Characteristics of thermally-induced transverse cracks in graphite epoxy composite laminates

NASA Technical Reports Server (NTRS)

Adams, D. S.; Bowles, D. E.; Herakovich, C. T.

1983-01-01

The characteristics of thermally induced transverse cracks in T300/5208 graphite-epoxy cross-ply and quasi-isotropic laminates were investigated both experimentally and analytically. The formation of transverse cracks and the subsequent crack spacing present during cool down to -250 F (116K) and thermal cycling between 250 and -250 F (116 and 394K) was investigated. The state of stress in the vicinity of a transverse crack and the influence of transverse cracking on the laminate coefficient of thermal expansion (CTE) was predicted using a generalized plane strain finite element analysis and a modified shear lag analysis. A majority of the cross-ply laminates experienced transverse cracking during the initial cool down to -250 F whereas the quasi-isotropic laminates remained uncracked. The in situ transverse strength of the 90 degree layers was more than 1.9 times greater than the transverse strength of the unidirectional 90 degree material for all laminates investigated.

Effects of partial interlaminar bonding on impact resistance and loaded-hole behavior of graphite/epoxy quasi-isotropic laminates

NASA Technical Reports Server (NTRS)

Illg, W.

1986-01-01

A partial-bonding interlaminar toughening concept was evaluated for resistance to impact and for behavior of a loaded hole. Perforated Mylar sheets were interleaved between all 24 plies of a graphite/epoxy quasi-isotropic lay-up. Specimens were impacted by aluminum spheres while under tensile or compressive loads. Impact-failure thresholds and residual strengths were obtained. Loaded-hole specimens were tested in three configurations that were critical in bearing, shear, or tension. Partial bonding reduced the tensile and compressive strengths of undamaged specimens by about one-third. For impact, partial bonding did not change the threshold for impact failure under tensile preload. However, under compressive preload, partial bonding caused serious degradation of impact resistance. Partial bonding reduced the maximum load-carrying capacity of all three types of loaded-hole specimens. Overall, partial bonding degraded both impact resistance and bearing strength of holes.

An endochronic theory for transversely isotropic fibrous composites

NASA Technical Reports Server (NTRS)

Pindera, M. J.; Herakovich, C. T.

1981-01-01

A rational methodology of modelling both nonlinear and elastic dissipative response of transversely isotropic fibrous composites is developed and illustrated with the aid of the observed response of graphite-polyimide off-axis coupons. The methodology is based on the internal variable formalism employed within the text of classical irreversible thermodynamics and entails extension of Valanis' endochronic theory to transversely isotropic media. Applicability of the theory to prediction of various response characteristics of fibrous composites is illustrated by accurately modelling such often observed phenomena as: stiffening reversible behavior along fiber direction; dissipative response in shear and transverse tension characterized by power-laws with different hardening exponents; permanent strain accumulation; nonlinear unloading and reloading; and stress-interaction effects.

Development of a Priest interferometer for measurement of the thermal expansion of a graphite epoxy in the temperature range 116-366 K

NASA Technical Reports Server (NTRS)

Short, J. S.; Hyer, M. W.; Bowles, D. E.; Tompkins, S. S.

1982-01-01

The thermal expansion behavior of graphite epoxy laminates between 116 and 366 degrees Kelvin was investigated using as implementation of the Priest interferometer concept. The design, construction and use of the interferometer along with the experimental results it was used to generate are described. The experimental program consisted of 25 tests on 25.4 mm and 6.35 mm wide, 8 ply pi/4 quasi-isotropic T300-5208 graphite/epoxy specimens and 3 tests on a 25.4 mm wide unidirectional specimen. Experimental results are presented for all tests along with a discussion of the interferometer's limitations and some possible improvements in its design.

Application of X-ray microcomputed tomography in the characterization of irradiated nuclear fuel and material specimens

DOE PAGES

Silva, Chinthaka M.; Snead, Lance Lewis; Hunn, John D.; ...

2015-08-03

X-ray microcomputed tomography (µCT) was applied in characterizing the internal structures of a number of irradiated materials, including carbon-carbon fibre composites, nuclear-grade graphite and tristructural isotropic-coated fuel particles. Local cracks in carbon-carbon fibre composites associated with their synthesis process were observed with µCT without any destructive sample preparation. Pore analysis of graphite samples was performed quantitatively, and qualitative analysis of pore distribution was accomplished. It was also shown that high-resolution µCT can be used to probe internal layer defects of tristructural isotropic-coated fuel particles to elucidate the resulting high release of radioisotopes. Layer defects of sizes ranging from 1 tomore » 5 µm and up could be isolated by to-mography. As an added advantage, µCT could also be used to identify regions with high densities of radioisotopes to deter-mine the proper plane and orientation of particle mounting for further analytical characterization, such as materialographic sectioning followed by optical and electron microscopy. Lastly, in fully ceramic matrix fuel forms, despite the highly absorbing matrix, characterization of tristructural isotropic-coated particles embedded in a silicon carbide matrix was accomplished usingµCT and related advanced image analysis techniques.« less

Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.

1989-01-01

The postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is studied. The results suggest that the change in the plate's axial stiffness is strongly dependent on cutout size and plate orthotropy. It is found that the cutout size and stacking sequence of a composite plate may be tailored to optimize postbuckling stiffness. Also, it is suggested that a cutout may influence model interaction in a plate. The effects of load-path eccentricity on buckling behavior are examined.

Molecular dynamics simulations of shock compressed heterogeneous materials. II. The graphite/diamond transition case for astrophysics applications

NASA Astrophysics Data System (ADS)

Pineau, N.; Soulard, L.; Colombet, L.; Carrard, T.; Pellé, A.; Gillet, Ph.; Clérouin, J.

2015-03-01

We present a series of molecular dynamics simulations of the shock compression of copper matrices containing a single graphite inclusion: these model systems can be related to some specific carbon-rich rocks which, after a meteoritic impact, are found to contain small fractions of nanodiamonds embedded in graphite in the vicinity of high impedance minerals. We show that the graphite to diamond transformation occurs readily for nanometer-sized graphite inclusions, via a shock accumulation process, provided the pressure threshold of the bulk graphite/diamond transition is overcome, independently of the shape or size of the inclusion. Although high diamond yields (˜80%) are found after a few picoseconds in all cases, the transition is non-isotropic and depends substantially on the relative orientation of the graphite stack with respect to the shock propagation, leading to distinct nucleation processes and size-distributions of the diamond grains. A substantial regraphitization process occurs upon release and only inclusions with favorable orientations likely lead to the preservation of a fraction of this diamond phase. These results agree qualitatively well with the recent experimental observations of meteoritic impact samples.

Method of making bonded or sintered permanent magnets

DOEpatents

McCallum, R.W.; Dennis, K.W.; Lograsso, B.K.; Anderson, I.E.

1993-08-31

An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density.

Method of making bonded or sintered permanent magnets

DOEpatents

McCallum, R.W.; Dennis, K.W.; Lograsso, B.K.; Anderson, I.E.

1995-11-28

An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density. 14 figs.

Method of making bonded or sintered permanent magnets

DOEpatents

McCallum, R. William; Dennis, Kevin W.; Lograsso, Barbara K.; Anderson, Iver E.

1995-11-28

An isotropic permanent magnet is made by mixing a thermally responsive, low viscosity binder and atomized rare earth-transition metal (e.g., iron) alloy powder having a carbon-bearing (e.g., graphite) layer thereon that facilitates wetting and bonding of the powder particles by the binder. Prior to mixing with the binder, the atomized alloy powder may be sized or classified to provide a particular particle size fraction having a grain size within a given relatively narrow range. A selected particle size fraction is mixed with the binder and the mixture is molded to a desired complex magnet shape. A molded isotropic permanent magnet is thereby formed. A sintered isotropic permanent magnet can be formed by removing the binder from the molded mixture and thereafter sintering to full density.

Synthesis of Diamond Nanoplatelets/Carbon Nanowalls on Graphite Substrate by MPCVD

NASA Astrophysics Data System (ADS)

Zhang, Wei; Lyu, Jilei; Lin, Xiaoqi; Zhu, Jinfeng; Man, Weidong; Jiang, Nan

2015-07-01

The films composed of carbon nanowalls and diamond nanoplatelets, respectively, can be simultaneously formed on graphite substrate by controlling the hydrogen etching rate during microwave plasma chemical vapor deposition. To modulate the etching rate, two kinds of substrate design were used: a bare graphite plate and a graphite groove covered with a single crystal diamond sheet. After deposition at 1200°C for 3 hours, we find that dense diamond nanoplatelets were grown on the bare graphite, whereas carbon nanowalls were formed on the grooved surface, indicating that not only reaction temperature but also etching behavior is a key factor for nanostructure formation. supported by the Public Welfare Technology Application Projects of Zhejiang Province, China (No. 2013C33G3220012)

Drilling Holes in Graphite/Epoxy Composites

NASA Technical Reports Server (NTRS)

Daniels, J. G.; Ledbetter, Frank E., III; Penn, B. G.; White, W. L.

1986-01-01

Slurry of silicon carbide powder in water fed onto bit while drilling. Slurry contains about 60 percent silicon carbide by weight. Slurry recirculated by low-power pump. With slurry, dull tools cut as fast as, or faster than, sharp ones. Holes drilled rapidly and efficiently regardless of ply orientation; whether unidirectional, quasi-isotropic symmetrical, or cross-ply.

The structural behavior of a graphite-polymide honeycomb sandwich panel with quasi-isotropic face sheets and an orthotropic core

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Hagaman, J. A.

1979-01-01

The results of a series of tests of graphite-polyimide honeycomb sandwich panels are presented. The panels were 1.22 m long, 0.508 m wide, and approximately 13.3 m thick. The face sheets were a T-300/PMR-15 fabric in a quasi-isotropic layup and were 0.279 mm thick. The core was Hexcel HRH 327-3/16 - 4.0 glass reinforced polyimide honeycomb, 12.7 mm thick. Three panels were used in the test: one was cut into smaller pieces for testing as beam, compression, and shear specimens; a second panel was used for plate bending tests; the third panel was used for in-plane stability tests. Presented are the experimental results of four point bending tests, short block compression tests, core transverse shear modulus, three point bending tests, vibration tests, plate bending tests, and panel stability tests. The results of the first three tests are used to predict the results of some of the other tests. The predictions and experimental results are compared, and the agreement is quite good.

Experimental Measurement and Numerical Modeling of the Effective Thermal Conductivity of TRISO Fuel Compacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Folsom, Charles; Xing, Changhu; Jensen, Colby

2015-03-01

Accurate modeling capability of thermal conductivity of tristructural-isotropic (TRISO) fuel compacts is important to fuel performance modeling and safety of Generation IV reactors. To date, the effective thermal conductivity (ETC) of tristructural-isotropic (TRISO) fuel compacts has not been measured directly. The composite fuel is a complicated structure comprised of layered particles in a graphite matrix. In this work, finite element modeling is used to validate an analytic ETC model for application to the composite fuel material for particle-volume fractions up to 40%. The effect of each individual layer of a TRISO particle is analyzed showing that the overall ETC ofmore » the compact is most sensitive to the outer layer constituent. In conjunction with the modeling results, the thermal conductivity of matrix-graphite compacts and the ETC of surrogate TRISO fuel compacts have been successfully measured using a previously developed measurement system. The ETC of the surrogate fuel compacts varies between 50 and 30 W m -1 K -1 over a temperature range of 50-600°C. As a result of the numerical modeling and experimental measurements of the fuel compacts, a new model and approach for analyzing the effect of compact constituent materials on ETC is proposed that can estimate the fuel compact ETC with approximately 15-20% more accuracy than the old method. Using the ETC model with measured thermal conductivity of the graphite matrix-only material indicate that, in the composite form, the matrix material has a much greater thermal conductivity, which is attributed to the high anisotropy of graphite thermal conductivity. Therefore, simpler measurements of individual TRISO compact constituents combined with an analytic ETC model, will not provide accurate predictions of overall ETC of the compacts emphasizing the need for measurements of composite, surrogate compacts.« less

Structural stiffness, strength and dynamic characteristics of large tetrahedral space truss structures

NASA Technical Reports Server (NTRS)

Mikulas, M. M., Jr.; Bush, H. G.; Card, M. F.

1977-01-01

Physical characteristics of large skeletal frameworks for space applications are investigated by analyzing one concept: the tetrahedral truss, which is idealized as a sandwich plate with isotropic faces. Appropriate analytical relations are presented in terms of the truss column element properties which for calculations were taken as slender graphite/epoxy tubes. Column loads, resulting from gravity gradient control and orbital transfer, are found to be small for the class structure investigated. Fundamental frequencies of large truss structures are shown to be an order of magnitude lower than large earth based structures. Permissible loads are shown to result in small lateral deflections of the truss due to low-strain at Euler buckling of the slender graphite/epoxy truss column elements. Lateral thermal deflections are found to be a fraction of the truss depth using graphite/epoxy columns.

Microwave limb sounder, graphite epoxy support structure

NASA Technical Reports Server (NTRS)

Pynchon, G.

1980-01-01

The manufacturing and processing procedures which were used to fabricate a precision graphite/epoxy support structure for a spherical microwave reflecting surface are described. The structure was made fromm GY-70/930 ultra high modulus graphite prepreg, laminated to achieve an isotropic in plane thermal expansion of less than + or - 0.1 PPM/F. The structure was hand assembled to match the interface of the reflective surface, which was an array of 18 flexure supported, aluminum, spherically contoured tiles. Structural adhesives were used in the final assembly to bond the elements into their final configuration. A eutectic metal coating was applied to the composite surface to reduce dimensional instabilities arising from changes in the composite epoxy moisture content due to environmental effects. Basic materials properties data are reported and the results of a finite element structural analysis are referenced.

Continious production of exfoliated graphite composite compositions and flow field plates

DOEpatents

Shi, Jinjun; Zhamu, Aruna; Jang, Bor Z.

2010-07-20

A process of continuously producing a more isotropic, electrically conductive composite composition is provided. The process comprises: (a) continuously supplying a compressible mixture comprising exfoliated graphite worms and a binder or matrix material, wherein the binder or matrix material is in an amount of between 3% and 60% by weight based on the total weight of the mixture; (b) continuously compressing the compressible mixture at a pressure within the range of from about 5 psi or 0.035 MPa to about 50,000 psi or 350 MPa in at least a first direction into a cohered graphite composite compact; and (c) continuously compressing the composite compact in a second direction, different from the first direction, to form the composite composition in a sheet or plate form. The process leads to composite plates with exceptionally high thickness-direction electrical conductivity.

