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Sample records for graphite interface studies

  1. Polymer matrix and graphite fiber interface study

    NASA Technical Reports Server (NTRS)

    Adams, D. F.; Zimmerman, R. S.; Odom, E. M.

    1985-01-01

    Hercules AS4 graphite fiber, unsized, or with EPON 828, PVA, or polysulfone sizing, was combined with three different polymer matrices. These included Hercules 3501-6 epoxy, Hercules 4001 bismaleimide, and Hexcel F155 rubber toughened epoxy. Unidirectional composites in all twelve combinations were fabricated and tested in transverse tension and axial compression. Quasi-isotropic laminates were tested in axial tension and compression, flexure, interlaminar shear, and tensile impact. All tests were conducted at both room temperature, dry and elevated temperature, and wet conditions. Single fiber pullout testing was also performed. Extensive scanning electron microphotographs of fracture surfaces are included, along with photographs of single fiber pullout failures. Analytical/experimental correlations are presented, based on the results of a finite element micromechanics analysis. Correlations between matrix type, fiber sizing, hygrothermal environment, and loading mode are presented. Results indicate that the various composite properties were only moderately influenced by the fiber sizings utilized.

  2. Scanning Tunneling Microscopy Study of Molecular Structure: Controlled Monolayer Formation on Graphite at the Liquid-solid Interface

    NASA Astrophysics Data System (ADS)

    Su, C.; Kannappan, K.; Chin, V. Nora; Avila-Bront, L.; Jayaraman, S.; Turro, N. J.; Flynn, G. W.

    2006-03-01

    The self-assembly of heptadecanoic acid 1 and racemic 2-bromoheptadecanoic acid 2 mixtures on the basal plane of a graphite surface has been studied using scanning tunneling microscopy at the liquid-solid interface. The domain structure varies as a function of the ratio of coadsorbed molecules. At lower concentration of acid 2, heptadecanoic acid controls the surface structure by forming a template with fixed lamellar axis-molecular axis angle and domains with alternating R- and S-enantiomer molecular rows. Increasing the concentration of acid 2 leads to the segregation of chiral domains. The inter-correlation between heptadecanoic acid and 2-bromoheptadecanoic acid determines the 2D chiral configuration in the mixed monolayer. A model based on energetically favorable molecular conformations is proposed and will be discussed.

  3. Ordered ionic liquid structure observed at terraced graphite interfaces.

    PubMed

    He, Xing; Wu, Chengyi; Rajagopal, Karjini; Punpongjareorn, Napat; Yang, Ding-Shyue

    2016-02-01

    Reflection high-energy electron diffraction is presented as a contactless, surface-specific method to probe the ion organization and layering at the ionic liquid-solid interfaces. Three regimes can be identified for the structure of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) on highly oriented pyrolytic graphite, which is strongly dependent on the distances of ions from the surface. Direct observations showed that the ultrathin ionic liquid (IL) assembly can exhibit bulk-like phase-transition behaviours as a result of the structural matching between the IL and graphite layers and the confinement template effect due to the surface topography of graphite. The present study illustrates the opportunities for conducting further studies of the structures and ultrafast dynamics of IL-solid interfaces. PMID:26775813

  4. Electronic structure of interfaces between hexagonal and rhombohedral graphite

    NASA Astrophysics Data System (ADS)

    Taut, M.; Koepernik, K.

    2016-07-01

    An analysis of the electronic structure of interfaces between hexagonal (A B ) and rhombohedral (A B C ) graphite based on density functional theory is presented. Both of the two simplest interface structures host (localized) interface bands, which are located around the K point in the Brillouin zone, and which give rise to strong peaks in the density of states at the Fermi level. All interface bands near the Fermi energy are localized at monomers (single atoms with dangling pz orbitals), whereas those around 0.5 eV belong to pz-bonded trimers, which are introduced by the interface and which are not found in the two adjacent bulk substances. There is also an interface band at the (A B ) side of the interface which resembles one of the interface states near a stacking fault in (A B ) graphite.

  5. Oxidation Resistant Graphite Studies

    SciTech Connect

    W. Windes; R. Smith

    2014-07-01

    The Very High Temperature Reactor (VHTR) Graphite Research and Development Program is investigating doped nuclear graphite grades exhibiting oxidation resistance. During a oxygen ingress accident the oxidation rates of the high temperature graphite core region would be extremely high resulting in significant structural damage to the core. Reducing the oxidation rate of the graphite core material would reduce the structural effects and keep the core integrity intact during any air-ingress accident. Oxidation testing of graphite doped with oxidation resistant material is being conducted to determine the extent of oxidation rate reduction. Nuclear grade graphite doped with varying levels of Boron-Carbide (B4C) was oxidized in air at nominal 740°C at 10/90% (air/He) and 100% air. The oxidation rates of the boronated and unboronated graphite grade were compared. With increasing boron-carbide content (up to 6 vol%) the oxidation rate was observed to have a 20 fold reduction from unboronated graphite. Visual inspection and uniformity of oxidation across the surface of the specimens were conducted. Future work to determine the remaining mechanical strength as well as graphite grades with SiC doped material are discussed.

  6. Mechanical and dielectric properties of SEBS modified by graphite inclusion and composite interface

    NASA Astrophysics Data System (ADS)

    Grigorescu, Ramona Marina; Ciuprina, Florin; Ghioca, Paul; Ghiurea, Marius; Iancu, Lorena; Spurcaciu, Bogdan; Panaitescu, Denis Mihaela

    2016-02-01

    Tough and flexible dielectrics were prepared using graphite (G), a natural and low-cost resource, as filler in polystyrene-b-(ethylene-co-butylene)-b-polystyrene (SEBS) and maleinized SEBS (SEBS-MA) matrices. The disintegration of graphite in submicron particles was accomplished by the shear forces during the melt processing step and it was highlighted by atomic force microscopy. Simultaneous increase of tensile strain, strength and Young's modulus was noticed for SEBS/G and SEBS-MA/G composites compared to unfilled matrices, this remarkable feature being previously reported only for some nanocomposites. Moreover, an exponential variation of the dielectric permittivity with the volume fraction of G was obtained. Higher reinforcing efficiency and better dielectric properties were observed in SEBS-MA/G composites, compared to the corresponding SEBS/G composites, due to the stronger polymer-filler interface and better dispersion of graphite. This study brings new insights into nanolevel properties of SEBS composites and it opens new perspectives on high performance composites by using graphite instead of expensive graphene and efficient melt mixing process.

  7. Prediction and measurement of thermal transport across interfaces between isotropic solids and graphitic materials.

    SciTech Connect

    Norris, Pamela M.; Smoyer, Justin L.; Duda, John Charles.; Hopkins, Patrick E.

    2010-06-01

    Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate.

  8. Effect of Co-60 gamma radiation on the mechanical properties of epoxy blends and epoxy-graphite fiber interface

    SciTech Connect

    Netravali, A.N.; Manji, A. )

    1991-06-01

    The effect of Co-60 gamma radiation of up to 100 Mrads on an IM6-G graphite fiber-epoxy interface was studied using the single-fiber-composite (SFC) technique. Flexible epoxy blends were formulated using DGEBA based and polyglycol diepoxide epoxies which were cured with aliphatic and aromatic curing agents. Bulk epoxy specimens and graphite fibers were tension tested to obtain their tensile properties. The fragment length distribution from SFC tests, single fiber strength data, and a Monte Carlo simulation of Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results indicate that while graphite fiber strength is not affected by radiation, the tensile properties of the epoxies used are adversely affected by the radiation. The interfacial shear strength, however, increases significantly with the radiation dose. 36 refs.

  9. Tunable resistance of a carbon nanotube-graphite interface.

    PubMed

    Paulson, S; Helser, A; Nardelli, M B; Taylor, R M; Falvo, M; Superfine, R; Washburn, S

    2000-12-01

    The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices. PMID:11099407

  10. Chemical Erosion Studies of Lithiated Graphite

    NASA Astrophysics Data System (ADS)

    Raman, Priya; Surla, Vijay; Burns, David; Ruzic, David

    2010-11-01

    Lithium evaporation treatments in the National Spherical Torus Experiment (NSTX) have shown dramatic improvements in plasma performance increasing the viability of lithium as Plasma facing Component (PFC) material. In order to understand the complex system of lithiated ATJ graphite, chemical erosion measurements of plain and lithiated ATJ graphite are conducted in the newly built RF plasma facility. A differential pumping scheme is employed and a Residual Gas Analyzer is used for chemical erosion measurements. Target is mounted on a substrate heater (0-500C) and it is connected to a biasing circuitry to allow for temperature dependent studies and energy dependent measurements. To study the effect of lithium on chemical erosion, lithium is evaporated in-situ onto ATJ graphite. The dominant chemical erosion products are known to be CD4 and C2D2. The challenges in measuring C2D2, as it interferes with N2 and CO peaks, are presented. It was found that lithium treatments have suppressed the CD4 signal, and the effect of lithium on other peaks is presented. The effect of temperature on chemical erosion is also investigated and it was found that temperature increases the erosion of graphite.

  11. The formation and stability of the solid electrolyte interface on the graphite anode

    NASA Astrophysics Data System (ADS)

    Agubra, Victor A.; Fergus, Jeffrey W.

    2014-12-01

    The solid electrolyte interface (SEI) layer plays a critical role in the cycle life of Li-ion batteries. The potential difference across the SEI during charging results in the potential for Li+ intercalation at the graphite-SEI interface to be lower than the potential at the SEI-electrolyte interface, which can prevent electrolyte reduction and decomposition. The stability of the SEI layer at certain critical battery operating conditions remains a challenge in the performance of lithium ion batteries. Electrolyte additives and surface modification of the anode electrode have been shown to improve the formation of an effective SEI layer. However, there is still a need for improving the robustness of the SEI to withstand extreme battery operating conditions. In this paper, the formation and stability of the SEI layer for lithium ion batteries is reviewed. This review includes discussion of the formation, growth and stability of the SEI on graphite anode materials.

  12. TEM Study of Internal Crystals in Supernova Graphites

    NASA Astrophysics Data System (ADS)

    Croat, T. K.; Bernatowicz, T.; Stadermann, F. J.; Messenger, S.; Amari, S.

    2003-03-01

    A coordinated TEM and isotopic study of ten supernova (SN) graphites from the Murchison meteorite has revealed many internal grains, mostly titanium carbides (TiCs) and TiC-kamacite composite grains, which were accreted during the graphite growth.

  13. Reaction layer formation at the graphite/copper-chromium alloy interface

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra M.; Michal, Gary M.

    1993-01-01

    Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

  14. Reaction layer formation at the graphite/copper-chromium alloy interface

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra M.; Michal, Gary M.

    1992-01-01

    Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

  15. Development of graphite/copper composites utilizing engineered interfaces. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra M.

    1991-01-01

    In situ measurements of graphite/copper alloy contact angles were made using the sessile drop method. The interfacial energy values obtained from these measurements were then applied to a model for the fiber matrix interfacial debonding phenomenon found in graphite/copper composites. The formation obtained from the sessile drop tests led to the development of a copper alloy that suitably wets graphite. Characterization of graphite/copper alloy interfaces subjected to elevated temperatures was conducted using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Auger Electron Spectroscopy, and X Ray Diffraction analyses. These analyses indicated that during sessile drop tests conducted at 1130 C for 1 hour, copper alloys containing greater than 0.98 at pct chromium form continuous reaction layers of approx. 10 microns in thickness. The reaction layers are adherent to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 deg or less. X ray diffraction results indicate that the reaction layer is Cr3C2.

  16. Anisotropic Thermal and Electrical Properties of Thin Thermal Interface Layers of Graphite Nanoplatelet-Based Composites

    PubMed Central

    Tian, Xiaojuan; Itkis, Mikhail E.; Bekyarova, Elena B.; Haddon, Robert C.

    2013-01-01

    Thermal interface materials (TIMs) are crucial components of high density electronics and the high thermal conductivity of graphite makes this material an attractive candidate for such applications. We report an investigation of the in-plane and through-plane electrical and thermal conductivities of thin thermal interface layers of graphite nanoplatelet (GNP) based composites. The in-plane electrical conductivity exceeds its through-plane counterpart by three orders of magnitude, whereas the ratio of the thermal conductivities is about 5. Scanning electron microscopy reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNP-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNP-based TIMs.

  17. Efficient simulations of the aqueous bio-interface of graphitic nanostructures with a polarisable model.

    PubMed

    Hughes, Zak E; Tomásio, Susana M; Walsh, Tiffany R

    2014-05-21

    To fully harness the enormous potential offered by interfaces between graphitic nanostructures and biomolecules, detailed connections between adsorbed conformations and adsorption behaviour are needed. To elucidate these links, a key approach, in partnership with experimental techniques, is molecular simulation. For this, a force-field (FF) that can appropriately capture the relevant physics and chemistry of these complex bio-interfaces, while allowing extensive conformational sampling, and also supporting inter-operability with known biological FFs, is a pivotal requirement. Here, we present and apply such a force-field, GRAPPA, designed to work with the CHARMM FF. GRAPPA is an efficiently implemented polarisable force-field, informed by extensive plane-wave DFT calculations using the revPBE-vdW-DF functional. GRAPPA adequately recovers the spatial and orientational structuring of the aqueous interface of graphene and carbon nanotubes, compared with more sophisticated approaches. We apply GRAPPA to determine the free energy of adsorption for a range of amino acids, identifying Trp, Tyr and Arg to have the strongest binding affinity and Asp to be a weak binder. The GRAPPA FF can be readily incorporated into mainstream simulation packages, and will enable large-scale polarisable biointerfacial simulations at graphitic interfaces, that will aid the development of biomolecule-mediated, solution-based graphene processing and self-assembly strategies. PMID:24722915

  18. Vacuum Ultraviolet Photon-stimulated Oxidation of Buried Ice: Graphite Grain Interfaces

    NASA Astrophysics Data System (ADS)

    Shi, J.; Grieves, G. A.; Orlando, T. M.

    2015-05-01

    The vacuum ultraviolet (VUV) synthesis of CO and CO2 on ice-coated graphite and isotopic labeled 13C graphite has been examined for temperatures between 40 and 120 K. The results show that CO and CO2 can be formed at the buried ice:graphite interface with Lyα photon irradiation via the reaction of radicals (O and OH) produced by direct photodissociation and the dissociative electron attachment of the interfacial water molecules. The synthesized CO and CO2 molecules can desorb in hot photon-dominated regions and are lost to space when ice coated carbonaceous dust grains cycle within the protoplanetary disks. Thus, the nonthermal formation of CO and CO2 at the buried ice:grain interface by VUV photons may help regulate the carbon inventory during the early stage of planet formation. This may contribute to the carbon deficits in our solar system and suggests that a universal carbon deficit gradient may be expected within astrophysical bodies surrounding center stars.

  19. Floatability study of graphite ore from southeast Sulawesi (Indonesia)

    NASA Astrophysics Data System (ADS)

    Florena, Fenfen Fenda; Syarifuddin, Fahmi; Hanam, Eko Sulistio; Trisko, Nici; Kustiyanto, Eko; Enilisiana, Rianto, Anton; Arinton, Ghenadi

    2016-02-01

    Graphite ore obtained from Kolaka Regency, South East Sulawesi, Indonesia have been succesfully investigated for beneficiation by froth flotation technique. Preliminary study have been done to determine the minerals types, fixed carbon content and liberation size of the graphite. Graphite is naturally floatable due to its hydrophobic property. Some suitable reagents are usually added to increase effectiveness of recovery. In this article, enrichment of graphite by froth flotation was studied by investigating the effect of reagents concentrations, rotation speed and particle size on the carbon grade and recovery of the concentrate. The carbon grade increased from 3.00% to 60.00% at the optimum flotation conditions.

  20. Chemical Sputtering Studies of Lithiated Graphite

    NASA Astrophysics Data System (ADS)

    Raman, Priya; Groll, Andrew; Abrams, Tyler; Curreli, Davide; Andruczyk, Daniel; Ruzic, D. N.

    2012-10-01

    Lithium treatments in the National Spherical Torus Experiment have shown dramatic improvements in plasma performance. In order to understand the complex system of lithiated ATJ graphite, chemical sputtering measurements of plain and lithiated ATJ graphite are conducted in IIAX (Ion Surface Interaction Experiment) facility with a differentially pumped Magnetic Sector Residual Gas Analyzer (MSRGA). The ATJ graphite target is mounted in such way that the target can be translated along a line to different positions to get direct comparison of ATJ and lithiated ATJ. Target is heated using joule heating and is connected to a biasing circuitry. Chemical sputtering of graphite is dependent on the ion energy and substrate temperature, hence the total effects of treating ATJ graphite with lithium in hydrogen plasma is investigated in terms of different target temperatures and bias voltages. For this purpose, lithium is evaporated in-situ onto ATJ graphite and chemically sputtered species in hydrogen plasma is measured using MSRGA. The dominant chemical sputtering product is CH4. It was found that lithium treatments have suppressed the chemical sputtering of ATJ Graphite. The suppression of chemical sputtering effect is presented as a function of varying lithium thickness on ATJ Graphite.

  1. Solder-Graphite Network Composite Sheets as High-Performance Thermal Interface Materials

    NASA Astrophysics Data System (ADS)

    Sharma, Munish; Chung, D. D. L.

    2015-03-01

    Low-cost solder-graphite composite sheets (≥55 vol.% solder), with solder and graphite forming interpenetrating networks to a degree, are excellent thermal interface materials (TIMs). Solders 63Sn-37Pb and 95.5Sn-4Ag-0.5Cu are separately used, with the latter performing better. In composite fabrication, a mixture of micrometer-size solder powder and ozone-treated exfoliated graphite is compressed to form a graphite network, followed by fluxless solder reflow and subsequent hot pressing to form the solder network. The network connectivity (enhanced by ozone treatment) is lower in the through-thickness direction. The electrical conductivity obeys the rule of mixtures (parallel model in-plane and series model through-thickness), with anisotropy 7. Thermal contact conductance ≤26 × 104 W/(m2 K) (with 15- μm-roughness copper sandwiching surfaces), through-thickness thermal conductivity ≤52 W/(m K), and in-plane thermal expansion coefficient 1 × 10-5/°C are obtained. The contact conductance exceeds or is comparable to that of all other TIMs, provided that solder reflow has occurred and the composite thickness is ≤100 μm. Upon decreasing the thickness below 100 μm, the sandwich thermal resistivity decreases abruptly, the composite through-thickness thermal conductivity increases abruptly to values comparable to the calculated values based on the rule of mixtures (parallel model), and the composite-copper interfacial thermal resistivity (rather than the composite resistivity) becomes dominant.

  2. Study of high resistance inorganic coatings on graphite fibers. [for graphite-epoxy composite materials

    NASA Technical Reports Server (NTRS)

    Galasso, F. S.; Veltri, R. D.; Scola, D. A.

    1979-01-01

    Coatings made of boron, silicon carbide, silica, and silica-like materials were studied to determine their ability to increase resistance of graphite fibers. The most promising results were attained by chemical vapor depositing silicon carbide on graphite fiber followed by oxidation, and drawing graphite fiber through ethyl silicate followed by appropriate heat treatments. In the silicon carbide coating studies, no degradation of the graphite fibers was observed and resistance values as high as three orders of magnitude higher than that of the uncoated fiber was attained. The strength of a composite fabricated from the coated fiber had a strength which compared favorably with those of composites prepared from uncoated fiber. For the silica-like coated fiber prepared by drawing the graphite fiber through an ethyl silicate solution followed by heating, coated fiber resistances about an order of magnitude greater than that of the uncoated fiber were attained. Composites prepared using these fibers had flexural strengths comparable with those prepared using uncoated fibers, but the shear strengths were lower.

  3. Low-energy electron diffraction study of potassium adsorbed on single-crystal graphite and highly oriented pyrolytic graphite

    SciTech Connect

    Ferralis, N.; Diehl, R.D.; Pussi, K.; Lindroos, M.; Finberg, S.E.; Smerdon, J.; McGrath, R.

    2004-12-15

    Potassium adsorption on graphite has been a model system for the understanding of the interaction of alkali metals with surfaces. The geometries of the (2x2) structure of potassium on both single-crystal graphite (SCG) and highly oriented pyrolytic graphite (HOPG) were investigated for various preparation conditions for graphite temperatures between 55 and 140 K. In all cases, the geometry was found to consist of K atoms in the hollow sites on top of the surface. The K-graphite average perpendicular spacing is 2.79{+-}0.03 A , corresponding to an average C-K distance of 3.13{+-}0.03 A , and the spacing between graphite planes is consistent with the bulk spacing of 3.35 A. No evidence was observed for a sublayer of potassium. The results of dynamical LEED studies for the clean SCG and HOPG surfaces indicate that the surface structures of both are consistent with the truncated bulk structure of graphite.

  4. Metasomatism and graphite formation at a lithological interface in Malaspina (Alpine Corsica, France)

    NASA Astrophysics Data System (ADS)

    Galvez, Matthieu E.; Martinez, Isabelle; Beyssac, Olivier; Benzerara, Karim; Agrinier, Pierre; Assayag, Nelly

    2013-12-01

    Multiple pieces of geologic evidence suggest that interfaces between contrasted lithologies exert a strong control on the fate of volatiles in subduction zones. Here we present results from a contact between serpentinites and sediments, located in Corsica and metamorphosed in the blueschist facies during the alpine orogeny. It was shown previously that carbonates in the sediments have been reduced to graphitic carbonaceous material within a 5-10-cm-thick reaction zone at the contact with serpentinites. In an effort to investigate the mechanisms governing this unusual process, bulk rock geochemical analyses incorporating a statistical analysis of compositional data are presented. Observations show that the fate of C was decoupled from that of other elements such as O, H, and large-ion lithophile elements—e.g. K, Sr, Ba...,As—that were extensively leached from the reaction zone. Notably, Na is strongly enriched in the reaction zone and structurally linked to pectolite. Reducing conditions, manifested by the depletion of O in the reaction zone compared to the bulk metasediment, were likely maintained by the presence of Fe(II) in the serpentinite. Moreover, thermodynamic calculations show that the low solubility of carbon in COH fluids at high-pressure and low-temperature conditions was the main driver for graphite precipitation synchronously with carbonate destabilization. This may have been kinetically favored by the presence of already existing graphitized carbonaceous material and phengite in the metasediment. Limited lateral flow might have contributed as well to the geochemical and petrological patterns observed in these rocks.

  5. Nickel-Graphite Composite Compliant Interface and/or Hot Shoe Material

    NASA Technical Reports Server (NTRS)

    Firdosy, Samad A.; Chun-Yip Li, Billy; Ravi, Vilupanur A.; Fleurial, Jean-Pierre; Caillat, Thierry; Anjunyan, Harut

    2013-01-01

    Next-generation high-temperature thermoelectric-power-generating devices will employ segmented architectures and will have to reliably withstand thermally induced mechanical stresses produced during component fabrication, device assembly, and operation. Thermoelectric materials have typically poor mechanical strength, exhibit brittle behavior, and possess a wide range of coefficient of thermal expansion (CTE) values. As a result, the direct bonding at elevated temperatures of these materials to each other to produce segmented leg components is difficult, and often results in localized microcracking at interfaces and mec hanical failure due to the stresses that arise from the CTE mismatch between the various materials. Even in the absence of full mechanical failure, degraded interfaces can lead to increased electrical and thermal resistances, which adversely impact conversion efficiency and power output. The proposed solution is the insertion of a mechanically compliant layer, with high electrical and thermal conductivity, between the low- and high-temperature segments to relieve thermomechanical stresses during device fabrication and operation. This composite material can be used as a stress-relieving layer between the thermoelectric segments and/or between a thermoelectric segment and a hot- or cold-side interconnect material. The material also can be used as a compliant hot shoe. Nickel-coated graphite powders were hot-pressed to form a nickel-graphite composite material. A freestanding thermoelectric segmented leg was fabricated by brazing the compliant pad layer between the high-temperature p- Zintl and low-temperature p-SKD TE segments using Cu-Ag braze foils. The segmented leg stack was heated in vacuum under a compressive load to achieve bonding. The novelty of the innovation is the use of composite material that re duces the thermomechanical stresses en - countered in the construction of high-efficiency, high-temperature therm - o-electric devices. The

  6. Efficient simulations of the aqueous bio-interface of graphitic nanostructures with a polarisable model

    NASA Astrophysics Data System (ADS)

    Hughes, Zak E.; Tomásio, Susana M.; Walsh, Tiffany R.

    2014-04-01

    To fully harness the enormous potential offered by interfaces between graphitic nanostructures and biomolecules, detailed connections between adsorbed conformations and adsorption behaviour are needed. To elucidate these links, a key approach, in partnership with experimental techniques, is molecular simulation. For this, a force-field (FF) that can appropriately capture the relevant physics and chemistry of these complex bio-interfaces, while allowing extensive conformational sampling, and also supporting inter-operability with known biological FFs, is a pivotal requirement. Here, we present and apply such a force-field, GRAPPA, designed to work with the CHARMM FF. GRAPPA is an efficiently implemented polarisable force-field, informed by extensive plane-wave DFT calculations using the revPBE-vdW-DF functional. GRAPPA adequately recovers the spatial and orientational structuring of the aqueous interface of graphene and carbon nanotubes, compared with more sophisticated approaches. We apply GRAPPA to determine the free energy of adsorption for a range of amino acids, identifying Trp, Tyr and Arg to have the strongest binding affinity and Asp to be a weak binder. The GRAPPA FF can be readily incorporated into mainstream simulation packages, and will enable large-scale polarisable biointerfacial simulations at graphitic interfaces, that will aid the development of biomolecule-mediated, solution-based graphene processing and self-assembly strategies.To fully harness the enormous potential offered by interfaces between graphitic nanostructures and biomolecules, detailed connections between adsorbed conformations and adsorption behaviour are needed. To elucidate these links, a key approach, in partnership with experimental techniques, is molecular simulation. For this, a force-field (FF) that can appropriately capture the relevant physics and chemistry of these complex bio-interfaces, while allowing extensive conformational sampling, and also supporting inter

  7. Combined friction force microscopy and quantum chemical investigation of the tribotronic response at the propylammonium nitrate-graphite interface.

    PubMed

    Li, H; Atkin, R; Page, A J

    2015-06-28

    The energetic origins of the variation in friction with potential at the propylammonium nitrate-graphite interface are revealed using friction force microscopy (FFM) in combination with quantum chemical simulations. For boundary layer lubrication, as the FFM tip slides energy is dissipated via (1) boundary layer ions and (2) expulsion of near-surface ion layers from the space between the surface and advancing tip. Simulations reveal how changing the surface potential changes the ion composition of the boundary and near surface layer, which controls energy dissipation through both pathways, and thus the friction. PMID:26027558

  8. Experimental study of graphitic nanoribbon films for ammonia sensing

    NASA Astrophysics Data System (ADS)

    Johnson, Jason L.; Behnam, Ashkan; An, Yanbin; Pearton, S. J.; Ural, Ant

    2011-06-01

    We fabricate and study the ammonia sensing properties of graphitic nanoribbon films consisting of multi-layer graphene nanoribbons. These films show very good sensitivity to parts-per-million (ppm) level concentrations of ammonia, which is further enhanced by platinum functionalization, resulting in a relative resistance response of ˜70% when exposed to 50 ppm ammonia. In addition, the sensing response exhibits excellent repeatability and full recovery in air. We also study in detail the dependence of the sensing response on ammonia concentration and temperature. We find that the relative resistance response of the graphitic nanoribbon films shows a power-law dependence on the ammonia concentration, which can be explained based on the Freundlich isotherm. The activation energy obtained from an Arrhenius plot of the temperature-dependent measurements is ˜50 meV, which is consistent with the theoretical calculations of the adsorption energies of ammonia on large graphene sheets and nanoribbons. Their simple and low-cost fabrication process and good sensing response open up the possibility of using graphitic nanoribbon films for large-scale sensing applications.

  9. Micro-mechanical studies on graphite strength prediction models

    NASA Astrophysics Data System (ADS)

    Kanse, Deepak; Khan, I. A.; Bhasin, V.; Vaze, K. K.

    2013-06-01

    The influence of type of loading and size-effects on the failure strength of graphite were studied using Weibull model. It was observed that this model over-predicts size effect in tension. However, incorporation of grain size effect in Weibull model, allows a more realistic simulation of size effects. Numerical prediction of strength of four-point bend specimen was made using the Weibull parameters obtained from tensile test data. Effective volume calculations were carried out and subsequently predicted strength was compared with experimental data. It was found that Weibull model can predict mean flexural strength with reasonable accuracy even when grain size effect was not incorporated. In addition, the effects of microstructural parameters on failure strength were analyzed using Rose and Tucker model. Uni-axial tensile, three-point bend and four-point bend strengths were predicted using this model and compared with the experimental data. It was found that this model predicts flexural strength within 10%. For uni-axial tensile strength, difference was 22% which can be attributed to less number of tests on tensile specimens. In order to develop failure surface of graphite under multi-axial state of stress, an open ended hollow tube of graphite was subjected to internal pressure and axial load and Batdorf model was employed to calculate failure probability of the tube. Bi-axial failure surface was generated in the first and fourth quadrant for 50% failure probability by varying both internal pressure and axial load.

  10. A versatile microcomputer interface and peripheral devices: An application in deuterium lamp background correction graphite furnace atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Gökmen, A.; Yalcin, S.

    1992-01-01

    A versatile interface card for Apple IIe computer and various peripheral devices are designed to control instruments which generates transient signals like in graphite furnace atomic spectrometer. The interface card consists of a multiplexed analog-to-digital converter, a digital-to-analog converter, and a timer/counter chip. The timer/counter chip with 16 built-in registers can be programmed in many modes which provides a time base for real-time measurements. A stepper motor runs under the control of timer/counter chip independent of computer. A light chopper connected to the stepper motor is controlled easily by computer. A dual high-voltage switch can modulate dc light sources under computer control. This system is applied to D2-lamp background correction graphite furnace atomic absorption spectrometer. The D2 lamp is chopped by a mechanical chopper driven by a stepper motor and a hollow cathode lamp is modulated electronically. The data acquisition program is written in machine language and synchronization between light sources and computer is provided by chopper position signal through the interrupts. A sampling rate of 16 during a signal period at 50-Hz chopping frequency is found to be the optimum value. A large number of data collected during atomization period is compressed in machine code. This saved storage space and analysis time.

  11. Coordinated Isotopic and TEM Studies of Presolar Graphites from Murchison

    NASA Astrophysics Data System (ADS)

    Croat, T. K.; Stadermann, F. J.; Zinner, E.; Bernatowicz, T. J.

    2004-03-01

    TEM and NanoSIMS investigations of the same presolar Murchison KFC graphites revealed high Zr, Mo, and Ru content in refractory carbides within the graphites. Along with isotopically light carbon, these suggest a low-metallicity AGB source.

  12. Application of Hybrid Fillers for Improving the Through-Plane Heat Transport in Graphite Nanoplatelet-Based Thermal Interface Layers

    NASA Astrophysics Data System (ADS)

    Tian, Xiaojuan; Itkis, Mikhail E.; Haddon, Robert C.

    2015-08-01

    The in-plane alignment of graphite nanoplatelets (GNPs) in thin thermal interface material (TIM) layers suppresses the though-plane heat transport thus limiting the performance of GNPs in the geometry normally required for thermal management applications. Here we report a disruption of the GNP in-plane alignment by addition of spherical microparticles. The degree of GNP alignment was monitored by measurement of the anisotropy of electrical conductivity which is extremely sensitive to the orientation of high aspect ratio filler particles. Scanning Electron Microscopy images of TIM layer cross-sections confirmed the suppression of the in-plane alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al2O3 and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs.

  13. Application of Hybrid Fillers for Improving the Through-Plane Heat Transport in Graphite Nanoplatelet-Based Thermal Interface Layers

    PubMed Central

    Tian, Xiaojuan; Itkis, Mikhail E.; Haddon, Robert C.

    2015-01-01

    The in-plane alignment of graphite nanoplatelets (GNPs) in thin thermal interface material (TIM) layers suppresses the though-plane heat transport thus limiting the performance of GNPs in the geometry normally required for thermal management applications. Here we report a disruption of the GNP in-plane alignment by addition of spherical microparticles. The degree of GNP alignment was monitored by measurement of the anisotropy of electrical conductivity which is extremely sensitive to the orientation of high aspect ratio filler particles. Scanning Electron Microscopy images of TIM layer cross-sections confirmed the suppression of the in-plane alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al2O3 and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs. PMID:26279183

  14. Photoemission studies of fluorine functionalized porous graphitic carbon

    SciTech Connect

    Ganegoda, Hasitha; Olive, Daniel; Cheng, Lidens; Segre, Carlo U.; Terry, Jeff; Jensen, David S.; Linford, Matthew R.

    2012-03-01

    Porous graphitic carbon (PGC) has unique properties desirable for liquid chromatography applications when used as a stationary phase. The polar retention effect on graphite (PREG) allows efficient separation of polar and non-polar solutes. Perfluorinated hydrocarbons however lack polarizabilty and display strong lipo- and hydrophobicity, hence common lipophilic and hydrophilic analytes have low partition coefficiency in fluorinated stationary phases. Attractive interaction between fluorinated stationary phase and fluorinated analytes results in strong retention compared to non-fluorinated analytes. In order to change the selectivities of PGC, it is necessary to develop a bonded PGC stationary phase. In this study, we have synthesized perfluorinated, PGC using hepatadecafluoro-1-iodooctane, under different temperature conditions. Surface functionalization of the raw material was studied using photoelectron spectroscopy (PES). Results indicate the existence of fluorine containing functional groups, -CF, -CF{sub 2} along with an intercalated electron donor species. Multiple oxygen functional groups were also observed, likely due to the presence of oxygen in the starting material. These oxygen species may be responsible for significant modifications to planer and tetrahedral carbon ratios.

  15. Photoemission studies of fluorine functionalized porous graphitic carbon

    NASA Astrophysics Data System (ADS)

    Ganegoda, Hasitha; Jensen, David S.; Olive, Daniel; Cheng, Lidens; Segre, Carlo U.; Linford, Matthew R.; Terry, Jeff

    2012-03-01

    Porous graphitic carbon (PGC) has unique properties desirable for liquid chromatography applications when used as a stationary phase. The polar retention effect on graphite (PREG) allows efficient separation of polar and non-polar solutes. Perfluorinated hydrocarbons however lack polarizabilty and display strong lipo- and hydrophobicity, hence common lipophilic and hydrophilic analytes have low partition coefficiency in fluorinated stationary phases. Attractive interaction between fluorinated stationary phase and fluorinated analytes results in strong retention compared to non-fluorinated analytes. In order to change the selectivities of PGC, it is necessary to develop a bonded PGC stationary phase. In this study, we have synthesized perfluorinated, PGC using hepatadecafluoro-1-iodooctane, under different temperature conditions. Surface functionalization of the raw material was studied using photoelectron spectroscopy (PES). Results indicate the existence of fluorine containing functional groups, -CF, -CF2 along with an intercalated electron donor species. Multiple oxygen functional groups were also observed, likely due to the presence of oxygen in the starting material. These oxygen species may be responsible for significant modifications to planer and tetrahedral carbon ratios.

  16. Interaction of boron with graphite: A van der Waals density functional study

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Wang, Chen; Liang, Tongxiang; Lai, Wensheng

    2016-08-01

    Boron doping has been widely investigated to improve oxidation resistance of graphite. In this work the interaction of boron with graphite is investigated by a van der Waals density-functional approach (vdW-DF). The traditional density-functional theory (DFT) is well accounted for the binding in boron-substituted graphite. However, to investigate the boron atom on graphite surface and the interstitial impurities require use of a description of graphite interlayer binding. Traditional DFT cannot describe the vdW physics, for instance, GGA calculations show no relevant binding between graphite sheets. LDA shows some binding, but they fail to provide an accurate account of vdW forces. In this paper, we compare the calculation results of graphite lattice constant and cohesive energy by several functionals, it shows that vdW-DF such as two optimized functionals optB88-vdW and optB86b-vdW give much improved results than traditional DFT. The vdW-DF approach is then applied to study the interaction of boron with graphite. Boron adsorption, substitution, and intercalation are discussed in terms of structural parameters and electronic structures. When adsorbing on graphite surface, boron behaves as π electron acceptor. The π electron approaches boron atom because of more electropositive of boron than carbon. For substitution situation, the hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. The B-doped graphite system with the hole has less ability to offer electrons to oxygen, ultimately resulted in the inhibition of carbon oxidation. For interstitial doping, vdW-DFs show more accurate formation energy than LDA. PBE functional cannot describe the interstitial boron in graphite reasonably because of the ignoring binding of graphite sheets. The investigation of electron structures of boron doped graphite will play an important role in understanding the oxidation mechanism in further study.

  17. Ultrafast transformation of graphite to diamond: an ab initio study of graphite under shock compression.

    PubMed

    Mundy, Christopher J; Curioni, Alessandro; Goldman, Nir; Will Kuo, I-F; Reed, Evan J; Fried, Laurence E; Ianuzzi, Marcella

    2008-05-14

    We report herein ab initio molecular dynamics simulations of graphite under shock compression in conjunction with the multiscale shock technique. Our simulations reveal that a novel short-lived layered diamond intermediate is formed within a few hundred of femtoseconds upon shock loading at a shock velocity of 12 kms (longitudinal stress>130 GPa), followed by formation of cubic diamond. The layered diamond state differs from the experimentally observed hexagonal diamond intermediate found at lower pressures and previous hydrostatic calculations in that a rapid buckling of the graphitic planes produces a mixture of hexagonal and cubic diamond (layered diamond). Direct calculation of the x-ray absorption spectra in our simulations reveals that the electronic structure of the final state closely resembles that of compressed cubic diamond. PMID:18532830

  18. Selection process for trade study: Graphite Composite Primary Structure (GCPS)

    NASA Technical Reports Server (NTRS)

    Greenberg, H. S.

    1994-01-01

    This TA 2 document describes the selection process that will be used to identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination. The most suitable unpressurized graphite composite structures and material selections is within this configuration and will be the prototype design for subsequent design and analysis and the basis for the design and fabrication of payload bay, wing, and thrust structure full scale test articles representing segments of the prototype structures. The selection process for this TA 2 trade study is the same as that for the TA 1 trade study. As the trade study progresses additional insight may result in modifications to the selection criteria within this process. Such modifications will result in an update of this document as appropriate.

  19. Two-year biocompatibility study of ORNL graphite.

    PubMed

    Kenner, G H; Williams, W S; Lovell, J E; Eatherly, W P

    1975-07-01

    A new grade of graphite-isotropic, fine-grained, and of superior strength-has been produced at the Oak Ridge National Laboratory. The possibility of using this material in orthopedic implants is under study at the University of Illinois. As part of this program, plugs 1/8 in. in diam were inserted in holes drilled in the proximal femur of 2 groups of 8-week old male rabbits. The groups were sacrificed at the end of 1 and 2 years. A single i.m. injection of achromycin was given 2 days prior to sacrifice. Thin sections of the plugs and surrounding tissue were examined by microradiography and optical microscopy (white light, polarizing, and fluorescent). All bone was normal. Minimal evidence of irritation or fibrous encapsulation appeared. PMID:1176511

  20. Imaging surface nanobubbles at graphite-water interfaces with different atomic force microscopy modes

    NASA Astrophysics Data System (ADS)

    Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

    2013-05-01

    We have imaged nanobubbles on highly ordered pyrolytic graphite (HOPG) surfaces in pure water with different atomic force microscopy (AFM) modes, including the frequency-modulation, the tapping, and the PeakForce techniques. We have compared the performance of these modes in obtaining the surface profiles of nanobubbles. The frequency-modulation mode yields a larger height value than the other two modes and can provide more accurate measurement of the surface profiles of nanobubbles. Imaging with PeakForce mode shows that a nanobubble appears smaller and shorter with increasing peak force and disappears above a certain peak force, but the size returns to the original value when the peak force is reduced. This indicates that imaging with high peak forces does not cause gas removal from the nanobubbles. Based on the presented findings and previous AFM observations, the existing models for nanobubbles are reviewed and discussed. The model of gas aggregate inside nanobubbles provides a better explanation for the puzzles of the high stability and the contact angle of surface nanobubbles.

  1. Brazing graphite to graphite

    DOEpatents

    Peterson, George R.

    1976-01-01

    Graphite is joined to graphite by employing both fine molybdenum powder as the brazing material and an annealing step that together produce a virtually metal-free joint exhibiting properties similar to those found in the parent graphite. Molybdenum powder is placed between the faying surfaces of two graphite parts and melted to form molybdenum carbide. The joint area is thereafter subjected to an annealing operation which diffuses the carbide away from the joint and into the graphite parts. Graphite dissolved by the dispersed molybdenum carbide precipitates into the joint area, replacing the molybdenum carbide to provide a joint of virtually graphite.

  2. Graphitic carbon in the Allende meteorite - A microstructural study

    NASA Technical Reports Server (NTRS)

    Smith, P. P. K.; Buseck, P. R.

    1981-01-01

    High-resolution transmission electron microscopy shows that carbon in the Allende carbonaceous chondrite meteorite is predominantly a poorly crystalline graphite. Such material is of interest as an important carrier of the isotopically anomalous noble gases found in carbonaceous chondrites.

  3. Overall evaluation study for isotropic graphite as fusion first wall material in japan

    NASA Astrophysics Data System (ADS)

    Yamashina, Toshiro; Hino, Tomoaki

    1989-04-01

    Isotropie graphite has been widely used as first wall material in present large fusion devices. For isotropic graphites with different properties, however, overall evaluations with respect to vacuum engineering properties, thermal-mechanical properties and interations with plasmas have not been performed systematically. In 1986, under the support of the Ministry of Education, Science and Culture, the "Graphite Project Team" was organized. Fifteen institutions participated in this project and eighteen isotropic graphites supplied from seven graphite manufactures of Japan were studied as "common samples". From each company, both high- and low-density graphites were supplied since it was presumed that the vacuum engineering and thermal-mechanical properties depended on the density. During an approximately two years research period, we have obtained several interesting results on surface roughness, gas desorption, hydrogen permeation, failure due to heat load and fracture toughness. It was found that the vacuum engineering properties such as the surface area, the gas desorption and the hydrogen permeation depended significanly on the pore structure of the graphite. The surface area increased with the bulk density and the hydrogen permeation rate decreased with the bulk density. The gas desorption was very small for the graphite baked in vacuum. Treated in the same way, the amount of gas released from low-density graphite was smaller. The ash content of the graphite could be reduced to ppm levels by halogen gas treatment. The heat load experiments showed that most of the graphites failed at roughly the same heat load. The measured value of the fracture toughness was approximately the same. The change of the surface morphology by hydrogen ion irradiation and the desorption of trapped ions are also discussed.

  4. Positron annihilation studies of moisture in graphite-reinforced composites

    SciTech Connect

    Singh, J.J.; Holt, W.H.; Mock, W., Jr.

    1980-07-01

    The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

  5. Positron annihilation studies of moisture in graphite-reinforced composites

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Holt, W. H.; Mock, W., Jr.; Buckingham, R. D.

    1980-01-01

    The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

  6. Graphite pseudomorphs after diamonds: An experimental study of graphite morphology and the role of H2O in the graphitisation process

    NASA Astrophysics Data System (ADS)

    Korsakov, Andrey V.; Zhimulev, Egor I.; Mikhailenko, Denis S.; Demin, Sergey P.; Kozmenko, Olga A.

    2015-11-01

    Experiments at 1 atmosphere and 2.0-2.5 GPa over a range of temperatures of 1400-2100 °C have been carried out to investigate the diamond-to-graphite transformation in "dry" and "wet" systems. Internal and external morphologies of graphite pseudomorphs after diamonds were studied by Raman spectroscopy, reflected light microscopy and scanning electron microscopy. In a "dry" system, the results show that at 2.0-2.5 GPa, graphite pseudomorphs preserve the finest details of external morphology of original diamond crystals, whereas at 1 atmosphere only the general outline of diamond crystals can be recognised on these pseudomorphs. In all experimental runs at P = 2.0-2.5 GPa under various temperatures, the growth of oriented graphite crystallites was observed only on the {111} diamond faces, while randomly oriented graphite crystals were observed on the {100} and especially {110} diamond faces. In a "wet" system, we were unable to reproduce graphite pseudomorphs after diamond. However, newly formed large graphite crystals were found on the partly dissolved diamonds. The diamond crystal form has been changed from that of a sharp octahedron to octahedron having rounded edges and corners. Flat-bottomed negatively oriented trigons were formed on the octahedral {111} faces. Large graphite crystals tend to be concentrated at {100} and {110} surfaces. Rare single euhedral graphite flakes occur on the {111} faces. Visible growth spirals on {001} faces of graphite crystals appear on all crystals. The {111} faces of diamond crystal are partly covered by translucent graphite coat. The diamond-to-graphite transformation in the "wet" system occurs via coupled dissolution-precipitation processes. All morphological features (e.g., negatively oriented trigons, rounded edges) described for partly dissolved diamonds are easily recognised. None of these features have been detected so far for partly graphitised metamorphic diamond crystals. Our results suggest that in geological

  7. Thermal charging study of compressed expanded natural graphite/phase change material composites

    DOE PAGESBeta

    Mallow, Anne; Abdelaziz, Omar; Graham, Jr., Samuel

    2016-08-12

    The thermal charging performance of paraffin wax combined with compressed expanded natural graphite foam was studied for different graphite bulk densities. Constant heat fluxes between 0.39 W/cm2 and 1.55 W/cm2 were applied, as well as a constant boundary temperature of 60 °C. Thermal charging experiments indicate that, in the design of thermal batteries, thermal conductivity of the composite alone is an insufficient metric to determine the influence of the graphite foam on the thermal energy storage. By dividing the latent heat of the composite by the time to end of melt for each applied boundary condition, the energy storage performancemore » was calculated to show the effects of composite thermal conductivity, graphite bulk density, and latent heat capacity. For the experimental volume, the addition of graphite beyond a graphite bulk density of 100 kg/m3 showed limited benefit on the energy storage performance due to the decrease in latent heat storage capacity. These experimental results are used to validate a numerical model to predict the time to melt and for future use in the design of heat exchangers with graphite-foam based phase change material composites. As a result, size scale effects are explored parametrically with the validated model.« less

  8. Quantum limit studies in single-crystal and pyrolytic graphite

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Sellmyer, D. J.; Dillon, R. O.; Spain, I. L.

    1974-01-01

    The occupied regions of momentum space in graphite are confined to very elongated volumes near the hexagonal Brillouin zone edges. The elongation is along the hexagonal axis (c axis) so that cross-sectional areas perpendicular to that axis are very small. Hence, when magnetic fields are applied parallel to the c axis only the n = 0 Landau levels remain below the Fermi energy for fields above 7 T (Woollam, 1971). The energy bands in graphite can be described by a set of seven parameters (McClure, 1971) (including the Fermi energy as a parameter). In a quantizing magnetic field the Landau levels are described by a secular equation determined by diagonalizing the Hamiltonian (McClure, 1960). A major unusual feature for the levels along the Brillouin zone edge is that the n = 0 Landau level for electrons is independent of magnetic field, while that for holes is field dependent.

  9. Quantum limit studies in single crystal and pyrolytic graphite

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Sellmyer, D. J.; Dillon, R. O.; Spain, I. L.

    1972-01-01

    The occupied regions of momentum space in graphite are confined to elongated volumes near the hexagonal Brillouin zone edges. The elongation is along the hexagonal axis (c-axis), so that cross sectional areas perpendicular to that axis are very small. When magnetic fields are applied parallel to the c-axis, only the n = 0 Landau levels remain below the Fermi energy for fields above 7 tesla. The energy bands in graphite can be described by a set of seven parameters (including the Fermi energy as a parameter). In a quantizing magnetic field the Landau levels are described by a secular equation determined by diagonalizing the Hamiltonian. A major feature for the levels along the Brillouin zone edge is that the n = 0 Landau level for electrons is independent of magnetic field, while that for holes is field-dependent.

  10. First-principles study of Se-intercalated graphite

    SciTech Connect

    BARTKOWIAK,M.; MODINE,NORMAND A.; SOFO,J.O.; MAHAN,G.D.

    2000-05-11

    Se-intercalated graphite compounds (Se-GICs) are considered as promising candidates for room-temperature thermoelectric cooling devices. Here the authors analyze the crystallographic structure and electronic properties of these materials within the framework of density-functional theory. First, the Adaptive-Coordinate Real-space Electronic Structure (ACRES) code is used to determine the stable structure of a representative stage-2 Se-GIC by relaxing atomic positions. The stable configuration is found to be a pendant-type structure, in which each selenium is bonded covalently to two atoms within the same carbon layer, causing a local distortion of the in-plane conjugation of the graphite. Then, they use the full potential linearized augmented plane wave (FP-LAPW) method to calculate the electronic band structure of the material and discuss its properties. Near the Fermi energy E{sub F}, there are wide bands originating from the host graphitic electronic structure and a few very narrow bands mainly of Se 4p character. The latter bands contribute to high peaks in the density of states close to E{sub F}. They show that this feature, although typical of many good thermoelectrics, does not necessarily imply high thermopower in the case of Se-GICs.

  11. Study of poly(acrylonitrile-methyl methacrylate) as binder for graphite anode and LiMn 2O 4 cathode of Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Zhang, S. S.; Jow, T. R.

    We evaluated poly(acrylonitrile-methyl methacrylate) (AMMA, AN/MMA=94:6) as a binder for the graphite anode and the LiMn 2O 4 cathode of Li-ion batteries by studying the cycling performance of lithium half-cells. The results showed that, using AMMA binder, both graphite and LiMn 2O 4 could be cycled well in 1 m LiPF 6 3:3:4 (weight) PC/EC/EMC electrolyte with less capacity fading. AMMA is chemically more stable than poly(vinylidene fluoride) (PVDF) against the lithiated graphite. More importantly, AMMA can help graphite to form a stable solid electrolyte interface (SEI) film. An impedance study showed that the SEI film formed with AMMA is more stable than the one formed with PVDF. Therefore, self-delithiation of the lithiated graphite can be reduced by use of AMMA instead of PVDF, which improves the storage performance of Li-ion batteries.

  12. Parametric study of graphite foam fins and application in heat exchangers

    NASA Astrophysics Data System (ADS)

    Collins, Michael

    This thesis focuses on the simulation and experimental studies of finned graphite foam extended surfaces to test their heat transfer characteristics and potential applications in condensers. Different fin designs were developed to conduct a parametric study on the thermal effectiveness with respect to thickness, spacing and fin offset angle. Each fin design was computationally simulated to estimate the heat transfer under specific conditions. The simulations showed that this optimal fin configuration could conduct more than 297% the amount of thermal energy as compared to straight aluminum fins. Graphite foam fins were then implemented into a simulation of the condenser system. The condenser was simulated with six different orientations of baffles to examine the incoming vapor and resulting two-phase flow patterns. The simulations showed that using both horizontal and vertical baffling provided the configuration with the highest heat transfer and minimized the bypass regions where the vapor would circumvent the graphite foam. This baffle configuration increased the amount of vapor flow through the inner graphite fins and cold water pipes, which gave this configuration the highest heat transfer. The results from experimental tests using the condenser system confirmed that using three baffles will increase performance consistent with the simulation results. The experimental data showed that the condenser using graphite foam had five times the heat transfer compared to the condenser using only aluminum fins. Incorporating baffles into the condenser using graphite foam enabled this system to conduct nearly ten times more heat transfer than the condenser system which only had aluminum fins without baffles. The results from this research indicate that graphite foam is a far superior material heat transfer enhancement material for heat transfer compared to aluminum used as an extended surface. The longitudinal and horizontal baffles incorporated into the condenser system

  13. Effect of graphite properties in thermal analysis of CHTR: A parametric study

    SciTech Connect

    Kaushik, Ankur; Basak, Abhishek; Dulera, I. V.; Vijayan, P. K.

    2013-06-12

    Compact High Temperature Reactor (CHTR) is a {sup 233}U-Thorium fuelled, lead-bismuth cooled reactor. The CHTR core mainly consists of graphite and beryllium oxide (BeO). The CHTR core consists of nineteen prismatic beryllium oxide (BeO) moderator blocks. These 19 blocks contain centrally located graphite fuel tubes. The BeO moderator blocks are surrounded by reflector blocks (partially graphite and partially BeO). The nuclear heat from the core is removed passively by natural circulation of the coolant between top and bottom plenums, upward through the fuel tubes and returning through the downcomer tubes at the periphery. The temperature gradient in fuel tubes, downcomer tubes and BeO is very high and therefore, to take care of the differential thermal expansion, gaps are provided in the core between the tubes and other core components. These gaps affect the heat transfer through the core in radial direction. In addition, there is a large variation in thermal properties of graphite which in turn affects the thermal behaviour of the core in various operating conditions. The fuel of CHTR is TRISO coated particle fuel. These particles are packed in with graphite powder as matrix and made into cylindrical compacts these compacts are packed in the bores of fuel tube. In this study, the effect of the thermal conductivity variation of the graphite on the temperature distribution of the core and density variation of the matrix graphite material in fuel compact on the maximum fuel kernel temperature is studied along with the overall role of graphite properties variation in heat transfer.

  14. Effect of graphite properties in thermal analysis of CHTR: A parametric study

    NASA Astrophysics Data System (ADS)

    Kaushik, Ankur; Basak, Abhishek; Dulera, I. V.; Vijayan, P. K.

    2013-06-01

    Compact High Temperature Reactor (CHTR) is a 233U-Thorium fuelled, lead-bismuth cooled reactor. The CHTR core mainly consists of graphite and beryllium oxide (BeO). The CHTR core consists of nineteen prismatic beryllium oxide (BeO) moderator blocks. These 19 blocks contain centrally located graphite fuel tubes. The BeO moderator blocks are surrounded by reflector blocks (partially graphite and partially BeO). The nuclear heat from the core is removed passively by natural circulation of the coolant between top and bottom plenums, upward through the fuel tubes and returning through the downcomer tubes at the periphery. The temperature gradient in fuel tubes, downcomer tubes and BeO is very high and therefore, to take care of the differential thermal expansion, gaps are provided in the core between the tubes and other core components. These gaps affect the heat transfer through the core in radial direction. In addition, there is a large variation in thermal properties of graphite which in turn affects the thermal behaviour of the core in various operating conditions. The fuel of CHTR is TRISO coated particle fuel. These particles are packed in with graphite powder as matrix and made into cylindrical compacts these compacts are packed in the bores of fuel tube. In this study, the effect of the thermal conductivity variation of the graphite on the temperature distribution of the core and density variation of the matrix graphite material in fuel compact on the maximum fuel kernel temperature is studied along with the overall role of graphite properties variation in heat transfer.

  15. Nonlinear optical studies of polymer interfaces

    SciTech Connect

    Shen, Y.R. |

    1993-11-01

    Second-order nonlinear optical processes can be used as effective surface probes. They can provide some unique opportunities for studies of polymer interfaces. Here the author describes two examples to illustrate the potential of the techniques. One is on the formation of metal/polymer interfaces. The other is on the alignment of liquid crystal films by mechanically rubbed polymer surfaces.

  16. Electronically induced structure transformations in graphite & silver, studied using ultrafast electron crystallography

    NASA Astrophysics Data System (ADS)

    Raman, Ramani K.

    photoexcited graphite surface. It is shown that such photoemission plays a minor role in the refraction shifts observed in the UEC study and a sub-surface dipole field is sufficient to explain the structural and charge relaxations observed. Investigations utilizing scanning electron microscope imaging of structures generated from laser ablation of graphite reveals the creation of geometrically faceted crystalline features, whose Raman spectrum exhibit sp3 like characteristics, though unambiguous identification of diamond structures generated requires further study. In the case of silver nanocrystals (Ag NC), photoexcitation near the surface plasmon resonance (SPR) is observed to lead to fragmentation at fluences below their melting threshold. By isolating each NC from other neighboring NCs in a surface supported geometry, the normally irreversible process becomes reversible and amenable to multi-shot pump-probe diffraction investigations just below the fragmentation threshold. Transient structural, thermal and Coulombic signatures of the pre-fragmented state are extracted from the UEC investigation and combined with a progressive Reverse Monte-Carlo structure refinement scheme to visualize the atomic dynamics leading up to the fragmentation. Such multi-faceted analysis reveals the fragmentation to proceed through the creation and growth of undercoordinated defect sites along which the lattice is weakened. These defects are likely seeded by the strong coupling between SPR dephasing pathways and inter-band transitions that can lead to bond-softening effects and local valence instabilities. The creation of sufficient number of such defect sites at elevated fluences are believed to lead to the eventual fragmentation of the entire NC. This thesis also details the design and principle of UEC systems employed in a surface probing geometry for the study of nanostructures and interfaces.

  17. Structural efficiency study of graphite-epoxy aircraft rib structures

    NASA Technical Reports Server (NTRS)

    Swanson, Gary D.; Gurdal, Zafer; Starnes, James H., Jr.

    1988-01-01

    Attention is given to the structural efficiencies obtainable with optimally designed graphite/epoxy wing rib panel configurations that are potentially economically manufacturable. Some ribs are commonly used as fuel cell closeout panels, and are accordingly subjected to out-of-plane pressure loads in addition to the in-plane axial compressive and shear loads resulting from the wing loading. The present minimum-weight panel designs satisfy buckling and strength constraints for wing rib panels subjected to a wide range of combined load conditions.

  18. Further studies of the interaction of hydrogen with graphite nanofibers

    SciTech Connect

    Park, C.; Anderson, P.E.; Chambers, A.; Tan, C.D.; Hidalgo, R.; Rodriguez, N.M.

    1999-12-02

    Catalytically grown graphite nanofibers (GNF) are molecularly engineered structures that are produced by the interaction of carbon-containing gases with small metal particles at temperatures around 600 C. The fibrous solids consist of minuscule graphene sheets stacked at various angles with respect to the fiber axis. This arrangement generates a material possessing unique chemical properties because unlike conventional graphite crystals, only edges are exposed. Such a conformation produces a material composed entirely of nanopores that can accommodate small-sized adsorbate molecules, such as hydrogen, in the most efficient manner. In addition, the nonrigid pore walls can expand to accommodate the gas in a multilayer conformation. GNF exhibit extraordinary behavior toward the sorption and retention of hydrogen at high pressures and abnormally high temperatures. In this paper the authors discuss some of the critical factors involved in the adsorption of molecular hydrogen and the influence that this process exerts on the structural characteristics of the material. In addition, the deleterious effect of water vapor on the performance of the GNF is highlighted.

  19. High temperature ceramic interface study

    NASA Technical Reports Server (NTRS)

    Lindberg, L. J.

    1984-01-01

    Monolithic SiC and Si3N4 are susceptible to contact stress damage at static and sliding interfaces. Transformation-toughened zirconia (TTZ) was evaluated under sliding contact conditions to determine if the higher material fracture toughness would reduce the susceptibility to contact stress damage. Contact stress tests were conducted on four commercially available TTZ materials at normal loads ranging from 0.455 to 22.7 kg (1 to 50 pounds) at temperatures ranging from room temperature to 1204C (2200 F). Static and dynamic friction were measured as a function of temperature. Flexural strength measurements after these tests determined that the contact stress exposure did not reduce the strength of TTZ at contact loads of 0.455, 4.55, and 11.3 kg (1, 10, and 25 pounds). Prior testing with the lower toughness SiC and Si3N4 materials resulted in a substantial strength reduction at loads of only 4.55 and 11.3 kg (10 and 25 pounds). An increase in material toughness appears to improve ceramic material resistance to contact stress damage. Baseline material flexure strength was established and the stress rupture capability of TTZ was evaluated. Stress rupture tests determined that TTZ materials are susceptible to deformation due to creep and that aging of TTZ materials at elevated temperatures results in a reduction of material strength.

  20. A kinetic model based on experimental study of structural evolution of natural carbonaceous material to graphite

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Yoshino, T.; Satish-Kumar, M.

    2015-12-01

    We report here new experimental kinetic data on the structural evolution of carbonaceous materials (CM) to graphite in a wide range of temperature conditions (1000 and 1450 °C) and treatment time (10 min to 115 hrs) under a pressure condition of 1GPa. The morphologies and crystallinities of natural CM, extracted from sediments in the Shimanto accretionary complex and Hidaka metamorphic belt, transformed to fully ordered graphite with increasing temperature and annealing duration. The time-temperature relations of each crystal parameter obtained using XRD analysis and micro-Raman spectroscopy demonstrated sigmoidal transformations from amorphous to graphitic structure, suggesting the complexity of chemical reactions undergoing during graphitization. To assess these kinetic processes, the results were analyzed using a superposition method in which the crystal parameters were superposed to reference temperature with non-linear regression curves. The master curves fitted by sigmoidal and power functions exhibited very good correlation coefficients of 0.940 to 0.991, suggesting the Arrhenian relation between temperature and time. On the basis of master curves and shift values, we obtained the effective activation energies of 274 +/- 9 kJmol-1 and 339 +/- 6 kJmol-1 for two different natural CM. When compared with the previous studies, our data gave remarkably low activation energies for natural graphitization, which can be represented in a time-temperature relation. In addition, the sigmoidal functions obtained from time-temperature relations can be extrapolated for low temperature condition at 1GPa. Our kinetic model predicts that if the CM underwent metamorphism for about one million years, it begins to crystallize at ≈ 420 °C and transform to fully ordered graphite at over ≈ 510 °C. Thus, natural graphitization could be discussed by the laboratory experiments using natural precursor materials under realistic pressure condition and time span in the Earth's crust.

  1. Study on joining method for Graphite Epoxy tubes

    NASA Astrophysics Data System (ADS)

    Yamagata, Tasuku; Namba, Kazuroh

    Graphite/Epoxy (GE) tubes are commonly used to construct truss assemblies for spacecraft applications. One of the most important items for developing these tubes is the joining method. The joining of these tubes usually employs metallic end fittings which are adhesively bonded to tubes. These methods, however, are not suitable for joining GE tubes because of heavy weight on metallic end fittings. This paper describes the design, fabrication and evaluation of the whole GE tubes which are formed into screwthreads on the inner surface of the tube simultaneously. Three types of tubes with different fiber arrangement in the region of the screw are designed. 40-mm diameter tubes constituted of 290 GPa modulus fibers in epoxy prepreg are used to fabricate 600 mm length specimens. The specimens are tested to measure the tensile strength and stiffness. The maximum loads of specimens range from 120 kN to 240 kN by the difference in fiber arrangement.

