.

  17. 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.

  18. Kinetics of desorption of KCL from polyvinyl alcohol-borate hydrogel in aqueous-alcoholic solvents at different temperatures

    NASA Astrophysics Data System (ADS)

    Saeed, Rehana; Abdeen, Zain Ul

    2015-11-01

    Desorption kinetics of adsorbed KCl from Polyvinyl alcohol borate hydrogel was studied by conductivity method in aqueous system and aqueous binary solvent system using 50% aqueous-methanol, aqueous- ethanol and aqueous-propanol at different temperature ranging from 293 to 313 K. Desorption process follows pseudo first order and intra particle diffusion kinetics was analyzed on the basis of linear regression coefficient R 2 and chi square test χ2 values. The process of desorption of KCl from hydrogel was favorable in aqueous system, the study reveals the fact that the polarity of solvent influenced the kinetics of desorption, on decrement of polarity of solvent rate, rate constant and intra particle rate constant decreases. Based on intra particle kinetic equation fitting it was concluded that desorption was initiated by removal of ions from surface of hydrogel later on ions interacted inside the cross linked unit was also become free. Temperature enhances the rate, rate constant and intra particle rate constant. Thermodynamic parameters attributed towards the fact that the process of desorption of KCl from hydrogel is non-spontaneous in nature.

  19. Controlling Hydrogen Activation, Spillover, and Desorption with Pd-Au Single-Atom Alloys.

    PubMed

    Lucci, Felicia R; Darby, Matthew T; Mattera, Michael F G; Ivimey, Christopher J; Therrien, Andrew J; Michaelides, Angelos; Stamatakis, Michail; Sykes, E Charles H

    2016-02-01

    Key descriptors in hydrogenation catalysis are the nature of the active sites for H2 activation and the adsorption strength of H atoms to the surface. Using atomically resolved model systems of dilute Pd-Au surface alloys and density functional theory calculations, we determine key aspects of H2 activation, diffusion, and desorption. Pd monomers in a Au(111) surface catalyze the dissociative adsorption of H2 at temperatures as low as 85 K, a process previously expected to require contiguous Pd sites. H atoms preside at the Pd sites and desorb at temperatures significantly lower than those from pure Pd (175 versus 310 K). This facile H2 activation and weak adsorption of H atom intermediates are key requirements for active and selective hydrogenations. We also demonstrate weak adsorption of CO, a common catalyst poison, which is sufficient to force H atoms to spill over from Pd to Au sites, as evidenced by low-temperature H2 desorption. PMID:26747698

  20. Adsorption and desorption kinetics of (60)Co and (137)Cs in fresh water rivers.

    PubMed

    Fiengo Pérez, Fabricio; Sweeck, Lieve; Bauwens, Willy; Van Hees, May; Elskens, Marc

    2015-11-01

    Radionuclides released in water systems--as well as heavy metals and organic toxicants--sorb to both the suspended solid particles and the bed sediments. Sorption is usually represented mathematically by the distribution coefficient. This approach implies equilibrium between phases and instantaneous fixation (release) of the pollutant onto (from) the surface of the soil particle. However, empirical evidence suggests that for some radionuclides the fixation is not achieved instantaneously and that the reversibility of the process can be slow. Here the adsorption/desorption kinetics of (60)Co and (137)Cs in fresh water environments were simulated experimentally and later on modelled mathematically, while the influence of the most relevant factors affecting the sorption were taken into account. The experimental results suggest that for adsorption and the desorption more than 24 h are needed to reach equilibrium, moreover, It was observed that the desorption rate constants for (60)Co and (137)Cs lie within ranges which are of two to three orders of magnitude lower than the adsorption rate constants. PMID:26218323

  1. Absorption and desorption of hydrogen, deuterium, and tritium for Zr--V--Fe getter

    SciTech Connect

    Ichimura, K.; Inoue, N.; Watanabe, K.; Takeuchi, T.

    1984-07-01

    Nonevaporable getters have wide applicability for developing the tritium handling techniques for thermonuclear fusion devices. From this viewpoint, mechanisms of the absorption and desorption of hydrogen isotopes and the isotope effects were investigated for a Zr--V--Fe alloy (St-707) by means of the mass analyzed thermal desorption spectroscopy. It was observed that the absorption rate was proportional to the first power of the pressure, indicating that the rate limiting step is the dissociative adsorption of hydrogen isotopes on the surface. The activation energy was very small, in the order of magnitude of a few tens of calories per mole in a temperature range from -196 to 200 /sup 0/C. The desorption rate was proportional to the square of the amount of absorption, indicating that the rate limiting step is the associative desorption reaction of hydrogen atoms or ions diffused to the surface from the bulk. The rate constants for hydrogen and deuterium were determined as k/sub d/(H/sub 2/) = (5.3/sup +2.6//sub -1.7/)exp(-(28.0 +- 0.7) x 10/sup 3//RT) and k/sub d/(D/sub 2/) = (5.0/sup +2.7//sub -1.7/)exp(-(28.6 +- 0.8) x 10/sup 3//RT) in (1/Pa 1 s), respectively, where R is in (cal/mol deg). With regard to tritium, the rate constant was evaluated as k/sub d/(T/sub 2/) = (5.0/sup +20//sub -4.0/)exp(-(29.3 +- 3) x 10/sup 3//RT), however, the frequency factor will have to be corrected by knowing the relative sensitivity factor of the mass spectrometer for tritium (T/sub 2/).

  2. Investigation of molecule-adsorption kinetics by a pulsed laser desorption technique

    NASA Astrophysics Data System (ADS)

    Varakin, V. N.; Lozovskii, A. D.; Panesh, A. M.; Simonov, A. P.

    1987-02-01

    The laser thermal desorption technique is used to measure the adsorption kinetics of SO2 and CO molecules on stainless steel with the aim of investigating the initial stage of oxidation of the steel by adsorbed CO molecules. Attention is given to the dependence of the rate of establishment of the equilibrium concentration of adsorbed molecules on SO2-gas pressure; CO adsorption kinetics on stainless steel at a gas pressure of 9 x 10 to the -8th torr; and the dependence of the concentration of adsorbed CO molecules on exposure in the gas at a pressure of 9 x 10 to the -8th torr under irradiation by laser pulses with repetition periods of 1-2, 2-4, 3-6, and 4-8 min.

  3. Uncertainty analysis of multi-rate kinetics of uranium desorption from sediments

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.; Zhang, Guannan

    2014-01-01

    Multi-rate surface complexation models have been proposed to describe the kinetics of uranyl (U(VI) surface complexation reactions (SCR) rate-limited by diffusive mass transfer to and from intragranular sorption sites in subsurface sediments. In this study, a Bayesian-based, Differential Evolution Markov Chain method was used to assess the uncertainty and to identify factors controlling the uncertainties of the multi-rate SCR model. The rate constants in the multi-rate SCR were estimated with and without assumption of a specified lognormal distribution to test the lognormal assumption typically used to minimize the number of the rate constants in the multi-rate model. U(VI) desorption under variable chemical conditions from a contaminated sediment at US Hanford 300 Area, Washington was used as an example. The results indicated that the estimated rate constants without a specified lognormal assumption approximately followed a lognormal distribution, indicating that the lognormal is an effective assumption for the rate constants in the multi-rate SCR model. However, those rate constants with their corresponding half-lives longer than the experimental durations for model characterization had larger uncertainties and could not be reliably estimated. The uncertainty analysis revealed that the time-scale of the experiments for calibrating the multi-rate SCR model, the assumption for the rate constant distribution, the geochemical conditions involved in predicting U(VI) desorption, and equilibrium U(VI) speciation reaction constants were the major factors contributing to the extrapolation uncertainties of the multi-rate SCR model. Overall, the results from this study demonstrated that the multi-rate SCR model with a lognormal distribution of its rate constants is an effective approach for describing rate-limited U(VI) desorption; however, the model contains uncertainties, especially for those smaller rate constants, that require careful consideration for predicting U

  4. Preparation and thermal desorption properties of dc sputtered zirconium-hydrogen-helium thin films

    SciTech Connect

    Wei, Y. C.; Shi, L. Q.; Zhang, L.; He, Z. J.; Zhang, B.; Wang, L. B.

    2008-11-15

    We developed a new approach for preparing hydrogen and helium co-containing zirconium films (Zr-H-He) to simulate aging metal tritides. We also studied the effect of hydrogen on helium behavior, in which we applied direct current magnetron sputtering in a mixture of working gases (helium, argon, and hydrogen). The amount and depth profile of helium and hydrogen trapped in the films were determined using the elastic recoil detection analysis. The microstructure and surface morphology of the Zr-H-He films were studied by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. To investigate the effect of hydrogen on the thermal release behavior of helium in the Zr film, thermal desorption spectrometry (TDS) was used, which revealed a similar desorption behavior to aged tritides. TDS experiments showed that the spectra were constituted by low-temperature peaks around 300 deg. C and high temperature peaks above 750 deg. C. Furthermore, the solid-phase {alpha} to {delta} transformation changed the shapes of the high-temperature peaks related to microstates of helium bubbles and caused the peak with a massive helium release shift toward lower temperature obviously.

  5. Arsenate adsorption and desorption kinetics on a Fe(III)-modified montmorillonite.

    PubMed

    Luengo, Carina; Puccia, Virginia; Avena, Marcelo

    2011-02-28

    The adsorption-desorption kinetics of arsenate on a Fe(III)-modified montmorillonite (Fe-M) was studied at different arsenate concentrations, pH and stirring rates. The synthesized solid was a porous sample with Fe(III) present as a mix of monomeric and polymeric Fe(III) species in the interlayer and on the external surface. Adsorption took place in a two-step mechanism, with an initial fast binding of arsenate to Fe(III) species at the external surface (half-lives of 1 min or shorter) followed by a slower binding to less accessible Fe(III) species in pores and the interlayer (half-lives of around 1 h). Desorption kinetics also reflected the presence of externally and internally adsorbed arsenate. At pH 6 the maximum adsorbed arsenate was 52 μmol/g, a value that is low as compared to adsorption on ferrihydrite (700 μmol/g) and goethite (192-220 μmol/g). However, since the Fe(III) content of Fe-M is much lower than that of ferrihydrite and goethite, Fe(III) species in Fe-M are more efficient in binding arsenate than in ferrihydrite or goethite (one As atom is attached every 8.95 iron atoms). This high binding efficiency indicates that Fe(III) species are well spread on montmorillonite, forming small oligomeric species or surface clusters containing just a few iron atoms. PMID:21242027

  6. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite

    SciTech Connect

    Tinnacher, Ruth M.; Begg, James D.; Mason, Harris; Ranville, James; Powell, Brian A.; Wong, Jennifer C.; Kersting, Annie B.; Zavarin, Mavrik

    2015-01-21

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu–FA–mineral complexes could enhance colloid-facilitated Pu transport. In conclusion, more representative natural conditions need to be investigated to quantify the relevance of these findings.

  7. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite

    DOE PAGESBeta

    Tinnacher, Ruth M.; Begg, James D.; Mason, Harris; Ranville, James; Powell, Brian A.; Wong, Jennifer C.; Kersting, Annie B.; Zavarin, Mavrik

    2015-01-21

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presencemore » of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu–FA–mineral complexes could enhance colloid-facilitated Pu transport. In conclusion, more representative natural conditions need to be investigated to quantify the relevance of these findings.« less

  8. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite.

    PubMed

    Tinnacher, Ruth M; Begg, James D; Mason, Harris; Ranville, James; Powell, Brian A; Wong, Jennifer C; Kersting, Annie B; Zavarin, Mavrik

    2015-03-01

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu-FA-mineral complexes could enhance colloid-facilitated Pu transport. However, more representative natural conditions need to be investigated to quantify the relevance of these findings. PMID:25607800

  9. Hydrogenation of CO-bearing species on grains: unexpected chemical desorption of CO

    NASA Astrophysics Data System (ADS)

    Minissale, M.; Moudens, A.; Baouche, S.; Chaabouni, H.; Dulieu, F.

    2016-05-01

    The amount of methanol in the gas phase and the CO depletion from the gas phase are still open problems in astrophysics. In this work, we investigate solid-state hydrogenation of CO-bearing species via H-exposure of carbon monoxide, formaldehyde, and methanol-thin films deposited on cold surfaces, paying attention to the possibility of a return to the gas phase. The products are probed via infrared spectroscopy (reflection absorption infrared spectroscopy), and two types of mass spectroscopy protocols: temperature-programmed desorption, and during-exposure desorption techniques. In the case of the [CO+H] reactive system, we have found that chemical desorption of CO is more efficient than H-addition reactions and HCO and H2CO formation; the studies of the [H2CO +H] reactive system show a strong competition between all surface processes, chemical desorption of H2CO, H-addition (CH3OH formation) and H-abstraction (CO formation); finally, [CH3OH + H] seems to be a non-reactive system and chemical desorption of methanol is not efficient. CO-bearing species present a see-saw mechanism between CO and H2CO balanced by the competition of H-addition and H2-abstraction that enhances the CO chemical desorption. The chemical network leading to methanol has to be reconsidered. The methanol formation on the surface of interstellar dust grain is still possible through CO+H reaction; nevertheless, its consumption of adsorbed H atoms should be higher than previously expected.

  10. Desorption of Hydrogen from Si(111) by Resonant Excitation of the Si-H Vibrational Stretch Mode

    SciTech Connect

    Liu, Zhiheng; Feldman, Leonard C.; Tolk, Norman; Zhang, Zhenyu; Cohen, Philip I

    2006-01-01

    Past efforts to achieve selective bond scission by vibrational excitation have been thwarted by energy thermalization. Here we report resonant photodesorption of hydrogen from a Si(111) surface using tunable infrared radiation. The wavelength dependence of the desorption yield peaks at 0.26 electron volt: the energy of the Si-H vibrational stretch mode. The desorption yield is quadratic in the infrared intensity. A strong H/D isotope effect rules out thermal desorption mechanisms, and electronic effects are not applicable in this low-energy regime. A molecular mechanism accounting for the desorption event remains elusive.

  11. Desorption Kinetics of Ar, Kr, Xe, N2, O2, CO, Methane, Ethane, and Propane from Graphene and Amorphous Solid Water Surfaces.

    PubMed

    Smith, R Scott; May, R Alan; Kay, Bruce D

    2016-03-01

    The desorption kinetics for Ar, Kr, Xe, N2, O2, CO, methane, ethane, and propane from graphene-covered Pt(111) and amorphous solid water (ASW) surfaces are investigated using temperature-programmed desorption (TPD). The TPD spectra for all of the adsorbates from graphene have well-resolved first, second, third, and multilayer desorption peaks. The alignment of the leading edges is consistent the zero-order desorption for all of the adsorbates. An Arrhenius analysis is used to obtain desorption energies and prefactors for desorption from graphene for all of the adsorbates. In contrast, the leading desorption edges for the adsorbates from ASW do not align (for coverages < 2 ML). The nonalignment of TPD leading edges suggests that there are multiple desorption binding sites on the ASW surface. Inversion analysis is used to obtain the coverage dependent desorption energies and prefactors for desorption from ASW for all of the adsorbates. PMID:26595145

  12. Kinetics of catalytic transfer hydrogenation of soybean lecithin

    SciTech Connect

    Naglic, M.; Smidovnik, A.; Koloini, T.

    1997-12-01

    Catalytic transfer hydrogenation of soybean lecithin has been studied using aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined at intensive stirring. Hydrogenation reactions followed the first-order kinetics with respect to fatty acids. In addition to short reaction time, this method offers safe and easy handling. Hydrogenated soybean lecithin provides products with increased stability with respect to oxidation.

  13. Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

    USGS Publications Warehouse

    Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

    2013-01-01

    Rates of U(VI) release from individual dry-sieved size fractions of a field-aggregated, field-contaminated composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through reactors to maintain quasi-constant chemical conditions. The principal source of variability in equilibrium U(VI) adsorption properties of the various size fractions was the impact of variable chemistry on adsorption. This source of variability was represented using surface complexation models (SCMs) with different stoichiometric coefficients with respect to hydrogen ion and carbonate concentrations for the different size fractions. A reactive transport model incorporating equilibrium expressions for cation exchange and calcite dissolution, along with rate expressions for aerobic respiration and silica dissolution, described the temporal evolution of solute concentrations observed during the flow-through reactor experiments. Kinetic U(VI) desorption was well described using a multirate SCM with an assumed lognormal distribution for the mass-transfer rate coefficients. The estimated mean and standard deviation of the rate coefficients were the same for all <2 mm size fractions but differed for the 2–8 mm size fraction. Micropore volumes, assessed using t-plots to analyze N2 desorption data, were also the same for all dry-sieved <2 mm size fractions, indicating a link between micropore volumes and mass-transfer rate properties. Pore volumes for dry-sieved size fractions exceeded values for the corresponding wet-sieved fractions. We hypothesize that repeated field wetting and drying cycles lead to the formation of aggregates and/or coatings containing (micro)pore networks which provided an additional mass-transfer resistance over that associated with individual particles. The 2–8 mm fraction exhibited a larger average and standard deviation in the distribution of mass-transfer rate coefficients, possibly caused by the abundance of

  14. Thermal desorption of hydrogen from carbon and graphite at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Atsumi, H.; Takemura, Y.; Konishi, T.; Tanabe, T.; Shikama, T.

    2013-07-01

    Thermal desorption spectrometry (TDS) has been investigated to obtain fundamental information of hydrogen behavior in graphite and CFC especially at high temperatures. Thirteen brands of graphite and CFC materials charged with deuterium gas are tested up to the temperature of 1720 K with a heating rate of 0.1 K/s. TDS spectra have at least four peaks at 600-700 K, around 900 K, 1300-1450 K and 1600-1650 K. The change of TDS spectra is measured for the samples, which are charged with deuterium at 1273 K under a different pressure in the range of 83 Pa to 79 kPa. Physical and chemical states of deuterium in graphite and mechanisms of desorption are discussed.

  15. Adsorption and desorption kinetics in ZrO2 TiO2 by photoacoustic techniques

    NASA Astrophysics Data System (ADS)

    Pinto Neto, A.; Moura, D.; Kuranaga, C.; Silva, M. D.; Miranda, L. C. M.

    2005-06-01

    In this paper we report on the photoacoustic (PA) characterization of ZrO2-TiO2 ceramic wafers as a sensing element for solvent adulteration evaluation. The experiments consisted of photoacoustic time dependent monitoring of the sorption and desorption of a droplet of a solvent deposited on the outer face of a ceramic wafer. The used solvents were isopropanol and chloroform. For the polar isopropanol molecule the results shown diffusion into the sample, with a characteristic diffusion time τ_1, accompanied by the evaporation at a rate with a time constant τ_2. Indeed, for the non polar chloroform, wetting-drying kinetics is adequately described by a simple diffusion-evaporation.

  16. Hydrogen diffusion kinetics and structural integrity of superhigh pressure Mg-5 wt%Ni alloys with dendrite interface

    NASA Astrophysics Data System (ADS)

    Fu, Hui; Wu, Wenshi; Dou, Yang; Liu, Baozhong; Li, Hanning; Peng, Qiuming

    2016-07-01

    A strategy of low-angle orientation dendrite interface-high index planes-which prepared by super-high pressure (SHP) technique, is proposed and successfully improved the hydrogen storage properties of Mg based materials for the first time, wherein a simple binary Mg-Ni alloy is used as a sample to elucidate its related mechanisms. The phase composition, morphology variation and hydrogen storage properties of the as-cast and SHP Mg-5Ni alloys in the temperature range of 1100-1600 °C are systemically investigated. The reversible hydrogen storage capacities and plateau hydrogen pressure of the as-cast and SHP alloys are close due to the same hydrogen storage phases (Mg and Mg2Ni). Note that although SHP treatment at 1600 °C has a large weight fraction of Mg6Ni compound, it still effectively reduces the onset temperature of dehydriding (∼262 °C), as well as improves the hydrogen desorption kinetics at low temperatures and structural integrity. The low onset temperature and outstanding hydrogen sorption/desorption kinetics are mainly associated with the formation of a large number of dendrite interface, in which the hydrogen atoms readily occur "zig-zag" jumps along {11-20} prismatic planes. This dendrite interface of high index planes which prepared by SHP technique paves a new pathway to enhance the hydrogen storage performances of magnesium based alloys.

  17. Real-time detection of hydrogen absorption and desorption in metallic palladium using vibrating wire method

    NASA Astrophysics Data System (ADS)

    Inagaki, Yuji; Nishimura, Atsuki; Yokooji, Honoka; Takata, Hiroki; Kawae, Tatsuya

    2015-09-01

    A vibrating wire (VW) method was applied to investigate the hydrogen absorption and desorption properties of palladium. At room temperature, a considerable shift in resonance frequency was successfully observed in VW spectra under H2 gas exposure. The shift is reversible in the initial stage of the exposure and is attributed to changes in the density and Young’s modulus of the VW sensor. Irreversibility of the shift because of embrittlement is detected after a sufficient exposure time. H absorption is slowed down enormously at T = 200 K owing to suppression of the thermal activation process.

  18. Laboratory investigation of the role of desorption kinetics on americium transport associated with bentonite colloids.