Facile morphology-controlled synthesis of nickel-coated graphite core-shell particles for excellent conducting performance of polymer-matrix composites and enhanced catalytic reduction of 4-nitrophenol

NASA Astrophysics Data System (ADS)

Bian, Juan; Lan, Fang; Wang, Yilong; Ren, Ke; Zhao, Suling; Li, Wei; Chen, Zhihong; Li, Jiangyu; Guan, Jianguo

2018-04-01

We have developed a novel seed-mediated growth method to fabricate nickel-coated graphite composite particles (GP@Ni-CPs) with controllable shell morphology by simply adjusting the concentration of sodium hydroxide ([NaOH]). The fabrication of two kinds of typical GP@Ni-CPs includes adsorption of Ni2+ via electrostatic attraction, sufficient heterogeneous nucleation of Ni atoms by an in situ reduction, and shell-controlled growth by regulating the kinetics of electroless Ni plating in turn. High [NaOH] results in fast kinetics of electroless plating, which causes heterogeneous nuclei to grow isotropically. After fast and uniform growth of Ni nuclei, GP@Ni-CPs with dense shells can be achieved. The first typical GP@Ni-CPs exhibit denser shells, smaller diameters and higher conductivities than the available commercial ones, indicating their important applications in the conducting of polymer-matrix composites. On the other hand, low [NaOH] favors slow kinetics. Thus, the reduction rate of Ni2+ slows down to a relatively low level so that electroless plating is dominated thermodynamically instead of kinetically, leading to an anisotropic crystalline growth of nuclei and finally to the formation of GP@Ni-CPs with nanoneedle-like shells. The second typical samples can effectively catalyze the reduction of p-nitrophenol into p-aminophenol with NaBH4 in comparison with commercial GP@Ni-CPs and RANEY® Ni, owing to the strong charge accumulation effect of needle-like Ni shells. This work proposes a model system for fundamental investigations and has important applications in the fields of electronic interconnection and catalysis.

Resistivity Correction Factor for the Four-Probe Method: Experiment I

NASA Astrophysics Data System (ADS)

Yamashita, Masato; Yamaguchi, Shoji; Enjoji, Hideo

1988-05-01

Experimental verification of the theoretically derived resistivity correction factor (RCF) is presented. Resistivity and sheet resistance measurements by the four-probe method are made on three samples: isotropic graphite, ITO film and Au film. It is indicated that the RCF can correct the apparent variations of experimental data to yield reasonable resistivities and sheet resistances.

Characterization of nuclear graphite elastic properties using laser ultrasonic methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeng, Fan W; Han, Karen; Olasov, Lauren R

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 beenmore » 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« less

Mechanism of chemical sputtering of graphite under high flux deuterium bombardment

NASA Astrophysics Data System (ADS)

Ueda, Y.; Sugai, T.; Ohtsuka, Y.; Nishikawa, M.

2000-12-01

Chemical sputtering of graphite materials (isotropic graphite and carbon fiber composite) was studied by irradiation of 5 keV D 3+ beam with a flux up to 4×10 21 m-2 s-1, which is more than one order magnitude higher than previous low flux beam experiments (< 10 20 m-2 s-1) . The chemical sputtering yield was obtained from measurements of the released methane signal with a quadrupole mass analyser. It was found that the methane yield at peak temperatures is almost independent of flux from 5×10 20 to 4×10 21 m-2 s-1. Peak temperatures range between 900 and 1000 K, which is higher than those of the previous low flux experiments (<900 K, <10 20 m-2 s-1) . By comparing our experimental results with calculation results based on Roth's model, the annealing effect of radiation damage to prevent methyl group formation appears to be unimportant.

Effects of fatigue and environment on residual strengths of center-cracked graphite/epoxy buffer strip panels

NASA Technical Reports Server (NTRS)

Bigelow, Catherine A.

1989-01-01

The effects of fatigue, moisture conditioning, and heating on the residual tension strengths of center-cracked graphite/epoxy buffer strip panels were evaluated using specimens made with T300/5208 graphite epoxy in a 16-ply quasi-isotropic layup, with two different buffer strip materials, Kevlar-49 or S-glass. It was found that, for panels subjected to fatigue loading, the residual strengths were not significantly affected by the fatigue loading, the number of repetitions of the loading spectrum, or the maximum strain level. The moisture conditioning reduced the residual strengths of the S-glass buffer strip panels by 10 to 15 percent below the ambient results, but increased the residual strengths of the Kevlar-49 buffer strip panels slightly. For both buffer strip materials, the heat increased the residual strengths of the buffer strip panels slightly over the ambient results.

Effect of specimen size and grain orientation on the mechanical and physical properties of NBG-18 nuclear graphite

DOE PAGES

Vasudevamurthy, G.; Byun, T. S.; Pappano, Pete; ...

2015-03-13

Here we present a comparison of the measured baseline mechanical and physical properties of with grain (WG) and against grain (AG) non-ASTM size NBG-18 graphite. The objectives of the experiments were twofold: (1) assess the variation in properties with grain orientation; (2) establish a correlation between specimen tensile strength and size. The tensile strength of the smallest sized (4 mm diameter) specimens were about 5% higher than the standard specimens (12 mm diameter) but still within one standard deviation of the ASTM specimen size indicating no significant dependence of strength on specimen size. The thermal expansion coefficient and elastic constantsmore » did not show significant dependence on specimen size. Lastly, experimental data indicated that the variation of thermal expansion coefficient and elastic constants were still within 5% between the different grain orientations, confirming the isotropic nature of NBG-18 graphite in physical properties.« less

Property changes of G347A graphite due to neutron irradiation

DOE PAGES

Campbell, Anne A.; Katoh, Yutai; Snead, Mary A.; ...

2016-08-18

A new, fine-grain nuclear graphite, grade G347A from Tokai Carbon Co., Ltd., has been irradiated in the High Flux Isotope Reactor at Oak Ridge National Laboratory to study the materials property changes that occur when exposed to neutron irradiation at temperatures of interest for Generation-IV nuclear reactor applications. Specimen temperatures ranged from 290°C to 800 °C with a maximum neutron fluence of 40 × 10 25 n/m 2 [E > 0.1 MeV] (~30dpa). Lastly, observed behaviors include: anisotropic behavior of dimensional change in an isotropic graphite, Young's modulus showing parabolic fluence dependence, electrical resistivity increasing at low fluence and additionalmore » increase at high fluence, thermal conductivity rapidly decreasing at low fluence followed by continued degradation, and a similar plateau value of the mean coefficient of thermal expansion for all irradiation temperatures.« less

Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states

NASA Astrophysics Data System (ADS)

Wåhlander, Martin; Nilsson, Fritjof; Carlmark, Anna; Gedde, Ulf W.; Edmondson, Steve; Malmström, Eva

2016-08-01

We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors. Electronic supplementary information (ESI) available: Figures of LCST, polymerization kinetics, melt-processed films, DLS, TGA, precipitated fiber and powder, TEM (of isotropic GO), birefringence, OP-data, DMTA-data and DSC. See DOI: 10.1039/c6nr01502f

Resistivity Correction Factor for the Four-Probe Method: Experiment III

NASA Astrophysics Data System (ADS)

Yamashita, Masato; Nishii, Toshifumi; Kurihara, Hiroshi; Enjoji, Hideo; Iwata, Atsushi

1990-04-01

Experimental verification of the theoretically derived resistivity correction factor F is presented. Factor F is applied to a system consisting of a rectangular parallelepiped sample and a square four-probe array. Resistivity and sheet resistance measurements are made on isotropic graphites and crystalline ITO films. Factor F corrects experimental data and leads to reasonable resistivity and sheet resistance.

The complex ion structure of warm dense carbon measured by spectrally resolved x-ray scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, D.; Barbrel, B.; Falcone, R. W.

2015-05-15

We present measurements of the complex ion structure of warm dense carbon close to the melting line at pressures around 100 GPa. High-pressure samples were created by laser-driven shock compression of graphite and probed by intense laser-generated x-ray sources with photon energies of 4.75 keV and 4.95 keV. High-efficiency crystal spectrometers allow for spectrally resolving the scattered radiation. Comparing the ratio of elastically and inelastically scattered radiation, we find evidence for a complex bonded liquid that is predicted by ab-initio quantum simulations showing the influence of chemical bonds under these conditions. Using graphite samples of different initial densities we demonstrate the capability ofmore » spectrally resolved x-ray scattering to monitor the carbon solid-liquid transition at relatively constant pressure of 150 GPa. Showing first single-pulse scattering spectra from cold graphite of unprecedented quality recorded at the Linac Coherent Light Source, we demonstrate the outstanding possibilities for future high-precision measurements at 4th Generation Light Sources.« less

Indentation-flexure and low-velocity impact damage in graphite/epoxy laminates

NASA Technical Reports Server (NTRS)

Kwon, Young S.; Sankar, Bhavani V.

1992-01-01

Static indentation and low velocity impact tests were performed on quasi-isotropic and cross ply graphite/epoxy composite laminates. The load deflection relations in static tests and impact force history in the impact tests were recorded. The damage was assessed by using ultrasonic C-scanning and photomicrographic techniques. The static behavior of the laminates and damage progression during loading, unloading, and reloading were explained by a simple plate delamination model. A good correlation existed between the static and impact responses. It was found that results from a few static indentation-flexture tests can be used to predict the response and damage in composite laminates due to a class of low velocity impact events.

Graphitization of Glassy Carbon after Compression at Room Temperature

NASA Astrophysics Data System (ADS)

Shiell, T. B.; McCulloch, D. G.; McKenzie, D. R.; Field, M. R.; Haberl, B.; Boehler, R.; Cook, B. A.; de Tomas, C.; Suarez-Martinez, I.; Marks, N. A.; Bradby, J. E.

2018-05-01

Glassy carbon is a technologically important material with isotropic properties that is nongraphitizing up to ˜3000 °C and displays complete or "superelastic" recovery from large compression. The pressure limit of these properties is not yet known. Here we use experiments and modeling to show permanent densification, and preferred orientation occurs in glassy carbon loaded to 45 GPa and above, where 45 GPa represents the limit to the superelastic and nongraphitizing properties of the material. The changes are explained by a transformation from its s p2 rich starting structure to a s p3 rich phase that reverts to fully s p2 bonded oriented graphite during pressure release.

Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Curren, A. N.; Sovey, J. S.

1981-01-01

Low secondary and reflected primary electron emission from the collector electrode surfaces is important for optimum collector efficiency and hence for high overall efficiency of microwave amplifier tubes used in communication satellites and in military systems. Ion sputter texturing of the surface effectively suppresses electron emission from pyrolytic graphite, which is a promising collector electrode material. Secondary and reflected primary electron emission characteristics of sputter textured pyrolytic graphite surfaces with microstructures of various sizes and densities are presented. The microstructure with the lowest electron emission levels, less than those of soot, consists of a dense array of tall, thin spires.

Damage tolerance and arrest characteristics of pressurized graphite/epoxy tape cylinders

NASA Technical Reports Server (NTRS)

Ranniger, Claudia U.; Lagace, Paul A.; Graves, Michael J.

1993-01-01

An investigation of the damage tolerance and damage arrest characteristics of internally-pressurized graphite/epoxy tape cylinders with axial notches was conducted. An existing failure prediction methodology, developed and verified for quasi-isotropic graphite/epoxy fabric cylinders, was investigated for applicability to general tape layups. In addition, the effect of external circumferential stiffening bands on the direction of fracture path propagation and possible damage arrest was examined. Quasi-isotropic (90/0/plus or minus 45)s and structurally anisotropic (plus or minus 45/0)s and (plus or minus 45/90)s coupons and cylinders were constructed from AS4/3501-6 graphite/epoxy tape. Notched and unnotched coupons were tested in tension and the data correlated using the equation of Mar and Lin. Cylinders with through-thickness axial slits were pressurized to failure achieving a far-field two-to-one biaxial stress state. Experimental failure pressures of the (90/0/plus or minus 45)s cylinders agreed with predicted values for all cases but the specimen with the smallest slit. However, the failure pressures of the structurally anisotropic cylinders, (plus or minus 45/0)s and (plus or minus 45/90)s, were above the values predicted utilizing the predictive methodology in all cases. Possible factors neglected by the predictive methodology include structural coupling in the laminates and axial loading of the cylindrical specimens. Furthermore, applicability of the predictive methodology depends on the similarity of initial fracture modes in the coupon specimens and the cylinder specimens of the same laminate type. The existence of splitting which may be exacerbated by the axial loading in the cylinders, shows that this condition is not always met. The circumferential stiffeners were generally able to redirect fracture propagation from longitudinal to circumferential. A quantitative assessment for stiffener effectiveness in containing the fracture, based on cylinder radius, slit size, and bending stiffnesses of the laminates, is proposed.

Lightweight Towed Howitzer Demonstrator. Phase 1 and Partial Phase 2. Volume A. Overview.

DTIC Science & Technology

1987-04-01

Reliability Floyd Manson............................... Test Plans Errol Quick................................. Systems Engrnq Coordi nati on Bob Schmidt ...FMC Structur*1 Verification o Beam stress calculations on the supporting trails which allow 70kpsi in a quasi-isotropic lay up of graphite epoxy...addressed utilizing a damage tolerant design criteria. o Strength calculations are questionable because of the dry room temperature values used. The

Ionospheric Modification from Under-Dense Heating by High-Power HF Transmitter

DTIC Science & Technology

2011-03-03

Auroral Research Program ( HAARP ) is a HF transmitter, which delivers 0.36 to 3.6 GW effective isotropic radiated powers (F.IRP) for the radiation...dense heating, the EIRP of the HAARP heater can be increased significantly by increasing the heater frequency. With higher heater frequency, the loss...1304 local time) and on 13 April from 0812 to 0844 UTC (0012 to 0044 local time), using the HAARP transmitter facility at Gakona, AK, at full power

Controlling the Surface Chemistry of Graphite by Engineered Self-Assembled Peptides

PubMed Central

Khatayevich, Dmitriy; So, Christopher R.; Hayamizu, Yuhei; Gresswell, Carolyn; Sarikaya, Mehmet

2012-01-01

The systematic control over surface chemistry is a long-standing challenge in biomedical and nanotechnological applications for graphitic materials. As a novel approach, we utilize graphite-binding dodecapeptides that self-assemble into dense domains to form monolayer thick long-range ordered films on graphite. Specifically, the peptides are rationally designed through their amino acid sequences to predictably display hydrophilic and hydrophobic characteristics while maintaining their self-assembly capabilities on the solid substrate. The peptides are observed to maintain a high tolerance for sequence modification, allowing the control over surface chemistry via their amino acid sequence. Furthermore, through a single step co-assembly of two different designed peptides, we predictably and precisely tune the wettability of the resulting functionalized graphite surfaces from 44 to 83 degrees. The modular molecular structures and predictable behavior of short peptides demonstrated here give rise to a novel platform for functionalizing graphitic materials that offers numerous advantages, including non-invasive modification of the substrate, bio-compatible processing in an aqueous environment, and simple fusion with other functional biological molecules. PMID:22428620

Embedded gage impact study

NASA Technical Reports Server (NTRS)

Schramm, S. W.; Daniel, I. M.