  2. Thermal Charging Study of Compressed Expanded Natural Graphite/Phase Change Material Composites

    SciTech Connect

    Mallow, Anne M; Abdelaziz, Omar; Graham, Samuel

    2016-01-01

    The thermal charging performance of phase change materials, specifically paraffin wax, combined with compressed expanded natural graphite foam is studied under constant heat flux and constant temperature conditions. By varying the heat flux between 0.39 W/cm2 and 1.55 W/cm2 or maintaining a boundary temperature of 60 C for four graphite foam bulk densities, the impact on the rate of thermal energy storage is discussed. Thermal charging experiments indicate that thermal conductivity of the composite is an insufficient metric to compare the influence of graphite foam on the rate of thermal energy storage of the PCM composite. By dividing the latent heat of the composite by the time to melt for various boundary conditions and graphite foam bulk densities, it is determined that bulk density selection is dependent on the applied boundary condition. A greater bulk density is advantageous for samples exposed to a constant temperature near the melting temperature as compared to constant heat flux conditions where a lower bulk density is adequate. Furthermore, the anisotropic nature of graphite foam bulk densities greater than 50 kg/m3 is shown to have an insignificant impact on the rate of thermal charging. These experimental results are used to validate a computational model for future use in the design of thermal batteries for waste heat recovery.

  3. NANOSIMS, TEM, and XANES Studies of a Unique Presolar Supernova Graphite Grain

    NASA Astrophysics Data System (ADS)

    Groopman, Evan; Nittler, Larry R.; Bernatowicz, Thomas; Zinner, Ernst

    2014-07-01

    We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.

  4. NanoSIMS, TEM, and XANES studies of a unique presolar supernova graphite grain

    SciTech Connect

    Groopman, Evan; Bernatowicz, Thomas; Zinner, Ernst; Nittler, Larry R.

    2014-07-20

    We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.

  5. Thermodynamic and kinetic study on interfacial reaction and diamond graphitization of Cu—Fe-based diamond composite

    NASA Astrophysics Data System (ADS)

    Li, Wen-Sheng; Zhang, Jie; Dong, Hong-Feng; Chu, Ke; Wang, Shun-Cai; Liu, Yi; Li, Ya-Ming

    2013-01-01

    Cu—Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressure-assisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu—Fe matrix. The interfacial reactions between diamond/graphite and Cr or Ti, and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods. The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically. The Cr3C2, Cr7C3, Cr23C6, and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.

  6. A micrographic and gravimetric study of intercalation and deintercalation of graphite fibers

    NASA Technical Reports Server (NTRS)

    Hung, C. C.

    1985-01-01

    Intercalation and deintercalation of Union Carbide P-100 graphite fibers with liquid and vaporous bromine was studied gravimetrically and microscopically. The mass of the bromine intercalated fibers was found to be 17 to 20 percent greater than their pristine counterpart. This variation decreased to 17 to 18 percent after heating in air for 3 days at 200 C and to 14.5 to 18 percent after 6 days of 260 C heating. The fiber length did not change throughout the experiment. The fiber diameter increased during intercalation and decreased slightly upon deintercalation but was not affected by heating to 260 C for 3 days in air. Comparing the mass and volume data to those with highly oriented pyrolitic graphite or natural single crystal graphite suggested the possibility that the intercalated P-100 fibers could be mostly stage 4.

  7. Bound and free self-interstitial defects in graphite and bilayer graphene: A computational study

    SciTech Connect

    Gulans, Andris; Puska, Martti J.; Nieminen, Risto M.

    2011-07-01

    The role of self-interstitials in the response of layered carbon materials such as graphite, bilayer graphene and multiwalled carbon nanotubes to irradiation has long remained a puzzle. Using density-functional-theory methods with an exchange and correlation functional which takes into account the interlayer van der Waals interaction in these systems without any material-specific empirical parameters, we study the energetics and migration of single- and di-interstitials in graphite and bilayer graphene. We show that two classes of interstitials, ''bound'' and ''free,'' can coexist. The latter are mobile at room and lower temperatures, which explains the experimental data and reconciles them with the results of atomistic simulations. Our results shed light on the behavior of graphite and carbon nanotubes under irradiation and have implications for irradiation-mediated processing of bilayer graphene.

  8. NMR studies of the conformation and motion of tetrahydrofuran in graphite intercalation compounds

    SciTech Connect

    Caplan, D. F.

    1991-11-01

    The behavior of tetrahydrofuran (THF) molecules intercalated in graphite layers in compounds Cs(THF){sub 1.3}C{sub 24} and K(THF){sub 2.5}C{sub 24} was studied by proton NMR. The graphite layers in these compounds impose a uniform ordering on the THF molecules, giving rise to sharp NMR spectra. Experimental and simulated proton NMR spectra were used to investigate geometry, orientation and conformation of intercalated THF, and to determine whether pseudorotation, a large amplitude low-frequency vibration observed in gaseous THF, can also occur in the constrained environment provided by the graphite intercalation compounds. Deuterium and multiple quantum proton NMR spectra were also simulated in order to determine if these techniques could further refine the proton NMR results.

  9. a Study on the Thermal Vibration Analysis of the Graphite Disk Under Thermal Shock

    NASA Astrophysics Data System (ADS)

    Lee, Young-Shin; Kim, Jae-Hoon; Kim, Hyun-Soo; Kim, Duck-Hoi; Ku, Seong-Hoi; Moon, Soon-Il

    Graphite is applied to structural material of the high temperature reactor and nozzle of high energy rocket engine. The excessive vibration and stress field can be occurred for this material due to the severe thermal condition. In this study, the thermal stress and vibration characteristics of ATJ graphite under high temperature condition are investigated by finite element analysis (FEA). The specimen is designed as a disk shape in order to simulate the rocket nozzle combustion condition. The experiment of thermal heat is also conducted using by CO2 laser.

  10. NMR studies of molecules in liquid crystals and graphite

    SciTech Connect

    Rosen, M.E.

    1992-06-01

    NMR experiments to measure proton dipole couplings were performed on a series of n-alkanes (n-hexane through n-decane) dissolved in nematic liquid crystals. Computer modeling of the experimental NMR-spectra was done using several different models for intermolecular interactions in these systems. The model of Photinos et al. was found to be best in describing the intermolecular interactions in these systems and can provide a statistical picture of the conformation and orientation of the alkane molecules in their partially-oriented environment. Order parameters and conformational distributions for the alkanes can be calculated from the modeling. The alkanes are found to have conformational distributions very much like those found in liquid alkanes. Proton NMR spectra of tetrahydrofuran (THF) intercalated in two graphite intercalation compounds were also measured. Computer simulations of these spectra provide a picture of THF in the constrained environment between the graphene layers where the THF is oriented at a particular angle, can translate and rotate freely, but does not appear to pseudorotate.

  11. Solar thermochemical process interface study

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The design and analyses of a subsystem of a hydrogen production process are described. The process is based on solar driven thermochemical reactions. The subject subsystem receives sulfuric acid of 60% concentration at 100 C, 1 atm pressure. The acid is further concentrated, vaporized, and decomposed (at a rate of 122 g moles/sec H2SO4) into SO2, O2, and water. The produce stream is cooled to 100 C. Three subsystem options, each being driven by direct solar energy, were designed and analyzed. The results are compared with a prior study case in which solar energy was provided indirectly through a helium loop.

  12. X-ray photoelectron spectroscopic studies of graphitic materials and interfacial interactions in carbon-fiber-reinforced polymer composites

    NASA Astrophysics Data System (ADS)

    Viswanathan, Hema L.

    This dissertation involves the X-ray photoelectron spectroscopic (XPS) study of the chemistry associated with carbon fiber-reinforced composites fabricated using PAN-based carbon fibers and a thermoplastic polyimide resin. The mechanical properties of the ultimate composite are significantly affected by the nature of the fiber/matrix interface. Interfacial interaction can be promoted by the electrochemical modification of the fiber surface. The determination of carbon fiber microstructure was conducted through angle-resolved valence band photoemission studies of highly ordered graphite. The change in orientation of the basal planes and reactive edge sites with take-off angle provided a method for the determination of surface microstructure. The electronic structure of solid-state graphite was described using a band structure model and the results obtained were compared with the multiple scattered wave X a calculations. PAN-based fibers were electrochemically oxidized and studied using monochromatic X-radiation. The extremely narrow natural linewidth of the monochromatized Al K a radiation allowed previously unresolved features to be seen. In addition, sample decomposition due to radiative heat from the X-ray source is eliminated. Fibers that were pretreated by the manufacturer were subjected to further electrochemical oxidation. The fibers behaved in an erratic and non-reproducible manner. The surface treatment was removed by heating the fibers in vacuum, followed by XPS analysis and electrochemical oxidation. The fiber/matrix interface was simulated by coating a very thin layer of the polyimide resin on the surface of the fiber followed by XPS analysis. The validity of a proposed structure for the resin was confirmed by comparison with ab initio calculations conducted on the resin repeat unit. A high level of fiber/matrix interaction was observed for electrochemically oxidized fibers. The possibility of solvent interaction with the fiber surface was eliminated by

  13. A molecular dynamics study of diamond and graphite under tritium bombardment

    SciTech Connect

    Dunn, A. R.; Duffy, D. M.

    2011-11-15

    Carbon has proven to be a promising plasma facing material in tokamak reactors because of its high thermal conductivity and limited radiative cooling as a plasma contaminant. It is used in a range of forms, mostly graphitic or amorphous. Diamond, however, has superior thermal properties to other forms of carbon but has been largely overlooked due to fears of graphitisation. Tritium retention is, perhaps, the major disadvantage of using carbon as a plasma facing material in a deuterium-tritium fusion reactor. Here, we use molecular dynamics to study the relative performance of diamond and graphite on exposure to tritium bombardment. We model the cumulative bombarded of diamond and graphitic surfaces with a high flux (10{sup 29} m{sup -2} s{sup -1}) of low energy 15 eV tritium atoms. This was done for substrate temperatures in the range 300-2100 K. Below temperatures of graphitisation ({approx}1000 K) the diamond structure confined tritium to the upper surface, this inhibited further structural damage and resulted in lower total retention. The graphitic surface allowed for deeper tritium penetration and therefore greater retention. These results corroborate with recent experimental evidence.

  14. Mössbauer Study of Graphite-Containing Iron Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Sorescu, Monica; Trotta, Richard

    2016-03-01

    Graphite-doped hematite and magnetite nanoparticles systems (~50 nm) were prepared by mechanochemical activation for milling times ranging from 2 to 12 hours. Their structural and magnetic properties were studied by 57Fe Mössbauer spectroscopy. The spectra corresponding to the hematite milled samples were analyzed by considering two sextets, corresponding to the incorporation of carbon atoms into the iron oxide structure. For ball-milling time of 12 hours a quadrupole split doublet has been added, representing the contribution of ultrafine particles. The Mössbauer spectra of graphite-doped magnetite were resolved considering a sextet and a magnetic hyperfine field distribution, corresponding to the tetrahedral and octahedral sublattices of magnetite, respectively. A quadrupole split doublet was incorporated in the fitting of the 12-hour milled sample. The recoilless fraction for all samples was determined using our previously developed dual absorber method. It was found that the recoilless fraction of the graphite-doped hematite nanoparticles decreases as function of ball-milling time. The f factor of graphite-containing magnetite nanoparticles for the tetrahedral sites stays constant, while that of the octahedral sublattice decreases as function of ball-milling time. These findings reinforce the idea that carbon atoms exhibit preference for the octahedral sites of magnetite.

  15. A study of the structural efficiency of fluted core graphite-epoxy panels

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1990-01-01

    The structural efficiency of compression-loaded graphite-epoxy sandwich panels with fluted cores is studied to determine their weight saving potential. Graphite-epoxy equilateral triangular elements are used to construct the fluted cores for the sandwich panels. Two panel configurations are considered. One configuration has two layers of triangular elements in the fluted core and the second configuration has only one layer of triangular elements in the core. An optimization code is used to find the minimum weight design for each panel configuration. Laminate ply orientations are limited to approx. 45, 0, and 90 deg. A constraint on the axial stiffness is included in the design process so the panel will conform to typical constraints for aircraft wing structures. Minimum thickness requirements for each laminate and maximum allowable strains are also included. A comparison is made of the calculated structural efficiency of the fluted core panels to the structural efficiency of aluminum transport aircraft structures and simple blade-stiffened graphite-epoxy panels. Limited experimental results are also included for comparison with the analytical predictions and to identify the critical failure mechanisms of graphite-epoxy fluted-core sandwich panels.

  16. Gas Gun Studies of Interface Wear Effects

    NASA Astrophysics Data System (ADS)

    Jackson, Tyler; Kennedy, Greg; Thadhani, Naresh

    2011-06-01

    The characteristics of interface wear were studied by performing gas gun experiments at velocities up to 1 km/s. The approach involved developing coefficients of constitutive strength models for Al 6061 and OFHC-Cu, then using those to design die geometry for interface wear gas gun experiments. Taylor rod-on-anvil impact experiments were performed to obtain coefficients of the Johnson-Cook constitutive strength model by correlating experimentally obtained deformed states of impacted samples with those predicted using ANSYS AUTODYN hydrocode. Simulations were used with validated strength models to design geometry involving acceleration of Al rods through a copper concentric cylindrical angular extrusion die. Experiments were conducted using 7.62 mm and 80 mm diameter gas guns. Differences in the microstructure of the interface layer and microhardness values illustrate that stress-strain conditions produced during acceleration of Al through the hollow concentric copper die, at velocities less than 800 m/s, result in formation of a layer via solid state alloying due to severe plastic deformation, while higher velocities produce an interface layer consisting of melted and re-solidified aluminum.

  17. Orientation relationships in graphitic cast irons

    NASA Astrophysics Data System (ADS)

    Kim, Sooho; Phillips, D. S.

    1987-11-01

    Ferrite/graphite and martensite/graphite interfaces in three commercial cast irons have been analyzed using transmission electron microscopy. Two recurring orientation relationships have been found to account for over 60 pct of the ferrite/graphite interfaces analyzed. A similar pair of relationships discovered in martensitic material strongly suggests that the prior austenite/graphite interface was also ordered. The same relationships were prominent in gray and ductile irons. One of the relationships observed can be transformed through the Kurdjumov-Sachs relationship to a previously-reported austenite/graphite relationship.

  18. A vibrational spectroscopy study of the orientational ordering in CH 3 Cl monolayers physisorbed on graphite

    NASA Astrophysics Data System (ADS)

    Nalezinski, R.; Bradshaw, A. M.; Knorr, K.

    1997-12-01

    Methylchloride physisorbed on highly ordered pyrolytic graphite (HOPG) has been investigated by infrared reflection-absorption spectroscopy (IRAS). The results confirm the change in orientation of the molecules from flat to inclined between the two 2D crystalline monolayer phases and the up-down staggering in the inclined phase as suggested by previous diffraction studies. At lower coverages the molecules are found to be oriented perpendicular to the substrate, in disagreement with calculations for single, isolated molecules physisorbed on a smooth graphite surface. Measurements of the transient growth behaviour show that this latter state is long-lived and gives rise to complex growth laws. The results show that IRAS is a valuable tool for the study of physisorbed molecular layers.

  19. Molecular design driving tetraporphyrin self-assembly on graphite: a joint STM, electrochemical and computational study

    NASA Astrophysics Data System (ADS)

    El Garah, M.; Santana Bonilla, A.; Ciesielski, A.; Gualandi, A.; Mengozzi, L.; Fiorani, A.; Iurlo, M.; Marcaccio, M.; Gutierrez, R.; Rapino, S.; Calvaresi, M.; Zerbetto, F.; Cuniberti, G.; Cozzi, P. G.; Paolucci, F.; Samorì, P.

    2016-07-01

    Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to control their organization at the supramolecular level. Such a tuning is particularly important when applied to sophisticated molecules combining functional units which possess specific electronic properties, such as electron/energy transfer, in order to develop multifunctional systems. Here we have synthesized two tetraferrocene-porphyrin derivatives that by design can selectively self-assemble at the graphite/liquid interface into either face-on or edge-on monolayer-thick architectures. The former supramolecular arrangement consists of two-dimensional planar networks based on hydrogen bonding among adjacent molecules whereas the latter relies on columnar assembly generated through intermolecular van der Waals interactions. Scanning Tunneling Microscopy (STM) at the solid-liquid interface has been corroborated by cyclic voltammetry measurements and assessed by theoretical calculations to gain multiscale insight into the arrangement of the molecule with respect to the basal plane of the surface. The STM analysis allowed the visualization of these assemblies with a sub-nanometer resolution, and cyclic voltammetry measurements provided direct evidence of the interactions of porphyrin and ferrocene with the graphite surface and offered also insight into the dynamics within the face-on and edge-on assemblies. The experimental findings were supported by theoretical calculations to shed light on the electronic and other physical properties of both assemblies. The capability to engineer the functional nanopatterns through self-assembly of porphyrins containing ferrocene units is a key step toward the bottom-up construction of multifunctional molecular nanostructures and nanodevices.Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to

  20. Molecular design driving tetraporphyrin self-assembly on graphite: a joint STM, electrochemical and computational study.

    PubMed

    El Garah, M; Santana Bonilla, A; Ciesielski, A; Gualandi, A; Mengozzi, L; Fiorani, A; Iurlo, M; Marcaccio, M; Gutierrez, R; Rapino, S; Calvaresi, M; Zerbetto, F; Cuniberti, G; Cozzi, P G; Paolucci, F; Samorì, P

    2016-07-14

    Tuning the intermolecular interactions among suitably designed molecules forming highly ordered self-assembled monolayers is a viable approach to control their organization at the supramolecular level. Such a tuning is particularly important when applied to sophisticated molecules combining functional units which possess specific electronic properties, such as electron/energy transfer, in order to develop multifunctional systems. Here we have synthesized two tetraferrocene-porphyrin derivatives that by design can selectively self-assemble at the graphite/liquid interface into either face-on or edge-on monolayer-thick architectures. The former supramolecular arrangement consists of two-dimensional planar networks based on hydrogen bonding among adjacent molecules whereas the latter relies on columnar assembly generated through intermolecular van der Waals interactions. Scanning Tunneling Microscopy (STM) at the solid-liquid interface has been corroborated by cyclic voltammetry measurements and assessed by theoretical calculations to gain multiscale insight into the arrangement of the molecule with respect to the basal plane of the surface. The STM analysis allowed the visualization of these assemblies with a sub-nanometer resolution, and cyclic voltammetry measurements provided direct evidence of the interactions of porphyrin and ferrocene with the graphite surface and offered also insight into the dynamics within the face-on and edge-on assemblies. The experimental findings were supported by theoretical calculations to shed light on the electronic and other physical properties of both assemblies. The capability to engineer the functional nanopatterns through self-assembly of porphyrins containing ferrocene units is a key step toward the bottom-up construction of multifunctional molecular nanostructures and nanodevices. PMID:27376633

  1. Trade study plan for Graphite Composite Primary Structure (GCPS)

    NASA Technical Reports Server (NTRS)

    Greenberg, H. S.

    1994-01-01

    This TA 2 document (with support from TA 1) describes the trade study plan that will identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination For this most suitable configuration the structural attachment of the wing, and the most suitable GCPS composite materials for intertank, wing, tail and thrust structure are identified. This trade study analysis uses extensive information derived in the TA 1 trade study plan and is identified within the study plan. In view of this, for convenience, the TA 1 study plan is included as an appendix to this document.

  2. Feasibility Study of Graphite Epoxy Antenna for a Microwave Limb Sounder Radiometer (MLSR)

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Results are presented of a feasibility study to design graphite epoxy antenna reflectors for a jet propulsion laboratory microwave limb sounder instrument (MLSR). Two general configurations of the offset elliptic parabolic reflectors are presented that will meet the requirements on geometry and reflector accuracy. The designs consist of sandwich construction for the primary reflectors, secondary reflector support structure and cross-tie members between reflector pairs. Graphite epoxy materials of 3 and 6 plies are used in the facesheets of the sandwich. An aluminum honeycomb is used for the core. A built-in adjustment system is proposed to reduce surface distortions during assembly. The manufacturing and environmental effects are expected to result in surface distortions less than .0015 inch and pointing errors less than .002 degree.

  3. Two-Fluid Interface Instability Being Studied

    NASA Technical Reports Server (NTRS)

    Niederhaus, Charles E.

    2003-01-01

    The interface between two fluids of different density can experience instability when gravity acts normal to the surface. The relatively well known Rayleigh-Taylor (RT) instability results when the gravity is constant with a heavy fluid over a light fluid. An impulsive acceleration applied to the fluids results in the Richtmyer-Meshkov (RM) instability. The RM instability occurs regardless of the relative orientation of the heavy and light fluids. In many systems, the passing of a shock wave through the interface provides the impulsive acceleration. Both the RT and RM instabilities result in mixing at the interface. These instabilities arise in a diverse array of circumstances, including supernovas, oceans, supersonic combustion, and inertial confinement fusion (ICF). The area with the greatest current interest in RT and RM instabilities is ICF, which is an attempt to produce fusion energy for nuclear reactors from BB-sized pellets of deuterium and tritium. In the ICF experiments conducted so far, RM and RT instabilities have prevented the generation of net-positive energy. The $4 billion National Ignition Facility at Lawrence Livermore National Laboratory is being constructed to study these instabilities and to attempt to achieve net-positive yield in an ICF experiment.

  4. Discrete polygonal supramolecular architectures of isocytosine-based Pt(ii) complexes at the solution/graphite interface.

    PubMed

    El Garah, Mohamed; Sinn, Stephan; Dianat, Arezoo; Santana-Bonilla, Alejandro; Gutierrez, Rafael; De Cola, Luisa; Cuniberti, Gianaurelio; Ciesielski, Artur; Samorì, Paolo

    2016-09-25

    Polygonal supramolecular architectures of a Pt(ii) complex including trimers, tetramers, pentamers and hexamers were self-assembled via hydrogen bonding between isocytosine moieties; their structure at the solid/liquid interface was unravelled by in situ scanning tunneling microscopy imaging. Density functional theory calculations provided in-depth insight into the thermodynamics of their formation by exploring the different energy contributions attributed to the molecular self-assembly and adsorption processes. PMID:27561126

  5. X-ray photoelectron spectroscopy study of catalyzed aluminum carbide formation at aluminum-carbon interfaces

    NASA Technical Reports Server (NTRS)

    Rabenberg, L.; Maruyama, Benji

    1990-01-01

    Aluminum carbide may form at aluminum-graphite interfaces during the high-temperature processing of graphite fiber-reinforced aluminum metal matrix composites. The chemical interactions leading to the formation of the aluminum carbide in the solid state involve the breaking of the carbon-carbon bonds within the graphite, the transport of the carbon atoms across the interface, and the reaction with the aluminum to form Al4C3. The aluminum carbide formation process has been followed using X-ray photoelectron spectroscopy of model, thin-film, reaction couples. The overall reaction is shown to be catalyzed by the presence of water vapor. Water at the interface increases reaction kinetics by apparently weakening the bonds between the surface carbon atoms and their substrate. This result is in general agreement with what is known to occur during the oxidation of graphite in air.

  6. Fluorosulfates of graphite and boron nitride and other high oxidation state studies

    SciTech Connect

    Biagioni, R.N.

    1980-10-01

    The adduct XeF/sub 2/.AsF/sub 5/ was re-examined and assessed to be intermediate between the salt formulation (FXe)/sup +/AsF/sub 6//sup -/ and the fluorine bridged molecular adduct. A series of graphite fluorosulfates were prepared, using as the oxidizing agent S/sub 2/O/sub 6/F/sub 2/, and the effects of incorporating varying amounts of fluorosulfonic acid were studied. Physical data indicated that the S/sub 2/O/sub 6/F/sub 2/ was incorported as SO/sub 3/F/sup -/, and the HSO/sub 3/F was bound tightly, probably due to hydrogen bonding. The c-spacings of HSO/sub 3/F containing materials were larger than those of acid free materials, and the influences of charging, guest size and guest orientation were examined. X-ray diffractometer studies of graphite slabs intercalated with SO/sub 3/F/HSO/sub 3/F and IrF/sub 6/ indicated structures consistent with the characterization of these materials as containing tetrahedral SO/sub 3/F and octahedral IrF/sub 6/. Boron nitride reacted with S/sub 2/O/sub 6/F/sub 2/ to yield a deep blue, conducting intercalation compound. This material was in many respects similar to its graphite analog, but chemically more labile.

  7. Studies of dielectrics on graphite and large-area graphene

    NASA Astrophysics Data System (ADS)

    Pirkle, Adam R.

    Graphene is a promising material as an alternative to Si in future logic devices due to extremely high carrier mobility and other attractive physical and electronic properties. While the exact structure of commercially viable graphene-based device architectures is not yet clear, adoption of graphene in such an architecture will certainly require the deposition of scaled dielectrics. Numerous challenges arise, many due to the surface chemistry of graphene which is dramatically different from that of bulk semiconductors due to the absence of bonding states resulting from the two-dimensional nature of sp2 C-C bonds in graphene. The low surface reactivity means that application of conventional dielectric deposition processes generally results in poor, non-uniform nucleation, hindering dielectric scaling below thicknesses of 20-50 nm. This dissertation focuses on studies of the graphene surface and potential routes to scalable dielectric deposition by means of atomic layer deposition (ALD) and physical vapor deposition (PVD). The role of initial surface condition and cleanliness is considered, and several approaches for the formation of dielectric nucleation layers are studied. Several physical and electrical techniques are employed including x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM) and electrical characterization of graphene FETs and capacitors. Additionally, the lack of commercial availability of high quality large-area graphene samples required for these dielectric studies led to the development of in-house capability for CVD growth of graphene on copper substrates and transfer to insulating substrates. Studies of this growth and transfer process are presented.

  8. AFM and STM studies of the carbonization and graphitization of polyimide films

    NASA Astrophysics Data System (ADS)

    Nysten, B.; Roux, J.-C.; Flandrois, S.; Daulan, C.; Saadaoui, H.

    1993-11-01

    Kapton polyimide and high-modulus polyimide (PPT) films were carbonized and graphitized at various temperatures from 600 to 3000 °C. Their surface was studied by atomic-force microscopy and/or by scanning tunneling microscopy in order to follow the modification of the large-scale morphology and the atomic structure as a function of the heat-treatment temperature (HTT). On the pristine Kapton films, the local order of the molecules is brought to the fore. With increasing HTT (600 to 1000 °C) the structure becomes more disordered while at larger scale a bumpy morphology appears. During graphitization, the bumpy morphology gradually disappears and is replaced by graphitized terraces whose size increases with HTT. At atomic scale, it is shown that the graphene layers progressively grow for HTT higher than 1800 °C. On the films treated between 1800 and 2400 °C, graphene layers containing point defects are imaged and (√3 × √3 )R 30° superstructures are observed near large defects. On the samples treated at 2400 and 2600 °C, moiré patterns are observed and are attributed to stacking faults (turbostratic structure).

  9. Analysis of solid electrolyte interface formation reaction and surface deposit of natural graphite negative electrode employing polyacrylic acid as a binder

    NASA Astrophysics Data System (ADS)

    Ui, Koichi; Fujii, Daisuke; Niwata, Yuki; Karouji, Tomohiro; Shibata, Yu; Kadoma, Yoshihiro; Shimada, Kazuaki; Kumagai, Naoaki

    2014-02-01

    We analyzed the solid electrolyte interface (SEI) formation reaction and surface deposit of a natural graphite (NG-3) electrode employing polyacrylic acid (PAA) as a binder in an ethylene carbonate-based electrolyte because it was reported that the initial charge-discharge characteristics of the NG-3 electrode were improved by employing the PAA binder. Poly(vinylidene fluoride) as a binder was used for comparison. We investigated the influence of the binder types on the coating of the NG-3 particles using the B.E.T. specific surface areas. The difference in the above phenomenon was explained by the relationship between the B.E.T. specific surface area and the irreversible capacity. The surface chemical composition of the NG-3 electrode was investigated by FE-SEM/EDX and XPS and then the difference between the PAA binder and the PVdF binder was discussed. The FE-SEM/EDX and the XPS results showed that the amount of the inorganic components of the SEI was relatively small in the case of the PAA binder NG-3 electrode. The AC impedance results showed that the SEI film resistance of the PAA binder NG-3 electrode was lower at 0.2 V. It was clarified that the binder types affected the coating state, the SEI formation reaction, and the SEI film composition.

  10. The Surface Interface Characteristics of Vertically Aligned Carbon Nanotube and Graphitic Carbon Fiber Arrays Grown by Thermal and Plasma Enhanced Chemical Vapor Deposition

    NASA Technical Reports Server (NTRS)

    Delzeit, Lance; Nguyen, Cattien; Li, Jun; Han, Jie; Meyyappan, M.

    2002-01-01

    The development of nano-arrays for sensors and devices requires the growth of arrays with the proper characteristics. One such application is the growth of vertically aligned carbon nanotubes (CNTs) and graphitic carbon fibers (GCFs) for the chemical attachment of probe molecules. The effectiveness of such an array is dependent not only upon the effectiveness of the probe and the interface between that probe and the array, but also the array and the underlaying substrate. If that array is a growth of vertically aligned CNTs or GCFs then the attachment of that array to the surface is of the utmost importance. This attachment provides the mechanical stability and durability of the array, as well as, the electrical properties of that array. If the detection is to be acquired through an electrical measurement, then the appropriate resistance between the array and the surface need to be fabricated into the device. I will present data on CNTs and GCFs grown from both thermal and plasma enhanced chemical vapor deposition. The focus will be on the characteristics of the metal film from which the CNTs and GCFs are grown and the changes that occur due to changes within the growth process.

  11. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    DOE PAGESBeta

    Appy, David; Lei, Huaping; Han, Yong; Wang, Cai -Zhuang; Tringides, Michael C.; Shao, Dahai; Kwolek, Emma J.; Evans, J. W.; Thiel, P. A.

    2014-11-05

    In this study, we observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  12. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    SciTech Connect

    Appy, David; Lei, Huaping; Han, Yong; Wang, Cai-Zhuang; Tringides, Michael C; Shao, Dahai; Kwolek, Emma J; Evans, J W; Thiel, P A

    2014-11-01

    We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  13. Spectroscopic study of energetic helium-ion irradiation effects on nuclear graphite tiles

    NASA Astrophysics Data System (ADS)

    Kim, Do Wan; Lee, K. W.; Choi, D. M.; Noh, S. J.; Kim, H. S.; Lee, Cheol Eui

    2016-02-01

    Helium ion-irradiation effects on the nuclear graphite tiles were studied in order to understand the structural modifications and damages that can be produced by fusion reaction in tokamaks. The surface morphological changes due to increasing dose of the irradiation were examined by the field-effect scanning electron microscopy, and X-ray photoelectron spectroscopy elucidated the changes in the shallow surface bonding configurations caused by the energetic irradiation. Raman spectroscopy revealed the structural defects and diamond-like carbon sites that increased with increasing irradiation dose, and the average inter-defect distance was found from the Raman peak intensities as a function of the irradiation dose.

  14. GRAPHITE EXTRUSIONS

    DOEpatents

    Benziger, T.M.

    1959-01-20

    A new lubricant for graphite extrusion is described. In the past, graphite extrusion mixtures have bcen composed of coke or carbon black, together with a carbonaceous binder such as coal tar pitch, and a lubricant such as petrolatum or a colloidal suspension of graphite in glycerin or oil. Sinee sueh a lubricant is not soluble in, or compatible with the biiider liquid, such mixtures were difficult to extrude, and thc formed pieees lacked strength. This patent teaches tbe use of fatty acids as graphite extrusion lubricants and definite improvemcnts are realized thereby since the fatty acids are soluble in the binder liquid.

  15. Experimental study on the oxidation of nuclear graphite and development of an oxidation model

    NASA Astrophysics Data System (ADS)

    Kim, Eung Soo; NO, Hee Cheon

    2006-02-01

    The present study investigates the graphite oxidation, which is one of the most serious problems during an air-ingress accident of a high temperature gas-cooled reactor (HTGR). In our study, oxidation experiments have been performed for IG-110 graphite by gas analysis under the various temperatures and oxygen concentrations. As a result, the order of reaction ( n) and activation energy ( Ea) were estimated as 0.75 ± 0.146 and 218 ± 3.76 kJ/mol, respectively within a 95% confidence level. The CO/CO 2 ratios were also measured and compared with Aurthur's and Rossberg's correlations. Most of data lie between their predictions, but for better prediction, an empirical correlation was newly developed. We measured reaction rates and analyzed them with a computational fluid dynamics (CFD) simulation by incorporating the oxidation parameters and the CO/CO 2 ratio estimated here. Finally, an analytical model that includes both the chemical reaction and mass transfer was proposed and validated against experimental data.

  16. Study of conformation and dynamic of surfactant molecules in graphite oxide via NMR

    NASA Astrophysics Data System (ADS)

    Ai, X. Q.; Ma, L. G.

    2016-08-01

    The conformation and dynamic of surfactant in graphite oxide (GO) was investigated by solid-state 13C magic-angle-spinning NMR and 1H-13C cross-polarization/magic-angle-spinning NMR spectra. The conformation ordering of the alkyl chains in the confined system shows strong dependence on its orientation. While the alkyl chains parallel to the GO layer in lateral monolayer arrangement are in gauche conformation in addition to a small amount of all-trans conformation, those with orientation radiating away from the GO in paraffin bilayer arrangement is in all-trans conformation in addition to some gauche conformation even though high-order diffraction peaks appears. NMR results suggest that the least mobile segment is located at the GO-surfactant interface corresponding to the N-methylene group. Further from it, the mobility of the alkyl chain increases. The terminal methyl and N-methyl carbon groups have the highest mobile. The chains in all-trans conformational state are characterized as more rigid than chains with gauche conformation; each segment of the confined alkyl chains with the lateral monolayer arrangement exhibits less mobility as compared to that with the paraffin bilayer arrangement.

  17. Structural study and crystal chemistry of the first stage calcium graphite intercalation compound

    SciTech Connect

    Emery, Nicolas; Herold, Claire . E-mail: Claire.Herold@lcsm.uhp-nancy.fr; Lagrange, Philippe

    2005-09-15

    A novel and efficient synthesis method concerning the preparation of the first stage calcium graphite intercalation compound is provided. It makes use of a reaction between liquid metallic alloy and pyrolytic graphite. From now on it is especially easy to obtain bulk CaC{sub 6} samples. Thanks to such samples, it was possible to study in detail the crystal structure of this binary intercalation compound. It has been entirely specified, so that we know that CaC{sub 6} crystal is rhombohedral and belongs to the R3-bar m space group with the following parameters: a=517pm and {alpha}=49.55 deg. The elemental unit cell contains one calcium atom and six carbon atoms. In this paper, we show also how the various MC{sub 6} structures evolve according to the size of the intercalated element and to the bond nature that appears in the final compound. CaC{sub 6} is unique, since all the other MC{sub 6} compounds exhibit a hexagonal symmetry.

  18. Analytical study of graphite-epoxy tube response to thermal loads

    NASA Technical Reports Server (NTRS)

    Knott, Tamara W.; Hyer, M. W.

    1988-01-01

    The thermally-induced stresses and deformations in graphite-epoxy tubes with aluminum foil bonded to both inner and outer surfaces, and to the outer surface only are computed. Tubes fabricated from three material systems, T300/934, P75s/934, and P75s/BP907, and having a 1 inch inner radius and a lamination sequence of (+15/0 + or - 10/0)sub s are studied. Radial, axial, and circumferential stresses in the various layers of the tube, in the foil, and in the adhesive bonding the foil to the tubes are computed using an elasticity solution. The results indicate that the coatings have no detrimental effect on the stress state in the tube, particularly those stresses that lead to microcracking. The addition of the aluminum foil does, however, significantly influence the axial expansion of the T300/934 tube, the tube with the softer graphite fibers. The addition of foil can change the sign of the axial coefficient of thermal expansion. Twist tendencies of the tubes are only slightly affected by the addition of the coatings, but are of second order compared to the axial response.

  19. Dynamics explorer: Interface definition study, volume 1

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Work done in response to the work statement wherein a specific deliverable was not identified but where design and analysis tasks were identified is reported. The summary and baseline change list is included along with design notes for the spacecraft system, thermal subsystem, power subsystem, communications subsystem, plasma wave instrument interface definition, and the structure.

  20. Graphite-diamond phase coexistence study employing a neural-network mapping of the ab initio potential energy surface

    NASA Astrophysics Data System (ADS)

    Khaliullin, Rustam Z.; Eshet, Hagai; Kühne, Thomas D.; Behler, Jörg; Parrinello, Michele

    2010-03-01

    An interatomic potential for the diamond and graphite phases of carbon has been created using a neural-network (NN) representation of the ab initio potential energy surface. The NN potential combines the accuracy of a first-principles description of both phases with the efficiency of empirical force fields and allows one to perform a molecular-dynamics study, of ab initio quality, of the thermodynamics of graphite-diamond coexistence. Good agreement between the experimental and calculated coexistence curves is achieved if nuclear quantum effects are included in the simulation.

  1. A study of the deposition of carbide coatings on graphite fibers. [to increase electrical resistance

    NASA Technical Reports Server (NTRS)

    Suplinskas, R. J.; Henze, T. W.

    1979-01-01

    The chemical vapor deposition of boron carbide and silicon carbide on graphite fibers to increase their electrical resistance was studied. Silicon carbide coatings were applied without degradation of the mechanical properties of the filaments. These coatings typically added 1000 ohms to the resistance of a filament as measured between two mercury pools. When SiC-coated filaments were oxidized by refluxing in boiling phosphoric acid, average resistance increased by an additional 1000 ohms; in addition resistance increases as high as 150 K ohms and breakdown voltages as high as 17 volts were noted. Data on boron carbide coatings indicated that such coatings would not be effective in increasing resistance, and would degrade the mechanical properties.

  2. Polymer Adsorption on Graphite and CVD Graphene Surfaces Studied by Surface-Specific Vibrational Spectroscopy.

    PubMed

    Su, Yudan; Han, Hui-Ling; Cai, Qun; Wu, Qiong; Xie, Mingxiu; Chen, Daoyong; Geng, Baisong; Zhang, Yuanbo; Wang, Feng; Shen, Y R; Tian, Chuanshan

    2015-10-14

    Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities. PMID:26367247

  3. Comparative Study of Atomic Force Imaging of DNA on Graphite and Mica Surfaces

    NASA Astrophysics Data System (ADS)

    Klinov, Dmitry; Dwir, Benjamin; Kapon, Eli; Borovok, Natalia; Molotsky, Tatiana; Kotlyar, Alexander

    2006-09-01

    Various DNA-based structures (single-, double-, triple-stranded and quadruplex-DNA) were characterized using non-contact atomic-force microscopy on two substrates: modified highly-oriented pyrolitic graphite (HOPG) and mica. Deposition on mica, a conventional substrate used in studies of bio-molecules, results in strong deformation of all above types of molecules while deposition on modified HOPG affects the morphology of DNA much less compared to mica. This is demonstrated by a larger measured height of the DNA molecules deposited on HOPG, as compared to mica, and an increased flexibility of the molecules, evidenced by a shorter molecular end-to-end distance on HOPG. The estimated heights of the triplex and the quadruplex DNA measured on HOPG are similar to the diameter of these molecules in liquid. We thus conclude that modified HOPG is a substrate more suitable than mica for AFM characterization of DNA morphology.

  4. Electronic applications of flexible graphite

    NASA Astrophysics Data System (ADS)

    Luo, Xiangcheng; Chugh, Randy; Biller, Brian C.; Hoi, Yie Meng; Chung, D. D. L.

    2002-05-01

    Flexible graphite is effective for electronic applications, specifically electromagnetic interference (EMI) gasketing, resistive heating, thermoelectric-energy generation, and heat dissipation. It is comparable to or better than conductive-filled silicone materials for EMI gasketing. The shielding effectiveness reaches 125 dB. Flexible graphite as a heating element provides temperatures up to 980°C, response half-time down to 4 sec, and heat output at 60 sec up to 5600 J. The through-thickness, absolute thermoelectric power of flexible graphite is -2.6 µV/°C. Flexible graphite is effective as a thermal-interface material if the thickness is low (0.13 mm), the density is low (1.1 g/cm3), and the contact pressure is high (11.1 MPa). These applications make use of the flexibility and compliance of flexible graphite, in addition to its electronic and thermal behavior. Compliance is particularly important for the use of flexible graphite as interface materials, whether the interface is electrom agnetic, thermoelectric, or thermal.

  5. Comparative study of van der Waals corrections to the bulk properties of graphite

    NASA Astrophysics Data System (ADS)

    Rêgo, Celso R. C.; Oliveira, Luiz N.; Tereshchuk, Polina; Da Silva, Juarez L. F.

    2015-10-01

    Graphite is a stack of honeycomb (graphene) layers bound together by nonlocal, long-range van der Waals (vdW) forces, which are poorly described by density functional theory (DFT) within local or semilocal exchange-correlation functionals. Several approximations have been proposed to add a vdW correction to the DFT total energies (Stefan Grimme (D2 and D3) with different damping functions (D3-BJ), Tkatchenko-Scheffler (TS) without and with self-consistent screening (TS  +  SCS) effects). Those corrections have remarkly improved the agreement between our results and experiment for the interlayer distance (from 3.8 to 0.1%) and high-level random-phase approximation (RPA) calculations for interlayer binding energy (from 56.2 to 0.6%). We report a systematic investigation of various structural, energetic and electron properties with the aforementioned vdW corrections followed by comparison with experimental and theoretical RPA data. Comparison between the resulting relative errors shows that the TS  +  SCS correction provides the best results; the other corrections yield significantly larger errors for at least one of the studied properties. If considerations of computational costs or convergence problems rule out the TS  +  SCS approach, we recommend the D3-BJ correction. Comparison between the computed {πz}Γ\\text{ } -splitting and experimental results shows disagreements of 10% or more with all vdW corrections. Even the computationally more expensive hybrid PBE0 has proved unable to improve the agreement with the measured splitting. Our results indicate that improvements of the exchange-correlation functionals beyond the vdW corrections are necessary to accurately describe the band structure of graphite.

  6. Disposal options for burner ash from spent graphite fuel. Final study report November 1993

    SciTech Connect

    Pinto, A.P.

    1994-08-01

    Three major disposal alternatives are being considered for Fort St. Vrain Reactor (FSVR) and Peach Bottom Reactor (PBR) spent fuels: direct disposal of packaged, intact spent fuel elements; (2) removal of compacts to separate fuel into high-level waste (HLW) and low-level waste (LLW); and (3) physical/chemical processing to reduce waste volumes and produce stable waste forms. For the third alternative, combustion of fuel matrix graphite and fuel particle carbon coatings is a preferred technique for head-end processing as well as for volume reduction and chemical pretreatment prior to final fixation, packaging, and disposal of radioactive residuals (fissile and fertile materials together with fission and activation products) in a final repository. This report presents the results of a scoping study of alternate means for processing and/or disposal of fissile-bearing particles and ash remaining after combustion of FSVR and PBR spent graphite fuels. Candidate spent fuel ash (SFA) waste forms in decreasing order of estimated technical feasibility include glass-ceramics (GCs), polycrystalline ceramic assemblages (PCAs), and homogeneous amorphous glass. Candidate SFA waste form production processes in increasing order of estimated effort and cost for implementation are: low-density GCs via fuel grinding and simultaneous combustion and waste form production in a slagging cyclone combustor (SCC); glass or low-density GCs via fluidized bed SFA production followed by conventional melting of SFA and frit; PCAs via fluidized bed SFA production followed by hot isostatic pressing (HIPing) of SFA/frit mixtures; and high-density GCs via fluidized bed SFA production followed by HIPing of Calcine/Frit/SFA mixtures.

  7. Micro-engineered cathode interface studies

    SciTech Connect

    Doshi, R.; Kueper, T.; Nagy, Z.; Krumpelt, M.

    1997-08-01

    The aim of this work is to increase the performance of the cathode in solid oxide fuel cells (SOFCs) operating at 1,000 C by decreasing the polarization resistance from 0.2 {Omega}-cm{sup 2} at 300 mA/cm{sup 2}. Decreased polarization resistance will allow operation at higher current densities. This work is in support of the Westinghouse tubular SOFC technology using YSZ electrolyte and strontium doped lanthanum manganite (LSM) cathode. As a result of work performed last year at Argonne National Laboratory and information derived from the literature, the limitations at the cathode/electrolyte interface can be classified into two main areas. First, the ionic conductivity of the LSM cathode material is low which limits the reaction zone to an area very close to the interface, while the rest of the cathode thickness acts essentially as current collector with channels for gas access. Second, the electronic conductivity in YSZ is very low which limits the reaction zone to areas that are the boundaries between LSM and YSZ rather than the YSZ surface away from LSM at the interface. Possible solutions to this problem being pursued are: (1) introducing an ionic conducting YSZ phase in LSM to form a porous two-phase mixture of LSM and YSZ; (2) applying a thin interlayer between the electrolyte and the cathode where the interlayer has high ionic and electronic conductivity and high catalytic activity for reduction of O{sub 2}; (3) increasing the ionic conductivity in the LSM by suitable doping; and (4) increasing the electronic conductivity in the electrolyte by doping or by depositing an appropriate mixed conducting layer on the YSZ before applying the cathode.

  8. Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys, and superlattices: Theoretical study of Cu/graphite bonding

    NASA Technical Reports Server (NTRS)

    Lambrecht, Walter R. L.

    1992-01-01

    The goals of the research were to provide a fundamental science basis for why the bonding of Cu to graphite is weak, to critically evaluate the previous analysis of the wetting studies with particular regard to the values used for the surface energies of Cu and graphite, and to make recommendations for future experiments or other studies which could advance the understanding and solution of this technological problem. First principles electronic structure calculations were used to study the problem. These are based on density functional theory in the local density approximation and the use of the linear muffin-tin orbital band structure method. Calculations were performed for graphite monolayers, single crystal graphite with the hexagonal AB stacking, bulk Cu, Cu(111) surface, and Cu/graphite superlattices. The study is limited to the basal plane of graphite because this is the graphite plane exposed to Cu and graphite surface energies and combined with the measured contact angles to evaluate the experimental adhesion energy.

  9. DUSTS AND RESIDUES FROM MACHINING AND INCINERATING GRAPHITE/EPOXY COMPOSITES. A PRELIMINARY STUDY

    EPA Science Inventory

    Preliminary laboratory experiments were carried out to obtain some information on the nature of potential carbon fiber emissions resulting from the machining and incineration of graphite/epoxy composites. Examination of residues by scanning electron microscopy following exposure ...

  10. Dye removal from textile industrial effluents by adsorption on exfoliated graphite nanoplatelets: kinetic and equilibrium studies.

    PubMed

    Carvallho, Marilda N; da Silva, Karolyne S; Sales, Deivson C S; Freire, Eleonora M P L; Sobrinho, Maurício A M; Ghislandi, Marcos G

    2016-01-01

    The concept of physical adsorption was applied for the removal of direct and reactive blue textile dyes from industrial effluents. Commercial graphite nanoplatelets were used as substrate, and the quality of the material was characterized by atomic force and transmission electron microscopies. Dye/graphite nanoplatelets water solutions were prepared varying their pH and initial dye concentration. Exceptionally high values (beyond 100 mg/L) for adsorptive capacity of graphite nanoplatelets could be achieved without complicated chemical modifications, and equilibrium and kinetic experiments were performed. Our findings were compared with the state of the art, and compared with theoretical models. Agreement between them was satisfactory, and allowed us to propose novel considerations describing the interactions of the dyes and the graphene planar structure. The work highlights the important role of these interactions, which can govern the mobility of the dye molecules and the amount of layers that can be stacked on the graphite nanoplatelets surface. PMID:27148721

  11. First-principles study on the adsorption properties of phenylalanine on carbon graphitic structures

    NASA Astrophysics Data System (ADS)

    Kang, Seoung-Hun; Kwon, Dae-Gyeon; Park, Sora; Kwon, Young-Kyun

    2015-12-01

    Using ab-initio density functional theory, we investigate the binding properties of phenylalanine, an amino acid, on graphitic carbon structures, such as graphene, nanotubes, and their modified structures. We focus especially on the effect of the adsorbate on the geometrical and the electronic structures of the absorbents. The phenylalanine molecule is found to bind weakly on pristine graphitic structures with a binding energy of 40-70 meV and not to change the electronic configuration of the graphitic structures, implying that the phenylalanine molecule may not be detected on pristine graphitic structures. On the other hand, the phenylalanine molecule exhibits a substantial increase in its binding energy up to ~2.60 eV on the magnesium-decorated boron-doped graphitic structures. We discover that the Fermi level of the system, which was shifted below the Dirac point of the graphitic structures due to p-doping by boron substitution, can be completely restored to the Dirac point because of the amino acid adsorption. This behavior implies that such modified structures can be utilized to detect phenylalanine molecules.

  12. Carbon isotope fractionation between calcite, graphite and CO2: an experimental study

    NASA Astrophysics Data System (ADS)

    Scheele, Norbert; Hoefs, Jochen

    1992-10-01

    The partitioning of stable carbon isotopes between calcite, graphite and CO2 was experimentally determined at temperatures from 500 to 1200 °C and 1 to 15 kbar pressure. Attainment of carbon isotope equilibrium in CO2-calcite runs was proven by achieving the same fractionation from isotopically opposite directions. The resultant CO2-calcite fractionation curve for carbon differs from Bottinga's calculation by 1.2‰ and confirms recent experiments of Chacko et al. and Mattey et al. In CO2-graphite experiments equilibrium fractions were extrapolated by applying the partial-exchange technique of Northrop and Clayton and by optimizing the contribution of surface reaction in graphite. CO2-graphite fractionations at temperatures up to 800 °C are in fair agreement with Bottinga's calculation, but yield a surprisingly high fractionation of ≈5‰ at upper mantle temperatures. The combination of CO2-calcite (carbon) and CO2-graphite fractionation results in a new experimentally determined calcite-grapite fractionation curve, expressed by the equation: 410_2004_Article_BF00310954_TeX2GIFE1.gif begin{gathered} 10^3 {text{ ln }}α _{{text{cc - gr}}} = 7.99 × 10^6 /T^2 - 9.58 × 10^3 / + 5.76 \\ {text{ (873 - 1473 Kelvin)}} \\ Applying the experimentally determined fractionation curve on graphite-bearing metacarbonates yields metamorphic temperatures distinctly higher than those obtained by Valley and O'Neil.

  13. Study of interaction between radioactive nuclides and graphite surface by the first-principles and statistic physics

    NASA Astrophysics Data System (ADS)

    Luo, Xiaofeng; Fang, Chao; Li, Xin; Lai, Wensheng; Sun, Lifeng; Liang, Tongxiang

    2013-11-01

    The adsorption and desorption of four kinds of main radioactive productions (cesium, iodine, strontium and silver) on graphite surface in high temperature gas cooled reactors (HTGRs) have been studied. Using the first-principles density-functional theory, adsorptive geometry, energy and electron structure on the perfect and defective graphite surfaces have been calculated. It turns out that the adsorption of Cs, I and Sr atoms belongs to chemisorption while the adsorption of Ag is a pure physisorption. When introducing a vacancy in graphite surface, nuclide adatoms will be trapped by the vacancy and form chemical bonds with three nearest neighbor carbon atoms, leading to significant increase of the adsorption energy. In addition, a model of grand canonical ensemble is employed to deduce the adsorption rate as a function of temperature and partial pressure of nuclides produced. The transition temperate from adsorption to desorption of nuclides on graphite surface is defined as the inflexion point of the adsorption rate and its variation with nuclide density is obtained.

  14. A GCMC simulation and experimental study of krypton adsorption/desorption hysteresis on a graphite surface.

    PubMed

    Prasetyo, Luisa; Horikawa, Toshihide; Phadungbut, Poomiwat; Johnathan Tan, Shiliang; Do, D D; Nicholson, D

    2016-09-15

    Adsorption isotherms and isosteric heats of krypton on a highly graphitized carbon black, Carbopack F, have been studied with a combination of Monte Carlo simulation and high-resolution experiments at 77K and 87K. Our investigation sheds light on the microscopic origin of the experimentally observed, horizontal hysteresis loop in the first layer, and the vertical hysteresis-loop in the second layer, and is found to be in agreement with our recent Monte Carlo simulation study (Diao et al., 2015). From detailed analysis of the adsorption isotherm, the latter is attributed to the compression of an imperfect solid-like state in the first layer, to form a hexagonally packed, solid-like state, immediately following the first order condensation of the second layer. To ensure that capillary condensation in the confined spaces between microcrystallites of Carbopack F does not interfere with these hysteresis loops, we carried out simulations of krypton adsorption in the confined space of a wedge-shaped pore that mimics the interstices between particles. These simulations show that, up to the third layer, any such interference is negligible. PMID:27343464

  15. A study of void effects on the interlaminar shear strength of unidirectional graphite fiber reinforced composites

    NASA Technical Reports Server (NTRS)

    Bowles, Kenneth J.; Frimpong, Stephen

    1990-01-01

    A study was conducted to evaluate the effect of voids on the interlaminar shear strength (ILSS) of a polyimide matrix composite system. The graphite/PRM-15 composite was chosen for study because of the extensive amount of experience that has been amassed in the processing of this material. Composite densities and fiber contents of more than thirty different laminates were measured along with ILSS. Void contents were calculated and the void geometry and distribution were noted using microscopic techniques such as those used in metallography. It was found that there was a good empirical correlation between ILSS and composite density. The most acceptable relationship between the ILSS and density was found to be a power equation which closely resembles theoretically derived expressions. An increase in scatter in the strength data was observed as the void content increased. In laminates with low void content, the void appears to be more segregated in one area of the laminate. It was found that void free composites could be processed in matched metal die molds at pressures greater than 1.4 and less than 6.9 MPa.

  16. Spectroscopic study of graphene nanoribbons formed by crystallographic etching of highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Sugiyama, Yoshihiro; Kubo, Osamu; Omura, Ryosuke; Shigehara, Masaaki; Tabata, Hiroshi; Mori, Nobuya; Katayama, Mitsuhiro

    2014-09-01

    We report a scanning tunneling spectroscopy study systematically performed on graphene nanoribbons (GNRs) with various widths and layer numbers. The GNRs are formed on highly oriented pyrolytic graphite (HOPG) by crystallographic etching, as reported by Datta and co-workers [Nano Lett. 8, 1912 (2008)]. Regardless of the width and layer numbers, GNRs having zigzag edges exhibit a peak at the Fermi energy in their local density of states (LDOS) when measured near the edges, whereas no peak appears away from the edges. On the other hand, a depression of the LDOS emerges at the Fermi energy in the case of a GNR having armchair edges with no relation to the measured position in an identical GNR. The energy gap of the LDOS depression monotonically decreases with increasing GNR width, whereas there is no apparent dependence on the layer numbers. By comparison with the band structure calculated by a nearest-neighbor tight-binding method, it is suggested that the overlap of wave functions between the topmost layer and the underlayers is negligible, resulting in an LDOS similar to that on an isolated monolayer GNR even on an HOPG substrate. From the quantitative scaling of energy gaps (Egap) of LDOS depression with respect to GNR widths (W), the relation between the two is obtained as Egap = 1.9 [eV nm]/W.

  17. Laboratory simulation and modeling of size, shape distributed interstellar graphite dust analogues: A comparative study

    NASA Astrophysics Data System (ADS)

    Boruah, Manash J.; Gogoi, Ankur; Ahmed, Gazi A.

    2016-06-01

    The computation of the light scattering properties of size and shape distributed interstellar graphite dust analogues using discrete dipole approximation (DDA) is presented. The light scattering properties of dust particles of arbitrary shapes having sizes ranging from 0.5 to 5.0 μm were computed using DDSCAT 7.3.0 software package and an indigenously developed post-processing tool for size and shape averaging. In order to model realistic samples of graphite dust and compute their light scattering properties using DDA, different target geometries were generated to represent the graphite particle composition in terms of surface smoothness, surface roughness and aggregation or their combination, for using as the target for DDSCAT calculations. A comparison of the theoretical volume scattering function at 543.5 nm and 632.8 nm incident wavelengths with laboratory simulation is also presented in this paper.

  18. Energy corrugation in atomic-scale friction on graphite revisited by molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Sun, Xiao-Yu; Qi, Yi-Zhou; Ouyang, Wengen; Feng, Xi-Qiao; Li, Qunyang

    2015-12-01

    Although atomic stick-slip friction has been extensively studied since its first demonstration on graphite, the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics (MD) simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding (known as energy corrugation) comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces. For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However, for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.

  19. Experimental study of interface properties between layer and substrate

    NASA Astrophysics Data System (ADS)

    Ko, Ray T.; Nagy, Peter B.; Adler, Laszlo

    A meshed intervening layer technique which makes it possible to study the interface properties between layer and substrate is presented. It is argued that the bonding condition of the interface can be monitored through the variation of the phase velocity of the modified Rayleigh mode. The experimental setup of the measurement of the reflection of ultrasonic waves from a layered substrate specimen is shown, and the frequency spectra from three typical bonding cases - perfectly bonded, partially bonded, and completely misbonded - are illustrated.

  20. In situ scanning tunneling microscopy studies of the SEI formation on graphite electrodes for Li(+)-ion batteries.

    PubMed

    Seidl, Lukas; Martens, Slađana; Ma, Jiwei; Stimming, Ulrich; Schneider, Oliver

    2016-08-01

    The SEI-formation on graphitic electrodes operated as an Li(+)-ion battery anode in a standard 1 M LiPF6 EC/DMC (1 : 1) electrolyte has been studied in situ by EC-STM. Two different modes of in situ study were applied, one, which allowed to follow topographic and crystallographic changes (solvent cointercalation, graphite exfoliation, SEI precipitation on the HOPG basal plane) of the graphite electrode during SEI-formation, and the second, which gave an insight into the SEI precipitation on the HOPG basal plane in real time. From the in situ EC-STM studies, not only conclusions about the SEI-topography could be drawn, but also about the formation mechanism and the chemical composition, which strongly depend on the electrode potential. It was shown that above 1.0 V vs. Li/Li(+) the SEI-formation is still reversible, since the molecular structure of the solvent molecules remains intact during an initial reduction step. During further reduction, the molecular structures of the solvents are destructed, which causes the irreversible charge loss. The STM studies were completed by electrochemical methods, like cyclic voltammetry, the potentiostatic intermittent titration technique and charge/discharge tests of MCMB electrodes. PMID:27140292

  1. Study of GaAs-oxide interface by transient capacitance spectroscopy - Discrete energy interface states

    NASA Technical Reports Server (NTRS)

    Kamieniecki, E.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

    1980-01-01

    Interface states and bulk GaAs energy levels were simultaneously investigated in GaAs MOS structures prepared by anodic oxidation. These two types of energy levels were successfully distinguished by carrying out a comparative analysis of deep level transient capacitance spectra of the MOS structures and MS structures prepared on the same samples of epitaxially grown GaAs. The identification and study of the interface states and bulk levels was also performed by investigating the transient capacitance spectra as a function of the filling pulse magnitude. It was found that in the GaAs-anodic oxide interface there are states present with a discrete energy rather than with a continuous energy distribution. The value of the capture cross section of the interface states was found to be 10 to the 14th to 10 to the 15th/sq cm, which is more accurate than the extremely large values of 10 to the -8th to 10 to the -9th/sq cm reported on the basis of conductance measurements.

  2. Physicochemical Characterization, and Relaxometry Studies of Micro-Graphite Oxide, Graphene Nanoplatelets, and Nanoribbons

    PubMed Central

    Paratala, Bhavna S.; Jacobson, Barry D.; Kanakia, Shruti; Francis, Leonard Deepak; Sitharaman, Balaji

    2012-01-01

    The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn2+ ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents. PMID:22685555

  3. High-temperature compatibility study of iridium (DOP-26 alloy) with graphite and plutonia

    SciTech Connect

    Axler, K.M.; Eash, D.T.

    1987-12-01

    This report outlines the materials compatibility tests conducted on DOP-26 iridium alloy and carbon. The carbon used was in the form of woven graphite as present in the impact shell used to encase plutonia in nuclear heat sources. In addition, compatibility tests of the DOP-26 alloy with plutonia are described. The reactivity observed in both systems is discussed. 4 refs., 6 figs.

  4. Styrene-terminated polysulfone oligomers as matrix material for graphite reinforced composites - An initial study

    NASA Technical Reports Server (NTRS)

    Garcia, Dana; Bowles, Kenneth J.; Vannucci, Raymond D.

    1987-01-01

    Results pertaining to graphite reinforced composites containing styrene-terminated oligomers as the matrix material are summarized. The processing parameters are determined and the properties of the resulting composite are evaluated. In terms of solvent impregnation techniques, CH2Cl2 is the preferred solvent due to its easy removal during the prepreg drying and consolidation steps.

  5. Lifetime experimental study of graphite cathode for relativistic backward wave oscillator

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Sun, Jun; Chen, Changhua

    2016-07-01

    Graphite cathodes are widely used due to their good emission properties, especially their long lifetime. Some previous papers have researched their lifetime under certain conditions and uncovered some important phenomena. This paper is dedicated to research the lifetime of the graphite cathode under higher power. In the lifetime test, the voltage and current amplitudes are about 970 kV and 9.7 kA, respectively. The repetition rate is 20 Hz. An X-band relativistic backward wave oscillator is used to generate high power microwave by utilizing the electron beam energy. The experimental results demonstrate that the emission property of the graphite cathode remains quite stable during 105 pulses, despite some slight deteriorations regarding the beam and microwave parameters. The macroscopic morphology change of the cathode blade due to material evaporation is observed by a laser microscope. The mass loss of the graphite cathode is about 60 μg/C. Meanwhile, the observation by a scanning electron microscope uncovers that the original numerous flaky micro-structures are totally replaced by a relatively smooth surface at the mid region of the cathode blade and a large number of new micro-protrusions at the blade edges during the lifetime test.

  6. Experimental Study of the Effect of Graphite Dispersion on the Heat Transfer Phenomena in a Reactor Cavity Cooling System

    SciTech Connect

    Vaghetto, Rodolfo; Capone, Luigi; Hassan, Yassin A

    2011-05-31

    An experimental activity was performed to observe and study the effects of graphite dispersion and deposition on thermal-hydraulic phenomena in a reactor cavity cooling system (RCCS). The small-scale RCCS experimental facility (16.5 x 16.5 x 30.4 cm) used for this activity represents half of the reactor cavity with an electrically heated vessel. Water flowing through five vertical pipes removes the heat produced in the vessel and releases it into the environment by mixing with cold water in a large tank. The particle image velocimetry technique was used to study the velocity field of the air inside the cavity. A set of 52 thermocouples was installed in the facility to monitor the temperature profiles of the vessel, pipe walls, and air. Ten grams of a fine graphite powder (average particle size 2 m) was injected into the cavity through a spraying nozzle placed at the bottom of the vessel. The temperatures and air velocity field were recorded and compared with the measurements obtained before the graphite dispersion, showing a decrease of the temperature surfaces that was related to an increase in their emissivity. The results contribute to the understanding of RCCS capability in an accident scenario.