    PubMed

    Dittrich, Timothy Mark; Boukhalfa, Hakim; Ware, Stuart Douglas; Reimus, Paul William

    2015-10-01

    Understanding the parameters that control colloid-mediated transport of radionuclides is important for the safe disposal of used nuclear fuel. We report an experimental and reactive transport modeling examination of americium transport in a groundwater-bentonite-fracture fill material system. A series of batch sorption and column transport experiments were conducted to determine the role of desorption kinetics from bentonite colloids in the transport of americium through fracture materials. We used fracture fill material from a shear zone in altered granodiorite collected from the Grimsel Test Site (GTS) in Switzerland and colloidal suspensions generated from FEBEX bentonite, a potential repository backfill material. The colloidal suspension (100 mg L(-1)) was prepared in synthetic groundwater that matched the natural water chemistry at GTS and was spiked with 5.5 × 10(-10) M (241)Am. Batch characterizations indicated that 97% of the americium in the stock suspension was adsorbed to the colloids. Breakthrough experiments conducted by injecting the americium colloidal suspension through three identical columns in series, each with mean residence times of 6 h, show that more than 95% of the bentonite colloids were transported through each of the columns, with modeled colloid filtration rates (k(f)) of 0.01-0.02 h(-1). Am recoveries in each column were 55-60%, and Am desorption rate constants from the colloids, determined from 1-D transport modeling, were 0.96, 0.98, and 0.91 h(-1) in the three columns, respectively. The consistency in Am recoveries and desorption rate constants in each column indicates that the Am was not associated with binding sites of widely-varying strengths on the colloids, as one binding site with fast kinetics represented the system accurately for all three sequential columns. Our data suggest that colloid-mediated transport of Am in a bentonite-fracture fill material system is unlikely to result in transport over long distance scales because

  19. Laboratory investigation of the role of desorption kinetics on americium transport associated with bentonite colloids

    DOE PAGESBeta

    Dittrich, Timothy Mark; Boukhalfa, Hakim; Ware, Stuart Douglas; Reimus, Paul William

    2015-07-13

    Understanding the parameters that control colloid-mediated transport of radionuclides is important for the safe disposal of used nuclear fuel. We report an experimental and reactive transport modeling examination of americium transport in a groundwater–bentonite–fracture fill material system. A series of batch sorption and column transport experiments were conducted to determine the role of desorption kinetics from bentonite colloids in the transport of americium through fracture materials. We used fracture fill material from a shear zone in altered granodiorite collected from the Grimsel Test Site (GTS) in Switzerland and colloidal suspensions generated from FEBEX bentonite, a potential repository backfill material. Themore » colloidal suspension (100 mg L–1) was prepared in synthetic groundwater that matched the natural water chemistry at GTS and was spiked with 5.5 × 10–10 M241Am. Batch characterizations indicated that 97% of the americium in the stock suspension was adsorbed to the colloids. Breakthrough experiments conducted by injecting the americium colloidal suspension through three identical columns in series, each with mean residence times of 6 h, show that more than 95% of the bentonite colloids were transported through each of the columns, with modeled colloid filtration rates (kf) of 0.01–0.02 h–1. Am recoveries in each column were 55–60%, and Am desorption rate constants from the colloids, determined from 1-D transport modeling, were 0.96, 0.98, and 0.91 h–1 in the three columns, respectively. The consistency in Am recoveries and desorption rate constants in each column indicates that the Am was not associated with binding sites of widely-varying strengths on the colloids, as one binding site with fast kinetics represented the system accurately for all three sequential columns. As a result, our data suggest that colloid-mediated transport of Am in a bentonite-fracture fill material system is unlikely to result in transport over long

  20. Laboratory investigation of the role of desorption kinetics on americium transport associated with bentonite colloids

    SciTech Connect

    Dittrich, Timothy Mark; Boukhalfa, Hakim; Ware, Stuart Douglas; Reimus, Paul William

    2015-07-13

    Understanding the parameters that control colloid-mediated transport of radionuclides is important for the safe disposal of used nuclear fuel. We report an experimental and reactive transport modeling examination of americium transport in a groundwater–bentonite–fracture fill material system. A series of batch sorption and column transport experiments were conducted to determine the role of desorption kinetics from bentonite colloids in the transport of americium through fracture materials. We used fracture fill material from a shear zone in altered granodiorite collected from the Grimsel Test Site (GTS) in Switzerland and colloidal suspensions generated from FEBEX bentonite, a potential repository backfill material. The colloidal suspension (100 mg L–1) was prepared in synthetic groundwater that matched the natural water chemistry at GTS and was spiked with 5.5 × 10–10 M241Am. Batch characterizations indicated that 97% of the americium in the stock suspension was adsorbed to the colloids. Breakthrough experiments conducted by injecting the americium colloidal suspension through three identical columns in series, each with mean residence times of 6 h, show that more than 95% of the bentonite colloids were transported through each of the columns, with modeled colloid filtration rates (kf) of 0.01–0.02 h–1. Am recoveries in each column were 55–60%, and Am desorption rate constants from the colloids, determined from 1-D transport modeling, were 0.96, 0.98, and 0.91 h–1 in the three columns, respectively. The consistency in Am recoveries and desorption rate constants in each column indicates that the Am was not associated with binding sites of widely-varying strengths on the colloids, as one binding site with fast kinetics represented the system accurately for all three sequential columns. As a result, our data suggest that colloid-mediated transport of Am in a bentonite-fracture fill

  1. The dissociation kinetics of NO on Rh(111) as studied by temperature programmed static secondary ion mass spectrometry and desorption

    NASA Astrophysics Data System (ADS)

    Borg, H. J.; Reijerse, J. F. C.-J. M.; van Santen, R. A.; Niemantsverdriet, J. W.

    1994-12-01

    Temperature programmed static secondary ion mass spectrometry (TPSSIMS) and temperature programmed desorption (TPD) have been used to study the kinetics of adsorption, dissociation, and desorption of NO on Rh(111). At 100 K, NO adsorption is molecular and proceeds via mobile precursor state kinetics with a high initial sticking probability. SSIMS indicates the presence of two distinct NO adsorption states, indicative of threefold adsorption at low coverage, and occupation of bridge sites at higher coverages. Three characteristic coverage regimes appear with respect to NO dissociation. At low coverages θNO<0.25 ML, NO dissociates completely at temperatures between 275 and 340 K. If we neglect lateral interactions and assume pure first order dissociation kinetics, we find effective values for the activation barrier and preexponential factor of 40±6 kJ/mol and 106±1 s-1 for the dissociation of 0.15-0.20 ML NO. However, if we assume that a NO molecule needs an ensemble of three to four vacant sites in order to dissociate, the preexponential factor and activation energy are ˜1011 s-1 and 65 kJ/mol, in better agreement with transition state theory expectations. The Nads and Oads dissociation products desorb as N2 and O2, respectively, with desorption parameters Edes=118±10 kJ/mol and νdes=1010.1±1.0 s-1 for N2 in the zero coverage limit. At higher coverages, the desorption kinetics of N2 is strongly influenced by the presence of coadsorbed oxygen. In the medium coverage range 0.25<θNO<0.50 ML, part of the NO desorbs molecularly, with an estimated desorption barrier of 113±10 kJ/mol and a preexponential of 1013.5±1.0 s-1. Dissociation of NO becomes progressively inhibited due to site blocking, the onset shifting from 275 K at 0.25 ML to 400 K, coinciding with the NO desorption temperature, at a coverage of 0.50 ML. The accumulation of nitrogen and oxygen atoms on the highly covered surface causes a destabilization of the nitrogen atoms, which results in an

  2. Eriobotrya japonica seed biocomposite efficiency for copper adsorption: Isotherms, kinetics, thermodynamic and desorption studies.

    PubMed

    Mushtaq, Mehwish; Bhatti, Haq Nawaz; Iqbal, Munawar; Noreen, Saima

    2016-07-01

    Adsorption techniques are widely used to remove pollutants from wastewater; however, composites are gaining more importance due to their excellent adsorption properties. Bentonite composite with Eriobotrya japonica seed was prepared and used for the adsorption of copper (Cu) metal from aqueous media. The process variables such as pH, Cu(II) ions initial concentration, adsorbent dose, contact time and temperature were optimized for maximum Cu(II) adsorption. At pH 5, adsorbent dose 0.1 g, contact time 45 min, Cu(II) ions initial concentration 75 mg/L and temperature 45 °C, maximum Cu(II) adsorption was achieved. Desorption studies revealed that biocomposite is recyclable. Langmuir, Freundlich and Harkins-Jura isotherms as well as pseudo-first and pseudo-second-order kinetics models were applied to understand the adsorption mechanism. Thermodynamic parameters (ΔG(0), ΔH(0) and ΔS(0)) suggest that the adsorption process was spontaneous and endothermic in nature. The pseudo-second-order kinetic model and Langmuir isotherm fitted well to the adsorption data. Results showed that biocomposite was more efficient for Cu(II) adsorption in comparison to individuals native Eriobotrya japonica seed biomass and Na-bentonite. PMID:27039361

  3. Chemistry of inorganic arsenic in soils: kinetics of arsenic adsorption-desorption.

    PubMed

    Smith, E; Naidu, R

    2009-04-01

    The influence of ionic strength, index cations and competing anions on arsenate (As(V)) adsorption-desorption kinetics was studied in an Alfisol soil. A flow-through reactor system similar to that developed by Carski and Sparks (Soil Sci Soc Am J 49:1114-1116, 1985) was constructed for the experiments. Arsenate adsorption kinetics for all the treatments were initially fast with 58-91% of As(V) adsorbed in the first 15 min. Beyond 15 min, As(V) adsorption continued at a slower rate for the observation period of the experiments. Changes in the solution composition had differing effects on the cumulative amount of As(V) adsorbed by the soil. Ionic strength and different index cations had little effect on the amount of As(V) adsorbed, while the presence of phosphate decreased the amount of As(V) adsorbed from 169 to 89 and 177 to 115 g As(V) microg(-1) in 0.03 M sodium nitrate and 0.01 M calcium nitrate, respectively. Considerably less As(V) was desorbed than was adsorbed, with only between 2 to 17% of the adsorbed As(V) desorbed. The presence of phosphate increased the amount of As(V) desorbed by 17%, but other changes in the solution ionic strength or index cation had little effect on the amount of As(V) desorbed. PMID:19101807

  4. Desorption isotherms and mathematical modeling of thin layer drying kinetics of tomato

    NASA Astrophysics Data System (ADS)

    Belghith, Amira; Azzouz, Soufien; ElCafsi, Afif

    2016-03-01

    In recent years, there is an increased demand on the international market of dried fruits and vegetables with significant added value. Due to its important production, consumption and nutrient intake, drying of tomato has become a subject of extended and varied research works. The present work is focused on the drying behavior of thin-layer tomato and its mathematical modeling in order to optimize the drying processes. The moisture desorption isotherms of raw tomato were determined at four temperature levels namely 45, 50, 60 and 65 °C using the static gravimetric method. The experimental data obtained were modeled by five equations and the (GAB) model was found to be the best-describing these isotherms. The drying kinetics were experimentally investigated at 45, 55 and 65 °C and performed at air velocities of 0.5 and 2 m/s. In order to investigate the effect of the exchange surface on drying time, samples were dried into two different shapes: tomato halves and tomato quarters. The impact of various drying parameters was also studied (temperature, air velocity and air humidity). The drying curves showed only the preheating period and the falling drying rate period. In this study, attention was paid to the modeling of experimental thin-layer drying kinetics. The experimental results were fitted with four different models.

  5. Hydrogen storage material and process using graphite additive with metal-doped complex hydrides

    DOEpatents

    Zidan, Ragaiy; Ritter, James A.; Ebner, Armin D.; Wang, Jun; Holland, Charles E.

    2008-06-10

    A hydrogen storage material having improved hydrogen absorbtion and desorption kinetics is provided by adding graphite to a complex hydride such as a metal-doped alanate, i.e., NaAlH.sub.4. The incorporation of graphite into the complex hydride significantly enhances the rate of hydrogen absorbtion and desorption and lowers the desorption temperature needed to release stored hydrogen.

  6. Removal of mercury contamination on primary mass standards by hydrogen plasma and thermal desorption

    NASA Astrophysics Data System (ADS)

    Fuchs, P.; Marti, K.; Russi, S.

    2013-02-01

    The removal of a high mercury contamination on a Pt reference mass by thermal desorption was studied directly by x-ray photoemission spectroscopy (XPS). Subsequently the contamination mechanism was investigated. Samples of PtIr and AuPt exposed to vapour of mercury in air were studied using XPS and gravimetric mass determination. We find an extremely rapid mercury contamination which takes place within minutes and reaches an initial equilibrium state after 2 h to 4 h. Roughly 1 to 2 monolayers of mercury adsorbs directly on the metal surface. A natural contamination of carbon and oxygen compounds is at the top. Due to the accumulation of mercury, we find a gain in mass which corresponds to 20 µg to 26 µg for a PtIr standard. XPS data from a historical Pt standard give strong evidence for further average mercury accumulation of (1.3 ± 0.1) µg/year during a period of more than a century. This can be explained by a two-step mechanism presented in this study. The speed of contamination depends on the initial surface conditions. Polishing activates the surface and results in an enhanced accumulation of mercury. Natural contamination by C and O can delay but not prevent contamination. We further demonstrate that the mercury contamination can be removed by both hydrogen plasma and thermal desorption. The removal of mercury by hydrogen plasma can directly be attributed to the synthesis of gaseous mercury dihydrides at low pressures.

  7. Enhanced hydrogen desorption properties of magnesium hydride by coupling non-metal doping and nano-confinement

    NASA Astrophysics Data System (ADS)

    He, Daliang; Wang, Yulong; Wu, Chengzhang; Li, Qian; Ding, Weizhong; Sun, Chenghua

    2015-12-01

    Magnesium hydride (MgH2) offers excellent capacity to store hydrogen, but it suffers from the high desorption temperature (>283 °C for starting release hydrogen). In this work, we calculated the hydrogen desorption energy of Mg76H152 clusters with/without non-metal dopants by density functional theory method. Phosphorus (P), as identified as the best dopant, can reduce the reaction energy for releasing one hydrogen molecule from 0.75 eV (bulk MgH2) to 0.20 eV. Inspired by the calculation, P-doped ordered mesoporous carbon (CMK-3) was synthesized by one-step method and employed as the scaffold for loading MgH2 nanoparticles, forming MgH2@P/CMK-3. Element analysis shows that phosphorus dopants have been incorporated into the CMK-3 scaffold and magnesium and phosphorus elements are well-distributed in carbon scaffold hosts. Tests of hydrogen desorption confirmed that P-doping can remarkably enhance the hydrogen release properties of nanoconfined MgH2 at low temperature, specifically ˜1.5 wt. % H2 released from MgH2@P/CMK-3 below 200 °C. This work, based on the combination of computational calculations and experimental studies, demonstrated that the combined approach of non-metal doping and nano-confinement is promising for enhancing the hydrogen desorption properties of MgH2, which provides a strategy to address the challenge of hydrogen desorption from MgH2 at mild operational conditions.

  8. Electronic structure of partially hydrogenated Si(100)-( 2 x 1) surfaces prepared by thermal and nonthermal desorption.

    PubMed

    Bobrov, K; Comtet, G; Dujardin, G; Hellner, L

    2001-03-19

    The electronic structure of partially hydrogenated Si(100)- (2 x 1) surfaces, prepared by controlled thermal annealing and nonthermal photon stimulated desorption of fully hydrogenated Si(100) surfaces, has been investigated by using valence band photoemission. Thermal and nonthermal desorption are found to produce very specific electronic surface structures. This led us to the discovery of two specific surface states having binding energies of 1.0 and 0.7 eV associated with the isolated Si dimers and single Si dangling bonds, respectively. PMID:11289998

  9. An investigation of the desorption of hydrogen from lithium oxide using temperature programmed desorption and diffuse reflectance infrared spectroscopy

    SciTech Connect

    Kopasz, J.P.; Johnson, C.E.; Ortiz-Villafuerte, J.

    1995-04-01

    The addition of hydrogen to the purge stream has been shown to enhance tritium release from ceramic breeder materials; however, this added hydrogen can lead to increased costs in the tritium purification system. The objective of this work is to develop an understanding of the interactions between hydrogen and lithium oxide surfaces so that the authors can take full advantage of the observed enhancement of tritium release caused by hydrogen addition without incurring high costs in the tritium purification plant.

  10. Thermodynamics and Kinetics of Phase Transformations in Hydrogen Storage Materials

    SciTech Connect

    Ceder, Gerbrand; Marzari, Nicola

    2011-08-31

    The aim of this project is to develop and apply computational materials science tools to determine and predict critical properties of hydrogen storage materials. By better understanding the absorption/desorption mechanisms and characterizing their physical properties it is possible to explore and evaluate new directions for hydrogen storage materials. Particular emphasis is on the determination of the structure and thermodynamics of hydrogen storage materials, the investigation of microscopic mechanisms of hydrogen uptake and release in various materials and the role of catalysts in this process. As a team we have decided to focus on a single material, NaAlH{sub 4}, in order to fully be able to study the many aspects of hydrogen storage. We have focused on phase stability, mass transport and size-dependent reaction mechanisms in this material.

  11. Effect of thermal desorption kinetics on vapor injection peak irregularities by a microscale gas chromatography preconcentrator.

    PubMed

    Seo, Jung Hwan; Liu, Jing; Fan, Xudong; Kurabayashi, Katsuo

    2012-08-01

    Microscale gas chromatography (μGC) is an emerging analytical technique for in situ analysis and on-site monitoring of volatile organic compounds (VOCs) in moderately complex mixtures. One of the critical subcomponents in a μGC system is a microfabricated preconcentrator (μ-preconcentrator), which enables detection of compounds existing in indoor/ambient air at low (~sub ppb) concentrations by enhancing their signals. The prevailing notion is that elution peak broadening and tailing phenomena resulting from undesirable conditions of a microfabricated separation column (μ-column) are the primary sources of poor chromatographic resolution. However, previous experimental results indicate that the resolution degradation still remains observed for a μ-column integrated with other μGC subcomponents even after setting optimal separation conditions. In this work, we obtain the evidence that the unoptimized μ-preconcentrator vapor release/injection performance significantly contributes to decrease the fidelity of μGC analysis using our state-of-the-art passive preconcentrator microdevice. The vapor release/injection performance is highly affected by the kinetics of the thermal desorption of compounds trapped in the microdevice. Decreasing the heating rate by 20% from the optimal rate of 90 °Cs(-1) causes a 340% increase in peak tailing as well as 70% peak broadening (30% peak height reduction) to the microscale vapor injection process. PMID:22780835

  12. Bulk Diffusion-Controlled Thermal Desorption Spectroscopy with Examples for Hydrogen in Iron

    NASA Astrophysics Data System (ADS)

    Kirchheim, Reiner

    2016-02-01

    Bulk diffusion-controlled thermal desorption spectroscopy (TDS) is studied by solving the corresponding transport equations numerically as well as analytically with appropriate approximations. The two solutions are compared in order to validate the derived equations including the Kissinger equation. Besides the diffusion of the desorbed species through the sample, trapping of the species at special lattice sites within the sample is included in the numerical and approximate analytical solutions. Trapping energies are mono-energetic, multi-energetic, or are described by a box-type distribution. TDS-peaks were simulated for different heating rates, sample thicknesses, trap concentrations, and initial degrees of trap saturation. It is shown that for the case of mono-energetic traps, Kissinger's equation is obeyed for both numerical and analytical results. This widely used equation for reaction rate-controlled studies is derived in an explicit form for diffusion-controlled processes. Together with a newly derived relation between maximum desorption rate and temperature, TDS-spectra yield information about diffusion coefficient, trap energies, and trap concentration as well as trap saturation. This is exemplified using data of two experimental studies. Although the numerical and analytical treatment is in general applicable to all diffusion species, hydrogen in iron alloys is used as a model system because of its technological importance and the increasing number of experimental work with this material.

  13. Effect of humic acid on the adsorption/desorption behavior of glyphosate on goethite. Isotherms and kinetics.

    PubMed

    Arroyave, Jeison Manuel; Waiman, Carolina C; Zanini, Graciela P; Avena, Marcelo J

    2016-02-01

    The effects of humic acid (HA) on the adsorption/desorption of glyphosate (Gly) on goethite were investigated under pseudo equilibrium conditions by adsorption isotherms and under kinetic conditions by ATR-FTIR spectroscopy. Isotherms reveal that the attachment of Gly is almost completely inhibited by HA molecules. The opposite effect is not observed: HA adsorption is not affected by the presence of Gly. ATR-FTIR allowed the simultaneous detection of adsorbed HA and Gly during kinetic runs, revealing that HA at the surface decreases markedly the adsorption rate of Gly likely as a result of a decreased availability of sites for Gly adsorption and because of electrostatic repulsion. In addition, HA in solution increases the desorption rate of Gly. The rate law for Gly desorption could be determined giving important insights on the desorption mechanism. The herbicide is desorbed by two parallel processes: i) a direct detachment from the surface, which is first order in adsorbed Gly; and ii) a ligand exchange with HA molecules, which is first order in adsorbed Gly and first order in dissolved HA. Rate constants for both processes were quantified, leading to half-lives of 3.7 h for the first process, and 1.4 h for the second process in a 400 mg L(-1) HA solution. These data are important for modeling the dynamics of glyphosate in environmentally relevant systems, such as soils and surface waters. PMID:26657085

  14. Influence of hydrogen oxidation kinetics on hydrogen environment embrittlement

    NASA Technical Reports Server (NTRS)

    Walter, R. J.; Kendig, M. W.; Meisels, A. P.

    1992-01-01

    Results are presented from experiments performed to determine the roles of hydrogen absorption and hydrogen electron transfer on the susceptibility of Fe- and Ni-base alloys to ambient-temperature hydroen embrittlement. An apparent independence is noted between hydrogen environment embrittlement and internal hydrogen embrittlement. The experiments were performed on Inconel 718, Incoloy 903, and A286. The electrochemical results obtained indicate that Inconel 718 either adsorbs hydrogen more rapidly and/or the electrochemical oxidation of the adsorbed hydrogen occurred more rapidly than in the other two materials.

  15. Kinetics of hydrogen release from lunar soil

    NASA Technical Reports Server (NTRS)

    Bustin, Roberta

    1990-01-01

    With increasing interest in a lunar base, there is a need for extensive examination of possible lunar resources. Hydrogen will be needed on a lunar base for many activities including providing fuel, making water, and serving as a reducing agent in the extraction of oxygen from its ores. Previous studies have shown the solar wind has implanted hydrogen in the lunar regolith and that hydrogen is present not only in the outer layer of soil but to considerable depths, depending on the sampling site. If this hydrogen is to be mined and used on the lunar surface, a number of questions need to be answered. How much energy must be expended in order to release the hydrogen from the soil. What temperatures must be attained, and how long must the soil be heated. This study was undertaken to provide answers to practical questions such as these. Hydrogen was determined using a Pyrolysis/GC technique in which hydrogen was released by heating the soil sample contained in a quartz tube in a resistance wire furnace, followed by separation and quantitative determination using a gas chromatograph with a helium ionization detector. Heating times and temperatures were varied, and particle separates were studied in addition to bulk soils. The typical sample size was 10 mg of lunar soil. All of the soils used were mature soils with similar hydrogen abundances. Pre-treatments with air and steam were used in an effort to find a more efficient way of releasing hydrogen.