1984-01-01

Impact damage in graphite/epoxy laminates was characterized and transient strain history during impact was correlated. The material investigated was AS-4/3501-6 graphite/epoxy. Eight-ply and sixteen-ply quasi-isotropic laminates of 45/0/-45/90 sub s and 45/0/-45/90 sub 2s layups were fabricated with strain gages embedded between plies during the strain gages and leads from the highly conductive graphite fibers. The specimens were circular plates 12.7 cm (5 in.) in diameter and clamped along their circumference. The specimens were impacted with a 185 gm impactor, dropped from heights of 1.20 m and 1.65 m. An accelerometer was attached to the back surface of the specimen opposite the impact point and was used to trigger the recording instrumentation. The transient strain data were recorded with an eight channel waveform digitizer capable of sampling data at 0.5 microsec intervals. The data were stored, processed, and plotted by means of a microcomputer. Transient strain data were correlated with results from ultrasonic inspection of the specimens.

Development of Encapsulated Dye for Surface Impact Damage Indicator System.

DTIC Science & Technology

1987-09-01

GROUP SUB-GROUP Composites Ultrasonics Dye Impact Microcapsules 11 04 NDE polyurethane 11 1 0Encapsulation Paint 19. ABSTRACT (Continue on reverse if...encapsulation, microencapsule incorporation into the USAF polyurethane paint, dnd initial correlation study of impact damage to impact coating indication. It is...project were to: 1. Refine the microcapsule formulation to be compatible with MIL-C-83286 paint. 2. Fabricate composite panels from isotropic graphite

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing [Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing

DOE PAGES

Li, Ling; Jones, Kodey E.; Sales, Brian C.; ...

2018-04-03

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ~5.2 g/cm 3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performedmore » at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Lastly, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.« less

Fabrication of highly dense isotropic Nd-Fe-B nylon bonded magnets via extrusion-based additive manufacturing [Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Ling; Jones, Kodey E.; Sales, Brian C.

Magnetically isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts. The density of the printed magnet is ~5.2 g/cm 3. The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 T), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability as revealed by flux aging loss measurements. Tensile tests performedmore » at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely low eddy current loss and high resistivity. Lastly, we demonstrate the performance of the 3D printed magnets in a DC motor configuration via back electromotive force measurements.« less

Self-assembled monolayers of shape-persistent macrocycles on graphite: interior design and conformational polymorphism.

PubMed

Vollmeyer, Joscha; Eberhagen, Friederike; Höger, Sigurd; Jester, Stefan-S

2014-01-01

Three shape-persistent naphthylene-phenylene-acetylene macrocycles of identical backbone structures and extraannular substitution patterns but different (empty, apolar, polar) nanopore fillings are self-assembled at the solid/liquid interface of highly oriented pyrolytic graphite and 1,2,4-trichlorobenzene. Submolecularly resolved images of the resulting two-dimensional (2D) crystalline monolayer patterns are obtained by in situ scanning tunneling microscopy. A concentration-dependent conformational polymorphism is found, and open and more dense packing motifs are observed. For all three compounds alike lattice parameters are found, therefore the intermolecular macrocycle distances are mainly determined by their size and symmetry. This is an excellent example that the graphite acts as a template for the macrocycle organization independent from their specific interior.

Guided waves and defect scattering in metal matrix composite plates

NASA Technical Reports Server (NTRS)

Datta, Subhendu K.; Bratton, Robert L.; Shah, Arvind H.

1989-01-01

Guided Rayleigh-Lamb waves in a continuous graphite fiber reinforced magnesium plate has been studied. The interest in this material arises from its high thermal stability and because it provides high strength-to-weight ratio. Previous studies have shown that for wavelengths much larger than the fiber diameters and spacing, the material can be characterized as transversely isotropic with the symmetry axis aligned with the fiber direction. Because of the high longitudinal stiffness of the graphite fibers, the material shows strong anisotropy, with very high modulus in the fiber direction. For this reason, dispersion of guided waves is strongly influenced by the deviation of the direction of propagation from the symmetry axis. Results are given for propagation in different directions and for scattering of antiplane shear waves by surface-breaking cracks and delaminations.

Investigation of non-linear contact for a clearance-fit bolt in a graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Prabhakaran, R.; Naik, R. A.

1986-01-01

Numerous analytical studies have been published for the nonlinear load-contact variations in clearance-fit bolted joints. In these studies, stress distributions have been obtained and failure predictions have been made. However, very little experimental work has been reported regarding the contact or the stresses. This paper describes a fiber-optic technique for measuring the angle of contact in a clearance-fit bolt-loaded hole. Measurements of the contact angle have been made in a quasi-isotropic graphite-epoxy laminate by the optical as well as an electrical technique, and the results have been compared with those obtained from a finite-element analysis. The results from the two experimental techniques show excellent agreement; the finite-element results show some discrepancy, probably due to the interfacial frictions.

Analysis of Symmetric Reinforcement of Quasi-Isotropic Graphite-Epoxy Plates with a Circular Cutout under Uniaxial Tensile Loading.

DTIC Science & Technology

1983-12-01

DISTRIBUTION LIST ............... 111 . •6 a’. . .’. ’’. ’’2"-;’,".".,:’..."-’’:’ .-.-. .-;.: ś " - "." "-" - ,".-",’-’-"...--..’%° -,’:’, LISr OF...Locations anld Szrain a 10,000 psi (Par Field) ... .. ..... . ... 96 W, :- .% .... 7 ".’ , .9. LISr OF FIGURES 2.1 Reinforcement Configuration, Iype 1

Resistivity Correction Factor for the Four-Probe Method: Experiment II

NASA Astrophysics Data System (ADS)

Yamashita, Masato; Yamaguchi, Shoji; Nishii, Toshifumi; Kurihara, Hiroshi; Enjoji, Hideo

1989-05-01

Experimental verification of the theoretically derived resistivity correction factor F is presented. Factor F can be applied to a system consisting of a disk sample and a four-probe array. Measurements are made on isotropic graphite disks and crystalline ITO films. Factor F can correct the apparent variations of the data and lead to reasonable resistivities and sheet resistances. Here factor F is compared to other correction factors; i.e. FASTM and FJIS.

Advanced Thermally Stable Coal-Based Jet Fuels

DTIC Science & Technology

2008-01-01

the refined chemical oil used previously is in full agreement with recomm fuendations provided by RAND. Rxploratory work was begun to evaluate the...possible production of nuclear graphite from the by-products of co-coking. This would allow use of distillation residua rather than decant oil as feed...isotropic, that also means that the coker feed could be a distillation residuum (resid) and is not required to be a decant oil . Thus we envision the

Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

NASA Technical Reports Server (NTRS)

Post, D.; Czarnek, R.; Joh, D.; Wood, J.

1984-01-01

Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests.

Improved modeling of two-dimensional transitions in dense phases on crystalline surfaces. Krypton–graphite system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ustinov, E. A., E-mail: eustinov@mail.wplus.net

This paper presents a refined technique to describe two-dimensional phase transitions in dense fluids adsorbed on a crystalline surface. Prediction of parameters of 2D liquid–solid equilibrium is known to be an extremely challenging problem, which is mainly due to a small difference in thermodynamic functions of coexisting phases and lack of accuracy of numerical experiments in case of their high density. This is a serious limitation of various attempts to circumvent this problem. To improve this situation, a new methodology based on the kinetic Monte Carlo method was applied. The methodology involves analysis of equilibrium gas–liquid and gas–solid systems undergoingmore » an external potential, which allows gradual shifting parameters of the phase coexistence. The interrelation of the chemical potential and tangential pressure for each system is then treated with the Gibbs–Duhem equation to obtain the point of intersection corresponding to the liquid/solid–solid equilibrium coexistence. The methodology is demonstrated on the krypton–graphite system below and above the 2D critical temperature. Using experimental data on the liquid–solid and the commensurate–incommensurate transitions in the krypton monolayer derived from adsorption isotherms, the Kr–graphite Lennard–Jones parameters have been corrected resulting in a higher periodic potential modulation.« less

The effect of calcination conditions on the graphitizability of novel synthetic and coal-derived cokes

NASA Astrophysics Data System (ADS)

Bennett, Barbara Ellen

The effects of calcination heating rate and ultimate calcination temperature upon calcined coke and subsequent graphitic material microstructures were studied for materials prepared from three different precursors. The pitch precursors used were Mitsubishi AR pitch (a synthetic, 100% mesophase pitch), the NMP-extracted portion of a raw coal, and the NMP-extracted fraction of a coal liquefaction residue obtained from an HTI pilot plant. These materials were all green-coked under identical conditions. Optical microscopy confirmed that the Mitsubishi coke was very anisotropic and the HTI coke was nearly as anisotropic. The coke produced from the direct coal extract was very isotropic. Crystalline development during calcination heating was verified by high-temperature x-ray diffraction. Experiments were performed to ascertain the effects of varying calcination heating rate and ultimate temperature. It was determined that calcined coke crystallite size increased with increasing temperature for all three materials but was found to be independent of heating rate. The graphene interplanar spacing decreased with increasing temperature for the isotropic NMP-extract material but increased with increasing temperature for the anisotropic materials---Mitsubishi and HTI cokes. Graphene interplanar spacing was also found to be independent of heating rate. Calcined coke real densities were, likewise, found to be independent of heating rate. The anisotropic cokes (Mitsubishi and HTI) exhibited increasing real density with increasing calcination temperature. The NMP-extract coke increased in density up to 1050°C and then suffered a dramatic reduction in real density when heated to 1250°C. This is indicative of puffing. Since there was no corresponding disruption in the crystalline structure, the puffing phenomena was determined to be intercrystalline rather than intracrystalline. After the calcined cokes were graphitized (under identical conditions), the microstructures were re-evaluated. The crystalline properties of the graphitic materials appeared to be independent of calcination conditions---both heating rate and final temperature---for all samples prepared from any given precursor. The calcination step did not influence the microstructure or graphitizability of any of the three materials. The crystallinity of a graphitic material appears to be dictated by the properties of the green coke and cannot be altered by manipulating calcination conditions.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite

NASA Astrophysics Data System (ADS)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-01

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

The Formation of Graphite Whiskers in the Primitive Solar Nebula

NASA Technical Reports Server (NTRS)

Nuth, Joseph A., III; Kimura, Yuki; Lucas, Christopher; Ferguson, Frank; Johnson, Natasha M.

2010-01-01

It has been suggested that carbonaceous grains are efficiently destroyed in the interstellar medium and must either reform in situ at very low pressures and temperatures or in an alternative environment more conducive to grain growth. Graphite whiskers have been discovered associated with high-temperature phases in meteorites such as calcium aluminum inclusions and chondrules, and it has been suggested that the expulsion of such material from proto stellar nebulae could significantly affect the optical properties of the average interstellar grain population. We have experimentally studied the potential for Fischer-Tropsch and Haber-Bosch type reactions to produce organic materials in protostellar systems from the abundant H2, CO, and N2 reacting on the surfaces of available silicate grains. When graphite grains are repeatedly exposed to H2, CO, and N2 at 875 K abundant graphite whiskers are observed to form on or from the surfaces of the graphite grains. In a dense, turbulent nebula, such extended whiskers are very likely to be broken off, and fragments could be ejected either in polar jets or by photon pressure after transport to the outer reaches of the nebula.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite.

PubMed

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-27

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states.

PubMed

Wåhlander, Martin; Nilsson, Fritjof; Carlmark, Anna; Gedde, Ulf W; Edmondson, Steve; Malmström, Eva

2016-08-21

We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.

Role of nuclear grade graphite in controlling oxidation in modular HTGRs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Windes, Willaim; Strydom, G.; Kane, J.

2014-11-01

The passively safe High Temperature Gas-cooled Reactor (HTGR) design is one of the primary concepts considered for Generation IV and Small Modular Reactor (SMR) programs. The helium cooled, nuclear grade graphite moderated core achieves extremely high operating temperatures allowing either industrial process heat or electricity generation at high efficiencies. In addition to their neutron moderating properties, nuclear grade graphite core components provide excellent high temperature stability, thermal conductivity, and chemical compatibility with the high temperature nuclear fuel form. Graphite has been continuously used in nuclear reactors since the 1940’s and has performed remarkably well over a wide range of coremore » environments and operating conditions. Graphite moderated, gas-cooled reactor designs have been safely used for research and power production purposes in multiple countries since the inception of nuclear energy development. However, graphite is a carbonaceous material, and this has generated a persistent concern that the graphite components could actually burn during either normal or accident conditions [ , ]. The common assumption is that graphite, since it is ostensibly similar to charcoal and coal, will burn in a similar manner. While charcoal and coal may have the appearance of graphite, the internal microstructure and impurities within these carbonaceous materials are very different. Volatile species and trapped moisture provide a source of oxygen within coal and charcoal allowing them to burn. The fabrication process used to produce nuclear grade graphite eliminates these oxidation enhancing impurities, creating a dense, highly ordered form of carbon possessing high thermal diffusivity and strongly (covalently) bonded atoms.« less

Elastic properties and fracture strength of quasi-isotropic graphite/epoxy composites

NASA Technical Reports Server (NTRS)

Sullivan, T. L.

1977-01-01

The layups of the studied laminates are (0, + or - 60) sub s, (0, + or - 45, 90) sub s, (0, + or - 30, + or - 60, 90) sub s (0, + or - 22 1/2, + or - 45, + or - 67 1/2, 90) sub s. The properties determined were tensile modulus, Poisson's ratio, bending stiffness, fracture strength and fracture strain. Measured properties and properties predicted using laminate theory were found to be in reasonable agreement. Reasons for data scatter were determined.

Theory and application of laser ultrasonic shear wave birefringence measurements to the determination of microstructure orientation in transversely isotropic, polycrystalline graphite materials

DOE PAGES

Zeng, Fan W.; Contescu, Cristian I.; Gallego, Nidia C.; ...

2016-12-18

Laser ultrasonic line source methods have been used to study elastic anisotropy in nuclear graphites by measuring shear wave birefringence. Depending on the manufacturing processes used during production, nuclear graphites can exhibit various degrees of material anisotropy related to preferred crystallite orientation and to microcracking. In this paper, laser ultrasonic line source measurements of shear wave birefringence on NBG-25 have been performed to assess elastic anisotropy. Laser line sources allow specific polarizations for shear waves to be transmitted – the corresponding wavespeeds can be used to compute bulk, elastic moduli that serve to quantify anisotropy. These modulus values can bemore » interpreted using physical property models based on orientation distribution coefficients and microcrack-modified, single crystal moduli to represent the combined effects of crystallite orientation and microcracking on material anisotropy. Finally, ultrasonic results are compared to and contrasted with measurements of anisotropy based on the coefficient of thermal expansion to show the relationship of results from these techniques.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Anne A.; Katoh, Yutai; Snead, Mary A.