  7. Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

    PubMed Central

    Müller, Thomas; Werblowsky, Tova L.; Florio, Gina M.; Berne, Bruce J.; Flynn, George W.

    2005-01-01

    A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for self-assembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent. PMID:15758073

  8. Interlayer interactions in graphites

    PubMed Central

    Chen, Xiaobin; Tian, Fuyang; Persson, Clas; Duan, Wenhui; Chen, Nan-xian

    2013-01-01

    Based on ab initio calculations of both the ABC- and AB-stacked graphites, interlayer potentials (i.e., graphene-graphene interaction) are obtained as a function of the interlayer spacing using a modified Möbius inversion method, and are used to calculate basic physical properties of graphite. Excellent consistency is observed between the calculated and experimental phonon dispersions of AB-stacked graphite, showing the validity of the interlayer potentials. More importantly, layer-related properties for nonideal structures (e.g., the exfoliation energy, cleave energy, stacking fault energy, surface energy, etc.) can be easily predicted from the interlayer potentials, which promise to be extremely efficient and helpful in studying van der Waals structures. PMID:24192753

  9. Interlayer interactions in graphites

    NASA Astrophysics Data System (ADS)

    Chen, Xiaobin; Tian, Fuyang; Persson, Clas; Duan, Wenhui; Chen, Nan-Xian

    2013-11-01

    Based on ab initio calculations of both the ABC- and AB-stacked graphites, interlayer potentials (i.e., graphene-graphene interaction) are obtained as a function of the interlayer spacing using a modified Möbius inversion method, and are used to calculate basic physical properties of graphite. Excellent consistency is observed between the calculated and experimental phonon dispersions of AB-stacked graphite, showing the validity of the interlayer potentials. More importantly, layer-related properties for nonideal structures (e.g., the exfoliation energy, cleave energy, stacking fault energy, surface energy, etc.) can be easily predicted from the interlayer potentials, which promise to be extremely efficient and helpful in studying van der Waals structures.

  10. [Study on the determination of trace gallium in molybdenum-coated pyrolytic graphite tube by electrothermal absorption spectrometry].

    PubMed

    Huang, Yu-an; Zhou, Fang-qin; Long, Si-hua; Yang, Liu

    2004-02-01

    The effects on gallium atomization in the pyrolytic graphite tube imposed by different matrix modifiers and different coatings were discussed detailedly in this paper. In the presence of matrix modifier of Ni(NO3)2 the matrix interference was eliminated efficiently. The pyrolytic graphite tubes were coated differently with lanthanum, zirconium, and molybdenum to avoid producing gallium carbide. Results showed that the tube with molybdenum coating was the best. On this basis, the mechanism of gallium atomization in the molybdenum-coated pyrolytic graphite tube using Ni(NO3)2 as a matrix modifier was studied furthermore; in addition, the parameters of the operation were optimized. As a result, a new method improved in many aspects was developed to detect trace gallium in complicated sample of gangue. The outcomes of practical applications indicated that the method could satisfy the requests of analysis and that the manipulations were simple to achieve. The characteristic content, the detection limit, and the adding recoveries were 2.12 x 10(-11) g, 1.4 x 10(-10) g and 97.4%-102.7% respectively, and the relative standard deviation was less than or equal to 3.6% (n = 11). PMID:15769028

  11. Combined study of the ground and unoccupied electronic states of graphite by electron energy-loss spectroscopy

    SciTech Connect

    Feng, Zhenbao; Löffler, Stefan; Eder, Franz; Meyer, Jannik C.; Su, Dangsheng; Schattschneider, Peter

    2013-11-14

    Both the unoccupied and ground electronic states of graphite have been studied by electron energy-loss spectroscopy in a transmission electron microscope. Electron energy-loss near-edge structures of the K-edge of carbon have been investigated in detail for scattering angles from 0 to 2.8 mrad. The π{sup *} and σ{sup *} components were separated. The angular and energy dependences of the π{sup *} and σ{sup *} structures were in fair agreement with theory. Electron energy loss Compton spectra of graphite were recorded at scattering angles from 45 to 68 mrad. One Compton scattering spectrum was obtained in 1 min compared with several hours or days using photons. The contributions of core electrons were calculated by the exact Hartree-Slater method in the Compton scattering region. The electron Compton profile for graphite is in good agreement with other conventional Compton profile measurements, as well as with theory, thus establishing the validity of the technique.

  12. Interfaces in polymer nanocomposites - An NMR study

    NASA Astrophysics Data System (ADS)

    Böhme, Ute; Scheler, Ulrich

    2016-03-01

    Nuclear Magnetic Resonance (NMR) is applied for the investigation of polymer nanocomposites. Solid-state NMR is applied to study the modification steps to compatibilize layered double hydroxides with non-polar polymers. 1H relaxation NMR gives insight on the polymer dynamics over a wide range of correlation times. For the polymer chain dynamics the transverse relaxation time T2 is most suited. In this presentation we report on two applications of T2 measurements under external mechanical stress. In a low-field system relaxation NMR studies are performed in-situ under uniaxial stress. High-temperature experiments in a Couette cell permit the investigation of the polymer dynamics in the melt under shear flow.

  13. Thermally exfoliated graphite oxide

    NASA Technical Reports Server (NTRS)

    Prud'Homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor); Abdala, Ahmed (Inventor)

    2011-01-01

    A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from about 300 sq m/g to 2600 sq m/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as determined by X-ray diffraction.

  14. High speed hydrogen/graphite interaction

    NASA Technical Reports Server (NTRS)

    Kelly, A. J.; Hamman, R.; Sharma, O. P.; Harrje, D. T.

    1974-01-01

    Various aspects of a research program on high speed hydrogen/graphite interaction are presented. Major areas discussed are: (1) theoretical predictions of hydrogen/graphite erosion rates; (2) high temperature, nonequilibrium hydrogen flow in a nozzle; and (3) molecular beam studies of hydrogen/graphite erosion.

  15. Computer modelling studies of the bilayer/water interface.

    PubMed

    Pasenkiewicz-Gierula, Marta; Baczynski, Krzysztof; Markiewicz, Michal; Murzyn, Krzysztof

    2016-10-01

    This review summarises high resolution studies on the interface of lamellar lipid bilayers composed of the most typical lipid molecules which constitute the lipid matrix of biomembranes. The presented results were obtained predominantly by computer modelling methods. Whenever possible, the results were compared with experimental results obtained for similar systems. The first and main section of the review is concerned with the bilayer-water interface and is divided into four subsections. The first describes the simplest case, where the interface consists only of lipid head groups and water molecules and focuses on interactions between the lipid heads and water molecules; the second describes the interface containing also mono- and divalent ions and concentrates on lipid-ion interactions; the third describes direct inter-lipid interactions. These three subsections are followed by a discussion on the network of direct and indirect inter-lipid interactions at the bilayer interface. The second section summarises recent computer simulation studies on the interactions of antibacterial membrane active compounds with various models of the bacterial outer membrane. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:26825705

  16. A study of the effect of selected material properties on the ablation performance of artificial graphite

    NASA Technical Reports Server (NTRS)

    Maahs, H. G.

    1972-01-01

    Eighteen material properties were measured on 45 different, commercially available, artificial graphites. Ablation performance of these same graphites were also measured in a Mach 2 airstream at a stagnation pressure of 5.6 atm. Correlations were developed, where possible, between pairs of the material properties. Multiple regression equations were then formulated relating ablation performance to the various material properties, thus identifying those material properties having the strongest effect on ablation performance. These regression equations reveal that ablation performance in the present test environment depends primarily on maximum grain size, density, ash content, thermal conductivity, and mean pore radius. For optimization of ablation performance, grain size should be small, ash content low, density and thermal conductivity high, and mean pore radius large.

  17. High Resolution Angle Resolved Photoemission Studies on Quasi-Particle Dynamics in Graphite

    SciTech Connect

    Leem, C.S.

    2010-06-02

    We obtained the spectral function of the graphite H point using high resolution angle resolved photoelectron spectroscopy (ARPES). The extracted width of the spectral function (inverse of the photo-hole lifetime) near the H point is approximately proportional to the energy as expected from the linearly increasing density of states (DOS) near the Fermi energy. This is well accounted by our electron-phonon coupling theory considering the peculiar electronic DOS near the Fermi level. And we also investigated the temperature dependence of the peak widths both experimentally and theoretically. The upper bound for the electron-phonon coupling parameter is 0.23, nearly the same value as previously reported at the K point. Our analysis of temperature dependent ARPES data at K shows that the energy of phonon mode of graphite has much higher energy scale than 125K which is dominant in electron-phonon coupling.

  18. Cryotribology of diamond and graphite

    SciTech Connect

    Iwasa, Yukikazu; Ashaboglu, A.F.; Rabinowicz, E.R.

    1996-12-31

    An experimental study was carried out on the tribological behavior of materials of interest in cryogenic applications, focusing on diamond and graphite. Both natural diamond (referred in the text as diamond) and chemical-vapor-deposition (CVD) diamond (CVD-diamond) were used. The experiment was carried out using a pin-on-disk tribometer capable of operating at cryogenic temperatures, from 4.2 to 293 K. Two basic scenarios of testing were used: (1) frictional coefficient ({mu}) vs velocity (v) characteristics at constant temperatures; (2) {mu} vs temperature (T) behavior at fixed sliding speeds. For diamond/CVD-diamond, graphite/CVD-diamond, stainless steel/CVD-diamond pairs, {mu}`s are virtually velocity independent. For each of diamond/graphite, alumina/graphite, and graphite/graphite pairs, the {partial_derivative}{mu}/{partial_derivative}v characteristic is favorable, i.e., positive. For diamond/CVD-diamond and graphite/CVD-diamond pairs, {mu}`s are nearly temperature independent between in the range 77 - 293 K. Each {mu} vs T plot for pin materials sliding on graphite disks has a peak at a temperature in the range 100 - 200 K.

  19. Styrene-terminated polysulfone oligomers as matrix material for graphite reinforced composites: An initial study

    NASA Technical Reports Server (NTRS)

    Garcia, Dana; Bowles, Kenneth J.; Vannucci, Raymond D.

    1987-01-01

    Styrene terminated polysulfone oligomers are part of an oligomeric class of compounds with end groups capable of thermal polymerization. These materials can be used as matrices for graphite reinforced composites. The initial evaluation of styrene terminated polysulfone oligomer based composites are summarized in terms of fabrication methods, and mechanical and environmental properties. In addition, a description and evaluation is provided of the NASA/Industry Fellowship Program for Technology Transfer.

  20. On the way to fullerenes: Molecular dynamics study of the curling and closure of graphitic ribbons

    SciTech Connect

    Robertson, D.H.; Brenner, D.W.; White, C.T.

    1992-07-23

    The short-time behavior of isolated graphitic ribbons is simulated at high temperature using a model hydrocarbon potential. These ribbons show large instantaneous deviations from planarity that often result in the formation of open-ended hollow carbon structures representing good fullerene precursors. While confirming the importance of pentagon formation in the production of these precursors, these results also point to the central role of relatively high temperatures in these processes. 20 refs., 4 figs., 1 tab.

  1. Electron Microscopy Studies of Solid Surfaces and Interfaces.

    NASA Astrophysics Data System (ADS)

    Gajdardziska-Josifovska, Marija

    1991-02-01

    Electron microscopy techniques for study of surfaces and interfaces have been investigated and applied to (100) and (111) surfaces of MgO and to interfaces of Mo/Si multilayers and CoSi_2/Si epitaxial films. MgO surfaces subjected to different annealing and chemical treatments have been characterized by reflection electron microscopy imaging, reflection high-energy electron diffraction (RHEED), and reflection electron energy-loss spectroscopy (REELS). An oxygen rich (sqrt {3} times sqrt{3})R 30^circ reconstruction was found on the polar (111) surface upon annealing in oxygen at temperatures higher than 1500 ^circC. Transformation of the surface topography and segregation of calcium were observed on the cleaved (100) surface due to annealing. RHEED resonance conditions have been employed and studied with geometrical constructions, rocking curves and REELS. These conditions are associated with parabolas in the Kikuchi (K) patterns whose nature had been subject of much controversy. The parabolas have been explained as K lines of two-dimensional (2D) lattices in a general scheme which describes the K pattern geometry in terms of intersections of Brillouin zone boundaries with a sphere of reflections. Full treatment of the cases of 2D and 1D real lattices has revealed previously unknown boundaries in the form of parabolic surfaces (2D) and paraboloids of revolution (1D). These boundaries have been applied to lines which arise from electron channeling in 3D crystals and to RHEED parabolas from 2D surface reconstructions. Nanodiffraction, low angle dark-field imaging, electron holography, high spatial resolution EELS, and shadow imaging have been evaluated as means for measuring interface abruptness and change in mean-inner potential and compared to other microscopy techniques. Refraction effects at interfaces were observed as streaking of the nanodiffraction disks which was found to depend on the crystalline nature of the interface. For polycrystalline

  2. Bridged graphite oxide materials

    NASA Technical Reports Server (NTRS)

    Herrera-Alonso, Margarita (Inventor); McAllister, Michael J. (Inventor); Aksay, Ilhan A. (Inventor); Prud'homme, Robert K. (Inventor)

    2010-01-01

    Bridged graphite oxide material comprising graphite sheets bridged by at least one diamine bridging group. The bridged graphite oxide material may be incorporated in polymer composites or used in adsorption media.

  3. Comprehensive Study of High-Tc Interface Superconductivity

    SciTech Connect

    Logvenov, G.; Gozar A.; Butko, V.Y.; Bollinger, A.T.; Bozovic, N.; Radovic, Z.; Bozovic, I.

    2010-08-01

    Using ALL-MBE technique, we have synthesized different heterostructures consisting of an insulator La{sub 2}CuO{sub 4} (I) and a metal La{sub 1.56}Sr{sub 0.44}CuO{sub 4} (M) layer neither of which is superconducting by itself. The M-I bilayers were superconducting with a critical temperature T{sub c} {approx} 30-36 K. This highly robust phenomenon is confined within 1-2 nm from the interface and is primarily caused by the redistribution of doped holes across the interface. In this paper, we present a comprehensive study of the interface superconductivity by a range of experimental techniques including transport measurements of superconducting properties.

  4. Structural Arrangement Trade Study. Volume 1: Reusable Hydrogen Composite Tank System (RHCTS) and Graphite Composite Primary Structures (GCPS). Executive summary

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This volume is the first of a three volume set that discusses the structural arrangement trade study plan that will identify the most suitable configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 deg inclination. The Reusable Hydrogen Composite Tank System (RHCTS), and Graphite Composite Primary Structures most suitable for intertank, wing and thrust structures are identified. This executive summary presents the trade study process, the selection process, requirements used, analysis performed and data generated. Conclusions and recommendations are also presented.

  5. Thermal Pyrolytic Graphite Enhanced Components

    NASA Technical Reports Server (NTRS)

    Hardesty, Robert E. (Inventor)

    2015-01-01

    A thermally conductive composite material, a thermal transfer device made of the material, and a method for making the material are disclosed. Apertures or depressions are formed in aluminum or aluminum alloy. Plugs are formed of thermal pyrolytic graphite. An amount of silicon sufficient for liquid interface diffusion bonding is applied, for example by vapor deposition or use of aluminum silicon alloy foil. The plugs are inserted in the apertures or depressions. Bonding energy is applied, for example by applying pressure and heat using a hot isostatic press. The thermal pyrolytic graphite, aluminum or aluminum alloy and silicon form a eutectic alloy. As a result, the plugs are bonded into the apertures or depressions. The composite material can be machined to produce finished devices such as the thermal transfer device. Thermally conductive planes of the thermal pyrolytic graphite plugs may be aligned in parallel to present a thermal conduction path.

  6. Ferric chloride graphite intercalation compounds prepared from graphite fluoride

    NASA Technical Reports Server (NTRS)

    Hung, Ching-Cheh

    1994-01-01

    The reaction between graphite fluoride and ferric chloride was observed in the temperature range of 300 to 400 C. The graphite fluorides used for this reaction have an sp3 electronic structure and are electrical insulators. They can be made by fluorinating either carbon fibers or powder having various degrees of graphitization. Reaction is fast and spontaneous and can occur in the presence of air. The ferric chloride does not have to be predried. The products have an sp2 electronic structure and are electrical conductors. They contain first stage FeCl3 intercalated graphite. Some of the products contain FeCl2*2H2O, others contain FeF3 in concentrations that depend on the intercalation condition. The graphite intercalated compounds (GIC) deintercalated slowly in air at room temperature, but deintercalated quickly and completely at 370 C. Deintercalation is accompanied by the disappearing of iron halides and the formation of rust (hematite) distributed unevenly on the fiber surface. When heated to 400 C in pure N2 (99.99 vol %), this new GIC deintercalates without losing its molecular structure. However, when the compounds are heated to 800 C in quartz tube, they lost most of its halogen atoms and formed iron oxides (other than hematite), distributed evenly in or on the fiber. This iron-oxide-covered fiber may be useful in making carbon-fiber/ceramic-matrix composites with strong bonding at the fiber-ceramic interface.

  7. Structural arrangement trade study. Volume 3: Reusable Hydrogen Composite Tank System (RHCTS) and Graphite Composite Primary Structures (GCPS). Addendum

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This volume is the third of a 3 volume set that addresses the structural trade study plan that will identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 deg inclination. The most suitable Reusable Hydrogen Composite Tank System (RHCTS), and Graphite Composite Tank System (GCPS) composite materials for intertank, wing and thrust structures are identified. Vehicle resizing charts, selection criteria and back-up charts, parametric costing approach and the finite element method analysis are discussed.

  8. Airborne Precision Spacing for Dependent Parallel Operations Interface Study

    NASA Technical Reports Server (NTRS)

    Volk, Paul M.; Takallu, M. A.; Hoffler, Keith D.; Weiser, Jarold; Turner, Dexter

    2012-01-01

    This paper describes a usability study of proposed cockpit interfaces to support Airborne Precision Spacing (APS) operations for aircraft performing dependent parallel approaches (DPA). NASA has proposed an airborne system called Pair Dependent Speed (PDS) which uses their Airborne Spacing for Terminal Arrival Routes (ASTAR) algorithm to manage spacing intervals. Interface elements were designed to facilitate the input of APS-DPA spacing parameters to ASTAR, and to convey PDS system information to the crew deemed necessary and/or helpful to conduct the operation, including: target speed, guidance mode, target aircraft depiction, and spacing trend indication. In the study, subject pilots observed recorded simulations using the proposed interface elements in which the ownship managed assigned spacing intervals from two other arriving aircraft. Simulations were recorded using the Aircraft Simulation for Traffic Operations Research (ASTOR) platform, a medium-fidelity simulator based on a modern Boeing commercial glass cockpit. Various combinations of the interface elements were presented to subject pilots, and feedback was collected via structured questionnaires. The results of subject pilot evaluations show that the proposed design elements were acceptable, and that preferable combinations exist within this set of elements. The results also point to potential improvements to be considered for implementation in future experiments.

  9. Insights from the study of high-temperature interface superconductivity.

    PubMed

    Pereiro, J; Bollinger, A T; Logvenov, G; Gozar, A; Panagopoulos, C; Bozović, I

    2012-10-28

    A brief overview is given of the studies of high-temperature interface superconductivity based on atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). A number of difficult materials science and physics questions have been tackled, frequently at the expense of some technical tour de force, and sometimes even by introducing new techniques. ALL-MBE is especially suitable to address questions related to surface and interface physics. Using this technique, it has been demonstrated that high-temperature superconductivity can occur in a single copper oxide layer-the thinnest superconductor known. It has been shown that interface superconductivity in cuprates is a genuine electronic effect-it arises from charge transfer (electron depletion and accumulation) across the interface driven by the difference in chemical potentials rather than from cation diffusion and mixing. We have also understood the nature of the superconductor-insulator phase transition as a function of doping. However, a few important questions, such as the mechanism of interfacial enhancement of the critical temperature, are still outstanding. PMID:22987034

  10. Nonlinear optical studies of aqueous interfaces, polymers, and nanowires

    NASA Astrophysics Data System (ADS)

    Onorato, Robert Michael

    Understanding the structure and composition of aqueous interfaces is one of the most important current problems in modern science. Aqueous interfaces are ubiquitous in Nature, ranging from aerosols to cellular structures. Aerosol chemistry is presently the most significant unknown factor in predicting climate change, and an understanding of the chemistry that occurs at aerosol interfaces would significantly improve climate models. Similarly, the nature of aqueous biological interfaces has a profound effect on the structure and function of proteins and other biological structures. Despite the importance of these problems, aqueous interfaces remain incompletely understood due to the challenges of experimentally probing them. Recent experimental and theoretical results have firmly established the existence of enhanced concentrations of selected ions at the air/water interface. In this dissertation, I use an interface-specific technique, UV second harmonic generation (SHG), to further investigate the adsorption of ions to the air/water interface and to extend the study of ion adsorption towards more biologically relevant systems, alcohol/water interfaces. In Chapter 2, I describe resonant UV-SHG studies of the strongly chaotropic thiocyanate ion adsorbed to the interface formed by water and a monolayer of dodecanol, wherein the Gibbs free energy of adsorption was determined to be -6.7 +/- 1.1 and -6.3 +/- 1.8 kJ/mol for sodium and potassium thiocyanate, respectively, coincident with the value determined for thiocyanate at the air/water interface. Interestingly, at concentrations near and above 4 M, the resonant SHG signal increases discontinuously, indicating a structural change in the interfacial region. Recent experimental and theoretical work has demonstrated that the adsorption of bromide is particularly important for chemical reactions on atmospheric aerosols, including the depletion of ozone. In Chapter 3, UV-SHG resonant with the bromide charge

  11. Atomic force microscopy study of nitrogen molecule self-assembly at the HOPG-water interface

    NASA Astrophysics Data System (ADS)

    Lu, Yi-Hsien; Yang, Chih-Wen; Hwang, Ing-Shouh

    2014-06-01

    In this work, we investigated the evolution of the graphite-water interface in a nitrogen atmosphere by using frequency-modulation atomic force microscopy (FM-AFM). A highly ordered pyrolytic graphite (HOPG) sample was immersed in pre-degassed water and subsequently placed in the nitrogen environment. The dissolved nitrogen molecules diffused in water and self-assembled into ordered row-like structural domains at the interface. Nucleation and growth processes of the domains were observed. When the coverage of the ordered structure surpassed 50%, small clusters began to appear on the ordered structure. The number density of the clusters increases as the coverage of the ordered structures increases and these clusters may hop on the ordered structures. A model is proposed to explain the evolution of the nitrogen molecule self-assembly process at the interface. The observation of nitrogen clusters may shed light on the nature and nucleation of the so-called nanobubbles at hydrophobic-water interfaces.

  12. Constraints on Grain Formation Around Carbon Stars from Laboratory Studies of Presolar Graphite

    NASA Technical Reports Server (NTRS)

    Bernatowicz, T. J.; Akande, O. W.; Croat, T. K.; Cowsik, R.

    2005-01-01

    We report the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, either with or without internal crystals of titanium carbide (TiC). In addition to providing detailed information about stellar nucleosynthesis, the structure and composition of presolar grains give unique information about the conditions of grain formation. In the present work we use laboratory observations of presolar graphite to gain insight into the physical conditions in circumstellar outflows from carbon AGB stars. The periodic pulsation of AGB stars enhances the gas density through shocks in the stellar atmosphere above the photosphere, promoting the condensation of dust grains. Copious mass outflow occurs largely because grains are coupled to the radiation field of the star, which accelerates them by radiation pressure; momentum is in turn transferred to gas molecules by collisions with grains. The dust/gas mixture is effectively a two-component fluid whose motion depends on atmospheric structure and which, in turn, influences that structure. In particular, the radiation pressure on the grains determines the velocity field of the outflow and thus the density distribution, while the density distribution itself determines the conditions of radiative transfer within the outflow and thus the effective radiation pressure.

  13. Determination of Neutron Spectra in a Graphite Sphere for Fusion Reactor Studies

    NASA Astrophysics Data System (ADS)

    Bashter, I. B.; Cooper, P. N.

    Calculated and experimental results for the neutron spectra at different radii in a graphite sphere irradiated with 14.1 MeV neutrons were shown to be in satisfactory agreement over the energy range 14.1 to 1.8 MeV neutrons. A group of curves were constructed which gives the radius of a graphite sphere shield required to attenuate the neutron intensity to a certain value. The data set used in the present work, with carbon-12 cross section, is shown to be useful for spherical calculations.Translated AbstractDie Bestimmung der Neutronenspektren in einer GraphitkugelDie Übereinstimmung experimentell bestimmter und berechneter Neutronenspektren in Abhängigkeit vom Ort in einer Graphitkugel wird in einem Energiebereich von 14,1 bis 1,8 MeV (bei einer Ausgangsenergie von 14,1 MeV je Neutron) gezeigt. Eine Gruppe von Kurven wird konstruiert, die den für eine bestimmte Dämpfung der Neutronenintensität notwendigen Radius einer Graphitkugel angeben. Es wird nachgewiesen, daß die in der Arbeit benutzte Datenbank für den 12C-Wirkungsquerschnitt in sphärischen Geometrien anwendbar ist.

  14. Preparation of graphitic articles

    DOEpatents

    Phillips, Jonathan; Nemer, Martin; Weigle, John C.

    2010-05-11

    Graphitic structures have been prepared by exposing templates (metal, metal-coated ceramic, graphite, for example) to a gaseous mixture that includes hydrocarbons and oxygen. When the template is metal, subsequent acid treatment removes the metal to yield monoliths, hollow graphitic structures, and other products. The shapes of the coated and hollow graphitic structures mimic the shapes of the templates.

  15. Interaction of a Self-Assembled Ionic Liquid Layer with Graphite(0001): A Combined Experimental and Theoretical Study.

    PubMed

    Buchner, Florian; Forster-Tonigold, Katrin; Bozorgchenani, Maral; Gross, Axel; Behm, R Jürgen

    2016-01-21

    The interaction between (sub)monolayers of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide [BMP](+)[TFSA](-) and graphite(0001), which serves as a model for the anode|electolyte interface in Li-ion batteries, was investigated under ultrahigh vacuum conditions in a combined experimental and theoretical approach. High-resolution scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and dispersion-corrected density functional theory (DFT-D) calculations were employed. After vapor deposition at 300 K, XPS indicates molecular adsorbates with a 1:1 ratio of cations/anions. Cool down to ∼100 K leads to the formation of an ordered (2D) crystalline phase, which coexists with a mobile (2D) liquid. DFT-D calculations reveal that adsorbed [BMP](+) and [TFSA](-) species are arranged alternately in a row-like adsorption structure (cation-anion-cation-anion) and that adsorption is dominated by dispersion interactions between adlayer and substrate, on the one hand, and electrostatic interactions between the ions in a row, on the other hand. Simulated STM images of that structure closely resemble the experimental molecular resolved STM images and show that the resolved features mostly stem from the cations. PMID:26713562

  16. DEMS study of gas evolution at thick graphite electrodes for lithium-ion batteries: the effect of γ-butyrolactone

    NASA Astrophysics Data System (ADS)

    Lanz, Martin; Novák, Petr

    Differential electrochemical mass spectrometry (DEMS) was used to study the reductive decomposition of an electrolyte based on ethylene carbonate/dimethyl carbonate (EC/DMC), as well as the formation of a solid electrolyte interphase (SEI) in this electrolyte, at thick (75-100 μm) porous graphite composite electrodes. A number of graphite electrodes differing in their electrochemical lithium intercalation properties were investigated in potential-sweep experiments. They proved to be similar with respect to the evolution of ethylene and hydrogen gas during the first two charge/discharge cycles. Due to an incomplete coulombic conversion, a high irreversible capacity, as well as slow diffusion kinetics and an enhanced ohmic resistance of the electrodes, SEI formation on these thick electrodes was not yet complete after the first charge/discharge cycle. Undesired gas evolution can be reduced by adding γ-butyrolactone (GBL) as an electrolyte co-solvent. The amount of ethylene and hydrogen gas evolved decreases with increasing percentages of GBL in an EC/DMC electrolyte, indicating that the SEI layer is built up from GBL rather than from EC decomposition products.

  17. Study of SEI layer formed on graphite anodes in PC/LiBOB electrolyte using IR spectroscopy

    SciTech Connect

    Zhuang, G.V.; Xu, K.; Jow, T.R.; Ross Jr., P.N.

    2003-10-30

    Formation of the SEI layer on graphite anodes cycled in propylene carbonate (PC) lithium bis(oxolato)borate (LiBOB) electrolyte was studied by ex-situ Fourier Transform Infrared Spectroscopy (FTIR) analysis in the attenuated total reflection (ATR) mode. The results provide a more refined description of the composition than earlier analyses with x-ray photoelectron spectroscopy (XPS). The vibrational spectra clearly show that electrochemical reduction of the BOB anion is a part of the SEI formation chemistry. Carboxylate and/or oxalate functional groups derived from the BOB anion were the components assigned as the ''semicarbonate'' species in the C 1s XPS spectra of the SEI layer formed in LiBOB electrolyte. Reduction of the BOB anion changes the oxygen coordination around the B atom from tetrahedral BO4 to trigonal BO3, e.g., meta- or orthoborate. Based on the combination of electrochemical and FTIR data, we propose that the preferential reduction of the BOB anion versus the PC solvent molecule is responsible for the cyclability of graphite anodes in purely PC-based electrolyte.

  18. Optical properties of graphite oxide and reduced graphite oxide

    NASA Astrophysics Data System (ADS)

    Jung, Eilho; Lee, Seokbae; Roh, Seulki; Hwang, Eunhee; Lee, Junghyun; Lee, Hyoyoung; Hwang, Jungseek

    2014-07-01

    We studied the optical properties of a graphite oxide and a reduced graphite oxide by using the optical spectroscopic technique. The graphite oxide does not show a finite dc conductivity and has several characteristic absorption modes in the mid-infrared region, caused by an epoxide functional group and hydroxyl and carboxyl moieties in the mid-infrared range. The reduced graphite oxide shows a Drude-like response in the far-infrared region and the estimated dc conductivity and electric mobility are around 200 Ω-1cm-1 and ˜100 cm2V-1s-1, respectively. We found that the optical conductivity cannot be fitted with a simple Drude model, which indicates that the charge carriers are correlated. We applied an extended Drude model and obtained the optical scattering rate and the optical effective mass. We found that the optical effective mass can carry information of both the enhanced mass by correlation and the electronic band structure.

  19. Synthesis of few layer graphene by direct exfoliation of graphite and a Raman spectroscopic study

    SciTech Connect

    Gayathri, S.; Jayabal, P.; Ramakrishnan, V.; Kottaisamy, M.

    2014-02-15

    The exfoliation of graphene from pristine graphite in a liquid phase was achieved successfully via sonication followed by centrifugation method. Ultraviolet–visible (UV–vis) spectra of the obtained graphene dispersions at different exfoliation time indicated that the concentration of graphene dispersion increased markedly with increasing exfoliation time. The sheet-like morphology of the exfoliated graphene was revealed by Scanning Electron Microscopy (SEM) image. Further, the morphological change in different exfoliation time was investigated by Atomic Force Microscopy (AFM). A complete structural and defect characterization was probed using micro-Raman spectroscopic technique. The shape and position of the 2D band of Raman spectra revealed the formation of bilayer to few layer graphene. Also, Raman mapping confirmed the presence of uniformly distributed bilayer graphene sheets on the substrate.

  20. Experimental study on the reaction between nuclear graphite IG-110 and carbon dioxide

    NASA Astrophysics Data System (ADS)

    Kim, Eung Soo; No, Hee Cheon

    2006-03-01

    With nuclear graphite IG-110, we measured various kinetic parameters and reaction rates of the C/CO 2 reaction. As a result, its activation energy is 295 ± 8 kJ/mol and the order of reaction is 0.9. It turns out that the rate of C/CO 2 reaction is much smaller than the rate of the C/O 2 reaction which is dominant in HTGR air-ingress below 1400 °C. Finally, we propose the following rate equation for the C/CO 2 reaction of IG-110: r(kg/m3s)=3.95×103·exp-{290 000}/{R·T}·(p)0.9.

  1. Experimental studies of graphite-epoxy and boron-epoxy angle ply laminates in shear

    NASA Technical Reports Server (NTRS)

    Weller, T.

    1977-01-01

    The nonlinear/inelastic response under inplane shear of a large variety of graphite-epoxy and boron-epoxy angle-ply laminates was tested. Their strength allowables were obtained and the mechanisms which govern their mode of failure were determined. Two types of specimens for the program were chosen, tested, and evaluated: shear panels stabilized by an aluminum honeycomb core and shear tubes. A modified biaxially compression/tension loaded picture frame was designed and utilized in the test program with the shear panels. The results obtained with this test technique categorically prefer the shear panels, rather than the tubes, for adequate and satisfactory experimental definition of the objectives. Test results indicate the existence of a so-called core-effect which ought to be considered when reducing experimental data for weak in shear laminates.

  2. H-1 NMR study of ternary ammonia-alkali metal-graphite intercalation compounds

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Fronko, R. M.; Resing, H. A.; Qian, X. W.; Solin, S. A.

    1987-01-01

    For the first-stage ternary ammonia-alkali metal-graphite intercalation compounds M(NH3)(x)C24(x of about 4, M = K, Rb, Cs), three sets of triplet H-1 NMR spectral lines have been observed at various temperatures and orientations due to the H-1 - H-1 and N-14 - H-1 dipolar interactions. The structures of these compounds have been inferred as mobile (liquid-like) intercalant layers of planar M(NH3)4 ions in between the carbon layers. For the intercalated ammonia molecules, the potential barrier is about 0.2 eV and the molecular geometry is very close to the free NH3 in gas phase.

  3. Scanning tunneling spectroscopy studies of angle-dependent van Hove singularities on twisted graphite surface layer

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Luo, Hong

    2013-12-01

    Slightly misoriented surface graphene layer on highly ordered pyrolytic graphite (HOPG) can result in Moiré patterns (MP). Two van Hove singularity (VHS) peaks in the density of states are observed with scanning tunneling spectroscopy on a series of the MPs with different periods on HOPG surface, flanking the Fermi energy. The energy difference between the two VHS peaks (ΔEVHS) is linearly proportional to the sine of interlayer rotation angle. A similar relation between ΔEVHS and MP periods has recently been reported on twisted graphene layers. Compared to the case of twisted graphene layers, the Fermi velocity of MPs on a HOPG surface is found to be larger, and the interlayer hopping is enhanced.

  4. Thermal behavior of deuterium implanted into nuclear graphite studied by NRA

    NASA Astrophysics Data System (ADS)

    Le Guillou, M.; Toulhoat, N.; Pipon, Y.; Moncoffre, N.; Bérerd, N.; Perrat-Mabilon, A.; Rapegno, R.

    2014-08-01

    This paper focuses on the thermal behavior of deuterium, simulating tritium, implanted into virgin nuclear graphite of French gas-cooled reactors, which are being decommissioned. Deuterium ions D+ were implanted into graphite (around 3 at.% at the projected range Rp) at two different depths (around 670 nm and 2.8 μm) and annealed up to about 300 h in a temperature range from 200 °C to 1200 °C under vacuum or argon flow. Before and after heat treatments, D distribution profiles in the samples were followed using the nuclear reaction D(3He,p)4He, with a millimetric beam at the 4 MV Van de Graaff accelerator of IPNL (Institut de Physique Nucléaire de Lyon, France). The results show that the deuterium release becomes significant at temperatures higher than 600 °C and is almost totally completed at 1200 °C. The comparison of the results, obtained for both implantation depths, points out the role of the porosity with respect to deuterium permeation. The release follows two stages: a rapid step where it occurs within a few hours, followed by a much slower step during which the release of deuterium saturates. The initial stage is characterized by an activation energy of 1.3 eV and might correspond to detrapping of D located at crystallite edges and its diffusion at the crystallite surfaces. We assume that the second stage kinetics corresponds to a very slow diffusion of D located inside the crystallites and chemisorbed to carbon atoms through sp2 or sp3 bonds.

  5. Experimental study of the oscillating interface of a falling drop

    NASA Astrophysics Data System (ADS)

    Choi, Suhwan; Ward, Thomas

    2012-11-01

    The drop interface oscillation generated from detachment from a nozzle due to gravity are experimentally studied. The fluids used in the experiments are glycerol-water mixtures with viscosities ranging from 0.005 to 0.410 Pa s, mineral oil having a viscosity of 0.0270 Pa s, and DI water with viscosity of 0.0009 Pa s. The drop oscillating is taken by fast camera to make observations. For large drops, where the interface relative to a polar angle may be measured, the periodic deformation is plotted as a function of time. For smaller drops we measure the deformation as switching between an oblate and prolate drop as a function of time. The phenomenon is clearly a function of the fluid viscosity but we seek to propose a pinch-off mechanism for understanding the source of the observed oscillations.

  6. X-Ray Studies of Thin Films and Interfaces.

    NASA Astrophysics Data System (ADS)

    Woronick, Steven Charles

    1990-01-01

    Presented here are a series of x-ray studies utilizing synchrotron radiation to investigate a variety of properties of thin films and interfaces in technologically important materials. By far the largest part of this dissertation is devoted to studies of x-ray reflectivity as a function of angle (mainly soft x rays), although some extended x -ray absorption fine structure (EXAFS) results are included as reprinted published papers (briefly discussed). The reflectivity discussion covers theory, experimental techniques, data analysis (by curve-fitting), and specific applications. The material systems studied by the x-ray reflectivity technique include: bulk silicon, GaAs, InAs, ~250 -A InAs layers deposited by molecular-beam epitaxy (MBE) on GaAs(100) substrates, four thicknesses (~ 126-1100 A) of SiO_2 /Si(100) produced by dry thermal oxidation, and ~250-A layers of CoSi_2 /Si(111) (two samples, one produced by MBE and one by solid-phase epitaxy). Results determined from the reflectivity measurements include: interfacial roughness parameters, refractive index of materials (in the energy range ~400-1100 eV), and overlayer thicknesses. It has been found for example that the indium -stabilized growth mode of InAs on GaAs(100) results in a smoother buried interface than the arsenic-stabilized growth mode, while the indium-stabilized growth mode on 2^circ-off GaAs(100) produces the smoothest buried interface (with typical roughness parameters in the range 10-19 A). Preliminary results indicate that growth of CoSi_2/Si(111) by MBE produces smoother buried interfaces than growth by solid-phase epitaxy. The roughness parameters have been explained in terms of growth conditions, lattice mismatch, and material inhomogeneity in the vicinity of the buried interface. The oxygen atomic scattering factor for photons in the range 400-800 eV (oxygen K edge ~ 540 eV) has also been deduced from a determination the Si and SiO_2 refractive indices. The EXAFS studies were used to

  7. Atomistic study on the FCC/BCC interface structure with {112}KS orientation

    SciTech Connect

    Kang, Keonwook; Beyerlein, Irene; Han, Weizhong; Wang, Jian; Mara, Nathan

    2011-09-23

    In this study, atomistic simulation is used to explore the atomic interface structure, the intrinsic defect network, and mechanism of twin formation from the {112}KS Cu-Nb interface. The interface structure of different material systems AI-Fe and AI-Nb are also compared with Cu-Nb interface.

  8. A Study of the Oxidation Behaviour of Pile Grade A (PGA) Nuclear Graphite Using Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and X-Ray Tomography (XRT).

    PubMed

    Payne, Liam; Heard, Peter J; Scott, Thomas B

    2015-01-01

    Pile grade A (PGA) graphite was used as a material for moderating and reflecting neutrons in the UK's first generation Magnox nuclear power reactors. As all but one of these reactors are now shut down there is a need to understand the residual state of the material prior to decommissioning of the cores, in particular the location and concentration of key radio-contaminants such as 14C. The oxidation behaviour of unirradiated PGA graphite was studied, in the temperature range 600-1050°C, in air and nitrogen using thermogravimetric analysis, scanning electron microscopy and X-ray tomography to investigate the possibility of using thermal degradation techniques to examine 14C distribution within irradiated material. The thermal decomposition of PGA graphite was observed to follow the three oxidation regimes historically identified by previous workers with limited, uniform oxidation at temperatures below 600°C and substantial, external oxidation at higher temperatures. This work demonstrates that the different oxidation regimes of PGA graphite could be developed into a methodology to characterise the distribution and concentration of 14C in irradiated graphite by thermal treatment. PMID:26575374

  9. A Study of the Oxidation Behaviour of Pile Grade A (PGA) Nuclear Graphite Using Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and X-Ray Tomography (XRT)

    PubMed Central

    Payne, Liam; Heard, Peter J.; Scott, Thomas B.

    2015-01-01

    Pile grade A (PGA) graphite was used as a material for moderating and reflecting neutrons in the UK’s first generation Magnox nuclear power reactors. As all but one of these reactors are now shut down there is a need to understand the residual state of the material prior to decommissioning of the cores, in particular the location and concentration of key radio-contaminants such as 14C. The oxidation behaviour of unirradiated PGA graphite was studied, in the temperature range 600–1050°C, in air and nitrogen using thermogravimetric analysis, scanning electron microscopy and X-ray tomography to investigate the possibility of using thermal degradation techniques to examine 14C distribution within irradiated material. The thermal decomposition of PGA graphite was observed to follow the three oxidation regimes historically identified by previous workers with limited, uniform oxidation at temperatures below 600°C and substantial, external oxidation at higher temperatures. This work demonstrates that the different oxidation regimes of PGA graphite could be developed into a methodology to characterise the distribution and concentration of 14C in irradiated graphite by thermal treatment. PMID:26575374

  10. Propagation of Stream Interfaces: An LFM-helio Study

    NASA Astrophysics Data System (ADS)

    Pahud, D. M.; Hughes, W.; Merkin, V. G.; McGregor, S. L.

    2012-12-01

    During the last solar minimum, the heliosphere was dominated by steady-state Stream Interaction Regions (SIRs). Carrington Rotation (CR) 2060, which occurred during this period, contained multiple SIRs and was free of transient phenomena which made it a good interval for the study of SIRs. We have used the Lyon-Fedder-Mobarry (LFM) heliospheric 3-D magnetohydrodynamic (MHD) model, the LFM-helio, to examine the radial evolution of SIRs, particularly the speed of the stream interface, from 0.1 AU to 2.0 AU. The LFM-helio is an adaptation of the magnetospheric LFM MHD code to heliospheric plasmas and fields. The ideal MHD equations are solved on a uniform spherical grid, excluding 10 degree cones centered at the poles. The inner boundary condition is obtained using the Wang-Sheeley-Arge (WSA) coronal model driven by photospheric magnetic field measurements for CR 2060. The global nature of the LFM-helio solution facilitates the study of the steepening of SIRs as well as their speed through the ambient plasma. For the SIR considered, the location of the stream interface is determined using multiple definitions, namely: the location of maximum total pressure, the location of maximum flow vorticity, the location of null azimuthal flow velocity and the location of steepest gradient of entropy. The speed of the plasma at these locations is compared to the mean speed of the interface to determine whether the interfaces are convected with the solar wind or propagate through it. In order to elucidate the physics of the evolution of the SIR, we also ran the LFM-helio using an idealized inner boundary condition. The idealized inner boundary specified the solar wind speed so as to ensure the presence of an SIR. Specifically, a source of fast wind was located at the same latitude as, and longitudinally near, a source of slow wind. The combined effect of radially outward plasma flow and rotation of the inner boundary align the fast wind behind the slow wind, creating an SIR. The

  11. A study of structurally efficient graphite-thermoplastic trapezoidal-corrugation sandwich and semi-sandwich panels

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1993-01-01

    The structural efficiency of compression-loaded trapezoidal-corrugation sandwich and semi-sandwich composite panels is studied to determine their weight savings potential. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered. An optimization code is used to find the minimum weight designs for critical compressive load levels ranging from 3,000 to 24,000 lb/in. Graphite-thermoplastic panels based on the optimal minimum weight designs were fabricated and tested. A finite-element analysis of several test specimens was also conducted. The results of the optimization study, the finite-element analysis, and the experiments are presented.

  12. a Heat Capacity Study of Para-Hydrogen Monolayers on Graphite.

    NASA Astrophysics Data System (ADS)

    Motteler, Frederick Clark

    The heat capacity of monolayer p-H(,2) adsorbed on graphite foam has been measured over the 0.0631(ANGSTROM)(' -2) to 0.0891(ANGSTROM)('-2) density range and the 2 to 25(DEGREES)K temperature range. Specific heat peaks are observed over almost the entire density range and are similar to those observed for ('4)He and ('3)He monolayers on graphite for similar densities. Low density data (0.0631(ANGSTROM)('-2) to 0.0727(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the commensurate order-disorder transition. At commensurate density. 0.0637(ANGSTROM)(' -2), the peak attains a maximum height of C/Nk(,b) = 11.7 at 21.4(DEGREES)K and may be characterized by the critical exponent (alpha) = 0.33. For temperatures below the order -disorder transition, the commensurate monolayer heat capacity is characterized by Einstein like behavior with (theta)(,E) = 53.4(DEGREES)K. High density data (0.0787(ANGSTROM)('-2) to 0.0815(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the disordering of a close packed triangular incommensurate solid. The incommensurate solid is characterized by its Debye like heat capacity behavior. The density region between the commensurate structure and incommensurate solid (0.0707(ANGSTROM)('-2) to 0.772(ANGSTROM)(' -2)) contains two heat capacity peaks. At about 20(DEGREES)K there is broad rounded remnant of the order-disorder peak. At lower temperatures (6 to 9(DEGREES)K) there is a small, but very sharp heat capacity peak. The peak attains a maximum height of C/Nk(,b) = 0.89 at a density of 0.0727(ANGSTROM)(' -2) and a temperature of 9.54(DEGREES)K. The remnant of the order-disorder transition seen in p-H(,2) data, together with re-examination of ('4)He data indicates that a shoulder-like remnant intersects the melting line. The melting peak of ('4)He undergoes significant change at the intersection point. The low temperature intermediate density region is consistent with a striped phase of domain walls. The sharp low

  13. Density functional studies of functionalized graphitic materials with late transition metals for Oxygen Reduction Reactions.

    PubMed

    Calle-Vallejo, Federico; Martínez, José Ignacio; Rossmeisl, Jan

    2011-09-14

    Low-temperature fuel cells are appealing alternatives to the conventional internal combustion engines for transportation applications. However, in order for them to be commercially viable, effective, stable and low-cost electrocatalysts are needed for the Oxygen Reduction Reaction (ORR) at the cathode. In this contribution, on the basis of Density Functional Theory (DFT) calculations, we show that graphitic materials with active sites composed of 4 nitrogen atoms and transition metal atoms belonging to groups 7 to 9 in the periodic table are active towards ORR, and also towards Oxygen Evolution Reaction (OER). Spin analyses suggest that the oxidation state of those elements in the active sites should in general be +2. Moreover, our results verify that the adsorption behavior of transition metals is not intrinsic, since it can be severely altered by changes in the local geometry of the active site, the chemical nature of the nearest neighbors, and the oxidation states. Nonetheless, we find that these catalysts trend-wise behave as oxides and that their catalytic activity is limited by exactly the same universal scaling relations. PMID:21796295

  14. Experimental and analytical study of fatigue damage in notched graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Whitcomb, J. D.

    1979-01-01

    Both tension and compression fatigue behaviors were investigated in four notched graphite/epoxy laminates. After fatigue loading, specimens were examined for damage type and location using visual inspection, light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. In general, ply cracks did not propagate into adjacent plies of differing fiber orientation. To help understand the varied fatigue observations, the interlaminar stress distribution was calculated with finite element analysis for the regions around the hole and along the straight free edge. Comparison of observed delamination locations with the calculated stresses indicated that both interlaminar shear and peel stresses must be considered when predicting delamination. The effects of the fatigue cycling on residual strength and stiffness were measured for some specimens of each laminate type. Fatigue loading generally caused only small stiffness losses. In all cases, residual strengths were greater than or equal to the virgin strengths.

  15. Ordering in quasi-two-dimensional planar ferromagnets: A neutron scattering study of graphite intercalation compounds

    NASA Astrophysics Data System (ADS)

    Wiesler, D. G.; Suzuki, M.; Zabel, H.

    1987-11-01

    The magnetic ordering of stage-2 CoCl2- and NiCl2-graphite intercalation compounds (GIC's) has been investigated by neutron diffraction. Both of these compounds are observed to undergo a two-step ordering process. For temperatures within the range Tl

  16. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2010-12-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  17. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2011-05-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  18. 2008 ULTRASONIC BENCHMARK STUDIES OF INTERFACE CURVATURE--A SUMMARY

    SciTech Connect

    Schmerr, L. W.; Huang, R.; Raillon, R.; Mahaut, S.; Leymarie, N.; Lonne, S.; Spies, M.; Lupien, V.

    2009-03-03

    In the 2008 QNDE ultrasonic benchmark session researchers from five different institutions around the world examined the influence that the curvature of a cylindrical fluid-solid interface has on the measured NDE immersion pulse-echo response of a flat-bottom hole (FBH) reflector. This was a repeat of a study conducted in the 2007 benchmark to try to determine the sources of differences seen in 2007 between model-based predictions and experiments. Here, we will summarize the results obtained in 2008 and analyze the model-based results and the experiments.

  19. Video STM Studies of Adsorbate Diffusion at Electrochemical Interfaces

    NASA Astrophysics Data System (ADS)

    Tansel, T.; Magnussen, O. M.

    2006-01-01

    Direct in situ studies of the surface diffusion of isolated adsorbates at an electrochemical interface by high-speed scanning tunneling microscopy (video STM) are presented for sulfide adsorbates on Cu(100) in HCl solution. As revealed by a quantitative statistical analysis, the adsorbate motion can be described by thermally activated hopping between neighboring adsorption sites with an activation energy that increases linearly with electrode potential by 0.50 eV per V. This can be explained by changes in the adsorbate dipole moment during the hopping process and contributions from coadsorbates.

  20. Analytical and experimental studies of graphite-epoxy and boron-epoxy angle ply laminates in shear

    NASA Technical Reports Server (NTRS)

    Weller, T.

    1977-01-01

    The results of a comparison study between a test program on the inelastic response under inplane shear over a wide range of graphite-epoxy and boron-epoxy angle-ply laminates are reported. This investigation was aimed at evaluating the applicability and adequacy of these analyses to predict satisfactorily the responses of angle-ply laminates. It was observed that these analytical tools are inadequate for this purpose as they fail to predict with sufficient confidence the shape of response and in particular the strength values associated with a given laminate configuration. Consequently, they do not provide the sought-after information about failure mechanisms which trigger failure of a particular designed laminate.

  1. Unoccupied-electronic-band structure of graphite studied by angle-resolved secondary-electron emission and inverse photoemission

    NASA Astrophysics Data System (ADS)

    Maeda, F.; Takahashi, T.; Ohsawa, H.; Suzuki, S.; Suematsu, H.

    1988-03-01

    Angle-resolved inverse photoemission spectroscopy (ARIPES) and angle-resolved secondary-electron emission spectroscopy (ARSEES) have been performed for graphite to establish experimentally the unoccupied-electronic-band structure as well as to study the difference between the two techniques. Remarkable differences have been found in the experimental two-dimensional band structures obtained by the two methods. The experimental results have been compared with the two different band calculations by R. C. Tatar and S. Rabii [Phys. Rev. B 25, 4126 (1982)] and by N. A. W. Holzwarth, S. G. Louie, and S. Rabii [Phys. Rev. B 26, 5382 (1982)] with special attention to the energy position of the three-dimensional interlayer band. The possible origin of the difference between ARIPES and ARSEES has also been discussed.

  2. Space station automation and robotics study. Operator-systems interface

    NASA Technical Reports Server (NTRS)

    1984-01-01

    This is the final report of a Space Station Automation and Robotics Planning Study, which was a joint project of the Boeing Aerospace Company, Boeing Commercial Airplane Company, and Boeing Computer Services Company. The study is in support of the Advanced Technology Advisory Committee established by NASA in accordance with a mandate by the U.S. Congress. Boeing support complements that provided to the NASA Contractor study team by four aerospace contractors, the Stanford Research Institute (SRI), and the California Space Institute. This study identifies automation and robotics (A&R) technologies that can be advanced by requirements levied by the Space Station Program. The methodology used in the study is to establish functional requirements for the operator system interface (OSI), establish the technologies needed to meet these requirements, and to forecast the availability of these technologies. The OSI would perform path planning, tracking and control, object recognition, fault detection and correction, and plan modifications in connection with extravehicular (EV) robot operations.

  3. Electrochemical impedance study of the hematite/water interface.

    PubMed

    Shimizu, Kenichi; Lasia, Andrzej; Boily, Jean-François

    2012-05-22

    Reactions taking place on hematite (α-Fe(2)O(3)) surfaces in contact with aqueous solutions are of paramount importance to environmental and technological processes. The electrochemical properties of the hematite/water interface are central to these processes and can be probed by open circuit potentials and cyclic voltammetric measurements of semiconducting electrodes. In this study, electrochemical impedance spectroscopy (EIS) was used to extract resistive and capacitive attributes of this interface on millimeter-sized single-body hematite electrodes. This was carried out by developing equivalent circuit models for impedance data collected on a semiconducting hematite specimen equilibrated in solutions of 0.1 M NaCl and NH(4)Cl at various pH values. These efforts produced distinct sets of capacitance values for the diffuse and compact layers of the interface. Diffuse layer capacitances shift in the pH 3-11 range from 2.32 to 2.50 μF·cm(-2) in NaCl and from 1.43 to 1.99 μF·cm(-2) in NH(4)Cl. Furthermore, these values reach a minimum capacitance at pH 9, near a probable point of zero charge for an undefined hematite surface exposing a variety of (hydr)oxo functional groups. Compact layer capacitances pertain to the transfer of ions (charge carriers) from the diffuse layer to surface hydroxyls and are independent of pH in NaCl, with values of 32.57 ± 0.49 μF·cm(-2)·s(-φ). However, they decrease with pH in NH(4)Cl from 33.77 at pH 3.5 to 21.02 μF·cm(-2)·s(-φ) at pH 10.6 because of the interactions of ammonium species with surface (hydr)oxo groups. Values of φ (0.71-0.73 in NaCl and 0.56-0.67 in NH(4)Cl) denote the nonideal behavior of this capacitor, which is treated here as a constant phase element. Because electrode-based techniques are generally not applicable to the commonly insulating metal (oxyhydr)oxides found in the environment, this study presents opportunities for exploring mineral/water interface chemistry by EIS studies of single

  4. Chapter 20: Graphite

    SciTech Connect

    Burchell, Timothy D

    2012-01-01

    Graphite is truly a unique material. Its structure, from the nano- to the millimeter scale give it remarkable properties that lead to numerous and diverse applications. Graphite bond anisotropy, with strong in-plane covalent bonds and weak van der Waals type bonding between the planes, gives graphite its unique combination of properties. Easy shear of the crystal, facilitated by weak interplaner bonds allows graphite to be used as a dry lubricant, and is responsible for the substances name! The word graphite is derived from the Greek to write because of graphites ability to mark writing surfaces. Moreover, synthetic graphite contains within its structure, porosity spanning many orders of magnitude in size. The thermal closure of these pores profoundly affects the properties for example, graphite strength increases with temperature to temperatures in excess of 2200 C. Consequently, graphite is utilized in many high temperature applications. The basic physical properties of graphite are reviewed here. Graphite applications include metallurgical; (aluminum and steel production), single crystal silicon production, and metal casting; electrical (motor brushes and commutators); mechanical (seals, bearings and bushings); and nuclear applications, (see Chapter 91, Nuclear Graphite). Here we discuss the structure, manufacture, properties, and applications of Graphite.

  5. Hydrogen and carbon isotope studies on the graphite-bearing metapelites in the northern Kiso district of central Japan

    NASA Astrophysics Data System (ADS)

    Morikiyo, Toshiro

    1986-06-01

    Measurements were made of the hydrogen isotope ratios of hydrous silicates (mica and amphibole) and whole rocks, and the carbon isotope ratios of graphite and carbonaceous matter in the metamorphic rocks from the northern Kiso district in central Japan. δD values of hydrous silicates in the graphite-bearing metapelites are always higher than those in graphite-free schists, even though the sample localities of the two rock-types are very close. Hydrogen isotopic equilibrium has been attained between the coexisting minerals. D/H ratios of water in the metamorphic fluids seem to depend strongly on the presence or absence of graphite and seem to be not constant throughout the district. The district is divided into three areas of low (metamorphic zones I, II), medium (zones IIIa V) and high δ 13Cgr value (zones VIa VII) areas. In the high δ 13Cgr values area, the carbon contents of the graphite-bearing rocks decrease slightly from zones VIa to VII, whereas the δ 13Cgr values increase sharply from the upper part of zone VIa to VIb. The δD values of biotite in these graphite-bearing rocks are higher than those in the medium δ 13Cgr area. This suggests that methane enriched in H and12C is produced and liberated by the devolatilization reactions between muscovite, graphite and water. The fluid produced is composed of water, methane and a subordinate amount of carbon dioxide, and its log fO2 value is deduced to be about 1.2 lower than that defined by the FMQ buffer. In the medium δ 13Cgr area, the δ 13C values of graphite are nearly constant (-20.8‰), while the Fe2O3/(Fe2O3 + FeO) ratio of the graphite-bearing rocks apparently decreases with increasing metamorphic grade. δD differences in hydrous silicates between graphite-bearing and graphite-free rocks are observed. These facts are interpreted to mean that methane was produced in addition to water and carbon dioxide, and that its generation (X_{{text{CH}}_{text{4}} } /X_{{text{CO}}_{text{2}} } ratio of the fluid

  6. Can doping graphite trigger room temperature superconductivity? Evidence for granular high-temperature superconductivity in water-treated graphite powder.

    PubMed

    Scheike, T; Böhlmann, W; Esquinazi, P; Barzola-Quiquia, J; Ballestar, A; Setzer, A

    2012-11-14

    Granular superconductivity in powders of small graphite grains (several tens of micrometers) is demonstrated after treatment with pure water. The temperature, magnetic field and time dependence of the magnetic moment of the treated graphite powder provides evidence for the existence of superconducting vortices with some similarities to high-temperature granular superconducting oxides but even at temperatures above 300 K. Room temperature superconductivity in doped graphite or at its interfaces appears to be possible. PMID:22949348

  7. Ultrafast studies of electron dynamics at metal-dielectric interfaces

    SciTech Connect

    Ge, Nien-Hui

    1998-10-01

    Femtosecond time- and angle-resolved two-photon photoemission spectroscopy has been used to study fundamental aspects of excited electron dynamics at metal-dielectric interfaces, including layer-by-layer evolution of electronic structure and two-dimensional electron localization. On bare Ag(111), the lifetimes of image states are dominated by their position with respect to the projected bulk band structure. The n = 2 state has a shorter lifetime than the n = 1 state due to degeneracy with the bulk conduction band. As the parallel momentum of the n = 1 image electron increases, the lifetime decreases. With decreasing temperatures, the n = 1 image electrons, with zero or nonzero parallel momentum, all become longer lived. Adsorption of one to three layers of n-heptane results in an approximately exponential increase in lifetime as a function of layer thickness. This results from the formation of a tunneling barrier through which the interfacial electrons must decay, consistent with the repulsive bulk electron affinity of n-alkanes. The lifetimes of the higher quantum states indicate that the presence of the monolayer significantly reduces coupling of the image states to the bulk band structure. These results are compared with predictions of a dielectric continuum model. The study of electron lateral motion shows that optical excitation creates interfacial electrons in quasifree states for motion parallel to the n-heptane/Ag(111) interface. These initially delocalized electrons decay into a localized state within a few hundred femtoseconds. The localized electrons then decay back to the metal by tunneling through the adlayer potential barrier. The localization time depends strongly on the electron's initial parallel momentum and exhibits a non-Arrhenius temperature dependence. The experimental findings are consistent with a 2-D self-trapping process in which electrons become localized by interacting with the topmost plane of the alkane layer. The energy dependence of

  8. Study of coal and graphite specimens by means of Raman and cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Kostova, Irena; Tormo, Laura; Crespo-Feo, Elena; Garcia-Guinea, Javier

    2012-06-01

    The weak luminescence shown by coals has been attributed to accessorial minerals and poly-nuclear aromatic hydrocarbons, such as exinite, vitrinite or inertinite, while the luminescence quenching has been found in asphaltenes produced by coal hydrogenation or in pyridine extracts. Nowadays, the spatial resolution and the improved luminescence efficiency of the modern spectrometers allow some details of the luminescent emission centers to be explained. We have selected museum historical coal specimens with different rank, i.e., peat, lignite, sub-bituminous, bituminous, and anthracite to be analyzed by their spectra from cathodoluminescence probe (CL) of an environmental scanning electron microscopy (ESEM), with an energy dispersive spectrometry analyzer (EDS). Additional analytical controls were also performed by X-ray diffraction (XRD), X-ray fluorescence (XRF) and Raman spectrometries. We conclude that coals may display different luminescence emission features coming from several different sources, as follows: (i) broadband of intense luminescence from polynuclear aromatic hydrocarbons, (ii) weakly visible broadband luminescence attributed to band-tail states caused by variations in the energy gap of individual sp2 carbon clusters, which are different in size and/or shape, (iii) silicate impurities causing the common luminescence peak at 325 nm observed in coals. This peak is due to non-bridging oxygen hole centres (tbnd Sisbnd Orad ) probably generated by precursor Sisbnd Osbnd C species formed by tbnd Sisbnd Orad defects and carbon atoms; (iv) a 710 nm CL emission commonly detected also in wood and ivory, which has been correlated with hydrocarbon groups of chlorophyll or lignine. Coals are very complex rocks, composed by both organic and inorganic phases with variable and complex spectra. More analyses are necessary and carbonaceous standards of graphite, silicon carbide, stuffed carbon silica and diamond at variable experimental conditions have to be

  9. Study of coal and graphite specimens by means of Raman and cathodoluminescence.

    PubMed

    Kostova, Irena; Tormo, Laura; Crespo-Feo, Elena; Garcia-Guinea, Javier

    2012-06-01

    The weak luminescence shown by coals has been attributed to accessorial minerals and poly-nuclear aromatic hydrocarbons, such as exinite, vitrinite or inertinite, while the luminescence quenching has been found in asphaltenes produced by coal hydrogenation or in pyridine extracts. Nowadays, the spatial resolution and the improved luminescence efficiency of the modern spectrometers allow some details of the luminescent emission centers to be explained. We have selected museum historical coal specimens with different rank, i.e., peat, lignite, sub-bituminous, bituminous, and anthracite to be analyzed by their spectra from cathodoluminescence probe (CL) of an environmental scanning electron microscopy (ESEM), with an energy dispersive spectrometry analyzer (EDS). Additional analytical controls were also performed by X-ray diffraction (XRD), X-ray fluorescence (XRF) and Raman spectrometries. We conclude that coals may display different luminescence emission features coming from several different sources, as follows: (i) broadband of intense luminescence from polynuclear aromatic hydrocarbons, (ii) weakly visible broadband luminescence attributed to band-tail states caused by variations in the energy gap of individual sp(2) carbon clusters, which are different in size and/or shape, (iii) silicate impurities causing the common luminescence peak at 325 nm observed in coals. This peak is due to non-bridging oxygen hole centres (≡Si-O·) probably generated by precursor Si-O-C species formed by ≡Si-O· defects and carbon atoms; (iv) a 710 nm CL emission commonly detected also in wood and ivory, which has been correlated with hydrocarbon groups of chlorophyll or lignine. Coals are very complex rocks, composed by both organic and inorganic phases with variable and complex spectra. More analyses are necessary and carbonaceous standards of graphite, silicon carbide, stuffed carbon silica and diamond at variable experimental conditions have to be developed. PMID:22366616

  10. Graphite Technology Development Plan

    SciTech Connect

    W. Windes; T. Burchell; M.Carroll

    2010-10-01

    The Next Generation Nuclear Plant (NGNP) will be a helium-cooled High Temperature Gas Reactor (HTGR) with a large graphite core. Graphite physically contains the fuel and comprises the majority of the core volume. Graphite has been used effectively as a structural and moderator material in both research and commercial high-temperature gas-cooled reactors. This development has resulted in graphite being established as a viable structural material for HTGRs. While the general characteristics necessary for producing nuclear grade graphite are understood, historical “nuclear” grades no longer exist. New grades must be fabricated, characterized, and irradiated to demonstrate that current grades of graphite exhibit acceptable non-irradiated and irradiated properties upon which the thermomechanical design of the structural graphite in NGNP is based. This Technology Development Plan outlines the research and development (R&D) activities and associated rationale necessary to qualify nuclear grade graphite for use within the NGNP reactor.