  16. Kinetics of hydrogen release from lunar soil

    NASA Astrophysics Data System (ADS)

    Bustin, Roberta

    1990-10-01

    With increasing interest in a lunar base, there is a need for extensive examination of possible lunar resources. Hydrogen will be needed on a lunar base for many activities including providing fuel, making water, and serving as a reducing agent in the extraction of oxygen from its ores. Previous studies have shown the solar wind has implanted hydrogen in the lunar regolith and that hydrogen is present not only in the outer layer of soil but to considerable depths, depending on the sampling site. If this hydrogen is to be mined and used on the lunar surface, a number of questions need to be answered. How much energy must be expended in order to release the hydrogen from the soil. What temperatures must be attained, and how long must the soil be heated. This study was undertaken to provide answers to practical questions such as these. Hydrogen was determined using a Pyrolysis/GC technique in which hydrogen was released by heating the soil sample contained in a quartz tube in a resistance wire furnace, followed by separation and quantitative determination using a gas chromatograph with a helium ionization detector. Heating times and temperatures were varied, and particle separates were studied in addition to bulk soils. The typical sample size was 10 mg of lunar soil. All of the soils used were mature soils with similar hydrogen abundances. Pre-treatments with air and steam were used in an effort to find a more efficient way of releasing hydrogen.

  17. Determining the Desorption Kinetics of U(VI) from Contaminated Sediments Under Complex and Changing Solution Conditions

    NASA Astrophysics Data System (ADS)

    Hay, M. B.; Curtis, G. P.; Johnson, K. J.; Greskowiak, J.; Davis, J. A.

    2009-12-01

    Uranium(VI) transport in contaminated sediments is strongly controlled by the thermodynamics and kinetics of adsorption on mineral surfaces. Many studies on natural sediments and synthetic mineral phases have demonstrated the dependence of U(VI) sorption equilibrium on aqueous chemical conditions, with alkalinity, pH, ionic strength, and Ca concentration of particular importance in many natural systems. Desorption of U(VI) from contaminated sediments from DOE sites in Hanford, WA, Rifle, CO, and Naturita, CO also exhibits a significant kinetic limitation, with timescales of several weeks to months required to reach desorption equilibrium in some cases. This kinetic limitation is believed to be due to diffusion in intragranular pore space, which includes small fractures within grains and pores within clay aggregates and grain coatings. Development of appropriate reactive transport models that can be applied to predict the fate and transport of U(VI) in contaminated aquifers relies on accurately quantifying sorption equilibrium and kinetics at the grain scale, which vary from site to site based on sediment characteristics. This analysis typically involves laboratory batch- and column-scale adsorption/desorption experiments performed under a variety of chemical conditions to fully constrain surface complexation and kinetic models, requiring a constant set of chemical conditions over the duration of the experiment. In practice, however, this can be difficult in experiments aiming to quantify long-term kinetics (weeks to months time scale), due to slow ion exchange, mineral dissolution/precipitation, and redox processes. Long-term changes in solution conditions affect U(VI) sorption equilibrium, making it necessary to determine model parameters for U(VI) surface complexation, diffusion kinetics, and chemical weathering/ion exchange processes simultaneously from a given data set. We will present kinetic surface complexation model results obtained for size

  18. Hydrogen absorption/desorption behavior with oxygen-contaminated boron film

    NASA Astrophysics Data System (ADS)

    Tsuzuki, K.; Eiki, H.; Inoue, N.; Sagara, A.; Noda, N.; Hirohata, Y.; Hino, T.

    The effect of oxygen contamination on hydrogen absorption and desorption behavior from a boron coating film has been studied. Oxygen atoms were implanted by glow discharge in an O 2/He gas mixture until near saturation, into the boron film deposited by PCVD. The depth profile measurement by AES showed that O atoms were retained up to the depth of 20 nm. Hydrogen discharges were carried out to investigate the H absorption behavior. The capability of H absorption decreased for 30-50% compared to the pure boron film without O contamination. After the discharge, the depth profile of the oxygen atoms was not changed, which means that a stable oxide layer had formed. The reduction of the H absorption capability occurs probably because the formation of the boron oxide prevents H atoms from trapping in the form of B-H bonding. Most of the retained H atoms can be released by a heating up to 500°C with the O contamination. The required temperature for H evacuation is slightly higher than that for pure boron film. In addition, a small peak was observed at around 200°C. From these results, the applicability of boronization to future long term discharges was discussed, in which the boron film saturates with O contamination.

  19. Diffusion, adsorption, and desorption of molecular hydrogen on graphene and in graphite.

    PubMed

    Petucci, Justin; LeBlond, Carl; Karimi, Majid; Vidali, Gianfranco

    2013-07-28

    The diffusion of molecular hydrogen (H2) on a layer of graphene and in the interlayer space between the layers of graphite is studied using molecular dynamics computer simulations. The interatomic interactions were modeled by an Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential. Molecular statics calculations of H2 on graphene indicate binding energies ranging from 41 meV to 54 meV and migration barriers ranging from 3 meV to 12 meV. The potential energy surface of an H2 molecule on graphene, with the full relaxations of molecular hydrogen and carbon atoms is calculated. Barriers for the formation of H2 through the Langmuir-Hinshelwood mechanism are calculated. Molecular dynamics calculations of mean square displacements and average surface lifetimes of H2 on graphene at various temperatures indicate a diffusion barrier of 9.8 meV and a desorption barrier of 28.7 meV. Similar calculations for the diffusion of H2 in the interlayer space between the graphite sheets indicate high and low temperature regimes for the diffusion with barriers of 51.2 meV and 11.5 meV. Our results are compared with those of first principles. PMID:23902002

  20. Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

    SciTech Connect

    Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

    2013-02-12

    Rates of contaminant U(VI) release from individual size fractions of a composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through batch reactors to maintain quasi-constant chemical conditions. Variability in equilibrium adsorption among the various size fractions was determined in static batch reactors and analyzed using the surface complexation modeling approach. The estimated stoichiometric coefficients of U(VI) surface complexation reactions with respect to pH and carbonate concentrations varied with size fractions. This source of variability significantly increased the uncertainty in U(VI) conditional equilibrium constants over that estimated from experimental errors alone. A minimum difference between conditional equilibrium constants was established in order to evaluate statistically significant differences between sediment adsorption properties. A set of equilibrium and kinetic expressions for cation exchange, calcite dissolution, aerobic respiration, and silica dissolution were incorporated in a reaction-rate model to describe the temporal evolution of solute concentrations observed during the flow-through batch experiments. Parameters in the reaction-rate model, calibrated using experimental data for select size fractions, predicted the changes in solute concentrations for the bulk, <2 mm, sediment sample. Kinetic U(VI) desorption was well described using a multi-rate surface complexation model with an assumed lognormal distribution for the rate constants. The estimated mean and standard deviation were the same for all < 2mm size fractions, but differed in the 2-8mm size fraction. Micropore volumes in the varied size fractions were also similar as assessed using t-plots to analyze N2 desorption data. These findings provide further support for the link between microporosity and particle-scale mass transfer rates controlling kinetic U(VI) adsorption/desorption and for the utility of N2 desorption

  1. Revisiting reaction-diffusion model of thermal desorption spectroscopy experiments on hydrogen retention in material for fusion applications

    NASA Astrophysics Data System (ADS)

    Guterl, Jerome; Smirnov, Roman; Krasheninnikov, Sergei

    2015-11-01

    Plasma-material interactions may strongly influence plasma performance and life-time of future magnetic fusion devices. Understanding the multifaceted physics of hydrogen retention in plasma-facing components (PFC) is thus crucial, but remains challenging due to the wide spectrum of retention processes on PFC surface and in PFC bulk induced by long-time exposure of PFC to high flux of energy and particles. We revisit here some aspects of reaction-diffusion models used to investigate hydrogen retention in material. We focus on analysis of thermal desorption spectroscopy (TDS) experiment considering only one type of traps in material and first neglecting surface effects. We show that solute hydrogen concentration in retention region usually remains in equilibrium during TDS experiments. In this regime, analytic description of thermal desorption spectra indicates that trapping of solute hydrogen during TDS cannot be ignored. Main features of thermal desorption are then analytically described and refined interpretation of Arrhenius plots is proposed. Effects of surface processes on hydrogen outgassing during TDS experiments are then introduced and surface-limited outgassing regimes are discussed.

  2. Catalytic reduction of CO with hydrogen sulfide. 4. Temperature-programmed desorption of methanethiol on anatase, rutile, and sulfided rutile

    SciTech Connect

    Beck, D.D.; White, J.M.; Ratcliffe, C.T.

    1986-07-03

    The interaction of methanethiol with anatase, rutile, and sulfided rutile was studied by temperature-programmed desorption. Dissociative adsorption occurs on rutile but is insignificant on anatase. Decomposition products are dominated by H/sub 2/ on rutile and by CH/sub 4/ on sulfided rutile. In both cases desorption occurs between 500 and 775 K. The 5- and 4-coordinate sites on the (110) face of rutile are proposed as the active sites for decomposition. The dominance of methane on a sulfided surface is attributed to the relatively large supply of highly mobile surface hydrogen atoms.

  3. First Observation of Charge Reduction and Desorption Kinetics of Multiply Protonated Peptides Soft Landed onto Self-Assembled Monolayer Surfaces

    SciTech Connect

    Hadjar, Omar; Futrell, Jean H.; Laskin, Julia

    2007-12-13

    The kinetics of charge reduction and desorption of different species produced by soft-landing of mass-selected ions was studied using in situ secondary ion mass spectrometry (SIMS) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). The improved SIMS capability described in this work utilizes an in-line 8 keV Cs+ ion gun and allows us to interrogate the surface both during the ion deposition and after the deposition is terminated. As a model system doubly protonated ions of Gramicidin S were deposited onto a fluorinated self-assembled monolayer (FSAM) surface. Our results demonstrate for the first time that various peptide-related peaks in FT-ICR SIMS spectra follow very different kinetics. We obtained unique kinetics signatures for doubly protonated, singly protonated and neutral peptides retained on the surface and followed their evolution as a function of time. The experimental results are in excellent agreement with a kinetic model that takes into account charge reduction and thermal desorption of different species from the surface.

  4. The Effect of Platinum-coatings on Hydrogen- and Water-absorption and Desorption Characteristics of Lithium Zirconate

    NASA Astrophysics Data System (ADS)

    Tsuchiya, B.; Bandow, S.; Nagata, S.; Saito, K.; Tokunaga, K.; Morita, K.

    Hydrogen (H)- and water (H2O)-storage and desorption characteristics of 25 nm thick Pt films onLi2ZrO3composite materials, exposed to normal air at room temperature, have been investigated by means of elastic recoil detection (ERD), Rutherford backscattering spectrometry (RBS), weight gain measurement (WGM), and thermal desorption spectroscopy (TDS) techniques. It was found by the ERD and TDS that H and H2O were absorbed into the Pt-coated Li2ZrO3 in air at room temperature and desorbed from it in vacuum at much low temperatures of approximately 317 and 309 K, respectively. In addition, the WGM and TDS spectra revealed that the absorption and desorption characters ofsome gases such as CH4, CO, and CO2including H as well as H2Ointo the Li2ZrO3 bulk were improved by Pt deposition.

  5. Hydrogen pickup measurements in zirconium alloys: Relation to oxidation kinetics

    NASA Astrophysics Data System (ADS)

    Couet, Adrien; Motta, Arthur T.; Comstock, Robert J.

    2014-08-01

    The optimization of zirconium-based alloys used for nuclear fuel cladding aims to reduce hydrogen pickup during operation, and the associated cladding degradation. The present study focuses on precisely and accurately measuring hydrogen pickup fraction for a set of alloys to specifically investigate the effects of alloying elements, microstructure and corrosion kinetics on hydrogen uptake. To measure hydrogen concentrations in zirconium alloys two techniques have been used: a destructive technique, Vacuum Hot Extraction, and a non-destructive one, Cold Neutron Prompt Gamma Activation Analysis. The results of both techniques show that hydrogen pickup fraction varies significantly with exposure time and between alloys. A possible interpretation of the results is that hydrogen pickup results from the need to balance charge. That is, the pickup of hydrogen shows an inverse relationship to oxidation kinetics, indicating that, if transport of charged species is rate limiting, oxide transport properties such as oxide electronic conductivity play a key role in the hydrogen pickup mechanism. Alloying elements (either in solid solution or in precipitates) would therefore impact the hydrogen pickup fraction by affecting charge transport.

  6. Experimental study of water desorption isotherms and thin-layer convective drying kinetics of bay laurel leaves

    NASA Astrophysics Data System (ADS)

    Ghnimi, Thouraya; Hassini, Lamine; Bagane, Mohamed

    2016-02-01

    The aim of this work is to determine the desorption isotherms and the drying kinetics of bay laurel leaves (Laurus Nobilis L.). The desorption isotherms were performed at three temperature levels: 50, 60 and 70 °C and at water activity ranging from 0.057 to 0.88 using the statistic gravimetric method. Five sorption models were used to fit desorption experimental isotherm data. It was found that Kuhn model offers the best fitting of experimental moisture isotherms in the mentioned investigated ranges of temperature and water activity. The Net isosteric heat of water desorption was evaluated using The Clausius-Clapeyron equation and was then best correlated to equilibrium moisture content by the empirical Tsami's equation. Thin layer convective drying curves of bay laurel leaves were obtained for temperatures of 45, 50, 60 and 70 °C, relative humidity of 5, 15, 30 and 45 % and air velocities of 1, 1.5 and 2 m/s. A non linear regression procedure of Levenberg-Marquardt was used to fit drying curves with five semi empirical mathematical models available in the literature, The R2 and χ2 were used to evaluate the goodness of fit of models to data. Based on the experimental drying curves the drying characteristic curve (DCC) has been established and fitted with a third degree polynomial function. It was found that the Midilli Kucuk model was the best semi-empirical model describing thin layer drying kinetics of bay laurel leaves. The bay laurel leaves effective moisture diffusivity and activation energy were also identified.

  7. Photosynthetic hydrogen and oxygen production - Kinetic studies

    NASA Astrophysics Data System (ADS)

    Greenbaum, E.

    1982-01-01

    The simultaneous photoproduction of hydrogen and oxygen was measured in a study of the steady-state turnover times of two biological systems, by driving them into the steady state with repetitive, single-turnover flash illumination. The systems were: (1) in vitro, isolated chloroplasts, ferredoxin and hydrogenase; and (2) the anaerobically-adapted green alga Chlamydomonas reinhardtii. It is found that the turnover times for production of both oxygen and hydrogen in photosynthetic water splitting are in milliseconds, and either equal to, or less than, the turnover time for carbon dioxide reduction in intact algal cells. There is therefore mutual compatibility between hydrogen and oxygen turnover times, and partial compatibility with the excitation rate of the photosynthetic reaction centers under solar irradiation conditions.

  8. Complex surface analytical investigations on hydrogen absorption and desorption processes of a TiMn2-based alloy.

    PubMed

    Schülke, Mark; Kiss, Gábor; Paulus, Hubert; Lammers, Martin; Ramachandran, Vaidyanath; Sankaran, Kannan; Müller, Karl-Heinz

    2009-04-01

    Metal hydrides are one of the most promising technologies in the field of hydrogen storage due to their high volumetric storage density. Important reaction steps take place at the very surface of the solid during hydrogen absorption. Since these reaction steps are drastically influenced by the properties and potential contamination of the solid, it is very important to understand the characteristics of the surface, and a variety of analytical methods are required to achieve this. In this work, a TiMn(2)-type metal hydride alloy is investigated by means of high-pressure activation measurements, X-ray photoelectron spectroscopy (XPS), secondary neutral mass spectrometry (SNMS) and thermal desorption mass spectrometry (TDMS). In particular, TDMS is an analytical tool that, in contrast to SIMS or SNMS, allows the hydrogen content in a metal to be quantified. Furthermore, it allows the activation energy for desorption to be determined from TDMS profiles; the method used to achieve this is presented here in detail. In the results section, it is shown that the oxide layer formed during manufacture and long-term storage prevents any hydrogen from being absorbed, and so an activation process is required. XPS measurements show the oxide states of the main alloy elements, and a layer 18 nm thick is determined via SNMS. Furthermore, defined oxide layers are produced and characterized in UHV using XPS. The influence of these thin oxide layers on the hydrogen sorption process is examined using TDMS. Finally, the activation energy of desorption is determined for the investigated alloy using the method presented here, and values of 46 kJ/mol for hydrogen sorbed in UHV and 103 kJ/mol for hydrogen originating from the manufacturing process are obtained. PMID:19294368

  9. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    NASA Technical Reports Server (NTRS)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  10. Electron-ion dynamics in laser-assisted desorption of hydrogen atoms from H-Si(111) surface

    SciTech Connect

    Bubin, Sergiy; Varga, Kalman

    2011-09-15

    In the framework of real time real space time-dependent density functional theory we have studied the electron-ion dynamics of a hydrogen-terminated silicon surface H-Si(111) subjected to intense laser irradiation. Two surface fragments of different sizes have been used in the simulations. When the intensity and duration of the laser exceed certain levels (which depend on the wavelength) we observe the desorption of the hydrogen atoms, while the underlying silicon layer remains essentially undamaged. Upon further increase of the laser intensity, the chemical bonds between silicon atoms break as well. The results of the simulations suggest that with an appropriate choice of laser parameters it should be possible to remove the hydrogen layer from the H-Si(111) surface in a matter of a few tens of femtoseconds. We have also observed that at high laser field intensities (2-4 V/A in this work) the desorption occurs even when the laser frequency is smaller than the optical gap of the silicon surface fragments. Therefore, nonlinear phenomena must play an essential role in such desorption processes.

  11. Hydrogen released from bulk ZnO single crystals investigated by time-of-flight electron-stimulated desorption

    SciTech Connect

    Dierre, Benjamin; Sekiguchi, Takashi; Yuan, Xiaoli; Ueda, Kazuyuki

    2010-11-15

    Electron beam (e-beam) irradiation effects on ZnO single crystals have been investigated by using time-of-flight electron-stimulated desorption (TOF-ESD). The samples were irradiated by using a continuous 0.5 or 1.5 keV e-beam, while the TOF-ESD spectra were taken by using a pulsed 0.5 keV e-beam. For both the O-terminated and Zn-terminated surfaces, the major desorption is H{sup +} desorption. The main trend of H{sup +} desorption intensity and evolution as a function of irradiation time is similar for both faces. The H{sup +} peak is much higher after 1.5 keV irradiation than after 0.5 keV irradiation. The intensity of the H{sup +} peak decreases exponentially as a function of irradiation time and partially recovers after the irradiation is stopped. These observations suggest that the main contribution of the H{sup +} desorption is hydrogen released from the dissociation of H-related defects and complexes in the bulk region of the ZnO by e-beam irradiation. This finding can be used to explain the reported ultraviolet degradation of ZnO single crystals under electron irradiation observed by cathodoluminescence. The surfaces play a lesser role for the H{sup +} desorption, as there are differences of the decreasing rate between the two faces and additionally the intensity of the H{sup +} peak for both the unclean O-face and Zn-facesis smaller than that for clean faces. While the H{sup +} desorption is mainly dominated by the bulk region, O{sup +} desorption is more influenced by the surfaces. There are two kinds of O{sup +} desorbed from ZnO having 13.0 {mu}s TOF and 14.2 {mu}s TOF. The O{sup +} desorption depends on the surface polarity, the surface conditions and the energy used for irradiation.

  12. Adsorption, Desorption, and Displacement Kinetics of H2O and CO2 on TiO2(110)

    SciTech Connect

    Smith, R. Scott; Li, Zhenjun; Chen, Long; Dohnalek, Zdenek; Kay, Bruce D.

    2014-07-17

    The adsorption, desorption, and displacement kinetics of H2O and CO2 on TiO2(110) are investigated using temperature programmed desorption (TPD) and molecular beam techniques. The TPD spectra for both H2O and CO2 have well-resolved peaks corresponding to desorption from bridge-bonded oxygen (BBO), Ti, and oxygen vacancies (VO) sites in order of increasing peak temperature. Analysis of the saturated monolayer peak for both species reveals that the corresponding adsorption energies on all sites are greater for H2O and for CO2. Sequential dosing of H2O and CO2 reveals that, independent of the dose order, H2O molecules will displace CO2 in order to occupy the highest energy binding sites available. Isothermal experiments show that the displacement of CO2 by H2O occurs between 75 and 80 K. Further analysis shows that a ratio of 4 H2O to 3 CO2 molecules is needed to displace CO2 from the TiO2(110) surface.

  13. Low-temperature thermal desorption of diesel polluted soil: influence of temperature and soil texture on contaminant removal kinetics.

    PubMed

    Falciglia, P P; Giustra, M G; Vagliasindi, F G A

    2011-01-15

    Five soil size aggregate fractions, corresponding to coarse (500-840 μm), medium (200-350 μm), fine (75-200 μm) sand, silt (10-75 μm) and clay (<4 μm), were artificially contaminated with diesel, and thermally treated using a laboratory scale apparatus to investigate the effect of soil texture on contaminant adsorption and removal. Ex situ thermal process was simulated using helium as the carrier gas at a flow rate of 1.5 L min(-1), different temperatures (100-300 °C) and different treatment times (5-30 min). The amount of contaminant adsorbed on the soil and the residual amount after thermal treatment was determined by gas chromatography. Results showed that adsorption phenomena and desorption efficiency were affected by the soil texture and that temperature and time of treatment were key factors in remedial process. A temperature of 175 °C is sufficient to remedy diesel polluted sandy and silty soils, whereas a higher temperature (250 °C) is needed for clays. Thermal desorption of diesel polluted soil was shown to be governed by first-order kinetics. Results are of practical interest and may be used in scaling-up and designing desorption systems for preliminary cost and optimal condition assessment. PMID:20940088

  14. Adsorption-desorption and leaching behavior of kresoxim-methyl in different soils of India: kinetics and thermodynamic studies.