A new, fine-grain nuclear graphite, grade G347A from Tokai Carbon Co., Ltd., has been irradiated in the High Flux Isotope Reactor at Oak Ridge National Laboratory to study the materials property changes that occur when exposed to neutron irradiation at temperatures of interest for Generation-IV nuclear reactor applications. Specimen temperatures ranged from 290°C to 800 °C with a maximum neutron fluence of 40 × 10 25 n/m 2 [E > 0.1 MeV] (~30dpa). Lastly, observed behaviors include: anisotropic behavior of dimensional change in an isotropic graphite, Young's modulus showing parabolic fluence dependence, electrical resistivity increasing at low fluence and additionalmore » increase at high fluence, thermal conductivity rapidly decreasing at low fluence followed by continued degradation, and a similar plateau value of the mean coefficient of thermal expansion for all irradiation temperatures.« less

Method of fabricating silicon carbide coatings on graphite surfaces

DOEpatents

Varacalle, D.J. Jr.; Herman, H.; Burchell, T.D.

1994-07-26

The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1,600 C which transforms the coating to silicon carbide. 3 figs.

Method of fabricating silicon carbide coatings on graphite surfaces

DOEpatents

Varacalle, Jr., Dominic J.; Herman, Herbert; Burchell, Timothy D.

1994-01-01

The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1600.degree.C. which transforms the coating to silicon carbide.

Investigation of Brittle Fractures in Graphite-Epoxy Composites Subjected to Impact

DTIC Science & Technology

1975-05-01

Dspertlmew of the Army position unless so des •i•ated by othr authrized documents. Men Goverment drawings. epeOsftions. or other data we used for any...FRACTURE CHARACTERISTICS OF SOME FIBER-STRENGTHEN,1ED EPOXY RESIN SYSTEMS, E. 1. duPont de Nemours and Company, Incorporated, Wilmington, Delaware...Corporation Report TR-0172(SZ816-15)- 1, December 1971. 35 a LAYERS WITH Ela DIFFERENIT C (EACH LAYER ISOTROPIC) E la E lb t Elc E’ In Vila V lb ý VIC

A high-efficiency 59- to 64-GHz TWT for intersatellite communications

NASA Technical Reports Server (NTRS)

Wilson, Jeffrey D.; Ramins, Peter; Force, Dale A.; Limburg, Helen C.; Tammaru, Ivo

1991-01-01

The design of a 75-W, 59- to 64- GHz TWT with a predicted overall efficiency in excess of 40 percent is described. This intersatellite communications TWT, designated Model 961HA, employs a coupled-cavity slow-wave structure with a two-step velocity taper and an isotropic graphite multistage depressed collector (MDC). Because the RF efficiency of this TWT is less than 8 percent, an MDC design providing a very high collector efficiency was necessary to achieve the overall efficiency goal of 40 percent.

Recent results concerning the stability of viscoelastic shear deformable plates under compressive edge loading

NASA Technical Reports Server (NTRS)

Librescu, L.; Chandiramani, N. K.

1989-01-01

Some recent results obtained by the authors are summarized concerning the stability of transversely isotropic flat panels whose materials exhibit a viscoelastic behavior and whose edges are subjected to in-plane biaxial compressive loads. Two transversely isotropic type materials, largely used in advanced technology, are considered: (1) the pyrolytic-graphite type, used in the thermal protection of aerospace vehicles, and (2) the type corresponding to unidirectional fiber-reinforced composites. In the former case, the planes of isotropy are parallel at each point to the midplane of the plate. In the latter case, they are normal to the fiber directions. The micromechanical relations developed by Aboudi (1984, 1986, 1987) are considered in conjunction with the correspondence principle of linear viscoelastic theory in order to predict the macroscopic viscoelastic properties of a material composed of uniaxial elastic fibers embedded in a linear viscoelastic matrix.

Liquid Crystal Mediated Nano-assembled Gold Micro-shells

NASA Astrophysics Data System (ADS)

Quint, Makiko; Sarang, Som; Quint, David; Huang, Kerwyn; Gopinathan, Ajay; Hirst, Linda; Ghosh, Sayantani

We have created 3D nano-assenbled micro-shell by using thermotropic liquid crystal (LC), 4-Cyano-4'-pentylbiphenyl (5CB), doped with mesogen-functionalized gold nanoparticles (AuNPs). The assembly process is driven by the isotropic-nematic phase transition dynamics. We uniformly disperse the functionalized AuNPs into isotropic liquid crystal matrix and the mixture is cooled from the isotropic to the nematic phase. During the phase transition, the separation of LC-AuNP rich isotropic and ordered 5CB rich domains cause the functionalized AuNPs to move into the shrinking isotropic regions. The mesogenic ligands are locally crystalized during this process, which leads to the formation of a spherical shell with a densely packed wall of AuNPs. These micro-shells are capable of encapsulating fluorescence dye without visible leakages for several months. Additionally, they demonstrate strong localized surface plasmon resonance, which leads to localized heating on optical excitation. This photothermal effect disrupts the structure, releasing contents within seconds. Our results exhibiting the capture and optically regulated release of encapsulated substances is a novel platform that combines drug-delivery and photothermal therapy in one versatile and multifunctional unit. This work is supported by the NSF Grants No. DMR-1056860, ECC-1227034, and a University of California Merced Faculty Mentor Fellowship.

A harmonic analysis approach to joint inversion of P-receiver functions and wave dispersion data in high dense seismic profiles

NASA Astrophysics Data System (ADS)

Molina-Aguilera, A.; Mancilla, F. D. L.; Julià, J.; Morales, J.

2017-12-01

Joint inversion techniques of P-receiver functions and wave dispersion data implicitly assume an isotropic radial stratified earth. The conventional approach invert stacked radial component receiver functions from different back-azimuths to obtain a laterally homogeneous single-velocity model. However, in the presence of strong lateral heterogeneities as anisotropic layers and/or dipping interfaces, receiver functions are considerably perturbed and both the radial and transverse components exhibit back azimuthal dependences. Harmonic analysis methods exploit these azimuthal periodicities to separate the effects due to the isotropic flat-layered structure from those effects caused by lateral heterogeneities. We implement a harmonic analysis method based on radial and transverse receiver functions components and carry out a synthetic study to illuminate the capabilities of the method in isolating the isotropic flat-layered part of receiver functions and constrain the geometry and strength of lateral heterogeneities. The independent of the baz P receiver function are jointly inverted with phase and group dispersion curves using a linearized inversion procedure. We apply this approach to high dense seismic profiles ( 2 km inter-station distance, see figure) located in the central Betics (western Mediterranean region), a region which has experienced complex geodynamic processes and exhibit strong variations in Moho topography. The technique presented here is robust and can be applied systematically to construct a 3-D model of the crust and uppermost mantle across large networks.

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.

Iosipescu shear properties of graphite fabric/epoxy composite laminates

NASA Technical Reports Server (NTRS)

Walrath, D. E.; Adams, D. F.

1985-01-01

The Iosipescu shear test method is used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/934 epoxy composite materials. Different weave geometries tested include an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties are obtained for laminates of all four fabric types. Overall, little difference in shear properties attributable to the fabric weave pattern is observed. The auxiliary warp material is significantly weaker and less stiff in interlaminar shear parallel to its fill direction. A conventional strain gage extensometer is modified to measure shear strains for use with the Iosipescu shear test. While preliminary results are encouraging, several design iterations failed to produce a reliable shear transducer prototype. Strain gages are still the most reliable shear strain transducers for use with this test method.

Mesocarbon microbead based graphite for spherical fuel element to inhibit the infiltration of liquid fluoride salt in molten salt reactor

NASA Astrophysics Data System (ADS)

Zhong, Yajuan; Zhang, Junpeng; Lin, Jun; Xu, Liujun; Zhang, Feng; Xu, Hongxia; Chen, Yu; Jiang, Haitao; Li, Ziwei; Zhu, Zhiyong; Guo, Quangui

2017-07-01

Mesocarbon microbeads (MCMB) and quasi-isostatic pressing method were used to prepare MCMB based graphite (MG) for spherical fuel element to inhibit the infiltration of liquid fluoride salt in molten salt reactor (MSR). Characteristics of mercury infiltration and molten salt infiltration in MG were investigated and compared with A3-3 (graphite for spherical fuel element in high temperature gas cooled reactor) to identify the infiltration behaviors. The results indicated that MG had a low porosity about 14%, and an average pore diameter of 96 nm. Fluoride salt occupation of A3-3 (average pore diameter was 760 nm) was 10 wt% under 6.5 atm, whereas salt gain did not infiltrate in MG even up to 6.5 atm. It demonstrated that MG could inhibit the infiltration of liquid fluoride salt effectively. Coefficient of thermal expansion (CTE) of MG lies in 6.01 × 10-6 K-1 (α∥) and 6.15 × 10-6 K-1 (α⊥) at the temperature range of 25-700 °C. The anisotropy factor of MG calculated by CTE maintained below 1.02, which could meet the requirement of the spherical fuel element (below 1.30). The constant isotropic property of MG is beneficial for the integrity and safety of the graphite used in the spherical fuel element for a MSR.

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.

Brazed graphite/refractory metal composites for first-wall protection elements

NASA Astrophysics Data System (ADS)

Šmid, I.; Croessmann, C. D.; Salmonson, J. C.; Whitley, J. B.; Kny, E.; Reheis, N.; Kneringer, G.; Nickel, H.

1991-03-01

The peak surface heat flux deposition on divertor elements of near term fusion devices is expected to exceed 10 MW/m 2. The needed reliability of brazed plasma interactive components, particularly under abnormal operating conditions with peak surface temperatures well beyond 1000°C, makes refractory metallic substrates and brazes with a high melting point very attractive. TZM, a high temperature alloy of molybdenum, and isotropic graphite, materials very closely matched in their thermal expansion, were brazed with four high-temperature brazes. The brazes used were Zr, 90Ni/10Ti, 90Cu/10Ti and 70Ag/27Cu/3Ti (nominal composition prior to brazing, wt%). The resulting composite tiles of 50 × 50 mm2 with a TZM thickness of 5 mm and a graphite thickness of 10 mm have been tested in high heat flux simulation for their thermal fatigue properties. Up to 600 loading cycles were carried out with an average heat flux of 10 MW/m 2 for 0.5 s pulses. The maximum surface temperature was 1100°C. In support of the experiment, the thermal response and temperature gradients of the samples were investigated using a finite element model.

Observation of inhibited electron-ion coupling in strongly heated graphite

PubMed Central

White, T. G.; Vorberger, J.; Brown, C. R. D.; Crowley, B. J. B.; Davis, P.; Glenzer, S. H.; Harris, J. W. O.; Hochhaus, D. C.; Le Pape, S.; Ma, T.; Murphy, C. D.; Neumayer, P.; Pattison, L. K.; Richardson, S.; Gericke, D. O.; Gregori, G.

2012-01-01

Creating non-equilibrium states of matter with highly unequal electron and lattice temperatures (Tele≠Tion) allows unsurpassed insight into the dynamic coupling between electrons and ions through time-resolved energy relaxation measurements. Recent studies on low-temperature laser-heated graphite suggest a complex energy exchange when compared to other materials. To avoid problems related to surface preparation, crystal quality and poor understanding of the energy deposition and transport mechanisms, we apply a different energy deposition mechanism, via laser-accelerated protons, to isochorically and non-radiatively heat macroscopic graphite samples up to temperatures close to the melting threshold. Using time-resolved x ray diffraction, we show clear evidence of a very small electron-ion energy transfer, yielding approximately three times longer relaxation times than previously reported. This is indicative of the existence of an energy transfer bottleneck in non-equilibrium warm dense matter. PMID:23189238

An Ultrahigh Capacity Graphite/Li 2S Battery with Holey-Li 2S Nanoarchitectures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Fangmin; Noh, Hyungjun; Lee, Hongkyung

The pairing of high-capacity Li 2S cathode (1166 mAh g -1) and lithium-free anode (LFA) provides an unparalleled potential in developing safe and energy-dense next-generation secondary batteries. However, the low utilization of the Li 2S cathode and the lack of electrolytes compatible to both electrodes are impeding the development. Here, a novel graphite/Li 2S battery system, which features a self-assembled, holey-Li 2S nanoarchitecture and a stable solid electrolyte interface (SEI) on the graphite electrode, is reported. The holey structure on Li 2S is beneficial in decomposing Li 2S at the first charging process due to the enhanced Li ion extractionmore » and transfer from the Li 2S to the electrolyte. In addition, the concentrated dioxolane (DOL)-rich electrolyte designed lowers the irreversible capacity loss for SEI formation. By using the combined strategies, the graphite/holey-Li 2S battery delivers an ultrahigh discharge capacity of 810 mAh g -1 at 0.1 C (based on the mass of Li 2S) and of 714 mAh g -1 at 0.2 C. Moreover, it exhibits a reversible capacity of 300 mAh g -1 after a record lifecycle of 600 cycles at 1 C. These results suggest the great potential of the designed LFA/holey-Li 2S batteries for practical use.« less

An Ultrahigh Capacity Graphite/Li 2S Battery with Holey-Li 2S Nanoarchitectures

DOE PAGES

Ye, Fangmin; Noh, Hyungjun; Lee, Hongkyung; ...

2018-05-07

The pairing of high-capacity Li 2S cathode (1166 mAh g -1) and lithium-free anode (LFA) provides an unparalleled potential in developing safe and energy-dense next-generation secondary batteries. However, the low utilization of the Li 2S cathode and the lack of electrolytes compatible to both electrodes are impeding the development. Here, a novel graphite/Li 2S battery system, which features a self-assembled, holey-Li 2S nanoarchitecture and a stable solid electrolyte interface (SEI) on the graphite electrode, is reported. The holey structure on Li 2S is beneficial in decomposing Li 2S at the first charging process due to the enhanced Li ion extractionmore » and transfer from the Li 2S to the electrolyte. In addition, the concentrated dioxolane (DOL)-rich electrolyte designed lowers the irreversible capacity loss for SEI formation. By using the combined strategies, the graphite/holey-Li 2S battery delivers an ultrahigh discharge capacity of 810 mAh g -1 at 0.1 C (based on the mass of Li 2S) and of 714 mAh g -1 at 0.2 C. Moreover, it exhibits a reversible capacity of 300 mAh g -1 after a record lifecycle of 600 cycles at 1 C. These results suggest the great potential of the designed LFA/holey-Li 2S batteries for practical use.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nuth, Joseph A.; Kimura, Yuki; Lucas, Christopher

It has been suggested that carbonaceous grains are efficiently destroyed in the interstellar medium and must either reform in situ at very low pressures and temperatures or in an alternative environment more conducive to grain growth. Graphite whiskers have been discovered associated with high-temperature phases in meteorites such as calcium aluminum inclusions and chondrules, and it has been suggested that the expulsion of such material from protostellar nebulae could significantly affect the optical properties of the average interstellar grain population. We have experimentally studied the potential for Fischer-Tropsch and Haber-Bosch type reactions to produce organic materials in protostellar systems frommore » the abundant H{sub 2}, CO, and N{sub 2} reacting on the surfaces of available silicate grains. When graphite grains are repeatedly exposed to H{sub 2}, CO, and N{sub 2} at 875 K abundant graphite whiskers are observed to form on or from the surfaces of the graphite grains. In a dense, turbulent nebula, such extended whiskers are very likely to be broken off, and fragments could be ejected either in polar jets or by photon pressure after transport to the outer reaches of the nebula.« less

Prediction of impact force and duration during low velocity impact on circular composite laminates

NASA Technical Reports Server (NTRS)

Shivakumar, K. N.; Elber, W.; Illg, W.