  11. Supported Lipid Bilayer Technology for the Study of Cellular Interfaces

    PubMed Central

    Crites, Travis J.; Maddox, Michael; Padhan, Kartika; Muller, James; Eigsti, Calvin; Varma, Rajat

    2015-01-01

    Glass-supported lipid bilayers presenting freely diffusing proteins have served as a powerful tool for studying cell-cell interfaces, in particular, T cell–antigen presenting cell (APC) interactions, using optical microscopy. Here we expand upon existing protocols and describe the preparation of liposomes by an extrusion method, and describe how this system can be used to study immune synapse formation by Jurkat cells. We also present a method for forming such lipid bilayers on silica beads for the study of signaling responses by population methods, such as western blotting, flow cytometry, and gene-expression analysis. Finally, we describe how to design and prepare transmembrane-anchored protein-laden liposomes, following expression in suspension CHO (CHOs) cells, a mammalian expression system alternative to insect and bacterial cell lines, which do not produce mammalian glycosylation patterns. Such transmembrane-anchored proteins may have many novel applications in cell biology and immunology. PMID:26331983

  12. Cathode interface studies of polymer light emitting devices

    NASA Astrophysics Data System (ADS)

    Swiontek, Stephen; Tzolov, Marian

    2010-03-01

    Efficient injection of charge carriers is a key factor for successful operation of any electronic device and especially of devices with non-crystalline or wide band gap active material. Our study concentrates on the cathode interface of light emitting devices with a conjugated polymer as light emitter. We apply two principally different methods for the cathode deposition, physical and chemical, in order to fundamentally understand if in addition to the commonly accepted notion for the matching of the work functions also material modification takes place. The completed devices are studies by steady-state electrical measurements, impedance spectroscopy, current and emission lifetime measurements, and electroluminescence spectroscopy. The morphology of the cathodes is studied by Scanning Electron Microscopy and the formation of additional phases by Energy Dispersive X-ray Spectroscopy. The results help to define ways for more cost efficient fabrication of light emitting devices with applications in displays, electronic newspapers, room illumination, etc.

  13. Body Machine Interfaces for Neuromotor Rehabilitation: a Case Study

    PubMed Central

    Pierella, Camilla; Abdollahi, Farnaz; Farshchiansadegh, Ali; Pedersen, Jessica; Chen, David; Mussa-Ivaldi, Ferdinando A.; Casadio, Maura

    2015-01-01

    High-level spinal cord injury (SCI) survivors face every day two related problems: recovering motor skills and regaining functional independence. Body machine interfaces (BoMIs) empower people with sever motor disabilities with the ability to control an external device, but they also offer the opportunity to focus concurrently on achieving rehabilitative goals. In this study we developed a portable, and low-cost BoMI that addresses both problems. The BoMI remaps the user’s residual upper body mobility to the two coordinates of a cursor on a computer monitor. By controlling the cursor, the user can perform functional tasks, such as entering text and playing games. This framework also allows the mapping between the body and the cursor space to be modified, gradually challenging the user to exercise more impaired movements. With this approach, we were able to change the behavior of our SCI subject, who initially used almost exclusively his less impaired degrees of freedom - on the left side - for controlling the BoMI. At the end of the few practice sessions he had restored symmetry between left and right side of the body, with an increase of mobility and strength of all the degrees of freedom involved in the control of the interface. This is the first proof of concept that our BoMI can be used to control assistive devices and reach specific rehabilitative goals simultaneously. PMID:25569980

  14. Body machine interfaces for neuromotor rehabilitation: a case study.

    PubMed

    Pierella, Camilla; Abdollahi, Farnaz; Farshchiansadegh, Ali; Pedersen, Jessica; Chen, David; Mussa-Ivaldi, Ferdinando A; Casadio, Maura

    2014-01-01

    High-level spinal cord injury (SCI) survivors face every day two related problems: recovering motor skills and regaining functional independence. Body machine interfaces (BoMIs) empower people with sever motor disabilities with the ability to control an external device, but they also offer the opportunity to focus concurrently on achieving rehabilitative goals. In this study we developed a portable, and low-cost BoMI that addresses both problems. The BoMI remaps the user's residual upper body mobility to the two coordinates of a cursor on a computer monitor. By controlling the cursor, the user can perform functional tasks, such as entering text and playing games. This framework also allows the mapping between the body and the cursor space to be modified, gradually challenging the user to exercise more impaired movements. With this approach, we were able to change the behavior of our SCI subject, who initially used almost exclusively his less impaired degrees of freedom - on the left side - for controlling the BoMI. At the end of the few practice sessions he had restored symmetry between left and right side of the body, with an increase of mobility and strength of all the degrees of freedom involved in the control of the interface. This is the first proof of concept that our BoMI can be used to control assistive devices and reach specific rehabilitative goals simultaneously. PMID:25569980

  15. Study on the structural evolution of modified phenol formaldehyde resin adhesive for the high-temperature bonding of graphite

    NASA Astrophysics Data System (ADS)

    Wang, Jigang; Jiang, Nan; Guo, Quangui; Liu, Lang; Song, Jinren

    2006-01-01

    A novel adhesive for carbon materials composed of phenol-formaldehyde resin, boron carbide and fumed silica, was prepared. The adhesive property of graphite joints bonded by the above adhesive treated at high-temperatures was tested. Results showed that the adhesive was found to have outstanding high-temperature bonding properties for graphite. The adhesive structure was dense and uniform even after the graphite joints were heat-treated at 1500 °C. Bonding strength was 17.1 MPa. The evolution of adhesive structure was investigated. The results indicated that the addition of the secondary additive, fumed silica, improved the bonding performance greatly. Borosilicate phase with better stability was formed during the heat-treatment process, and the volume shrinkage was restrained effectively, which was responsible for the satisfactory high-temperature bonding performance of graphite.

  16. Adhesion at WC/diamond interfaces - A theoretical study

    SciTech Connect

    Padmanabhan, Haricharan; Rao, M. S. Ramachandra; Nanda, B. R. K.

    2015-06-24

    We investigate the adhesion at the interface of face-centered tungsten-carbide (001) and diamond (001) from density-functional calculations. Four high-symmetry model interfaces, representing different lattice orientations for either side of the interface, are constructed to incorporate different degrees of strain arising due to lattice mismatch. The adhesion, estimated from the ideal work of separation, is found to be in the range of 4 - 7 J m{sup −2} and is comparable to that of metal-carbide interfaces. Maximum adhesion occurs when WC and diamond slabs have the same orientation, even though such a growth induces large epitaxial strain at the interface. From electronic structure calculations, we attribute the adhesion to covalent interaction between carbon p-orbitals as well as partial ionic interaction between the tungsten d- and carbon p-orbitals across the interface.

  17. Removal of carbon-14 from irradiated graphite

    NASA Astrophysics Data System (ADS)

    Dunzik-Gougar, Mary Lou; Smith, Tara E.

    2014-08-01

    Approximately 250,000 tonnes of irradiated graphite waste exists worldwide and that quantity is expected to increase with decommissioning of Generation II reactors and deployment of Generation IV gas-cooled, graphite moderated reactors. This situation indicates the need for a graphite waste management strategy. On of the isotopes of great concern for long-term disposal of irradiated graphite is carbon-14 (14C), with a half-life of 5730 years. Study of irradiated graphite from some nuclear reactors indicates 14C is concentrated on the outer 5 mm of the graphite structure. The aim of the research presented here is to develop a practical method by which 14C can be removed. In parallel with these efforts, the same irradiated graphite material is being characterized to identify the chemical form of 14C in irradiated graphite. A nuclear-grade graphite, NBG-18, and a high-surface-area graphite foam, POCOFoam®, were exposed to liquid nitrogen (to increase the quantity of 14C precursor) and neutron-irradiated (1013 neutrons/cm2/s). During post-irradiation thermal treatment, graphite samples were heated in the presence of an inert carrier gas (with or without the addition of an oxidant gas), which carries off gaseous products released during treatment. Graphite gasification occurs via interaction with adsorbed oxygen complexes. Experiments in argon only were performed at 900 °C and 1400 °C to evaluate the selective removal of 14C. Thermal treatment also was performed with the addition of 3 and 5 vol% oxygen at temperatures 700 °C and 1400 °C. Thermal treatment experiments were evaluated for the effective selective removal of 14C. Lower temperatures and oxygen levels correlated to more efficient 14C removal.

  18. Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A., III; Ferguson, Frank T.; Lucas, Christopher; Kimura, Yuki; Hohenberg, Charles

    2009-01-01

    The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments.

  19. Graphite Formation in Cast Iron

    NASA Technical Reports Server (NTRS)

    Stefanescu, D. M.

    1985-01-01

    In the first phase of the project it was proven that by changing the ratio between the thermal gradient and the growth rate for commercial cast iron samples solidifying in a Bridgman type furnace, it is possible to produce all types of graphite structures, from flake to spheroidal, and all types of matrices, from ferritic to white at a certain given level of cerium. KC-135 flight experiments have shown that in a low-gravity environment, no flotation occurs even in spheroidal graphite cast irons with carbon equivalent as high as 5%, while extensive graphite flotation occurred in both flake and spheroidal graphite cast irons, in high carbon samples solidified in a high gravity environment. This opens the way for production of iron-carbon composite materials, with high carbon content (e.g., 10%) in a low gravity environment. By using KC-135 flights, the influence of some basic elements on the solidification of cast iron will be studied. The mechanism of flake to spheroidal graphite transition will be studied, by using quenching experiments at both low and one gravity for different G/R ratios.

  20. Drainage flows: A mountain-plains interface numerical case study

    SciTech Connect

    Poulos, G.S.; Bossert, J.E.

    1992-01-01

    In January/February, 1991 an intensive set of measurements was taken around Rocky Flats near Denver, CO, USA under the auspices of the Atmospheric Studies in Complex Terrain (ASCOT) program. This region of the country is known as the Front Range, and is characterized by a transition from the relatively flat terrain of the Great Plains to the highly varied terrain of the Rocky Mountains. The mountains are oriented north-south and rise from 1800m above mean sea level (MSL) to 3600m MSL at the Continental Divide. Numerous east-west oriented valleys begin in the mountains and end at the plains interface. This terrain makes the Front Range a challenging region to model. One of the more important flows created by this severe terrain are the highly-varying drainage flows found during stagnant, wintertime conditions. These flows can interact with larger-scale mountain and synoptic winds. One goal of the ASCOT 1991 program was to gain insight into multi-scale meteorological interaction by observing wintertime drainage conditions at the mountain-valley-plains interface. ASCOT data included surface and upper air measurements on approximately a 50km{sup 2} scale. Simultaneously, an SF{sub 6} tracer release study was being conducted around Rocky Flats, a nuclear materials production facility. Detailed surface concentration measurements were completed for the SF{sub 6} plume. This combination of meteorological and tracer concentration data provided a unique data set for comparisons of mesoscale and dispersion modeling results with observations and for evaluating our capability to predict pollutant transport. Our approach is to use the Regional Atmospheric Modeling System (RAMS) mesoscale model to simulate atmospheric conditions and the Lagrangian Particle Dispersion Model (LPDM) to model the dispersion of the SF{sub 6}.

  1. Drainage flows: A mountain-plains interface numerical case study

    SciTech Connect

    Poulos, G.S.; Bossert, J.E.

    1992-09-01

    In January/February, 1991 an intensive set of measurements was taken around Rocky Flats near Denver, CO, USA under the auspices of the Atmospheric Studies in Complex Terrain (ASCOT) program. This region of the country is known as the Front Range, and is characterized by a transition from the relatively flat terrain of the Great Plains to the highly varied terrain of the Rocky Mountains. The mountains are oriented north-south and rise from 1800m above mean sea level (MSL) to 3600m MSL at the Continental Divide. Numerous east-west oriented valleys begin in the mountains and end at the plains interface. This terrain makes the Front Range a challenging region to model. One of the more important flows created by this severe terrain are the highly-varying drainage flows found during stagnant, wintertime conditions. These flows can interact with larger-scale mountain and synoptic winds. One goal of the ASCOT 1991 program was to gain insight into multi-scale meteorological interaction by observing wintertime drainage conditions at the mountain-valley-plains interface. ASCOT data included surface and upper air measurements on approximately a 50km{sup 2} scale. Simultaneously, an SF{sub 6} tracer release study was being conducted around Rocky Flats, a nuclear materials production facility. Detailed surface concentration measurements were completed for the SF{sub 6} plume. This combination of meteorological and tracer concentration data provided a unique data set for comparisons of mesoscale and dispersion modeling results with observations and for evaluating our capability to predict pollutant transport. Our approach is to use the Regional Atmospheric Modeling System (RAMS) mesoscale model to simulate atmospheric conditions and the Lagrangian Particle Dispersion Model (LPDM) to model the dispersion of the SF{sub 6}.

  2. A Case Study on the Design of Learning Interfaces

    ERIC Educational Resources Information Center

    Perry, Gabriela Trindade; Schnaid, Fernando

    2012-01-01

    The design of educational software interfaces is a complex task, given its high domain dependency and multidisciplinary nature. It requires that teachers' knowledge and pedagogical beliefs be incorporated into the interface, posing a challenge to both teachers and designers, as they have to act as partners from the earliest phases of the process,…

  3. Studies of interfaces and vapors with Optical Second Harmonic Generation

    SciTech Connect

    Mullin, C. S.

    1993-12-01

    Optical Second Harmonic Generation (SHG) has been applied to the study of soap-like molecules adsorbed to the water-air interface. By calibrating the signal from a soluble monolayer with that of an insoluble homolog, absolute measurements of the surface density could be obtained and related to the bulk concentration and surface tension. We could then demonstrate that the soluble surfactant forms a single monolayer at the interface. Furthermore, it deviates significantly from the ideal case in that its activity coefficients are far from 1, yet those coefficients remain constant over a broad range of surface pressures. We present evidence of a first-order phase transition taking place during the adsorption of this soluble monolayer. We consider the effects of the non-ideal behavior and the phase transition on the microscopic model of adsorption, and formulate an alternative to the Langmuir picture of adsorption which is just as simple, yet it can more easily allow for non-ideal behavior. The second half of this thesis considers the problem of SHG in bulk metal vapors. The symmetry of the vapor forbids SHG, yet it has been observed. We consider several models whereby the symmetry of the vapor is broken by the presence of the laser and compare their predictions to new observations we have made using a few-picosecond laser pulse. The two-lobed output beam profile shows that it is the vapor-plus-beam combination whose symmetry is important. The dependence on vapor pressure demonstrates the coherent nature of the radiation, while the dependence on buffer gas pressure hints at a change of the symmetry in time. The time-dependence is measured directly with a preliminary pump-probe measurement. The magnitude and intensity dependence of the signal are also measured. All but one of the models are eliminated by this comparison.

  4. Neutron irradiation damage of nuclear graphite studied by high-resolution transmission electron microscopy and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Krishna, R.; Jones, A. N.; McDermott, L.; Marsden, B. J.

    2015-12-01

    Nuclear graphite components are produced from polycrystalline artificial graphite manufacture from a binder and filler coke with approximately 20% porosity. During the operational lifetime, nuclear graphite moderator components are subjected to fast neutron irradiation which contributes to the change of material and physical properties such as thermal expansion co-efficient, young's modulus and dimensional change. These changes are directly driven by irradiation-induced changes to the crystal structure as reflected through the bulk microstructure. It is therefore of critical importance that these irradiation changes and there implication on component property changes are fully understood. This work examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor; a low temperature, low fluence, air-cooled Materials Test Reactor which operated in the UK. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) have been employed to characterise the effect of increased irradiation fluence on graphite microstructure and understand low temperature irradiation damage processes. HRTEM confirms the structural damage of the crystal lattice caused by irradiation attributed to a high number of defects generation with the accumulation of dislocation interactions at nano-scale range. Irradiation-induced crystal defects, lattice parameters and crystallite size compared to virgin nuclear graphite are characterised using selected area diffraction (SAD) patterns in TEM and Raman Spectroscopy. The consolidated 'D'peak in the Raman spectra confirms the formation of in-plane point defects and reflected as disordered regions in the lattice. The reduced intensity and broadened peaks of 'G' and 'D' in the Raman and HRTEM results confirm the appearance of turbulence and disordering of the basal planes whilst maintaining their coherent layered graphite structure.

  5. Fundamental Studies of Low Velocity Impact Resistance of Graphite Fiber Reinforced Polymer Matrix Composites. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Bowles, K. J.

    1985-01-01

    A study was conducted to relate the impact resistance of graphite fiber reinforced composites with matrix properties through gaining an understanding of the basic mechanics involved in the deformation and fracture process, and the effect of the polymer matrix structure on these mechanisms. It was found that the resin matrix structure influences the composite impact resistance in at least two ways. The integration of flexibilizers into the polymer chain structure tends to reduce the T sub g and the mechanical properties of the polymer. The reduction in the mechanical properties of the matrix does not enhance the composite impact resistance because it allows matrix controlled failure to initiate impact damage. It was found that when the instrumented dropweight impact tester is used as a means for assessing resin toughness, the resin toughness is enhanced by the ability of the clamped specimen to deflect enough to produce sufficient membrane action to support a significant amount of the load. The results of this study indicate that crossplied composite impact resistance is very much dependent on the matrix mechanical properties.

  6. Multiaxial graphite test specimen

    SciTech Connect

    1988-09-01

    A multiaxial test program is to be conducted by Oak Ridge National Laboratory (ORNL) on the core component graphite. The objectives of the tests are to obtain failure data under uniaxial and biaxial states of stress in order to construct a failure surface in a two-dimensional stress space. These data will be used in verifying the accuracy of the maximum stress failure theory being proposed for use in designing the core graphite components. Tubular specimens are proposed to be used and are either loaded axially and/or subjected to internal pressure. This report includes a study on three specimen configurations. The conclusions of that study indicate that an elliptical transition geometry procedures the smallest discontinuity effects. Several loading combustions were studied using the elliptical transition specimen. The primary purpose is to establish the location of the highest stress state and its relation to the gage section for all of the loading conditions. The tension/internal pres sure loading condition (1:1) indicated that the high stress area is just outside the gage section but still should be acceptable. 5 refs., 18 figs.

  7. A study of dilational rheological properties of polymers at interfaces.

    PubMed

    Cao, Xulong; Li, Yang; Jiang, Shengxiang; Sun, Huanquan; Cagna, Alain; Dou, Lixia

    2004-02-15

    Viscoelastic properties of two polymers, partially hydrolyzed polyacrylamide and partially hydrolyzed modified polyacrylamide, widely used in chemical flooding in the petroleum industry, were investigated at three interfaces, water-air, water-dodecane, and water-crude oil, by means of a dilational method provided by I.T. Concept, France, at 85 degrees C. Polymer solutions were prepared in brine with 10,000 mg/l sodium chloride and 2000 mg/l calcium chloride. It has been shown that the viscoelastic modulus increases with the increment of polymer concentration in the range of 0-1500 mg/l at the water-air interface. Each polymer shows different viscoelatic behavior at different interfaces. Generally speaking, values of the viscoelastic modulus (E), the real part (E'), and the imaginary part (E") at the crude oil-water interface for each polymer are lower than at the air-water or water-dodecane interface. The two polymers display different interfacial properties at the same interface. Polymer No. 2 gives more viscous interfaces than polymer No. 1. All the information obtained from this paper will be helpful in understanding the interfacial rheology of ultra-high-molecular-weight polymer solutions. PMID:14697692

  8. Pyrolytic graphite collector development program

    NASA Technical Reports Server (NTRS)

    Wilkins, W. J.

    1982-01-01

    Pyrolytic graphite promises to have significant advantages as a material for multistage depressed collector electrodes. Among these advantages are lighter weight, improved mechanical stiffness under shock and vibration, reduced secondary electron back-streaming for higher efficiency, and reduced outgassing at higher operating temperatures. The essential properties of pyrolytic graphite and the necessary design criteria are discussed. This includes the study of suitable electrode geometries and methods of attachment to other metal and ceramic collector components consistent with typical electrical, thermal, and mechanical requirements.

  9. A coupled thermal and electrochemical study of lithium-ion battery cooled by paraffin/porous-graphite-matrix composite

    NASA Astrophysics Data System (ADS)

    Greco, Angelo; Jiang, Xi

    2016-05-01

    Lithium-ion (Li-ion) battery cooling using a phase change material (PCM)/compressed expanded natural graphite (CENG) composite is investigated, for a cylindrical battery cell and for a battery module scale. An electrochemistry model (average model) is coupled to the thermal model, with the addition of a one-dimensional model for the solution and solid diffusion using the nodal network method. The analysis of the temperature distribution of the battery module scale has shown that a two-dimensional model is sufficient to describe the transient temperature rise. In consequence, a two-dimensional cell-centred finite volume code for unstructured meshes is developed with additions of the electrochemistry and phase change. This two-dimensional thermal model is used to investigate a new and usual battery module configurations cooled by PCM/CENG at different discharge rates. The comparison of both configurations with a constant source term and heat generation based on the electrochemistry model showed the superiority of the new design. In this study, comparisons between the predictions from different analytical and computational tools as well as open-source packages were carried out, and close agreements have been observed.

  10. Theoretical study of the electronic structure of binary and ternary first-stage alkali intercalation compounds of graphite

    SciTech Connect

    Tatar, R.C.

    1985-01-01

    Despite the tremendous number of theoretical and experimental studies of the electronic properties of the first-stage heavy alkali intercalation compounds of graphite - KC8, RbC8, and CsC8 - there is still a great deal of uncertainty in the electronic structures of these materials. The electronic structures of these materials - required for the interpretation of experimental results - were calculated previously by several techniques. Because of the inability of these calculations to satisfactorily resolve the interpretation of experiments, and questions concerning the approximations used in the previous calculations, an attempt is made to estimate the electronic structure in these materials using a state-of-the-art, self consistent pseudopotential technique with a mixed basis of plane waves and localized atomic orbitals. The goal is to provide a detailed first principles model of the electronic interactions in these materials that can form the basis for a variety of additional, model calculations that address the experimental issues. In addition, and attempt is made to elucidate more fully the microscopic basis for differences between the heavy-alkali compounds as well as the difference between the heavy-alkali compounds as a class and the compounds formed from the light alkali, lithium.

  11. Ballistic Electron Emission Microscopy Studies of Ferromagnet - Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Mather, P. G.; Perrella, A. C.; Yurtsever, A.; Buhrman, R. A.

    2004-03-01

    Devices that employ spin as well as charge effects have been the subjects of extensive study recently. The magnetic tunneling transistor (1) is one important device that demonstrates an electrical means of injecting spin-polarized electrons into a semiconductor. A Schottky barrier lies at the heart of the device, and a high quality spatially homogenous and uniform barrier formed on GaAs is highly desirable. We have used ballistic electron emission microscopy (BEEM) to study CoFe, Fe and permalloy deposited on a GaAs substrate to give nanometer resolved evaluation of hot electron transport through the films and across the Schottky barrier. All films give a homogenous, uniform barrier as compared with evaporated Au/GaAs and Ag/GaAs interfaces. We will report on BEEM measurements of the hot electron transfer ratio across the Schottky barrier for the different ferromagnetic materials, and on the energy and spin-dependent hot electron attenuation lengths of the CoFe, Fe, and permalloy films. (1) Sebastiaan van Dijken, Xin Jiang, Stuart S. P. Parkin, APL, 80, 3364.

  12. Radiation Effects in Graphite

    SciTech Connect

    Burchell, Timothy D

    2012-01-01

    The requirements for a solid moderator are reviewed and the reasons that graphite has become the solid moderator of choice discussed. The manufacture and properties of some currently available near-isotropic and isotropic grades are described. The major features of a graphite moderated reactors are briefly outlined. Displacement damage and the induced structural and dimensional changes in graphite are described. Recent characterization work on nano-carbons and oriented pyrolytic graphites that have shed new light on graphite defect structures are reviewed, and the effect of irradiation temperature on the defect structures is highlighted. Changes in the physical properties of nuclear graphite caused by neutron irradiation are reported. Finally, the importance of irradiation induced creep is presented, along with current models and their deficiencies.

  13. Studies of Reduced Graphene Oxide and Graphite Oxide in the Aspect of Their Possible Application in Gas Sensors

    PubMed Central

    Drewniak, Sabina; Muzyka, Roksana; Stolarczyk, Agnieszka; Pustelny, Tadeusz; Kotyczka-Morańska, Michalina; Setkiewicz, Maciej

    2016-01-01

    The paper presents the results of investigations on resistance structures based on graphite oxide (GRO) and graphene oxide (rGO). The subject matter of the investigations was thaw the sensitivity of the tested structures was affected by hydrogen, nitrogen dioxide and carbon dioxide. The experiments were performed at a temperature range from 30 °C to 150 °C in two carrier gases: nitrogen and synthetic air. The measurements were also aimed at characterization of the graphite oxide and graphene oxide. In our measurements we used (among others) techniques such as: Atomic Force Microscopy (AFM); Scanning Electron Microscopy (SEM); Raman Spectroscopy (RS); Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Microscopy (XPS). The data resulting from the characterizations of graphite oxide and graphene oxide have made it possible to interpret the obtained results from the point of view of physicochemical changes occurring in these structures. PMID:26784198

  14. Studies of Reduced Graphene Oxide and Graphite Oxide in the Aspect of Their Possible Application in Gas Sensors.

    PubMed

    Drewniak, Sabina; Muzyka, Roksana; Stolarczyk, Agnieszka; Pustelny, Tadeusz; Kotyczka-Morańska, Michalina; Setkiewicz, Maciej

    2015-01-01

    The paper presents the results of investigations on resistance structures based on graphite oxide (GRO) and graphene oxide (rGO). The subject matter of the investigations was thaw the sensitivity of the tested structures was affected by hydrogen, nitrogen dioxide and carbon dioxide. The experiments were performed at a temperature range from 30 °C to 150 °C in two carrier gases: nitrogen and synthetic air. The measurements were also aimed at characterization of the graphite oxide and graphene oxide. In our measurements we used (among others) techniques such as: Atomic Force Microscopy (AFM); Scanning Electron Microscopy (SEM); Raman Spectroscopy (RS); Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Microscopy (XPS). The data resulting from the characterizations of graphite oxide and graphene oxide have made it possible to interpret the obtained results from the point of view of physicochemical changes occurring in these structures. PMID:26784198

  15. Producing graphite with desired properties

    NASA Technical Reports Server (NTRS)

    Dickinson, J. M.; Imprescia, R. J.; Reiswig, R. D.; Smith, M. C.

    1971-01-01

    Isotropic or anisotropic graphite is synthesized with precise control of particle size, distribution, and shape. The isotropic graphites are nearly perfectly isotropic, with thermal expansion coefficients two or three times those of ordinary graphites. The anisotropic graphites approach the anisotropy of pyrolytic graphite.

  16. Experimental study of an isochorically heated heterogeneous interface. A progress report

    SciTech Connect

    Fernandez, Juan Carlos

    2015-08-20

    Outline of the presentation: Studying possible mix / interface motion between heterogeneous low/high Z interfaces driven by 2-fluid or kinetic plasma effects (Heated to few eV, Sharp (sub µm) interface); Isochoric heating to initialize interface done with Al quasimonoenergetic ion beams on Trident; Have measured isochoric heating in individual materials intended for compound targets; Fielded experiments on Trident to measure interface motion (Gold-diamond, tin-aluminium); Measured heated-sample temperature with streaked optical pyrometry (SOP) (UT Austin led (research contract), SOP tests → heating uniformity Vs thickness on Al foils. Results are being analyzed.

  17. High-energy photoemission studies of oxide interfaces

    NASA Astrophysics Data System (ADS)

    Claessen, Ralph

    2015-03-01

    The interfaces of complex oxide heterostructures can host novel quantum phases not existing in the bulk of the constituents, with the high-mobility 2D electron system (2DES) in LaAlO3/SrTiO3 (LAO/STO) representing a prominent example. Despite extensive research the origin of the 2DES and its unusual properties - including the supposed coexistence of superconductivity and ferromagnetism - are still a matter of intense debate. Photoelectron spectroscopy, recently extended into the soft (SX-ARPES) and hard (HAXPES) X-ray regime, is a powerful method to provide detailed insight into the electronic structure of these heterostructures and, in particular, of the buried interface. This includes the identification of the orbital character of the 2DES as well as the determination of vital band structure information, such as band alignment, band bending, and even k-resolved band dispersions and Fermi surface topology. Moreover, resonant photoemission at the Ti L-edge reveals the existence of two different species of Ti 3d states, localized and itinerant, which can be distinguished and identified by their different resonance behavior. The role of oxygen vacancies is studied by controlled in-situ oxidation, which allows us to vary the composition from fully stoichiometric to strongly O-deficient. By comparison to free STO surfaces we can thus demonstrate that the metallicity of the heteointerfaces is intrinsic, i . e . it persists even in the absence of O defects. I will discuss our photoemission results on LAO/STO heterostructures in both (100) and (111) orientation as well as on the related system γ-Al2O3/STO(100), which also hosts a 2DES with an even higher mobility. Work in collaboration with J. Mannhart (MPI-FKF, Stuttgart), N. Pryds (TU Denmark), G. Rijnders (U Twente), S. Suga (U Osaka), M. Giorgoi (BESSY, HZB), W. Drube (DESY Photon Science), V.N. Strocov (Swiss Light Source), J. Denlinger (Advanced Light Source, LBNL), and T.-L. Lee (Diamond Light Source). Support by

  18. Wetting transitions of water on graphite and graphene.

    PubMed

    Kim, Hye-Young; dos Santos, Maria Cristina; Cole, Milton W

    2014-09-18

    Water has been predicted theoretically and observed experimentally to exhibit a wetting transition on graphite. Previous study of this problem was based on quite uncertain water-graphite interaction potentials. This paper computes the wetting temperature on graphite using recent, more realistic, interactions. Similar calculations are presented for the case of water on a suspended (free-standing) graphene sheet. PMID:24617914

  19. Kinetics of the Formation of Intercalation Compounds in Crystalline Graphite

    NASA Technical Reports Server (NTRS)

    Sharma, P. K.; Hickey, G. S.

    1995-01-01

    Crystalline graphite has a structure that can be best described as an ordered stack of flat aromatic layers. It is known to form intercalation compounds with bromine and nitric acid. Their formation was studied using thermal measurements and analytical techniques. Samples of graphite treated with either bromine or nitric acid were prepared by contacting these reagents with powdered graphite.

  20. Experimental Studies of Nanobubbles at Solid-Water Interfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehua

    2013-11-01

    When a hydrophobic substrate is in contact with water, gas bubbles thinner than 100 nm can form at the interface and stay for long time under ambient conditions. These nanobubbles have significant influence on a range of interfacial processes. For example, they give rise to hydrodynamic slip on the boundary, initiate the rupture of thin liquid films, facilitate the long-ranged interactions between hydrophobic surfaces, and enhance the attachment of a macroscopic bubble to the substrate. Experimentally, it is nontrivial to characterize such small fragile bubbles and unravel their fundamental physical properties. Based on our established procedure for the nanobubble formation, we have systematically studied the formation, stability and response of nanobubbles to external fields (e.g. sonication, pressure drop and temperature rise). By following the bubble morphology by atomic force microscopy, we show that the loss or gain of the nanobubble volume is achieved mainly by the change in the bubble height. The pinning on the three-phase boundary has significant implication on the properties of nanobubbles under various conditions. This talk will cover the effects of the substrate structures on the nanobubble formation, and the response of nanobubbles to the gas dissolution, the temperature increase, the extended gentle ultrasound or the substantial pressure drop in the environment. We acknowledge the support from Australian Research Council (FFT120100473).

  1. Ultrafast optical studies of surface reaction processes at semiconductor interfaces

    SciTech Connect

    Miller, R.J.D.

    1993-03-01

    Rectifying properties of semiconductor liquid junctions make them a simple system for converting and storing optical energy. However, interfacial electron or hole carrier transfer and competing non-radiative (energy loss) channels are not well understood at surfaces. This research has explored the use of three optical techniques, Surface Space Charge Electrooptic Sampling, Surface Restricted Transient Grating Spectroscopy, and Femtosecond Optical Kerr Spectroscopy (OKE) to obtain time evolution of the surface spatial distribution of photogenerated charge carriers, photocarrier population dynamics at semiconductor interfaces, and solvent modes responsible for charge localization and separation. These studies have shown that carriers arrive at GaAs(100) surfaces on the hundred femtosecond time scale. Improvements in time resolution, using surface grating spectroscopy, have shown interfacial hole transfer is occurring on the picosecond time scale. The OKE approach to solvent dynamics has determined the response of water to a field is multiexpontential with a major relaxation component of 100 femtoseconds. The observed interfacial hole transfer to Se[sup [minus]2] acceptors is occurring on this same time scale. This observation illustrates charge transfer processes can occur in the strong electronic coupling limit and can be competitive with carrier thermalization.

  2. Interphase tailoring in graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Subramanian, R. V.; Sanadi, A. R.; Crasto, A. S.

    1988-01-01

    The fiber-matrix interphase in graphite fiber-epoxy matrix composites is presently modified through the electrodeposition of a coating of the polymer poly(styrene-comaleic anhydride), or 'SMA' on the graphite fibers; optimum conditions have been established for the achievement of the requisite thin, uniform coatings, as verified by SEM. A single-fiber composite test has shown the SMA coating to result in an interfacial shear strength to improve by 50 percent over commercially treated fibers without sacrifice in impact strength. It is suggested that the epoxy resin's superior penetration into the SMA interphase results in a tougher fiber/matrix interface which possesses intrinsic energy-absorbing mechanisms.

  3. Inhibition of Oxidation in Nuclear Graphite

    SciTech Connect

    Phil Winston; James W. Sterbentz; William E. Windes

    2013-10-01

    Graphite is a fundamental material of high temperature gas cooled nuclear reactors, providing both structure and neutron moderation. Its high thermal conductivity, chemical inertness, thermal heat capacity, and high thermal structural stability under normal and off normal conditions contribute to the inherent safety of these reactor designs. One of the primary safety issues for a high temperature graphite reactor core is the possibility of rapid oxidation of the carbon structure during an off normal design basis event where an oxidizing atmosphere (air ingress) can be introduced to the hot core. Although the current Generation IV high temperature reactor designs attempt to mitigate any damage caused by a postualed air ingress event, the use of graphite components that inhibit oxidation is a logical step to increase the safety of these reactors. Recent experimental studies of graphite containing between 5.5 and 7 wt% boron carbide (B4C) indicate that oxidation is dramatically reduced even at prolonged exposures at temperatures up to 900°C. The proposed addition of B4C to graphite components in the nuclear core would necessarily be enriched in B-11 isotope in order to minimize B-10 neutron absorption and graphite swelling. The enriched boron can be added to the graphite during billet fabrication. Experimental oxidation rate results and potential applications for borated graphite in nuclear reactor components will be discussed.

  4. Study of Composite Interface Fracture and Crack Growth Monitoring Using Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Bily, Mollie A.; Kwon, Young W.; Pollak, Randall D.

    2010-08-01

    Interface fracture of woven fabric composite layers was studied using Mode II fracture testing. Both carbon fiber and E-glass fiber composites were used with a vinyl ester resin. First, the single-step cured (i.e., co-cured) composite interface strength was compared to that of the two-step cured interface as used in the scarf joint technique. The results showed that the two-step cured interface was as strong as the co-cured interface. Carbon nanotubes were then applied to the composite interface using two-step curing, and then followed by Mode II fracture testing. The results indicated a significant improvement of the interface fracture toughness due to the dispersed carbon nanotube layer for both carbon fiber and E-glass fiber composites. The carbon nanotube layer was then evaluated as a means to monitor crack growth along the interface. Because carbon nanotubes have very high electrical conductivity, the electrical resistance was measured through the interface as a crack grew, thus disrupting the carbon nanotube network and increasing the resistance. The results showed a linear relationship between crack length and interface resistance for the carbon fiber composites, and allowed initial detection of failure in the E-glass fiber composites. This study demonstrated that the application of carbon nanotubes along a critical composite interface not only improves fracture properties but can also be used to detect and monitor interfacial damage.

  5. Discrete Element study of granular material - Bumpy wall interface behavior

    NASA Astrophysics Data System (ADS)

    El Cheikh, Khadija; Rémond, Sébastien; Pizette, Patrick; Vanhove, Yannick; Djelal, Chafika

    2016-09-01

    This paper presents a DEM study of a confined granular material sheared between two parallel bumpy walls. The granular material consists of packed dry spherical particles. The bumpiness is modeled by spheres of a given diameter glued on horizontal planes. Different bumpy surfaces are modeled by varying diameter or concentration of glued spheres. The material is sheared by moving the two bumpy walls at fixed velocity. During shear, the confining pressure applied on each bumpy wall is controlled. The effect of wall bumpiness on the effective friction coefficient and on the granular material behavior at the bumpy walls is reported for various shearing conditions. For given bumpiness and confining pressure that we have studied, it is found that the shear velocity does not affect the shear stress. However, the effective friction coefficient and the behavior of the granular material depend on the bumpiness. When the diameter of the glued spheres is larger than about the average grains diameter of the medium, the latter is uniformly sheared and the effective friction coefficient remains constant. For smaller diameters of the glued spheres, the effective friction coefficient increases with the diameter of glued spheres. The influence of glued spheres concentration is significant only for small glued spheres diameters, typically half of average particle diameter of the granular material. In this case, increasing the concentration of glued spheres leads to a decrease in effective friction coefficient and to shear localization at the interface. For different diameters and concentrations of glued spheres, we show that the effect of bumpiness on the effective friction coefficient can be characterized by the depth of interlocking.

  6. Positron annihilation lifetime study of interfaces in ternary polymer blends

    NASA Astrophysics Data System (ADS)

    Meghala, D.; Ramya, P.; Pasang, T.; Raj, J. M.; Ranganathaiah, C.; Williams, J. F.

    2013-06-01

    A new method based on positron lifetime spectroscopy is developed to characterize individual interfaces in ternary polymer blends and hence determine the composition dependent miscibility level. The method owes its origin to the Kirkwood-Risemann-Zimm (KRZ) model for the evaluation of the hydrodynamic interaction parameters (αij) which was used successfully for a binary blend with a single interface. The model was revised for the present work for ternary polymer blends to account for three interfaces. The efficacy of this method is shown for two ternary blends namely poly(styrene-co-acrylonitrile)/poly (ethylene-co-vinylacetate)/poly(vinyl chloride) (SAN/EVA/PVC) and polycaprolactone /poly(styrene-co-acrylonitrile)/poly(vinyl chloride) (PCL/SAN/PVC) at different compositions. An effective hydrodynamic interaction parameter, αeff, was introduced to predict the overall miscibility of ternary blends.

  7. Diffusion Of Hydrophobin Proteins In Solution And Interactions With A Graphite Surface

    SciTech Connect

    Mereghetti, Paolo; Wade, Rebecca C.

    2011-04-21

    Background Hydrophobins are small proteins produced by filamentous fungi that have a variety of biological functions including coating of spores and surface adhesion. To accomplish these functions, they rely on unique interface-binding properties. Using atomic-detail implicit solvent rigid-body Brownian dynamics simulations, we studied the diffusion of HFBI, a class II hydrophobin from Trichoderma reesei, in aqueous solution in the presence and absence of a graphite surface. Results In the simulations, HFBI exists in solution as a mixture of monomers in equilibrium with different types of oligomers. The oligomerization state depends on the conformation of HFBI. When a Highly Ordered Pyrolytic Graphite (HOPG) layer is present in the simulated system, HFBI tends to interact with the HOPG layer through a hydrophobic patch on the protein. Conclusions From the simulations of HFBI solutions, we identify a tetrameric encounter complex stabilized by non-polar interactions between the aliphatic residues in the hydrophobic patch on HFBI. After the formation of the encounter complex, a local structural rearrangement at the protein interfaces is required to obtain the tetrameric arrangement seen in HFBI crystals. Simulations performed with the graphite surface show that, due to a combination of a geometric hindrance and the interaction of the aliphatic sidechains with the graphite layer, HFBI proteins tend to accumulate close to the hydrophobic surface.

  8. Kinetic studies of the sucrose adsorption onto an alumina interface

    NASA Astrophysics Data System (ADS)

    Singh, Kaman; Mohan, Sudhanshu

    2004-01-01

    An account is given of an experimental kinetic study of adsorption of analar reagent sucrose (ARS) onto an alumina interface spectrometrically ( λmax=570 nm) at pH 8.0 and at room temperature. The adsorption isotherm is a typical Langmuirian isotherm (S-type) and adsorption parameters have been deduced according to the Langmuir's model. The adsorption coefficient evaluated from the Langmuir's equation was found to be 2.52×10 2 l mol -1. Adsorption mechanism has been interpreted on the basis of metal-saccharide interaction as found in organometallic compounds and interaction due to negatively charged ends on the disaccharide molecules and positively charge groups on the surface on alumina which depends on the pH value. The effects of variation in experimental conditions of the adsorption system have also been investigated. The adsorption exhibited a typical response to the pH effect and on going towards the PZC the net charge decreases and any reaction making dependence on charge and maximum adsorption (amount) was found near the isoelectric point of alumina (pH 9.0). The presence of ions like Cl -, SO 42- and PO 43- affect the adsorbed amount quantitatively and it seems that these anions compete with sucrose for the positively charged surface sites. The addition of similar concentration of cations was found to reduce the adsorbed amount. The temperature was found to have an inverse effect on adsorption. The additions of catonic and anionic detergents influence both the adsorbed amount and the adsorption rate. The thermodynamics of the titled adsorption model indicates the spontaneous and exothermic nature. The negative value of entropy is an indication of probability of favorable and complex nature of the adsorption.

  9. Study of lumineers' interfaces by means of optical coherence tomography

    NASA Astrophysics Data System (ADS)

    de Andrade Borges, Erica; Fernandes Cassimiro-Silva, Patrícia; Osório Fernandes, Luana; Leônidas Gomes, Anderson Stevens

    2015-06-01

    OCT has been used to evaluate dental materials, and is employed here to evaluate lumineers for the first time. Lumineers are used as esthetical indirect restoration, and after wearing and aging, several undesirable features such as gaps, bubbles and mismatch can appear in which would only be seen by invasive analysis. The OCT (spectral domain SD-OCT, 930nm central wavelength) was used to evaluate noninvasively the lumineer- cement-tooth interface. We analyzed 20 specimens of lumineers-teeth that were prepared in bovine teeth and randomly allocated in 4 experimental groups (n=5) with two different cementation techniques and two different types of cementing agent (RelyX U200 and RelyX Veneer, 3M ESPE, with the adhesive recommended by the manufacture). The lumineers were made of lithium disilicate and obtained using a vacuum injection technique. The analysis was performed by using 2D and 3D OCT images, obtained before and after cementing and the thermal cycling process to simulate thermal stress in a oral cavity. Initial measurements showed that the SD-OCT was able to see through the 500μm thick lumineer, as delivered by the fabricant, and internal stress was observed. Failures were found in the cementing process and also after ageing simulation by thermal cycling. The adhesive failures as bubbles, gaps and degradation of the cementation line are the natural precursors of other defects reported by several studies of clinical follow-up (detachments, fractures and cracks). Bubble dimensions ranging from 146 μm to 1427 μm were measured and the OCT was validated as an investigative and precise tool for evaluation of the lumineer-cement-tooth.

  10. Theoretical studies of radiation effects in composite materials for space use. [graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Chang, C. K.; Kamaratos, E.

    1982-01-01

    Tetraglycidyl 4,4'-diamino diphenyl methane epoxy cured with diamino diphenyl sulfone was used as a model compound. Computer programs were developed to calculate (1) energy deposition coefficients of protons and electrons of various energies at different depths of the material; (2) ranges of protons and electrons of various energies in the material; and (3) cumulative doses received by the composite in different geometric shapes placed in orbits of various altitudes and inclination. A preliminary study on accelerated testing was conducted and it was found that an elliptical equitorial orbit of 300 km perigee by 2750 km apogee can accumulate, in 2 years or less, enough radiation dose comparable to geosynchronous environment for 30 years. The local plasma model calculated the mean excitation energies for covalent and ionic compounds. Longitudinal and lateral distributions of excited species by electron and proton impact as well as the probability of overlapping of two tracks due to two charged particles within various time intervals were studied.

  11. Coating method for graphite

    DOEpatents

    Banker, John G.; Holcombe, Jr., Cressie E.

    1977-01-01

    A method of limiting carbon contamination from graphite ware used in induction melting of uranium alloys is provided comprising coating the graphite surface with a suspension of Y.sub.2 O.sub.3 particles in water containing about 1.5 to 4% by weight sodium carboxymethylcellulose.

  12. Coating method for graphite

    DOEpatents

    Banker, J.G.; Holcombe, C.E. Jr.

    1975-11-06

    A method of limiting carbon contamination from graphite ware used in induction melting of uranium alloys is provided. The graphite surface is coated with a suspension of Y/sub 2/O/sub 3/ particles in water containing about 1.5 to 4 percent by weight sodium carboxymethylcellulose.

  13. Method for producing dustless graphite spheres from waste graphite fines

    DOEpatents

    Pappano, Peter J; Rogers, Michael R

    2012-05-08

    A method for producing graphite spheres from graphite fines by charging a quantity of spherical media into a rotatable cylindrical overcoater, charging a quantity of graphite fines into the overcoater thereby forming a first mixture of spherical media and graphite fines, rotating the overcoater at a speed such that the first mixture climbs the wall of the overcoater before rolling back down to the bottom thereby forming a second mixture of spherical media, graphite fines, and graphite spheres, removing the second mixture from the overcoater, sieving the second mixture to separate graphite spheres, charging the first mixture back into the overcoater, charging an additional quantity of graphite fines into the overcoater, adjusting processing parameters like overcoater dimensions, graphite fines charge, overcoater rotation speed, overcoater angle of rotation, and overcoater time of rotation, before repeating the steps until graphite fines are converted to graphite spheres.

  14. Swift heavy ion-induced radiation damage in isotropic graphite studied by micro-indentation and in-situ electrical resistivity

    NASA Astrophysics Data System (ADS)

    Hubert, Christian; Voss, Kay Obbe; Bender, Markus; Kupka, Katharina; Romanenko, Anton; Severin, Daniel; Trautmann, Christina; Tomut, Marilena

    2015-12-01

    Due to its excellent thermo-physical properties and radiation hardness, isotropic graphite is presently the most promising material candidate for new high-power ion accelerators which will provide highest beam intensities and energies. Under these extreme conditions, specific accelerator components including production targets and beam protection modules are facing the risk of degradation due to radiation damage. Ion-beam induced damage effects were tested by irradiating polycrystalline, isotropic graphite samples at the UNILAC (GSI, Darmstadt) with 4.8 MeV per nucleon 132Xe, 150Sm, 197Au, and 238U ions applying fluences between 1 × 1011 and 1 × 1014 ions/cm2. The overall damage accumulation and its dependence on energy loss of the ions were studied by in situ 4-point resistivity measurements. With increasing fluence, the electric resistivity increases due to disordering of the graphitic structure. Irradiated samples were also analyzed off-line by means of micro-indentation in order to characterize mesoscale effects such as beam-induced hardening and stress fields within the specimen. With increasing fluence and energy loss, hardening becomes more pronounced.

  15. Effective catalytic media using graphitic nitrogen-doped site in graphene for a non-aqueous Li-O2 battery: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Yun, Kyung-Han; Hwang, Yubin; Chung, Yong-Chae

    2015-03-01

    The cell performance of lithium-oxygen batteries using nitrogen doped graphene as a catalytic cathode has been validated in recent research, but the cathode reaction mechanism of lithium and oxygen still remains unclear. Since the oxygen reduction reaction (ORR) mechanism by ionic lithium and catalytic surface is predicted to be distinct for different defective sites such as graphitic, pyridinic, and pyrrolic, it is necessary to observe the behavior of ionic lithium and oxygen gas at each defective site in nitrogen doped graphene. In this study, density functional theory (DFT) calculations are adopted to analyze at an atomic scale how effectively each defective site acts as a catalytic cathode. Interestingly, unlike pyridinic or pyrrolic N is known to be the most effective catalytic site for ORR in fuel cells. Among the other defective sites, it is found that the graphitic N site is the most effective catalytic media activating ORR by ionic lithium in lithium-oxygen batteries due to the electron accepting the reaction of Li-O formation by the graphitic N site.

  16. Studies on Hot-Melt Prepregging on PRM-II-50 Polyimide Resin with Graphite Fibers

    NASA Technical Reports Server (NTRS)

    Shin, E. Eugene; Sutter, James K.; Juhas, John; Veverka, Adrienne; Klans, Ojars; Inghram, Linda; Scheiman, Dan; Papadopoulos, Demetrios; Zoha, John; Bubnick, Jim

    2004-01-01

    A second generation PMR (in situ Polymerization of Monomer Reactants) polyimide resin PMR-II-50, has been considered for high temperature and high stiffness space propulsion composites applications for its improved high temperature performance. As part of composite processing optimization, two commercial prepregging methods: solution vs. hot-melt processes were investigated with M40J fabrics from Toray. In a previous study a systematic chemical, physical, thermal and mechanical characterization of these composites indicated the poor resin-fiber interfacial wetting, especially for the hot-melt process, resulted in poor composite quality. In order to improve the interfacial wetting, optimization of the resin viscosity and process variables were attempted in a commercial hot-melt prepregging line. In addition to presenting the results from the prepreg quality optimization trials, the combined effects of the prepregging method and two different composite cure methods, i.e. hot press vs. autoclave on composite quality and properties are discussed.

  17. Studies on Hot-Melt Prepregging of PMR-II-50 Polyimide Resin with Graphite Fibers

    NASA Technical Reports Server (NTRS)

    Shin, E. Eugene; Sutter, James K.; Juhas, John; Veverka, Adrienne; Klans, Ojars; Inghram, Linda; Scheiman, Dan; Papadopoulos, Demetrios; Zoha, John; Bubnick, Jim

    2003-01-01

    A Second generation PMR (in situ Polymerization of Monomer Reactants) polyimide resin, PMR-II-50, has been considered for high temperature and high stiffness space propulsion composites applications for its improved high temperature performance. As part of composite processing optimization, two commercial prepregging methods: solution vs. hot-melt processes were investigated with M40J fabrics from Toray. In a previous study a systematic chemical, physical, thermal and mechanical characterization of these composites indicated that poor resin-fiber interfacial wetting, especially for the hot-melt process, resulted in poor composite quality. In order to improve the interfacial wetting, optimization of the resin viscosity and process variables were attempted in a commercial hot-melt prepregging line. In addition to presenting the results from the prepreg quality optimization trials, the combined effects of the prepregging method and two different composite cure methods, i.e., hot press vs. autoclave on composite quality and properties are discussed.

  18. FT-IR studies of graphite after keV-energy hydrogen ion irradiation

    NASA Astrophysics Data System (ADS)

    Gotoh, Yoshitaka; Kajiura, Soji

    Fourier-transform infrared absorption spectroscopy (FT-IR) studies were made on vapor-grown carbon fiber (VGCF) after successive irradiations of 6, 3 and 1 keV-H + to saturation at 373-923 K, and after the irradiations at 623 K followed by a heat-treatment at 893-1150 K. Reference hydrocarbons, cholesterol (C 27H 45OH) and menthol (C 10H 19OH), were also measured for C-H stretch band frequencies and relative integrated intensity factors, κ--CH x. For the irradiated VGCF, a band was found to be centered at 2892 cm -1, in between a -CH 3 symmetric (2873 cm -1) and a >CH 2 asymmetric (2924 cm -1) stretch band, which was assigned to a >CH- stretch band. Relative densities of the CH x groups, assuming κCH--: κ--CH 3: κ>CH 2: κ>CH-- =0.12:2.2:1.1:1.0, showed that >CH 2 decreases in density with increasing the irradiation temperature beyond 1000 K, while >CH- reaches maximum at around 823 K and then decreases. The -CH 3 group decreases to a minimum from 623 to 823 K, and increases at above 823 K, indicating that methane forms at around 800 K through abstraction of H from >CH- by free CH 3. The density ratio of >CH- to >CH 2 reached a maximum at 0.4 at around 800 K, indicating that, in the keV-H + implantation layer, the implanted H atoms are trapped mainly at >CH 2, and subsidiarily at >CH-, and -CH 3, at defects, below 900 K.

  19. Hypervelocity impacts into graphite

    NASA Astrophysics Data System (ADS)

    Latunde-Dada, S.; Cheesman, C.; Day, D.; Harrison, W.; Price, S.

    2011-03-01

    Studies have been conducted into the characterisation of the behaviour of commercial graphite (brittle) when subjected to hypervelocity impacts by a range of projectiles. The experiments were conducted with a two-stage gas gun capable of launching projectiles of differing density and strength to speeds of about 6kms-1 at right angles into target plates. The damage caused is quantified by measurements of the crater depth and diameters. From the experimental data collected, scaling laws were derived which correlate the crater dimensions to the velocity and the density of the projectile. It was found that for moderate projectile densities the crater dimensions obey the '2/3 power law' which applies to ductile materials.

  20. Characterization of a superlubricity nanometer interface by Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yunsheng; Yang, Xing; Liu, Bingqi; Dong, Hualai; Zheng, Quanshui

    2016-08-01

    Despite being known for almost two decades, the use of micro-/nano-electromechanical systems in commercial applications remains a challenge because of stiction, friction, and the wear of the interface. Superlubricity may be the solution to these challenges. In this paper, we study factors affecting the realization of superlubricity. Raman spectroscopy and other methods were used to characterize a graphite interface which can realize superlubricity and another graphite interface which cannot realize superlubricity. Raman spectra of the interfaces were obtained with the mapping mode and then processed to obtain the Raman images of the characteristic peaks. The Raman spectra provided the distribution of the surface defects and probed defects. Combined with atomic force microscopy and x-ray photoelectron spectroscopy, the Raman spectra show that the sp3 carbons and carbon–oxygen bond stuck at the edge of the graphite mesa are some of the determinants of large-area superlubricity realization. The characterization results can also be used to understand the friction and wear of large-area superlubricity, which are important for development and application of superlubricity. Furthermore, the methods used in this study are useful techniques and tools for the mechanism analysis of other nanometer interfaces.

  1. Characterization of a superlubricity nanometer interface by Raman spectroscopy.

    PubMed

    Shi, Yunsheng; Yang, Xing; Liu, Bingqi; Dong, Hualai; Zheng, Quanshui

    2016-08-12

    Despite being known for almost two decades, the use of micro-/nano-electromechanical systems in commercial applications remains a challenge because of stiction, friction, and the wear of the interface. Superlubricity may be the solution to these challenges. In this paper, we study factors affecting the realization of superlubricity. Raman spectroscopy and other methods were used to characterize a graphite interface which can realize superlubricity and another graphite interface which cannot realize superlubricity. Raman spectra of the interfaces were obtained with the mapping mode and then processed to obtain the Raman images of the characteristic peaks. The Raman spectra provided the distribution of the surface defects and probed defects. Combined with atomic force microscopy and x-ray photoelectron spectroscopy, the Raman spectra show that the sp(3) carbons and carbon-oxygen bond stuck at the edge of the graphite mesa are some of the determinants of large-area superlubricity realization. The characterization results can also be used to understand the friction and wear of large-area superlubricity, which are important for development and application of superlubricity. Furthermore, the methods used in this study are useful techniques and tools for the mechanism analysis of other nanometer interfaces. PMID:27348089

  2. XPS Study of Oxide/GaAs and SiO2/Si Interfaces

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Grunthaner, P. J.; Vasquez, R. P.; Lewis, B. F.; Maserjian, J.; Madhukar, A.

    1982-01-01

    Concepts developed in study of SiO2/Si interface applied to analysis of native oxide/GaAs interface. High-resolution X-ray photoelectron spectroscopy (XPS) has been combined with precise chemical-profiling technique and resolution-enhancement methods to study stoichiometry of transitional layer. Results are presented in report now available.

  3. Computation of dimensional changes in isotropic cesium-graphite reservoirs

    NASA Astrophysics Data System (ADS)

    Smith, Joe N.; Heffernan, Timothy

    1992-01-01

    Cs-graphite reservoirs have been utilized in many operating thermionic converters and TFEs, in both in-core and out-of-core tests. The vapor pressure of cesium over Cs-intercalated graphite is well documented for unirradiated reservoirs. The vapor pressure after irradiation is the subject of on-going study. Dimensional changes due to both intercalation and to neutron irradiation have been quantified only for highly oriented graphite. This paper describes extrapolation of the data for intercalated oriented graphite, to provide a qualitative description of the response of isotropic graphite to exposure to both cesium and neutrons.

  4. Terahertz plasmonic properties of highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Nguyen, T. D.; Liu, S.; Kumar, G.; Nahata, A.; Vardeny, Z. V.

    2013-04-01

    We demonstrate that highly oriented pyrolytic graphite is a potentially useful material for plasmonic applications in the terahertz (THz) spectral range. Using THz time-domain spectroscopy, we studied the transmission properties of a ˜7.5 μm thick graphite film made via mechanical exfoliation and found that the complex dielectric constant follows the Drude model with a plasma frequency νp ˜ 34 THz. To assess the graphite plasmonic properties, we fabricated a subwavelength periodic aperture array in the graphite film and in a free-standing stainless steel film. Despite the low conductivity of graphite compared to conventional metals, the resonant transmission properties are similar.

  5. Recycling Irradiated Nuclear Graphite - A Greener Path Forward

    SciTech Connect

    Burchell, Timothy D; Pappano, Peter J

    2012-01-01

    Here we report the successful recycle of irradiated graphite to fabricate new nuclear graphite using conventional manufacturing processes (albeit on a bench scale). Radiological concerns such as the containment of contamination in industrial scale manufacturing plants, or the release of 14C, were not considered. Moreover, a study of the annealing kinetics was conducted to elucidate the extent of property recovery over a representative temperature range. The goal of the preliminary work reported here was to determine if nuclear graphite, produced through the normal graphite fabrication process, but using crushed, previously irradiated nuclear graphite could be manufactured with sufficient mechanical integrity to warrant further investigation.

  6. Recycling Irradiated Nuclear Graphite - A Greener Path Forward

    SciTech Connect

    Burchell, Timothy D; Pappano, Peter J

    2010-01-01

    Here we report the successful recycle of irradiated graphite to fabricate new nuclear graphite using conventional manufacturing processes (albeit on a on a bench scale). Radiological concerns such as the containment of contamination in industrial scale manufacturing plants, or the release of 14C, were not considered. Moreover, a study of the annealing kinetics was conducted to elucidate the extent of property recovery over a representative temperature range. The goal of the preliminary work reported here was to determine if nuclear graphite, produced through the normal graphite fabrication process, but using crushed, previously irradiated nuclear graphite, could be manufactured with sufficient mechanical integrity to warrant further investigation

  7. Mechanism for direct graphite-to-diamond phase transition

    PubMed Central

    Xie, Hongxian; Yin, Fuxing; Yu, Tao; Wang, Jian-Tao; Liang, Chunyong

    2014-01-01

    Using classical molecular dynamics with a more reliable reactive LCBOPII potential, we have performed a detailed study on the direct graphite-to-diamond phase transition. Our results reveal a new so-called “wave-like buckling and slipping” mechanism, which controls the transformation from hexagonal graphite to cubic diamond. Based on this mechanism, we have explained how polycrystalline cubic diamond is converted from hexagonal graphite, and demonstrated that the initial interlayer distance of compressed hexagonal graphite play a key role to determine the grain size of cubic diamond. These results can broaden our understanding of the high pressure graphite-to-diamond phase transition. PMID:25088720

  8. Feasibility study for future implantable neural-silicon interface devices.

    PubMed

    Al-Armaghany, Allann; Yu, Bo; Mak, Terrence; Tong, Kin-Fai; Sun, Yihe

    2011-01-01

    The emerging neural-silicon interface devices bridge nerve systems with artificial systems and play a key role in neuro-prostheses and neuro-rehabilitation applications. Integrating neural signal collection, processing and transmission on a single device will make clinical applications more practical and feasible. This paper focuses on the wireless antenna part and real-time neural signal analysis part of implantable brain-machine interface (BMI) devices. We propose to use millimeter-wave for wireless connections between different areas of a brain. Various antenna, including microstrip patch, monopole antenna and substrate integrated waveguide antenna are considered for the intra-cortical proximity communication. A Hebbian eigenfilter based method is proposed for multi-channel neuronal spike sorting. Folding and parallel design techniques are employed to explore various structures and make a trade-off between area and power consumption. Field programmable logic arrays (FPGAs) are used to evaluate various structures. PMID:22254974

  9. TEM and XPS studies on CdS/CIGS interfaces

    NASA Astrophysics Data System (ADS)

    Han, Jun-feng; Liao, Cheng; Cha, Li-mei; Jiang, Tao; Xie, Hua-mu; Zhao, Kui; Besland, M.-P.