    PubMed

    Sabale, Rupali P; Shabeer T P, Ahammed; Dasgupta, Soma; Utture, Sagar C; Banerjee, Kaushik; Oulkar, Dasharath P; Adsule, Pandurang G; Deshmukh, Madhukar B

    2015-07-01

    The sorption and leaching behavior of kresoxim-methyl was explored in four different soils, viz., clay, sandy loam, loamy sand, and sandy loam (saline), representing vegetables and fruits growing regions of India. Adsorption of kresoxim-methyl in all the soils reached equilibrium within 48 h. The rate constants for adsorption and desorption at two different temperatures were obtained from the Lindstrom model, which simultaneously evaluated adsorption and desorption kinetics. The data for rate constants, activation energies, enthalpy of activation, entropy of activation, and free energy indicated physical adsorption of kresoxim-methyl on soil. The relative adsorptivity of the test soils could be attributed to different organic matter and clay contents of the soils. A good fit to the linear and Freundlich isotherms was observed for both adsorption as well as desorption. The groundwater ubiquity score (GUS) for different soils varied between 0 and 2.26. The GUS and leaching study indicated moderately low leaching potential of kresoxim-methyl. The adsorption on four soil types largely depended on the soil physicochemical properties such as organic carbon content, cation-exchange capacity, and texture of the soil. PMID:26082423

  15. Control of Uniform and Interconnected Macroporous Structure in PolyHIPE for Enhanced CO2 Adsorption/Desorption Kinetics.

    PubMed

    Wang, Quanyong; Liu, Yao; Chen, Jian; Du, Zhongjie; Mi, Jianguo

    2016-07-19

    The highly uniform and interconnected macroporous polymer materials were prepared within the high internal phase hydrosol-in-oil emulsions (HIPEs). Impregnated with polyethylenimine (PEI), the polyHIPEs were then employed as solid adsorbents for CO2 capture. Thermodynamic and kinetic capture-and-release tests were performed with pure CO2, 10% CO2/N2, and moist CO2, respectively. It has shown that the polyHIPE with suitable surface area and PEI impregnation exhibits high CO2 adsorption capacity, remarkable CO2/N2 selectivity, excellent adsorption/desorption kinetics, enhanced efficiency in the presence of water, and admirable stability in capture and release cycles. The results demonstrate the superior comprehensive performance of the present PEI-impregnated polyHIPE for CO2 capture from the postcombustion flue gas. PMID:27322734

  16. EFFECTS OF TEMPERATURE ON TRICHLOROETHYLENE DESORPTION FROM SILICA GEL AND NATURAL SEDIMENTS. 2. KINETICS. (R822626)

    EPA Science Inventory

    Isothermal desorption rates were measured at 15, 30, and 60 src="/ncer/pubs/images/deg.gif">C for trichloroethylene (TCE) on a silica gel,
    an aquifer sediment, a soil, a sand fraction, and a clay and silt fraction, all
    at 100% relative humidity. Temperature-st...

  17. Uncertainty analysis of multi-rate kinetics of uranium desorption from sediments

    SciTech Connect

    Zhang, Xiaoying; Liu, Chongxuan; Hu, Bill X.; Zhang, Guannan

    2014-01-01

    A multi-rate expression for uranyl [U(VI)] surface complexation reactions has been proposed to describe diffusion-limited U(VI) sorption/desorption in heterogeneous subsurface sediments. An important assumption in the rate expression is that its rate constants follow a certain type probability distribution. In this paper, a Bayes-based, Differential Evolution Markov Chain method was used to assess the distribution assumption and to analyze parameter and model structure uncertainties. U(VI) desorption from a contaminated sediment at the US Hanford 300 Area, Washington was used as an example for detail analysis. The results indicated that: 1) the rate constants in the multi-rate expression contain uneven uncertainties with slower rate constants having relative larger uncertainties; 2) the lognormal distribution is an effective assumption for the rate constants in the multi-rate model to simualte U(VI) desorption; 3) however, long-term prediction and its uncertainty may be significantly biased by the lognormal assumption for the smaller rate constants; and 4) both parameter and model structure uncertainties can affect the extrapolation of the multi-rate model with a larger uncertainty from the model structure. The results provide important insights into the factors contributing to the uncertainties of the multi-rate expression commonly used to describe the diffusion or mixing-limited sorption/desorption of both organic and inorganic contaminants in subsurface sediments.

  18. The first layer of water on Rh(111): Microscopic structure and desorption kinetics

    SciTech Connect

    Beniya, Atsushi; Yamamoto, Susumu; Mukai, Kozo; Yamashita, Yoshiyuki; Yoshinobu, Jun

    2006-08-07

    The adsorption states and growth process of the first water (D{sub 2}O) layer on Rh(111) were investigated using infrared reflection absorption spectroscopy, temperature programed desorption, and spot-profile-analysis low energy electron diffraction. Water molecules wet the Rh(111) surface intact. At the early stage of first layer growth, a ({radical}3x{radical}3)R30 deg. commensurate water layer grows where 'up' and 'down' species coexist; the up and down species represent water molecules which have free OD, pointing to a vacuum and the substrate, respectively. The up domain was a flatter structure than an icelike bilayer. Water desorption from Rh(111) was a half-order process. The activation energy and the preexponential factor of desorption are estimated to be 60 kJ/mol and 4.8x10{sup 16} ML{sup 1/}2/s at submonolayer coverage, respectively. With an increase in water coverage, the flat up domain becomes a zigzag layer, like an ice bilayer. At the saturation coverage, the amount of down species is 1.3 times larger than that of the up species. In addition, the activation energy and the preexponential factor of desorption decrease to 51 kJ/mol and 1.3x10{sup 14} ML{sup 1/2}/s, respectively.

  19. Kinetics of Hydrogen Reduction of Chalcopyrite Concentrate

    NASA Astrophysics Data System (ADS)

    Chatterjee, Ritayan; Ghosh, Dinabandhu

    2015-12-01

    A Ghatshila chalcopyrite concentrate (average particle size, 50 μm) containing primarily CuFeS2 and SiO2 (Cu 16 pct) was reduced by a stream of hydrogen in a thermogravimetric analyzer (TGA) at selected temperatures [1173 K to 1323 K (900 °C to 1050 °C)], hydrogen flow rates, partial pressures of hydrogen (0.33 × 101.3 to 101.3 kPa), and sample bed heights. The product was a mixture of Cu (26 pct), SiO2, CuFeO2, and Fe. The rate equations for the three typical controlling mechanisms, namely, gas film diffusion (mass transfer), pore diffusion, and interfacial reaction, have been derived for the system geometry under study and applied to identify the rate-controlling steps. The first stage of the reduction, which extended up to the first 13 minutes, was rate controlled by the interfacial reaction. The last stage, which spanned over the last 60 to 120 minutes and accounted for a small percentage of reduction, was controlled by pore diffusion through the built-up Cu (and Fe) layer. The activation energy in the first stage was 101 kJ mol-1 and that in the second stage was 76 kJ mol-1. Subsequent acid leaching with 1 M HCl solution of the reduction product removed all soluble species, leaving a Cu (53.3 pct) + SiO2 mixture, with a small concentration (2.7 pct) of Cu2O in it. This result compares well with the predicted final mixture of Cu (59 pct)-SiO2 based on a mass balance on the starting concentrate. A follow-up heating at 1523 K (1250 °C) produced a sintered Cu-SiO2 composite with spherical copper particles of 400 µm diameter embedded in a silica matrix. Elemental chemical analyses were carried out by energy-dispersive X-ray spectroscopy/atomic absorption spectroscopy. The phase identification and microstructural characterization of Cu-SiO2 mixtures were carried out by X-ray powder diffraction and optical microscopy.

  20. In-situ neutron investigation of hydrogen absorption kinetics in La(FexSi1-x)13 magnetocaloric alloys for room-temperature refrigeration application

    NASA Astrophysics Data System (ADS)

    Hai, Xueying; Mayer, Charlotte; Colin, Claire V.; Miraglia, Salvatore

    2016-02-01

    Promising magnetocaloric material La(Fe,Si)13 with a first-order magnetic transition has been widely investigated. The observed instability of hydrogen in the material is detrimental for its industrial upscale and a better control of the hydrogen absorption/desorption is necessary to optimize its application potential. In this article, the hydrogen absorption kinetics is studied through an in-situ neutron diffraction experiment. The results allow us to have an inside look at the structure "breathing" to accommodate the interstitial atoms and compare the effect of hydrides with carbohydrides.

  1. Kinetics of hydrogen peroxide decomposition by catalase: hydroxylic solvent effects.

    PubMed

    Raducan, Adina; Cantemir, Anca Ruxandra; Puiu, Mihaela; Oancea, Dumitru

    2012-11-01

    The effect of water-alcohol (methanol, ethanol, propan-1-ol, propan-2-ol, ethane-1,2-diol and propane-1,2,3-triol) binary mixtures on the kinetics of hydrogen peroxide decomposition in the presence of bovine liver catalase is investigated. In all solvents, the activity of catalase is smaller than in water. The results are discussed on the basis of a simple kinetic model. The kinetic constants for product formation through enzyme-substrate complex decomposition and for inactivation of catalase are estimated. The organic solvents are characterized by several physical properties: dielectric constant (D), hydrophobicity (log P), concentration of hydroxyl groups ([OH]), polarizability (α), Kamlet-Taft parameter (β) and Kosower parameter (Z). The relationships between the initial rate, kinetic constants and medium properties are analyzed by linear and multiple linear regression. PMID:22565543

  2. NaAlH4 Mixed with Carbon Nanotubes, Fullerene, and Titanium to Yield the Lowest Temperature for Hydrogen Desorption

    NASA Astrophysics Data System (ADS)

    Hildebrand, Jennifer; McFadden, Patrick; Kim, Sanga; Dobbins, Tabbetha

    Recent research in hydrogen storage has improved dehydrogenation methods with solid-state compounds. NaAlH4 is a complex hydrides which release hydrogen at a lower temperature making the compound a great candidate for hydrogen storage. However, a catalyst should be combined with NaAlH4 to release the lowest desorption temperature. Prior research showed that interaction of NaAlH4 with nanotube or fullerene effectively weakens the Al-H bonds causing hydrogen desorption at lower temperatures. In the present study, NaAlH4 is ball milled with three of these catalysts: titanium, carbon nanotubes and fullerene and the milling time is varied from 10 to 30 minutes to compare the dehydrogenation rates in each setup. The phase structures were identified using the X-ray diffraction. Of these catalysts, the fullerene yielded the most interesting result showing nanostructuring of the hydride during ball milling. The possibility of ``shot peening'' of the NaAlH4 by the fullerenes is explored.

  3. Improved hydrogen storage kinetics of nanoconfined NaAlH₄ catalyzed with TiCl₃ nanoparticles.

    PubMed

    Nielsen, Thomas K; Polanski, Marek; Zasada, Dariusz; Javadian, Payam; Besenbacher, Flemming; Bystrzycki, Jerzy; Skibsted, Jørgen; Jensen, Torben R

    2011-05-24

    Nanoparticles of NaAlH(4) have been infiltrated in nanoporous carbon aerogel with TiCl(3) nanoparticles in order to explore possible synergetic effects between nanoconfinement and a functionalized catalytic scaffold. Resorcinol formaldehyde carbon aerogels with an average pore size of 17 nm and total pore volume of 1.26 mL/g were infiltrated with TiCl(3) to obtain an aerogel doped with 3.0 wt % TiCl(3) nanoparticles. NaAlH(4) was melt-infiltrated into the functionalized carbon aerogel at 189 °C and p(H(2)) ∼ 186-199 bar. Energy-dispersive spectrometry (EDS) combined with focused ion beam (FIB) techniques revealed the presence of Na, Al, Ti, and Cl inside the aerogel scaffold material. The infiltrated NaAlH(4) was X-ray amorphous, whereas (27)Al magic-angle spinning (MAS) NMR spectroscopy confirmed the presence of nanoconfined NaAlH(4). Temperature-programmed desorption mass spectroscopy (TPD-MS) and Sieverts' measurements demonstrated significantly improved hydrogen desorption kinetics for this new nanoconfined NaAlH(4)-TiCl(3) material as compared to nanoconfined NaAlH(4) without the catalysts TiCl(3) and to bulk ball-milled samples of NaAlH(4)-TiCl(3). We find that the onset temperature for hydrogen release was close to room temperature (T(onset) = 33 °C), and the hydrogen release rate reached a maximum value at 125 °C, which demonstrates favorable synergetic effects between nanoconfinement and catalyst addition. PMID:21446760

  4. Determination of toluene hydrogenation kinetics with neutron diffraction.

    PubMed

    Falkowska, Marta; Chansai, Sarayute; Manyar, Haresh G; Gladden, Lynn F; Bowron, Daniel T; Youngs, Tristan G A; Hardacre, Christopher

    2016-06-29

    Total neutron scattering has been used to follow the hydrogenation of toluene-d8 to methylcyclohexane-d14 over 3 wt% platinum supported on highly ordered mesoporous silica (MCM-41) at 298 K and under 150 mbar D2 pressure. The detailed kinetic information so revealed indicates that liquid reorganisation inside pores is the slowest step of the whole process. Additionally, the results were compared with the reaction performed under 250 mbar D2 pressure as well as with toluene-h8 hydrogenation using D2 at 150 mbar. PMID:27052196

  5. Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide

    NASA Astrophysics Data System (ADS)

    Vetter, Tiffany A.; Colombo, D. Philip, Jr.

    2003-07-01

    CIBA Vision Corporation markets a contact lens cleaning system that consists of an AOSEPT disinfectant solution and an AOSEPT lens cup. The disinfectant is a buffered 3.0% m/v hydrogen peroxide solution and the cup includes a platinum-coated AOSEPT disc. The hydrogen peroxide disinfects by killing bacteria, fungi, and viruses found on the contact lenses. Because the concentration of hydrogen peroxide needed to disinfect is irritating to eyes, the hydrogen peroxide needs to be neutralized, or decomposed, before the contact lenses can be used again. A general chemistry experiment is described where the kinetics of the catalyzed decomposition of the hydrogen peroxide are studied by measuring the amount of oxygen generated as a function of time. The order of the reaction with respect to the hydrogen peroxide, the rate constant, and the energy of activation are determined. The integrated rate law is used to determine the time required to decompose the hydrogen peroxide to a concentration that is safe for eyes.

  6. Stereoselective thymol hydrogenation. I. Kinetics of thymol hydrogenation on charcoal-supported platinum catalysts

    SciTech Connect

    Besson, M.; Bullivant, L.; Nicolaus, N.; Gallezot, P. )

    1993-03-01

    The kinetics of thymol hydrogenation on a well-characterized supported platinum catalyst have been investigated in cyclohexane at temperatures between 313 and 373 K and under 3 MPa of hydrogen pressure. The relative rate constants of the different reaction pathways (hydrogenation via menthone or isomenthone, and direct hydrogenation to the four menthol diastereoisomers) were determined from the changes in composition of the reaction medium during the reaction process. It has been shown that hydrogenation via the menthone intermediates is the major route, the formation of the cis isomer (isomenthone) being favored. The configuration of the menthols, produced from direct hydrogenation or from the ketone intermediates, is controlled by the geometry of adsorption of the precursors on the metal surface, so that neoisomenthol with all substituents in the cis position is by far the most abundant steroisomer produced. 21 refs., 11 figs., 2 tabs.

  7. Kinetics of histidine sorption and desorption on Fumasep® FTCM cation-exchange membranes

    NASA Astrophysics Data System (ADS)

    Maigurova, N. I.; Eliseeva, T. V.; Lantsuzskaya, E. V.; Sholokhova, A. Yu.

    2015-05-01

    The sorption of the basic amino acid histidine by Fumasep® FTCM membranes in different ionic forms is investigated over a wide range of solution concentrations. It is established that sorption limited by the stage of external diffusion. The time required for equilibrium to be established in the membrane-amino acid solution system is found to grow from 4 to 9 h when the initial concentration of the solution is reduced. The reversibility of histidine sorption is demonstrated, and the conditions of effective desorption are determined.

  8. Structural and kinetic studies of metal hydride hydrogen storage materials using thin film deposition and characterization techniques

    NASA Astrophysics Data System (ADS)

    Kelly, Stephen Thomas

    absorption and desorption kinetics and degrades the material texture. Cycling the films to greater hydrogen loading accelerates the changes to the kinetics and material texture. In addition to in situ XRD experiments, in situ neutron reflectivity experiments on epitaxial Mg films exposed to hydrogen gas reveal details about the microstructural development of the growing hydride layer as the film absorbs and releases hydrogen. Small (10 wt%) additions of Ti to epitaxial Mg films during growth result in metastable solid solution films of Ti in Mg that deposit epitaxially on (001) Al2O3 substrates with epitaxy similar to the pure Mg films. These metastable alloy films absorb hydrogen faster than pure Mg films under identical conditions. Subsequent film cycling results in altered reaction kinetics and a transition to a different kinetic mechanism during desorption than for pure Mg films.

  9. Improvement in hydrogen desorption from β- and γ-MgH2 upon transition-metal doping.

    PubMed

    Hussain, Tanveer; Maark, Tuhina Adit; Chakraborty, Sudip; Ahuja, Rajeev

    2015-08-24

    A thorough study of the structural, electronic, and hydrogen-desorption properties of β- and γ-MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125 % in both the hydrides. This insertion of TMs causes a variation in the cell volumes of β- and γ-MgH2 . The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both β- and γ-MgH2 and cause destabilization by weakening the MgH bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from β- and γ-MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis. PMID:26079892

  10. The development of microstructure during hydrogenation-disproportionation-desorption-recombination treatment of sintered neodymium-iron-boron-type magnets

    NASA Astrophysics Data System (ADS)

    Sheridan, R. S.; Harris, I. R.; Walton, A.

    2016-03-01

    The hydrogen absorption and desorption characteristics of the hydrogenation disproportionation desorption and recombination (HDDR) process on scrap sintered neodymium-iron-boron (NdFeB) type magnets have been investigated. At each stage of the process, the microstructural changes have been studied using high resolution scanning electron microscopy. It was found that the disproportionation reaction initiates at grain boundaries and triple points and then propagates towards the centre of the matrix grains. This process was accelerated at particle surfaces and at free surfaces produced by any cracks in the powder particles. However, the recombination reaction appeared to initiate randomly throughout the particles with no apparent preference for particle surfaces or internal cracks. During the hydrogenation of the grain boundaries and triple junctions, the disproportionation reaction was, however, affected by the much higher oxygen content of the sintered NdFeB compared with that of the as-cast NdFeB alloys. Throughout the entire HDDR reaction the oxidised triple junctions (from the sintered structure) remained unreacted and hence, remained in their original form in the fine recombined microstructure. This resulted in a very significant reduction in the proportion of cavitation in the final microstructure and this could lend to improved consolidation in the recycled magnets.

  11. Isotherms and Kinetics of Water Vapor Sorption/Desorption for Surface Films of Polyion-Surfactant Ion Complex Salts.

    PubMed

    Gustavsson, Charlotte; Piculell, Lennart

    2016-07-14

    Thin films of "complex salts" (CS = ionic surfactants with polymeric counterions) have recently been shown to respond to humidity changes in ambient air by changing their liquid crystalline structure. We here report isotherms and kinetics of water sorption/desorption for ∼10-100 μm films of alkyltrimethylammonium polyacrylate CS, measured in a dynamic gravimetric vapor sorption instrument over a 0-95% relative humidity (RH) range. The sorption per ion pair was similar to that observed for common ionomers. A kinetic model for the water exchange is presented, assuming that the "external" transport between the vapor reservoir and the film surface is rate-determining. The model predicts that the water content, after a small stepwise change of the reservoir RH, should vary exponentially with time, with a time constant proportional to both the slope of the sorption isotherm and the film thickness. These predictions were confirmed for our films over large RH ranges, and the external mass transfer coefficient in our setup was calculated from the experimental data. Expressions derived for the Biot number (ratio of characteristic times for internal and external water transport) for the considered limiting case strongly indicate that external water transport should quite generally affect, or even dominate, the measured kinetics for similarly thin hydrated films. PMID:27327628

  12. The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry.

    PubMed

    Ellis, Wade C; Lewis, Charlotte R; Openshaw, Anna P; Farnsworth, Paul B

    2016-09-01

    We demonstrate the effectiveness of using hydrogen-doped argon as the support gas for the dielectric barrier discharge (DBD) ambient desorption/ionization (ADI) source in mass spectrometry. Also, we explore the chemistry responsible for the signal enhancement observed when using both hydrogen-doped argon and hydrogen-doped helium. The hydrogen-doped argon was tested for five analytes representing different classes of molecules. Addition of hydrogen to the argon plasma gas enhanced signals for gas-phase analytes and for analytes coated onto glass slides in positive and negative ion mode. The enhancements ranged from factors of 4 to 5 for gas-phase analytes and factors of 2 to 40 for coated slides. There was no significant increase in the background. The limit of detection for caffeine was lowered by a factor of 79 using H2/Ar and 2 using H2/He. Results are shown that help explain the fundamental differences between the pure-gas discharges and those that are hydrogen-doped for both argon and helium. Experiments with different discharge geometries and grounding schemes indicate that observed signal enhancements are strongly dependent on discharge configuration. Graphical Abstract ᅟ. PMID:27380389

  13. The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Ellis, Wade C.; Lewis, Charlotte R.; Openshaw, Anna P.; Farnsworth, Paul B.

    2016-07-01

    We demonstrate the effectiveness of using hydrogen-doped argon as the support gas for the dielectric barrier discharge (DBD) ambient desorption/ionization (ADI) source in mass spectrometry. Also, we explore the chemistry responsible for the signal enhancement observed when using both hydrogen-doped argon and hydrogen-doped helium. The hydrogen-doped argon was tested for five analytes representing different classes of molecules. Addition of hydrogen to the argon plasma gas enhanced signals for gas-phase analytes and for analytes coated onto glass slides in positive and negative ion mode. The enhancements ranged from factors of 4 to 5 for gas-phase analytes and factors of 2 to 40 for coated slides. There was no significant increase in the background. The limit of detection for caffeine was lowered by a factor of 79 using H2/Ar and 2 using H2/He. Results are shown that help explain the fundamental differences between the pure-gas discharges and those that are hydrogen-doped for both argon and helium. Experiments with different discharge geometries and grounding schemes indicate that observed signal enhancements are strongly dependent on discharge configuration.