1983-01-01

Two simple and improved models--energy-balance and spring-mass--were developed to calculate impact force and duration during low velocity impact of circular composite plates. Both models include the contact deformation of the plate and the impactor as well as bending, transverse shear, and membrane deformations of the plate. The plate was transversely isotropic graphite/epoxy composite laminate and the impactor was a steel sphere. Calculated impact forces from the two analyses agreed with each other. The analyses were verified by comparing the results with reported test data.

Seismic gradiometry using ambient seismic noise in an anisotropic Earth

NASA Astrophysics Data System (ADS)

de Ridder, S. A. L.; Curtis, A.

2017-05-01

We introduce a wavefield gradiometry technique to estimate both isotropic and anisotropic local medium characteristics from short recordings of seismic signals by inverting a wave equation. The method exploits the information in the spatial gradients of a seismic wavefield that are calculated using dense deployments of seismic arrays. The application of the method uses the surface wave energy in the ambient seismic field. To estimate isotropic and anisotropic medium properties we invert an elliptically anisotropic wave equation. The spatial derivatives of the recorded wavefield are evaluated by calculating finite differences over nearby recordings, which introduces a systematic anisotropic error. A two-step approach corrects this error: finite difference stencils are first calibrated, then the output of the wave-equation inversion is corrected using the linearized impulse response to the inverted velocity anomaly. We test the procedure on ambient seismic noise recorded in a large and dense ocean bottom cable array installed over Ekofisk field. The estimated azimuthal anisotropy forms a circular geometry around the production-induced subsidence bowl. This conforms with results from studies employing controlled sources, and with interferometry correlating long records of seismic noise. Yet in this example, the results were obtained using only a few minutes of ambient seismic noise.

Low temperature synthesis of coiled carbon nanotubes and their magnetic properties

NASA Astrophysics Data System (ADS)

Krishna, Vemula Mohana; Somanathan, T.; Manikandan, E.

2018-04-01

In this paper, coiled like structure of carbon nanotubes (c-CNTs) have been effectively grown on bi-metal substituted α-alumina nanoparticles catalyst by chemical vapor deposition (CVD) system. Highly graphitized and dense bundles of carbon product were attained at a low temperature of 550 °C. The coiled carbon nanostructures in very longer lengths were noticed by field emission scanning electron microscope (FESEM) observation. Furthermore, high purity material was achieved, which correlates the energy dispersive x-ray spectroscopy (EDX) analysis. High resolution transmission electron microscope (HRTEM) revealed the diameter and graphitization of coiled structures. The superparamagnetic like behavior was observed at room temperature for the as-synthesized product, which was found by VSM investigation.

Unusual Enhancement in Intrinsic Thermal Conductivity of Multilayer Graphene by Tensile Strains

DOE PAGES

Kuang, Youdi; Lindsay, Lucas R.; Huang, Baoling

2015-01-01

High basal plane thermal conductivity k of multi-layer graphene makes it promising for thermal management applications. Here we examine the effects of tensile strain on thermal transport in this system. Using a first principles Boltzmann-Peierls equation for phonon transport approach, we calculate the room-temperature in-plane lattice k of multi-layer graphene (up to four layers) and graphite under different isotropic tensile strains. The calculated in-plane k of graphite, finite mono-layer graphene and 3-layer graphene agree well with previous experiments. The dimensional transitions of the intrinsic k and the extent of the diffusive transport regime from mono-layer graphene to graphite are presented.more » We find a peak enhancement of intrinsic k for multi-layer graphene and graphite with increasing strain and the largest enhancement amplitude is about 40%. In contrast the calculated intrinsic k with tensile strain decreases for diamond and diverges for graphene, we show that the competition between the decreased mode heat capacities and the increased lifetimes of flexural phonons with increasing strain contribute to this k behavior. Similar k behavior is observed for 2-layer hexagonal boron nitride systems, suggesting that it is an inherent thermal transport property in multi-layer systems assembled of purely two dimensional atomic layers. This study provides insights into engineering k of multi-layer graphene and boron nitride by strain and into the nature of thermal transport in quasi-two-dimensional and highly anisotropic systems.« less

Combined investigation of Eddy current and ultrasonic techniques for composite materials NDE

NASA Technical Reports Server (NTRS)

Davis, C. W.; Nath, S.; Fulton, J. P.; Namkung, M.

1993-01-01

Advanced composites are not without trade-offs. Their increased designability brings an increase in the complexity of their internal geometry and, as a result, an increase in the number of failure modes associated with a defect. When two or more isotropic materials are combined in a composite, the isotropic material failure modes may also combine. In a laminate, matrix delamination, cracking and crazing, and voids and porosity, will often combine with fiber breakage, shattering, waviness, and separation to bring about ultimate structural failure. This combining of failure modes can result in defect boundaries of different sizes, corresponding to the failure of each structural component. This paper discusses a dual-technology NDE (Non Destructive Evaluation) (eddy current (EC) and ultrasonics (UT)) study of graphite/epoxy (gr/ep) laminate samples. Eddy current and ultrasonic raster (Cscan) imaging were used together to characterize the effects of mechanical impact damage, high temperature thermal damage and various types of inserts in gr/ep laminate samples of various stacking sequences.

Properties of three graphite/toughened resin composites

NASA Technical Reports Server (NTRS)

Smith, Donald L.; Dow, Marvin B.

1991-01-01

Results are presented from an experimental evaluation of IM7/977-2, IM7/F655, and T800/F3900. Data presented include ply-level (unidirectional laminate) strength and moduli, unnotched and notched (open hole) tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths. These data are compared with properties of other toughened (IM7/8551-7 and IM6/18081) and brittle (T300/5208) graphite-epoxy materials. The IM7/977-2, IM7/F655, and T800/F3900 materials are substantially stronger and more damage tolerant than widely used first generation composite materials such as T300/5208. The T800/F3900 outperforms IM7/977-2 and IM7/F655 materials in tolerance to projectile impacts. Compression-after-impact strengths were found to be dependent on impactor velocity for a given impact energy. The open hole compression properties of all three materials are degraded by the combination of heat and moisture.

Scaling effects in the impact response of graphite-epoxy composite beams

NASA Technical Reports Server (NTRS)

Jackson, Karen E.; Fasanella, Edwin L.

1989-01-01

In support of crashworthiness studies on composite airframes and substructure, an experimental and analytical study was conducted to characterize size effects in the large deflection response of scale model graphite-epoxy beams subjected to impact. Scale model beams of 1/2, 2/3, 3/4, 5/6, and full scale were constructed of four different laminate stacking sequences including unidirectional, angle ply, cross ply, and quasi-isotropic. The beam specimens were subjected to eccentric axial impact loads which were scaled to provide homologous beam responses. Comparisons of the load and strain time histories between the scale model beams and the prototype should verify the scale law and demonstrate the use of scale model testing for determining impact behavior of composite structures. The nonlinear structural analysis finite element program DYCAST (DYnamic Crash Analysis of STructures) was used to model the beam response. DYCAST analysis predictions of beam strain response are compared to experimental data and the results are presented.

Preliminary report on tests of tensile specimens with a part-through surface notch for a filament wound graphite/epoxy material

NASA Technical Reports Server (NTRS)

Harris, C. E.; Morris, D. H.

1985-01-01

The behavior of tensile coupons with surface notches of various semi-elliptical shapes were evaluated for specimens obtained from a filament wound graphite/epoxy cylinder. The quasi-static test results, in some instances, are inadequate for defining complete trend curves and the interpretive analysis is considered to be preliminary. Specimens with very shallow notches were observed to be notch insensitive and the unnotched strength from these specimens was determined to be 54.97 Ksi. The failure strain of the laminate was found to be 1.328%. Specimens with deeper notches were sensitive to notch depth, notch aspect ratio, and specimen width. Using the unnotched strength of 54.97 Ksi and Poe's general toughness parameter, the fracture toughness was estimated to be 27.2 Ksi square root of In. Isotropic linear elastic fracture mechanics together with the estimated fracture toughness correctly predicted the influence of notch depth, aspect ratio, and specimen finitewidth.

Fatigue degradation in compressively loaded composite laminates. [graphite-epoxy composites

NASA Technical Reports Server (NTRS)

Ramkumar, R. L.

1981-01-01

The effect of imbedded delaminations on the compression fatigue behavior of quasi-isotropic, T300/5208, graphite/epoxy laminates was investigated. Teflon imbedments were introduced during panel layup to create delaminations. Static and constant amplitude (R=10, omega = 10 Hz) fatigue tests were conducted. S-N data and half life residual strength data were obtained. During static compression loading, the maximum deflection of the buckled delaminated region was recorded. Under compression fatigue, growth of the imbedded delamination was identified as the predominant failure mode in most of the test cases. Specimens that exhibited others failures had a single low stiffness ply above the Teflon imbedment. Delamination growth during fatigue was monitored using DIB enhanced radiography. In specimens with buried delaminations, the dye penetrant (DIB) was introduced into the delaminated region through a minute laser drilled hole, using a hypodermic needle. A low kV, microfocus, X-ray unit was mounted near the test equipment to efficiently record the cyclic growth of buried delaminations on Polaroid film.

AGR-2 and AGR-3/4 Release-to-Birth Ratio Data Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Binh T.; Einerson, Jeffrey J.; Scates, Dawn M.

A series of Advanced Gas Reactor (AGR) irradiation tests is being conducted in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) in support of development and qualification of tristructural isotropic (TRISO) low enriched fuel used in the High Temperature Gas-cooled Reactor (HTGR). Each AGR test consists of multiple independently controlled and monitored capsules containing fuel compacts placed in a graphite cylinder shrouded by a steel shell. These capsules are instrumented with thermocouples embedded in the graphite enabling temperature control. AGR configuration and irradiation conditions are based on prismatic HTGR technology that is distinguished primarily through use of heliummore » coolant, a low-power-density ceramic core capable of withstanding very high temperatures, and TRISO coated particle fuel. Thus, these tests provide valuable irradiation performance data to support fuel process development, qualify fuel for normal operating conditions, and support development and validation of fuel performance and fission product transport models and codes.« less

High heat flux Langmuir probe array for the DIII-D divertor platesa)

NASA Astrophysics Data System (ADS)

Watkins, J. G.; Taussig, D.; Boivin, R. L.; Mahdavi, M. A.; Nygren, R. E.

2008-10-01

Two modular arrays of Langmuir probes designed to handle a heat flux of up to 25 MW/m2 for 10 s exposures have been installed in the lower divertor target plates of the DIII-D tokamak. The 20 pyrolytic graphite probe tips have more than three times higher thermal conductivity and 16 times larger mass than the original DIII-D isotropic graphite probes. The probe tips have a fixed 12.5° surface angle to distribute the heat flux more uniformly than the previous 6 mm diameter domed collectors and a symmetric "rooftop" design to allow operation with reversed toroidal magnetic field. A large spring-loaded contact area improves heat conduction from each probe tip through a ceramic insulator into a cooled graphite divertor floor tile. The probe tips, brazed to molybdenum foil to ensure good electrical contact, are mounted in a ceramic tray for electrical isolation and reliable cable connections. The new probes are located 1.5 cm radially apart in a staggered arrangement near the entrance to the lower divertor pumping baffle and are linearly spaced 3 cm apart on the shelf above the in-vessel cryopump. Typical target plate profiles of Jsat, Te, and Vf with 4 mm spatial resolution are shown.

Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Curren, A. N.; Sovey, J. S.

1981-01-01

Measurements are presented of secondary electron emission and reflected primary electron characteristics of sputter-textured pyrolitic graphite surfaces with microstructures of various sizes and densities, made with an Auger cylindrical mirror analyzer in a high-vacuum chamber at pressures below 1.33 x 10 to the -7th N/sq m (10 to the -9th torr). A dense, tall, thin, spire-like microstructure, obtained at ion energies of 1000 eV and ion current densities of 5 mA/sq cm, is the most effective. The secondary electron emission from such a surface is lower than that of soot, whose secondary emission is among the lowest of any material. At a primary electron energy of 1000 eV, the secondary electron emission yield of smooth CU is about 350% greater than the lowest value obtained for sputter-textured pyrolitic graphite. The reflected primary electron index of smooth Cu is a factor of 80 greater. If the secondary electron emission yield is reduced to 0.3, which is possible with sputter-textured pyrolitic graphite, the traveling wave tube collector efficiency could be improved by as much as 4% over that for smooth copper.

Flat-band superconductivity in strained Dirac materials

NASA Astrophysics Data System (ADS)

Kauppila, V. J.; Aikebaier, F.; Heikkilä, T. T.

2016-06-01

We consider superconducting properties of a two-dimensional Dirac material such as graphene under strain that produces a flat-band spectrum in the normal state. We show that in the superconducting state, such a model results in a highly increased critical temperature compared to the case without the strain, inhomogeneous order parameter with two-peak shaped local density of states and yet a large and almost uniform and isotropic supercurrent. This model could be realized in strained graphene or ultracold atom systems and could be responsible for unusually strong superconductivity observed in some graphite interfaces and certain IV-VI semiconductor heterostructures.

Superelastic carbon spheres under high pressure

NASA Astrophysics Data System (ADS)

Li, Meifen; Guo, Junjie; Xu, Bingshe

2013-03-01

We report a superelastic deformation behavior of carbon spheres by the in situ Raman spectroscopy in a high-pressure diamond anvil cell. The carbon spheres produced by arc discharging in toluene have a mean diameter of 200 nm and an onion-like multilayer graphitic structure. We find that the elastic coefficients, during both the compression and decompression processes, remain a constant up to 10 GPa, indicating a superior high-pressure structural stability. Such superelastic behavior is related to the isotropic and concentric configuration of carbon spheres and provides additional insight into improving the microscopic mechanical properties of small-scale particles.

Laser Engineered Graphene Paper for Mass Spectrometry Imaging

PubMed Central

Qian, Kun; Zhou, Liang; Liu, Jian; Yang, Jie; Xu, Hongyi; Yu, Meihua; Nouwens, Amanda; Zou, Jin; Monteiro, Michael J.; Yu, Chengzhong

2013-01-01

A pulsed laser engineering approach is developed to prepare novel functional graphene paper with graphitic nanospheres homogeneously decorated on the surface and the superior performance of engineered paper is revealed in matrix-free mass spectrometry (MS) detection and imaging. We demonstrate that the stability of graphene paper under intense irradiation can be dramatically increased through a designed laser engineering process by forming densely packed graphitic nanospheres on the paper surface. Moreover, the surface hydrophobicity is enhanced and electric conductivity is improved. The engineered graphene paper can image the invisible micro-patterns of trace amount molecules and increases the detection limit towards diverse molecules by over two orders of magnitude compared to the pristine graphene paper and commercial products in MS analysis. PMID:23475267

Dynamic Failure Processes Under Confining Stress in AlON, a Transparent Polycrystalline Ceramic

DTIC Science & Technology

2008-12-01

axes, the dynamic loading is imposed (using MKB) along the second specimen axis and the third axis is used for the ultra-high-speed photography. The...to its optically isotropic cubic crystal structure, fully dense, polycrystalline bodies can be rendered completely transparent, making it a viable... tribological loading conditions. During indentation, the region beneath the indenter is effectively confined due to the surrounding medium, and it

Tensor spherical harmonics theories on the exact nature of the elastic fields of a spherically anisotropic multi-inhomogeneous inclusion

NASA Astrophysics Data System (ADS)

Shodja, H. M.; Khorshidi, A.