    2014-12-01

    Copper indium gallium selenide (CIGS) was deposited by metallic precursors sputtering and subsequently submitted to a selenization process. The upper CdS layers were deposited by chemical bath deposition (CBD) technique. The CdS/CIGS interfaces were investigated by Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). As checked by XPS analysis, the CIGS surface exhibited a hydroxide-terminated CdSe layer when treated with Cd Partial Electrolyte solution (Cd PE). Its thickness was roughly estimated to several nanometers. A 100 nm thick CdS layer was deposited onto CIGS surface. The TEM images revealed a clear and sharp interface between CdS and CIGS. XPS analysis showed a CIGS surface covered by a pinhole free and homogeneous CdS layer. XPS depth profile measurement of the CdS/CIGS interface did not evidence elemental inter-diffusion between the CIGS and CdS layers, in very good agreement with TEM observations.

  10. Thermal stability study of semimetal graphite n-InP and n-GaN Schottky diodes

    NASA Astrophysics Data System (ADS)

    Yatskiv, R.; Grym, J.

    2013-05-01

    The electrical properties of highly rectifying semimetal-graphite Schottky contacts fabricated by printing colloid graphite on n-type InP and GaN are investigated as a function of annealing temperature by current-voltage and capacitance-voltage techniques. As-deposited Schottky diodes exhibit excellent current-voltage rectifying characteristics of 7.5 × 107 and 1.9 × 1011 with Schottky barrier height of 1.13 and 1.29 eV at room temperature for InP and GaN, respectively. The key aspect of this technique, compared with conventional vacuum evaporation, is low deposition energy process, leaving the surface undisturbed.

  11. Interaction of monovalent ions with the water liquid-vapor interface - A molecular dynamics study

    NASA Technical Reports Server (NTRS)

    Wilson, Michael A.; Pohorille, Andrew

    1991-01-01

    Results of molecular dynamics calculations are presented for a series of ions at infinite dilution near the water liquid-vapor interface. The free energies of ion transfer from the bulk to the interface are discussed, as are the accompanying changes of water structure at the surface and ion mobilities as a function of their proximity to the interface. It is shown that simple dielectric models do not provide an accurate description of ions at the water surface. The results of the study should be useful in the development of better models incorporating the shape and molecular structure of the interface.

  12. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J. . Dept. of Mechanical Engineering); Pedraza, D.F. )

    1992-01-01

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  13. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J.; Pedraza, D.F.

    1992-12-31

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  14. First-principles study on oxidation of Ge and its interface electronic structures

    NASA Astrophysics Data System (ADS)

    Ono, Tomoya; Saito, Shoichiro; Iwase, Shigeru

    2016-08-01

    We review a series of first-principles studies on the defect generation mechanism and electronic structures of the Ge/GeO2 interface. Several experimental and theoretical studies proved that Si atoms at the Si/SiO2 interface are emitted to release interface stress. In contrast, total-energy calculation reveals that Ge atoms at the Ge/GeO2 interface are hardly emitted, resulting in the low trap density. Even if defects are generated, those at the Ge/GeO2 interface are found to behave differently from those at the Si/SiO2 interface. The states attributed to the dangling bonds at the Ge/GeO2 interface lie below the valence-band maximum of Ge, while those at the Si/SiO2 interface generate the defect state within the band gap of Si. First-principles electron-transport calculation elucidates that this characteristic behavior of the defect states is relevant to the difference in the leakage current through the Si/SiO2 and Ge/GeO2 interfaces.

  15. Laser nanoablation of graphite

    NASA Astrophysics Data System (ADS)

    Frolov, V. D.; Pivovarov, P. A.; Zavedeeev, E. V.; Komlenok, M. S.; Kononenko, V. V.; Konov, V. I.

    2014-01-01

    Experimental data on laser ablation of highly oriented pyrolitic graphite by nanosecond pulsed UV ( nm) and green ( nm) lasers are presented. It was found that below graphite vaporization threshold 1 J/cm, the nanoablation regime can be realized with material removal rates as low as 10 nm/pulse. The difference between physical (vaporization) and physical-chemical (heating + oxidation) ablation regimes is discussed. Special attention is paid to the influence of laser fluence and pulse number on ablation kinetics. Possibility of laser-induced graphite surface nanostructuring has been demonstrated. Combination of tightly focused laser beam and sharp tip of scanning probe microscope was applied to improve material nanoablation.

  16. Layering-induced Superlubricity: Gold on Graphite

    NASA Astrophysics Data System (ADS)

    Vanossi, Andrea; Guerra, Roberto; Tosatti, Erio; Nanofriction Group Sissa Team

    2015-03-01

    By means of realistic MD simulations, we explore the static friction trend as a function of the true contact area and the model dimensionality for 2D gold nanoislands and 3D gold nanoclusters deposited on graphite, interesting tribological systems whose slow and fast dynamics have been previously investigated. For increasing island size, because of the relative gold-graphite lattice mismatch, the interface stress energy has the chance to pile up by forming frustrated unmatched (i.e., incommensurate) regions and to develop a continuous solitonic pathway, foreshadowing a possible condition for the occurrence of ultra-low friction regimes. The significant reduction of the depinning threshold, towards superlubricity, with the system dimensionality can be ascribed to a layering-induced effective stiffness of the interface contact, favoring the natural Au-C lattice incommensurability. Partly sponsored under SNSF Sinergia Grant CRSII2 136287/1, EU ERC Grant No. 320796 MODPHYSFRICT, EU COST Action MP1303.

  17. NEW METHOD OF GRAPHITE PREPARATION

    DOEpatents

    Stoddard, S.D.; Harper, W.T.

    1961-08-29

    BS>A method is described for producing graphite objects comprising mixing coal tar pitch, carbon black, and a material selected from the class comprising raw coke, calcined coke, and graphite flour. The mixture is placed in a graphite mold, pressurized to at least 1200 psi, and baked and graphitized by heating to about 2500 deg C while maintaining such pressure. (AEC)

  18. Ion-induced modification of graphite coatings

    NASA Astrophysics Data System (ADS)

    Gupta, B. K.; Janting, J.; Jensen, U. M.; Pedersen, G. N.; Sørensen, G.

    1992-09-01

    Burnished graphite powders and physical vapor-deposition (PVD) coatings of layered crystalline materials such as MoSx have often been used as solid lubricants. This letter will report on a novel ion-induced modification of a graphite-powder coating on a silicon surface. Even at very low ion doses, the bombardment results in structural modifications observed as a considerable reduction in x rays reflected from the (002) sliding planes, which indicates an amorphization process. Transmission electron microscopy (TEM) studies have confirmed almost complete amorphization with 200 keV Ar ions at 1016 ions cm-2. A commercial scanning tunneling microscope (STM) was used as an advanced profilometer to study ion-induced changes in the surface morphology at the powder surface. The mechanical properties of the combined graphite-coating/silicon system were studied by nanoindentation technique, and the perspectives in ion-beam burnishing of graphite coatings will be discussed.

  19. Water at an electrochemical interface - a simulation study

    SciTech Connect

    Willard, Adam; Reed, Stewart; Madden, Paul; Chandler, David

    2008-08-22

    The results of molecular dynamics simulations of the properties of water in an aqueous ionic solution close to an interface with a model metallic electrode are described. In the simulations the electrode behaves as an ideally polarizable hydrophilic metal, supporting image charge interactions with charged species, and it is maintained at a constant electrical potential with respect to the solution so that the model is a textbook representation of an electrochemical interface through which no current is passing. We show how water is strongly attracted to and ordered at the electrode surface. This ordering is different to the structure that might be imagined from continuum models of electrode interfaces. Further, this ordering significantly affects the probability of ions reaching the surface. We describe the concomitant motion and configurations of the water and ions as functions of the electrode potential, and we analyze the length scales over which ionic atmospheres fluctuate. The statistics of these fluctuations depend upon surface structure and ionic strength. The fluctuations are large, sufficiently so that the mean ionic atmosphere is a poor descriptor of the aqueous environment near a metal surface. The importance of this finding for a description of electrochemical reactions is examined by calculating, directly from the simulation, Marcus free energy profiles for transfer of charge between the electrode and a redox species in the solution and comparing the results with the predictions of continuum theories. Significant departures from the electrochemical textbook descriptions of the phenomenon are found and their physical origins are characterized from the atomistic perspective of the simulations.

  20. Atomic-Scale Studies of Defect Interactions with Homo- and Heterophase Interfaces

    NASA Astrophysics Data System (ADS)

    Martínez, Enrique; Uberuaga, Blas P.; Beyerlein, Irene J.

    2016-04-01

    Interfaces are planar metastable defects with singular features capable of controlling diverse material properties, including mechanical response and the microstructure evolution in materials under irradiation. This ability of interfaces to dictate the material response resides inherently in their atomic structure, which controls the interactions of dislocations as well as point and defect clusters with the interface. We recently showed how dislocations nucleated from defect clusters interact with a heterophase interface in Cu-Nb layered composites. We also showed how the ability of the interface to absorb vacancy clusters depends on the atomic structure at the interface. Herein, we elaborate on the effect of the atomic structure on the ability of the interface to absorb dislocations as well as vacancy and self-interstitial defect clusters. We study a physical-vapor-deposited Kurdjumov-Sachs orientation in a Cu-Nb interface and an asymmetric Σ 11 grain boundary in pure Cu. On the one hand, the manner in which dislocations react with the interface depends on the misfit dislocation arrangement, which substantially differs between these two cases. On the other hand, vacancy and self-interstitial clusters are absorbed similarly upon interaction with both structures.

  1. Atomic-Scale Studies of Defect Interactions with Homo- and Heterophase Interfaces

    NASA Astrophysics Data System (ADS)

    Martínez, Enrique; Uberuaga, Blas P.; Beyerlein, Irene J.

    2016-06-01

    Interfaces are planar metastable defects with singular features capable of controlling diverse material properties, including mechanical response and the microstructure evolution in materials under irradiation. This ability of interfaces to dictate the material response resides inherently in their atomic structure, which controls the interactions of dislocations as well as point and defect clusters with the interface. We recently showed how dislocations nucleated from defect clusters interact with a heterophase interface in Cu-Nb layered composites. We also showed how the ability of the interface to absorb vacancy clusters depends on the atomic structure at the interface. Herein, we elaborate on the effect of the atomic structure on the ability of the interface to absorb dislocations as well as vacancy and self-interstitial defect clusters. We study a physical-vapor-deposited Kurdjumov-Sachs orientation in a Cu-Nb interface and an asymmetric Σ 11 grain boundary in pure Cu. On the one hand, the manner in which dislocations react with the interface depends on the misfit dislocation arrangement, which substantially differs between these two cases. On the other hand, vacancy and self-interstitial clusters are absorbed similarly upon interaction with both structures.

  2. Surface directed reversible imidazole ligation to nickel(ii) octaethylporphyrin at the solution/solid interface: a single molecule level study.

    PubMed

    Nandi, Goutam; Chilukuri, Bhaskar; Hipps, K W; Mazur, Ursula

    2016-07-27

    Scanning tunneling microscopy (STM) is used to study for the first time the reversible binding of imidazole (Im) and nickel(ii) octaethylporphyrin (NiOEP) supported on highly oriented pyrolytic graphite (HOPG) at the phenyloctane/NiOEP/HOPG interface at 25 °C. The ligation of Im to the NiOEP receptor while not observed in fluid solution is readily realized at the solution/HOPG interface. The coordination process scales with increasing Im concentration and can be effectively modeled by the Langmuir isotherm. At room temperature it is determined that the standard free energy of adsorption is ΔGc = -15.8 kJ mol(-1) and the standard enthalpy of adsorption is estimated to be ΔHc ≈ -80 kJ mol(-1). The reactivity of imidazole toward NiOEP adsorbed on HOPG is attributed to charge donation from the graphite stabilizing the Im-Ni bond. This charge transfer pathway is supported by molecular and periodic modeling calculations which indicate that the Im ligand behaves as a π-acceptor. DFT calculations also show that the nickel ion in the Im-NiOEP/HOPG complex is in a singlet ground state. This is surprising since both our calculations and previous experimental studies find a triplet ground state for the five and six coordinated Im-nickel(ii) porphyrins in the gas-phase or in solution. Both the experimental and the theoretical findings provide information that is useful for better understanding of chemical sensing/recognition and catalytic processes that utilize metal-organic complexes adsorbed on surfaces where the reactivity of the metal is moderated by the substrate. PMID:27416994

  3. Formation of metastable graphite inclusions during diamond crystallization in model systems

    NASA Astrophysics Data System (ADS)

    Nechaev, D. V.; Khokhryakov, A. F.

    2014-03-01

    Metastable graphite inclusions have been studied in diamond, forsterite, and orthopyroxene synthesized in silicate-carbonate-fluid and aqueous chloride systems at 6.3-7.5 GPa and 1400-1600°C. The graphite inclusions were studied using optic microscopy and Raman spectroscopy. It has been established that graphite in diamond and liquidus silicate minerals is represented by a highly ordered variety. Depending on parameters of runs, the graphite inclusions are hexagonal, irregular polygonal, or rounded in shape. The morphology of graphite inclusions involving metastable graphite in run products is compared with previously established crystallization sequence of carbon phases. It has been revealed that the protogenetic graphite inclusions in diamond are rounded, and this shape was caused by dissolution of the newly formed graphite. Polygonal graphite inclusions are syngenetic and represented by metastable graphite that crystallized contemporaneously with diamond.

  4. Maintenance support: case study for a multimodal mobile user interface

    NASA Astrophysics Data System (ADS)

    Fuchs, G.; Reichart, D.; Schumann, H.; Forbrig, P.

    2006-02-01

    Maintaining and repairing complex technical facilities such as generating plants requires comprehensive knowledge on subsystems, operational and safety procedures by the technician. Upgrades to the facility may mean that knowledge about these becomes outdated, raising the need for documentation at the working site. Today's commonplace availability of mobile devices motivates the use of digital, interactive manuals over printed ones. Such applications should provide high-quality illustrations and interaction techniques tailored for specific tasks, while at the same time allow flexible deployment of these components on a multitude of (mobile) hardware platforms. This includes the integration of multimodal interaction facilities like speech recognition into the user interface. To meet these demands, we propose a model-based approach that combines task, object and dialog models to specify platform-independent user interfaces. New concepts like relating tasks to domain objects and dialog views allow us to generate abstract canonical prototypes. Another focus is on the necessary adaptation of visual representations to the platform capabilities to remain effective and adequate, requiring tight coupling of the underlying model, the visualization, and alternative input/output modes. The above aspects have been addressed in a prototype for air-condition unit maintenance, presented on the CeBIT 2005 fair.

  5. A Theoretical Study of Remobilizing Surfactant Retarded Fluid Particle Interfaces

    NASA Technical Reports Server (NTRS)

    Wang, Yanping; Papageorgiou, Dimitri; Maldarelli, Charles

    1996-01-01

    Microgravity processes must rely on mechanisms other than bouyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. When a fluid particle contacts this gradient, one pole of the particle becomes warmer than the opposing pole. The interfacial tension between the drop or bubble phase and the continuous phase usually decreases with temperature. Thus the cooler pole is of higher interfacial tension than the warmer pole, and the interface is tugged in the direction of the cooler end. This thermocapillary or thermally induced Marangoni surface stress causes a fluid streaming in the continuous phase from which develops a viscous shear traction and pressure gradient which together propel the particle in the direction of the warmer fluid. In this paper, we provide a theoretical basis for remobilizing surfactant retarded fluid particle interfaces in an effort to make viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity,

  6. Neutral buoyancy methodology for studying satellite servicing EVA crewmember interfaces

    NASA Technical Reports Server (NTRS)

    Barnby, Mary E.; Griffin, Thomas J.; Lewis, Ruthan

    1989-01-01

    Current economic constraints indicate the need for incorporating the satellite servicing philosophy of commonality within the design of spacecraft subsytems. This philosophy is essential for conserving resources including hardware/software development and implementation costs, on-orbit and ground-based manpower, crew training/testing time, and documentation. In addition, spacecraft subsystem commonality may be coupled with standardization of operation procedures, and test and verification techniques for spacecraft design. Several spacecraft have adopted this practice, including Hubble Space Telescope, Space Station Freedom, and the Explorer Platform. As these and other programs continue and if effective crew interfaces and procedures are clearly and consistently defined, crew retraining for similar spacecraft subsystems will lessen, and procurement efforts will diminish. A relatively high fidelity zero-gravity simulation using water immersion is available to establish crew interfaces economically. The flexibility and utility of this space simulation medium for planning and assisting on-orbit operations was exemplified by astronaut evaluations of potential EVA electrical connectors. The testing was conducted at a NASA underwater neutral buoyancy training facility.

  7. Graphite design handbook

    SciTech Connect

    Ho, F.H.

    1988-09-01

    The objectives of the Graphite Design Handbook (GDH) are to provide and maintain a single source of graphite properties and phenomenological model of mechanical behavior to be used for design of MHTGR graphite components of the Reactor System, namely, core support, permanent side reflector, hexagonal reflector elements, and prismatic fuel elements; to provide a single source of data and material models for use in MHTGR graphite component design, performance, and safety analyses; to present properties and equations representing material models in a form which can be directly used by the designer or analyst without the need for interpretation and is compatible with analytical methods and structural criteria used in the MHTGR project, and to control the properties and material models used in the MHTGR design and analysis to proper Quality Assurance standards and project requirements. The reference graphite in the reactor internal components is the nuclear grade 2020. There are two subgrades of interest, the cylinder nuclear grade and the large rectangular nuclear grade. The large rectangular nuclear grade is molded in large rectangular blocks. It is the reference material for the permanent side reflector and the central column support structure. The cylindrical nuclear grade is isostatically pressed and is intended for use as the core support component. This report gives the design properties for both H-451 and 2020 graphite as they apply to their respective criteria. The properties are presented in a form for design, performance, and safety calculations that define or validate the component design. 103 refs., 20 figs., 19 tabs.

  8. Graphite Technology Development Plan

    SciTech Connect

    W. Windes; T. Burchell; R. Bratton

    2007-09-01

    This technology development plan is designed to provide a clear understanding of the research and development direction necessary for the qualification of nuclear grade graphite for use within the Next Generation Nuclear Plant (NGNP) reactor. The NGNP will be a helium gas cooled Very High Temperature Reactor (VHTR) with a large graphite core. Graphite physically contains the fuel and comprises the majority of the core volume. Considerable effort will be required to ensure that the graphite performance is not compromised during operation. Based upon the perceived requirements the major data needs are outlined and justified from the perspective of reactor design, reatcor performance, or the reactor safety case. The path forward for technology development can then be easily determined for each data need. How the data will be obtained and the inter-relationships between the experimental and modeling activities will define the technology development for graphite R&D. Finally, the variables affecting this R&D program are discussed from a general perspective. Factors that can significantly affect the R&D program such as funding, schedules, available resources, multiple reactor designs, and graphite acquisition are analyzed.

  9. Protection of nuclear graphite toward liquid fluoride salt by isotropic pyrolytic carbon coating

    NASA Astrophysics Data System (ADS)

    He, Xiujie; Song, Jinliang; Xu, Li; Tan, Jie; Xia, Huihao; Zhang, Baoliang; He, Zhoutong; Gao, Lina; Zhou, Xingtai; Zhao, Mingwen; Zhu, Zhiyong; Bai, Shuo

    2013-11-01

    Infiltration studies were performed on uncoated nuclear graphite and isotropic pyrolytic carbon (PyC) coated graphite in molten FLiNaK salt at 650 °C under argon atmosphere at 1, 3 and 5 atm. Uncoated graphite shows weight gain more obviously than that of PyC coated graphite. Nuclear graphite with PyC coating exhibits excellent infiltration resistance in molten salt due to the small open porosity as conformed from scanning electron microscopy and mercury injection experiments.

  10. Decay of neutron pulses in graphite assemblies

    SciTech Connect

    Malik, U.; Kothari, L.S.

    1982-09-01

    A new neutron scattering kernel for graphite has been developed with the frequency distribution function generated by the authors using the unfolding technique. This has been used to study the decay of neutron pulses in different graphite assemblies. This kernel (with theta /SUB D/ = 2000 K) can give a slightly better explanation of the experimental results than those based on the Krumhansl and Brooks model or the Young and Koppel model of lattice vibrations.

  11. Spin labelled polymers for composite interface studies: Synthesis and characterization

    SciTech Connect

    Snow, A.W.; Pace, M.D.

    1993-12-31

    For the purpose of investigating the epoxy resin composite interface, a series of spin labelled epoxy polymers and model compounds were synthesized and characterized. Linear epoxy polymers were prepared by reacting systematically varying quantities of 4-amino-2,2,6,6-tetramethylpiperid-1-yloxy and cyclohexyl amine with an equivalence bisphenol A diglycidyl ether. The adducts of phenylgylcidyl ether and 4-cumylphenylgylcidyl ether with 4-amino-2,2,6,6-tetramethylpiperid-1-yloxy were synthesized as model compounds. Characterization determined that the 125{degrees}C polymerization temperature did not cause significant decomposition of the nitroxyl free radical, magnetic dilution of the spin label in the epoxy polymer to 3% of the amine repeat units is sufficient for observation of unobscured nitroxyl hyperfine structure in the ESR spectrum of the labelled epoxy polymer in the solid state, and a polymer glass transition temperature of 66{degrees}C as not affected by variation in the amine composition.

  12. A Study of Electrochemical Reduction of Ethylene and PropyleneCarbonate Electrolytes on Graphite Using ATR-FTIR Spectroscopy

    SciTech Connect

    Zhuang, Guorong V.; Yang, Hui; Blizanac, Berislav; Ross Jr.,Philip N.

    2005-05-12

    We present results testing the hypothesis that there is a different reaction pathway for the electrochemical reduction of PC versus EC-based electrolytes at graphite electrodes with LiPF6 as the salt in common. We examined the reduction products formed using ex-situ Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflection (ATR) geometry. The results show the pathway for reduction of PC leads nearly entirely to lithium carbonate as the solid product (and presumably ethylene gas as the co-product) while EC follows a path producing a mixture of organic and inorganic compounds. Possible explanations for the difference in reaction pathway are discussed.

  13. Study of Tribological Properties of MoS{sub 2}+Graphite Sputtered Composite Coatings under various Environment Pressures

    SciTech Connect

    Liu Yong; Luo Chongtai; Ye Zhuyu; Yang Jianqun; Yang Dezhuang

    2009-01-05

    MoS{sub 2}+Graphite composite coatings were synthesized onto 2024 aluminum alloy substrates by sputtering. The friction and wear test were performed at different environment pressures in vacuum using a ball-on-disk tribometer. The worn surface of the coating was examined by scanning electron microscopy (SEM). The results show that the friction coefficients and wear rate are increasing with increased environment pressure. A second surface layer was formed on the worn surface, that is harder than the original surface. The hardness of this second surface layer is decreased with increasing environment pressure.

  14. Study of Tribological Properties of MoS2+Graphite Sputtered Composite Coatings under various Environment Pressures

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Luo, Chongtai; Ye, Zhuyu; Yang, Jianqun; Yang, Dezhuang

    2009-01-01

    MoS2+Graphite composite coatings were synthesized onto 2024 aluminum alloy substrates by sputtering. The friction and wear test were performed at different environment pressures in vacuum using a ball-on-disk tribometer. The worn surface of the coating was examined by scanning electron microscopy (SEM). The results show that the friction coefficients and wear rate are increasing with increased environment pressure. A second surface layer was formed on the worn surface, that is harder than the original surface. The hardness of this second surface layer is decreased with increasing environment pressure.

  15. Structural and phonon transmission study of Ge-Au-Ge eutectically bonded interfaces

    SciTech Connect

    Knowlton, W.B. |

    1995-07-01

    This thesis presents a structural analysis and phonon transparency investigation of the Ge-Au-Ge eutectic bond interface. Interface development was intended to maximize the interfacial ballistic phonon transparency to enhance the detection of the dark matter candidate WIMPs. The process which was developed provides an interface which produces minimal stress, low amounts of impurities, and insures Ge lattice continuity through the interface. For initial Au thicknesses of greater than 1,000 {angstrom} Au per substrate side, eutectic epitaxial growth resulted in a Au dendritic structure with 95% cross sectional and 90% planar Au interfacial area coverages. In sections in which Ge bridged the interface, lattice continuity across the interface was apparent. Epitaxial solidification of the eutectic interface with initial Au thicknesses < 500 A per substrate side produced Au agglomerations thereby reducing the Au planar interfacial area coverage to as little as 30%. The mechanism for Au coalescence was attributed to lateral diffusion of Ge and Au in the liquid phase during solidification. Phonon transmission studies were performed on eutectic interfaces with initial Au thicknesses of 1,000 {angstrom}, 500 {angstrom}, and 300 {angstrom} per substrate side. Phonon imaging of eutectically bonded samples with initial Au thicknesses of 300 {angstrom}/side revealed reproducible interfacial percent phonon transmissions from 60% to 70%. Line scan phonon imaging verified the results. Phonon propagation TOF spectra distinctly showed the predominant phonon propagation mode was ballistic. This was substantiated by phonon focusing effects apparent in the phonon imaging data. The degree of interface transparency to phonons and resulting phonon propagation modes correlate with the structure of the interface following eutectic solidification. Structural studies of samples with initial Au thickness of 1,000 {angstrom}/side appear to correspond with the phonon transmission study.

  16. Shuttle payload interface verification equipment study. Volume 2: Technical document, part 1

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The technical analysis is reported that was performed during the shuttle payload interface verification equipment study. It describes: (1) the background and intent of the study; (2) study approach and philosophy covering all facets of shuttle payload/cargo integration; (3)shuttle payload integration requirements; (4) preliminary design of the horizontal IVE; (5) vertical IVE concept; and (6) IVE program development plans, schedule and cost. Also included is a payload integration analysis task to identify potential uses in addition to payload interface verification.

  17. Numerical and experimental study of the nonlinear interaction between a shear wave and a frictional interface.

    PubMed

    Blanloeuil, Philippe; Croxford, Anthony J; Meziane, Anissa

    2014-04-01

    The nonlinear interaction of shear waves with a frictional interface are presented and modeled using simple Coulomb friction. Analytical and finite difference implementations are proposed with both in agreement and showing a unique trend in terms of the generated nonlinearity. A dimensionless parameter ξ is proposed to uniquely quantify the nonlinearity produced. The trends produced in the numerical study are then validated with good agreement experimentally. This is carried out loading an interface between two steel blocks and exciting this interface with different amplitude normal incidence shear waves. The experimental results are in good agreement with the numerical results, suggesting the simple friction model does a reasonable job of capturing the fundamental physics. The resulting approach offers a potential way to characterize a contacting interface; however, the difficulty in activating that interface may ultimately limit its applicability. PMID:25234971

  18. Comparative optical study of the two-dimensional donor-type intercalation compounds graphite-KHx and their binary counterparts C8K and C24K

    NASA Astrophysics Data System (ADS)

    Doll, G. L.; Yang, M. H.; Eklund, P. C.

    1987-06-01

    We report the results of optical reflectivity studies of the stage-1 and -2 graphite-KHx intercalation compounds prepared by direct reaction of highly ordered pyrolytic graphite and KH powder. The stage-1 and -2 binary graphite-K compounds are studied for comparison. The optical data are analyzed in terms of a model involving two-dimensional (2D) graphitic π electrons and three-dimensional (3D) nearly free K(4s) electrons. The model is used to interpret the observed values of the free-carrier unscreened plasma frequencies and the position of the interband absorption threshold to determine experimental values for the Fermi level (EF) in the carbon π band(s) and the fractional occupation of the K(4s) band. For the hydrides, we find quantitative evidence that the hydrogen states lie below EF. Thus, hydrogen is present as H-, acting as an acceptor, thereby compensating the electron donation to the π bands from the K(4s) states. This assumption and the optical data for the stage-1 and -2 hydrides results in a [H]/[K] ratio of 0.8, in excellent agreement with chemical analyses reported by Guérard and co-workers, and leads to very small values for the fractional K(4s) band occupation fK<0.03 electrons per K atom. Within the framework of a superimposed 2D (π) and 3D [K(4s)] rigid-band model, our experimental results support an empty K(4s) band (i.e., fK=0) in stage-2 C24K. In stage-1 C8K, the rigid-band model yields large values for fK (fK>0.5 electrons per K atom), unless the value of the optical mass of the electrons in the K(4s) states is larger than ~2. The C8K results are also discussed in terms of more sophisticated energy-band calculations.

  19. Fabrication and testing of non-graphitic superhybrid composites

    NASA Technical Reports Server (NTRS)

    Lark, R. F.; Sinclair, J. H.; Chamis, C. C.

    1979-01-01

    A study was conducted to determine the fabrication feasibility and the mechanical properties of adhesively-bonded boron aluminum/titanium and non-graphitic fiber/epoxy resin superhybrid (NGSH) composite laminates for potential aerospace applications. The major driver for this study was the elimination of a potential graphite fiber release problem in the event of a fire. The results of the study show that non-graphitic fibers, such as S-glass and Kevlar 49, may be substituted for the graphite fibers used in superhybrid (SH) composites for some applications. As is to be expected, however, the non-graphitic superhybrids have lower stiffness properties than the graphitic superhybrids. In-plane and flexural moduli of the laminates studied in this program can be predicted reasonably well using linear laminate theory while nonlinear laminate theory is required for strength predictions.

  20. Structure and functionality of bromine doped graphite.

    PubMed

    Hamdan, Rashid; Kemper, A F; Cao, Chao; Cheng, H P

    2013-04-28

    First-principles calculations are used to study the enhanced in-plane conductivity observed experimentally in Br-doped graphite, and to study the effect of external stress on the structure and functionality of such systems. The model used in the numerical calculations is that of stage two doped graphite. The band structure near the Fermi surface of the doped systems with different bromine concentrations is compared to that of pure graphite, and the charge transfer between carbon and bromine atoms is analyzed to understand the conductivity change along different high symmetry directions. Our calculations show that, for large interlayer separation between doped graphite layers, bromine is stable in the molecular form (Br2). However, with increased compression (decreased layer-layer separation) Br2 molecules tend to dissociate. While in both forms, bromine is an electron acceptor. The charge exchange between the graphite layers and Br atoms is higher than that with Br2 molecules. Electron transfer to the Br atoms increases the number of hole carriers in the graphite sheets, resulting in an increase of conductivity. PMID:23635160

  1. Structure and functionality of bromine doped graphite

    SciTech Connect

    Hamdan, Rashid; Kemper, A. F.; Cao Chao; Cheng, H. P.

    2013-04-28

    First-principles calculations are used to study the enhanced in-plane conductivity observed experimentally in Br-doped graphite, and to study the effect of external stress on the structure and functionality of such systems. The model used in the numerical calculations is that of stage two doped graphite. The band structure near the Fermi surface of the doped systems with different bromine concentrations is compared to that of pure graphite, and the charge transfer between carbon and bromine atoms is analyzed to understand the conductivity change along different high symmetry directions. Our calculations show that, for large interlayer separation between doped graphite layers, bromine is stable in the molecular form (Br{sub 2}). However, with increased compression (decreased layer-layer separation) Br{sub 2} molecules tend to dissociate. While in both forms, bromine is an electron acceptor. The charge exchange between the graphite layers and Br atoms is higher than that with Br{sub 2} molecules. Electron transfer to the Br atoms increases the number of hole carriers in the graphite sheets, resulting in an increase of conductivity.

  2. Behavior of adhesively bonded concrete-graphite/epoxy composite bridge girders

    SciTech Connect

    Gordaninejad, F.; Saiidi, M.S.; Wehbe, N. )

    1994-01-01

    The focus of this paper is on the behavior of composite bridge girders constructed from carbon fiber reinforced plastic sections and concrete slabs. The study examined four-point bending of three beams, one bare, I-type, graphite/epoxy beam, and two constructed from concrete slab and graphite/epoxy sections. The concrete slab and graphite/epoxy section were adhesively bonded and no shear connectors were used. All three beams are approximately one-eighth scale models of bridge girders. The sections are geometrically symmetric and have the same symmetric lamination schemes. Theoretical and experimental studies were performed on the bare I-sections to develop basic understanding of the bending behavior. The analyses and tests were then extended to the composite girders. The theoretical and experimental results for the failure loads were in close agreement. It was found that the slip at the interface of the concrete slab and the graphite/epoxy beam had minor effects on the failure load, but it significantly reduced the stiffness of the composite sections. 8 refs., 14 figs., 2 tabs.

  3. Thermal boundary conductance enhancement using experimentally achievable nanostructured interfaces - analytical study combined with molecular dynamics simulation.

    PubMed

    Lee, Eungkyu; Zhang, Teng; Hu, Ming; Luo, Tengfei

    2016-06-22

    Interfacial thermal resistance presents great challenges to the thermal management of modern electronics. In this work, we perform an analytical study to enhance the thermal boundary conductance (TBC) of nanostructured interfaces with square-shape pillar arrays, extendable to the characteristic lengths that can be fabricated in practice. As a representative system, we investigate a SiC substrate with the square-shape pillar array combined with epitaxial GaN as the nanostructured interface. By applying a first-order ray tracing method and molecular dynamics simulations to analyze phonon incidence and transmission at the nanostructured interface, we systematically study the impact of the characteristic dimensions of the pillar array on the TBC. Based on the multi-scale analysis we provide a general guideline to optimize the nanostructured interfaces to achieve higher TBC, demonstrating that the optimized TBC value of the nanostructured SiC/GaN interfaces can be 42% higher than that of the planar SiC/GaN interfaces without nanostructures. The model used and results obtained in this study will guide the further experimental realization of nanostructured interfaces for better thermal management in microelectronics. PMID:27275647

  4. Shuttle payload interface verification equipment study. Volume 2: Technical document. Part 2: Appendices

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Appendices to the shuttle payload integration study provide for: (1) The interface verification equipment hardware utilization list; (2) the horizontal IVE in-field assembly procedure; and (3) payload integration baseline functional flow block diagrams and options.

  5. Elemental and structural studies at the bone-cartilage interface

    NASA Astrophysics Data System (ADS)

    Kaabar, W.; Daar, E.; Bunk, O.; Farquharson, M. J.; Laklouk, A.; Bailey, M.; Jeynes, C.; Gundogdu, O.; Bradley, D. A.

    2011-10-01

    Micro-Proton Induced X-ray Emission (μ-PIXE) and Proton Induced Gamma-ray Emission (PIGE) techniques were employed in the investigation of trace and essential elements distribution in normal and diseased human femoral head sections affected by osteoarthritis (OA). PIGE was exploited in the determination of elements of low atomic number z<15 such as Na and F whereas elements with z>15 viz Ca, Z, P and S were determined by PIXE. Accumulations of key elements in the bone and cartilage sections were observed, significant S and Na concentrations being found in the cartilage region particularly in normal tissues. Zn showed enhanced concentrations at the bone-cartilage interface. At a synchrotron facility, small angle X-ray scattering (SAXS) was utilized on a decalcified human femoral head section affected by OA, direct measurements being made of spatial alterations of collagen fibres. The SAXS results showed a slight decrease in the axial periodicity between normal collagen type I and that in diseased tissue in various sites, in contrast with the findings of others.

  6. Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study.

    PubMed

    Campana, M; Hosking, S L; Petkov, J T; Tucker, I M; Webster, J R P; Zarbakhsh, A; Lu, J R

    2015-05-26

    The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL(-1) a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane. PMID:25875917

  7. Change in macrostructure and porosity of graphite on prolonged irradiation

    SciTech Connect

    Virgil'ev, Y.S.; Butyrin, G.M.; Kalyagina, I.P.; Nikishina, L.M.; Shurshakova, T.N.

    1986-02-01

    This work studies the variation in the microstructure of strongly irradiated reactor-grade graphite samples by mercury porosimetry, optical microscopy, and x-ray analysis. The chief characteristics of the samples are listed. Experimental study of the nature of porous and crystal structure of reactor graphite show that prolonged neutron irradiation at 360 and 1220 degrees K up to a luence of 10/sup 22/ neutrons/cm/sup 2/ causes marked irreversible changes in the graphite macrostructure.

  8. Epoxide composites with thermally reduced graphite oxide and their properties

    NASA Astrophysics Data System (ADS)

    Arbuzov, A. A.; Muradyan, V. E.; Tarasov, B. P.; Sokolov, E. A.; Babenko, S. D.

    2016-05-01

    The properties of epoxide composites modified by thermal reduced graphite oxide are studied. The dielectric permittivities of epoxide composites with additives of up to 1.5 wt % of reduced graphite oxide are studied at a frequency of 9.8 GHz. It is shown that despite its low electrical conductivity, the large specific surface area of reduced graphite oxide allows us to create epoxide composites with high complex dielectric permittivities and dielectric loss tangents.

  9. Recompressed exfoliated graphite articles

    DOEpatents

    Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z

    2013-08-06

    This invention provides an electrically conductive, less anisotropic, recompressed exfoliated graphite article comprising a mixture of (a) expanded or exfoliated graphite flakes; and (b) particles of non-expandable graphite or carbon, wherein the non-expandable graphite or carbon particles are in the amount of between about 3% and about 70% by weight based on the total weight of the particles and the expanded graphite flakes combined; wherein the mixture is compressed to form the article having an apparent bulk density of from about 0.1 g/cm.sup.3 to about 2.0 g/cm.sup.3. The article exhibits a thickness-direction conductivity typically greater than 50 S/cm, more typically greater than 100 S/cm, and most typically greater than 200 S/cm. The article, when used in a thin foil or sheet form, can be a useful component in a sheet molding compound plate used as a fuel cell separator or flow field plate. The article may also be used as a current collector for a battery, supercapacitor, or any other electrochemical cell.

  10. Graphite Gamma Scan Results

    SciTech Connect

    Mark W. Drigert

    2014-04-01

    This report documents the measurement and data analysis of the radio isotopic content for a series of graphite specimens irradiated in the first Advanced Graphite Creep (AGC) experiment, AGC-1. This is the first of a series of six capsules planned as part of the AGC experiment to fully characterize the neutron irradiation effects and radiation creep behavior of current nuclear graphites. The AGC-1 capsule was irradiated in the Advanced Test Reactor (ATR) at INL at approximately 700 degrees C and to a peak dose of 7 dpa (displacements per atom). Details of the irradiation conditions and other characterization measurements performed on specimens in the AGC-1 capsule can be found in “AGC-1 Specimen Post Irradiation Data Report” ORNL/TM 2013/242. Two specimens from six different graphite types are analyzed here. Each specimen is 12.7 mm in diameter by 25.4 mm long. The isotope with the highest activity was 60Co. Graphite type NBG-18 had the highest content of 60Co with an activity of 142.89 µCi at a measurement distance of 47 cm.

  11. Development of polyphenylquinoxaline graphite composites

    NASA Technical Reports Server (NTRS)

    Hoggatt, J. T.; Hergenrother, P. M.; Shdo, J. G.

    1973-01-01

    The potential of polyphenylquinoxaline (PPQ)/graphite composites to serve as structural material at 316 C (600 F)has been demonstrated using a block copolymer, BlCo(13), PPQ derivative. Initially, thirteen polyphenylquinoxalines were evaluated. From this work, four candidate polymers were selected for preliminary evaluation as matrices for HMS graphite fiber reinforced composites. The preliminary composite evaluation enabled selection of one of the four polymers for advanced composite preparation and testing. Using an experimentally established cure schedule for each of the four polymers, preliminary laminates of 50% resin volume content, prepared without postcure, were tested for flexure strength and modulus, interlaminar shear strength (short beam), and tensile strength and modulus at ambient temperature. A block copolymer (Bl Co 13) derived from one mole p-bis (phenylglyoxalyl) benzene, one fourth mole 3,3'-diaminobenzidine and three-fourths mole 3,3', 4,4'-tetraminobenzophenone was selected for extensive study. Tensile, flexural, and interlaminar shear values were obtained after aging and testing postcured BlCo(13) laminates at 316 C (600 F). The potential of PPQ/graphite laminates to serve as short term structural materials at temperatures up to 371 C (700 F) was demonstrated through weight loss experiments.

  12. Dissolution rates of coals and graphite in Fe-C-S melts in direct ironmaking: Influence of melt carbon and sulfur on carbon dissolution

    NASA Astrophysics Data System (ADS)

    Wu, C.; Sahajwalla, V.

    2000-04-01

    Carbon dissolution from graphite and coals was investigated by using a carburizer cover technique in an induction furnace. The intent of the study was to investigate the influence of factors governing the rate of carbon dissolution from carbonaceous materials, especially coals, into Fe-C-S melts. The factors studied were the initial melt carbon and sulfur concentrations and the wettability between carbonaceous materials and the melt. It was found that graphite dissolves markedly faster than coal. The rate of carbon dissolution from graphite could be decreased by increasing the sulfur in the melt. Also, poor wetting could retard the rate of carbon dissolution by reducing the surface area for mass transfer. Carbon dissolution from graphite is controlled by mass transfer in the liquid boundary layer adjacent to the solid/liquid interface. The rate of carbon dissolution from coal is more sensitive to the molten iron composition. A higher initial melt carbon and sulfur content retards the rate of carbon dissolution from coal more significantly than from graphite. However, the rate constant of coal char dissolution does not show a strong dependence on the wettability. Carbon dissolution from coals is most likely governed by a mixed-control mechanism that includes liquid-side mass transfer. The mechanisms underlying the influence of bath sulfur on carbon dissolution from graphite and coals are discussed.

  13. Hybrid density functional study of oligothiophene/ZnO interface for photovoltaics

    SciTech Connect

    Sai, Na; Leung, Kevin; Chelikowsky, James R.

    2011-03-21

    Organic-inorganic donor-acceptor interfaces are gaining growing attention in organic photovoltaic applications as each component of the interface offers unique attributes. Here we use hybrid density functional theory to examine the electronic structure of sexithiophene/ZnO interfaces. We find that interfacial molecular orientations strongly influence the adsorption energy, the energy level alignment, and the open-circuit voltage. We attribute the orientation dependence to the varied strength of electronic coupling between the molecule and the substrate. Our study suggests that photovoltaic performance can be optimized by controlling the interfacial design of molecular orientations.

  14. Adsorption Characteristics of Binary Mixtures of Two Halomethanes on Graphite Surface

    NASA Astrophysics Data System (ADS)

    Khanal, Kiran; Leuty, Gary; Tsige, Mesfin

    Understanding the physisorption mechanism of mixtures of small molecules on graphite substrate has been a growing interest in materials science in order to investigate the changes in adsorption behavior of mixtures near interfaces vs. the individual components. Using atomic-scale molecular dynamics simulations, we have studied the structure and dynamics of multilayer adsorption of binary mixtures of two halomethanes (CF4 and CF3Cl) on graphite substrates for different bulk compositions of CF4. Simulations were performed in the temperature range 60-120K. The goal of this study is to explore how the compositions of individual components as well as temperature, affect the structure of films near the interface, the mobility of molecules, the molecular orientation and the substrate affinity. Preliminary results suggest a strong influence of the concentration of CF4 and temperature on the structure and mobility of molecules in first adsorbed layer on the graphite surface. In agreement with the recent experimental results, CF4 displaces CF3Cl from the first absorbed layer at all temperatures in our range and becomes the leading component in the mixture at high temperature for large CF4 concentrations in the mixture. ``This work is supported by NSF Grant CHE #1506275''.

  15. Computational Study of ions binding to the liquid interface of water

    SciTech Connect

    Dang, Liem X. )

    2002-08-12

    We have performed extensive classical molecular dynamics simulations to examine the molecular transport mechanisms of the I-, Br-, Cl- and Na+ ions across the liquid/vapor interface of water. The potentials of mean force were calculated using the constrained mean force approach and polarizable potential models were used to describe the interactions among the species. The simulated potentials of mean force were found to be different, depending on the type of anion. The larger I- and Br- anions bind more strongly to the liquid/vapor interface of water than did the smaller Cl-ion. It is important to note here that most of the gas phase and solution phase properties of the Br- anion are quite similar to that of the Cl- ion. At the interface, however, the interactions of the Br- and Cl- anions with the water interface appeared to be significantly different. We found that the anions approach the interface more closely do than cations. We have also studied the transport mechanism of an I- across the water/dichloromethane interface. The computed potential of mean force showed no well-defined minimum as in the liquid/vapor case, but a stabilization free energy of about?1 kcal/mol near the interface with respect to the bulk liquid was observed. The I- anion carried a water molecule with it as it crossed the interface. This result is in agreement with a recent experimental study on a similar system. Our work differs from earlier contributions in that our potential models have taken many-body effects into account, and in some cases, these effects cannot be neglected. To the best of our knowledge, this work significantly advances our understanding of molecular processes at the liquid interfaces.

  16. Cesium diffusion in graphite

    SciTech Connect

    Evans, R.B. III; Davis, W. Jr.; Sutton, A.L. Jr.

    1980-05-01

    Experiments on diffusion of /sup 137/Cs in five types of graphite were performed. The document provides a completion of the report that was started and includes a presentation of all of the diffusion data, previously unpublished. Except for data on mass transfer of /sup 137/Cs in the Hawker-Siddeley graphite, analyses of experimental results were initiated but not completed. The mass transfer process of cesium in HS-1-1 graphite at 600 to 1000/sup 0/C in a helium atmosphere is essentially pure diffusion wherein values of (E/epsilon) and ..delta..E of the equation D/epsilon = (D/epsilon)/sub 0/ exp (-..delta..E/RT) are about 4 x 10/sup -2/ cm/sup 2//s and 30 kcal/mole, respectively.

  17. Irradiation Creep in Graphite

    SciTech Connect

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

  18. Coatings for graphite fibers

    NASA Technical Reports Server (NTRS)

    Galasso, F. S.; Scola, D. A.; Veltri, R. D.

    1980-01-01

    Graphite fibers released from composites during burning or an explosion caused shorting of electrical and electronic equipment. Silicon carbide, silica, silicon nitride and boron nitride were coated on graphite fibers to increase their electrical resistances. Resistances as high as three orders of magnitude higher than uncoated fiber were attained without any significant degradation of the substrate fiber. An organo-silicone approach to produce coated fibers with high electrical resistance was also used. Celion 6000 graphite fibers were coated with an organo-silicone compound, followed by hydrolysis and pyrolysis of the coating to a silica-like material. The shear and flexural strengths of composites made from high electrically resistant fibers were considerably lower than the shear and flexural strengths of composites made from the lower electrically resistant fibers. The lower shear strengths of the composites indicated that the coatings on these fibers were weaker than the coating on the fibers which were pyrolyzed at higher temperature.

  19. In operando neutron diffraction study of a commercial graphite/(Ni, Mn, Co) oxide-based multi-component lithium ion battery

    NASA Astrophysics Data System (ADS)

    Nazer, N. S.; Yartys, V. A.; Azib, T.; Latroche, M.; Cuevas, F.; Forseth, S.; Vie, P. J. S.; Denys, R. V.; Sørby, M. H.; Hauback, B. C.; Arnberg, L.; Henry, P. F.

    2016-09-01

    In situ neutron diffraction was employed to investigate the structural evolution of the electrode materials in an ICR 10440 commercial cylindrical lithium-ion battery, which has a discharge capacity of 360 mAh and a nominal voltage of 3.7 V. A three-phase mixture of Li(Ni,Mn,Co)O2, LiCoO2 and LiMn2O4 was identified as the active material of the cathode, with graphite acting as the anode material. The study revealed that the graphite anode underwent structural changes to form a series of insertion-type lithiated derivatives, with up to 12.7% volume expansion for the Li-saturated compound LiC6. The charge-discharge behavior was more complex for the cathode. Here, the charge process was associated with partial lithium depletion from the initially Li-saturated compounds, leading to volume shrinkage for Li(Ni,Mn,Co)O2, in contrast to (Ni,Mn)-free LiCoO2. Electrochemical discharge experiments performed under a fast regime (2 C) at 5, 25 and 45 °C revealed that the discharge capacity followed the trend of an increased diffusion rate of Li+ ions in the electrolyte and Li atoms in both electrodes, being highest for 45 °C. At the lowest tested temperature (5 °C), a rapid drop in the discharge capacity took place using the same kinetic regime.

  20. Computer Simulation study of polyhedral nanoparticle self-assembly at interfaces

    NASA Astrophysics Data System (ADS)

    Thapar, Vikram; Gupta, Unmukt; Escobedo, Fernando

    The self-assembly of polyhedral particles confined to a fluid-fluid interface is studied using Monte Carlo simulations. Several polyhedral shapes are studied, which are selected from a family of truncated cubes which include cubes, cuboctahedra, and octahedra. First we studied the case of hard particles pinned to the interface by restricting their movement in the direction perpendicular to it while allowing their free rotations. Our results suggest that the known solid phases and mesophases of these shapes in the 3D bulk are ``translated'' into variants in 2D space. These insights on 2D entropic self-assembly of polyhedral particles is a first step toward understanding the self-assembly of particles at fluid-fluid interfaces, which is driven by a complex interplay of entropic and enthalpic forces. As a second step we hence studied the particle-surface and particle-particle interactions associated with a fluid-fluid interface using both continuum and polybead models to assess the role of enthalpic interactions in determining the particle orientation behavior with respect to interface. We find that the thickness of the interface can introduce non-trivial effects on the preferential particle orientations.

  1. Modeling Initial Stage of Ablation Material Pyrolysis: Graphitic Precursor Formation and Interfacial Effects

    NASA Technical Reports Server (NTRS)

    Desai, Tapan G.; Lawson, John W.; Keblinski, Pawel

    2010-01-01

    Reactive molecular dynamics simulations are used to study initial stage of pyrolysis of ablation materials and their composites with carbon nanotubes and carbon fibers. The products formed during pyrolysis are characterized and water is found as the primary product in all cases. The water formation mechanisms are analyzed and the value of the activation energy for water formation is estimated. A detailed study on graphitic precursor formation reveals the presence of two temperature zones. In the lower temperature zone (less than 2000 K) polymerization occurs resulting in formation of large, stable graphitic precursors, and in the high temperature zone (greater than 2000 K) polymer scission results in formation of short polymer chains/molecules. Simulations performed in the high temperature zone on the phenolic resin composites (with carbon nanotubes and carbon fibers) shows that the presence of interfaces had no substantial effect on the chain scission rate or the activation energy value for water formation.

  2. Improved graphite furnace atomizer

    DOEpatents

    Siemer, D.D.

    1983-05-18

    A graphite furnace atomizer for use in graphite furnace atomic absorption spectroscopy is described wherein the heating elements are affixed near the optical path and away from the point of sample deposition, so that when the sample is volatilized the spectroscopic temperature at the optical path is at least that of the volatilization temperature, whereby analyteconcomitant complex formation is advantageously reduced. The atomizer may be elongated along its axis to increase the distance between the optical path and the sample deposition point. Also, the atomizer may be elongated along the axis of the optical path, whereby its analytical sensitivity is greatly increased.

  3. Lightweight graphite/polyimide panels

    NASA Technical Reports Server (NTRS)

    Poesch, J. G.; Merlette, J. B.

    1973-01-01

    Panels are constructed of honeycombed polyimide/graphite core covered with thin face sheet of same material. Fabrication is based on extension of thin-gage graphite technology and modification of glass filament polyimide honeycomb techniques.

  4. Flexible graphite as battery anode and current collector

    NASA Astrophysics Data System (ADS)

    Yazici, M. S.; Krassowski, D.; Prakash, J.

    In making graphite-based electrodes and current collectors, there is significant simplification if a flexible graphite process is used. The lithium intercalation capacity of Grafoil ® flexible graphite sheet and its powder was evaluated using electrochemical charge-discharge cycling in half-cell configuration (coin cell with Li anode and graphite cathode). The sheet form was used with and without a copper current collector. Excellent electrical conductivity of the monolithic material with very low interface resistance helps as current collector and electrode. The comparatively low capacity of Grafoil ® sheet is thought to be due to diffusion limitation of the structure, especially in the light of the very high capacity of its powder form. The highly irreversible capacity of the powdered material may be due to unfunctionalized graphitic structures or impurities present in the powder. Impedance response for the first intercalation-deintercalation was different than responses taken after several cycles. The presence of a second impedance arc suggests structural modification is taking place in the graphite anode, possibly through formation of a porous structure as a result of graphite expansion. ®GRAFOIL is a registered trademark of Advanced Energy Technology Inc.

  5. Processing, Microstructure, and Mechanical Properties of Interpenetrating Biomorphic Graphite/Copper Composites

    NASA Astrophysics Data System (ADS)

    Childers, Amanda Esther Sall

    Composite properties can surpass those of the individual phases, allowing for the development of advanced, high-performance materials. Bio-inspired and naturally-derived materials have garnered attention as composite constituents due to their inherently efficient and complex structures. Wood-derived ceramics, produced by converting a wood precursor into a ceramic scaffold, can exhibit a wide range of microstructures depending on the wood species, including porosity, pore size and distribution, and connectivity. The focus of this work was to investigate the processing, microstructure, and properties of graphite/copper composites produced using wood-derived graphite scaffolds. Graphite/copper composites combine low specific gravity, high thermal conductivity, and tailorable thermal expansion properties, and due to the non-wetting behavior of copper to graphite, offer a unique system in which mechanically bonded interfaces in composites can be studied. Graphite scaffolds were produced from red oak, beech, and pine precursors using a catalytic pyrolyzation method, resulting in varying types of pore networks. Two infiltration methods were investigated to overcome challenges associated with non-wetting systems: copper electrodeposition and pressure-assisted melt infiltration. The phase distributions, constituent properties, interfacial characteristics, mechanical behavior, and load partitioning of these biomorphic graphite/copper composites were investigated, and were correlated to the wood species. The multi-domain feature sizes in the graphite scaffolds resulted in composites with copper relegated not only to the large, connected channels produced from the transport features in the wood, but also within the smaller, lower aspect ratio fibrous regions of the scaffold. Both features contributed to the mechanical behavior of the composites to varying degrees depending on the wood species. A multi-component predictive model also was developed and used to guide the additive

  6. Electrical properties of a graphite-rich quartzite from a former lower continental crust exposed in the Serre San Bruno, Calabria (southern Italy)

    NASA Astrophysics Data System (ADS)

    Jödicke, Hartmut; Nover, Georg; Kruhl, Jörn H.; Markfort, Rudolf

    2007-11-01

    In this study electrical properties of a graphite-rich quartzite from the former lower crust exposed in the Serre San Bruno, Calabria (southern Italy) have been analysed by means of complex electrical conductivity measurements in the frequency range 10 -3 to 10 6 Hz on plug samples of 25 mm in diameter and 22 mm high. The samples were identified as a former oil sandstones containing up to 12-15% flake-like graphite, which present highly metamorphosed relics of its former hydrocarbon filling. Though high concentrations of graphite were detected, the graphite quartzite is highly resistive. The spatial ordering of isolated graphite grains like tiles prevent the generation of interconnected electrical pathways. These isolated good conductors are interconnected by electrolyte bridges, thus causing the high polarizability, indicating redox reactions at the electrolyte/graphite interfaces that could be modelled using CPE elements. The type of graphite ordering was caused by the early formation of isolated oil droplets in the reservoir sandstone. After high-grade metamorphism and shearing, they appear as flat graphite grains in the foliation plane and were smeared together because of the rigidity of sillimanite and quartz, the main rock constituents. Thus this graphite quartzite is by no means a candidate to enhance the electrical conductivity of the deep continental crust. Syngenetic graphite in former lower crustal rocks is largely resistant against varying geochemical conditions during prograde and retrograde metamorphism. This had also been shown for graphite that is contained in normal metapelites as accessory mineral, or enriched in former black shales where it may cause high conductivity [Jödicke, H., Kruhl, J.H., Ballhaus, C., Giese, P., Untiedt, J., 2004. Syngenetic, thin graphite-rich horizons in lower crustal rocks from the Serre San Bruno, Calabria (Italy), and implications for the nature of high-conducting deep crustal layers. PEPI 141, 37-58; Nover, G., 2005

  7. Studies of the Si/SiO2 interface using synchrotron radiation

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Grunthaner, F. J.

    1985-01-01

    Synchrotron radiation photoemission spectroscopy (SRPS) in the 1-4 KeV photon energy range is a useful tool for interface characterization. Results are presented of a series of studies of the near-interface region of Si/SiO2 which confirm that a bond strain gradient exists in the oxide as a result of lattice mismatch. These experiments include measurement of photoemission lineshape changes as a function of photon energy, corresponding changes in the electron escape depth near the interface, and surface extended X-ray absorption fine structure (SEXAFS) measurements directly indicating the shortening of the Si-Si second nearest neighbor distance in the near-interface region of the oxide.

  8. Advanced EVA system design requirements study: EVAS/space station system interface requirements

    NASA Technical Reports Server (NTRS)

    Woods, T. G.

    1985-01-01

    The definition of the Extravehicular Activity (EVA) systems interface requirements and accomodations for effective integration of a production EVA capability into the space station are contained. A description of the EVA systems for which the space station must provide the various interfaces and accomodations are provided. The discussion and analyses of the various space station areas in which the EVA interfaces are required and/or from which implications for EVA system design requirements are derived, are included. The rationale is provided for all EVAS mechanical, fluid, electrical, communications, and data system interfaces as well as exterior and interior requirements necessary to facilitate EVA operations. Results of the studies supporting these discussions are presented in the appendix.

  9. Graphite-based photovoltaic cells

    DOEpatents

    Lagally, Max; Liu, Feng

    2010-12-28

    The present invention uses lithographically patterned graphite stacks as the basic building elements of an efficient and economical photovoltaic cell. The basic design of the graphite-based photovoltaic cells includes a plurality of spatially separated graphite stacks, each comprising a plurality of vertically stacked, semiconducting graphene sheets (carbon nanoribbons) bridging electrically conductive contacts.

  10. (Irradiation creep of graphite)

    SciTech Connect

    Kennedy, C.R.

    1990-12-21

    The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

  11. GRAPHITE BONDING METHOD

    DOEpatents

    King, L.D.P.

    1964-02-25

    A process for bonding or joining graphite members together in which a thin platinum foil is placed between the members, heated in an inert atmosphere to a temperature of 1800 deg C, and then cooled to room temperature is described. (AEC)

  12. Graphite criteria peer review

    SciTech Connect

    1986-09-01

    This report documents a review of the stress criteria proposed for the graphite components of the modular high temperature gas-cooled reactor (MHTGR) core. The review was conducted by a panel of six independent consultants, chosen for their expertise over a range of relevant disciplines.

  13. Graphite technology development plan

    SciTech Connect

    1986-07-01

    This document presents the plan for the graphite technology development required to support the design of the 350 MW(t) Modular HTGR within the US National Gas-Cooled Reactor Program. Besides descriptions of the required technology development, cost estimates, and schedules, the plan also includes the associated design functions and design requirements.

  14. Structural graphitic carbon foams

    SciTech Connect

    Kearns, K.M.; Anderson, H.J.

    1998-12-31

    Graphitic carbon foams are a unique material form with very high structural and thermal properties at a light weight. A process has been developed to produce microcellular, open-celled graphitic foams. The process includes heating a mesophase pitch preform above the pitch melting temperature in a pressurized reactor. At the appropriate time, the pressure is released, the gas nucleates bubbles, and these bubbles grow forming the pitch into the foam structure. The resultant foamed pitch is then stabilized in an oxygen environment. At this point a rigid structure exists with some mechanical integrity. The foam is then carbonized to 800 C followed by a graphitization to 2700 C. The shear action from the growing bubbles aligns the graphitic planes along the foam struts to provide the ideal structure for good mechanical properties. Some of these properties have been characterized for some of the foam materials. It is known that variations of the blowing temperature, blowing pressure and saturation time result in foams of variously sized with mostly open pores; however, the mechanism of bubble nucleation is not known. Therefore foams were blown with various gases to begin to determine the nucleation method. These gases are comprised of a variety of molecular weights as well as a range of various solubility levels. By examining the resultant structures of the foam, differences were noted to develop an explanation of the foaming mechanism.

  15. Coatings for Graphite Fibers

    NASA Technical Reports Server (NTRS)

    Galasso, F. S.; Scola, D. A.; Veltri, R. D.

    1980-01-01

    Several approaches for applying high resistance coatings continuously to graphite yarn were investigated. Two of the most promising approaches involved (1) chemically vapor depositing (CVD) SiC coatings on the surface of the fiber followed by oxidation, and (2) drawing the graphite yarn through an organo-silicone solution followed by heat treatments. In both methods, coated fibers were obtained which exhibited increased electrical resistances over untreated fibers and which were not degraded. This work was conducted in a previous program. In this program, the continuous CVD SiC coating process used on HTS fiber was extended to the coating of HMS, Celion 6000, Celion 12000 and T-300 graphite fiber. Electrical resistances three order of magnitude greater than the uncoated fiber were measured with no significant degradation of the fiber strength. Graphite fibers coated with CVD Si3N4 and BN had resistances greater than 10(exp 6) ohm/cm. Lower pyrolysis temperatures were used in preparing the silica-like coatings also resulting in resistances as high as three orders of magnitude higher than the uncoated fiber. The epoxy matrix composites prepared using these coated fibers had low shear strengths indicating that the coatings were weak.