  14. The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Ellis, Wade C.; Lewis, Charlotte R.; Openshaw, Anna P.; Farnsworth, Paul B.

    2016-09-01

    We demonstrate the effectiveness of using hydrogen-doped argon as the support gas for the dielectric barrier discharge (DBD) ambient desorption/ionization (ADI) source in mass spectrometry. Also, we explore the chemistry responsible for the signal enhancement observed when using both hydrogen-doped argon and hydrogen-doped helium. The hydrogen-doped argon was tested for five analytes representing different classes of molecules. Addition of hydrogen to the argon plasma gas enhanced signals for gas-phase analytes and for analytes coated onto glass slides in positive and negative ion mode. The enhancements ranged from factors of 4 to 5 for gas-phase analytes and factors of 2 to 40 for coated slides. There was no significant increase in the background. The limit of detection for caffeine was lowered by a factor of 79 using H2/Ar and 2 using H2/He. Results are shown that help explain the fundamental differences between the pure-gas discharges and those that are hydrogen-doped for both argon and helium. Experiments with different discharge geometries and grounding schemes indicate that observed signal enhancements are strongly dependent on discharge configuration.

  15. Adsorption, Desorption, and Displacement Kinetics of H2O and CO2 on Forsterite, Mg2SiO4(011)

    SciTech Connect

    Smith, R. Scott; Li, Zhenjun; Dohnalek, Zdenek; Kay, Bruce D.

    2014-12-18

    We have examined the adsorbate-substrate interaction kinetics of CO2 and H2O on a natural forsterite crystal surface, Mg2SiO4(011), with 10-15% of substitutional Fe2+. We use temperature programmed desorption (TPD) and molecular beam techniques to determine the adsorption, desorption, and displacement kinetics for H2O and CO2. Neither CO2 nor H2O has distinct sub-monolayer desorption peaks but instead both have a broad continuous desorption feature that evolve smoothly into multilayer desorption. Inversion of the monolayer coverage spectra for both molecules reveals that the corresponding binding energies for H2O are greater than that for CO2 on all sites. The relative strength of these interactions is the dominant factor in the competitive adsorption/displacement kinetics. In experiments where the two adsorbates are co-dosed, H2O always binds to the highest energy binding sites available and displaces CO2. The onset of CO2 displacement by H2O occurs between 65 and 75 K.

  16. Chemical kinetic performance losses for a hydrogen laser thermal thruster

    NASA Technical Reports Server (NTRS)

    Mccay, T. D.; Dexter, C. E.

    1985-01-01

    Projected requirements for efficient, economical, orbit-raising propulsion systems have generated investigations into several potentially high specific impulse, moderate thrust, advanced systems. One of these systems, laser thermal propulsion, utilizes a high temperature plasma as the enthalpy source. The plasma is sustained by a focused laser beam which maintains the plasma temperature at levels near 20,000 K. Since such temperature levels lead to total dissociation and high ionization, the plasma thruster system potentially has a high specific impulse decrement due to recombination losses. The nozzle flow is expected to be sufficiently nonequilibrium to warrant concern over the achievable specific impluse. This investigation was an attempt at evaluation of those losses. The One-Dimensional Kinetics (ODK) option of the Two-Dimensional Kinetics (TDK) Computer Program was used with a chemical kinetics rate set obtained from available literature to determine the chemical kinetic energy losses for typical plasma thruster conditions. The rates were varied about the nominal accepted values to band the possible losses. Kinetic losses were shown to be highly significant for a laser thermal thruster using hydrogen. A 30 percent reduction in specific impulse is possible simply due to the inability to completely extract the molecular recombination energy.

  17. Desorption kinetics of N,N-dimethylformamide vapor from granular activated carbon and hydrophobic zeolite

    SciTech Connect

    Ching-Yuan Chang; Wen-Tien Tsai; Horng-Chia Lee

    1996-07-01

    Such thermodynamic properties as enthalpy, free energy, and entropy of adsorption have been computed for N,N-dimethylformamide (DMF) vapor on two commercial adsorbents: coconut shell Type PCB of activated carbon and Type DAY of hydrophobic zeolite. The computation is based on the Langmuir adsorption isotherms obtained at 293, 303, and 313 K as reported by Tsai et al. The laden adsorbents were regenerated with hot inert nitrogen gas and studied by thermal gravimetric analysis at three different heating rates. The apparent activation energies (E{sub des}) of thermal desorption were determined by using the Friedman method. The zeolite DAY has an adsorption potential higher than that of activated carbon PCB as indicated by the more negative value of the adsorption enthalpy of DMF vapor. The average value of E{sub des} of zeolite DAY is larger than that of activated carbon PCB.

  18. Kinetic modelling of molecular hydrogen transport in microporous carbon materials.

    SciTech Connect

    Hankel, M.; Zhang, H.; Nguyen, T. X.; Bhatia, S. K.; Gray, S. K.; Smith, S. C.

    2011-01-01

    The proposal of kinetic molecular sieving of hydrogen isotopes is explored by employing statistical rate theory methods to describe the kinetics of molecular hydrogen transport in model microporous carbon structures. A Lennard-Jones atom-atom interaction potential is utilized for the description of the interactions between H{sub 2}/D{sub 2} and the carbon framework, while the requisite partition functions describing the thermal flux of molecules through the transition state are calculated quantum mechanically in view of the low temperatures involved in the proposed kinetic molecular sieving application. Predicted kinetic isotope effects for initial passage from the gas phase into the first pore mouth are consistent with expectations from previous modeling studies, namely, that at sufficiently low temperatures and for sufficiently narrow pore mouths D{sub 2} transport is dramatically favored over H{sub 2}. However, in contrast to expectations from previous modeling, the absence of any potential barrier along the minimum energy pathway from the gas phase into the first pore mouth yields a negative temperature dependence in the predicted absolute rate coefficients - implying a negative activation energy. In pursuit of the effective activation barrier, we find that the minimum potential in the cavity is significantly higher than in the pore mouth for nanotube-shaped models, throwing into question the common assumption that passage through the pore mouths should be the rate-determining step. Our results suggest a new mechanism that, depending on the size and shape of the cavity, the thermal activation barrier may lie in the cavity rather than at the pore mouth. As a consequence, design strategies for achieving quantum-mediated kinetic molecular sieving of H{sub 2}/D{sub 2} in a microporous membrane will need, at the very least, to take careful account of cavity shape and size in addition to pore-mouth size in order to ensure that the selective step, namely passage

  19. Fully reversible hydrogen absorption and desorption reactions with Sc(Al{sub 1-x}Mg{sub x}), x=0.0, 0.15, 0.20

    SciTech Connect

    Sahlberg, Martin; Zlotea, Claudia; Latroche, Michel; Andersson, Yvonne

    2011-01-15

    The hydrogen storage properties of Sc(Al{sub 1-x}Mg{sub x}), x=0.0, 0.15, 0.20, have been studied by X-ray powder diffraction, thermal desorption spectroscopy, pressure-composition-isotherms and scanning electron microscopy techniques. Hydrogen is absorbed from the gas phase at 70 kPa and 400 {sup o}C under the formation of ScH{sub 2} and aluminium with magnesium in solid solution. The reaction is fully reversible in vacuum at 500 {sup o}C and shows the hydrogenation-disproportionation-desorption-recombination (HDDR) behaviour. The activation energy of desorption was determined by the Kissinger method to 185 kJ/mol. The material is stable up to at least six absorption-desorption cycles and there is no change in particle size during cycling. -- Graphical abstract: XRD pattern of Sc(Al{sub 1-x}Mg{sub x}). From the top: x=0, 0.15, 0.20. The hydrogen absorption properties were studied by thermal desorption spectroscopy, pressure-composition-isotherms and scanning electron microscopy techniques. Display Omitted

  20. Comparison of PAH Biodegradation and Desorption Kinetics During Bioremediation of Aged Petroleum Hydrocarbon Contaminated Soils

    SciTech Connect

    Huesemann, Michael H.; Hausmann, Tom S.; Fortman, Timothy J.

    2000-09-20

    It is commonly assumed that mass-transfer limitations are the cause for slow and incomplete biodegradation of PAHs in aged soils. In order to test this hypothesis, the biodegradation rate and the abiotic release rate were measured and compared for selected PAHs in three different soils. It was found that PAH biodegradation was not mass-transfer limited during slurry bioremediation of an aged loamy soil. By contrast, PAH biodegradation rates were much larger than abiotic release rates in kaolinite clay indicating that sorbed-phase PAHs can apparently be biodegraded directly from mineral surfaces without prior desorption or dissolution into the aqueous phase. A comparison of PAH biodegradation rates and abiotic release rates at termination of the slurry bioremediation treatment revealed that abiotic release rates are much larger than the respective biodegradation rates. In addition, it was found that the number of hydrocarbon degraders decreased by four orders of magnitude during the bioremediation treatment. It can therefore be concluded that the slow and incomplete biodegradation of PAHs is not caused by mass-transfer limitations but rather by microbial factors. Consequently, the residual PAHs that remain after extensive bioremediation treatment are still bioavailable and for that reason could pose a greater risk to environmental receptors than previously thought.

  1. Kinetic Method for Hydrogen-Deuterium-Tritium Mixture Distillation Simulation

    SciTech Connect

    Sazonov, A.B.; Kagramanov, Z.G.; Magomedbekov, E.P.

    2005-07-15

    Simulation of hydrogen distillation plants requires mathematical procedures suitable for multicomponent systems. In most of the present-day simulation methods a distillation column is assumed to be composed of theoretical stages, or plates. However, in the case of a multicomponent mixture theoretical plate does not exist.An alternative kinetic method of simulation is depicted in the work. According to this method a system of mass-transfer differential equations is solved numerically. Mass-transfer coefficients are estimated with using experimental results and empirical equations.Developed method allows calculating the steady state of a distillation column as well as its any non-steady state when initial conditions are given. The results for steady states are compared with ones obtained via Thiele-Geddes theoretical stage technique and the necessity of using kinetic method is demonstrated. Examples of a column startup period and periodic distillation simulations are shown as well.

  2. Adsorption and desorption of arsenate on sandy sediments from contaminated and uncontaminated saturated zones: Kinetic and equilibrium modeling.

    PubMed

    Hafeznezami, Saeedreza; Zimmer-Faust, Amity G; Dunne, Aislinn; Tran, Tiffany; Yang, Chao; Lam, Jacquelyn R; Reynolds, Matthew D; Davis, James A; Jay, Jennifer A

    2016-08-01

    Application of empirical models to adsorption of contaminants on natural heterogeneous sorbents is often challenging due to the uncertainty associated with fitting experimental data and determining adjustable parameters. Sediment samples from contaminated and uncontaminated portions of a study site in Maine, USA were collected and investigated for adsorption of arsenate [As(V)]. Two kinetic models were used to describe the results of single solute batch adsorption experiments. Piecewise linear regression of data linearized to fit pseudo-first order kinetic model resulted in two distinct rates and a cutoff time point of 14-19 h delineating the biphasic behavior of solute adsorption. During the initial rapid adsorption stage, an average of 60-80% of the total adsorption took place. Pseudo-second order kinetic models provided the best fit to the experimental data (R(2) > 0.99) and were capable of describing the adsorption over the entire range of experiments. Both Langmuir and Freundlich isotherms provided reasonable fits to the adsorption data at equilibrium. Langmuir-derived maximum adsorption capacity (St) of the studied sediments ranged between 29 and 97 mg/kg increasing from contaminated to uncontaminated sites. Solid phase As content of the sediments ranged from 3.8 to 10 mg/kg and the As/Fe ratios were highest in the amorphous phase. High-pH desorption experiments resulted in a greater percentage of solid phase As released into solution from experimentally-loaded sediments than from the unaltered samples suggesting that As(V) adsorption takes place on different reversible and irreversible surface sites. PMID:27218893

  3. Kinetics of CO{sub 2} desorption from highly concentrated and CO{sub 2}-loaded methyldiethanolamine aqueous solutions in the range 312--383 K

    SciTech Connect

    Cadours, R.; Bouallou, C.; Gaunand, A.; Richon, D.

    1997-12-01

    Absorption by aqueous alkanolamine solutions is the dominant industrial process for acid gases removal, in particular CO{sub 2} and H{sub 2}S, from natural gas. Kinetics of CO{sub 2} desorption from CO{sub 2}-loaded methyldiethanolamine (MDEA) aqueous solutions were measured in the following conditions: 312--383 K, 25--50 wt% MDEA aqueous solutions, CO{sub 2} loadings from 5 to 85%. A thermoregulated constant interfacial area reaction cell was operated by measuring the pressure over the solution. Producing a very slight depression in the cell, the time-dependent equilibrium pressure recovery is accurately recorded during batch desorption. Kinetics are in agreement with a fast reaction regime of desorption according to the film theory. For CO{sub 2} loadings below 0.50 mol of gas/mol of amine, desorption rates are well predicted by using the kinetic constant and orders determined from absorption experiments for the reaction between CO{sub 2} and MDEA. Some discrepancies were pointed out for loadings above 0.50 mol of gas/mol of amine.

  4. Initial hydrogen attack kinetics in a carbon steel

    NASA Astrophysics Data System (ADS)

    McKimpson, Marvin; Shewmon, Paul G.

    1981-05-01

    The kinetics of the initial stages of hydrogen attack in a commercial 0.3 pct C steel (grade A516) were investigated using an in situ dilatometer. The time, temperature and hydrogen pressure dependences of the rate of sample expansion were measured at hydrogen pressures from 1 to 20 MPa, and temperatures from 350 to 475 °C for sample strains of 10-6 to 10-3. Sample expansion began shortly after hydrogen exposure and proceeded at a nearly constant rate throughout the “incubation period” preceding rapid attack. At high temperatures and low pressures, this rate was proportional to PH 2 1.9±0.2 and had an apparent activation energy of 115 ± 9 kJ. At high pressures and low temperatures, the rate was proportional to PPH 2 1.0.62±0.07 and showed an apparent activation energy of 210 ± 13 kJ. This suggests that bubble growth during the incubation period occurs predominantly by grain boundary diffusion and is driven by near-equilibrium internal methane pressures. Sample expansion in the subsequent stages of accelerating growth probably is controlled by creep and methane generation.

  5. Preparation of ultrafine jet-milled powders for Nd-Fe-B sintered magnets using hydrogenation-disproportionation-desorption-recombination and hydrogen decrepitation processes

    NASA Astrophysics Data System (ADS)

    Nakamura, Michihide; Matsuura, Masashi; Tezuka, Nobuki; Sugimoto, Satoshi; Une, Yasuhiro; Kubo, Hirokazu; Sagawa, Masato

    2013-07-01

    Dy addition is used to increase the coercivity of Nd-Fe-B sintered magnets. Given that Dy is rare and expensive, a method is needed for reducing the Dy content in such magnets without decreasing their coercivity. Refining Nd2Fe14B grains is a prospective method for increasing the coercivity of Nd-Fe-B magnets. Conventional jet milling, however, cannot crush strip-casted Nd-Fe-B alloys into powders less than 1 μm in size. We report a process for preparing ultrafine jet-milled powders with an average size of 0.33 μm for Nd-Fe-B sintered magnets: a combination of hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and He jet milling.

  6. Hydrogen recombination kinetics and nuclear thermal rocket performance prediction

    SciTech Connect

    Wetzel, K.K.; Solomon, W.C.

    1994-07-01

    The rate constants for the hydrogen three-body collisional recombination reaction with atomic and molecular hydrogen acting as third bodies have been determined by numerous investigators during the past 30 yr, but these rates exhibit significant scatter. The discrepancies in the rate constants determined by different investigators are as great as two orders of magnitude in the temperature range of interest for nuclear thermal rocket (NTR) operation, namely, 2000-3300 K. The impact of this scatter on our ability to predict the specific impulse (I(sub sp)) delivered by a 30-klbf NTR has been determined for chamber pressures and temperatures from, respectively, 20-1000 psia and 2700-3300 K. The variation in I(sub sp) produced by using the different rate constants is as great as 10%, or 100 s. This variation also obscures the influence of chamber pressure on I(sub sp); using fast kinetics, low pressures yield significantly improved performance, while using slow or nominal kinetics, the pressure dependence of I(sub sp) is negligible. Because the flow composition freezes at very small area ratios, optimization of the nozzle contour in the near-throat region maximizes recombination. Vibrational relaxation is found to produce negligible losses in I(sub sp). 36 refs.

  7. Study of kinetic desorption rate constant in fish muscle and agarose gel model using solid phase microextraction coupled with liquid chromatography with tandem mass spectrometry.

    PubMed

    Togunde, Oluranti Paul; Oakes, Ken; Servos, Mark; Pawliszyn, Janusz

    2012-09-12

    This study aims to use solid phase microextraction (SPME), a simple tool to investigate diffusion rate (time) constant of selected pharmaceuticals in gel and fish muscle by comparing desorption rate of diffusion of the drugs in both agarose gel prepared with phosphate-buffered saline (PBS; pH 7.4) and fish muscle. The gel concentration (agarose gel model) that could be used to simulate tissue matrix (fish muscle) for free diffusion of drugs under in vitro and in vivo conditions was determined to model mass transfer phenomena between fibre polymer coating and environmental matrix such that partition coefficients and desorption time constant (diffusion coefficient) can be determined. SPME procedure involves preloading the extraction phase (fibre) with the standards from spiked PBS for 1h via direct extraction. Subsequently, the preloaded fibre is introduced to the sample such fish or agarose gel for specified time ranging from 0.5 to 60 h. Then, fibre is removed at specified time and desorbed in 100 μL of desorption solution (acetonitrile: water 1:1) for 90 min under agitation speed of 1000 rpm. The samples extract were immediately injected to the instrument and analysed using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). The limit of detection of the method in gel and fish muscle was 0.01-0.07 ng mL(-1) and 0.07-0.34 ng g(-1), respectively, while the limit quantification was 0.10-0.20 ng mL(-1) in gel samples and 0.40-0.97 ng g(-1) in fish sample. The reproducibility of the method was good (5-15% RSD). The results suggest that kinetics of desorption of the compounds in fish tissue and different viscosity of gel can be determined using desorption time constant. In this study, desorption time constant which is directly related to desorption rate (diffusion kinetics) of selected drugs from the fibre to the gel matrix is faster as the viscosity of the gel matrix reduces from 2% (w/v) to 0.8% (w/v). As the concentration of gel reduces

  8. Ultra high vacuum high precision low background setup with temperature control for thermal desorption mass spectroscopy (TDA-MS) of hydrogen in metals.

    PubMed

    Merzlikin, Sergiy V; Borodin, S; Vogel, D; Rohwerder, M

    2015-05-01

    In this work, a newly developed UHV-based high precision low background setup for hydrogen thermal desorption analysis (TDA) of metallic samples is presented. Using an infrared heating with a low thermal capacity enables a precise control of the temperature and rapid cool down of the measurement chamber. This novel TDA-set up is superior in sensitivity to almost every standard hydrogen analyzer available commercially due to the special design of the measurement chamber, resulting in a very low hydrogen background. No effects of background drift characteristic as for carrier gas based TDA instruments were observed, ensuring linearity and reproducibility of the analysis. This setup will prove to be valuable for detailed investigations of hydrogen trapping sites in steels and other alloys. With a determined limit of detection of 5.9×10(-3)µg g(-1) hydrogen the developed instrument is able to determine extremely low hydrogen amounts even at very low hydrogen desorption rates. This work clearly demonstrates the great potential of ultra-high vacuum thermal desorption mass spectroscopy instrumentation. PMID:25702992

  9. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media.

    PubMed

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-01-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability-inherent to their nanoporosity-are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery. PMID:27327254

  10. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media

    NASA Astrophysics Data System (ADS)

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-06-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability--inherent to their nanoporosity--are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery.

  11. Activated desorption at heterogeneous interfaces and long-time kinetics of hydrocarbon recovery from nanoporous media

    PubMed Central

    Lee, Thomas; Bocquet, Lydéric; Coasne, Benoit

    2016-01-01

    Hydrocarbon recovery from unconventional reservoirs (shale gas) is debated due to its environmental impact and uncertainties on its predictability. But a lack of scientific knowledge impedes the proposal of reliable alternatives. The requirement of hydrofracking, fast recovery decay and ultra-low permeability—inherent to their nanoporosity—are specificities of these reservoirs, which challenge existing frameworks. Here we use molecular simulation and statistical models to show that recovery is hampered by interfacial effects at the wet kerogen surface. Recovery is shown to be thermally activated with an energy barrier modelled from the interface wetting properties. We build a statistical model of the recovery kinetics with a two-regime decline that is consistent with published data: a short time decay, consistent with Darcy description, followed by a fast algebraic decay resulting from increasingly unreachable energy barriers. Replacing water by CO2 or propane eliminates the barriers, therefore raising hopes for clean/efficient recovery. PMID:27327254

  12. Comparison of the growth kinetics of In2O3 and Ga2O3 and their suboxide desorption during plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2016-08-01

    We present a comprehensive study of the In2O3 growth kinetics during plasma-assisted molecular beam epitaxy and compare it to that of the related oxide Ga2O3 [P. Vogt and O. Bierwagen, Appl. Phys. Lett. 108, 072101 (2016)]. The growth rate and desorbing fluxes were measured during growth in-situ by a laser reflectometry set-up and line-of-sight quadrupole mass spectrometer, respectively. We extracted the In incorporation as a function of the provided In flux, different growth temperatures TG, and In-to-O flux ratios r. The data are discussed in terms of the competing formation of In2O3 and desorption of the suboxide In2O and O. The same three growth regimes as in the case of Ga2O3 can be distinguished: (i) In-transport limited, O-rich (ii) In2O-desorption limited, O-rich, and (iii) O-transport limited, In-rich. In regime (iii), In droplets are formed on the growth surface at low TG. The growth kinetics follows qualitatively that of Ga2O3 in agreement with their common oxide and suboxide stoichiometry. The quantitative differences are mainly rationalized by the difference in In2O and Ga2O desorption rates and vapor pressures. For the In2O, Ga2O, and O desorption, we extracted the activation energies and frequency factors by means of Arrhenius-plots.