2013-04-01

Eshelby's theories on the nature of the disturbance strains due to polynomial eigenstrains inside an isotropic ellipsoidal inclusion, and the form of homogenizing eigenstrains corresponding to remote polynomial loadings in the equivalent inclusion method (EIM) are not valid for spherically anisotropic inclusions and inhomogeneities. Materials with spherically anisotropic behavior are frequently encountered in nature, for example, some graphite particles or polyethylene spherulites. Moreover, multi-inclusions/inhomogeneities/inhomogeneous inclusions have abundant engineering and scientific applications and their exact theoretical treatment would be of great value. The present work is devoted to the development of a mathematical framework for the exact treatment of a spherical multi-inhomogeneous inclusion with spherically anisotropic constituents embedded in an unbounded isotropic matrix. The formulations herein are based on tensor spherical harmonics having orthogonality and completeness properties. For polynomial eigenstrain field and remote applied loading, several theorems on the exact closed-form expressions of the elastic fields associated with the matrix and all the phases of the inhomogeneous inclusion are stated and proved. Several classes of impotent eigenstrain fields associated to a generally anisotropic inclusion as well as isotropic and spherically anisotropic multi-inclusions are also introduced. The presented theories are useful for obtaining highly accurate solutions of desired accuracy when the constituent phases of the multi-inhomogeneous inclusion are made of functionally graded materials (FGMs).

Sub-ply level scaling approach investigated for graphite-epoxy composite beam columns

NASA Technical Reports Server (NTRS)

Jackson, Karen E.; Kellas, Sotiris

1994-01-01

Scale model graphite-epoxy composite specimens were fabricated using the 'sub-ply level' approach and tested as beam-columns under an eccentric axial load to determine the effect of specimen size on flexural response and failure. In the current research project, although the fiber diameters are not scaled, the thickness of the pre-preg material itself has been scaled by adjusting the number of fibers through the thickness of a single ply. Three different grades of graphite-epoxy composite material (AS4/3502) were obtained from Hercules, Inc., in which the number of fibers through the thickness of a single ply was reduced (Grade 190 with 12 to 16 fibers, Grade 95 with 6 to 8 fibers, and Grade 48 with 3 to 4 fibers). Thus, using the sub-ply level approach, a baseline eight ply quasi-isotropic laminate could be fabricated using either the Grade 48 or Grade 95 material and the corresponding full-scale laminate would be constructed from Grade 95 or standard Grade 190 material, respectively. Note that in the sub-ply level approach, the number of ply interfaces is constant for the baseline and full-scale laminates. This is not true for the ply level and sublaminate level scaled specimens. The three grades of graphite-epoxy composite material were used to fabricate scale model beam-column specimens with in-plane dimensions of 0.5*n x 5.75*n, where n=1,2,4 corresponsing to 1/4, 1/2, and full-scale factors. Angle ply, cross ply, and quasi-isotropic laminate stacking sequences were chosen for the investigation and the test matrices for each laminate type are given. Specimens in each laminate family with the same in-plane dimensions but different thicknesses were tested to isolate the influence of the thickness dimension on the flexural response and failure. Also, specific lay-ups were chosen with blocked plies and dispersed plies for each laminate type. Specimens were subjected to an eccentric axial load until failure. The load offset was introduced through a set of hinges which were attached to the platens of a standard load test machine. Three sets of geometrically scaled hinges were used to ensure that scaled loading conditions were applied. This loading condition was chosen because it promotes large flexural deformations and specimens fail at the center of the beam, away from the grip supports. Five channels of data including applied vertical load, end shortening displacement, strain from gages applied back-to-back at the midspan of the beam, and rotation of the hinge from a bubble inclinometer were recorded for each specimen. The beam-column test configuration was used previously to study size effects in ply level scaled composite specimens of the same material system, sizes, and stacking sequences. Thus, a direct comparison between the two scaling approaches is possible. Ply level scaled beam-columns with angle ply, cross ply, and quasi-isotropic lay-ups exhibited no size dependencies in the flexural response, but significant size effects in strength. The reduction in strength with increasing specimen size was not predicted successfully by analysis techniques. It is anticipated that results from this investigation will lead to a better understanding of the strength scale effect in composite structures.

Molecular dynamics simulation study of the structure of poly(ethylene oxide) brushes on nonpolar surfaces in aqueous solution.

PubMed

Bedrov, Dmitry; Smith, Grant D

2006-07-04

The structure of poly(ethylene oxide) (PEO, M(w) = 526) brushes of various grafting density (sigma) on nonpolar graphite and hydrophobic (oily) surfaces in aqueous solution has been studied using atomistic molecular dynamics simulations. Additionally, the influence of PEO-surface interactions on the brush structure was investigated by systematically reducing the strength of the (dispersion) attraction between PEO and the surfaces. PEO chains were found to adsorb strongly to the graphite surface due primarily to the relative strength of dispersion interactions between PEO and the atomically dense graphite compared to those between water and graphite. For the oily surface, PEO-surface and water-surface dispersion interactions are much weaker, greatly reducing the energetic driving force for PEO adsorption. This reduction is mediated to some extent by a hydrophobic driving force for PEO adsorption on the oily surface. Reduction in the strength of PEO-surface attraction results in reduced adsorption of PEO for both surfaces, with the effect being much greater for the graphite surface where the strong PEO-surface dispersion interactions dominate. At high grafting density (sigma approximately 1/R(g)(2)), the PEO density profiles exhibited classical brush behavior and were largely independent of the strength of the PEO-surface interaction. With decreasing grafting density (sigma < 1/R(g)(2)), coverage of the surface by PEO requires an increasingly large fraction of PEO segments resulting in a strong dependence of the PEO density profile on the nature of the PEO-surface interaction.

Local buckling and crippling of composite stiffener sections

NASA Technical Reports Server (NTRS)

Bonanni, David L.; Johnson, Eric R.; Starnes, James H., Jr.

1988-01-01

Local buckling, postbuckling, and crippling (failure) of channel, zee, and I- and J-section stiffeners made of AS4/3502 graphite-epoxy unidirectional tape are studied by experiment and analysis. Thirty-six stiffener specimens were tested statically to failure in axial compression as intermediate length columns. Web width is 1.25 inches for all specimens, and the flange width-to-thickness ratio ranges from 7 to 28 for the specimens tested. The radius of the stiffener corners is either 0.125 or 0.250 inches. A sixteen-ply orthotropic layup, an eight-ply quasi-isotropic layup, and a sixteen-ply quasi-isotropic layup are examined. Geometrically nonlinear analyses of five specimens were performed with the STAGS finite element code. Analytical results are compared to experimental data. Inplane stresses from STAGS are used to conduct a plane stress failure analysis of these specimens. Also, the development of interlaminar stress equations from equilibrium for classical laminated plate theory is presented. An algorithm to compute high order displacement derivatives required by these equations based on the Discrete Fourier Transform (DFT) is discussed.

Solid Lubricated Rolling Element Bearings

DTIC Science & Technology

1979-02-15

lubricant into uneven patches of varnish . This varnish , along with the file-like action of the exposed ball carbides on the relatively softer races, can...its structure. Fluorine , one of the most reactive elements, reacts with graphite without combustion from about 790’F to 1022°F, forming a grey-colored...to allow for molding and machining after molding. 0 Method 2 (Hughes) Impregnating these dense weaves with a Thermid 600 polyimide varnish

Hydrogen Decrepitation Press-Less Process recycling of NdFeB sintered magnets

NASA Astrophysics Data System (ADS)

Xia, Manlong; Abrahamsen, Asger B.; Bahl, Christian R. H.; Veluri, Badrinath; Søegaard, Allan I.; Bøjsøe, Poul

2017-11-01

A Hydrogen Decrepitation Press-Less Process (HD-PLP) recycling method for recycling of anisotropic NdFeB magnets is demonstrated. The method combines hydrogen decrepitation (HD) disintegration of the initial magnet, powder sieving and the Press-Less Process (PLP), where hydride powder is sintered in a graphite mold. Coercivities up to 534 kA/m were obtained in porous samples based on powder size d < 100 μm. Adding a ball milling step resulted in full density isotropic magnets for d > 100 μm. The coercivity reached Hci = 957 kA/m being 86% of the original N48M material without addition of rare earth elements.

The fracture behavior of filament wound cylinders with surface flaws

NASA Technical Reports Server (NTRS)

Harris, C. E.; Morris, D. H.; Poe, C. C., Jr.

1985-01-01

The behavior of tensile coupons with surface notches of various semielliptical shapes has been evaluated for specimens obtained from a thick filament wound graphite/epoxy cylinder. Specimens with very shallow notches were observed to be notch insensitive and the unnotched strength from these specimens was determined to be 54.97 Ksi with an associated failure strain of 1.328 percent. Specimens with deeper notches were sensitive to notch depth and notch aspect ratio. Isotropic linear elastic fracture mechanics with an estimated fracture toughness of 27.2 Ksi-in.-to the 1/2 correctly predicted the influence of notch depth, aspect ratio and specimen finite width.

Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

NASA Technical Reports Server (NTRS)

Stinchcomb, W. W.; Henneke, E. G.; Reifsnider, K. L.; Kress, G. R.

1985-01-01

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

Gap Size Uncertainty Quantification in Advanced Gas Reactor TRISO Fuel Irradiation Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Binh T.; Einerson, Jeffrey J.; Hawkes, Grant L.

The Advanced Gas Reactor (AGR)-3/4 experiment is the combination of the third and fourth tests conducted within the tristructural isotropic fuel development and qualification research program. The AGR-3/4 test consists of twelve independent capsules containing a fuel stack in the center surrounded by three graphite cylinders and shrouded by a stainless steel shell. This capsule design enables temperature control of both the fuel and the graphite rings by varying the neon/helium gas mixture flowing through the four resulting gaps. Knowledge of fuel and graphite temperatures is crucial for establishing the functional relationship between fission product release and irradiation thermal conditions.more » These temperatures are predicted for each capsule using the commercial finite-element heat transfer code ABAQUS. Uncertainty quantification reveals that the gap size uncertainties are among the dominant factors contributing to predicted temperature uncertainty due to high input sensitivity and uncertainty. Gap size uncertainty originates from the fact that all gap sizes vary with time due to dimensional changes of the fuel compacts and three graphite rings caused by extended exposure to high temperatures and fast neutron irradiation. Gap sizes are estimated using as-fabricated dimensional measurements at the start of irradiation and post irradiation examination dimensional measurements at the end of irradiation. Uncertainties in these measurements provide a basis for quantifying gap size uncertainty. However, lack of gap size measurements during irradiation and lack of knowledge about the dimension change rates lead to gap size modeling assumptions, which could increase gap size uncertainty. In addition, the dimensional measurements are performed at room temperature, and must be corrected to account for thermal expansion of the materials at high irradiation temperatures. Uncertainty in the thermal expansion coefficients for the graphite materials used in the AGR-3/4 capsules also increases gap size uncertainty. This study focuses on analysis of modeling assumptions and uncertainty sources to evaluate their impacts on the gap size uncertainty.« less

Importance of intrinsic properties of dense caseinate dispersions for structure formation.

PubMed

Manski, Julita M; van Riemsdijk, Lieke E; van der Goot, Atze J; Boom, Remko M

2007-11-01

Rheological measurements of dense calcium caseinate and sodium caseinate dispersions (> or =15%) provided insight into the factors determining shear-induced structure formation in caseinates. Calcium caseinate at a sufficiently high concentration (30%) was shown to form highly anisotropic structures during shearing and concurrent enzymatic cross-linking. In contrast, sodium caseinate formed isotropic structures using similar processing conditions. The main difference between the two types of caseinates is the counterion present, and as a consequence, the size of structural elements and their interactions. The rheological behavior of calcium caseinate and sodium caseinate reflected these differences, yielding non-monotonic and shear thinning flow behavior for calcium caseinate whereas sodium caseinate behaved only slightly shear thinning. It appears that the intrinsic properties of the dense caseinate dispersions, which are reflected in their rheological behavior, affect the structure formation that was found after applying shear. Therefore, rheological measurements are useful to obtain an indication of the structure formation potential of caseinate dispersions.

Small amplitude waves and linear firehose and mirror instabilities in rotating polytropic quantum plasma

NASA Astrophysics Data System (ADS)

Bhakta, S.; Prajapati, R. P.; Dolai, B.

2017-08-01

The small amplitude quantum magnetohydrodynamic (QMHD) waves and linear firehose and mirror instabilities in uniformly rotating dense quantum plasma have been investigated using generalized polytropic pressure laws. The QMHD model and Chew-Goldberger-Low (CGL) set of equations are used to formulate the basic equations of the problem. The general dispersion relation is derived using normal mode analysis which is discussed in parallel, transverse, and oblique wave propagations. The fast, slow, and intermediate QMHD wave modes and linear firehose and mirror instabilities are analyzed for isotropic MHD and CGL quantum fluid plasmas. The firehose instability remains unaffected while the mirror instability is modified by polytropic exponents and quantum diffraction parameter. The graphical illustrations show that quantum corrections have a stabilizing influence on the mirror instability. The presence of uniform rotation stabilizes while quantum corrections destabilize the growth rate of the system. It is also observed that the growth rate stabilizes much faster in parallel wave propagation in comparison to the transverse mode of propagation. The quantum corrections and polytropic exponents also modify the pseudo-MHD and reverse-MHD modes in dense quantum plasma. The phase speed (Friedrichs) diagrams of slow, fast, and intermediate wave modes are illustrated for isotropic MHD and double adiabatic MHD or CGL quantum plasmas, where the significant role of magnetic field and quantum diffraction parameters on the phase speed is observed.

Surface modification of GC and HOPG with diazonium, amine, azide, and olefin derivatives.