  16. Graphite Oxidation Simulation in HTR Accident Conditions

    SciTech Connect

    El-Genk, Mohamed

    2012-10-19

    Massive air and water ingress, following a pipe break or leak in steam-generator tubes, is a design-basis accident for high-temperature reactors (HTRs). Analysis of these accidents in both prismatic and pebble bed HTRs requires state-of-the-art capability for predictions of: 1) oxidation kinetics, 2) air helium gas mixture stratification and diffusion into the core following the depressurization, 3) transport of multi-species gas mixture, and 4) graphite corrosion. This project will develop a multi-dimensional, comprehensive oxidation kinetics model of graphite in HTRs, with diverse capabilities for handling different flow regimes. The chemical kinetics/multi-species transport model for graphite burning and oxidation will account for temperature-related changes in the properties of graphite, oxidants (O2, H2O, CO), reaction products (CO, CO2, H2, CH4) and other gases in the mixture (He and N2). The model will treat the oxidation and corrosion of graphite in geometries representative of HTR core component at temperatures of 900°C or higher. The developed chemical reaction kinetics model will be user-friendly for coupling to full core analysis codes such as MELCOR and RELAP, as well as computational fluid dynamics (CFD) codes such as CD-adapco. The research team will solve governing equations for the multi-dimensional flow and the chemical reactions and kinetics using Simulink, an extension of the MATLAB solver, and will validate and benchmark the model's predictions using reported experimental data. Researchers will develop an interface to couple the validated model to a commercially available CFD fluid flow and thermal-hydraulic model of the reactor , and will perform a simulation of a pipe break in a prismatic core HTR, with the potential for future application to a pebble-bed type HTR.

  17. Study of compression-loaded and impact-damaged structurally efficient graphite-thermoplastic trapezoidal-corrugation sandwich and semisandwich panels

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1992-01-01

    The structural efficiency of compression-loaded trapezoidal-corrugation sandwich and semisandwich composite panels is studied to determine their weight savings potential. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them and semisandwich panels with a corrugation attached to a single skin are considered. An optimization code is used to find the minimum weight designs for critical compressive load levels ranging from 3000 to 24,000 lb/in. Graphite-thermoplastic panels based on the optimal minimum weight designs were fabricated and tested. A finite element analysis of several test specimens was also conducted. The results of the optimization study, the finite element analysis, and the experiments are presented. The results of testing impact damage panels are also discussed.

  18. A study of interface crack branching in dissimilar anisotropic bimaterial composites including thermal effects

    NASA Astrophysics Data System (ADS)

    Li, Renfu

    The interface crack branching phenomena, including thermal effects, has been investigated by using complex variable method and Stroh's dislocation theory, extended to thermo-elasticity in matrix notation. As one of the most catastrophic failure modes in structures like laminated and sandwich composites in aerospace and marine construction, thin film in electronic packaging, rotators in high speed engine of aircraft and reactor in nuclear power station, the study of interface crack branching has become a topic not only having theoretical importance, but also having practical significance. A unified approach is presented to address the thermoelastic interface crack problems in dissimilar anisotropic bimaterial composites, and a compact closed form solution is formulated by analytical continuation principle of complex analysis. Employing the contour integral method, an explicit solution to the interaction between the dislocations and the interface crack is obtained. By modeling the branched portion as a continuous distribution of the dislocations, the thermoelastic interface crack branching problem is then converted to a set of semi-coupled singular integral equations and solved by Gauss-Jacobi integration schemes. The influence of material property mismatches between the two constituents and the thermal loading effects on the interface crack branching are demonstrated by extensive numerical simulation. Some useful criteria for predicting the interface crack branching growth and guidance for optimal composites design are suggested. Further, a contact model to eliminate the overlapping between the two surfaces of an interface crack is also proposed and some new parameters which could influence the interpenetrating phenomena are also discovered. The technique to extend the current method to three dimensional problems is also outlined. Furthermore, the C++ source code has been implemented to manipulate the complicated complex operations for numerically solving the

  19. A systematic study of some promising electrolyte additives in Li[Ni1/3Mn1/3Co1/3]O2/graphite, Li[Ni0.5Mn0.3Co0.2]/graphite and Li[Ni0.6Mn0.2Co0.2]/graphite pouch cells

    NASA Astrophysics Data System (ADS)

    Ma, Lin; Self, Julian; Nie, Mengyun; Glazier, Stephen; Wang, David Yaohui; Lin, Yong-Shou; Dahn, J. R.

    2015-12-01

    Li[Ni1/3Mn1/3Co1/3]O2/graphite, Li[Ni0.5Mn0.3Co0.2]O2/graphite and Li[Ni0.6Mn0.2Co0.2O2]/graphite pouch cells were examined with and without electrolyte additives using the ultra high precision charger at Dalhousie University, electrochemical impedance spectroscopy, gas evolution measurements and "cycle-store" tests. The electrolyte additives tested were vinylene carbonate (VC), prop-1-ene-1,3-sultone (PES), pyridine-boron trifluoride (PBF), 2% PES + 1% methylene methanedisulfonate (MMDS) + 1% tris(trimethylsilyl) phosphite (TTSPi) and 0.5% pyrazine di-boron trifluoride (PRZ) + 1% MMDS. The charge end-point capacity slippage, capacity fade, coulombic efficiency, impedance change during cycling, gas evolution and voltage drop during "cycle-store" testing were compared to gain an understanding of the effects of these promising electrolyte additives or additive combinations on the different types of pouch cells. It is hoped that this report can be used as a guide or reference for the wise choice of electrolyte additives in Li[Ni1/3Mn1/3Co1/3]O2/graphite, Li[Ni0.5Mn0.3Co0.2]O2/graphite and Li[Ni0.6Mn0.2Co0.2O2]/graphite pouch cells and also to show the shortcomings of particular positive electrode compositions.

  20. Graphite matrix materials for nuclear waste isolation

    SciTech Connect

    Morgan, W.C.

    1981-06-01

    At low temperatures, graphites are chemically inert to all but the strongest oxidizing agents. The raw materials from which artificial graphites are produced are plentiful and inexpensive. Morover, the physical properties of artificial graphites can be varied over a very wide range by the choice of raw materials and manufacturing processes. Manufacturing processes are reviewed herein, with primary emphasis on those processes which might be used to produce a graphite matrix for the waste forms. The approach, recommended herein, involves the low-temperature compaction of a finely ground powder produced from graphitized petroleum coke. The resultant compacts should have fairly good strength, low permeability to both liquids and gases, and anisotropic physical properties. In particular, the anisotropy of the thermal expansion coefficients and the thermal conductivity should be advantageous for this application. With two possible exceptions, the graphite matrix appears to be superior to the metal alloy matrices which have been recommended in prior studies. The two possible exceptions are the requirements on strength and permeability; both requirements will be strongly influenced by the containment design, including the choice of materials and the waste form, of the multibarrier package. Various methods for increasing the strength, and for decreasing the permeability of the matrix, are reviewed and discussed in the sections in Incorporation of Other Materials and Elimination of Porosity. However, it would be premature to recommend a particular process until the overall multi-barrier design is better defined. It is recommended that increased emphasis be placed on further development of the low-temperature compacted graphite matrix concept.

  1. Shuttle payload interface verification equipment study. Volume 3: Specification data

    NASA Technical Reports Server (NTRS)

    1976-01-01

    A complete description is given of the IVE physical and performance design requirements as evolved in this study. The data are presented in a format to facilitate the development of an item specification. Data were used to support the development of the project plan data (schedules, cost, etc.) contained in Volume 4 of this report.

  2. Intercalating oleylamines in graphite oxide.

    PubMed

    Yang, Kaikun; Liang, Si; Zou, Lianfeng; Huang, Liwei; Park, Cheol; Zhu, Lisheng; Fang, Jiye; Fu, Qiang; Wang, Howard

    2012-02-01

    Graphite oxide has been synthesized from raw graphite particles and been treated with various mass amounts of oleylamine as intercalants to form intercalation compounds. X-ray diffraction patterns reveal that the inter-sheet distances strongly depend on the graphite oxide to oleylamine mass ratios. The equilibrium-like behavior implies diffusion-dominated oleylamine adsorption on graphite oxide in solution and excluded volume intercalations among oleylamine-adsorbed graphite oxide during restacking. The intercalation compounds are soluble in organic solvents, and their applications in the fabrication of transparent and conductive coatings have been demonstrated. PMID:22229856

  3. Gas Evolution in LiNi0.5Mn1.5O4/Graphite Cells Studied In Operando by a Combination of Differential Electrochemical Mass Spectrometry, Neutron Imaging, and Pressure Measurements.

    PubMed

    Michalak, Barbara; Berkes, Balázs B; Sommer, Heino; Bergfeldt, Thomas; Brezesinski, Torsten; Janek, Jürgen

    2016-03-01

    The cycling performance and in operando gas analysis of LiNi0.5Mn1.5O4 (LNMO)/graphite cells with reasonably high loading, containing a "standard" carbonate-based electrolyte is reported. The gas evolution over the first couple of cycles was thoroughly investigated via differential electrochemical mass spectrometry (DEMS), neutron imaging and pressure measurements. The main oxidation and reduction products were identified as CO2, H2 and C2H4. In different sets of experiments graphite was substituted with delithiated LiFePO4 (LFP) and LNMO with LFP to distinguish between processes occurring at either anode or cathode and gain mechanistic insights. Both C2H4 and H2 were found to be mainly formed at the anode side, while CO2 is generated at the cathode. The results from DEMS analysis further suggest that the Ni redox couples play a profound role in the evolution of CO2 at the LNMO/electrolyte interface. Lastly, it is shown that the cycling stability and capacity retention of LNMO/graphite cells can be considerably improved by a simple cell formation procedure. PMID:26813026

  4. Atmosphere explorer missions C, D, and E. Spacecraft experiment interface definition study

    NASA Technical Reports Server (NTRS)

    1972-01-01

    The Atmosphere Explorer Missions C, D, & E Spacecraft/Experiment Interface Definition Study is discussed. The objectives of the study included an analysis of the accommodation requirements of the experiments for the three missions, an assessment of the overall effect of these requirements on the spacecraft system design and performance, and the detailed definition of all experiment/spacecraft electrical, mechanical, and environmental interfaces. In addition, the study included the identification and definition of system characteristics required to ensure compatibility with the consolidated STADAN and MSFN communications networks.

  5. Interstellar dust: interfacing laboratory, theoretical and observational studies

    NASA Astrophysics Data System (ADS)

    Jones, Anthony Peter

    2015-08-01

    In this talk I will consider how our understanding of interstellar dust can only be advanced through a combination of laboratory, theoretical and observational studies, which provide the critical framework for advancing our understanding. I will summarise what we currently know, or think we know, about the physical and compositional properties of dust and their evolution in interstellar media. Along the way I will question the utility of astronomical dust analogues and show, based on data from the laboratory, theoretical studies and from astronomical observations, that some of our prior interpretations need to be subjected to a critical re-evaluation. I will present interstellar dust modelling from a new vantage point and review ideas on the interpretation of observations within the framework of this model and its predictions for dust evolution within and between interstellar media. Finally, I will summarise some of the current outstanding issues and what we would like to learn in the future.

  6. Adhesion study of thermoplastic polyimides with Ti-6Al-4V alloy and PEEK-graphite composites

    SciTech Connect

    Yoon Taeho.

    1991-01-01

    High glass transition (e.g. 360C) melt processable thermoplastic polyimide homopolymers and poly(imide-siloxane) segmented copolymers were prepared from a number of diamines and dianhydrides via solution imidization, polydimethylsilxane segment incorporation and molecular weight control with non-reactive phthalimide end-groups. The adhesive bond performance of these polyimides was investigated as a function of molecular weight, siloxane incorporation, residual solvent, test temperature, and polyimide structure via single-lap shear samples prepared from treated Ti-6Al-4V alloy adherends and compression-molded film adhesives of scrim-cloth adhesives. The adhesive bond strengths increased greatly with siloxane-segment incorporation at 10, 20 and 30 wt% and decreased slightly with total polymer molecular weight. As the test temperature was increased, adhesive bond strength increased, decreased or showed a maximum at some temperatures depending on the polyimide structure and siloxane content. The poly(imide-30% siloxane) segmented copolymer and a miscible poly(ether-imide) also demonstrated excellent adhesive bond strength with poly(arylene ether ketone) PEEK{reg sign}-graphite composites.

  7. In situ electrochemical STM study of platinum nanodot arrays on highly oriented pyrolythic graphite prepared by electron beam lithography

    NASA Astrophysics Data System (ADS)

    Foelske-Schmitz, A.; Peitz, A.; Guzenko, V. A.; Weingarth, D.; Scherer, G. G.; Wokaun, A.; Kötz, R.

    2012-12-01

    Model electrodes consisting of platinum dots with a mean diameter of (30 ± 5) nm and heights of 3-5 nm upon highly oriented pyrolytic graphite (HOPG) were prepared by electron beam lithography and subsequent sputtering. The Pt nanodot arrays were stable during scanning tunnelling microscopy (STM) measurements in air and in sulphuric acid electrolyte, indicating the presence of "anchors", immobilising the dots on the HOPG surface. Electrochemical STM was used to visualise potential induced Pt, carbon and Pt-influenced carbon corrosion in situ in 0.5 M sulphuric acid under ambient conditions. Potentiostatic hold experiments show that the Pt dots start to disappear at electrode potentials of E > 1.4 V vs. SHE. With increasing time and potential a hole pattern congruent to the original dot pattern appears on the HOPG basal planes. Corrosion and peeling of the HOPG substrate could also be followed in situ. Dissolution of Pt dots appears to be accelerated for potential cycling experiments compared to the potential hold statistics.

  8. On biomolecules and semiconductors: Analytical studies of interface dynamics

    NASA Astrophysics Data System (ADS)

    Slavin, John William Joseph

    The studies discussed here were undertaken to examine the use of III-V semiconducting materials as templates for biomolecules, to be applied in such technologies as Field-Effect Transistor (FET) and Light-emitting Diode (LED) biosensors. Materials application requires an informed analysis of interactions between chemical environments. Specific to surfaces, this means investigating the molecular interactions between the substrate and the bonding moieties. The analytical tools used to probe these interactions, and the changes that such communication causes on specific substrates are specifically discussed. Surface analysis tools included in this review are Atomic Force Microscopy (AFM), Nanoindentation, X-ray Photoelectron Spectroscopy (XPS), and Raman Microscopy. The interaction of biomolecules - deoxyribonucleic acid (DNA), proteins adhered to nanoparticles, and amino acids - on semiconductor surfaces is also examined. Proper investigation follows, as well, the methods of applying these biomolecular structures to the specified surfaces, through procedures such as solution phase transfer, as well as Dip-pen Nanolithography (DPN). The stretching and enzymatic cleavage of DNA, on silicon oxide surfaces, was studied to determine the recognition properties of dual-enzymatic systems on surfaces. Fundamental questions such as the interaction of functional groups with InAs(100) surfaces, the mechanical properties of protein modified systems, and the DPN application of biologically relevant linker molecules to InAs(100) surfaces were explored. These studies provide information applicable to the development of novel sensing platforms in the future.

  9. Interfacing anthropology and epidemiology: the Bedouin Arab Infant Feeding Study.

    PubMed

    Hundt, G A; Forman, M R

    1993-04-01

    This paper encapsulates a 10 year effort of multi-disciplinary research on the relationship between infant feeding, growth, and morbidity among the Negev Bedouin Arabs of Israel as they underwent a transition from semi-nomadism to urban settlement. The research team was multi-disciplinary including a nutritional epidemiologist and an anthropologist who both came to the study with previous experience in interdisciplinary work. The specific study objectives were (1) a description of infant feeding practices among Negev Bedouin Arab women at various stages of settlement, (2) an examination of the trend in these infant feeding practices, (3) a comparison of the extent to which different infant feeding practices are related to infant morbidity and growth after adjustment for exposure to social change and other covariates. The data collection took place in 1981-83 and the analysis from 1984-88. In this paper, two areas of the study are discussed in depth: the duration of exclusive breast feeding during the practice of the traditional postpartum 40 day rest period, and the development of a culture-specific scale of socioeconomic status. Through these examples, we highlight the use of ethnographic data and the merging of epidemiology and anthropology from hypothesis generation through data collection, data analysis and interpretation. PMID:8480241

  10. Thermal contact conductance measurements on Doublet III armor tile graphite

    SciTech Connect

    Doll, D.W.; Reis, E.

    1983-12-01

    Several tests were performed on the Doublet III wall armor tiles to determine the cool-down rate and to evaluate improvements made by changing the conditions at the interface between the graphite tile and the stainless steel backing plate. Thermal diffusivity tests were performed in vacuum on both TiC coated and bare graphite tiles with and without 0.13 mm (.005'') thick silver foil at the interface. The results of the armor tile cool-down tests showed improvement when a 0.13 mm (0.005'') silver foil is used at the interface. At 2.1 x 10/sup 5/ Pa (30 psi) contact pressure, the e-folding cool-down times for a TiC coated tile, bare graphite and bare graphite with a 0.06 mm (0.0035'') silver shim were 10 min., 5.0 min., and 4.1 min., respectively. Tests using high contact pressures showed that the cool-down rates converged to approx. 4.0 min. At this limit, the conduction path along the backing plate to the two cooling tubes controls the heat flow, and no further improvement could be expected. Thermal diffusivity measurements confirmed the results of the cool-down test showing that by introducing a silver foil at the interface, the contact conductance between Poco AXF-5Q graphite and 316 stainless steel could be improved by a factor of three to eight. The tests showed an increasing improvement over a range of temperatures from 25/sup 0/C to 400/sup 0/C. The data provides a technical basis for further applications of graphite tiles to cooled backing plates.

  11. Online time-differential perturbed angular correlation study with an 19O beam - Residence sites of oxygen atoms in highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Sato, W.; Ueno, H.; Watanabe, H.; Miyoshi, H.; Yoshimi, A.; Kameda, D.; Ito, T.; Shimada, K.; Kaihara, J.; Suda, S.; Kobayashi, Y.; Shinohara, A.; Ohkubo, Y.; Asahi, K.

    2008-01-01

    The online time-differential perturbed angular correlation (TDPAC) method was applied to a study of the physical states of a probe 19F, the β- decay product of 19O (t1/2 = 26.9 s), implanted in highly oriented pyrolytic graphite. The observed magnitude of the electric field gradient at the probe nucleus, ∣Vzz∣ = 2.91(17) × 1022 V m-2, suggests that the incident 19O atoms are stabilized at an interlayer position with point group C3v. Exhibiting observed TDPAC spectra having a clear sample-to-detector configuration dependence, we demonstrate the applicability of the present online method with a short-lived radioactive 19O beam.

  12. Resin/graphite fiber composites

    NASA Technical Reports Server (NTRS)

    Cavano, P. J.; Jones, R. J.; Vaughan, R. W.

    1972-01-01

    High temperature resin matrices suitable for use in advanced graphite fiber composites for jet engine applications were evaluated. A series of planned, sequential screening experiments with resin systems in composite form were performed to reduce the number of candidates to a single A-type polyimide resin that repetitively produced void-free, high strength and modulus composites acceptable for use in the 550 F range for 1000 hours. An optimized processing procedure was established for this system. Extensive mechanical property studies characterized this single system, at room temperature, 500 F, 550 F and 600 F, for various exposure times.

  13. First principles study of band line up at defective metal-oxide interface: oxygen point defects at Al/SiO2 interface

    NASA Astrophysics Data System (ADS)

    Tea, Eric; Huang, Jianqiu; Hin, Celine

    2016-03-01

    The dielectric breakdown at metal-oxide interfaces is a critical electronic device failure mechanism. Electronic tunneling through dielectric layers is a well-accepted explanation for this phenomenon. Theoretical band alignment studies, providing information about tunneling, have already been conducted in the literature for metal-oxide interfaces. However, most of the time materials were assumed defect free. Oxygen vacancies being very common in oxides, their effect on band lineup is of prime importance in understanding electron tunneling in realistic materials and devices. This work explores the effect of oxygen vacancy and oxygen di-vacancy at the Al/SiO2 interface on the band line up within Density Functional Theory using PBE0 hybrid exchange and correlation functional. It is found that the presence of defects at the interface, and their charge state, strongly alters the band line up.

  14. Thermal-expansion hysteresis in graphite/glass composites

    SciTech Connect

    Janas, V.F.

    1988-07-01

    The thermal-expansion hysteresis phenomena in graphite/glass composites was studied. Neat (unfilled) glass and unidirectional composites showed no observable hysteresis, while (0/90) cross-ply composites showed significant residual thermal strain (approx. 20 PPM) after thermal cycling (25 ..-->.. 150 ..-->.. 25/sup 0/C). Multiple thermal cycling of the composite and the strengthening of the fiber/matrix bond were found to greatly reduce the magnitude of the residual thermal strain. Bond strengthening also weakened and embrittled the composite, supporting a fiber-slippage mechanism for hysteresis. Thermal precycling and interface modification are proposed as methods of diminishing the effects of thermal-expansion hysteresis. 11 references, 6 figures, 4 tables.

  15. First-principles study of interface doping in ferroelectric junctions

    PubMed Central

    Wang, Pin-Zhi; Cai, Tian-Yi; Ju, Sheng; Wu, Yin-Zhong

    2016-01-01

    Effect of atomic monolayer insertion on the performance of ferroelectric tunneling junction is investigated in SrRuO3/BaTiO3/SrRuO3 heterostrucutures. Based on first-principles calculations, the atomic displacement, orbital occupancy, and ferroelectric polarization are studied. It is found that the ferroelectricity is enhanced when a (AlO2)− monolayer is inserted between the electrode SRO and the barrier BTO, where the relatively high mobility of doped holes effectively screen ferroelectric polarization. On the other hand, for the case of (LaO)+ inserted layer, the doped electrons resides at the both sides of middle ferroelectric barrier, making the ferroelectricity unfavorable. Our findings provide an alternative avenue to improve the performance of ferroelectric tunneling junctions. PMID:27063704

  16. Theoretical study of reactions at the electrode-electrolyte interface

    SciTech Connect

    Halley, J.W.

    1993-01-01

    Electron transfer rates are predicted by numerical methods, in a collaboration with Argonne National Laboratory . Emphasis is on electron transfer involving ions known to be important in enhancing stress corrosion cracking in light water reactors and on electron transfer at oxide surfaces. We have produced a new theory for description of the Jahn Teller effect in the solvation shell of the cuprous ion in aqueous solution, have implemented it in a molecular dynamics simulation and compared the results with experimental neutron scattering measurements on solutions containing the cuprous ion. A large amount of numerical data has been collected on the transition state of the ferrous ferric electron transfer reaction at an electrode. Work was completed on a polarizable and dissociable model of water for use in the electron transfer studies. New calculations of the conductivity in models of oxides have shown the existence of impurity conduction bands in such models for the first time.

  17. Enhanced performance of graphite anode materials by AlF3 coating for lithium-ion batteries

    SciTech Connect

    Ding, Fei; Xu, Wu; Choi, Daiwon; Wang, Wei; Li, Xiaolin; Engelhard, Mark H.; Chen, Xilin; Yang, Zhenguo; Zhang, Jiguang

    2012-04-27

    In order to form the stable surface film and to further enhance the long-term cycling stability of the graphite anodes of lithium-ion batteries, the surface of graphite powders has been modified by AlF3 coating through chemical precipitation method. The AlF3-coated graphite shows no evident changes in the bulk structure and a thin AlF3-coating layer of about 2 nm thick is found to uniformly cover the graphite particles with 2 wt% AlF3 content. However, it delivers a higher initial discharge capacity and largely improved rate performances compared to the pristine graphite. Remarkably, AlF3 coated graphite demonstrated a much better cycle life. After 300 cycles, AlF3 coated graphite and uncoated graphite show capacity retention of 92% and 81%, respectively. XPS measurement shows that a more conductive solid electrode interface (SEI) layer was formed on AlF3 coated graphite as compared to uncoated graphite. SEM monograph also reveals that the AlF3-coated graphite particles have a much more stable surface morphology after long-term cycling. Therefore, the improved electrochemical performance of AlF3 coated graphite can be attributed to a more stable and conductive SEI formed on coated graphite anode during cycling process.

  18. An experimental study of recirculating flow through fluid sediment interfaces

    NASA Astrophysics Data System (ADS)

    Khalili, A.; Basu, A. J.; Pietrzyk, U.; Raffel, M.

    1999-03-01

    We report here visualizations and quantitative measurements of scalar transport, under the influence of rotation, through permeable sediments with an overlying fluid layer. The experimental set-up considered here is a stationary cylinder containing a fluid-saturated porous medium up to its midheight, with supernatant water on top. A rotating lid generates, in the upper fluid region, a flow that partially percolates into the porous layer below. The velocity field in the fluid layer is obtained using particle image velocimetry (PIV). Further, dye transport from the sediment is studied using two different techniques. The first one is positron emission tomography (PET), a non-invasive method which allowed us to ‘see’ through the opaque solid matrix, and to obtain full three-dimensional pictures of dye transport through the sediment. The second one is digital photographic visualization from outside, and subsequent image processing in order to obtain the near-wall dye-washout depth. The experimental data suggest that the temporal evolution of washout depth for different sediments follows near-logarithmic behaviour. This finding is of importance for the a priori estimation of the transport of fluid and other solute substances in sandy aquatic sediments.

  19. Iron oxide mineral-water interface reactions studied by AFM

    SciTech Connect

    Hawley, M.E.; Rogers, P.S.Z.

    1994-07-01

    Natural iron mineral surfaces have been examined in air by atomic force (AFM) and scanning tunneling (STM) microscopies. A number of different surface features were found to be characteristic of the native surface. Even surfaces freshly exposed by crushing larger crystals were found to have a pebbly surface texture caused by the presence of thin coatings of what might be surface precipitates. This finding is interpreted as evidence for previous exposure to water, probably through an extensive network of microfractures. Surface reactions on the goethite crystals were studied by AFM at size resolutions ranging from microns to atomic resolution before, during, and after reaction with distilled water and 0.lN HCl. Immediate and extensive surface reconfiguration occurred on contact with water. In one case, after equilibration with water for 3 days, surface reprecipitation, etching and pitting were observed. Atomic resolution images taken under water were found to be disordered. The result of surface reaction was generally to increase the surface area substantially through the extension of surface platelet arrays, present prior to reaction. This work is being done in support of the site characterization project at Yucca Mountain.

  20. Space shuttle/payload interface analysis (study 2.4). Volume 1: Executive summary

    NASA Technical Reports Server (NTRS)

    Pritchard, E. I.

    1973-01-01

    The space shuttle/payload interface analysis is presented. The analysis consists of the following sections: (1) payload capture and cost analysis, (2) business risk and value of operations in space analysis, and (3) payload community analysis. The primary objective of the study was to furnish a method for tracing capture/cost analyses conducted by other study groups.

  1. Development of a submersible shadowgraph for the study of interfaces in salt-gradient solar ponds

    SciTech Connect

    Huacuz, J.M.; Sierra, F.; Venegas, C.; Ramos, C. )

    1989-01-01

    In this paper the processes of development and testing of a submersible shadowgraph are described. This instrument was devised as a tool for the study of interfaces in salt-gradient solar ponds. Tests were carried out in the solar pond of the University of Texas at El Paso. Photographs of interfaces inside the pond were taken for the first time. The submersible shadowgraph can be stationed inside the pond for time dependent studies of a given region, or it can be used to scan the pond depth.

  2. First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Miao, Masoehng; Kioussis, Nicholas; Aqariden, Fikri; Chang, Y.; Grein, Christoph

    CdZnTe and CdTe based semiconductor X-Ray and Gamma-Ray detectors have been intensively studied recently due to their promising potentials for achieving high-resolution, high signal-to-noise ratios and low leakage current, all are desirable features in applications ranging from medical diagnostics to homeland security. Using density functional calculations, we systematically studied the stability, the atomic and electronic structures of the interfaces between CdTe (111) surfaces (Cd- and Te-terminated) and the selected metals (Cu, Al Ni, Pd and Pt). We also calculated the Schottky barrier height (SBH) by aligning the electrostatic potentials in semiconductor and metal regions. Our calculations revealed significant differences between the Cd- and Te- terminated interfaces. While metals tend to deposit directly on reconstructed Te-terminated surfaces, they form a Te-metal alloy layer at the Cd-Terminated metal/CdTe interface. For both Te- and Cd- terminated interfaces, the Schottky barrier heights do not depend much on the choice of metals despite the large variation of the work functions. On the other hand, the interface structure is found to have large effect on the SBH, which is attributed to the metal induced states in the gap.

  3. Experimental Study of the Richtmyer-Meshkov Instability for a He -- SF6 Interface

    NASA Astrophysics Data System (ADS)

    Motl, Bradley; Ranjan, Devesh; Oakley, Jason; Anderson, Mark; Bonazza, Riccardo

    2007-11-01

    Results are presented from a series of experiments studying the Richtmyer-Meshkov (RM) instability for the case of a perturbed gas interface at the Wisconsin Shock Tube Laboratory. A membraneless interface is formed by the head-on flow of helium and sulfur-hexafluoride (seeded with smoke) which creates a stagnation surface. A sinusoidal interface is created at the gas stagnation plane in the test section by oscillating pistons that are initially flush with the shock tube walls. Flow visualization for the initial condition and post-shock images is carried out using Mie scattering from a planar laser sheet. The RM instability is studied for varying incident shock wave strengths (1.1 <=M <= 2), and results are reported in the form of experimental images and perturbation growth rates which are compared to several analytic models.

  4. Usefulness of O-18 and deuterium to study transport processes at aquatic interfaces

    NASA Astrophysics Data System (ADS)

    Lewandowski, Jörg; Pöschke, Franziska; Rudnick, Sebastian; Meinikmann, Karin; Périllon, Cécile

    2014-05-01

    Several different tracers are used in ecohydrology to study the manifold transport processes across groundwater-surface water interfaces. The stable isotopes of oxygen (O-18) and hydrogen (deuterium) as parts of the water molecule might be perfect tracers since their behavior in the environment is quite conservative. Isotope signatures of water differ due to origin of the water and can help to identify processes such as in- or exfiltration at groundwater-surface water interfaces. The recent development of cavity ring-down spectroscopy facilitates reliable measurements by far compared to the previously common method of mass spectroscopy. Nowadays, stable isotope measurements are orders of magnitude cheaper, faster and easier than five years ago. Based on that analytical progress, an increasing number of studies employ the stable isotopes O-18 and deuterium. Ecohydrological applications and their limitations are critically discussed in this contribution focusing on aquifer-lake interfaces.

  5. Effects of boron and glass hybrid epoxy-composites on graphite-fiber release in an aircraft fire

    NASA Technical Reports Server (NTRS)

    Tompkins, S. S.; Brewer, W. D.

    1979-01-01

    Recent studies have shown that the benefits gained by using graphite-epoxy composite structures may not be realized without some risk. The graphite fibers are very good electrical conductors and fibers released into the environment during a fire create a possible hazard to electrical equipment. Several graphite-epoxy hybrids were exposed to a fire and simulated explosion and their graphite fiber retention characteristics were examined. Several low melting-temperature glasses which wet and clump graphite-fibers and a glass/graphite fabric which reduced impact damage were identified as promising hybridizing components to minimize graphite fiber release.

  6. Experimental study on interface region of two-dimensional Si layers by forming gas annealing

    NASA Astrophysics Data System (ADS)

    Mizuno, Tomohisa; Suzuki, Yuhya; Kikuchi, Reika; Suzuki, Ayaka; Inoue, Ryohsuke; Yamanaka, Masahiro; Yokoyama, Miki; Nagamine, Yoshiki; Aoki, Takashi; Maeda, Tatsuro

    2016-04-01

    We experimentally studied the SiO2/Si and Si/buried oxide (BOX) interface regions of a two-dimensional (2D) Si layer, by forming gas annealing (FGA). A photoluminescence (PL) result measured at various lattice temperature, T L, values shows that the PL intensity I PL of the 2D-Si layer rapidly increases and then saturates with increasing FGA temperature, T A, and time, t A. I PL also increases with decreasing T L. A one-dimensional (1D) Schroedinger equation simulator indicates that some of the electrons in the 2D-Si layer generated by a PL excitation laser are quantum-mechanically transmitted into Si interface regions. Actually, we experimentally confirmed that the PL spectra of the 2D-Si layer can be fitted by the PL emission from two regions with different PL peak photon energy values, E PH, which consist of a typical 2D-Si and the interface regions of both the surface SiO2/Si and Si/BOX. Thus, this forming gas dependence is probably attributable to the improved lifetime τ of electrons in the surface interface region, because the Si surface is terminated by H atoms. Moreover, the E PH of the interface region is higher than that of the 2D-Si layer, because of the graded increased bandgap in the interface regions. However, the E PH of 2D-Si is independent of both T A and T L, and this T L independence does not agree with that of a 3D-Si layer. Consequently, we experimentally verified the larger impact of the Si interface on the performance of 2D-Si layer.

  7. First-principles study of Mg(0001)/MgO(1-11) interfaces

    NASA Astrophysics Data System (ADS)

    Song, Hong-Quan; Zhao, Ming; Li, Jian-Guo

    2016-06-01

    By means of first-principles density-functional calculations, we studied the surface energy of a nonstoichiometric MgO(1-11) slab, the interfacial energy and interfacial bonding characteristics of Mg-terminated and O-terminated Mg/MgO(1-11) interfaces with three stacking-site (TOP, HCP and FCC sites) models, and the effect of the thickness of Mg films on the O-terminated MgO(1-11) surface. The results indicate that the surface energies of the nonstoichiometric MgO(1-11) slab and interfacial energies of Mg/Mg(1-11) interface depend on Mg chemical potential. We found that the Mg-terminated MgO(1-11) surface is more stable than the O-terminated MgO(1-11) surface at high Mg chemical potential, and Mg/MgO(1-11) with FCC stacking-site model is the most stable configuration in the Mg/MgO(1-11) interfaces. The results of the electronic structure reveals that the interfacial bonding of Mg-terminated interface with FCC site model mainly consists of metallic bond and of the O-terminated interface with FCC site model is mainly ionic with a small degree of σ-type covalent bond. Although the interfacial energy of Mg-terminated Mg/MgO interface with FCC stacking-site model is slightly higher than that of O-terminated Mg/MgO interface, the molten Mg would epitaxially grow on the FCC sites of the Mg-terminated MgO(1-11) surface because of the high evaporation pressure of Mg at high temperature.

  8. Graphite Polyhedral Crystals

    NASA Astrophysics Data System (ADS)

    Gogotsi, Yury; Libera, Joseph A.; Kalashnikov, Nikolay; Yoshimura, Masahiro

    2000-10-01

    Polyhedral nano- and microstructures with shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids, which we call graphite polyhedral crystals (GPCs), have been discovered. They were found in pores of glassy carbon. They have nanotube cores and graphite faces, and they can exhibit unusual sevenfold, ninefold, or more complex axial symmetry. Although some are giant radially extended nanotubes, Raman spectroscopy and transmission electron microscopy suggest GPCs have a degree of perfection higher than in multiwall nanotubes of similar size. The crystals are up to 1 micrometer in cross section and 5 micrometers in length, and they can probably be grown in much larger sizes. Preliminary results suggest a high electrical conductivity, strength, and chemical stability of GPC.

  9. Angular dependence of the auger lineshape of graphite

    SciTech Connect

    Rogers, J.W. Jr.; Houston, J.E.; Rye, R.R.

    1986-01-01

    The Auger lineshape of graphite is of interest as a model for studying initial-state, core-hole screening and final-state, hole-hole correlation effects in aromatic systems. We have obtained the Auger spectra from POCO (amorphous) and HOPG (highly-oriented pyrolytic) graphite.

  10. Misorientations in spheroidal graphite: some new insights about spheroidal graphite growth in cast irons

    NASA Astrophysics Data System (ADS)

    Lacaze, J.; Theuwissen, K.; Laffont, L.; Véron, M.

    2016-03-01

    Local diffraction patterning, orientation mapping and high resolution transmission electron microscopy imaging have been used to characterize misorientations in graphite spheroids of cast irons. Emphasis is put here on bulk graphite, away from the nucleus as well as from the outer surface of the spheroids in order to get information on their growth during solidification. The results show that spheroidal graphite consists in conical sectors made of elementary blocks piled up on each other. These blocks are elongated along the prismatic a direction of graphite with the c axes roughly parallel to the radius of the spheroids. This implies that the orientation of the blocks rotates around the spheroid centre giving low angle tilting misorientations along tangential direction within each sector. Misorientations between neighbouring sectors are of higher values and their interfaces show rippled layers which are characteristic of defects in graphene. Along a radius of the spheroid, clockwise and anticlockwise twisting between blocks is observed. These observations help challenging some of the models proposed to explain spheroidal growth in cast ions.

  11. Modeling the Role of Bulk and Surface Characteristics of Carbon Fiber on Thermal Conductance across the Carbon-Fiber/Matrix Interface.

    PubMed

    Varshney, Vikas; Roy, Ajit K; Baur, Jeffery W

    2015-12-01

    The rapid heating of carbon-fiber-reinforced polymer matrix composites leads to complex thermophysical interactions which not only are dependent on the thermal properties of the constituents and microstructure but are also dependent on the thermal transport between the fiber and resin interfaces. Using atomistic molecular dynamics simulations, the thermal conductance across the interface between a carbon-fiber near-surface region and bismaleimide monomer matrix is calculated as a function of the interface and bulk features of the carbon fiber. The surface of the carbon fiber is modeled as sheets of graphitic carbon with (a) varying degrees of surface functionality, (b) varying defect concentrations in the surface-carbon model (pure graphitic vs partially graphitic), (c) varying orientation of graphitic carbon at the interface, (d) varying interface saturation (dangling vs saturated bonds), (e) varying degrees of surface roughness, and (f) incorporating high conductive fillers (carbon nanotubes) at the interface. After combining separately equilibrated matrix system and different surface-carbon models, thermal energy exchange is investigated in terms of interface thermal conductance across the carbon fiber and the matrix. It is observed that modifications in the studied parameters (a-f) often lead to significant modulation of thermal conductance across the interface and, thus, showcases the role of interface tailoring and surface-carbon morphology toward thermal energy exchange. More importantly, the results provide key bounds and a realistic degree of variation to the interface thermal conductance values at fiber/matrix interfaces as a function of different surface-carbon features. PMID:26551435

  12. Thermodynamic Study of the Role of Interface Curvature on Multicomponent Vapor-Liquid Phase Equilibrium.

    PubMed

    Shardt, Nadia; Elliott, Janet A W

    2016-04-14

    The effect of interface curvature on phase equilibrium has been much more studied for single-component than multicomponent systems. We isolate the effect of curvature on multicomponent vapor-liquid equilibrium (VLE) phase envelopes and phase composition diagrams using the ideal system methanol/ethanol and the nonideal system ethanol/water as illustrative examples. An important finding is how nanoscale interface curvature shifts the azeotrope (equal volatility point) of nonideal systems. Understanding of the effect of curvature on VLE can be exploited in future nanoscale prediction and design. PMID:27028744

  13. Theoretical study of vibrational energy transfer of free OH groups at the water-air interface

    NASA Astrophysics Data System (ADS)

    Zheng, Renhui; Wei, Wenmei; Sun, Yuanyuan; Song, Kai; Shi, Qiang

    2016-04-01

    Recent experimental studies have shown that the vibrational dynamics of free OH groups at the water-air interface is significantly different from that in bulk water. In this work, by performing molecular dynamics simulations and mixed quantum/classical calculations, we investigate different vibrational energy transfer pathways of free OH groups at the water-air interface. The calculated intramolecular vibrational energy transfer rate constant and the free OH bond reorientation time scale agree well with the experiment. It is also found that, due to the small intermolecular vibrational couplings, the intermolecular vibrational energy transfer pathway that is very important in bulk water plays a much less significant role in the vibrational energy relaxation of the free OH groups at the water-air interface.

  14. A novel X-ray photoelectron spectroscopy study of the Al/SiO2 interface

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Vasquez, R. P.; Grunthaner, F. J.; Zamani, N.; Maserjian, J.

    1985-01-01

    The nondestructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films is reported. Both X-ray phototelectron spectroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing at 450 C induces reduction of the SiO2 by the aluminum, at a rate consistent with the bulk reaction rate. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and related interfaces.

  15. Theoretical study of vibrational energy transfer of free OH groups at the water-air interface.

    PubMed

    Zheng, Renhui; Wei, Wenmei; Sun, Yuanyuan; Song, Kai; Shi, Qiang

    2016-04-14

    Recent experimental studies have shown that the vibrational dynamics of free OH groups at the water-air interface is significantly different from that in bulk water. In this work, by performing molecular dynamics simulations and mixed quantum/classical calculations, we investigate different vibrational energy transfer pathways of free OH groups at the water-air interface. The calculated intramolecular vibrational energy transfer rate constant and the free OH bond reorientation time scale agree well with the experiment. It is also found that, due to the small intermolecular vibrational couplings, the intermolecular vibrational energy transfer pathway that is very important in bulk water plays a much less significant role in the vibrational energy relaxation of the free OH groups at the water-air interface. PMID:27083739

  16. Geochemical Insight from Nonlinear Optical Studies of Mineral-Water Interfaces

    NASA Astrophysics Data System (ADS)

    Covert, Paul A.; Hore, Dennis K.

    2016-05-01

    The physics and chemistry of mineral-water interfaces are complex, even in idealized systems. Our need to understand this complexity is driven by both pure and applied sciences, that is, by the need for basic understanding of earth systems and for the knowledge to mitigate our influences upon them. The second-order nonlinear optical techniques of second-harmonic generation and sum-frequency generation spectroscopy have proven adept at probing these types of interfaces. This review focuses on the contributions to geochemistry made by nonlinear optical methods. The types of questions probed have included a basic description of the structure adopted by water molecules at the mineral interface, how flow and porosity affect this structure, adsorption of trace metal and organic species, and dissolution mechanisms. We also discuss directions and challenges that lie ahead and the outlook for the continued use of nonlinear optical methods for studies of mineral-water boundaries.

  17. NiAl(110)/Cr(110) interface: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Liu, W.; Li, J. C.; Zheng, W. T.; Jiang, Q.

    2006-05-01

    The optimal geometries, thermodynamic properties, and electronic structures of NiAl(110)/Cr(110) interface are studied using a first-principle density functional plane-wave ultrasoft pseudopotential method. Surface energies of different NiAl surfaces are compared with those obtained based on the classical broken-bond rule. Simulation results indicate that the structure of Ni and Al placed in the hollow sites of Cr atoms at the interface is more thermodynamically stable, and the NiCr bonding is dominated by 3d electrons of Ni and Cr. It is found that NiAl(110)/Cr(110) alloying could lower brittleness of NiAl compounds. With simulated values of adhesion work and interface energy for NiAl(110)/Cr(110) system, its mechanical and thermodynamic properties are also discussed.

  18. Atomic Scale Study of Interfaces Involved in Epitaxial Fe/MgO/Fe Magnetic Tunnel Junctions

    SciTech Connect

    Andrieu, S.; Serra, R.; Bonell, F.; Tiusan, C.; Calmels, L.; Snoeck, E.; Varela del Arco, Maria; Pennycook, Stephen J; Walls, M.; Colliex, C.

    2009-01-01

    Epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions grown by Molecular Beam Epitaxy have been studied by using spatially resolved Electron Energy Loss Spectroscopy (EELS). The structure, the chemical composition as well as the bonding variations across the interfaces were investigated up to the atomic scale.

  19. An experimental study of liquid drop - interface coalescence in the presence of surfactants

    NASA Astrophysics Data System (ADS)

    Angeli, Panagiota; Chinaud, Maxime; Li, Kai; Wang, Wei; University College London Team; Beijing Key Laboratory of Urban Oil; Gas Distribution Technology Team

    2014-11-01

    Drop-interface coalescence has been the subject of many studies both theoretical and experimental. It is of particular interest for the oil industries particularly during the transportation of multiphase mixtures where coalescence rates can affect the stability and separation of dispersions. It is well-known that the presence of surfactants can significantly affect the coalescence rates. In this work a silicon oil -water system has been studied in a rectangular coalescence cell. Both rising oil drops and falling water drops coalescing with the water-oil interface have been investigated. A water soluble surfactant, SPAN 80, was used. High speed imaging has been performed to study the coalescence phenomenon and obtain the coalescence time of the drops with the interface with and without the presence of the surfactant. The velocity fields in the bulk fluid and in the liquid film forming between the drop and the interface were studied with shadowgraphy (bright field Particle Image Velocimetry). To increase the spatial resolution particularly in the liquid film microscope lenses were implemented. Results have been compared against existing literature.

  20. Does Interface Matter? A Study of Web Authoring and Editing by Inexperienced Web Writers

    ERIC Educational Resources Information Center

    Dick, Rodney F.

    2006-01-01

    This study explores the complicated nature of the interface as a mediational tool for inexperienced writers as they composed hypertext documents. Because technology can become so quickly and inextricably connected to people's everyday lives, it is essential to explore the effects on these technologies before they become invisible. Because…

  1. Uranium(IV) Interaction with Aqueous/Solid Interfaces Studied by Nonlinear Optics

    SciTech Connect

    Geiger, Franz

    2015-03-27

    This is the Final Technical Report for "Uranium(IV) Interaction with Aqueous/Solid Interfaces Studied by Nonlinear Optics", by Franz M. Geiger, PI, from Northwestern University, IL, USA, Grant Number SC0004101 and/or DE-PS02-ER09-07.

  2. Directional solidification of flake and spheroidal graphite cast iron in low and normal gravity environment

    NASA Technical Reports Server (NTRS)

    Hendrix, J. C.; Stefanescu, D. M.; Curreri, P. A.

    1987-01-01

    A NASA KC-135 research aircraft, flying repeated low-g trajectories that yield 20-30 sec of 0.1-0.001 g microgravity, has been used to study microgravity solidification's elimination of sedimentation and convection (with formation of unique and advantageous microstructures) for the case of eutectic-composition cast irons. The solidification interface of hypereutectic flake and spheroidal graphite cast irons has been slowly advanced through a 4 mm-diameter rod sample. Sample solidification rates have been correlated with accelerometer data, while independently controlling thermal gradients and solidification rates.

  3. X-ray photoelectron spectroscopic and morphologic studies of Ru nanoparticles deposited onto highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Bavand, R.; Yelon, A.; Sacher, E.

    2015-11-01

    Ruthenium nanoparticles (Ru NPs) function as effective catalysts in specific reactions, such as methanation and Fischer-Tropsch syntheses. It is our purpose to physicochemically characterize their surfaces, at which catalysis occurs, by surface-sensitive X-ray photoelectron spectroscopy (XPS), using the symmetric peak component anaylsis technique developed in our laboratory to reveal previously hidden components. Ru NPs were deposited by evaporation (0.25-1.5 nm nominal deposition range) onto highly oriented pyrolytic graphite (HOPG). In addition to their surfaces being characterized by XPS, an indication of morphology was obtained from transmission electron microscopy (TEM). Our use of symmetric peak component XPS analysis has revealed detailed information on a previously unidentified surface oxide initially formed, as well as on the valence electronic structure and its variation with NP size, information that is of potential importance in the use of these NPs in catalysis. Each of the several Ru core XPS spectra characterized (3d, 3p and 3s) was found to be composed of three symmetric components. Together with two metal oxide O1s components, these give evidence of a rather complex, previously unidentified oxide that is initially formed. The Ru valence band (4d and 5s) spectra clearly demonstrate a loss of metallicity, a simultaneous increase of the Kubo gap, and an abrupt transfer in valence electron density from the 4d to the 5s orbitals (known as electron spill-over), as the NP size decreases below 0.5 nm. TEM photomicrographs, as a function of deposition rate, show that, at a rate that gives insufficient time for the NP condensation energy to dissipate, the initially well-separated NPs are capable of diffusing laterally and aggregating. This indicates weak NP bonding to the HOPG substrate. Carbide is formed, at both high and low deposition rates, at Ru deposition thicknesses greater than 0.25 nm, its formation explained by Ru NPs reacting with residual

  4. Thermal conductivity degradation of graphites irradiated at low temperature

    SciTech Connect

    Snead, L.L.; Burchell, T.D.

    1995-04-01

    The objective of this work is to study the thermal conductivity degradation of new, high thermal conductivity graphites and to compare these results to more standard graphites irradiated at low temperatures. Several graphites and graphite composites (C/C`s) have been irradiated near 150{degree}C and at fluences up to a displacement level of 0.24 dpa. The materials ranged in unirradiated room temperature thermal conductivity of these materials varied from 114 W/m-K for H-451 isotropic graphite, to 670 W/m-K for unidirectional FMI-1D C/C composite. At the irradiation temperature a saturation reduction in thermal conductivity was seen to occur at displacement levels of approximately 0.1 dpa. All materials were seen to degrade to approximately 10 to 14 % of their original thermal conductivity after irradiation. The effect of post irradiation annealing on the thermal conductivity was also studied.

  5. AN INTRALABORATORY COMPARATIVE STUDY OF HYDRIDE GENERATION AND GRAPHITE FURNACE ATOMIC ABSORPTION TECHNIQUES FOR DETERMINING ORGANIC AND INORGANIC ARSENIC IN COMPLEX WASTEWATERS

    EPA Science Inventory

    A detailed intralaboratory comparison of the determination of arsenic in complex wastewater samples by hydride generation and graphite furnace atomic absorption techniques has been conducted. Two hydride generation techniques were employed. One consisted of the use of sodium boro...

  6. Phonon-interface scattering in multilayer graphene on an amorphous support

    PubMed Central

    Sadeghi, Mir Mohammad; Jo, Insun; Shi, Li

    2013-01-01

    The recent studies of thermal transport in suspended, supported, and encased graphene just began to uncover the richness of two-dimensional phonon physics, which is relevant to the performance and reliability of graphene-based functional materials and devices. Among the outstanding questions are the exact causes of the suppressed basal-plane thermal conductivity measured in graphene in contact with an amorphous material, and the layer thickness needed for supported or embedded multilayer graphene (MLG) to recover the high thermal conductivity of graphite. Here we use sensitive in-plane thermal transport measurements of graphene samples on amorphous silicon dioxide to show that full recovery to the thermal conductivity of the natural graphite source has yet to occur even after the MLG thickness is increased to 34 layers, considerably thicker than previously thought. This seemingly surprising finding is explained by long intrinsic scattering mean free paths of phonons in graphite along both basal-plane and cross-plane directions, as well as partially diffuse scattering of MLG phonons by the MLG-amorphous support interface, which is treated by an interface scattering model developed for highly anisotropic materials. Based on the phonon transmission coefficient calculated from reported experimental thermal interface conductance results, phonons emerging from the interface consist of a large component that is scattered across the interface, making rational choice of the support materials a potential approach to increasing the thermal conductivity of supported MLG. PMID:24067656

  7. METHOD OF FABRICATING A GRAPHITE MODERATED REACTOR

    DOEpatents

    Kratz, H.R.

    1963-05-01

    S>A nuclear reactor formed of spaced bodies of uranium and graphite blocks is improved by diffusing helium through the graphite blocks in order to replace the air in the pores of the graphite with helium. The helium-impregnated graphite conducts heat better, and absorbs neutrons less, than the original air- impregnated graphite. (AEC)

  8. CMB-13 research on carbon and graphite

    NASA Technical Reports Server (NTRS)

    Smith, M. C.

    1972-01-01

    Preliminary results of the research on carbon and graphite accomplished during this report period are presented. Included are: particle characteristics of Santa Maria fillers, compositions and density data for hot-molded Santa Maria graphites, properties of hot-molded Santa Maria graphites, and properties of hot-molded anisotropic graphites. Ablation-resistant graphites are also discussed.

  9. Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering

    NASA Astrophysics Data System (ADS)

    Renaud, Gilles

    important physical properties such as superconductivity or magnetism is also briefly reviewed. The strengths and limitations of the technique, such as the need for single crystals and surfaces of high crystalline quality are discussed. Finally, an outlook of future prospects in the field is given, such as the study of more complex oxide surfaces, vicinal surfaces, reactive metal/oxide interfaces, metal oxidation processes, the use of surfactants to promote wetting of a metal deposited on an oxide surface or the study of oxide/liquid interfaces in a non-UHV environment.

  10. Development of polyphenylquinoxaline graphite composites

    NASA Technical Reports Server (NTRS)

    Hoggatt, J. T.; Hill, S. G.; Shdo, J. G.

    1974-01-01

    This exploratory program was divided into four basic tasks. The initial phase was devoted toward investigating processing variables associated with previously developed PPO resins. These polymers were derived from p-bis(phenyl glyoxalyl)benzene reacted with 3,3'-diamino benzidine and/or 3,3',4,4'-tetramino benzophenone. Four new phenyl quinoxaline polymers were synthesized and characterized in Tasks 2 and 3. These consisted of a hydroxyl group containing PPQ synthesized from 3,3'-diamino benzidine (DAB), m-bis(phenyl glyoxal)benzene and m-bis(p'-hydroxy phenyl glyoxalyl) benzene; a cyano group containing PPQ from the reaction of DAB and p-bis(p'-cyano phenoxy phenyl glyoxalyl)benzene; an end-capped block copolymer; and a polymer from the reaction of 3,3',4,4'-tetraamino benzo phenone and m-bis(phenyl glyoxalyl)benzene. The latter two polymers were chosen for composite studies in the latter two tasks of the program. Mechanical properties of the graphite reinforced PPQ composites were determined over the temperature range of +21 C to 316 C. Flexural strengths of the HMS graphite fiber composites were in excess of 8.97 X 10 to the 8th power N/sq m (130,000 psi) at +21 C (70 F) with over 50% strength retention at +316 C.

  11. Design and usability study of an iconic user interface to ease information retrieval of medical guidelines

    PubMed Central

    Griffon, Nicolas; Kerdelhué, Gaétan; Hamek, Saliha; Hassler, Sylvain; Boog, César; Lamy, Jean-Baptiste; Duclos, Catherine; Venot, Alain; Darmoni, Stéfan J

    2014-01-01

    Background and objective Doc'CISMeF (DC) is a semantic search engine used to find resources in CISMeF-BP, a quality controlled health gateway, which gathers guidelines available on the internet in French. Visualization of Concepts in Medicine (VCM) is an iconic language that may ease information retrieval tasks. This study aimed to describe the creation and evaluation of an interface integrating VCM in DC in order to make this search engine much easier to use. Methods Focus groups were organized to suggest ways to enhance information retrieval tasks using VCM in DC. A VCM interface was created and improved using the ergonomic evaluation approach. 20 physicians were recruited to compare the VCM interface with the non-VCM one. Each evaluator answered two different clinical scenarios in each interface. The ability and time taken to select a relevant resource were recorded and compared. A usability analysis was performed using the System Usability Scale (SUS). Results The VCM interface contains a filter based on icons, and icons describing each resource according to focus group recommendations. Some ergonomic issues were resolved before evaluation. Use of VCM significantly increased the success of information retrieval tasks (OR=11; 95% CI 1.4 to 507). Nonetheless, it took significantly more time to find a relevant resource with VCM interface (101 vs 65 s; p=0.02). SUS revealed ‘good’ usability with an average score of 74/100. Conclusions VCM was successfully implemented in DC as an option. It increased the success rate of information retrieval tasks, despite requiring slightly more time, and was well accepted by end-users. PMID:24650636

  12. Heat exchanger using graphite foam

    SciTech Connect

    Campagna, Michael Joseph; Callas, James John

    2012-09-25

    A heat exchanger is disclosed. The heat exchanger may have an inlet configured to receive a first fluid and an outlet configured to discharge the first fluid. The heat exchanger may further have at least one passageway configured to conduct the first fluid from the inlet to the outlet. The at least one passageway may be composed of a graphite foam and a layer of graphite material on the exterior of the graphite foam. The layer of graphite material may form at least a partial barrier between the first fluid and a second fluid external to the at least one passageway.

  13. Effects of prestresses on mechanical properties of isotropic graphite materials

    NASA Astrophysics Data System (ADS)

    Oku, T.; Kurumada, A.; Imamura, Y.; Kawamata, K.; Shiraishi, M.

    1998-10-01

    Graphite materials which are used for plasma facing components and other components are subjected to stresses due to the high heat flux from the fusion plasma. Some mechanical properties of graphite materials can change due to the prestresses. The property changes should be considered for the design of the plasma facing components. The purpose of this study is to examine the effects of prestresses on the mechanical properties of isotropic graphite materials. Compressive prestresses were applied to two kinds of isotropic fine-grained graphites (IG-430 and IG-11) at 298 K (both), 1873 K (IG-11), 2273 K (IG-11) and 2283 K (IG-430). As a result, the decrease in Young's modulus for IG-430 due to high-temperature prestressing was 56% which was much larger than the 6.4% that was due to prestressing at 298 K. The results for IG-11 were the same as those for IG-430 graphite. This finding was considered to be due primarily to a difference in degree of the preferred orientation of crystallites in the graphite on the basis of the Bacon anisotropy factor (BAF) obtained from X-ray diffraction measurement of the prestressed specimens. Furthermore, high-temperature compressive prestressing produced an increase in the strength of the isotropic graphite, although room temperature prestressing produced no such effect. The results obtained here suggest that the isotropic graphite which is subjected to high-temperature compressive stresses can become anisotropic in service.

  14. First principles studies of the stability and Shottky barriers of metal/CdTe(111) interfaces

    NASA Astrophysics Data System (ADS)

    Dorj, Odkhuu; Miao, M. S.; Kioussis, N.; Tari, S.; Aqariden, F.; Chang, Y.; Grein, C.

    2015-03-01

    CdZnTe and CdTe based semiconductor X-Ray and Gamma-Ray detectors have been intensively studied recently due to their promising potentials for achieving high-resolution, high signal-to-noise ratios and low leakage current, all are desirable features in applications ranging from medical diagnostics to homeland security. Understanding the atomic and electronic structures of the metal/semiconductor interfaces is essential for the further improvements of performance. Using density functional calculations, we systematically studied the stability, the atomic and electronic structures of the interfaces between Cd-terminated CdTe (111) surface and the selected metals. We also calculated the Schottky barrier height (SBH) by aligning the electrostatic potentials in semiconductor and metal regions. Our calculations revealed the importance of intermixing between semiconductor and metal layers and the formation of Te-metal alloys at the interface. The obtained SBH does not depend much on the choice of metals despite the large variation of the work functions. On the other hand, the interface structure is found to have large effect to the SBH, which is attributed to the metal induced states in the gap. The position of such states is insensitive to the metal work functions, as revealed by the analysis of the electronic structures.

  15. Reactive ZnO/Ti/ZnO interfaces studied by hard x-ray photoelectron spectroscopy

    SciTech Connect

    Knut, Ronny Lindblad, Rebecka; Rensmo, Håkan; Karis, Olof; Grachev, Sergey; Faou, Jean-Yvon; Søndergård, Elin

    2014-01-28

    The chemistry and intermixing at buried interfaces in sputter deposited ZnO/Ti/ZnO thin layers were studied by hard x-ray photoelectron spectroscopy. The long mean free path of the photoelectrons allowed for detailed studies of the oxidation state, band bending effects, and intrinsic doping of the buried interfaces. Oxidation of the Ti layer was observed when ZnO was deposited on top. When Ti is deposited onto ZnO, Zn Auger peaks acquire a metallic character indicating a strong reduction of ZnO at the interface. Annealing of the stack at 200 °C results in further reduction of ZnO and oxidation of Ti. Above 300 °C, oxygen transport from the bulk of the ZnO layer takes place, leading to re-oxidation of ZnO at the interface and further oxidation of Ti layer. Heating above 500 °C leads to an intermixing of the layers and the formation of a Zn{sub x}TiO{sub y} compound.

  16. Density functional theory based study of chlorine doped WS2-metal interface

    NASA Astrophysics Data System (ADS)

    Chanana, Anuja; Mahapatra, Santanu

    2016-03-01

    Investigation of a transition metal dichalcogenide (TMD)-metal interface is essential for the effective functioning of monolayer TMD based field effect transistors. In this work, we employ the Density Functional Theory calculations to analyze the modulation of the electronic structure of monolayer WS2 with chlorine doping and the relative changes in the contact properties when interfaced with gold and palladium. We initially examine the atomic and electronic structures of pure and doped monolayer WS2 supercell and explore the formation of midgap states with band splitting near the conduction band edge. Further, we analyze the contact nature of the pure supercell with Au and Pd. We find that while Au is physiosorbed and forms n-type contact, Pd is chemisorped and forms p-type contact with a higher valence electron density. Next, we study the interface formed between the Cl-doped supercell and metals and observe a reduction in the Schottky barrier height (SBH) in comparison to the pure supercell. This reduction found is higher for Pd in comparison to Au, which is further validated by examining the charge transfer occurring at the interface. Our study confirms that Cl doping is an efficient mechanism to reduce the n-SBH for both Au and Pd, which form different types of contact with WS2.

  17. Polymeric Additives For Graphite/Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Kourtides, D. A.; Nir, Z.

    1990-01-01

    Report describes experimental studies of properties of several graphite/epoxy composites containing polymeric additives as flexibilizing or toughening agents. Emphasizes effects of brominated polymeric additives (BPA's) with or without carboxy-terminated butadiene acrylonitrile rubber. Reviews effects of individual and combined additives on fracture toughnesses, environmental stabilities, hot/wet strengths, thermomechanical behaviors, and other mechanical properties of composites.

  18. US graphite reactor D&D experience

    SciTech Connect

    Garrett, S.M.K.; Williams, N.C.

    1997-02-01

    This report describes the results of the U.S. Graphite Reactor Experience Task for the Decommissioning Strategy Plan for the Leningrad Nuclear Power Plant (NPP) Unit 1 Study. The work described in this report was performed by the Pacific Northwest National Laboratory (PNNL) for the Department of Energy (DOE).

  19. Graphite Composite Panel Polishing Fixture

    NASA Technical Reports Server (NTRS)

    Hagopian, John; Strojny, Carl; Budinoff, Jason

    2011-01-01

    The use of high-strength, lightweight composites for the fixture is the novel feature of this innovation. The main advantage is the light weight and high stiffness-to-mass ratio relative to aluminum. Meter-class optics require support during the grinding/polishing process with large tools. The use of aluminum as a polishing fixture is standard, with pitch providing a compliant layer to allow support without deformation. Unfortunately, with meter-scale optics, a meter-scale fixture weighs over 120 lb (.55 kg) and may distort the optics being fabricated by loading the mirror and/or tool used in fabrication. The use of composite structures that are lightweight yet stiff allows standard techniques to be used while providing for a decrease in fixture weight by almost 70 percent. Mounts classically used to support large mirrors during fabrication are especially heavy and difficult to handle. The mount must be especially stiff to avoid deformation during the optical fabrication process, where a very large and heavy lap often can distort the mount and optic being fabricated. If the optic is placed on top of the lapping tool, the weight of the optic and the fixture can distort the lap. Fixtures to support the mirror during fabrication are often very large plates of aluminum, often 2 in. (.5 cm) or more in thickness and weight upwards of 150 lb (68 kg). With the addition of a backing material such as pitch and the mirror itself, the assembly can often weigh over 250 lb (.113 kg) for a meter-class optic. This innovation is the use of a lightweight graphite panel with an aluminum honeycomb core for use as the polishing fixture. These materials have been used in the aerospace industry as structural members due to their light weight and high stiffness. The grinding polishing fixture consists of the graphite composite panel, fittings, and fixtures to allow interface to the polishing machine, and introduction of pitch buttons to support the optic under fabrication. In its

  20. Graphitic packing removal tool

    DOEpatents

    Meyers, K.E.; Kolsun, G.J.