  13. Erbium hydride decomposition kinetics.

    SciTech Connect

    Ferrizz, Robert Matthew

    2006-11-01

    Thermal desorption spectroscopy (TDS) is used to study the decomposition kinetics of erbium hydride thin films. The TDS results presented in this report are analyzed quantitatively using Redhead's method to yield kinetic parameters (E{sub A} {approx} 54.2 kcal/mol), which are then utilized to predict hydrogen outgassing in vacuum for a variety of thermal treatments. Interestingly, it was found that the activation energy for desorption can vary by more than 7 kcal/mol (0.30 eV) for seemingly similar samples. In addition, small amounts of less-stable hydrogen were observed for all erbium dihydride films. A detailed explanation of several approaches for analyzing thermal desorption spectra to obtain kinetic information is included as an appendix.

  14. Kinetic Controls on the Desorption/Dissolution of Sorbed U(VI) and their Influence on Reactive Transport

    SciTech Connect

    Zachara, John M.; Chongxuan Liu; Qafoku, Nikolla P.; McKinley, James P.; Catalano, Jeffrey G.; Brown, Gordon E., Jr.; Davis, James A.

    2006-04-05

    source to groundwater. (2) Measure desorption/dissolution rates of sorbed U(VI), quantify controlling factors, and develop descriptive kinetic models to provide a scientific basis to forecast U(VI) fluxes to groundwater, future plume dynamics, and long-term contaminant attenuation. (3) Establish reaction networks and determine geochemically/ physically realistic reaction parameters to drive state-of-the-art reactive transport modeling of U in vadose zone pore fluids and groundwater.

  15. Electron-stimulated desorption study of hydrogen-exposed aluminum films

    NASA Technical Reports Server (NTRS)

    Park, CH.; Bujor, M.; Poppa, H.

    1984-01-01

    H2 adsorption of evaporated clean and H2-exposed aluminum films is investigated by using the electron-stimulated desorption (ESD) method. A strong H(+)ESD signal is observed on a freshly evaporated aluminum surface which is clean according to previously proposed cleanlines criteria. An increased H(+) yield on H2 exposure is also observed. However, the increasing rate of H(+) emission could be directly correlated with small increases in H2O partial pressure during H2 exposure. It is proposed that the oxidation of aluminum by water vapor and subsequent adsorption of H2 or water is the primary process of the enhanced high H(+) yield during H2 exposure.

  16. Kinetic modeling of α-hydrogen abstractions from unsaturated and saturated oxygenate compounds by hydrogen atoms.

    PubMed

    Paraskevas, Paschalis D; Sabbe, Maarten K; Reyniers, Marie-Françoise; Papayannakos, Nikos G; Marin, Guy B

    2014-10-01

    Hydrogen-abstraction reactions play a significant role in thermal biomass conversion processes, as well as regular gasification, pyrolysis, or combustion. In this work, a group additivity model is constructed that allows prediction of reaction rates and Arrhenius parameters of hydrogen abstractions by hydrogen atoms from alcohols, ethers, esters, peroxides, ketones, aldehydes, acids, and diketones in a broad temperature range (300-2000 K). A training set of 60 reactions was developed with rate coefficients and Arrhenius parameters calculated by the CBS-QB3 method in the high-pressure limit with tunneling corrections using Eckart tunneling coefficients. From this set of reactions, 15 group additive values were derived for the forward and the reverse reaction, 4 referring to primary and 11 to secondary contributions. The accuracy of the model is validated upon an ab initio and an experimental validation set of 19 and 21 reaction rates, respectively, showing that reaction rates can be predicted with a mean factor of deviation of 2 for the ab initio and 3 for the experimental values. Hence, this work illustrates that the developed group additive model can be reliably applied for the accurate prediction of kinetics of α-hydrogen abstractions by hydrogen atoms from a broad range of oxygenates. PMID:25209711

  17. Kinetics of hydrogenation of nitrobenzene to aniline on a copper catalyst

    SciTech Connect

    Petrov, L.A.; Kirkov, N.V.; Shopov, D.M.

    1986-02-01

    The kinetics of the vapor-phase, catalytic hydrogenation of nitrobenzene to aniline on an industrial copper catalyst has been studied in the 503-563/sup 0/K range. A kinetic model of the process is presented which assumes the sequential addition of hydrogen from the gas phase and the absence of retardation by aniline.

  18. Principles of hydrogen radical mediated peptide/protein fragmentation during matrix-assisted laser desorption/ionization mass spectrometry.

    PubMed

    Asakawa, Daiki

    2016-07-01

    Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) is a very easy way to obtain large sequence tags and, thereby, reliable identification of peptides and proteins. Recently discovered new matrices have enhanced the MALDI-ISD yield and opened new research avenues. The use of reducing and oxidizing matrices for MALDI-ISD of peptides and proteins favors the production of fragmentation pathways involving "hydrogen-abundant" and "hydrogen-deficient" radical precursors, respectively. Since an oxidizing matrix provides information on peptide/protein sequences complementary to that obtained with a reducing matrix, MALDI-ISD employing both reducing and oxidizing matrices is a potentially useful strategy for de novo peptide sequencing. Moreover, a pseudo-MS(3) method provides sequence information about N- and C-terminus extremities in proteins and allows N- and C-terminal side fragments to be discriminated within the complex MALDI-ISD mass spectrum. The combination of high mass resolution of a Fourier transform-ion cyclotron resonance (FTICR) analyzer and the software suitable for MALDI-ISD facilitates the interpretation of MALDI-ISD mass spectra. A deeper understanding of the MALDI-ISD process is necessary to fully exploit this method. Thus, this review focuses first on the mechanisms underlying MALDI-ISD processes, followed by a discussion of MALDI-ISD applications in the field of proteomics. © 2014 Wiley Periodicals, Inc., Mass Spec Rev 35:535-556, 2016. PMID:25286767

  19. Electron beam exposure mechanisms in hydrogen silsesquioxane investigated by vibrational spectroscopy and in-situ electron beam induced desorption

    SciTech Connect

    Olynick, D.L.; Cord, B.; Schipotinin, A.; Ogletree, D.F.; Schuck, P.J.

    2009-11-13

    Hydrogen Silsesquioxane (HSQ) is used as a high-resolution resist with resolution down below 10nm half-pitch. This material or materials with related functionalities could have widespread impact in nanolithography and nanoscience applications if the exposure mechanism was understood and instabilities controlled. Here we have directly investigated the exposure mechanism using vibrational spectroscopy (both Raman and Fourier transform Infrared) and electron beam desorption spectrocscopy (EBDS). In the non-networked HSQ system, silicon atoms sit at the corners of a cubic structure. Each silicon is bonded to a hydrogen atom and bridges 3 oxygen atoms (formula: HSiO3/2). For the first time, we have shown, via changes in the Si-H2 peak at ~;;2200 cm -1 in the Raman spectra and the release of SiHx products in EBID, that electron-bam exposed materials crosslinks via a redistribution reaction. In addition, we observe the release of significantly more H2 than SiH2 during EBID, which is indicative of additional reaction mechanisms. Additionally, we compare the behavior of HSQ in response to both thermal and electron-beam induced reactions.

  20. Kinetics of hydrogen/deuterium exchanges in cometary ices

    NASA Astrophysics Data System (ADS)

    Faure, Mathilde; Quirico, Eric; Faure, Alexandre; Schmitt, Bernard; Theulé, Patrice; Marboeuf, Ulysse

    2015-11-01

    The D/H composition of volatile molecules composing cometary ices brings key constraints on the origin of comets, on the extent of their presolar heritage, as well as on the origin of atmospheres and hydrospheres of terrestrial planets. Nevertheless, the D/H composition may have been modified to various extents in the nucleus when a comet approaches the Sun and experiences deep physical and chemical modifications in its subsurface. We question here the evolution of the D/H ratio of organic species by proton exchanges with water ice. We experimentally studied the kinetics of D/H exchanges on the ice mixtures H2O:CD3OD, H2O:CD3ND2 and D2O:HCN. Our results show that fast exchanges occur on the -OH and -NH2 chemical groups, which are processed through hydrogen bonds exchanges with water and by the molecular mobility triggered by structural changes, such as glass transition or crystallization. D/H exchanges kinetic is best described by a second-order kinetic law with activation energies of 4300 ± 900 K and 3300 ± 100 K for H2O:CD3OD and H2O:CD3ND2 ice mixtures, respectively. The corresponding pre-exponential factors ln(A(s-1)) are 25 ± 7 and 20 ± 1, respectively. No exchange was observed in the case of HCN trapped in D2O ice. These results strongly suggest that upon thermal heating (1) -OH and -NH2 chemical groups of any organic molecules loose their primordial D/H composition and equilibrate with water ice, (2) HCN does not experience proton transfer and keeps a primordial D/H composition and (3) C-H chemical groups are not isotopically modified.

  1. Detailed and global chemical kinetics model for hydrogen

    SciTech Connect

    Marinov, N.M.; Westbrook, C.K.; Pitz, W.J.

    1995-03-01

    Detailed and global chemical kinetic computations for hydrogen-air mixtures have been performed to describe flame propagation, flame structure and ignition phenomena. Simulations of laminar flame speeds, flame compositions and shock tube ignition delay times have been successfully performed. Sensitivity analysis was applied to determine the governing rate-controlling reactions for the experimental data sets examined. In the flame propagation and structure studies, the reactions, OH + H{sub 2} = H{sub 2}0 + H, 0 + H{sub 2} = OH + H and 0 + OH = 0{sub 2} + H were the most important in flames. The shock tube ignition delay time study indicated the H + 0{sub 2} + M = H0{sub 2} + M (M = N{sub 2}, H{sub 2}) and 0 + OH = 0{sub 2} + H reactions controlled ignition. A global rate expression for a one-step overall reaction was developed and validated against experimental hydrogen-air laminar flame speed data. The global reaction expression was determined to be 1.8 {times} 10{sup 13} exp({minus}17614K/T)[H{sub 2}]{sup 1.0}[O{sub 2}]{sup 0.5} for the single step reaction H{sub 2} + 1/2O{sub 2} = H{sub 2}O.

  2. Determination of bacterial and viral transport parameters in a gravel aquifer assuming linear kinetic sorption and desorption

    NASA Astrophysics Data System (ADS)

    Mallén, G.; Maloszewski, P.; Flynn, R.; Rossi, P.; Engel, M.; Seiler, K.-P.

    2005-05-01

    The bacteria Escherichia coli and Pseudomonas putida, and the bacteriophage virus H40/1 are examined both for their transport behaviour relative to inert solute tracers and for their modelability under natural flow conditions in a gravel aquifer. The microbes are attenuated in the following sequence: H40/1≥ P. putida≫ E. coli. The latter is desorbed almost completely within a few days. Breakthrough and recovery curves of the simultaneously injected non-reactive tracers are simulated with the 2D and 1D dispersion equation, in order to ascertain longitudinal dispersivity ( αL) and mean flow time ( T0). Mathematical modelling is difficult due to the aquifer heterogeneity, which results in preferential flow paths between injection and observation wells. Therefore, any attempt of fitting the dispersion model (DM) to the entire inert-tracer breakthrough curve (BTC) fails. Adequate fitting of the model to measured data only succeeds using a DM consisting of a superposition of several BTCs, each representing another set of flow paths. This gives rise to a multimodal, rather than a Gaussian groundwater velocity distribution. Only hydraulic parameters derived from the fastest partial curve, which is fitted to the rising part of the Uranine BTC, are suitable to model microbial breakthroughs. The hydraulic parameters found using 2D and 1D models were nearly identical. Their values were put into an analytical solution of 1D advective-dispersive transport combined with two-site reaction model introduced by Cameron and Klute [Cameron, D.R., Klute, A., 1977. Convective-dispersive solute transport with a combined equilibrium and kinetic adsorption model. Water Resour. Res. 13, 183-189], in order to identify reactive transport parameters (sorption/desorption) and attenuation mechanisms for the microbes migration. This shows that the microbes are almost entirely transported through preferential flow paths, which are represented by the first partial curve. Inert tracers, however

  3. Role of Desorption Kinetics and Porous Medium Heterogeneity in Colloid-Facilitated Transport of Cesium and Strontium: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Dittrich, T. M.; Ryan, J. N.

    2008-12-01

    The presence of mobile colloids (particles between 1 nm and 1 μm in size) in natural soil and groundwater systems has been well established. Colloids generally have a high sorptive capacity resulting from their high surface area to mass ratio, which makes them effective sorbents of low solubility, strongly sorbing contaminants. Mobile colloids that sorb contaminants can increase the apparent solubility and rate of transport of the contaminants when desorption from the colloids is slow relative to the rate of flow. This process is known as colloid-facilitated transport (CFT). The additional transport of contaminants associated with mobile colloids should be accounted for to accurately predict transport rates of strongly-sorbing contaminants in the environment. Some examples of contaminants that have the potential for CFT are hydrophobic pesticides, polycyclic aromatic hydrocarbons (PAHs), actinide cations (e.g., Th, U, Pu, Am), and many metals (e.g, Pb, Cu, Hg). Many low solubility contaminants that have the potential for CFT are also harmful or toxic to humans, underscoring the importance of accurate modeling techniques to protect water sources from contamination. Contaminated Department of Energy (DOE) sites have been particularly valuable research opportunities for studying the transport of radionuclides in the natural environment. The DOE has conducted energy and weapons research and development in thirty-one states and Puerto Rico and has introduced many toxic and radioactive chemicals into surface waters, soils, and groundwater. Field experiments on DOE sites including the Nevada Test Site, the Hanford 200 Area tank farm, Rocky Flats CO, and Oak Ridge TN, have confirmed that metals and radionuclides have moved further than expected due to colloid-facilitated transport. The major goal of this research project is to identify and quantify the effects of sorption kinetics on colloid- facilitated transport in unsaturated porous media. This information will be used

  4. Implementation of New TPD Analysis Techniques in the Evaluation of Second Order Desorption Kinetics of Cyanogen from Cu(001)

    SciTech Connect

    E Ciftlikli; E Lee; J Lallo; S Rangan; S Senanayake; B Hinch

    2011-12-31

    The interactions of cyanide species with a copper (001) surface were studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Adsorbed cyanide species (CN{sub (a)}) undergo recombinative desorption evolving molecular cyanogen (C{sub 2}N{sub 2}). As the adsorbed CN species charge upon adsorption, mutually repulsive dipolar interactions lead to a marked desorption energy reduction with increasing CN{sub (a)} coverages. Two new TPD analysis approaches were developed, which used only accurately discernible observables and which do not assume constant desorption energies, E{sub d}, and pre-exponential values, v. These two approaches demonstrated a linear variation of E{sub d} with instantaneous coverage. The first approach involved an analysis of the variations of desorption peak asymmetry with initial CN coverages. The second quantitative approach utilized only temperatures and intensities of TPD peaks, together with deduced surface coverages at the peak maxima, also as a function of initial surface coverages. Parameters derived from the latter approach were utilized as initial inputs for a comprehensive curve fit analysis technique. Excellent fits for all experimental desorption curves were produced in simulations. The curve fit analysis confirms that the activation energy of desorption of 170-180 kJ/mol at low coverage decreases by up to 14-15 kJ/mol at CN saturation.

  5. Implementation of New TPD Analysis Techniques in the Evaluation of Second Order Desorption Kinetics of Cyanogen from Cu(001)

    SciTech Connect

    Hinch, B.J.; Senanayake, S.; Ciftlikli, E.Z.; Lee, E.Y.M.; Lallo, J.; Rangan, S.

    2010-12-21

    The interactions of cyanide species with a copper (001) surface were studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Adsorbed cyanide species (CN{sub (a)}) undergo recombinative desorption evolving molecular cyanogen (C{sub 2}N{sub 2}). As the adsorbed CN species charge upon adsorption, mutually repulsive dipolar interactions lead to a marked desorption energy reduction with increasing CN{sub (a)} coverages. Two new TPD analysis approaches were developed, which used only accurately discernible observables and which do not assume constant desorption energies, E{sub d}, and pre-exponential values, v. These two approaches demonstrated a linear variation of E{sub d} with instantaneous coverage. The first approach involved an analysis of the variations of desorption peak asymmetry with initial CN coverages. The second quantitative approach utilized only temperatures and intensities of TPD peaks, together with deduced surface coverages at the peak maxima, also as a function of initial surface coverages. Parameters derived from the latter approach were utilized as initial inputs for a comprehensive curve fit analysis technique. Excellent fits for all experimental desorption curves were produced in simulations. The curve fit analysis confirms that the activation energy of desorption of 170-180 kJ/mol at low coverage decreases by up to 14-15 kJ/mol at CN saturation.

  6. Tailoring Thermodynamics and Kinetics for Hydrogen Storage in Complex Hydrides towards Applications.

    PubMed

    Liu, Yongfeng; Yang, Yaxiong; Gao, Mingxia; Pan, Hongge

    2016-02-01

    Solid-state hydrogen storage using various materials is expected to provide the ultimate solution for safe and efficient on-board storage. Complex hydrides have attracted increasing attention over the past two decades due to their high gravimetric and volumetric hydrogen densities. In this account, we review studies from our lab on tailoring the thermodynamics and kinetics for hydrogen storage in complex hydrides, including metal alanates, borohydrides and amides. By changing the material composition and structure, developing feasible preparation methods, doping high-performance catalysts, optimizing multifunctional additives, creating nanostructures and understanding the interaction mechanisms with hydrogen, the operating temperatures for hydrogen storage in metal amides, alanates and borohydrides are remarkably reduced. This temperature reduction is associated with enhanced reaction kinetics and improved reversibility. The examples discussed in this review are expected to provide new inspiration for the development of complex hydrides with high hydrogen capacity and appropriate thermodynamics and kinetics for hydrogen storage. PMID:26638824

  7. Trapping state of hydrogen isotopes in carbon and graphite investigated by thermal desorption spectrometry

    SciTech Connect

    Atsumi, H.; Tanabe, T.; Shikama, T.

    2015-03-15

    Thermal desorption spectrometry (TDS) has been investigated to obtain fundamental information of tritium behavior in graphite and carbon materials especially at high temperatures. 29 brands of graphite, HOPG, glassy carbon and CFC materials charged with deuterium gas are tested up to the temperature of 1735 K with a heating rate of 0.1 K/s. TDS spectra have five peaks at 600-700 K, around 900 K, 1200 K, 1300-1450 K and 1600-1650 K. The amounts of released deuterium have been compared with crystallographic parameters derived from XRD analysis. The results can be summarized as follows. First, TDS spectra of deuterium were quite varied among the samples tested, such as existence of peaks, peak temperatures and release amounts of deuterium. Secondly, TDS spectra may consist of five peaks, which are peak 1 (600-700 K), peak 2 (around 900 K), peak 3 (around 1200 K), peak 4 (1300-1450 K) and peak 5 (1600-1650 K). Thirdly, the correlations between the estimated surface area of edge surface and the total amount of released deuterium could be observed for peaks 4 and 5. Fourthly, high energy trapping site (peak 5) may exist even at edge surface or a near surface region, not only for intercalary. And fifth, in order to obtain the lower tritium retention for graphite and CFC materials, the material should be composed of a filler grain with a smaller crystallite size or having the smaller net edge surface in its structure. It is shown that heat treatment does not reduce originally existing trapping sites but trapping sites generated by neutron irradiation for instance can be reduced in some degree.

  8. Effectiveness of passivation techniques on hydrogen desorption in a tritium environment

    NASA Astrophysics Data System (ADS)

    Woodall, Steven Michael

    2009-11-01

    Tritium is a radioactive isotope of hydrogen. It is used as a fuel in fusion reactors, a booster material in nuclear weapons and as a light source in commercial applications. When tritium is used in fusion reactors, and especially when used in the manufacture of nuclear weapons, purity is critical. For U.S. Department of Energy use, tritium is recycled by Savannah River Site in South Carolina and is processed to a minimum purity of 99.5%. For use elsewhere in the country, it must be shipped and stored, while maintaining the highest purity possible. As an isotope of hydrogen it exchanges easily with the most common isotope of hydrogen, protium. Stainless steel bottles are used to transport and store tritium. Protium, present in air, becomes associated in and on the surface of stainless steel during and after the manufacture of the steel. When filled, the tritium within the bottle exchanges with the protium in and on the surface of the stainless steel, slowly contaminating the pure tritium with protium. The stainless steel is therefore passivated to minimize the protium outgrowth of the bottles into the pure tritium. This research is to determine how effective different passivation techniques are in minimizing the contamination of tritium with protium. Additionally, this research will attempt to determine a relationship between surface chemistry of passivated steels and protium contamination of tritium. The conclusions of this research found that passivated bottles by two companies which routinely provide passivated materials to the US Department of Energy provide low levels of protium outgrowth into pure tritium. A bottle passivated with a material to prevent excessive corrosion in a highly corrosive environment, and a clean and polished bottle provided outgrowth rates roughly twice those of the passivated bottles above. Beyond generally high levels of chromium, oxygen, iron and nickel in the passivated bottles, there did not appear to be a strong correlation

  9. Synthesis and Hydrogen Desorption Properties of Mg1.7Al0.15Ti0.15Ni-CNT Nanocomposite Powder

    NASA Astrophysics Data System (ADS)

    Enayati, M. H.; Karimzadeh, F.; Jafari, M.; Sabooni, S.

    2015-03-01

    In this research, the effects of nanocrystallization and incorporation of aluminum, titanium, and carbon nanotubes (CNTs) on hydrogen desorption behavior of Mg2Ni alloy were investigated. Toward this purpose, nanocrystalline Mg2Ni intermetallic compound with average grain size of 20 nm was prepared by ball milling of elemental magnesium and nickel powders. Mg2Ni powder was then ball milled with aluminum and titanium powders for 20 h to dissolve these elements into the Mg2Ni structure, leading to the formation of Mg1.7Al0.15Ti0.15Ni compound. The elemental x-ray mapping analysis revealed the uniform dissolution of aluminum and titanium inside the Mg2Ni structure. Mg2Ni and Mg1.7Al0.15Ti0.15Ni compounds were further ball milled with 3 wt.% CNT for 5 h. The high-resolution field emission scanning electron microscopy and transmission electron microscopy revealed that CNTs have retained their tubular shape after ball-milling process. The hydrogen desorption properties of the samples were identified using a Sieverts-type apparatus at 473 K. The Mg2Ni, Mg2Ni-CNT, and Mg1.7Ti0.15Al0.15-CNT samples showed the desorbed hydrogen of 0.17, 0.25, and 0.28 wt.% after 1 h, respectively, indicating 47 and 65% increase in the hydrogen desorption capability of Mg2Ni via CNT addition and co-presence of aluminum-titanium-CNT. The direct hydrogen diffusion through CNTs and development of local atomic distortion due to substitution of magnesium atoms by aluminum and titanium appears to be responsible for enhancement of desorption behavior of Mg1.7Al0.15Ti0.15-3 wt.% CNT.