PubMed

Tanaka, Mutsuo; Sawaguchi, Takahiro; Sato, Yukari; Yoshioka, Kyoko; Niwa, Osamu

2011-01-04

Surface modification of glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) was carried out with diazonium, amine, azide, and olefin derivatives bearing ferrocene as an electroactive moiety. Features of the modified surfaces were evaluated by surface concentrations of immobilized molecule, blocking effect of the modified surface against redox reaction, and surface observation using cyclic voltammetry and electrochemical scanning tunneling microscope (EC-STM). The measurement of surface concentrations of immobilized molecule revealed the following three aspects: (i) Diazonium and olefin derivatives could modify substrates with the dense-monolayer concentration. (ii) The surface concentration of immobilized amine derivative did not reach to the dense-monolayer concentration reflecting their low reactivity. (iii) The surface modification with the dense-monolayer concentration was also possible with azide derivative, but the modified surface contained some oligomers produced by the photoreaction of azides. Besides, the blocking effect against redox reaction was observed for GC modified with diazonium derivative and for HOPG modified with diazonium and azide derivatives, suggesting fabrication of a densely modified surface. Finally, the surface observation for HOPG modified with diazonium derivative by EC-STM showed a typical monolayer structure, in which the ferrocene moieties were packed densely at random. On the basis of those results, it was demonstrated that surface modification of carbon substrates with diazonium could afford a dense monolayer similar to the self-assembled monolayer (SAM) formation.

Advanced Metals and Ceramics for Armor and Anti-Armor Applications. High-Fidelity Design and Processing of Advanced Armor Ceramics

DTIC Science & Technology

2007-06-01

microstructures through advanced powder processing , (7) nondestructive evaluation of ceramic armor, (8) investigation of the relation between quasi-static...of a green microstructure of a compact prepared by this process using Superior Graphite 490 powder that had been twice beneficiated by settling and...create a dense, uniform microstructure of highly oriented grains • Determined the relationship between processing parameters, such as shear and solids

Morphology and Structural Characterization of Carbon Nanowalls Grown via VHF-PECVD

NASA Astrophysics Data System (ADS)

Akmal Hasanudin, M.; Wahab, Y.; Ismail, A. K.; Zahid Jamal, Z. A.

2018-03-01

A 150 MHz very high frequency plasma enhanced chemical vapor deposition (150 MHz VHF-PECVD) system was utilized to fabricate two-dimensional carbon nanostructure from the mixture of methane and hydrogen. Morphology and structural properties of the grown nanostructure were investigated by FESEM imaging and Raman spectroscopy. Carbon nanowalls (CNW) with dense and wavy-like structure were successfully synthesized. The wavy-like morphology of CNW was found to be more distinct during growth at small electrode spacing and denser with increasing deposition time due to better flux of hydrocarbon radicals to the substrate and higher rate of reaction, respectively. Typical characteristics of CNW were observed from strong D band, narrow bandwidth of G band and single broad peak of 2D band of Raman spectra indicating the presence of disordered nanocrystalline graphite structure with high degree of graphitization.

Sintered tantalum carbide coatings on graphite substrates: Highly reliable protective coatings for bulk and epitaxial growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakamura, Daisuke; Suzumura, Akitoshi; Shigetoh, Keisuke

2015-02-23

Highly reliable low-cost protective coatings have been sought after for use in crucibles and susceptors for bulk and epitaxial film growth processes involving wide bandgap materials. Here, we propose a production technique for ultra-thick (50–200 μmt) tantalum carbide (TaC) protective coatings on graphite substrates, which consists of TaC slurry application and subsequent sintering processes, i.e., a wet ceramic process. Structural analysis of the sintered TaC layers indicated that they have a dense granular structure containing coarse grain with sizes of 10–50 μm. Furthermore, no cracks or pinholes penetrated through the layers, i.e., the TaC layers are highly reliable protective coatings. The analysismore » also indicated that no plastic deformation occurred during the production process, and the non-textured crystalline orientation of the TaC layers is the origin of their high reliability and durability. The TaC-coated graphite crucibles were tested in an aluminum nitride (AlN) sublimation growth process, which involves extremely corrosive conditions, and demonstrated their practical reliability and durability in the AlN growth process as a TaC-coated graphite. The application of the TaC-coated graphite materials to crucibles and susceptors for use in bulk AlN single crystal growth, bulk silicon carbide (SiC) single crystal growth, chemical vapor deposition of epitaxial SiC films, and metal-organic vapor phase epitaxy of group-III nitrides will lead to further improvements in crystal quality and reduced processing costs.« less

Enhancing the oxidation resistance of graphite by applying an SiC coat with crack healing at an elevated temperature

NASA Astrophysics Data System (ADS)

Park, Jae-Won; Kim, Eung-Seon; Kim, Jae-Un; Kim, Yootaek; Windes, William E.

2016-08-01

The potential of reducing the oxidation of the supporting graphite components during normal and/or accident conditions in the Very High Temperature Reactor (VHTR) design has been studied. In this work efforts have been made to slow the oxidation process of the graphite with a thin SiC coating (∼ 10 μm). Upon heating at ≥ 1173 K in air, the spallations and cracks were formed in the dense columnar structured SiC coating layer grown on the graphite with a functionally gradient electron beam physical vapor deposition (EB-PVD. In accordance with the formations of these defects, the sample was vigorously oxidized, leaving only the SiC coating layer. Then, efforts were made to heal the surface defects using additional EB-PVD with ion beam bombardment and chemical vapor deposition (CVD). The EB-PVD did not effectively heal the cracks. But, the CVD was more appropriate for crack healing, likely due to its excellent crack line filling capability with a high density and high aspect ratio. It took ∼ 34 min for the 20% weight loss of the CVD crack healed sample in the oxidation test with annealing at 1173 K, while it took ∼ 8 min for the EB-PVD coated sample, which means it took ∼4 times longer at 1173 K for the same weight reduction in this experimental set-up.

Dynamic Failure Processes Under Confining Stress in AlON, a Transparent Polycrystalline Ceramic

DTIC Science & Technology

2009-09-01

in a prismatic specimen along one of the three specimen axes, the dynamic loading is imposed (using MKB) along the second specimen axis and the third ...AlON are generally comparable to those of α-Al2O3. Owing to its optically isotropic cubic crystal structure, fully dense, polycrystalline bodies can...illustrated in indentation experiments on Al2O3 [46]) or under tribological loading conditions. During indentation, the region beneath the indenter is

Analysis of a Circular Composite Disk Subjected to Edge Rotations and Hydrostatic Pressure

NASA Technical Reports Server (NTRS)

Oliver, Stanley T.

2004-01-01

The structural analysis results for a graphite/epoxy quasi-isotropic circular plate subjected to a forced rotation at the boundary and pressure is presented. The analysis is to support a specialized material characterization test for composite cryogenic tanks. Finite element models were used to ensure panel integrity and determine the pressure necessary to achieve a predetermined equal biaxial strain value. The displacement results due to the forced rotation at the boundary led to a detailed study of the bending stiffness matrix [D]. The variation of the bending stiffness terms as a function of angular position is presented graphically, as well as, an illustrative technique of considering the laminate as an I-beam.

Contributions and mechanisms of action of graphite nanomaterials in ultra high performance concrete

NASA Astrophysics Data System (ADS)

Sbia, Libya Ahmed

Ultra-high performance concrete (UHPC) reaches high strength and impermeability levels by using a relatively large volume fraction of a dense binder with fine microstructure in combination with high-quality aggregates of relatively small particle size, and reinforcing fibers. The dense microstructure of the cementitions binder is achieved by raising the packing density of the particulate matter, which covers sizes ranging from few hundred nanometers to few millimeters. The fine microstructure of binder in UHPC is realized by effective use of pozzolans to largely eliminate the coarse crystalline particles which exist among cement hydrates. UHPC incorporates (steel) fibers to overcome the brittleness of its dense, finely structured cementitious binder. The main thrust of this research is to evaluate the benefits of nanmaterials in UHPC. The dense, finely structure cementitious binder as well as the large volume fraction of the binder in UHPC benefit the dispersion of nanomaterials, and their interfacial interactions. The relatively close spacing of nanomaterials within the cementitious binder of UHPC enables them to render local reinforcement effects in critically stressed regions such as those in the vicinity of steel reinforcement and prestressing strands as well as fibers. Nanomaterials can also raise the density of the binder in UHPC by extending the particle size distribution down to the few nanometers range. Comprehensive experimental studies supported by theoretical investigations were undertake in order to optimize the use of nanomaterials in UHPC, identity the UHPC (mechanical) properties which benefit from the introduction of nanomaterials, and define the mechanisms of action of nanomaterials in UHPC. Carbon nanofiber was the primary nanomaterial used in this investigation. Some work was also conducted with graphite nanoplates. The key hypotheses of the project were as follows: (i) nanomaterials can make important contributions to the packing density of the particulate matter in UHPC by extending the particle size distribution down to the few nanometers range; (ii) there are synergistic reinforcing actions of steel fibers and graphite nanomaterials in UHPC, which can be explained by their complementary spacing and also the benefit of nanomaterials to the interfacial bonding and pullout behavior of steel fibers; and (iii) nanomaterials make important contributions to the bonding and pullout behavior of prestressing strands and deformed bars in concrete, which can be attributed to the close spacing of nanomaterials within the highly stressed interfacial regions occurring in the vicinity of strands and reinforcing bars; steel fibers are loss effective in this regard due to the disturbance of their distribution and orientation in the vicinity of strands and bars. These hypotheses were successfully verified through the experimental and theoretical investigations conducted in this research.

Experimental data on single-bolt joints in quasi isotropic graphite/polyimide laminates

NASA Technical Reports Server (NTRS)

Wichorek, G. R.

1982-01-01

Sixteen ply, quasi-isotropic laminates of Celanese Celion 6000/PMR-15 and Celion 6000/LARC-160 with a fiber orientation of (0/45/90/-45) sub 2S were evaluated. Tensile and open hole specimens were tested at room temperature to establish laminate tensile strength and net tensile strength at an unloaded bolt hole. Double lap joint specimens with a single 4.83-mm (0.19 in.) diameter bolt torqued to 1.7 N-m (15 lbf-in.) were tested in tension at temperatures of 116 K (-250F), 297 K (75F), and 589 K (600F). The joint ratios of w/d (specimen width to hole diameter) and e/d (edge distance to hole diameter) were varied from 4 to 6 and from 2 to 4, respectively. The effect of joint geometry and temperature on failure mode and joint stresses are shown. Joint stresses calculated at maximum load for each joint geometry and test temperature are reported. Joint strength in net tension, bearing, and shear out at 116 K (-250F), 297 K (75F), and 589 K (600F) are given for the Celion 6000/PMR-15 and Celion 6000/LARC-160 laminates.

Aqueous alteration of VHTR fuels particles under simulated geological conditions

NASA Astrophysics Data System (ADS)

Ait Chaou, Abdelouahed; Abdelouas, Abdesselam; Karakurt, Gökhan; Grambow, Bernd

2014-05-01

Very High Temperature Reactor (VHTR) fuels consist of the bistructural-isotropic (BISO) or tristructural-isotropic (TRISO)-coated particles embedded in a graphite matrix. Management of the spent fuel generated during VHTR operation would most likely be through deep geological disposal. In this framework we investigated the alteration of BISO (with pyrolytic carbon) and TRISO (with SiC) particles under geological conditions simulated by temperatures of 50 and 90 °C and in the presence of synthetic groundwater. Solid state (scanning electron microscopy (SEM), micro-Raman spectroscopy, electron probe microanalyses (EPMA) and X-ray photoelectron spectroscopy (XPS)) and solution analyses (ICP-MS, ionique chromatography (IC)) showed oxidation of both pyrolytic carbon and SiC at 90 °C. Under air this led to the formation of SiO2 and a clay-like Mg-silicate, while under reducing conditions (H2/N2 atmosphere) SiC and pyrolytic carbon were highly stable after a few months of alteration. At 50 °C, in the presence and absence of air, the alteration of the coatings was minor. In conclusion, due to their high stability in reducing conditions, HTR fuel disposal in reducing deep geological environments may constitute a viable solution for their long-term management.

Micromechanical modeling of elastic properties of cortical bone accounting for anisotropy of dense tissue.

PubMed

Salguero, Laura; Saadat, Fatemeh; Sevostianov, Igor

2014-10-17

The paper analyzes the connection between microstructure of the osteonal cortical bone and its overall elastic properties. The existing models either neglect anisotropy of the dense tissue or simplify cortical bone microstructure (accounting for Haversian canals only). These simplifications (related mostly to insufficient mathematical apparatus) complicate quantitative analysis of the effect of microstructural changes - produced by age, microgravity, or some diseases - on the overall mechanical performance of cortical bone. The present analysis fills this gap; it accounts for anisotropy of the dense tissue and uses realistic model of the porous microstructure. The approach is based on recent results of Sevostianov et al. (2005) and Saadat et al. (2012) on inhomogeneities in a transversely-isotropic material. Bone's microstructure is modeled according to books of Martin and Burr (1989), Currey (2002), and Fung (1993) and includes four main families of pores. The calculated elastic constants for porous cortical bone are in agreement with available experimental data. The influence of each of the pore types on the overall moduli is examined. Copyright © 2014 Elsevier Ltd. All rights reserved.

Magnetic and microstructural investigation of high-coercivity net-shape Nd-Fe-B-type magnets produced from spark-plasma-sintered melt-spun ribbons blended with DyF3

NASA Astrophysics Data System (ADS)

Žagar, Kristina; Kocjan, Andraž; Kobe, Spomenka

2016-04-01

Nanostructured Nd-Fe-B-type materials produced by melt-spinning (MS) are used in a variety of applications in the electronics, automotive, and sensor industries. The very rapid MS process leads to flake-like powders with metastable, nanoscale, Nd2Fe14B grains. These powders are then formed into net-shaped, isotropic, polymer-bonded magnets, or they are hot formed into fully dense, metallic magnets that are isotropic and anisotropic. These fully dense magnets are usually produced with a conventional hot press without the inclusion of additives prior to the hot pressing. As a result, their properties, particularly the coercivity (Hci), are insufficient at automotive-relevant temperatures of 100-150 °C since the material Hci has a large temperature coefficient. In this study, we instead add a thin layer of DyF3 to the melt-spun ribbons prior to their hot consolidation in order to enhance the coercivity through a diffusion-based, partial substitution of the Nd by Dy. This is accomplished by applying extremely rapid, spark-plasma sintering to minimize any growth of the nanoscale Nd2Fe14B grains during consolidation. The result is a very high-coercivity magnet with drastically reduced amounts of heavy rare earths that is suitable for high-temperature applications. This work clearly demonstrates how rapidly formed, metastable states can provide us with properties that are unobtainable with conventional techniques.

Acoustic emission monitoring of low velocity impact damage in graphite/epoxy laminates during tensile loading

NASA Technical Reports Server (NTRS)

Parker, Bradford H.

1992-01-01

An acoustic emission (AE) system was set up in a linear location data acquisition mode to monitor the tensile loading of eight-ply quasi-isotropic graphite/epoxy specimens containing low velocity impact damage. The impact damage was induced using an instrumented drop weight tower. During impact, specimens were supported by either an aluminum plate or a membrane configuration. Cross-sectional examinations revealed that the aluminum plate configuration resulted in primarily matrix cracking and back surface fiber failure. The membrane support resulted in only matrix cracking and delamination damage. Penetrant enhanced radiography and immersion ultrasonics were used in order to assess the amount of impact damage in each tensile specimen. During tensile loading, AE reliably detected and located the damage sites which included fiber failure. All specimens with areas of fiber breakage ultimately failed at the impact site. AE did not reliably locate damage which consisted of only delaminations and matrix cracking. Specimens with this type of damage did not ultimately fail at the impact site. In summary, AE demonstrated the ability to increase the reliability of structural proof tests; however, the successful use of this technique requires extensive baseline testing.