    1997-11-11

    Graphitic packing removal tools for removal of the seal rings in one piece are disclosed. The packing removal tool has a cylindrical base ring the same size as the packing ring with a surface finish, perforations, knurling or threads for adhesion to the seal ring. Elongated leg shanks are mounted axially along the circumferential center. A slit or slits permit insertion around shafts. A removal tool follower stabilizes the upper portion of the legs to allow a spanner wrench to be used for insertion and removal. 5 figs.

  1. Graphitic packing removal tool

    DOEpatents

    Meyers, Kurt Edward; Kolsun, George J.

    1997-01-01

    Graphitic packing removal tools for removal of the seal rings in one piece. he packing removal tool has a cylindrical base ring the same size as the packing ring with a surface finish, perforations, knurling or threads for adhesion to the seal ring. Elongated leg shanks are mounted axially along the circumferential center. A slit or slits permit insertion around shafts. A removal tool follower stabilizes the upper portion of the legs to allow a spanner wrench to be used for insertion and removal.

  2. Graphitic packing removal tool

    SciTech Connect

    Meyers, K.E.; Kolsun, G.J.

    1996-12-31

    Graphitic packing removal tools are described for removal of the seal rings in one piece from valves and pumps. The packing removal tool has a cylindrical base ring the same size as the packing ring with a surface finish, perforations, knurling or threads for adhesion to the seal ring. Elongated leg shanks are mounted axially along the circumferential center. A slit or slits permit insertion around shafts. A removal tool follower stabilizes the upper portion of the legs to allow a spanner wrench to be used for insertion and removal.

  3. Purification and preparation of graphite oxide from natural graphite

    NASA Astrophysics Data System (ADS)

    Panatarani, C.; Muthahhari, N.; Rianto, Anton; Joni, I. Made

    2016-03-01

    Graphite oxide has attracted much interest as a possible route for preparation of natural graphite in the large-scale production and manipulation of graphene as a material with extraordinary electronic properties. Graphite oxide was prepared by modified Hummers method from purified natural graphite sample from West Kalimantan. We demonstrated that natural graphite is well-purified by acid leaching method. The purified graphite was proceed for intercalating process by modifying Hummers method. The modification is on the reaction time and temperature of the intercalation process. The materials used in the intercalating process are H2SO4 and KMNO4. The purified natural graphite is analyzed by carbon content based on Loss on Ignition test. The thermo gravimetricanalysis and the Fouriertransform infrared spectroscopy are performed to investigate the oxidation results of the obtained GO which is indicated by the existence of functional groups. In addition, the X-ray diffraction and energy dispersive X-ray spectroscopy are also applied to characterize respectively for the crystal structure and elemental analysis. The results confirmed that natural graphite samples with 68% carbon content was purified into 97.68 % carbon content. While the intercalation process formed a formation of functional groups in the obtained GO. The results show that the temperature and reaction times have improved the efficiency of the oxidation process. It is concluded that these method could be considered as an important route for large-scale production of graphene.

  4. Electronic and geometric properties of Au nanoparticles on Highly Ordered Pyrolytic Graphite (HOPG) studied using X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

    PubMed

    Lopez-Salido, Ignacio; Lim, Dong Chan; Dietsche, Rainer; Bertram, Nils; Kim, Young Dok

    2006-01-26

    Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example. PMID:16471654

  5. Probing dispersion and re-agglomeration phenomena upon melt-mixing of polymer-functionalized graphite nanoplates.

    PubMed

    Santos, R M; Vilaverde, C; Cunha, E; Paiva, M C; Covas, J A

    2016-01-01

    A one-step melt-mixing method is proposed to study dispersion and re-agglomeration phenomena of the as-received and functionalized graphite nanoplates in polypropylene melts. Graphite nanoplates were chemically modified via 1,3-dipolar cycloaddition of an azomethine ylide and then grafted with polypropylene-graft-maleic anhydride. The effect of surface functionalization on the dispersion kinetics, nanoparticle re-agglomeration and interface bonding with the polymer is investigated. Nanocomposites with 2 or 10 wt% of as-received and functionalized graphite nanoplates were prepared in a small-scale prototype mixer coupled to a capillary rheometer. Samples were collected along the flow axis and characterized by optical microscopy, scanning electron microscopy and electrical conductivity measurements. The as-received graphite nanoplates tend to re-agglomerate upon stress relaxation of the polymer melt. The covalent attachment of a polymer to the nanoparticle surface enhances the stability of dispersion, delaying the re-agglomeration. Surface modification also improves interfacial interactions and the resulting composites presented improved electrical conductivity. PMID:26439171

  6. A theoretical study of wave dispersion and thermal conduction for HMX/additive interfaces

    NASA Astrophysics Data System (ADS)

    Long, Yao; Chen, Jun

    2014-04-01

    The wave dispersion rule for non-uniform material is useful for ultrasonic inspection and engine life prediction, and also is key in achieving an understanding of the energy dissipation and thermal conduction properties of solid material. On the basis of linear response theory and molecular dynamics, we derive a set of formulas for calculating the wave dispersion rate of interface systems, and study four kinds of interfaces inside plastic bonded explosives: HMX/{HMX, TATB, F2312, F2313}. (HMX: octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine; TATB: 1,3,5-triamino-2,4,6-trinitrobenzene; F2312, F2313: fluoropolymers). The wave dispersion rate is obtained over a wide frequency range from kHz to PHz. We find that at low frequency, the rate is proportional to the square of the frequency, and at high frequency, the rate couples with the molecular vibration modes at the interface. By using the results, the thermal conductivities of HMX/additive interfaces are derived, and a physical model is built for describing the total thermal conductivity of mixture explosives, including HMX multi-particle systems and {TATB, F2312, F2313}-coated HMX.

  7. A Study of Fluid Interface Configurations in Exploration Vehicle Propellant Tanks

    NASA Technical Reports Server (NTRS)

    Zimmerli, Gregory A.; Asipauskas, Marius; Chen, Yongkang; Weislogel, Mark M.

    2010-01-01

    The equilibrium shape and location of fluid interfaces in spacecraft propellant tanks while in low-gravity is of interest to system designers, but can be challenging to predict. The propellant position can affect many aspects of the spacecraft such as the spacecraft center of mass, response to thruster firing due to sloshing, liquid acquisition, propellant mass gauging, and thermal control systems. We use Surface Evolver, a fluid interface energy minimizing algorithm, to investigate theoretical equilibrium liquid-vapor interfaces for spacecraft propellant tanks similar to those that have been considered for NASA's new class of Exploration vehicles. The choice of tank design parameters we consider are derived from the NASA Exploration Systems Architecture Study report. The local acceleration vector employed in the computations is determined by estimating low-Earth orbit (LEO) atmospheric drag effects and centrifugal forces due to a fixed spacecraft orientation with respect to the Earth or Moon, and rotisserie-type spacecraft rotation. Propellant/vapor interface positions are computed for the Earth Departure Stage and Altair lunar lander descent and ascent stage tanks for propellant loads applicable to LEO and low-lunar orbit. In some of the cases investigated the vapor ullage bubble is located at the drain end of the tank, where propellant management device hardware is often located.

  8. Study of natural convection and interface shape in directional solidification of succinonitrile

    NASA Technical Reports Server (NTRS)

    Kawaji, M.; Ojah, M.; Stojanovic, M.; De Groh, H. C.

    1992-01-01

    Flow visualization experiments in a Bridgman furnace at zero growth velocity have been performed. The experiments were intended to investigate if the photochromic dye activation method could be used in a crystal growth study. The results from this work have confirmed that with a carefully designed experimental setup, the photochromic-dye method permits qualitative and quantitative evaluation of the flow field near the interface in crystal growth experiments. For the horizontal orientation of a 6 mm x 6 mm ampoule and an axial temperature gradient of 26.5 C/cm, velocity profiles have been obtained accurately at various positions near the interface. The maximum velocity of 1.29 mm/sec was measured in the central vertical plane and the flow was symmetrical about that plane. A flow inversion point was also noted, above which the flow was towards the interface and below it, away from the interface. The results obtained are useful for validating 3-dimensional numerical models and establishing a link between the macroscopic processing conditions and the formation of crystalline defects.

  9. First principles study of Al/SrTiO3 interface formation

    NASA Astrophysics Data System (ADS)

    Hamze, Ali; Posadas, Agham; Kormondy, Kristy; Demkov, Alexander

    Two-dimensional electron gasses (2DEGs) at the interfaces of oxides have been the subject of much interest in recent years due to their relatively high carrier mobilities and potential for use in all-oxide devices. In particular, the γ-Al2O3 (γ-alumina)-SrTiO3 (STO) system has been the focus of much research. It exhibits a 2DEG at the interface with a carrier mobility ranging from 103-105 cm2V-1 s-1, depending on the thickness of the STO and how the γ-alumina film was grown. It is believed that Al atoms steal oxygen from the STO substrate at growth temperature and thus create a conductive channel in STO near the interface. We investigate the initial studies of the interface formation using density functional theory. The results of first principles calculations are compared with those of x-ray photoemission spectroscopy (XPS) performed in situ on thin Al films deposited on STO by molecular beam epitaxy. Analysis of the Al 2p XPS spectrum shows one layer of aluminum is fully oxidized during growth at 40°C and 4 layers of aluminum are fully oxidized during growth at 600°C. Furthermore, the Ti 2p XPS spectrum shows the titanium atoms are reduced, which is consistent with the presence of oxygen vacancies in STO.

  10. Experimental Study of the Richtmyer-Meshkov Instability on a Coupled Multimode and Inclined Interface Perturbation

    NASA Astrophysics Data System (ADS)

    Reilly, David; Creel, Skylar; McFarland, Jacob; Mitruka, Jatin; McDonald, Christopher; Ranjan, Devesh

    2013-11-01

    The inclined shock tube in the Texas A&M Shock Tube and Advanced Mixing Laboratory was used to study the effect of small amplitude, long wavelength multimode perturbations imposed on the inclined interface initial condition of the Richtmyer-Meshkov instability. The inclined interface is essentially a long wavelength, extremely large amplitude perturbation. Images of the shocked flow-field were captured with the angle of the shock tube with respect to the horizontal at 60° (η/ λ = √{ 3}/6). The modal content of the initial conditions was determined by taking the Fourier decomposition of the interface. This work is a proof of concept for creating a coupled multimode and inclined interface. Work that is currently underway will investigate the effect of these initial conditions on intermediate and late-time mixing as well as the transition to turbulence before reshock by using qualitative comparisons of Mie scattering images, mixing width measurements, and circulation from Particle Image Velocimetry (PIV). This research was funded by the Air Force Office of Scientific Research Young Investigator Research Program (AFOSR-YIP) grant.

  11. Molecular dynamics study on condensation/evaporation coefficients of chain molecules at liquid–vapor interface

    SciTech Connect

    Nagayama, Gyoko Takematsu, Masaki; Mizuguchi, Hirotaka; Tsuruta, Takaharu

    2015-07-07

    The structure and thermodynamic properties of the liquid–vapor interface are of fundamental interest for numerous technological implications. For simple molecules, e.g., argon and water, the molecular condensation/evaporation behavior depends strongly on their translational motion and the system temperature. Existing molecular dynamics (MD) results are consistent with the theoretical predictions based on the assumption that the liquid and vapor states in the vicinity of the liquid–vapor interface are isotropic. Additionally, similar molecular condensation/evaporation characteristics have been found for long-chain molecules, e.g., dodecane. It is unclear, however, whether the isotropic assumption is valid and whether the molecular orientation or the chain length of the molecules affects the condensation/evaporation behavior at the liquid–vapor interface. In this study, MD simulations were performed to study the molecular condensation/evaporation behavior of the straight-chain alkanes, i.e., butane, octane, and dodecane, at the liquid–vapor interface, and the effects of the molecular orientation and chain length were investigated in equilibrium systems. The results showed that the condensation/evaporation behavior of chain molecules primarily depends on the molecular translational energy and the surface temperature and is independent of the molecular chain length. Furthermore, the orientation at the liquid–vapor interface was disordered when the surface temperature was sufficiently higher than the triple point and had no significant effect on the molecular condensation/evaporation behavior. The validity of the isotropic assumption was confirmed, and we conclude that the condensation/evaporation coefficients can be predicted by the liquid-to-vapor translational length ratio, even for chain molecules.

  12. Molecular dynamics study on condensation/evaporation coefficients of chain molecules at liquid-vapor interface

    NASA Astrophysics Data System (ADS)

    Nagayama, Gyoko; Takematsu, Masaki; Mizuguchi, Hirotaka; Tsuruta, Takaharu

    2015-07-01

    The structure and thermodynamic properties of the liquid-vapor interface are of fundamental interest for numerous technological implications. For simple molecules, e.g., argon and water, the molecular condensation/evaporation behavior depends strongly on their translational motion and the system temperature. Existing molecular dynamics (MD) results are consistent with the theoretical predictions based on the assumption that the liquid and vapor states in the vicinity of the liquid-vapor interface are isotropic. Additionally, similar molecular condensation/evaporation characteristics have been found for long-chain molecules, e.g., dodecane. It is unclear, however, whether the isotropic assumption is valid and whether the molecular orientation or the chain length of the molecules affects the condensation/evaporation behavior at the liquid-vapor interface. In this study, MD simulations were performed to study the molecular condensation/evaporation behavior of the straight-chain alkanes, i.e., butane, octane, and dodecane, at the liquid-vapor interface, and the effects of the molecular orientation and chain length were investigated in equilibrium systems. The results showed that the condensation/evaporation behavior of chain molecules primarily depends on the molecular translational energy and the surface temperature and is independent of the molecular chain length. Furthermore, the orientation at the liquid-vapor interface was disordered when the surface temperature was sufficiently higher than the triple point and had no significant effect on the molecular condensation/evaporation behavior. The validity of the isotropic assumption was confirmed, and we conclude that the condensation/evaporation coefficients can be predicted by the liquid-to-vapor translational length ratio, even for chain molecules.

  13. Superconductivity in graphite intercalation compounds

    SciTech Connect

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; Dean, Mark P. M.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. This paper recontextualizes the field in light of the discovery of superconductivity in CaC₆ and YbC₆ in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  14. Superconductivity in graphite intercalation compounds

    DOE PAGESBeta

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; Dean, Mark P. M.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. This paper recontextualizes the field in light of the discovery of superconductivity in CaC₆ and YbC₆ in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic statesmore » and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.« less

  15. Co-Evolution of User and Organizational Interfaces: A Longitudinal Case Study of WWW Dissemination of National Statistics.

    ERIC Educational Resources Information Center

    Marchionini, Gary

    2002-01-01

    Describes how user interfaces for the Bureau of Labor Statistics (BLS) web site evolved over a 5-year period along with the larger organizational interface and how this co-evolution has influenced the institution. Interviews with BLS staff and transaction log analysis are the foci of this study, as well as user information-seeking studies and user…

  16. Examining graphite reinforcement in composites

    NASA Technical Reports Server (NTRS)

    Sanders, R. E.; Yates, C. I.

    1980-01-01

    Structure of graphite layers in composite parts can be checked by pyrolizing epoxy portion of composite samples. After 2-3 hours in nitrogen atmosphere at 540 C, only graphite fibers remain. These can be separated and checked for proper number, thickness, and orientation.

  17. REFRACTORY COATING FOR GRAPHITE MOLDS

    DOEpatents

    Stoddard, S.D.

    1958-06-24

    Refractory coating for graphite molds used in the casting of uranium is described. The coating is an alumino-silicate refractory composition which may be used as a mold surface in solid form or as a coating applied to the graphite mold. The composition consists of a mixture of ball clay, kaolin, alumina cement, alumina, water, sodium silicate, and sodium carbonate.

  18. Nucleation, growth, and graphitization of diamond nanocrystals during chlorination of carbides

    NASA Astrophysics Data System (ADS)

    Welz, Sascha; Gogotsi, Yury; McNallan, Michael J.

    2003-04-01

    Synthesis of nano- and microcrystalline sp3-bonded carbon (diamond) with cubic and hexagonal structure by extraction of silicon from silicon carbide in chlorine-containing gases has been reported recently. This process is attractive because it can produce diamond at ambient pressure and temperatures below 1000 °C. No plasma or other high-energy activation is required, thus providing an opportunity for large-scale synthesis. However, the mechanism of diamond formation has not been previously analyzed. This work reports on the formation mechanisms of diamond as well as the transformation of diamond to graphite and onionlike carbon upon heating. Study of SiC/carbon interfaces showed that direct epitaxial growth of diamond on SiC is possible, in agreement with previous molecular-dynamics simulation. However, random nucleation of diamond from amorphous sp3-bonded carbon produced as the result of extraction of Si from SiC has also been demonstrated. It has been shown that the presence of hydrogen in the environment is not required for diamond synthesis. However, hydrogen can stabilize the nanocrystals and lead to the growth of thick diamond layers. If no hydrogen is added, diamond nanocrystals transform to graphite, forming carbon onions and other curved graphitic nanostructures.

  19. Studies in RF Power Communication, SAR, and Temperature Elevation in Wireless Implantable Neural Interfaces

    PubMed Central

    Zhao, Yujuan; Tang, Lin; Rennaker, Robert; Hutchens, Chris; Ibrahim, Tamer S.

    2013-01-01

    Implantable neural interfaces are designed to provide a high spatial and temporal precision control signal implementing high degree of freedom real-time prosthetic systems. The development of a Radio Frequency (RF) wireless neural interface has the potential to expand the number of applications as well as extend the robustness and longevity compared to wired neural interfaces. However, it is well known that RF signal is absorbed by the body and can result in tissue heating. In this work, numerical studies with analytical validations are performed to provide an assessment of power, heating and specific absorption rate (SAR) associated with the wireless RF transmitting within the human head. The receiving antenna on the neural interface is designed with different geometries and modeled at a range of implanted depths within the brain in order to estimate the maximum receiving power without violating SAR and tissue temperature elevation safety regulations. Based on the size of the designed antenna, sets of frequencies between 1 GHz to 4 GHz have been investigated. As expected the simulations demonstrate that longer receiving antennas (dipole) and lower working frequencies result in greater power availability prior to violating SAR regulations. For a 15 mm dipole antenna operating at 1.24 GHz on the surface of the brain, 730 uW of power could be harvested at the Federal Communications Commission (FCC) SAR violation limit. At approximately 5 cm inside the head, this same antenna would receive 190 uW of power prior to violating SAR regulations. Finally, the 3-D bio-heat simulation results show that for all evaluated antennas and frequency combinations we reach FCC SAR limits well before 1 °C. It is clear that powering neural interfaces via RF is possible, but ultra-low power circuit designs combined with advanced simulation will be required to develop a functional antenna that meets all system requirements. PMID:24223123

  20. Interactions of anesthetics with the water-hexane interface. A molecular dynamics study

    NASA Technical Reports Server (NTRS)

    Chipot, C.; Wilson, M. A.; Pohorille, A.

    1997-01-01

    The free energy profiles characterizing the transfer of nine solutes across the liquid-vapor interfaces of water and hexane and across the water-hexane interface were calculated from molecular dynamics simulations. Among the solutes were n-butane and three of its halogenated derivatives, as well as three halogenated cyclobutanes. The two remaining molecules, dichlorodifluoromethane and 1,2-dichloroperfluoroethane, belong to series of halo-substituted methanes and ethanes, described in previous studies (J. Chem. Phys. 1996, 104, 3760; Chem. Phys. 1996, 204, 337). Each series of molecules contains structurally similar compounds that differ greatly in anesthetic potency. The accuracy of the simulations was tested by comparing the calculated and the experimental free energies of solvation of all nine compounds in water and in hexane. In addition. the calculated and the measured surface excess concentrations of n-butane at the water liquid-vapor interface were compared. In all cases, good agreement with experimental results was found. At the water-hexane interface, the free energy profiles for polar molecules exhibited significant interfacial minima, whereas the profiles for nonpolar molecules did not. The existence of these minima was interpreted in terms of a balance between the free energy contribution arising from solute-solvent interactions and the work to form a cavity that accommodates the solute. These two contributions change monotonically, but oppositely, across the interface. The interfacial solubilities of the solutes, obtained from the free energy profiles, correlate very well with their anesthetic potencies. This is the case even when the Meyer-Overton hypothesis, which predicts a correlation between anesthetic potency and solubility in oil, fails.

  1. Baseline Graphite Characterization: First Billet

    SciTech Connect

    Mark C. Carroll; Joe Lords; David Rohrbaugh

    2010-09-01

    The Next Generation Nuclear Plant Project Graphite Research and Development program is currently establishing the safe operating envelope of graphite core components for a very high temperature reactor design. To meet this goal, the program is generating the extensive amount of quantitative data necessary for predicting the behavior and operating performance of the available nuclear graphite grades. In order determine the in-service behavior of the graphite for the latest proposed designs, two main programs are underway. The first, the Advanced Graphite Creep (AGC) program, is a set of experiments that are designed to evaluate the irradiated properties and behavior of nuclear grade graphite over a large spectrum of temperatures, neutron fluences, and compressive loads. Despite the aggressive experimental matrix that comprises the set of AGC test runs, a limited amount of data can be generated based upon the availability of space within the Advanced Test Reactor and the geometric constraints placed on the AGC specimens that will be inserted. In order to supplement the AGC data set, the Baseline Graphite Characterization program will endeavor to provide supplemental data that will characterize the inherent property variability in nuclear-grade graphite without the testing constraints of the AGC program. This variability in properties is a natural artifact of graphite due to the geologic raw materials that are utilized in its production. This variability will be quantified not only within a single billet of as-produced graphite, but also from billets within a single lot, billets from different lots of the same grade, and across different billets of the numerous grades of nuclear graphite that are presently available. The thorough understanding of this variability will provide added detail to the irradiated property data, and provide a more thorough understanding of the behavior of graphite that will be used in reactor design and licensing. This report covers the

  2. Study of the ESI and APCI interfaces for the UPLC-MS/MS analysis of pesticides in traditional Chinese herbal medicine.

    PubMed

    Chen, Lina; Song, Fengrui; Liu, Zhiqiang; Zheng, Zhong; Xing, Junpeng; Liu, Shuying

    2014-02-01

    In this work, 53 selected pesticides of different chemical groups were extracted from Chinese herbal medicines and determined by ultra-high-performance liquid chromatography (UHPLC)-tandem mass spectrometry (MS/MS) using both electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI). Extracts were obtained using the acetonitrile-based quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample preparation technique. Cleanup was performed by dispersive solid-phase extraction using primary secondary amine, graphitized carbon black, and octadecylsilane. Two atmospheric-pressure interfaces, ESI and APCI, were checked and compared. The validation study, including detection limits, linearity, and matrix effects, was conducted on fritillaria, radix ginseng, folium isatidis, semen persicae, and flos lonicerae in multiple reaction monitoring mode. These matrices represent a variety of plants used in traditional Chinese medicine. Fritillaria and radix ginseng were chosen as representatives for roots, folium isatidis was chosen as a representative for leaves, semen persicae was chosen as a representative for seeds, and flos lonicerae was chosen as a representative for flowers. The limits of detection for pesticides were lower in the UHPLC-ESI-MS/MS method than in the UHPLC-APCI-MS/MS method. Matrix effects on the two ionizations were evaluated for the five matrices. Soft signal enhancement in UHPLC-APCI-MS/MS and signal suppression in UHPLC-ESI-MS/MS were observed. PMID:24346143

  3. Electronic structure of graphite oxide

    NASA Astrophysics Data System (ADS)

    Jeong, Hae Kyung; Yang, Cheolsoo; Kim, Bong Soo; Kim, Ki-Jeong

    2011-03-01

    We have investigated the electronic structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp 2 hybridization states found in graphite were also seen in graphite oxide. However, the π state disappeared near the Fermi level because of bonding between the π and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV. This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2010-0004592), and partly by the MEST (2009-0087138). Experiments at the PLS were supported in part by POSTECH and MEST.

  4. Evaluation of a Novel Conjunctive Exploratory Navigation Interface for Consumer Health Information: A Crowdsourced Comparative Study

    PubMed Central

    Cui, Licong; Carter, Rebecca

    2014-01-01

    Background Numerous consumer health information websites have been developed to provide consumers access to health information. However, lookup search is insufficient for consumers to take full advantage of these rich public information resources. Exploratory search is considered a promising complementary mechanism, but its efficacy has never before been rigorously evaluated for consumer health information retrieval interfaces. Objective This study aims to (1) introduce a novel Conjunctive Exploratory Navigation Interface (CENI) for supporting effective consumer health information retrieval and navigation, and (2) evaluate the effectiveness of CENI through a search-interface comparative evaluation using crowdsourcing with Amazon Mechanical Turk (AMT). Methods We collected over 60,000 consumer health questions from NetWellness, one of the first consumer health websites to provide high-quality health information. We designed and developed a novel conjunctive exploratory navigation interface to explore NetWellness health questions with health topics as dynamic and searchable menus. To investigate the effectiveness of CENI, we developed a second interface with keyword-based search only. A crowdsourcing comparative study was carefully designed to compare three search modes of interest: (A) the topic-navigation-based CENI, (B) the keyword-based lookup interface, and (C) either the most commonly available lookup search interface with Google, or the resident advanced search offered by NetWellness. To compare the effectiveness of the three search modes, 9 search tasks were designed with relevant health questions from NetWellness. Each task included a rating of difficulty level and questions for validating the quality of answers. Ninety anonymous and unique AMT workers were recruited as participants. Results Repeated-measures ANOVA analysis of the data showed the search modes A, B, and C had statistically significant differences among their levels of difficulty (P<.001

  5. XPS Study of SiO2 and the Si/SiO2 Interface

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Grunthaner, P. J.; Vasquez, R. P.; Lewis, B. F.; Maserjian, J.; Madhukar, A.

    1982-01-01

    X-ray photoelectron spectroscopy (XPS) is analytical technique for understanding electronic structure of atoms close to surface in solids, in preference to bulk structure of material. Study found evidence for core-level chemical shifts arising from changes in local structural environment in amorphous SiO2 and at Si/SiO2 interface. Observed XPS spectra may be understood as sequential convolution of several functions, each with well-defined physical interpretation.

  6. Studies of the analyte-carrier interface in flow injection analysis

    SciTech Connect

    Brown, S.D.

    1992-01-01

    Chemical analysis in flowing solution is popular for automation of classical methods. However, most of the classical methods are not specific enough for direct multicomponent analysis of simple mixtures. This research project has the goals of study of rapid multicomponent analysis of transient species in flowing media, and investigations of chemical reactions at interfaces and of effects of competition on distribution of products from interfacial reaction. This report summarizes work done over the past 4.5 years; support has been terminated.

  7. Studies on the enhancement of solid electrolyte interphase formation on graphitized anodes in LiX-carbonate based electrolytes using Lewis acid additives for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Li, L. F.; Xie, B.; Lee, H. S.; Li, H.; Yang, X. Q.; McBreen, J.; Huang, X. J.

    The new electrolyte systems utilizing one type of Lewis acids, the boron based anion receptors (BBARs) with LiF, Li 2O, or Li 2O 2 in carbonate solutions have been developed and reported by us. These systems open up a new approach in developing non-aqueous electrolytes with higher operating voltage and less moisture sensitivity for lithium-ion batteries. However, the formation of a stable solid electrolyte interphase (SEI) layer on the graphitized anodes is a serious problem needs to be solved for these new electrolyte systems, especially when propylene carbonate (PC) is used as a co-solvent. Using lithium bis(oxalato)borate (LiBOB) as an additives, the SEI layer formation on mesophase carbon microbeads (MCMB) anode is significantly enhanced in these new electrolytes containing boron-based anion receptors, such as tris(pentafluorophenyl) borane, and lithium salt such as LiF, or lithium oxides such as Li 2O or Li 2O 2 in PC and dimethyl carbonate (DMC) solvents. The cells using these electrolytes and MCMB anodes cycled very well and the PC co-intercalation was suppressed. Fourier transform infrared spectroscopy (FTIR) studies show that one of the electrochemical decomposition products of LiBOB, lithium carbonate (Li 2CO 3), plays a quite important role in the stablizing SEI layer formation.

  8. A comparative study of polyacrylic acid and poly(vinylidene difluoride) binders for spherical natural graphite/LiFePO 4 electrodes and cells

    NASA Astrophysics Data System (ADS)

    Chong, Jin; Xun, Shidi; Zheng, Honghe; Song, Xiangyun; Liu, Gao; Ridgway, Paul; Wang, Ji Qiang; Battaglia, Vincent S.

    Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO 4, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X = Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO 4 electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO 4 cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO 4 full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.

  9. A high precision study of the electrolyte additives vinylene carbonate, vinyl ethylene carbonate and lithium bis(oxalate)borate in LiCoO2/graphite pouch cells

    NASA Astrophysics Data System (ADS)

    Wang, David Yaohui; Sinha, N. N.; Burns, J. C.; Petibon, R.; Dahn, J. R.

    2014-12-01

    The effects of three well-known electrolyte additives, used singly or in combination, on LiCoO2/graphite pouch cells has been investigated using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS) and long term cycling Vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and lithium bis(oxalato) borate (LiBOB) were chosen for study. The results show that combinations of electrolyte additives that act synergistically can be more effective than a single electrolyte additive. However, simply using 2% VC yielded cells very competitive in coulombic efficiency (CE), charge endpoint capacity slippage and charge transfer resistance (Rct). For cells with 1% LiBOB and VC (1, 2, 4 or 6%), adding VC above 2% does not increase the CE, but increases the electrode charge transfer impedances. Rct for cells containing 1% LiBOB and VEC (0.5, 1 or 4%) decreased after long term cycling (1800 h), compared to that tested after the UHPC cycling (500 h) indicating that VEC might be useful for the design of power cells. However, the opposite behaviour (increasing Rct with cycle number) was observed for the control cells or cells containing LiBOB and/or VC.

  10. A preliminary scanning tunnelling microscopy study of the surface-organised structures of gramicidin S hydrochloride on highly oriented pyrolytic graphite.

    PubMed

    Brown, N M; You, H X

    1991-12-01

    For an initial study of potentially surface-structural self-organising systems of biological significance by scanning tunnelling microscopy (STM), gramicidin S, a pseudocentrosymmetric cyclodecapeptide with antibiotic properties, was chosen as prototype, recognising its structure as having both intramolecular and intermolecular hydrogen-bond forming propensity. The surface-organised structures, based on gramicidin S hydrochloride deposited on a highly oriented pyrolytic graphite (HOPG) substrate, have been observed by STM in air under ambient conditions. These are characterised in the main by rectangular or rectangle-like structural elements identified with the individual gramicidin S hydrochloride molecules. Two kinds of arrangements of gramicidin S hydrochloride in a two-dimensional array are found, i.e., as a centred rectangular lattice and a primitive rectangular lattice. The STM topographical arrays and the molecular dimensions obtained are in good quantitative agreement with the corresponding X-ray crystallographic data. The differences between the STM results, the theoretical models, and the X-ray crystallographic data are attributed to the intermolecular interactions present in the three-dimensional gramicidin S crystal but absent in the lower dimensional arrays and to the environments in which a gramicidin S hydrochloride molecule finds itself during deposition and drying on the HOPG substrate. PMID:1725492

  11. Hyperthermal oxidation of graphite and diamond.

    PubMed

    Paci, Jeffrey T; Minton, Timothy K; Schatz, George C

    2012-11-20

    Carbon materials have mechanical, electrical, optical, and tribological properties that make them attractive for use in a wide range of applications. Two properties that make them attractive, their hardness and inertness in many chemical environments, also make them difficult to process into useful forms. The use of atomic oxygen and other forms of oxidation has become a popular option for processing of these materials (etching, erosion, chemical functionalization, etc.). This Account provides an overview of the use of theory to describe the mechanisms of oxidation of diamond and graphite using hyperthermal (few electronvolts) oxygen atoms. The theoretical studies involve the use of Born-Oppenheimer molecular dynamics calculations in which on-the-fly electronic structure calculations have been performed using either density functional theory or density-functional-tight-binding semiempirical methods to simulate collisions of atomic oxygen with diamond or graphite. Comparisons with molecular-beam scattering on surfaces provide indirect verification of the results. Graphite surfaces become oxidized when exposed to hyperthermal atomic oxygen, and the calculations have revealed the mechanisms for formation of both CO and CO(2). These species arise when epoxide groups form and diffuse to holes on the surface where carbonyls are already present. CO and CO(2) form when these carbonyl groups dissociate from the surface, resulting in larger holes. We also discuss mechanisms for forming holes in graphite surfaces that were previously hole-free. For diamond, the (111) and (100) surfaces are oxidized by the oxygen atoms, forming mostly oxy radicals and ketones on the respective surfaces. The oxy-covered (111) surface can then react with hyperthermal oxygen to give gaseous CO(2), or it can become graphitized leading to carbon removal as with graphite. The (100) surface is largely unreactive to hyperthermal atomic oxygen, undergoing large amounts of inelastic scattering and

  12. Storable droplet interface lipid bilayers for cell-free ion channel studies.

    PubMed

    Jung, Sung-Ho; Choi, Sangbaek; Kim, Young-Rok; Jeon, Tae-Joon

    2012-01-01

    An artificially created lipid bilayer is an important platform in studying ion channels and engineered biosensor applications. However, a lipid bilayer created using conventional techniques is fragile and short-lived, and the measurement of ion channels requires expertise and laborious procedures, precluding practical applications. Here, we demonstrate a storable droplet lipid bilayer precursor frozen with ion channels, resulting in a droplet interface bilayer upon thawing. A small vial with an aqueous droplet in organic solution was flash frozen in -80 °C methanol immediately after an aqueous droplet was introduced into the organic solution and gravity draws the droplet down to the interface upon thawing. A lipid bilayer created along the interface using this method had giga-ohm resistance and typical specific capacitance values. The noise level of this system is favorably comparable to the conventional system. The subsequent incorporation of ion channels, alpha-hemolysin and gramicidin A, showed typical conductance values consistent with those in previous literatures. This novel system to create a lipid bilayer as a whole can be automated from its manufacture to use and indefinitely stored when frozen. As a result, ion channel measurements can be carried out in any place, increasing the accessibility of ion channel studies as well as a number of applications, such as biosensors, ion channel drug screening, and biophysical studies. PMID:21909672

  13. Fermi-level pinning through defects at GaAs/oxide interfaces: A density functional study

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Miceli, Giacomo; Pasquarello, Alfredo

    2015-09-01

    Using density functional calculations, we study a set of candidate defects for Fermi-level pinning at GaAs/oxide interfaces. The set of considered defects comprises both bulklike and interfacial defects, including As antisites, Ga and As dangling bonds, the As-As dimer/dangling bond defect, and several defect complexes. The defects are generated within atomistic model structures representing the GaAs /Al2O3 interface. Formation energies of bulklike defects are obtained and compared with those of corresponding bulk defects, while interfacial defects are studied through their relative defect energies. Finite-size corrections to the defect energies are applied through a scheme that accounts for the interfacial geometry of our models. Defect levels are defined as thermodynamic transition levels between different charge states and are calculated for all considered defects. Through an alignment procedure based on hybrid functional calculations, the defect levels are then positioned within the calculated band gap of GaAs that reproduces the experimental one, thereby enabling direct comparisons with the experimental density of defect states. Our study shows that several As-related defects show a similar amphoteric bistability between an As-As dimer state and a configuration with two doubly occupied As dangling bonds. The associated charge transition levels generally lie in the midgap region, in accord with experimental observations. This mechanism is proposed as the origin of the observed Fermi-level pinning at GaAs/oxide interfaces.

  14. Graphene-nickel interfaces: a review

    NASA Astrophysics Data System (ADS)

    Dahal, Arjun; Batzill, Matthias

    2014-02-01

    Graphene on nickel is a prototypical example of an interface between graphene and a strongly interacting metal, as well as a special case of a lattice matched system. The chemical interaction between graphene and nickel is due to hybridization of the metal d-electrons with the π-orbitals of graphene. This interaction causes a smaller separation between the nickel surface and graphene (0.21 nm) than the typical van der Waals gap-distance between graphitic layers (0.33 nm). Furthermore, the physical properties of graphene are significantly altered. Main differences are the opening of a band gap in the electronic structure and a shifting of the π-band by ~2 eV below the Fermi-level. Experimental evidence suggests that the ferromagnetic nickel induces a magnetic moment in the carbon. Substrate induced geometric and electronic changes alter the phonon dispersion. As a consequence, monolayer graphene on nickel does not exhibit a Raman spectrum. In addition to reviewing these fundamental physical properties of graphene on Ni(111), we also discuss the formation and thermal stability of graphene and a surface-confined nickel-carbide. The fundamental growth mechanisms of graphene by chemical vapor deposition are also described. Different growth modes depending on the sample temperature have been identified in ultra high vacuum surface science studies. Finally, we give a brief summary for the synthesis of more complex graphene and graphitic structures using nickel as catalyst and point out some potential applications for graphene-nickel interfaces.

  15. Interaction between dimer interface residues of native and mutated SOD1 protein: a theoretical study.

    PubMed

    Keerthana, S P; Kolandaivel, P

    2015-04-01

    Cu-Zn superoxide dismutase 1 (SOD1) is a highly conserved bimetallic protein enzyme, used for the scavenging the superoxide radicals (O2 (-)) produced due to aerobic metabolism in the mitochondrial respiratory chain. Over 100 mutations have been identified and found to be in the homodimeric structure of SOD1. The enzyme has to be maintained in its dimeric state for the structural stability and enzymatic activity. From our investigation, we found that the mutations apart from the dimer interface residues are found to affect the dimer stability of protein and hence enhancing the aggregation and misfolding tendency of mutated protein. The homodimeric state of SOD1 is found to be held together by the non-covalent interactions. The molecular dynamics simulation has been used to study the hydrogen bond interactions between the dimer interface residues of the monomers in native and mutated forms of SOD1 in apo- and holo-states. The results obtained by this analysis reveal the fact that the loss of hydrogen bond interactions between the monomers of the dimer is responsible for the reduced stability of the apo- and holo-mutant forms of SOD1. The conformers with dimer interface residues in native and mutated protein obtained by the molecular dynamics simulation is subjected to quantum mechanical study using M052X/6-31G(d) level of theory. The charge transfer between N-H···O interactions in the dimer interface residues were studied. The weak interaction between the monomers of the dimer accounts for the reduced dimerization and enhanced deformation energy in the mutated SOD1 protein. PMID:25578810

  16. Functionalization of Natural Graphite for Use as Reinforcement in Polymer Nanocomposites.

    PubMed

    Araujo, Rafael; Marques, Maria F V; Jonas, Renato; Grafova, Iryna; Grafov, Andriy

    2015-08-01

    Graphite is a naturally abundant material that has been used as reinforcing filler to produce polymeric nanocomposites for various applications including automotive, aerospace and electric-electronic. The objective of this study was to develop methodologies of graphite nanosheets preparation and for incorporation into polymer matrices. By means of different chemical and physical treatments, natural graphite was modified and subsequently characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetry (TGA) and the particle size determination. The results obtained clearly show that after the treatments employed, polar chemical groups were inserted on the natural graphite surface. Nanosized graphite particles of high aspect ratio were obtained. PMID:26369221

  17. Effects of fiber/matrix interactions on the properties of graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Mcmahon, P. E.; Ying, L.

    1982-01-01

    A state-of-the-art literature review of the interactions between fibers and resin within graphite epoxy composite materials was performed. Emphasis centered on: adhesion theory; wetting characteristics of carbon fiber; load transfer mechanisms; methods to evaluate and measure interfacial bond strengths; environmental influence at the interface; and the effect of the interface/interphase on composite performance, with particular attention to impact toughness. In conjunction with the literature review, efforts were made to design experiments to study the wetting behavior of carbon fibers with various finish variants and their effect on adhesion joint strength. The properties of composites with various fiber finishes were measured and compared to the base-line properties of a control. It was shown that by tailoring the interphase properties, a 30% increase in impact toughness was achieved without loss of mechanical properties at both room and elevated temperatures.

  18. Stiffener attachment concepts for graphite-epoxy panels designed for postbuckling strength

    NASA Technical Reports Server (NTRS)

    Dickson, John N.; Biggers, Sherrill B.; Starnes, James H., Jr.

    1985-01-01

    Stiffener attachment concepts for suppressing or delaying the onset of the skin-stiffener separation failure mode in graphite-epoxy compression panels designed for postbuckling strength were experimentally studied. The effectiveness of these concepts was evaluated using panels with 16-ply skins and a single centrally-located I-shaped stiffener with both static and cyclic compressive loadings. Analytical results suggest that tailoring the relative thicknesses of the panel skin, stiffener attachment flange, and the stiffener web rotational stiffness can minimize the adverse effects of high interface shear and normal stresses. Interface stress levels may be reduced by tapering the thickness of the stiffener attachment flange and properly selecting the stacking sequences of the skin and stiffener attachment flange laminates.

  19. Cr/B4C multilayer mirrors: Study of interfaces and X-ray reflectance

    DOE PAGESBeta

    Burcklen, C.; Soufli, R.; Gullikson, E.; Meltchakov, E.; Dennetiere, D.; Polack, F.; Capitanio, B.; Thomasset, M.; Jerome, A.; de Rossi, S.; et al

    2016-03-24

    Here, we present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4C-on-Cr interface, which we modeled with a 1–1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (opticalmore » constants) values for Cr.« less

  20. The Pt(111)/electrolyte interface under oxygen reduction reaction conditions: an electrochemical impedance spectroscopy study.

    PubMed

    Bondarenko, Alexander S; Stephens, Ifan E L; Hansen, Heine A; Pérez-Alonso, Francisco J; Tripkovic, Vladimir; Johansson, Tobias P; Rossmeisl, Jan; Nørskov, Jens K; Chorkendorff, Ib

    2011-03-01

    The Pt(111)/electrolyte interface has been characterized during the oxygen reduction reaction (ORR) in 0.1 M HClO(4) using electrochemical impedance spectroscopy. The surface was studied within the potential region where adsorption of OH* and O* species occur without significant place exchange between the adsorbate and Pt surface atoms (0.45-1.15 V vs RHE). An equivalent electric circuit is proposed to model the Pt(111)/electrolyte interface under ORR conditions within the selected potential window. This equivalent circuit reflects three processes with different time constants, which occur simultaneously during the ORR at Pt(111). Density functional theory (DFT) calculations were used to correlate and interpret the results of the measurements. The calculations indicate that the coadsorption of ClO(4)* and Cl* with OH* is unlikely. Our analysis suggests that the two-dimensional (2D) structures formed in O(2)-free solution are also formed under ORR conditions. PMID:21244087

  1. A comparative study of the thermal interface materials with graphene and boron nitride fillers

    NASA Astrophysics Data System (ADS)

    Kargar, F.; Salgado, R.; Legedza, S.; Renteria, J.; Balandin, A. A.

    2014-09-01

    We report the results of an experimental study that compares the performance of graphene and boron nitride flakes as fillers in the thermal interface materials. The thickness of both fillers varied from a single atomic plane to about a hundred. The measurements have been conducted using a standard TIM tester. Our results show that the addition of a small fraction of graphene (f=4 wt%) to a commercial thermal interface material increases the resulting apparent thermal conductivity substantially stronger than the addition of boron nitride. The obtained data suggest that graphene and fewlayer graphene flakes couple better to the matrix materials than the boron nitride fillers. A combination of both fillers can be used to increase the thermal conductivity while controlling the electrical conduction.

  2. X-ray absorption studies of Ti/polymer and Cr/polymer interfaces

    SciTech Connect

    Opila, R.L.; Konstadinidis, K.; Ibidunni, A.O; Davenport, A.J.; Isaacs, H.S.

    1993-11-01

    The interface formed between metals, Ti and Cr, and polymers, epoxy, and triazine, have been studied, non-destructively, using x-ray absorption spectroscopy. The metals were sputtered onto the polymer surfaces. Titanium reacts extensively, up to Ti thickness of 100 {Angstrom} while Cr remains primarily metallic. In situ heating at 200{degree}C increases the extent of reaction for both metals. Heating has a greater effect on metal/epoxy interfaces than metal/triazine. Titanium and Cr were ion implanted into the polymer in order to determine the interactions of isolated metal atoms with the polymer. Titanium and Cr appear to form oxides as the final reaction product, and the Ti is tetrahedrally coordinated.

  3. First-principles study of the Fe | MgO(0 0 1) interface: magnetic anisotropy.

    PubMed

    Bose, Thomas; Cuadrado, Ramon; Evans, Richard F L; Chepulskii, Roman V; Apalkov, Dmytro; Chantrell, Roy W

    2016-04-20

    We present a systematic first-principles study of Fe | MgO bilayer systems emphasizing the influence of the iron layer thickness on the geometry, the electronic structure and the magnetic properties. Our calculations ensure the unconstrained structural relaxation at scalar relativistic level for various numbers of iron layers placed on the magnesium oxide substrate. Our results show that due to the formation of the interface the electronic structure of the interface iron atoms is significantly modified involving charge transfer within the iron subsystem. In addition, we find that the magnetic anisotropy energy increases from 1.9 mJ m(-2) for 3 Fe layers up to 3.0 mJ m(-2) for 11 Fe layers. PMID:26987845

  4. Cr/B4C multilayer mirrors: Study of interfaces and X-ray reflectance

    NASA Astrophysics Data System (ADS)

    Burcklen, C.; Soufli, R.; Dennetiere, D.; Polack, F.; Capitanio, B.; Gullikson, E.; Meltchakov, E.; Thomasset, M.; Jérome, A.; de Rossi, S.; Delmotte, F.

    2016-03-01

    We present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4C-on-Cr interface, which we modeled with a 1-1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

  5. Application of Neutron Reflectivity for Studies of Biomolecular Structures and Functions at Interfaces

    SciTech Connect

    Johs, Alexander; Liang, Liyuan; Gu, Baohua; Ankner, John Francis; Wang, Wei

    2009-01-01

    Structures and functions of cell membranes are of central importance in understanding processes such as cell signaling, chemotaxis, redox transformation, biofilm formation, and mineralization occurring at interfaces. This chapter provides an overview of the application of neutron reflectivity (NR) as a unique tool for probing biomolecular structures and mechanisms as a first step toward understanding protein protein, protein lipid, and protein mineral interactions at the membrane substrate interfaces. Emphasis is given to the review of existing literature on the assembly of biomimetic membrane systems, such as supported membranes for NR studies, and demonstration of model calculations showing the potential of NR to elucidate molecular fundamentals of microbial cell mineral interactions and structure functional relationships of electron transport pathways. The increased neutron flux afforded by current and upcoming neutron sources holds promise for elucidating detailed processes such as phase separation, formation of microdomains, and membrane interactions with proteins and peptides in biological systems.

  6. Theoretical Study of Excess Si Emitted from Si-oxide/Si Interfaces

    NASA Astrophysics Data System (ADS)

    Kageshima, Hiroyuki; Uematsu, Masahi; Akagi, Kazuto; Tsuneyuki, Shinji; Akiyama, Toru; Shiraishi, Kenji

    2004-12-01

    The excess Si emitted from the Si-oxide/Si interface is studied using the first-principles calculations. It is shown that the excess Si can have many (meta-) stable positions around the interface. In addition, some positions in the oxide do not have any dangling bonds or floating bonds in contrast to those in the bulk crystalline Si. The results indicate that the emitted Si can be located in the oxide layer but they do not necessarily cause charge traps in the oxide. The emitted Si atoms are thought to just be oxidized and absorbed into the oxide while a portion of them cause the E' centers, the Pb centers or charge traps.

  7. Molecular dynamics study of two-dimensional sum frequency generation spectra at vapor/water interface

    SciTech Connect

    Ishiyama, Tatsuya; Morita, Akihiro; Tahara, Tahei

    2015-06-07

    Two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectra at vapor/water interface were studied by molecular dynamics (MD) simulation with a classical flexible and nonpolarizable model. The present model well describes the spectral diffusion of 2D infrared spectrum of bulk water as well as 2D HD-VSFG at the interface. The effect of isotopic dilution on the 2D HD-VSFG was elucidated by comparing the normal (H{sub 2}O) water and HOD water. We further performed decomposition analysis of 2D HD-VSFG into the hydrogen-bonding and the dangling (or free) OH vibrations, and thereby disentangled the different spectral responses and spectral diffusion in the 2D HD-VSFG. The present MD simulation demonstrated the role of anharmonic coupling between these modes on the cross peak in the 2D HD-VSFG spectrum.

  8. Ti/CeOx(111) interfaces studied by XPS and STM

    NASA Astrophysics Data System (ADS)

    Zhou, Yinghui; Zhou, Jing

    2012-04-01

    Low coverage of Ti was deposited on the well-ordered CeOx(111) (1.5 < x < 2) thin films grown on Ru(0001) by physical vapor deposition at room temperature. The structure and interaction of Ti/ceria interfaces were investigated with X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) techniques under ultrahigh vacuum conditions. XPS data indicate that the deposition of Ti on both oxidized and reduced ceria surfaces causes the partial reduction of Ce from + 4 to + 3 state. Ti is formally in the + 4 state. STM data show the formation of small atomic-like titania features at 300 K, which coalesce to form chain structures upon heating. It is demonstrated in the study that the deposition of Ti can form mixed metal oxides at the interface and modify both electronic and structural properties of the ceria support. The structural study of Ti/ceria interfaces can be a key for understanding the higher catalytic activity of the Ti-CeOx mixed oxide catalysts as compared with the individual pure oxides.

  9. Studies of ferroelectric heterostructure thin films and interfaces via in situ analytical techniques.

    SciTech Connect

    Auciello, O.; Dhote, A.; Gao, Y.; Gruen, D. M.; Im, J.; Irene, E. A.; Krauss, A. R.; Mueller, A. H.; Ramesh, R.

    1999-08-30

    The science and technology of ferroelectric thin films has experienced an explosive development during the last ten years. Low-density non-volatile ferroelectric random access memories (NVFRAMs) are now incorporated in commercial products such as ''smart cards'', while high permittivity capacitors are incorporated in cellular phones. However, substantial work is still needed to develop materials integration strategies for high-density memories. We have demonstrated that the implementation of complementary in situ characterization techniques is critical to understand film growth and interface processes, which play critical roles in film microstructure and properties. We are using uniquely integrated time of flight ion scattering and recoil spectroscopy (TOF-ISARS) and spectroscopic ellipsometry (SE) techniques to perform in situ, real-time studies of film growth processes in the high background gas pressure required to growth ferroelectric thin films. TOF-ISARS provides information on surface processes, while SE permits the investigation of buried interfaces as they are being formed. Recent studies on SrBi{sub 2}Ta{sub 2}O{sub 9} (SBT) and Ba{sub x}Sr{sub 1{minus}x}TiO{sub 3} (BST) film growth and interface processes are discussed.

  10. Single-crystal-silicon-based microinstrument to study friction and wear at MEMS sidewall interfaces

    NASA Astrophysics Data System (ADS)

    Ansari, N.; Ashurst, W. R.

    2012-02-01

    Since the advent of microelectromechanical systems (MEMS) technology, friction and wear are considered as key factors that determine the lifetime and reliability of MEMS devices that contain contacting interfaces. However, to date, our knowledge of the mechanisms that govern friction and wear in MEMS is insufficient. Therefore, systematically investigating friction and wear at MEMS scale is critical for the commercial success of many potential MEMS devices. Specifically, since many emerging MEMS devices contain more sidewall interfaces, which are topographically and chemically different from in-plane interfaces, studying the friction and wear characteristics of MEMS sidewall surfaces is important. The microinstruments that have been used to date to investigate the friction and wear characteristics of MEMS sidewall surfaces possess several limitations induced either by their design or the structural film used to fabricate them. Therefore, in this paper, we report on a single-crystal-silicon-based microinstrument to study the frictional and wear behavior of MEMS sidewalls, which not only addresses some of the limitations of other microinstruments but is also easy to fabricate. The design, modeling and fabrication of the microinstrument are described in this paper. Additionally, the coefficients of static and dynamic friction of octadecyltrichlorosilane-coated sidewall surfaces as well as sidewall surfaces with only native oxide on them are also reported in this paper.

  11. Theoretical study of binding and permeation of ether-based polymers through interfaces.

    PubMed

    Samanta, Susruta; Hezaveh, Samira; Roccatano, Danilo

    2013-11-27

    We present a molecular dynamics simulation study on the interactions of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and their ABA-type block copolymer, poloxamers, at water/n-heptane and 1,2-dimyristoyl-sn-glycero-3-phospatidycholine (DMPC) lipid bilayer/water interfaces. The partition coefficients in water/1-octanol of the linear polyethers up to three monomers were calculated. The partition coefficients evidenced a higher hydrophobicity of the PPO in comparison to PEO. At the water/n-heptane interface, the polymers tend to adopt elongated conformations in agreement with similar experimental ellipsometry studies of different poloxamers. In the case of the poloxamers at the n-heptane/water interface, the stronger preference of the PPO block for the hydrophobic phase resulted in bottle-brush-type polymer conformations. At lipid bilayer/water interface, the PEO polymers, as expected from their hydrophilic nature, are weakly adsorbed on the surface of the lipid bilayer and locate in the water phase close to the headgroups. The free energy barriers of permeation calculated for short polymer chains suggest a thermodynamics propensity for the water phase that increase with the chain length. The lower affinity of PEO for the hydrophobic interior of the lipid bilayer resulted in the spontaneous expulsion within the simulation time. On the contrary, PPO chains and poloxamers have a longer residence time inside the bilayer, and they tend to concentrate in the tail region of the bilayer near the polar headgroups. In addition, polymers with PPO unit length comparable to the thickness of the hydrophobic region of the bilayer tend to span across the bilayer. PMID:24219592

  12. The Origin of High Thermal Conductivity and Ultralow Thermal Expansion in Copper-Graphite Composites.

    PubMed

    Firkowska, Izabela; Boden, André; Boerner, Benji; Reich, Stephanie

    2015-07-01

    We developed a nanocomposite with highly aligned graphite platelets in a copper matrix. Spark plasma sintering ensured an excellent copper-graphite interface for transmitting heat and stress. The resulting composite has superior thermal conductivity (500 W m(-1) K(-1), 140% of copper), which is in excellent agreement with modeling based on the effective medium approximation. The thermal expansion perpendicular to the graphite platelets drops dramatically from ∼20 ppm K(-1) for graphite and copper separately to 2 ppm K(-1) for the combined structure. We show that this originates from the layered, highly anisotropic structure of graphite combined with residual stress under ambient conditions, that is, strain-engineering of the thermal expansion. Combining excellent thermal conductivity with ultralow thermal expansion results in ideal materials for heat sinks and other devices for thermal management. PMID:26083322

  13. Biopolymer-modified graphite oxide nanocomposite films based on benzalkonium chloride-heparin intercalated in graphite oxide

    NASA Astrophysics Data System (ADS)

    Meng, Na; Zhang, Shuang-Quan; Zhou, Ning-Lin; Shen, Jian

    2010-05-01

    Heparin is a potent anticoagulant agent that interacts strongly with antithrombin III to prevent the formation of fibrin clots. In the present work, poly(dimethylsiloxane)(PDMS)/graphite oxide-benzalkonium chloride-heparin (PDMS/modified graphite oxide) nanocomposite films were obtained by the solution intercalation technique as a possible drug delivery system. The heparin-benzalkonium chloride (BAC-HEP) was intercalated into graphite oxide (GO) layers to form GO-BAC-HEP (modified graphite oxide). Nanocomposite films were characterized by XRD, SEM, TEM, ATR-FTIR and TGA. The modified graphite oxide was observed to be homogeneously dispersed throughout the PDMS matrix. The effect of modified graphite oxide on the mechanical properties of the nanocomposite film was investigated. When the modified graphite oxide content was lower than 0.2 wt%, the nanocomposites showed excellent mechanical properties. Furthermore, nanocomposite films become delivery systems that release heparin slowly to make the nanocomposite films blood compatible. The in vitro studies included hemocompatibility testing for effects on platelet adhesion, platelet activation, plasma recalcification profiles, and hemolysis. Results from these studies showed that the anticoagulation properties of PDMS/GO-BCA-HEP nanocomposite films were greatly superior to those for no treated PDMS. Cell culture assay indicated that PDMS/GO-BCA-HEP nanocomposite films showed enhanced cell adhesion.

  14. A Highly Efficient and Facile Approach for Fabricating Graphite Nanoplatelets

    NASA Astrophysics Data System (ADS)

    Van Thanh, Dang; Van Thien, Nguyen; Thang, Bui Hung; Van Chuc, Nguyen; Hong, Nguyen Manh; Trang, Bui Thi; Lam, Tran Dai; Huyen, Dang Thi Thu; Hong, Phan Ngoc; Minh, Phan Ngoc

    2016-05-01

    In this study, we report a highly efficient, convenient, and cost-effective technique for producing graphite nanoplatelets (GNPs) from plasma-expanded graphite oxides (PEGOs) obtained directly from low-cost, recycled graphite electrodes of used batteries, x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy confirmed the successful preparation of GNPs. Scanning electron microscopy revealed that the GNPs have lateral width from several hundreds of nanometers to 1.5 μm with an approximate thickness of 20-50 nm. These GNPs can serve as a precursor for the preparation of GNPs-based nanocomposite.

  15. Characterization of nuclear graphite elastic properties using laser ultrasonic methods

    SciTech Connect

    Zeng, Fan W; Han, Karen; Olasov, Lauren R; Gallego, Nidia C; Contescu, Cristian I; Spicer, James B

    2015-01-01

    Laser ultrasonic methods have been used to characterize the elastic behaviors of commercially-available and legacy nuclear graphites. Since ultrasonic techniques are sensitive to various aspects of graphite microstructure including preferred grain orientation, microcrack orientation and porosity, laser ultrasonics is a candidate technique for monitoring graphite degradation and structural integrity in environments expected in high-temperature, gas-cooled nuclear reactors. Aspects of materials texture can be assessed by studying ultrasonic wavespeeds as a function of propagation direction and polarization. Shear wave birefringence measurements, in particular, can be used to evaluate elastic anisotropy. In this work, laser ultrasonic measurements of graphite moduli have been made to provide insight into the relationship between the microstructures and the macroscopic stiffnesses of these materials. In particular, laser ultrasonic measurements have been made using laser line sources to produce shear waves with specific polarizations. By varying the line orientation relative to the sample, shear wave birefringence measurements have been recorded. Results from shear wave birefringence measurements show that an isostatically molded graphite, such as PCIB, behaves isotropically, while an extruded graphite, such as H-451, displays significant ultrasonic texture. Graphites have complicated microstructures that depend on the manufacturing processes used, and ultrasonic texture in these materials could originate from grain orientation and preferred microcrack alignment. Effects on material isotropy due to service related microstructural changes are possible and the ultimate aim of this work is to determine the degree to which these changes can be assessed nondestructively using laser ultrasonics measurements

  16. Comparison of Oxidation Behaviors of Different Grades of Nuclear Graphite

    SciTech Connect

    Luo Xiaowei; Robin, Jean-Charles; Yu Suyuan

    2005-09-15

    The oxidation behaviors of different grades of nuclear graphite - PAEB, PCEB, PPEA, and IG-11 - were studied thermogravimetrically at 400, 800, and 1200 deg. C as a part of work to select one grade of nuclear graphite for use in a gas turbine-modular helium reactor (GT-MHR). The results showed that all grades of nuclear graphite resist oxidation at 400 deg. C. The difference in oxidation between different grades of nuclear graphite was greater at 800 deg. C than at 400 deg. C and 1200 deg. C. At 800 deg. C, for the same grade of nuclear graphite, when the centerline of the specimen is parallel to the axis of extrusion (with grain), the oxidation rate is greater than that of the graphite specimen with the centerline perpendicular to the axis of extrusion (against grain). The experimental results revealed that PPEA had the best oxidation resistance, and IG-11 had the worst due to high impurities. Moreover, the oxidation experiment exhibited that there were some oxidizable materials in unclear nuclear graphite.

  17. Phosphomolybdic acid immobilized on graphite as an environmental photoelectrocatalyst.

    PubMed

    Aber, Soheil; Yaghoubi, Zeynab; Zarei, Mahmoud

    2016-10-01

    A new phosphomolybdic acid (PMA)/Graphite surface was prepared based on electrostatic interactions between phosphomolybdic acid and graphite surface. The PMA/Graphite was characterized by cyclic voltammetry (CV) analysis and scanning electron microscope (SEM). SEM images showed that the phosphomolybdic acid particles were well stabilized on the graphite surface and they were evidenced the size of particles (approximately 10 nm). The CV results not only showed that the modified surface has good electrochemical activity toward the removal of the dyestuff, but also exhibits long term stability. The PMA/Graphite was used as a photoanode for decolorization of Reactive Yellow 39 by photoelectrocatalytic system under UV irradiation. The effects of parameters such as the amount of phosphomolybdic acid used in preparation of PMA/Graphite surface, applied potential on anode electrode and solution pH were studied by response surface methodology. The optimum conditions were obtained as follows: dye solution pH 3, 1.5 g of immobilized PMA on graphite surface and applied potential on anode electrode 1 V. Under optimum conditions after 90 min of reaction time, the decolorization efficiency was 95%. PMID:27448755

  18. Research and development of plasma sprayed tungsten coating on graphite and copper substrates

    NASA Astrophysics Data System (ADS)

    Liu, Xiang; Zhang, Fu; Tao, Shunyan; Cao, Yunzhen; Xu, Zengyu; Liu, Yong; Noda, N.

    2007-06-01

    Vacuum plasma sprayed tungsten coating on graphite and copper substrates has been prepared. VPS-W coated graphite has multilayered silicon and tungsten interface pre-deposited by physical vapor deposition (PVD) and VPS-W coated copper has graded transition interlayer. VPS-W coating was characterized, and then the high heat flux properties of the coating were examined. Experimental results indicated that both VPS-W coated graphite and VPS-W coated copper could endure 1000 cycles without visible failure under a heat flux of approximately 5 MW/m2 absorbed power density and 5 s pulse duration. A comparison between the present VPS-W coated graphite and VPS-W coated carbon fiber composite (CX-2002U) with Re interface made by Plansee Aktiengesllshaft was carried out. Results show that both Re and Si are suitable as intermediate layer for tungsten coating on carbon substrates.