  10. Kinetic Interpretation of Water Vapor Adsorption-Desorption Behavior of a Desiccant Rotor Showing S-shaped Adsorption Isotherm

    NASA Astrophysics Data System (ADS)

    Okamoto, Kumiko; Oshima, Kazunori; Takewaki, Takahiko; Kodama, Akio

    Adsorption / desorption behavior of water vapor in a desiccant rotor containing an iron aluminophosphate type zeolite FAM-Z01 (Functional Adsorbent Material Zeolite 01) was experimentally investigated for humidity swing. This rotor exhibited an S-shaped adsorption isotherm with its temperature dependence. Humidity swing, using a small piece of the rotor, could be usefully applied to interpret adsorption / desorption mechanisms by observing their rates. The most significant finding was that the adsorption / desorption rates in humidity swing could be described by the amount of adsorption, temperature and amplitude of the humidity swing, not by cycle time. Also, using the liner driving force (LDF) model, the overall mass transfer coefficient changed with the elapse of time or with the amount of adsorbed water. This implied that the LDF model, considering constant value of the overall mass transfer coefficient, was probably unable to explain the water adsorption / desorption behavior of FAM-Z01 desiccant rotor.

  11. Effect of Clay Nanoparticle Transport, Desorption Kinetics and Redox Equilibrium on Radionuclide Mobility in Fractured Rock investigated at the Grimsel Test Site (Switzerland)

    NASA Astrophysics Data System (ADS)

    Schaefer, T.; Huber, F. M.; Lagos, M.; Quinto, F.; Heck, S.; Martin, A. J.; Blechschmidt, I.; Lanyon, G. W.; Reiche, T.; Noseck, U.

    2015-12-01

    Transport of contaminants in crystalline environments might occur through dissolved species or attached to colloidal or nanoparticulate phases being mobile in water conducting features of the host rock. In this presentation we will discuss the mobility of clay nanoparticles as detected by laser-induced breakdown detection (LIBD) as a function of fracture surface roughness and groundwater chemistry. The on site observed Tc-99, U-233, Np-237, Pu-242 and Am-243 sorption/desorption kinetics with and without natural or synthetic clay minerals (smectites) are compared to laboratory studies under similar groundwater conditions. The desorption or redox kinetics were monitored over a duration of up to 426 days using natural fracture filling material as a concurrence ligand and monitoring the colloid attachment via detection of Al, Si, Ni and Zn as smectite structural elements. For trivalent actinides smectite desorption rates in the range of 1.2-3.7E-3 per hour could be determined and significantly lower desorption rates for tetravalent actinides were found. This results will be compared with field data of migration experiments performed at the Grimsel Test Site (GTS, Switzerland) using the same radionuclides and clay colloidal phases varying the fracture residence time by flow rate adjustment. Furthermore, the long-term actinide mobility will be addressed by presenting AMS/RIMS measurements of (a) samples collected several months into the tailing of the breakthrough curves not any longer detectable by HR-ICP-MS and (b) background samples of different GTS ground waters showing fallout U-236, whereas fallout Pu could not be detected indicating a much lower mobility under the given conditions.

  12. FAR-INFRARED SPECTROSCOPY OF CATIONIC POLYCYCLIC AROMATIC HYDROCARBONS: ZERO KINETIC ENERGY PHOTOELECTRON SPECTROSCOPY OF PENTACENE VAPORIZED FROM LASER DESORPTION

    SciTech Connect

    Zhang Jie; Han Fangyuan; Pei Linsen; Kong Wei; Li Aigen

    2010-05-20

    The distinctive set of infrared (IR) emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 {mu}m are ubiquitously seen in a wide variety of astrophysical environments. They are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. However, not a single PAH species has yet been identified in space, as the mid-IR vibrational bands are mostly representative of functional groups and thus do not allow one to fingerprint individual PAH molecules. In contrast, the far-IR (FIR) bands are sensitive to the skeletal characteristics of a molecule, hence they are important for chemical identification of unknown species. With an aim to offer laboratory astrophysical data for the Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy, and similar future space missions, in this work we report neutral and cation FIR spectroscopy of pentacene (C{sub 22}H{sub 14}), a five-ring PAH molecule. We report three IR active modes of cationic pentacene at 53.3, 84.8, and 266 {mu}m that may be detectable by space missions such as the SAFARI instrument on board SPICA. In the experiment, pentacene is vaporized from a laser desorption source and cooled by a supersonic argon beam. We have obtained results from two-color resonantly enhanced multiphoton ionization and two-color zero kinetic energy photoelectron (ZEKE) spectroscopy. Several skeletal vibrational modes of the first electronically excited state of the neutral species and those of the cation are assigned, with the aid of ab initio and density functional calculations. Although ZEKE is governed by the Franck-Condon principle different from direct IR absorption or emission, vibronic coupling in the long ribbon-like molecule results in the observation of a few IR active modes. Within the experimental resolution of {approx}7 cm{sup -1}, the frequency values from our calculation agree with the experiment for the cation, but differ for the electronically excited intermediate state. Consequently, modeling of the

  13. Kinetics study of solid ammonia borane hydrogen release--modeling and experimental validation for chemical hydrogen storage.

    PubMed

    Choi, Young Joon; Rönnebro, Ewa C E; Rassat, Scot; Karkamkar, Abhi; Maupin, Gary; Holladay, Jamie; Simmons, Kevin; Brooks, Kriston

    2014-05-01

    Ammonia borane (AB), NH3BH3, is a promising material for chemical hydrogen storage with 19.6 wt% gravimetric hydrogen capacity of which maximum 16.2 wt% hydrogen can be released via an exothermic thermal decomposition below 200 °C. We have investigated the kinetics of hydrogen release from AB and from an AB-methyl cellulose (AB/MC) composite at temperatures of 160-300 °C using both experiments and modeling. The hydrogen release rate at 300 °C is twice as fast as at 160 °C. The purpose of our study was to show safe hydrogen release without thermal runaway effects and to validate system model kinetics. AB/MC released hydrogen at ∼20 °C lower than neat AB and at a faster release rate in that temperature range. Based on the experimental results, the kinetics equations were revised to better represent the growth and nucleation process during decomposition of AB. We explored two different reactor concepts; auger and fixed bed. The current auger reactor concept turned out to not be appropriate, however, we demonstrated safe self-propagation of the hydrogen release reaction of solid AB/MC in a fixed bed reactor. PMID:24647627

  14. Kinetics Study of Solid Ammonia Borane Hydrogen Release – Modeling and Experimental Validation for Chemical Hydrogen Storage

    SciTech Connect

    Choi, Yong-Joon; Ronnebro, Ewa; Rassat, Scot D.; Karkamkar, Abhijeet J.; Maupin, Gary D.; Holladay, Jamelyn D.; Simmons, Kevin L.; Brooks, Kriston P.

    2014-02-24

    Ammonia borane (AB), NH3BH3, is a promising material for chemical hydrogen storage with 19.6 wt% gravimetric hydrogen capacity of which 16.2 wt% hydrogen can be utilized below 200°C. We have investigated the kinetics of hydrogen release from AB and from an AB-methyl cellulose (AB/MC) composite at temperatures of 160-300°C using both experiments and modeling. The purpose of our study was to show safe hydrogen release without thermal runaway effects and to validate system model kinetics. AB/MC released hydrogen at ~20°C lower than neat AB and at a rate that is two times faster. Based on the experimental results, the kinetics equations were revised to better represent the growth and nucleation process during decomposition of AB. We explored two different reactor concepts; Auger and fixed bed. The current Auger reactor concept turned out to not be appropriate, however, we demonstrated safe self-propagation of the hydrogen release reaction of solid AB/MC in a fixed bed reactor.

  15. Nucleation and growth mechanisms of nano magnesium hydride from the hydrogen sorption kinetics.

    PubMed

    Mooij, Lennard; Dam, Bernard

    2013-07-21

    We use a combination of hydrogenography and Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses to identify (1) the driving force dependence of the nucleation and growth mechanism of MgH2 in thin film multilayers of Mg (10 nm) and (2) the nucleation and growth mechanism of Mg in the earlier formed MgH2, i.e. the hydrogen desorption process. We conclude that JMAK may be successfully applied to obtain the nucleation and growth mechanism of hydrogen absorption. The desorption mechanism, however, is not simply the reverse of the absorption mechanism. We find evidence that the barrier for nucleation of Mg is small. The dehydrogenation probably involves the formation of voids, which is energetically more favorable than elastic and plastic deformation of the multilayer. PMID:23749082

  16. Theoretical evidence of the difference in kinetics of water sorption and desorption in Nafion® membrane and experimental validation

    NASA Astrophysics Data System (ADS)

    Didierjean, S.; Perrin, J. C.; Xu, F.; Maranzana, G.; Klein, M.; Mainka, J.; Lottin, O.

    2015-12-01

    Water transport during sorption and desorption in Nafion® 117 samples is studied by means of dynamic model and experiments as a response of relative humidity step. The model takes into account a transfer resistance at the interface between the membrane and the surrounding medium, and considers that the water content of the membrane remains uniform at all times during sorption and desorption, which was confirmed using NMR imaging. Thus, its main hypothesis is that the membrane is in equilibrium with the humid gas located at the interface whose relative humidity is different than in the bulk. The calculated time-variations in the water content of a membrane sample (in acid form) during sorption and desorption show that desorption is faster than sorption due to the variations in the slope of the water uptake isotherm. The theoretical results and the experimental data show a good agreement which allows the determination of the mass transfer coefficient. The influence of diffusion and thermal effects are also discussed.

  17. Effects of hydrogen surface processes on hydrogen retention in plasma facing components

    NASA Astrophysics Data System (ADS)

    Guterl, Jerome; Smirnov, Roman; Krasheninnikov, Sergei

    2014-10-01

    Hydrogen retention and recycling on metallic plasma-facing components (PFCs) are among the key-issues for future fusion devices due to both safety and operational reasons. For tungsten, which has been chosen as divertor material in ITER, parameters of hydrogen desorption from Wsurfaces, experimentally measured for fusion-related conditions, show a large discrepancy. Indeed, various complex phenomena may affect hydrogen desorption (e.g atomic islands, roughness, surface reconstruction, impurities, ect). In this work, we investigate effects of hydrogen desorption from W surfaces on hydrogen retention in W material. Two regimes of hydrogen surface desorption (readsorption-limited and recombination-limited) can be identified and may affect the kinetic order of desorption. Within these desorption regimes, it is shown that release of hydrogen from W material in fusion-related conditions may be surface-limited at low temperature and diffusion-limited at high temperature. Analyses of hydrogen release regimes for thermodesorption experiments and plasma operations in fusion reactors show that surface processes may strongly affect retention and release of hydrogen from W material. In this context, effects of W surface coverage with oxygen on hydrogen desorption are discussed since high concentrations of oxygen on PFCs surfaces are expected in future fusion devices. This work is performed under the auspices of USDOE Grant No. DE-FG02-04ER54739 and the PSI Science Center Grant DE-SC0001999 at UCSD.

  18. Kinetics, equilibrium, and mechanisms of sorption and desorption of 17α-ethinyl estradiol in two natural soils and their organic fractions.

    PubMed

    Li, Jianzhong; Fu, Jing; Xiang, Xi; Wu, Miaomiao; Liu, Xiang

    2013-05-01

    A study was conducted on the kinetics, equilibrium, and mechanisms of sorption and desorption of 17α-ethinyl estradiol (EE2) in six sorbents, which were two natural soils (Bulk1 and Bulk2) and their fractions obtained by alkaline extraction, namely, humic acids (HA1 and HA2), and mineral-bond humins (MHU1 and MHU2). These sorbents, characterized by total organic carbon (TOC), black carbon (BC), gas adsorption and Fourier transform infrared spectra, were shown to be porous solids containing aromatic (hard carbon) and aliphatic carbon (soft carbon). The two-compartment first-order model fitted the kinetics of sorption very well (R(2)>0.990). The fast and slow sorption rate constants ranged from 1.110 h(-1) and 0.026 h(-1) to 2.063 h(-1) and 0.067 h(-1), respectively. The slow sorption was attributed to the diffusion of EE2 in micropores rather than organic matter. The Freundlich model fitted the equilibrium of sorption and desorption very well. The nonlinearity of sorption took the order MHU>bulk soil>HA and was positively related to BC/TOC (p<0.01). The hysteresis in MHU2 with higher BC/TOC was stronger than that in Bulk2 with lower BC/TOC, but a contrary observation was found in MHU1 and Bulk1. This contradictory phenomenon could be attributed to the location difference of hard carbon which greatly affected the desorption process. These findings could give an insight into the sorption mechanisms and promote an accurate model for the transport, fate and risk assessment of EE2 in the environment. PMID:23542434

  19. Reaction kinetics for the oxygen hydrogenation process on Pt(111) derived from temperature-programmed XPS

    NASA Astrophysics Data System (ADS)

    Näslund, Lars-Åke

    2013-12-01

    Oxygen hydrogenation under ultra high vacuum conditions at the platinum surface was explored using temperature-programmed X-ray photoelectron spectroscopy. Through modeling of the oxygen consumption, information on the reaction kinetics was obtained indicating that the reaction rate of the oxygen hydrogenation process depends on the hydrogen diffusion and on the lifetime of hydroxyl intermediates. The reaction rate is, however, enhanced when an autocatalytic process stabilizes the hydroxyl intermediates through hydrogen bonding to neighboring water molecules. The overall activation energy for the hydrogenation of atomic oxygen to form water was determined to be 0.20 eV with a frequency factor of only 103 s- 1.

  20. Effects of soil organic matter on the kinetics and mechanisms of Pb(II) sorption and desorption in soil

    SciTech Connect

    Strawn, D.G.; Sparks, D.L.

    2000-02-01

    To improve predictions of the toxicity and threat from Pb contaminated soil, it is critical that time-dependent sorption and desorption behavior be understood. In this paper, the sorption and desorption behavior of Pb in a Matapeake silt loam soil (Typic Hapludult) were studied by stirred-flow and batch experiments. In addition, the authors studied the effects of soil organic matter (SOM) on sorption and desorption behavior by treating the soil with sodium hypochlorite to remove the SOM fraction, and using a soil with six times as much SOM (St. Johns loamy sand [Typic Haplaquods]) as the Matapeake soil. Lead sorption consisted of a fast initial reaction in which all of the Pb added to the stirred-flow chamber was sorbed. Following this initial fast reaction, sorption continued and appears to be rate limited. The total amount of Pb sorbed was 102, 44, and 27 mmol kg{sup {minus}1} for the St. Johns soil and the untreated and treated Matapeake soils, respectively. Desorption experiments were conducted on the soils with the background electrolyte as the eluent in the stirred-flow chamber. In the St. Johns soil only, 32% of the total sorbed Pb was desorbed, while 47 and 76% of the sorbed Pb was released from the untreated and treated Matapeake soil, respectively. The correlation between SOM in the soils, and the percentage Pb desorbed from the soils suggests that SOM plays an important role in slow desorption reactions of Pb from soil materials. Aging experiments in which sorbed Pb was incubated for 1, 10, and 32 d showed that sorption incubation time had no effect on Pb desorption behavior. Analysis of the treated and untreated Matapeake soils by x-ray absorption fine structure (XAFS) spectroscopy revealed that the local atomic structure of sorbed Pb is distinctly different in the two samples. In the soil treated to remove SOM, the data were well represented by theoretical models using O, Si, and Pb backscattering atoms. In the untreated soil, the XAFS data were best

  1. Kinetic Monte Carlo and density functional study of hydrogen enhanced dislocation glide in silicon

    NASA Astrophysics Data System (ADS)

    Scarle, S.; Ewels, C. P.

    2006-05-01

    We investigate Hydrogen Enhanced Dislocation Glide [HEDG], using n-fold way Kinetic Monte Carlo simulations of the interaction between hydrogen and 90° partial dislocations in silicon, and a range of new density functional calculations. We examine two different hydrogen arrival species, as well as hydrogen recombination at the dislocation. The Monte Carlo simulations use a line-wise description of the dislocation line parameterized using density functional calculations of migration and formation energies of various dislocation line defects and their complexes with hydrogen. From this we suggest that the rate of H2 expulsion from the dislocation core increases as we approach HEDG, but that if the concentration of the hydrogen species goes beyond that required for HEDG it then slows dislocation motion by choking the line with defects comprised of two hydrogen atoms in a reconstruction bond. A `dislocation engine' model is proposed whereby hydrogen enters the dislocation line, catalyses motion, and is expelled along the core as H2.

  2. Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure.

    PubMed

    Losurdo, Maria; Giangregorio, Maria Michela; Capezzuto, Pio; Bruno, Giovanni

    2011-12-14

    Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates. PMID:22006173

  3. Changes in metal availability, desorption kinetics and speciation in contaminated soils during repeated phytoextraction with the Zn/Cd hyperaccumulator Sedum plumbizincicola.

    PubMed

    Li, Zhu; Jia, Mingyun; Wu, Longhua; Christie, Peter; Luo, Yongming

    2016-02-01

    Phytoextraction is one of the most promising technologies for the remediation of metal contaminated soils. Changes in soil metal availability during phytoremediation have direct effects on removal efficiency and can also illustrate the interactive mechanisms between hyperaccumulators and metal contaminated soils. In the present study the changes in metal availability, desorption kinetics and speciation in four metal-contaminated soils during repeated phytoextraction by the zinc/cadmium hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) over three years were investigated by chemical extraction and the DGT-induced fluxes in soils (DIFS) model. The available metal fractions (i.e. metal in the soil solution extracted by CaCl2 and by EDTA) decreased greatly by >84% after phytoextraction in acid soils and the deceases were dramatic at the initial stages of phytoextraction. However, the decreases in metal extractable by CaCl2 and EDTA in calcareous soils were not significant or quite low. Large decreases in metal desorption rate constants evaluated by DIFS were found in calcareous soils. Sequential extraction indicated that the acid-soluble metal fraction was easily removed by S. plumbizincicola from acid soils but not from calcareous soils. Reducible and oxidisable metal fractions showed discernible decreases in acid and calcareous soils, indicating that S. plumbizincicola can mobilize non-labile metal for uptake but the residual metal cannot be removed. The results indicate that phytoextraction significantly decreases metal availability by reducing metal pool sizes and/or desorption rates and that S. plumbizincicola plays an important role in the mobilization of less active metal fractions during repeated phytoextraction. PMID:26650084

  4. Hydrogenation of Acetylene-Ethylene Mixtures over Pd and Pd-Ag Alloys: First-Principles Based Kinetic Monte Carlo Simulations

    SciTech Connect

    Mei, Donghai; Neurock, Matthew; Smith, C Michael

    2009-10-22

    The kinetics for the selective hydrogenation of acetylene-ethylene mixtures over model Pd(111) and bimetallic Pd-Ag alloy surfaces were examined using first principles based kinetic Monte Carlo (KMC) simulations to elucidate the effects of alloying as well as process conditions (temperature and hydrogen partial pressure). The mechanisms that control the selective and unselective routes which included hydrogenation, dehydrogenation and C-C bond breaking pathways were analyzed using first-principle density functional theory (DFT) calculations. The results were used to construct an intrinsic kinetic database that was used in a variable time step kinetic Monte Carlo simulation to follow the kinetics and the molecular transformations in the selective hydrogenation of acetylene-ethylene feeds over Pd and Pd-Ag surfaces. The lateral interactions between coadsorbates that occur through-surface and through-space were estimated using DFT-parameterized bond order conservation and van der Waal interaction models respectively. The simulation results show that the rate of acetylene hydrogenation as well as the ethylene selectivity increase with temperature over both the Pd(111) and the Pd-Ag/Pd(111) alloy surfaces. The selective hydrogenation of acetylene to ethylene proceeds via the formation of a vinyl intermediate. The unselective formation of ethane is the result of the over-hydrogenation of ethylene as well as over-hydrogenation of vinyl to form ethylidene. Ethylidene further hydrogenates to form ethane and dehydrogenates to form ethylidyne. While ethylidyne is not reactive, it can block adsorption sites which limit the availability of hydrogen on the surface and thus act to enhance the selectivity. Alloying Ag into the Pd surface decreases the overall rated but increases the ethylene selectivity significantly by promoting the selective hydrogenation of vinyl to ethylene and concomitantly suppressing the unselective path involving the hydrogenation of vinyl to ethylidene

  5. Kinetic and Prediction of Hydrogen Outgassing from Lithium Hydride

    SciTech Connect

    Dinh, L N; Schildbach, M A; Smith, R A; Balazs, B; McLean II, W

    2006-08-31

    In most industrial or device applications, LiH is placed in either an initially dry or a vacuum environment with other materials that may release moisture slowly over many months, years, or even decades. In such instances, the rate of hydrogen outgassing from the reaction of LiH with H{sub 2}O can be reasonably approximated by the rate at which H{sub 2}O is released from the moisture containing materials. In a vacuum or dry environment, LiOH decomposes slowly with time into Li{sub 2}O even at room temperature according to: 2LiOH(s) {yields} Li{sub 2}O(s) + H{sub 2}O(g) (1). The kinetics of the decomposition of LiOH depends on the dryness/vacuum level and temperature. It was discovered by different workers that vacuum thermal decomposition of bulk LiOH powder (grain sizes on the order of tens to hundreds of micrometers) into Li{sub 2}O follows a reaction front moving from the surface inward. Due to stress at the LiOH/vacuum interface and defective and missing crystalline bonding at surface sites, lattice vibrations at the surfaces/interfaces of most materials are at frequencies different than those in the bulk, a phenomenon observed in most solids. The chemical reactivity and electronic properties at surfaces and interfaces of materials are also different than those in the bulk. It is, therefore, expected that the amount of energy required to break bonds at the LiOH/vacuum interface is not as large as in the bulk. In addition, in an environment where there is a moisture sink or in the case of a continuously pumped vacuum chamber, H{sub 2}O vapor is continuously removed and LiOH decomposes into Li{sub 2}O from the LiOH/vacuum interface (where it is thermally less stable) inward according to reaction (1) in an effort to maintain the equilibrium H{sub 2}O vapor pressure at the sample/vacuum interface. In a closed system containing both LiH and LiOH, the H{sub 2}O released from the decomposition of LiOH reacts with LiH to form hydrogen gas according to the following

  6. Reaction kinetics and growth window for plasma-assisted molecular beam epitaxy of Ga2O3: Incorporation of Ga vs. Ga2O desorption

    NASA Astrophysics Data System (ADS)

    Vogt, Patrick; Bierwagen, Oliver

    2016-02-01

    A detailed study of the reaction kinetics of the plasma-assisted molecular beam epitaxy (MBE) growth of the n-type semiconducting oxide Ga2O3 is presented. The growth rate as a function of gallium flux is measured in situ by laser reflectometry at different growth temperatures (TG) and gallium-to-oxygen ratios (rGa). The flux of the suboxide Ga2O desorbed off the growth surface is identified in situ by line-of-sight quadrupole mass spectroscopy. The measurements reveal the influence of TG and rGa on the competing formation of Ga2O3 and desorption of Ga2O resulting in three different growth regimes: (i) Ga transport limited, (ii) Ga2O desorption limited, and (iii) O transport limited. As a result, we present a growth diagram of gallium oxide. This diagram illustrates the regimes of complete, partial, and no Ga incorporation as a function of TG and rGa, and thus provides guidance for the MBE growth of Ga2O3.