  19. Graphitized needle cokes and natural graphites for lithium intercalation

    SciTech Connect

    Tran, T.D.; Spellman, L.M.; Pekala, R.W.; Goldberger, W.M.; Kinoshita, K.

    1996-05-10

    This paper examined effects of heat treatment and milling (before or after heat treatment) on the (electrochemical) intercalating ability of needle petroleum coke; natural graphite particles are included for comparison. 1 tab, 4 figs, 7 refs.

  20. Spent graphite fuel element processing

    SciTech Connect

    Holder, N.D.; Olsen, C.W.

    1981-07-01

    The Department of Energy currently sponsors two programs to demonstrate the processing of spent graphite fuel elements. General Atomic in San Diego operates a cold pilot plant to demonstrate the processing of both US and German high-temperature reactor fuel. Exxon Nuclear Idaho Company is demonstrating the processing of spent graphite fuel elements from Rover reactors operated for the Nuclear Rocket Propulsion Program. This work is done at Idaho National Engineering Laboratory, where a hot facility is being constructed to complete processing of the Rover fuel. This paper focuses on the graphite combustion process common to both programs.

  1. Synchrotron-radiation photoemission study of the ultrathin Ba/3C-SiC(111) interface

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Benemanskaya, G. V.; Dementev, P. A.; Timoshnev, S. N.; Senkovskiy, B.

    2016-03-01

    Electronic structure of the Ba/3C-SiC(111) interface has been detailed studied in situ in an ultrahigh vacuum using synchrotron radiation photoemission spectroscopy with photon energies in the range of 100-450 eV. The 3C-SiC(111) samples were grown by a new method of epitaxy of low-defect unstressed nanoscaled silicon carbide films on silicon substrates. Valence band photoemission and both the Si 2p, C 1s core level spectra have been investigated as a function of Ba submonolayer coverage. Under Ba adsorption two induced surface bands are found at binding energies of 2 eV and 6 eV. It is obtained that Ba/3C-SiC(111) interface can be characterized as metallic-like. Modification of both the Si 2p and C 1s surface-related components were ascertained and shown to be provided by redistribution effect of electron density between Ba adatoms and both the Si surface and C interface atoms.

  2. First-Principles Study of Enhanced Magnetoelectric Effects at the Fe/MgO(001) Interface

    NASA Astrophysics Data System (ADS)

    Niranjan, M. K.; Jaswal, S. S.; Tsymbal, E. Y.; Duan, C.-G.

    2010-03-01

    The magnetoelectric effect allows affecting magnetic properties of materials by electric fields with potential for technological applications such as electrically controlled magnetic data storage. In this study we explore, using first-principles methods, the magnetoelectric effect at the Fe/MgO(001) interface^,1. By explicitly introducing an electric field in our density-functional calculations we demonstrate that the magnetic moment of Fe atoms at the interface changes linearly as a function of the applied electric field with the surface magnetoelectric coefficient being strongly enhanced as compared to that for the clean Fe(001) surface.^1 The effect originates from the increased screening charge associated with a large dielectric constant of MgO. The influence of electric field on relative occupancy of the Fe-3d orbitals leads to significant change in the surface magnetocrystalline anisotropy. These results are compared with the available experimental work.^2 Our results indicate that using high-k dielectrics at the interface with ferromagnetic metals may be very effective in controlling the magnetic properties by electric fields thereby leading to interesting device applications. ^1 C.-G. Duan et al., Phys. Rev. Lett. 101, 137201 (2008). ^2 T. Maruyama et al., Nat. Nanotech., 4, 158 (2009).

  3. A comparative study about electronic structures at rubrene/Ag and Ag/rubrene interfaces

    SciTech Connect

    Sinha, Sumona Mukherjee, M.

    2015-10-15

    The contact between the electrode and the organic semiconductor is one of the most crucial factors in determining the organic device performance. The development and production technology of different organic devices require the understanding of different types of metal/organic semiconducting thin film interfaces. Comparisons about the electronic structures at Rubrene/Ag and Ag/Rubrene interfaces have been studied using photoemission spectroscopy. The Ag on rubrene interfaces is found to show more interesting and complex natures than its counterpart. The vacuum level (VL) was shifted about 0.51 eV from push back effect for deposition of 5 Å rubrene onto Ag film whereas the electronic features of silver was only suppressed and no energy shift was resulted. While the deposition of 5 Å Ag onto rubrene film leads to the diffusion of the Ag atoms, as a cluster with quantum size effect, inside the film. Angle dependent XPS measurement indicates that diffused metal clusters were present at entire probed depth of the film. Moreover these clusters dope the uppermost surface of the rubrene film which consequences a shift of the electronic states of thick organic film towards higher binding energy. The VL was found to shift about 0.31 eV toward higher binding energy whereas the shift was around 0.21 eV for the electronic states of rubrene layer.

  4. XPS study of interface formation of CVD SiO2 on InSb

    NASA Astrophysics Data System (ADS)

    Vasquez, R. P.; Grunthaner, F. J.

    1981-10-01

    The interfacial chemistry of CVD SiO2 films deposited on thin native oxides grown on InSb substrates is examined using X-ray photoemission spectroscopy (XPS) and a relatively benign chemical etching technique for depth profiling. An intensity analysis of XPS spectra is used to derive the compositional structure of the interfaces obtained in the SiO2/native oxide/InSb system. Peak positions in these spectra are used to follow the change in substrate surface potential during the etch sequence, and to establish the chemical nature of the species formed during deposition and subsequent processing. Reaction of the substrate with oxygen resulted in an In-rich native oxide and 1-2 monolayers of excess elemental Sb at the native-oxide/substrate interface, incompletely oxidized silane reduced the native oxide, leaving less than 1 monolayer of elemental In at the SiO2/native oxide interface. Etch removal of this thin In-rich layer leads to a change in the substrate surface potential of 0.06 eV, corresponding to a net increase in positive charge. The results are consistent with simple thermodynamic considerations; they are also compared to previously reported studies of deposited dielectrics on III-V compound semiconductors.

  5. Spectroscopic studies of U(VI) sorption at the kaolinite-water interface. Final report

    SciTech Connect

    Thompson, H.A.; Parks, G.A.; Brown, G.E. Jr.

    1994-06-01

    Efficient use of U as a resource and safe handling, recycling and disposal of U-containing wastes require an understanding of the factors controlling the fate of U, where fate refers to the destination of U, typically expressed as an environmental medium or a process phase. The sorption process constitutes a change in elemental fate. Partitioning of an element from solution to a solid phase, or sorption, can be divided into three broad categories: adsorption, surface precipitation, and absorption. Extended X-ray absorption fine structure (EXAFS), a type of X-ray absorption spectroscopy (XAS), offers the possibility for distinguishing among different modes of sorption by characterizing the atomic environment of the sorbing element. In this study, the authors use EXAFS to determine the structure of U(VI) sorption complexes at the kaolinite-water interface. In Chapter One, they present an overview of selected aspects of U structural chemistry as a basis for considering the structural environment of U at the solid-water interface. To evaluate the utility of XAS for characterization of the structural environment of U(VI) at the solid-water interface, they have carried out an in-depth analysis of XAS data from U(VI)-containing solid and solution model compounds, which they describe in Chapter Two. In Chapter three, they consider sorption of U by kaolinite as a means of effecting the removal of U from surface collection pond waters on the Rocky Flats Plant site in northern Colorado.

  6. Solid-state {sup 19}F and {sup 13}C NMR of room temperature fluorinated graphite and samples thermally treated under fluorine: Low-field and high-resolution studies

    SciTech Connect

    Giraudet, J.; Dubois, M.; Guerin, K.; Pinheiro, J.P.; Hamwi, A.; Stone, W.E.E.; Pirotte, P.; Masin, F. . E-mail: fmasin@ulb.ac.be

    2005-04-15

    Room temperature graphite fluorides consisting of raw material and samples post-treated in pure fluorine atmosphere in the temperature range 100-500 deg. C have been studied by solid-state NMR. Several NMR approaches have been used, both high and low-field {sup 19}F, {sup 19}F MAS and {sup 13}C MAS with {sup 19}F to {sup 13}C cross polarization. The modifications, in the graphitic lattice, of the catalytic iodine fluorides products have been examined. A transformation of the C-F bond character from semi-ionic to covalent has been found to occur at a post-treatment temperature close to 400 deg. C. It is shown that covalency increases with temperature.

  7. Mineral resource of the month: graphite

    USGS Publications Warehouse

    U.S. Geological Survey

    2008-01-01

    The article presents facts about graphite ideal for industrial applications. Among the characteristics of graphite are its metallic luster, softness, perfect basal cleavage and electrical conductivity. Batteries, brake linings and powdered metals are some of the products that make use of graphite. It attributes the potential applications for graphite in high-technology fields to innovations in thermal technology and acid-leaching techniques.

  8. Method of Obtaining Uniform Coatings on Graphite

    DOEpatents

    Campbell, I. E.

    1961-04-01

    A method is given for obtaining uniform carbide coatings on graphite bodies. According to the invention a metallic halide in vapor form is passed over the graphite body under such conditions of temperature and pressure that the halide reacts with the graphite to form a coating of the metal carbide on the surface of the graphite.

  9. METHOD OF OBTAINING UNIFORM COATINGS ON GRAPHITE

    DOEpatents

    Campbell, I.E.

    1961-04-01

    A method is given for obtaining uniform carbide coatings on graphite bodies. According to the invention a metallic halide in vapor form is passed over the graphite body under such conditions of temperature and pressure that the halide reacts with the graphite to form a coating of the metal carbide on the surface of the graphite.

  10. Performance Properties of Graphite Reinforced Composites with Advanced Resin Matrices

    NASA Technical Reports Server (NTRS)

    Kourtides, Demetrius A.

    1980-01-01

    This article looks at the effect of different resin matrices on thermal and mechanical properties of graphite composites, and relates the thermal and flammability properties to the anaerobic char yield of the resins. The processing parameters of graphite composites utilizing graphite fabric and epoxy or other advanced resins as matrices are presented. Thermoset resin matrices studied were: aminecured polyfunctional glycidyl aminetype epoxy (baseline), phenolicnovolac resin based on condensation of dihydroxymethyl-xylene and phenol cured with hexamine, two types of polydismaleimide resins, phenolic resin, and benzyl resin. The thermoplastic matrices studied were polyethersulfone and polyphenylenesulfone. Properties evaluated in the study included anaerobic char yield, limiting oxygen index, smoke evolution, moisture absorption, and mechanical properties at elevated temperatures including tensile, compressive, and short-beam shear strengths. Generally, it was determined that graphite composites with the highest char yield exhibited optimum fire-resistant properties.

  11. Study of microdosimetric energy deposition patterns in tissue-equivalent medium due to low-energy neutron fields using a graphite-walled proportional counter.

    PubMed

    Waker, A J; Aslam

    2011-06-01

    To improve radiation protection dosimetry for low-energy neutron fields encountered in nuclear power reactor environments, there is increasing interest in modeling neutron energy deposition in metrological instruments such as tissue-equivalent proportional counters (TEPCs). Along with these computational developments, there is also a need for experimental data with which to benchmark and test the results obtained from the modeling methods developed. The experimental work described in this paper is a study of the energy deposition in tissue-equivalent (TE) medium using an in-house built graphite-walled proportional counter (GPC) filled with TE gas. The GPC is a simple model of a standard TEPC because the response of the counter at these energies is almost entirely due to the neutron interactions in the sensitive volume of the counter. Energy deposition in tissue spheres of diameter 1, 2, 4 and 8 µm was measured in low-energy neutron fields below 500 keV. We have observed a continuously increasing trend in microdosimetric averages with an increase in neutron energy. The values of these averages decrease as we increase the simulated diameter at a given neutron energy. A similar trend for these microdosimetric averages has been observed for standard TEPCs and the Rossi-type, TE, spherical wall-less counter filled with propane-based TE gas in the same energy range. This implies that at the microdosimetric level, in the neutron energy range we employed in this study, the pattern of average energy deposited by starter and insider proton recoil events in the gas is similar to those generated cumulatively by crosser and stopper events originating from the counter wall plus starter and insider recoil events originating in the sensitive volume of a TEPC. PMID:21476858

  12. Dual functions of TiC nanoparticles on tribological performance of Al/graphite composites

    NASA Astrophysics Data System (ADS)

    Fallahdoost, Hamid; Nouri, Alireza; Azimi, Amin

    2016-06-01

    In this study, the effect of TiC nanoparticles as a reinforcement on the mechanical and tribological properties of Aluminum-based self lubricating composite was investigated. The microstructure, relative density, hardness, and tribological properties of Al/graphite and Al/TiC/graphite composites were examined as a function of graphite content. The tribo-surfaces of the samples were analyzed using SEM and EDS elemental mapping. The results indicated that the addition of TiC nanoparticles not only decreased the wear rate and coefficient of friction of the composites, but also facilitated the formation of a stable graphite layer at longer sliding distances and high sliding velocities by forming a durable graphite/TiC composite on the tribo-surface. Therefore, the stability of graphite layer can be considered as a possible cause for decrease in wear rate of the Al/TiC/graphite composite.

  13. Ultrasonic-Assisted Synthesis of Graphite-Reinforced Al Matrix Nanocomposites

    NASA Astrophysics Data System (ADS)

    Christy Roshini, P.; Nagasivamuni, B.; Raj, Baldev; Ravi, K. R.

    2015-06-01

    A novel approach to produce Al-2 vol.% graphite nanocomposites using micron-sized graphite particles has been reported using conventional stir casting technique combined with ultrasonic treatment. Microstructural observations indicate that the visible agglomerations and porosities are significantly reduced after ultrasonic treatment. Transmission electron microscopy studies of ultrasonic-treated composites reveal that the size of the graphite particles is reduced substantially and its morphology is transformed into flake type structures. The width of the graphite flakes is reduced markedly with the increase in ultrasonic processing time and it is found to be in the range of 100-120 nm with an aspect ratio of 8.83 after 5 min of ultrasonication. Added to that, considerable improvement in the hardness values are noted for ultrasonic-treated Al-2 vol.% graphite composites when compared to conventional untreated composites. The mechanism behind the significant reduction in graphite particle size and porosity, uniform distribution of graphite particles and hardness increments are discussed.

  14. Effects of Oxidation on Oxidation-Resistant Graphite

    SciTech Connect

    Windes, William; Smith, Rebecca; Carroll, Mark

    2015-05-01

    The Advanced Reactor Technology (ART) Graphite Research and Development Program is investigating doped nuclear graphite grades that exhibit oxidation resistance through the formation of protective oxides on the surface of the graphite material. In the unlikely event of an oxygen ingress accident, graphite components within the VHTR core region are anticipated to oxidize so long as the oxygen continues to enter the hot core region and the core temperatures remain above 400°C. For the most serious air-ingress accident which persists over several hours or days the continued oxidation can result in significant structural damage to the core. Reducing the oxidation rate of the graphite core material during any air-ingress accident would mitigate the structural effects and keep the core intact. Previous air oxidation testing of nuclear-grade graphite doped with varying levels of boron-carbide (B4C) at a nominal 739°C was conducted for a limited number of doped specimens demonstrating a dramatic reduction in oxidation rate for the boronated graphite grade. This report summarizes the conclusions from this small scoping study by determining the effects of oxidation on the mechanical strength resulting from oxidation of boronated and unboronated graphite to a 10% mass loss level. While the B4C additive did reduce mechanical strength loss during oxidation, adding B4C dopants to a level of 3.5% or more reduced the as-fabricated compressive strength nearly 50%. This effectively minimized any benefits realized from the protective film formed on the boronated grades. Future work to infuse different graphite grades with silicon- and boron-doped material as a post-machining conditioning step for nuclear components is discussed as a potential solution for these challenges in this report.

  15. A (13)C NMR analysis of the effects of electron radiation on graphite/polyetherimide composites

    NASA Technical Reports Server (NTRS)

    Ferguson, Milton W.

    1989-01-01

    Initial investigations have been made into the use of high resolution nuclear magnetic resonance (NMR) for the characterization of radiation effects in graphite and Kevlar fibers, polymers, and the fiber/matrix interface in graphite/polyetherimide composites. Sample preparation techniques were refined. Essential equipment has been procured. A new NMR probe was constructed to increase the proton signal-to-noise ratio. Problem areas have been identified and plans developed to resolve them.

  16. Structure and Phase Transitions of Monolayers of Intermediate-length n-alkanes on Graphite Studied by Neutron Diffraction and Molecular Dynamics Simulation

    SciTech Connect

    Taub, H.; Hansen, F.Y.; Diama, Amand; Matthies, Blake; Criswell, Leah; Mo, Haiding; Bai, M; Herwig, Kenneth W

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a 'smectic' phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  17. The effect of the increase in graphite volumetric percentage on the strength and hardness of Al-4 weight percent Mg-graphite composites

    NASA Astrophysics Data System (ADS)

    Hassan, Adel Mahammod; Hayajneh, Mohammed T.; Al-Omari, Mohammad Abdul-Hameed

    2002-06-01

    In this study, the fabrication of an Al-4 wt.% Mg-graphite particle composite is described. Composites of Al-4 wt.% Mg alloys containing 1 10 volume percentages of graphite particles were prepared using the compocasting technique. A pitched-blade stirrer was used to stir the graphite particles in the semi-solid melt, and the slurry was then poured into a metallic mould to obtain the cast bars. The emphasis of the investigation was on the important features of the castings obtained by this method, specifically the distribution of graphite particles along the cast bars and porosities. Then we studied the effect of the addition of the graphite on the strength and hardness of these cast bars. The results show that both the tensile strength and the hardness decrease with the increase in graphite content.

  18. Nonlinear vibrational spectroscopic studies of molecular interaction and charging behavior at solid/liquid interfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Luning

    Solid-liquid interfaces have been the focus of different communities of scientists due to its importance in industrial applications and chemical processes in nature. Molecular interactions and surface charges affect the physicochemical properties of these interfaces and a thorough understanding is still lacking now. This thesis describes our work in studying several model solid-liquid interfaces using sum-frequency vibrational spectroscopy. Through the studies of interfacial vibrational spectra, we hope to gain better understanding of molecular interactions in competitive adsorption process and also surface charging behavior at different pH and salt concentrations. We start by studying alcohol-water mixture and the adsorption behavior at both hydrophilic and hydrophobic surfaces. In both cases, alcohol adsorbs preferentially from water. The tendency for water to form strong hydrogen-bonding network is the driving force for preferential adsorption of alcohol. We proposed two different interfacial molecular structures on hydrophilic and hydrophobic surfaces. We move on to study the interaction of pure water with a solid surface. Single crystal alumina is used as a model system. At different pH, the surface can undergo protonation and deprotonation reactions and accumulates surface charge. Both the hydrogen-bonding with water and the surface field created by surface charge can affect interfacial water structure. Combining the information obtained with intensity and phase spectra, we find water molecules have two types of bonding within the interfacial layer: weakly hydrogen-bonded species near 3450 cm-1 that does not flip with switching surface charge, and strongly hydrogen-bonded species at 3200 cm-1 that readily flips with switching surface field. One other system we have studied is nanoporous silica-water interface. We found that signal from interfacial water is reduced due to the porous nature of the film. The water spectral features tell us about the interfacial

  19. Graphite for the nuclear industry

    SciTech Connect

    Burchell, T.D.; Fuller, E.L.; Romanoski, G.R.; Strizak, J.P.

    1991-01-01

    Graphite finds applications in both fission and fusion reactors. Fission reactors harness the energy liberated when heavy elements, such as uranium or plutonium, fragment or fission''. Reactors of this type have existed for nearly 50 years. The first nuclear fission reactor, Chicago Pile No. 1, was constructed of graphite under a football stand at Stagg Field, University of Chicago. Fusion energy devices will produce power by utilizing the energy produced when isotopes of the element hydrogen are fused together to form helium, the same reaction that powers our sun. The role of graphite is very different in these two reactor systems. Here we summarize the function of the graphite in fission and fusion reactors, detailing the reasons for their selection and discussing some of the challenges associated with their application in nuclear fission and fusion reactors. 10 refs., 15 figs., 1 tab.

  20. Graphite-reinforced bone cement

    NASA Technical Reports Server (NTRS)

    Knoell, A. C.

    1976-01-01

    Chopped graphite fibers added to surgical bone cement form bonding agent with mechanical properties closely matched to those of bone. Curing reaction produces less heat, resulting in reduced traumatization of body tissues. Stiffness is increased without affecting flexural strength.

  1. CALANDRIA TYPE SODIUM GRAPHITE REACTOR

    DOEpatents

    Peterson, R.M.; Mahlmeister, J.E.; Vaughn, N.E.; Sanders, W.J.; Williams, A.C.

    1964-02-11

    A sodium graphite power reactor in which the unclad graphite moderator and fuel elements are contained within a core tank is described. The core tank is submersed in sodium within the reactor vessel. Extending longitudinally through the core thnk are process tubes with fuel elements positioned therein. A bellows sealing means allows axial expansion and construction of the tubes. Within the core tank, a leakage plenum is located below the graphite, and above the graphite is a gas space. A vent line regulates the gas pressure in the space, and another line removes sodium from the plenum. The sodium coolant flows from the lower reactor vessel through the annular space between the fuel elements and process tubes and out into the reactor vessel space above the core tank. From there, the heated coolant is drawn off through an outlet line and sent to the heat exchange. (AEC)

  2. A novel nanoporous graphitic composite.

    PubMed

    Wang, Zheng-Ming; Hoshinoo, Kumiko; Xue, M; Kanoh, Hirofumi; Ooi, Kenta

    2002-08-21

    A novel nanoporous composite containing micrographitic carbon layers is synthesized by preliminarily expanding the interlayer of an oxidized product of graphite using surfactant, followed by Si bridging/pillaring, and carbonization. PMID:12211211

  3. Intercalated hybrid graphite fiber composite

    NASA Technical Reports Server (NTRS)

    Gaier, James R. (Inventor)

    1993-01-01

    The invention is directed to a highly conductive lightweight hybrid material and methods of producing the same. The hybrid composite is obtained by weaving strands of a high strength carbon or graphite fiber into a fabric-like structure, depositing a layer of carbon onto the structure, heat treating the structure to graphitize the carbon layer, and intercalating the graphitic carbon layer structure. A laminate composite material useful for protection against lightning strikes comprises at least one layer of the hybrid material over at least one layer of high strength carbon or graphite fibers. The composite material of the present invention is compatible with matrix compounds, has a coefficient of thermal expansion which is the same as underlying fiber layers, and is resistant to galvanic corrosion in addition to being highly conductive. These materials are useful in the aerospace industry, in particular as lightning strike protection for airplanes.

  4. Molecular interactions at the hexadecane/water interface in the presence of surfactants studied with second harmonic generation

    NASA Astrophysics Data System (ADS)

    Sang, Yajun; Yang, Fangyuan; Chen, Shunli; Xu, Hongbo; Zhang, Si; Yuan, Qunhui; Gan, Wei

    2015-06-01

    It is important to investigate the influence of surfactants on structures and physical/chemical properties of oil/water interfaces. This work reports a second harmonic generation study of the adsorption of malachite green (MG) on the surfaces of oil droplets in a hexadecane/water emulsion in the presence of surfactants including sodium dodecyl sulfate, polyoxyethylene-sorbitan monooleate (Tween80), and cetyltrimethyl ammonium bromide. It is revealed that surfactants with micromolar concentrations notably influence the adsorption of MG at the oil/water interface. Both competition adsorption and charge-charge interactions played very important roles in affecting the adsorption free energy and the surface density of MG at the oil/water interface. The sensitive detection of the changing oil/water interface with the adsorption of surfactants at such low concentrations provides more information for understanding the behavior of these surfactants at the oil/water interface.

  5. Molecular interactions at the hexadecane/water interface in the presence of surfactants studied with second harmonic generation.

    PubMed

    Sang, Yajun; Yang, Fangyuan; Chen, Shunli; Xu, Hongbo; Zhang, Si; Yuan, Qunhui; Gan, Wei

    2015-06-14

    It is important to investigate the influence of surfactants on structures and physical/chemical properties of oil/water interfaces. This work reports a second harmonic generation study of the adsorption of malachite green (MG) on the surfaces of oil droplets in a hexadecane/water emulsion in the presence of surfactants including sodium dodecyl sulfate, polyoxyethylene-sorbitan monooleate (Tween80), and cetyltrimethyl ammonium bromide. It is revealed that surfactants with micromolar concentrations notably influence the adsorption of MG at the oil/water interface. Both competition adsorption and charge-charge interactions played very important roles in affecting the adsorption free energy and the surface density of MG at the oil/water interface. The sensitive detection of the changing oil/water interface with the adsorption of surfactants at such low concentrations provides more information for understanding the behavior of these surfactants at the oil/water interface. PMID:26071724

  6. Atom-probe tomographic study of interfaces of Cu{sub 2}ZnSnS{sub 4} photovoltaic cells

    SciTech Connect

    Tajima, S. Asahi, R.; Itoh, T.; Hasegawa, M.; Ohishi, K.; Isheim, D.; Seidman, D. N.

    2014-09-01

    The heterophase interfaces between the CdS buffer layer and the Cu{sub 2}ZnSnS{sub 4} (CZTS) absorption layers are one of the main factors affecting photovoltaic performance of CZTS cells. We have studied the compositional distributions at heterophase interfaces in CZTS cells using three-dimensional atom-probe tomography. The results demonstrate: (a) diffusion of Cd into the CZTS layer; (b) segregation of Zn at the CdS/CZTS interface; and (c) a change of oxygen and hydrogen concentrations in the CdS layer depending on the heat treatment. Annealing at 573 K after deposition of CdS improves the photovoltaic properties of CZTS cells probably because of the formation of a heterophase epitaxial junction at the CdS/CZTS interface. Conversely, segregation of Zn at the CdS/CZTS interface after annealing at a higher temperature deteriorates the photovoltaic properties.

  7. The dependence of natural graphite anode performance on electrode density

    SciTech Connect

    Shim, Joongpyo; Striebel, Kathryn A.

    2003-11-01

    The effect of electrode density for lithium intercalation and irreversible capacity loss on the natural graphite anode in lithium ion batteries was studied by electrochemical methods. Both the first-cycle reversible and irreversible capacities of the natural graphite anode decreased with an increase in the anode density though compression. The reduction in reversible capacity was attributed to a reduction in the chemical diffusion coefficient for lithium though partially agglomerated particles with a larger stress. For the natural graphite in this study the potentials for Li (de)insertion shifted between the first and second formation cycles and the extent of this shift was dependent on electrode density. The relation between this peak shift and the irreversible capacity loss are probably both due to the decrease in graphite surface area with compression.

  8. Development and fabrication of a graphite polyimide box beam

    NASA Technical Reports Server (NTRS)

    Nadler, M. A.; Darms, F. J.

    1972-01-01

    The state-of-the-art of graphite/polyimide structures was evaluated and key design and fabrication issues to be considered in future hardware programs are defined. The fabrication and testing at 500 F of a graphite/polyimide center wing box beam using OV-10A aircraft criteria was accomplished. The baseline design of this box was developed in a series of studies of other advanced composite materials: glass/epoxy, boron/epoxy, and boron/polyimide. The use of this basic design permits ready comparison of the performance of graphite/polyimide with these materials. Modifications to the baseline composite design were made only in those areas effected by the change of materials. Processing studies of graphite fiber polyimide resins systems resulted in the selection of a Modmor II/Gemon L material.

  9. Irradiation Induced Creep of Graphite

    SciTech Connect

    Burchell, Timothy D; Murty, Prof K.L.; Eapen, Dr. Jacob

    2010-01-01

    The current status of graphite irradiation induced creep strain prediction is reviewed and the major creep models are described. The ability of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work is made and the need for improved creep models across multi-scales is highlighted.

  10. Study on Orbital Liquid Transport and Interface Behavior in Vane Tank

    NASA Astrophysics Data System (ADS)

    Kang, Qi; Rui, Wei

    2016-07-01

    Liquid propellant tank is used to supply gas free liquid for spacecraft as an important part of propulsion system. The liquid behavior dominated by surface tension in microgravity is obviously different with that on the ground, which put forward a new challenge to the liquid transport and relocation. The experiments which are investigated at drop tower in National Microgravity Lab have concentrated on liquid relocation following thruster firing. Considered that the liquid located at the bottom in the direction of the acceleration vector, a sphere scale vane tank is used to study the liquid-gas interface behaviors with different acceleration vector and different filling independently and we obtain a series of stable equilibrium interface and relocation time. We find that there is an obvious sedimentation in the direction of acceleration vector when fill rate greater than 2% fill. Suggestions have been put forward that outer vanes transferring liquid to the outlet should be fixed and small holes should be dogged at the vane close to the center post to improve the liquid flow between different vanes when B0 is greater than 2.5. The research about liquid transport alone ribbon vanes is simulated though software Flow3D. The simulation process is verified by comparing the liquid lip and vapor-liquid interface obtained from drop tower experiment and simulation result when fill rate is 15%. Then the influence of fill rate, numbers of vanes and the gap between vane and wall is studied through the same simulate process. Vanes' configurations are also changed to study the effect on the lip and liquid volume below some section. Some suggestions are put forward for the design of vanes.

  11. Bidimensional intercalation of Ge between SiC(0001) and a heteroepitaxial graphite top layer

    SciTech Connect

    Kubler, L.; Dentel, D.; Bischoff, J.-L.; Derivaz, M.; Aiet-Mansour, K.; Diani, M.

    2005-09-15

    High temperature annealing of 4H- or 6H-SiC(0001) crystals is well known to desorb Si from the surface and to generate a C-rich (6{radical}3x6{radical}3)R30 deg. (6{radical}3) reconstruction explained as a graphite monolayer in heteroepitaxial registry with the substrate. Ge deposition at room temperature and in the monolayer range on this graphitized reconstruction results in Ge islands. Using a number of surface techniques, we follow subsequent Ge morphology evolutions as a function of isochronal post-annealing treatments at increasing temperatures. In a particular temperature window Ge reacts with the substrate by diffusion under the graphite planes and wets the Si-terminated SiC surface. In spite of this bidimensional insertion of a Ge layer, the epitaxial relationship between the SiC substrate and the graphite is maintained as shown by very clear graphite-(1x1) LEED or RHEED patterns. They denote extended and well-ordered graphite planes at the surface of a graphite/Ge/SiC heterostructure. XPS analyses reveal a complete passivation of the intercalated Ge layer against oxidation by the overlying graphite sheets. Moreover, drastic spectroscopic changes on the bulk-SiC Si 2p and C 1s core levels are observed, depending on whether graphite(6{radical}3)/SiC or graphite(1x1)/Ge/SiC terminations are analyzed. In the latter case, the observed core level splitting of the bulk components is interpreted by a significant upward band bending ({approx}1.2 eV) of the n-doped SiC, making this second interface to act as a Schottky barrier. Above 1300 deg. C, a delayed Ge desorption takes place that allows the graphite sheets to re-form in their initial 6{radical}3 form, i.e., without Ge and with flatter bands.

  12. First-principles study of point defects at a semicoherent interface

    PubMed Central

    Metsanurk, E.; Tamm, A.; Caro, A.; Aabloo, A.; Klintenberg, M.

    2014-01-01

    Most of the atomistic modeling of semicoherent metal-metal interfaces has so far been based on the use of semiempirical interatomic potentials. We show that key conclusions drawn from previous studies are in contradiction with more precise ab-initio calculations. In particular we find that single point defects do not delocalize, but remain compact near the interfacial plane in Cu-Nb multilayers. We give a simple qualitative explanation for this difference on the basis of the well known limited transferability of empirical potentials. PMID:25524061

  13. Dual-probe scanning tunneling microscope for study of nanoscale metal-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Yi, W.; Kaya, I. I.; Altfeder, I. B.; Appelbaum, I.; Chen, D. M.; Narayanamurti, V.

    2005-06-01

    Using a dual-probe scanning tunneling microscope, we have performed three-terminal ballistic electron emission spectroscopy on Au /GaAs(100) by contacting the patterned metallic thin film with one tip and injecting ballistic electrons with another tip. The collector current spectra agree with a Monte-Carlo simulation based on modified planar tunneling theory. Our results suggest that it is possible to study nanoscale metal-semiconductor interfaces without the requirement of an externally-contacted continuous metal thin film.

  14. Ion Scattering Studies of Silicon Surfaces and Interfaces: Structure and Neutralization.

    NASA Astrophysics Data System (ADS)

    Haight, Richard Alan

    This thesis chronicles three experiments which represent the major thrust of studies performed during my tenure as a graduate student at the State University of New York at Albany. Chapter 1 introduces the fundamental considerations of the physics of ion scattering and its applications to studies of surfaces, interfaces and ion neutralization. Basic formula are stated and the two atom model using the Coulomb interaction potential is developed as an approximate prediction of the surface peak intensity. The second chapter discusses a study of the neutralization of 75-180 KeV He ions scattered from clean and Cs covered Si (100); an experiment performed at Bell Laboratories. It is shown that ion neutralization occurs at the surface of the solid; the ion retains no memory of its journey within the bulk. It is also observed that the ion fraction exhibits no dependence upon takeoff angle, a result which differs markedly from the exponential angular dependence observed at lower velocities. Changes in the Si scattered ion fraction upon cesiation of the Si surface are correlated with the work function change observed by other workers. A model is proposed, and developed in mathematical detail, which includes resonant transitions to the motionally broadened He n=2 quantum level and is compared with the experimental data. The third chapter discusses an ion scattering study of the interfacial structure of the Si-SiO(,2) interface. It is shown that the oxide is stoichiometric to within (TURN)1 monolayer of the interface. Measurements to determine the magnitude and direction of the Si atomic displacements at the interface were compared with Monte Carlo computer simulations and show small lateral and larger vertical displacements in two layers. A model, consistent with the data, is proposed and the effects of these displacements are related qualitatively with theory. The fourth chapter describes a thin Si (111) crystal transmission channeling experiment. In this experiment, the use

  15. First-principles study of point defects at a semicoherent interface

    DOE PAGESBeta

    Metsanurk, E.; Tamm, A.; Caro, A.; Aabloo, A.; Klintenberg, M.

    2014-12-19

    Most of the atomistic modeling of semicoherent metal-metal interfaces has so far been based on the use of semiempirical interatomic potentials. Here, we show that key conclusions drawn from previous studies are in contradiction with more precise ab-initio calculations. In particular we find that single point defects do not delocalize, but remain compact near the interfacial plane in Cu-Nb multilayers. Lastly, we give a simple qualitative explanation for this difference on the basis of the well known limited transferability of empirical potentials.

  16. Resonant photoemission study of the 4f spectral function of cerium in Ce/Fe(100) interfaces

    SciTech Connect

    Witkowski, N.; Bertran, F.; Gourieux, T.; Kierren, B.; Malterre, D.; Panaccione, G. |

    1997-11-01

    In this paper, we present a resonant photoemission study of the cerium 4f spectral function in Ce/Fe(100) interfaces. By covering cerium ultrathin films with lanthanum, we completely suppress the surface contribution of the spectra. Then we show that the cerium atoms at the interface are in an intermediate valent state, whereas the f{sup 1} configuration is stabilized in the top layer. This method allows us to obtain the genuine 4f spectral function of the interface, and could be extended to a study of Ce-based compounds. {copyright} {ital 1997} {ital The American Physical Society}

  17. Study on crystal-melt interface shape of sapphire crystal growth by the KY method

    NASA Astrophysics Data System (ADS)

    Liu, Weina; Lu, Jijun; Chen, Hongjian; Yan, Wenbo; Min, Chunhua; Lian, Qingqing; Wang, Yunman; Cheng, Peng; Liu, Caichi; Xu, Yongliang

    2015-12-01

    In this article, the influence of the flow field structure and temperature gradient of forefront interface on the shape of crystal-melt interface which may reflect the interface stability were analyzed through the method of numerical simulation by using CGSim software. In order to get a suitable interface shape and grow high-quality sapphire crystal, the heater arrangement should be adjusted during the KY process. The results indicate that the effect of Marangoni convection cannot be neglected at the last stage, the crystal-melt interface is governed by the flow field structure and the temperature gradient in melt at the crystal-melt interface. The phenomenon of shoulder concave appears at the stage of shoulder turning and interface inversion appears at the last stage during the crystal growth is discussed. Adjusting heater arrangement may effectively optimize the shape of crystal-melt interface.

  18. Slurry sampling graphite furnace atomic absorption spectrometry: a preliminary examination of results from an international collaborative study

    NASA Astrophysics Data System (ADS)

    Miller-Ihli, N. J.

    1995-06-01

    An international collaborative study was initiated to evaluate the current state-of-the-art for solid sampling. Samples were sent to 28 laboratories and data were received from 18 collaborators, 16 of which reported slurry results. A preliminary check of performance using NIST SRM 1643c acidified water, showed that at least 13 laboratories were able to provide accurate results within ±10% of the mean certified Pb and Cr concentrations. The focus of this work was slurry analytical data reported by collaborators. Average performance by collaborators for the determination of Pb in NIST SRM 2704 Buffalo River Sediment was 103% recovery based on the mean certified reference value and was 84% recovery based on the mean certified reference value for NRCC PACS-1, a marine estuarine sediment, which was identified to collaborators as an unknown sediment. Average performance by collaborators for Cr in SRM 2704 was 96% based on the mean certified reference value and was 78% recovery based on the mean certified reference value for PACS-1. The use of secondary wavelengths and the importance of analysis of a representative subsample are highlighted. Possible problems leading to inaccurate results being reported by collaborators are discussed including the use of mini-flows, matrix modifiers, low atomization temperatures, short atomization times, and expulsion losses.

  19. A density functional study of silver clusters on a stepped graphite surface: formation of self-assembled nano-wires.

    PubMed

    Singh, Akansha; Sen, Prasenjit

    2015-05-21

    Adsorption and diffusion of silver adatoms and clusters containing up to eight atoms on an HOPG substrate with an armchair step are studied using density functional methods. Step edges act as attractive sinks for adatoms and clusters. The diffusion barrier of an Ag adatom along the step edge is much larger than that on a clean terrace. At zero temperature, Ag clusters either distort or dissociate by forming covalent bonds with the edge C atoms. At 600 K, Ag5 and Ag8 clusters diffuse to the step edges, and then break up so as to maximize Ag-C bonds. The Ag atoms try to form a nanowire structure along the step edge. At such high temperatures, diffusion of clusters along the step edge involves diffusion of individual Ag atoms not bonded to the edge C atoms. Assumption of complete immobility of clusters trapped at step edges in the Gates-Robins model is not valid at high temperatures in this particular system. PMID:25903308

  20. Analysis of cementless implants using interface nonlinear friction--experimental and finite element studies.

    PubMed

    Dammak, M; Shirazi-Adl, A; Zukor, D J

    1997-02-01

    Measured interface nonlinear friction properties are used to develop models to study the short-term fixation response of smooth- and porous-surfaced posts, bone screws, and plates fixed with and without posts/screws. Experimental studies are carried out to validate the model predictions and identify the relative role of posts and screws in fixation of a plate on a polyurethane block under symmetric/eccentric axial compression loads. The idealized Coulomb's friction is also used for the sake of comparison. The incorporation of measured nonlinear, rather than the idealized Coulomb, friction is essential to compute realistic results. For plate fixation, the experimental and finite element results show that the screw fixation yields the stiffest response followed by the smooth- and then porous-coated post fixation. For example, under 1000 N eccentric axial compression, the edge of the plate opposite the loaded edge is measured to lift by 1147 +/- 72, 244 +/- 38, or 112 +/- 28 microns, respectively, for the cases with no fixation, with smooth-surfaced posts, or with screws. The corresponding models predict, respectively, values of 1538, 347, or 259 microns and also 556 microns for the plate fixed with porous coated posts. The satisfactory agreement between numerical and experimental results confirms the importance of proper interface modelling for the analysis of posts, screws, and complex fixation systems. This becomes further evident when considering cementless implants in which the bone-implant interface exhibits relatively large displacements as the maximum resistance force is reached. The developed models can be used to investigate the post-operative short-term stability of various cementless implant designs. PMID:9001932

  1. Mechanical properties of the interface structure of nanodiamond composite films: First-principles studies

    NASA Astrophysics Data System (ADS)

    Zhang, Suhui; Liu, Xuejie; Jiang, Yongjun; Ren, Yuan; Li, Suozhi

    2016-02-01

    The elastic properties of the interface structure of nanodiamond composite films are investigated using first-principles calculations. The nanodiamond grains in the films are surrounded by a monolayer heterogeneous interface. The interface phase comprises B, Si, P, and Ge. The elastic constants, bulk, shear and Young's modulus of the interface structures are all obtained with first principle calculations. Calculated elastic constants of the diamond (0 0 1) interface are larger than those of the (1 1 1) interface. For the B, Si, P, and Ge interface structures, as the average atomic distance increases, the average Young's modulus decrease, which follows the sequence EbarB>EbarSi >EbarP > EbarGe , with corresponding values of 927.05, 843.841, 840.152, and 819.805 GPa. The ductility and plasticity, as well as the anisotropy values (A and AU) of the interface structures were discussed based on the obtained mechanical parameters. The results show that P interface structures demonstrate ductile property when stressed longitudinally, whereas the other interface structures are all brittle. Then the visualization of the directional dependence of the Young's modulus are also presented. These reflected an interesting results. For the B, Si, and Ge interface structures, whether they show isotropy or anisotropy depends on the crystal structure, while it depends on the direction of the applied strain for the P interface structures.

  2. Laser studies of chemical dynamics at the gas-solid interface

    NASA Astrophysics Data System (ADS)

    Cavanagh, Richard R.; King, David S.

    The DOE funded research program Laser Studies of Chemical Dynamics at the Gas-Solid Interface has taken a detailed, microscopic view of molecules desorbed from surfaces in order to gain an understanding of energy flow and interaction potentials and how these control chemical reactivity at interfaces. Successful completion of these experiments required technical expertise both in surface science and laser-based molecular dynamics, a collaborative situation that exists in the NIST center for Atomic, Molecular and Optical Physics. During the three year period covered by this progress report, our goal was to use state-resolved techniques to examine a single chemisorption system in detail, and to observe how changes in the interaction potential or method of surface excitation are manifest in the desorption dynamics. The system chosen was NO/Pt(111). Studies were undertaken in which the effects on the NO-Pt interaction potential of coadsorbates--both weakly (CO) and strongly (NH(sub 3)) interacting-- could be examined. In addition, attempts were to be made to study non- equilibrium dynamics by using pulsed laser heating.

  3. Mechanism and modulation of terahertz generation from a semimetal - graphite

    NASA Astrophysics Data System (ADS)

    Ye, Tong; Meng, Sheng; Zhang, Jin; E, Yiwen; Yang, Yuping; Liu, Wuming; Yin, Yan; Wang, Li

    2016-03-01

    Semi-metals might offer a stronger interaction and a better confinement for terahertz wave than semiconductors, while preserve tunability. Particularly, graphene-based materials are envisioned as terahertz modulators, filters and ultra-broadband sources. However, the understanding of terahertz generation from those materials is still not clear, thus limits us recognizing the potential and improving device performances. Graphite, the mother material of graphene and a typical bulk semi-metal, is a good system to study semi-metals and graphene-based materials. Here we experimentally modulate and maximize the terahertz signal from graphite surface, thus reveal the mechanism - surface field driving photon induced carriers into transient current to radiate terahertz wave. We also discuss the differences between graphite and semiconductors; particularly graphite shows very weak temperature dependency from room temperature to 80 °C. Above knowledge will help us understand terahertz generations, achieve maximum output and electric modulation, in semi-metal or graphene based devices.

  4. Powder properties of hydrogenated ball-milled graphite

    SciTech Connect

    Zhang, Y.; Wedderburn, J.; Harris, R.; Book, D.

    2014-12-15

    Ball milling is an effective way of producing defective and nanostructured graphite. In this work, the hydrogen storage properties of graphite, ball-milled in a tungsten carbide milling pot under 3 bar hydrogen for various times (0–40 h), were investigated by TGA-Mass Spectrometry, XRD, SEM and laser diffraction particle size analysis. For the conditions used in this study, 10 h is the optimum milling time resulting in desorption of 5.5 wt% hydrogen upon heating under argon to 990 °C. After milling for 40 h, the graphite became significantly more disordered, and the amount of desorbed hydrogen decreased. After milling up to 10 h, the BET surface area increased while particle size decreased; however, there is no apparent correlation between these parameters, and the hydrogen storage properties of the hydrogenated ball-milled graphite.

  5. First principles studies of interface dielectric properties of polymer/metal-oxide nanocomposites

    NASA Astrophysics Data System (ADS)

    Yu, Liping

    This thesis is devoted to studying interface dielectric properties of polymer nanocomposites from first principles. We aim to understand at atomic scale the role of interface effects and the dielectric finite size effects of nanoparticles in determining the effective dielectric properties of polymer nanocomposites. To study surface effects from first principles, we first investigate the two common methods, namely dipole correction and Coulomb cutoff, used to eliminate the artificial effects introduced by using the supercell approximation. We implement Coulomb cutoff technique in a plane-wave-based density functional theory code and compare it with dipole correction for the same system under the same conditions. By comparison, both methods are shown to be equivalent and able to remove the artificial effects of periodic images very accurately. We also find that a combination of these two methods offers an easy way to distinguish the localized bound states of interest from highly delocalized unoccupied states while using a relatively small supercell, and to ascertain the convergence of the results with respect to supercell size. To understand the dielectric properties at the atomic scale, we develop a new nanoscale averaging model to connect the macroscopic quantities to the corresponding microscopic ones. This model allows us to compute the spatially resolved local dielectric permittivity, including the critically important ionic contributions, for interfaces and other complex structures. In this model, a simple way of evaluating real-space decay length of the nonlocal dielectric functions is also proposed. By using the dipole correction and our averaging model in supercells, we calculate the optical and static local dielectric permittivity profiles for polymer (polypropylene)/metal-oxide (PbTiO3 and alumina) nanocomposites. Our ab-initio results show that metal-oxide/polymer interface effects are very localized and are mostly confined to the metal-oxide surface side

  6. A first-principles study on interaction of Mg/Ni interface and its hydrogen absorption characteristics

    NASA Astrophysics Data System (ADS)

    Chen, Yuying; Dai, Jianhong; Xie, Ruiwen; Song, Yan

    2016-07-01

    We have investigated the interaction of Mg/Ni interface and its hydrogen adsorption characteristics using first-principles calculations to obtain a better understanding of the Mg/Ni interface as a hydrogen storage material. The smallest work of adhesion of Mg/Ni interface is 4.28 J/m2 with AB stacking sequence in the studied systems. Hydrogen adsorption energy and electronic structures were evaluated to study the interaction characteristics between hydrogen and Mg/Ni interface. The hydrogen adsorption is energetically favored on all considered sites. The hydrogen atom prefers to adsorb on the tetrahedral site of the Ni side of the interface owning the lowest adsorption energy. The plane-averaged charge density and the density of states analysis indicate that the absorption of hydrogen could stabilize the Mg/Ni interface owing to the strongly bonding interactions between hydrogen atom and the host Mg and Ni atoms. Therefore, Mg/Ni interface provides a promising medium for hydrogen storage.

  7. Latent laser-induced graphitization of diamond

    NASA Astrophysics Data System (ADS)

    Kononenko, V. V.; Gololobov, V. M.; Konov, V. I.

    2016-03-01

    Basic features and mechanism of femtosecond laser graphitization of diamond surface were studied in the two regimes of irradiation: (1) by an intensive (>10 J/cm2) single shot and (2) by a train of pulses with near-threshold intensity (~1-10 J/cm2). Special attention was paid to the so-called accumulative regime, when multipulse laser treatment results in prolonged delay of an appearance of crystal modification of the crystal. The light absorption mechanisms dominating in each regime are discussed. The experiments with fundamental (800 nm), second (400 nm) and third (266 nm) harmonics of Ti-sapphire laser (100 fs) have revealed that thermally stimulated processes play an essential role in latent diamond graphitization.

  8. Interfacial Effects on the Thermal and Mechanical Properties of Graphite/Copper Composites. Final Contractor Report Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra Marie

    1995-01-01

    Graphite surfaces are not wet by pure copper. This lack of wetting has been responsible for a debonding phenomenon that has been found in continuous graphite fiber reinforced copper matrix composites subjected to elevated temperatures. By suitably alloying copper, its ability to wet graphite surfaces can be enhanced. Information obtained during sessile drop testing has led to the development of a copper-chromium alloy that suitably wets graphite. Unidirectionally reinforced graphite/copper composites have been fabricated using a pressure infiltration casting procedure. P100 pitch-based fibers have been used to reinforce copper and copper-chromium alloys. X-ray radiography and optical microscopy have been used to assess the fiber distribution in the cast composites. Scanning electron microscopy and Auger electron spectroscopy analyses were conducted to study the distribution and continuity of the chromium carbide reaction phase that forms at the fiber/matrix interface in the alloyed matrix composites. The effects of the chromium in the copper matrix on the mechanical and thermal properties of P100Gr/Cu composites have been evaluated through tensile testing, three-point bend testing, thermal cycling and thermal conductivity calculations. The addition of chromium has resulted in an increased shear modulus and essentially zero thermal expansion in the P100Gr/Cu-xCr composites through enhanced fiber/matrix bonding. The composites have longitudinal tensile strengths in excess of 700 MPa with elastic moduli of 393 GPa. After 100 hr at 760 deg C 84 percent of the as-cast strength is retained in the alloyed matrix composites. The elastic moduli are unchanged by the thermal exposure. It has been found that problems with spreading of the fiber tows strongly affect the long transverse tensile properties and the short transverse thermal conductivity of the P100Gr/Cu-xCr composites. The long transverse tensile strength is limited by rows of touching fibers which are paths of

  9. Ferrix Chloride-Graphite Intercalation Compounds Prepared From Graphite Flouride

    NASA Technical Reports Server (NTRS)

    Hung, Ching-Cheh

    1995-01-01

    The reaction between graphite fluoride and ferric chloride was observed in the temperature range of 300 to 400 C. The graphite fluorides used for this reaction have an sp(sup 3) electronic structure and are electrical insulators. They can be made by fluorinating either carbon fibers or powder having various degrees of graphitization. Reaction is fast and spontaneous and can occur in the presence of air. The ferric chloride does not have to be predried. The products have an sp(sup 2) electronic structure and are electrical conductors. They contain first-stage FeCl3 intercalated graphite. Some of the products contain FeCl2 (center dot) 2H2O, others contain FeF3, in concentrations that depend on the intercalation condition. The graphite intercalated compounds (GIC) deintercalated slowly in air at room temperature, but deintercalated quickly and completely at 370 C. Deintercalation is accompanied by the disappearance of iron halides and the formation of rust (hematite) distributed unevenly on the fiber surface. When heated to 400 C in pure N2 (99.99 vol%), this new GIC deintercalates without losing its molecular structure. However, when the compounds are exposed to 800 C N2, in a quartz tube, they lost most of their halogen atoms and formed iron oxides (other than hematite), distributed evenly in or on the fiber.

  10. MHD modeling of atlas experiments to study transverse shear interface interactions

    SciTech Connect

    Cochran, F. L.; Hammerberg, J. E.; Keinigs, R. K.; Faehl, R. J.

    2001-01-01

    The transverse shear established at the interface of two solids moving at differential velocities on the order of the sound speed is being studied in experiments on the ATLAS capacitor bank at Los Alamos. The ATLAS bank has finished certification tests and has demonstrated peak currents of 27.5 MA into an inductive load with a risetime of 5 microseconds. One- and two-dimensional MHD calculations have been performed in support of these 'friction-like' ATLAS experiments. Current flowing along the outer surface of a thick aluminum liner, 10 mm thick at impact with the interaction target, accelerates the liner to velocities of {approx}1.0-1.5 km/s. This cylindrically imploding liner impacts a target assembly composed of alternating disks of high- and low-density materials. Different shock speeds in the two materials leads to a differential velocity along the interface. Shock heating, elastic-plastic flow, and stress transport are included in the calculations. Material strength properties are modeled with a Steinburg-Guinan treatment in these first studies. Various design configurations for the ATLAS experiments are now being considered and will be presented.

  11. Tunneling of electrons via rotor-stator molecular interfaces: Combined ab initio and model study

    NASA Astrophysics Data System (ADS)

    Petreska, Irina; Ohanesjan, Vladimir; Pejov, Ljupčo; Kocarev, Ljupčo

    2016-07-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green's Function Formalism.

  12. Experimental study of the minority-carrier transport at the polysilicon-monosilicon interface

    NASA Astrophysics Data System (ADS)

    Neugroschel, A.; Arienzo, M.; Isaac, R. D.; Komem, Y.

    1985-04-01

    This paper presents the results of an experimental study designed to explore both qualitatively and quantitatively the mechanism of the improved current gain in bipolar transistors with polysilicon emitter contacts. Polysilicon contacts were deposited and heat treated at different conditions. The electrical properties were measured using p-n junction test structures that are much more sensitive to the contact properties than are bipolar transistors. A simple phenomenological model was used to correlate the structural properties with electrical measurements. Possible transport mechanisms are examined and estimates are made about upper bounds on transport parameters in the principal regions of the devices. The main conclusion of this study is that the minority-carrier transport in the polycrystalline silicon is dominated by a highly disordered layer at the polysilicon-monosilicon interface characterized by very low minority-carrier mobility. The effective recombination velocity at the n(+) polysilicon-n(+) monosilicon interface was found to be a strong function of fabrication conditions. The results indicate that the recombination velocity can be much smaller than 10,000 cm/s.

  13. The effect of copolymers on the interfaces in incompatible homopolymers blend: Molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Ryu, Jiho; Lee, Won Bo

    2015-03-01

    Using molecular dynamics simulations the effect of copolymers as compatibilizer for reducing interfacial tension and enhancement of interfacial adhesion at the interface of thermodynamic unfavorable homopolymers blend is studied with block- and graft-copolymers. We have calculated local pressure tensor of system along the axis perpendicular to interface, varying bending potential energy of one part, which consist of just one kind of beads, of copolymer chain to examine the effect of stiffness of surfactin molecules. Here we consider symmetric diblock copolymer (f =1/2) having 1/2 N make of beads of type A and the other part made of beads of type B, and graft copolymer having backbone linear chain consist of 1/2 N beads of type of A and branched with two side-chain consist of 1/4 N beads of type B. All simulations were performed under the constant NPT ensemble at T* =1, ρ* ~0.85. Also we studied changes of effect of copolymers with increasing pairwise repulsive interaction potential between two beads of types A and B while homopolymers chain length are fixed, N =30. Chemical and Biomolecular Engineering, Sogang University, Seoul, South Korea.

  14. Dispersion of pollutants over land-water-land interface: Study using CALPUFF model

    NASA Astrophysics Data System (ADS)

    Indumati, S.; Oza, R. B.; Mayya, Y. S.; Puranik, V. D.; Kushwaha, H. S.

    The CALMET/CALPUFF modeling system is used to study atmospheric dispersion of pollutant over land-water-land interface. It is shown that the default scheme used by CALMET/CALPUFF to handle inhomogeneous surfaces does not take care of the different turbulence characteristics over such surfaces. An alternative method is suggested to incorporate different turbulent characteristics over inhomogeneous surfaces by using the appropriate atmospheric stability category over different surfaces. The results show that the presence of water body can increase the ground level concentration by a factor of up to 50 for the width of water body varying from 1 km to 5 km. It is also shown that the effect of water body on the ground level concentration decreases as the distance from the water body increases. The present study showed that for land-water interface, the realistic specification of turbulence characteristics over inhomogeneous surfaces significantly changes the estimation of ground level concentration as compared to the default scheme available in the CALMET/CALPUFF modeling system and is expected to give realistic results.

  15. Ab initio study of the epitaxial ZrO2 /Si interface

    NASA Astrophysics Data System (ADS)

    Dogan, Mehmet; Kumah, Divine; Ahn, Charles; Walker, Frederick; Ismail-Beigi, Sohrab

    2015-03-01

    Growing thin films of crystalline metal oxides on semiconductors has been of much scientific interest because of the potential applications of such systems in electronic devices. One particular research goal is to achieve ferroelectricity in a crystalline and thin oxide film that is epitaxial on a semiconductor. This would enable one to realize non-volatile field-effect transistors where the state of the system is encoded in the polarization direction of the oxide. In this work, we study oxides that are not ferroelectric in the bulk but become ferroelectric as an ultrathin film on a semiconductor such as silicon. Recent developments in epitaxial growth methods also permit fabrication of such systems. Here, we use density functional theory to study the interface between ZrO2 and Si. When the oxide is only 1 monolayer thick, we find a set of stable structures with a variety of positive and negative out-of-plane ferroelectric polarizations. We present an analysis of these structures as a function of oxide thickness and the size of interface unit cell. Furthermore, the ZrO2 can be used as a buffer layer to induce ferroelectricity in ultrathin perovskite oxides such as SrTiO3 on Si which can couple the oxide polarization to the silicon carrier density. This work is supported by the National Science Foundation through Grant MRSEC NSF DMR-1119826.

  16. A study of System Interface Sets (SIS) for the host, target and integration environments of the Space Station Program (SSP)

    NASA Technical Reports Server (NTRS)

    Mckay, Charles; Auty, David; Rogers, Kathy

    1987-01-01

    System interface sets (SIS) for large, complex, non-stop, distributed systems are examined. The SIS of the Space Station Program (SSP) was selected as the focus of this study because an appropriate virtual interface specification of the SIS is believed to have the most potential to free the project from four life cycle tyrannies which are rooted in a dependance on either a proprietary or particular instance of: operating systems, data management systems, communications systems, and instruction set architectures. The static perspective of the common Ada programming support environment interface set (CAIS) and the portable common execution environment (PCEE) activities are discussed. Also, the dynamic perspective of the PCEE is addressed.

  17. Electrochemical oxidation of phenol using graphite anodes

    SciTech Connect

    Awad, Y.M.; Abuzaid, N.S.

    1999-02-01

    The effects of current and pH on the electrochemical oxidation of phenol on graphite electrodes is investigated in this study. There was no sign of deterioration of the graphite bed after 5 months of operation. Phenol removal efficiency was a function of the current applied and was around 70% at a current of 2.2 A. The increase of phenol removal efficiency with current is attributed to the increase of ionic transport which increases the rate of electrode reactions responsible for the removal process. The percentage of complete oxidation of phenol increases with current, with a maximum value of about 50%. However, at pH 0.2 it is slightly higher than that at pH 0.5 at all currents. The phenol removal rate increases with increases of current and pH. While the current (CO{sub 2}) efficiency reaches a maximum value in the current range of 1.0--1.2 A, it increases with an increase of acid concentration. The findings of this study have important implications: while anodic oxidation of phenol on graphite can achieve acceptable removal of phenol, the extent of oxidation should not be overlooked.

  18. Design of a monochromatic ellipsometer for studies at the solid-liquid interface

    NASA Astrophysics Data System (ADS)

    Pai-Panandiker, R. S.; Dorgan, J. R.

    1995-02-01

    A new design for a monochromatic ellipsometer used for studies at the solid-liquid interface is described. The design of the ellipsometer incorporates two novel features—a special optical glass cell and a thermally controlled sample oven. The ellipsometer design allows for in situ kinetic studies through use of the optical glass cell. Furthermore, the apparatus is modified to allow thermal equilibration over a range of temperatures. The temperature response of the cell assembly is presented and the response time is seen to be approximately 1 h. Data on the adsorption of a diblock copolymer [poly(ethylene oxide)-block-polystyrene] are presented; the analyzed data agree with previous studies on the same system.

  19. Study of the roles of chemical modifiers in determining boron using graphite furnace atomic absorption spectrometry and optimization of the temperature profile during atomization.

    PubMed

    Yamamoto, Yuhei; Shirasaki, Toshihiro; Yonetani, Akira; Imai, Shoji

    2015-01-01

    The measurement conditions for determining boron using graphite furnace-atomic absorption spectrometry (GF-AAS) were investigated. Differences in the boron absorbance profiles were found using three different commercially available GF-AAS instruments when the graphite atomizers in them were not tuned. The boron absorbances found with and without adjusting the graphite atomizers suggested that achieving an adequate absorbance for the determination of boron requires a sharp temperature profile that overshoots the target temperature during the atomization process. Chemical modifiers that could improve the boron absorbance without the need for using coating agents were tested. Calcium carbonate improved the boron absorbance but did not suppress variability in the peak height. Improvement of boron absorbance was comparatively less using iron nitrate or copper nitrate than using calcium carbonate, but variability in the peak height was clearly suppressed using iron nitrate or copper nitrate. The limit of detection was 0.0026 mg L(-1) when iron nitrate was used. It appears that iron nitrate is a useful new chemical modifier for the quick and simple determination of boron using GF-AAS. PMID:25958863

  20. Interface Effects in Sunlight-Driven Ag/g-C3N4 Composite Catalysts: Study of the Toluene Photodegradation Quantum Efficiency.

    PubMed

    Fontelles-Carceller, Olga; Muñoz-Batista, Mario J; Fernández-García, Marcos; Kubacka, Anna

    2016-02-01

    Metallic silver (ranging from 1 to 10 wt %) was deposited onto a graphite-like carbon nitride photocatalyst through a microemultion method. Surface, morphological, and structural properties of the resulting materials were characterized using BET and porosity measurements, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and UV-vis and photoluminescence spectroscopy. The activity of the composite samples under sunlight-type and visible illumination was measured for toluene photodegradation and was analyzed by means of the reaction rate and the quantum efficiency parameter. To obtain the latter observable, the lamp emission properties as well as the radiation field interaction with the catalyst inside the reactor were modeled and numerically calculated. The stability of the samples under both illumination conditions was also studied. The results evidence that the composite samples containing 1-10 silver wt % outperform carbon nitride for sunlight-type and visible illumination, but the optimal use of the charge generated after light absorption is obtained for the sample with 1 wt % of silver acording to the quantum efficiency calculation. The study shows that the optimum silver-g-C3N4 contact is able to outperform TiO2 reference systems (nano-TiO2 and P25) under sunlight illumination and points out that this occurs as a direct consequence of the charge handling through the interface between catalyst components. This indicates that composite systems based on g-C3N4 can be competitive in sunlight-triggered photodegradation processes to eliminate tough polluctants such as toluene, rendering active and stable systems. PMID:26714203