  7. Complex hydrides for hydrogen storage

    DOEpatents

    Zidan, Ragaiy

    2006-08-22

    A hydrogen storage material and process of forming the material is provided in which complex hydrides are combined under conditions of elevated temperatures and/or elevated temperature and pressure with a titanium metal such as titanium butoxide. The resulting fused product exhibits hydrogen desorption kinetics having a first hydrogen release point which occurs at normal atmospheres and at a temperature between 50.degree. C. and 90.degree. C.

  8. Hydrogen Reduction Kinetics of Magnetite Concentrate Particles Relevant to a Novel Flash Ironmaking Process

    NASA Astrophysics Data System (ADS)

    Wang, Haitao; Sohn, H. Y.

    2013-02-01

    A novel ironmaking technology is under development at the University of Utah. The purpose of this research was to determine comprehensive kinetics of the flash reduction reaction of magnetite concentrate particles by hydrogen. Experiments were carried out in the temperature range of 1423 K to 1673 K (1150 °C to 1400 °C) with the other experimental variables being hydrogen partial pressure and particle size. The nucleation and growth kinetics expression was found to describe the reduction rate of fine concentrate particles and the reduction kinetics had a 1/2-order dependence on hydrogen partial pressure and an activation energy of 463 kJ/mol. Unexpectedly, large concentrate particles reacted faster at 1423 K and 1473 K (1150 °C and 1200 °C), but the effect of particle size was negligible when the reduction temperature was above 1573 K (1300 °C). A complete reaction rate expression incorporating all these factors was formulated.

  9. A study of spin isomer conversion kinetics in supercritical fluid hydrogen for cyrogenic fuel storage technologies

    NASA Astrophysics Data System (ADS)

    Matthews, Manyalibo J.; Petitpas, Guillaume; Aceves, Salvador M.

    2011-08-01

    A detailed kinetic study of para-ortho hydrogen conversion under supercritical conditions using rotational Raman scattering is presented. Isochoric measurements of initially low ortho concentrations over temperatures 32 < T < 280 K and densities 0.014 < ρ < 0.060 g/cm3 were used to derive kinetic rate constants k(ρ, T) by solving an autocatalytic kinetic rate equation. At low ortho concentrations and T < 100 K, k is found to be ˜2× higher than previous results based on thermal conductivity measurements, decreasing weakly with temperature, similar to Wigner's original paramagnetic theory. Accurate modeling of k(ρ, T) is critical in predicting cryogenic hydrogen fuel tank dormancy performance for hydrogen-power vehicles.

  10. Mechanisms and kinetics of coal hydrogenation. Quarterly progress report, October-December 1979

    SciTech Connect

    Gary, J. H.; Baldwin, R. M.; Bain, R. L.

    1980-02-01

    Colorado School of Mines is conducting coal hydrogenation research with the following objectives and scope of work: (1) Comparison of the rates of coal hydrogenation in continuous flow stirred tank and tube flow reactors using pure hydrogen, catalyzed CO-STEAM, and syngas processing conditions; (2) Investigation of the influence of coal rank on the rate of hydrogenation of coal to preasphaltene, asphaltenes, and oil in batch reactors; (3) Batch evaluation of the effect of operating conditions (temperature and pressure) on the rate of hydrogenation of coal-derived preasphaltanes and asphaltenes; (4) Determination of the effect of selected disposable catalysts on the rate of batch hydrogenation of preasphaltenes and asphaltenes and selected bituminous coals. Testing and evaluation of promising catalyst systems in the contunuous processing unit; (5) Formulation of a unified kinetic/mechanistic model for coal liquefaction taking into account petrography of the feed coal and hydrocarbon lumps in the product oil.

  11. Hydrogenation kinetics in oxidized boron-doped silicon irradiated by keV electrons

    NASA Astrophysics Data System (ADS)

    Lin, Wallace Wan-Li; Sah, Chih-Tang

    1988-08-01

    Hydrogenation kinetics of boron acceptors in oxidized silicon during and after repeated 8-keV electron irradiation (225-2700-μC/cm2 stresses and 10-168-h interirradiation anneals) at room temperature are reported. Hydrogenation proceeds rapidly during irradiation but continues for many hours after the 8-keV electron beam is removed. Postoxidation process dependencies show that postoxidation and postmetallization annealing processes reduce the hydrogenation effect during the 8-keV electron irradiation, while exposure of the oxide to water prior to aluminum electrode deposition enhances it. The data can be interpreted by our two-reaction model consisting of the hydrogen capture reaction by the boron acceptor and the hydrogen recombination reaction to form hydrogen molecule.

  12. Optimisation of sorbent trapping and thermal desorption-gas chromatography-mass spectrometric conditions for sampling and analysis of hydrogen cyanide in air.

    PubMed

    Juillet, Yannick; Le Moullec, Sophie; Bégos, Arlette; Bellier, Bruno

    2005-06-01

    Among the chemicals belonging to the schedules of the Chemical Weapons Convention (CWC), sampling and analysis of highly volatile compounds such as hydrogen cyanide (HCN) require special consideration. The latter is present in numerous old chemical weapons that are stockpiled awaiting destruction in Northeastern France: thus, sampling on stockpile area and subsequent verification of HCN levels is compulsory to ensure safety of workers on these areas. The ability of several commercial sorbents to trap hydrogen cyanide at various concentration levels and in various humidity conditions, was evaluated. Furthermore, thermal desorption of the corresponding samples, followed by analysis by gas chromatography-mass spectrometry was also optimised. Carbosieve S-III, a molecular sieve possessing a very high specific area, proved the most efficient sorbent for HCN sampling in all conditions tested. Conversely, the presented results show that Tenax, albeit generally considered as the reference sorbent for air monitoring and analysis of CWC-related chemicals, is not suitable for HCN trapping. PMID:15912249

  13. Kinetics of Hydrogen Diffusion in LaNi(sub 5-x)Sn(sub x) Alloys

    NASA Technical Reports Server (NTRS)

    Ratnakumar, B. V.; Hightower, A.; Witham, C.; Bowman, R. C.; Fultz, B.

    1996-01-01

    Solid-state diffusion of hydrogen in metal hydride (MH) alloys is recognized as the rate determining step in the discharge of MH alloys in alkaline Ni-MH rechargeable cells. In our pursuit of new ternary solutes in LaNi(sub 5) for extended cycle lifetimes, we have observed noticeable improvement in the cycle life with small substitutions of Sn and Ge for Ni. Furthermore, these substituents also facilitate enhanced charge transfer kinetics for hydriding-dehydriding process. In this paper, we report our studies on the kinetics of hydrogen diffusion in LaNi(sub 5-x) Sn(sub x) alloys by electrochemical pulse techniques, chronoamperometry and chronocoulometry.

  14. Kinetics of fatigue cracks in iron in electrolytic hydrogen impregnation

    SciTech Connect

    Pokhmurskii, V.I.; Bilyi, L.M.

    1985-05-01

    Fatigue failure of metals is localized in the zone of plastic deformation at the tip of the developing crack. Crack development depends to a large extent upon the parameters of the deformed volume, the loading conditions, and features of the material microstructure. It may be assumed that the medium, especially a hydrogen-impregnating medium, leads to a change in the zone of plastic deformation and thereby influences the rate of fatigue crack growth. This work is devoted to a study of cyclic crack resistance and determination of the zone of plastic deformation of failure specimens of Armco iron under conditions of the action of a hydrogen-impregnating medium.

  15. Pyrrole Hydrogenation over Rh(111) and Pt(111) Single-Crystal Surfaces and Hydrogenation Promotion Mediated by 1-Methylpyrrole: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    SciTech Connect

    Kliewer, Christopher J.; Bieri, Marco; Somorjai, Gabor A.

    2008-03-04

    Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H{sub 2}) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate, which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.

  16. Methane ice photochemistry and kinetic study using laser desorption time-of-flight mass spectrometry at 20 K.

    PubMed

    Bossa, J-B; Paardekooper, D M; Isokoski, K; Linnartz, H

    2015-07-14

    The ice photochemistry of pure methane (CH4) is studied at 20 K upon VUV irradiation from a microwave discharge H2 flow lamp. Laser Desorption Post-Ionization Time-Of-Flight Mass Spectrometry (LDPI TOF-MS) is used for the first time to determine branching ratios of primary reactions leading to CH3, CH2, and CH radicals, typically for fluences as expected in space. This study is based on a stable end-products analysis and the mass spectra are interpreted using an appropriate set of coupled reactions and rate constants. This yields clearly different values from previous gas phase studies. The matrix environment as well as the higher efficiency of reverse reactions in the ice clearly favor CH3 radical formation as the main first generation photoproduct. PMID:26073296

  17. 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.

    1993-01-01

    The goal of this program 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 degradation. 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. The interaction of hydrogen with the surfaces of alpha-2(Ti3Al) titanium aluminide, gamma(TiAl) titanium aluminide, and beryllium were studied.

  18. A Chemical Kinetic Mechanism for the Ignition of Silane/Hydrogen Mixtures

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.; Mclain, A. G.

    1983-01-01

    A chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed. Shock-tube ignition delay time data were used to evaluate and refine the mechanism. Good agreement between experimental results and the results predicted by the mechanism was obtained by adjusting the rate coefficient for the reaction SiH3 + O2 yields SiH2O + OH. The reaction mechanism was used to theoretically investigate the ignition characteristics of silane/hydrogen mixtures. The results revealed that over the entire range of temperature examined (800 K to 1200 K), substantial reduction in ignition delay times is obtained when silane is added to hydrogen.

  19. Measuring Drug Metabolism Kinetics and Drug-Drug Interactions Using Self-Assembled Monolayers for Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry.

    PubMed

    Anderson, Lyndsey L; Berns, Eric J; Bugga, Pradeep; George, Alfred L; Mrksich, Milan

    2016-09-01

    The competition of two drugs for the same metabolizing enzyme is a common mechanism for drug-drug interactions that can lead to altered kinetics in drug metabolism and altered elimination rates in vivo. With the prevalence of multidrug therapy, there is great potential for serious drug-drug interactions and adverse drug reactions. In an effort to prevent adverse drug reactions, the FDA mandates the evaluation of the potential for metabolic inhibition by every new chemical entity. Conventional methods for assaying drug metabolism (e.g., those based on HPLC) have been established for measuring drug-drug interactions; however, they are low-throughput. Here we describe an approach to measure the catalytic activity of CYP2C9 using the high-throughput technique self-assembled monolayers for matrix-assisted laser desorption-ionization (SAMDI) mass spectrometry. We measured the kinetics of CYP450 metabolism of the substrate, screened a set of drugs for inhibition of CYP2C9 and determined the Ki values for inhibitors. The throughput of this platform may enable drug metabolism and drug-drug interactions to be interrogated at a scale that cannot be achieved with current methods. PMID:27467208

  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. Capacitively Coupled Radio Frequency Discharge Plasmas In Hydrogen: Particle Modeling and Negative Ion Kinetics

    SciTech Connect

    Diomede, P.; Longo, S.; Capitelli, M.

    2005-05-16

    We present a 1D(r)2D(v) particle code for capacitively coupled radio frequency discharge plasmas in hydrogen, which includes a rigorous kinetic modeling of ion transport and several solutions to speed up the convergence. In a test case the effect of surface atom recombination and molecule vibrational deactivation on H- concentration is investigated.

  3. Mechanisms and kinetics of coal hydrogenation. Quarterly progress report, April-June

    SciTech Connect

    Baldwin, R.M.; Furlong, M.W.

    1981-07-01

    Colorado School of Mines is engaged in an experimental program for the Department of Energy to develop comprehensive models for the effects of coal composition upon the kinetics and mechanisms of coal hydrogenation, for the effects of mineral matter additives (disposable catalysts) upon kinetics and mechanisms of coal hydrogenation, and for the kinetics and mechanisms of the hydrogenation of coal derived products such as preasphaltenes and asphaltenes. The continuous flow coal processing unit was modified to alleviate problems with non-representative sampling during the course of operation. A synthetic recycle oil solvent was prepared to allay any doubts regarding the distribution of reacted solvent components in the product samples. Data from the coal reactivity study was fitted by true second-order reversible kinetics expressions. The forward rate constants were correlated with H/C ratio, mean-max reflectance, and fraction reactive macerals of the parent coals. Kinetic reactivities were also shown to correlate with the percentage of volatile carbon in the parent coals. Intrinsic THF solubilities of the parent coals were measured experimentally and the resulting values incorporated in the evaluation of second-order rate constants. The reactivities were not significantly affected by this modification. Reproductibility tests were initiated in the disposable catalysts study. Agreement between these data and those from the initial phase of this study were fair. Further tests will be made to verify these results.

  4. Characterization of electron kinetics regime with electron energy probability functions in inductively coupled hydrogen plasmas

    NASA Astrophysics Data System (ADS)

    Kim, June Young; Cho, Won-Hwi; Dang, Jeong-Jeung; Chung, Kyoung-Jae; Hwang, Y. S.

    2016-02-01

    Electron kinetics regime is characterized with the evolution of electron energy probability functions (EEPFs) in inductively coupled hydrogen plasmas. Measurements on EEPFs are carried out with a radio-frequency-compensated single Langmuir probe at the center of a planar-type hydrogen plasma driven by 13.56 MHz wave frequency. Measured EEPFs deviate considerably from the Maxwellian distribution only at relatively high pressures (15-40 mTorr), and the effective electron temperature steeply decreases as the gas pressure increases. Such evolution of the EEPF shapes with pressures is discussed in the consideration of the electron energy relaxation length and various characteristic frequencies. It is found that the EEPFs show locally depleted electron energy distribution where the electron-molecule vibrational collision frequency exceeds the electron-electron collision frequency at the local kinetics regime, while the measured EEPF is not dependent on the vibrational collision frequency at the non-local kinetics regime. Variation of the EEPF shape with distance from the heating region at the local kinetics regime is also well explained in the context of the energy relaxation length and electron-molecule collision frequencies. This study indicates that the control of electron energy distribution should be carried out in the consideration of electron kinetic regime depending on the energy relaxation length for various hydrogen plasma sources.

  5. Kinetics of the reaction of nitric oxide with hydrogen

    NASA Technical Reports Server (NTRS)

    Flower, W. L.; Hanson, R. K.; Kruger, C. H.

    1974-01-01

    Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.

  6. Kinetics of hydrogen attack of 2 1/4 Cr-1 Mo steel

    SciTech Connect

    Parthasarathy, T.A.

    1983-01-01

    The effect of welding on the kinetics of hydrogen attack of 2 1/4 Cr-1 Mo quenched and tempered steel was studied using a highly sensitive capacitance dilatometer, in the temperature range of 490 C to 590 C and hydrogen pressures of 10 to 23 MPa. The strain rate of the weld metal was an order of magnitude greater than that of the base metal at 500 C and 20.3 MPa of hydrogen, but it was the same as that of the base metal at 570 C. The base metal exhibited an activation energy of 256 +/- 5 KJ/mol and a methane pressure dependence of 1.76 +/- 0.4. The weld metal had an activation energy of 313 +/- 36 KJ/mol and a methane pressure dependence of 6.6 +/- 1.5. The bubbles in the base metal formed preferentially at the grain boundaries, but those in the weld metal showed no such preference. The effects of tempering on the hydrogen attack kinetics was studied by measuring strain rates and carbon activities of 2 1/4 Cr-1 Mo steel samples tempered to different extents. Both carbon activity and the hydrogen attack strain rate decreased monotonically with tempering. Tempering for up to 500 hrs at 700 C does not decrease carbon activity below 0.05 and appreciable strain rates were measured at 550 C and 20.3 MPa. Bubble growth mechanism maps were drawn for both carbon and low alloy steels, and the maps give the predicted mechanisms controlling bubble growth at various temperatures and hydrogen pressures. Commercial 2 1/4 Cr-1 Mo Q and T steel was found to suffer hydrogen attack by grain boundary diffusion up to about 25 MPa hydrogen. The weld metal however was found to suffer hydrogen attack by the growth of bubbles by power-law creep of the matrix.

  7. The kinetics of catalytic hydrogenation of pyrene-implications for direct coal liquefaction processing

    SciTech Connect

    Stephens, H.P.; Chapman, R.N.

    1983-01-01

    Although recycling heavy solvents has recently re-emerged as a key to cutting the cost of direct coal liquefaction, little data for the hydrogenation of heavy solvent donors have been reported. This study addresses the kinetic and thermodynamic aspects of catalytic hydrogenation of pyrene, a donor solvent precursor thought to play an important role in coal liquefaction processes that use heavy recycle solvents. In the presence of a catalyst, pyrene (Py) is hydrogenated to di- (H/sub 2/Py), tetra- (H/sub 4/Py), hexa- (H/sub 6/Py), deca- (H/sub 10/Py) and perhydro- (H/sub 16/Py) species via a complex mechanism involving a network of reversible parallel and series reactions. Though several studies have dealt with aspects of pyrene hydrogenation, including hydrocracking reactions, reaction product distributions and thermodynamic properties, the kinetics of hydrogenation have not been previously reported. Ultimate application of kinetic and thermodynamic data to direct coal liquefaction must take into consideration the conditions imposed by the particular process used. However, two generalizations may be made regarding hydrogen supplied by the dihydropyrene component of donor solvents: (1) Increasing hydrogen partial pressure increases both the rate at which H/sub 2/Py is formed and the equilibrium concentration of H/sub 2/Py. Therefore, pyrene rehydrogenation should be done at as high a pressure as is cost effective. Although an increase in temperature favors the rate of attainment of equilibrium between Py and H/sub 2/Py, the position of the equilibrium is shifted toward pyrene. Temperature must therefore be adjusted to achieve an optimum trade-off between rate of formation and maximum possible concentration of H/sub 2/Py.

  8. Diffusion of hydrogen within idealized grains of bcc Fe: A kinetic Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Du, Yaojun A.; Rogal, Jutta; Drautz, Ralf

    2012-11-01

    Structural defects in materials such as vacancies, grain boundaries, and dislocations may trap hydrogen and a local accumulation of hydrogen at these defects can lead to the degradation of the materials properties. An important aspect in obtaining insight into hydrogen-induced embrittlement on the atomistic level is to understand the diffusion of hydrogen in these materials. In our study we employ kinetic Monte Carlo (kMC) simulations to investigate hydrogen diffusion in bcc iron within different microstructures. All input data to the kMC model, such as available sites, solution energies, and diffusion barriers, are obtained from first-principles calculations. We find that hydrogen mainly diffuses within the interface region with an overall diffusivity that is lower than in pure bcc Fe bulk. The concentration dependence of the diffusion coefficient is strongly nonlinear and the diffusion coefficient may even decrease with an increasing hydrogen concentration. To describe the macroscopic diffusion coefficient we derive an analytic expression as a function of hydrogen concentrations and temperatures which is in excellent agreement with our numerical results for idealized microstructures.

  9. Mechanisms and kinetics of coal hydrogenation. Quarterly progress report, October-December 1980

    SciTech Connect

    Gary, J H; Baldwin, R M; Bain, R L; Furlong, M W

    1981-01-01

    Colorado School of Mines is engaged in an experimental program to develop comprehensive models for the effects of coal composition upon the kinetics and mechanisms of coal hydrogenation, for the effects of mineral matter additives (disposable catalysts) upon kinetics and mechanisms of coal hydrogenation, and for the kinetics and mechanisms of the hydrogenation of coal-derived products such as preasphaltenes and asphaltenes. Safety modifications to the CSM continuous processing unit were completed to shield the control room from the gas and liquid-solid product sampling systems. A mass balance analysis of sample validity was begun. All but two of sixteen coals in the suite of coal reactivity study coals have been run. Computer modelling of proposed reaction networks was started. Initial efforts at coal property versus reactivity correlations were begun. Feed material preparation for the asphaltene hydrogenation study was completed, and preliminary testing of the reactor system was begun. The experimental portion of the disposable catalyst study screening program was completed. Conclusions are pending statistical analyses of the data.

  10. Influence of hydrogen chemisorption kinetics on the interpretation of hydrogen transport through iron membranes

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.; Taslami, A.; Nelson, H. G.

    1981-01-01

    The influence of a specific surface reaction on the transport of gas-phase hydrogen through iron membranes has been investigated on the basis of model calculations. The surface reaction involves an adsorbed molecular hydrogen precursor between the gas phase and the dissociated chemisorbed state. The calculations demonstrate that the surface reaction for the H2/Fe system makes significant contributions to the time delay associated with the transient hydrogen transport through iron membranes, even under conditions where the steady-state hydrogen transport is independent of the surface reaction. These contributions to the time delay are interpreted in terms of an effective diffusivity, which is a function of the pressure on the entrance side and the thickness of the membrane.