Experimental investigation of graphite/polyimide sandwich panels in edgewise compression

NASA Technical Reports Server (NTRS)

Camarda, C. J.

1980-01-01

The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression was investigated. Material properties of adhesive and facings were determined from flatwise tension and sandwich beam flexure tests. Tensile and compressive material properties of the facings were determined at 116, R.T., and 589 K (-250, R.T., and 600 F) using the sandwich beam flexure test method. Results indicate that Gr/PI is a usable structural material for short term use at temperatures as high as 589 K (600 F). Buckling specimens were 30.5 X 33.0 cm (12 x 13 in.), had quasi-isotropic symmetric facings and a glass/polyimide honeycomb core. Core thicknesses varied and three panels of each thickness were tested in edgewise compression at room temperature to investigate failure modes and corresponding buckling formulas. Specimens 0.635 cm (0.25 in.) thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the winkling tests indicate that several buckling formulas were unconservative and therefore not suitable for design purposes; recommended wrinkling equations are presented.

Verification of computer-aided designs of traveling-wave tubes utilizing novel dynamic refocusers and graphite electrodes for the multistage depressed collector

NASA Technical Reports Server (NTRS)

Ramins, P.; Kosmahl, H. G.; Force, D. A.; Palmer, R. W.; Dayton, J. A., Jr.

1985-01-01

A computational procedure for the design of TWT-refocuser-MDC systems was used to design a short dynamic refocusing system and highly efficient four-stage depressed collector for a 200-W, 8- to 18-GHz, TWT. The computations were carried out with advanced, multidimensional computer programs which model the electron beam as a series of disks of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure and refocusing section, to their points of impact in the depressed collector. Secondary emission losses in the MDC were treated semi-quantitatively by injecting a representative beam of secondary electrons into the MDC analysis at the point of impact of each primary beam. A comparison of computed and measured TWT and MDC performance showed very good agreement. The electrodes of the MDC were fabricated from a particular form of isotropic graphite that was selected for its low secondary electron yield, ease of machinability, and vacuum properties. This MDC was tested (at CW) for more than 1000 hr with negligible degradation in TWT and MDC performances.

Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.

1990-01-01

An experimental study of the postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is presented. Results are presented for unidirectional (0 sub 10)s and (90 sub 10)s plates, (0/90 sub 5)s plates, and for aluminum plates. Results are also presented for (+ or - O sub 6)s angle-ply plates for values of O = 30, 46, and 60 degrees. The experimental results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramtically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout.

Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO₂ Coating Deposited on Graphite for Supercapacitor.

PubMed

Huang, Wenxin; Li, Jun; Xu, Yunhe

2017-10-19

The nucleation and growth mechanisms of porous MnO₂ coating deposited on graphite in MnSO₄ solution were investigated in detail by cyclic voltammetry, chronoamperometry and scanning electron microscopy. The electrochemical properties of honeycomb-like MnO₂ were evaluated by cycle voltammetry and galvanostatic charge-discharge. Results indicated that MnO₂ was synthesized by the following steps: Mn 2+ → Mn 3+ + e⁻, Mn 3+ +2H2O → MnOOH + 3H⁺, and MnOOH → MnO₂ + H⁺+ e⁻. The deposition of MnO₂ was divided into four stages. A short incubation period (approximately 1.5 s) was observed, prior to nucleation. The decreasing trend of the current slowed as time increased due to nucleation and MnO₂ growth in the second stage. A huge number of nuclei were formed by instantaneous nucleation, and these nuclei grew and connected with one another at an exceedingly short time (0.5 s). In the third stage, the gaps in-between initial graphite flakes were filled with MnO₂ until the morphology of the flakes gradually became similar to that of the MnO₂-deposited layer. In the fourth stage, the graphite electrode was covered completely with a thick and dense layer of MnO₂ deposits. All MnO₂ electrodes at different deposition times obtained nearly the same specific capacitance of approximately 186 F/g, thus indicating that the specific capacitance of the electrodes is not related with deposition time.

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE PAGES

Zhou, Jun; Li, Junjie; Correa, Alfredo A.; ...

2014-10-24

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Jun; Li, Junjie; Correa, Alfredo A.

We report the first systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which are escaping into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We alsomore » developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.« less

Preconditioner-free Wiener filtering with a dense noise matrix

NASA Astrophysics Data System (ADS)

Huffenberger, Kevin M.

2018-05-01

This work extends the Elsner & Wandelt (2013) iterative method for efficient, preconditioner-free Wiener filtering to cases in which the noise covariance matrix is dense, but can be decomposed into a sum whose parts are sparse in convenient bases. The new method, which uses multiple messenger fields, reproduces Wiener-filter solutions for test problems, and we apply it to a case beyond the reach of the Elsner & Wandelt (2013) method. We compute the Wiener-filter solution for a simulated Cosmic Microwave Background (CMB) map that contains spatially varying, uncorrelated noise, isotropic 1/f noise, and large-scale horizontal stripes (like those caused by atmospheric noise). We discuss simple extensions that can filter contaminated modes or inverse-noise-filter the data. These techniques help to address complications in the noise properties of maps from current and future generations of ground-based Microwave Background experiments, like Advanced ACTPol, Simons Observatory, and CMB-S4.

Charged pion spectra in proton—carbon interactions at 31 GeV/c

NASA Astrophysics Data System (ADS)

Zofia Posiadała, Magdalena; NA61/SHINE Collaboration

2013-02-01

The NA61/SHINE experiment at CERN SPS measured charged pion spectra in p+C interactions at 31 GeV/c. These measurements are necessary to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. Presented analysis was based on the data collected during the first NA61/SHINE run in 2007 with an isotropic graphite target with a thickness of 4% of nuclear interaction length. Three different methods which were used in order to obtain π+ and π- spectra are introduced. Differential cross sections for negatively and positively charged pions are presented as a function of laboratory momentum in ten intervals of the laboratory polar angle up to 420 mrad.

Collapse of Composite Cylinders in Bending

NASA Technical Reports Server (NTRS)

Fuchs, Hannes P.; Starnes, James H., Jr.; Hyer, Michael W.

1998-01-01

This paper summarizes the results of a numerical and experimental study of the collapse behavior of small-scale graphite-epoxy cylindrical shells subjected to overall bending loads, and in one case, an initial internal pressure. Shells with quasi-isotropic and orthotropic inplane stiffness properties are studied. Numerical results from geometrically nonlinear finite element analyses and results from experiments using a specially-built apparatus indicate that extensive stable postbuckling responses occur. Orthotropy influences the buckling values and the extent to which the bending moment decreases after buckling. Material damage is observed to initiate in the vicinity of the nodal lines of the postbuckled deflection patterns. Numerical results indicate that the magnitudes of the shear stress resultants are greatest in these nodal regions. Failure of the internally pressurized cylinder is catastrophic.

Inter-diffusion analysis of joint interface of tungsten-rhenium couple

NASA Astrophysics Data System (ADS)

Hua, Y. F.; Li, Z. X.; Zhang, X.; Du, J. H.; Huang, C. L.; Du, M. H.

2011-09-01

The tungsten-rhenium couple was prepared by using glow plasma physical vapor deposition (PVD) on the isotropic fine grained graphite (IG) substrates. Diffusion anneals of the tungsten-rhenium couple were conducted at the temperature from 1100 °C to 1400 °C to investigate the inter-diffusion behaviors. The results showed that the thickness of the inter-diffusion zone increased with increasing annealing temperature. The relationship between the inter-diffusion coefficient and the annealing temperature accorded with the Arrhenius manner. The value of inter-diffusion activation energies was 189 kJ/mole (1.96 eV). The service time of tungsten-rhenium multilayer diffusion barrier was limited by the inter-diffusion for rhenium and tungsten rather than the diffusion of carbon in rhenium.

Nonlinear temperature dependent failure analysis of finite width composite laminates

NASA Technical Reports Server (NTRS)

Nagarkar, A. P.; Herakovich, C. T.

1979-01-01

A quasi-three dimensional, nonlinear elastic finite element stress analysis of finite width composite laminates including curing stresses is presented. Cross-ply, angle-ply, and two quasi-isotropic graphite/epoxy laminates are studied. Curing stresses are calculated using temperature dependent elastic properties that are input as percent retention curves, and stresses due to mechanical loading in the form of an axial strain are calculated using tangent modulii obtained by Ramberg-Osgood parameters. It is shown that curing stresses and stresses due to tensile loading are significant as edge effects in all types of laminate studies. The tensor polynomial failure criterion is used to predict the initiation of failure. The mode of failure is predicted by examining individual stress contributions to the tensor polynomial.

Composite theory applied to elastomers

NASA Technical Reports Server (NTRS)

Clark, S. K.

1986-01-01

Reinforced elastomers form the basis for most of the structural or load carrying applications of rubber products. Computer based structural analysis in the form of finite element codes was highly successful in refining structural design in both isotropic materials and rigid composites. This has lead the rubber industry to attempt to make use of such techniques in the design of structural cord-rubber composites. While such efforts appear promising, they were not easy to achieve for several reasons. Among these is a distinct lack of a clearly defined set of material property descriptors suitable for computer analysis. There are substantial differences between conventional steel, aluminum, or even rigid composites such as graphite-epoxy, and textile-cord reinforced rubber. These differences which are both conceptual and practical are discussed.

Microanalysis of vitrous char and associated polymers: reference and ancient assemblages

NASA Astrophysics Data System (ADS)

Allue, E.; Bonnamy, S.; Courty, M. M.; Gispert I Guirado, F.

2012-12-01

Formation of vitrous char that occur in ancient charcoal assemblages have remained unsolved. Laboratory experiments refuted vitrification to resulting from high temperature charring of green or resinous wood. This puzzling problem has been refreshed by showing the association to the charcoal and vitrous char of plastics that were originally supposed to only be produced by petroleum industry. Extraction of similar polymers within geological glassy products from cosmic airbursts has suggested impact processes to possibly forming the carbonaceous polymorphs. The pulverisation at the ground in the Angles village (French Eastern Pyrenees) following the 2011 August 2nd high altitude meteor explosion of exotic debris with vitrous char and polymers, just alike the puzzling ones of the geological and archaeological records, has provided potential reference materials. We present here their microanalysis by Environmental SEM with EDS, Raman micro-spectrometry and FTIR, XRD, TEM, ICP-MS and isotope analyses. The characterization helps elucidating how the carbonaceous polymorphs formed by transient heating and transient high pressure of atmospheric aerosols. Under TEM the vesicular, dense, vitrous char show high structural organization with a dense pattern of nano-sized graphitized domains, metals and mineral inclusions. The coupled Raman-ESEM has allowed identifying a complex pattern at micro scales of ordered "D" peak at 1320-1350 cm-1 and the graphitic, ordered peak at 1576-1590 cm-1, in association to amorphous and poorly graphitic ordered carbon. The later occurs within plant cells that have been extracted from the dense vitrous char by performing controlled combustion under nitrogen up to 1000°C. In contrast, the brittle, vesicular vitrous char and the polymers encountered at the rear of the pulverised airburst debris reveal to be formed of agglutinated micro spherules of amorphous carbon with rare crystallized carbon nano-domains and scattered mineral inclusions. They completely vaporised at 300°C under stepped-heating without leaving extractable residues. The link established between the structure of these exceptional carbon polymorphs and their forming processes provide diagnostic keys for interpreting vitrous carbon in ancient charcoal assemblage. The hardest ones offer reliable impact markers with their distinctive nanostructure produced by the transient high pressure and heating of carbonaceous aerosols by cosmic airbursts. In contrast, the weakly graphitised ones with distinctive plant structures would possibly express moderate effects of the airburst shock wave on vegetation at the ground. Thus micro-structural characterization of charcoal in archaeological assemblages would help tracing possible exploitation of blasted wood forest and related fossil fuel produced by ancient cosmic airbursts.

Reinforcement of cement-based matrices with graphite nanomaterials

NASA Astrophysics Data System (ADS)

Sadiq, Muhammad Maqbool

Cement-based materials offer a desirable balance of compressive strength, moisture resistance, durability, economy and energy-efficiency; their tensile strength, fracture energy and durability in aggressive environments, however, could benefit from further improvements. An option for realizing some of these improvements involves introduction of discrete fibers into concrete. When compared with today's micro-scale (steel, polypropylene, glass, etc.) fibers, graphite nanomaterials (carbon nanotube, nanofiber and graphite nanoplatelet) offer superior geometric, mechanical and physical characteristics. Graphite nanomaterials would realize their reinforcement potential as far as they are thoroughly dispersed within cement-based matrices, and effectively bond to cement hydrates. The research reported herein developed non-covalent and covalent surface modification techniques to improve the dispersion and interfacial interactions of graphite nanomaterials in cement-based matrices with a dense and well graded micro-structure. The most successful approach involved polymer wrapping of nanomaterials for increasing the density of hydrophilic groups on the nanomaterial surface without causing any damage to the their structure. The nanomaterials were characterized using various spectrometry techniques, and SEM (Scanning Electron Microscopy). The graphite nanomaterials were dispersed via selected sonication procedures in the mixing water of the cement-based matrix; conventional mixing and sample preparation techniques were then employed to prepare the cement-based nanocomposite samples, which were subjected to steam curing. Comprehensive engineering and durability characteristics of cement-based nanocomposites were determined and their chemical composition, microstructure and failure mechanisms were also assessed through various spectrometry, thermogravimetry, electron microscopy and elemental analyses. Both functionalized and non-functionalized nanomaterials as well as different micro-scale fibers were used for comparison purposes at different volume fractions. Replicated mixes and tests were considered to provide the basis for statistically reliable inferences. Theoretical studies were conducted in order to develop insight into the reinforcement mechanisms of properly functionalized graphite nanomaterials. The results suggested that modified graphite nanomaterials improve the mechanical performance of cement-based matrices primarily through control of microcrack size and propagation, relying on their close spacing within matrix and dissipation of substantial energy by debonding and frictional pullout over their enormous surface areas. The gains in barrier qualities of cement-based materials with introduction of modified graphite nanomaterials could be attributed to the increased tortuosity of diffusion paths in the presence of closely spaced nanomaterials. Experimental investigations were designed and implemented towards identification of the optimum (nano- and micro-scale) reinforcement systems for high-performance concrete through RSA (Response Surface Analysis). A comprehensive experimental data base was developed on the mechanical, physical and durability characteristics as well as the structure and composition of high-performance cementitious nanocomposites reinforced with modified graphite nanomaterials and/ or different micro-fibers.

Fluctuation-driven anisotropy in effective pair interactions between nanoparticles: Thiolated gold nanoparticles in ethane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jabes, B. Shadrack; Yadav, Hari O. S.; Chakravarty, Charusita, E-mail: charus@chemistry.iitd.ac.in

2014-10-21

Fluctuations within the ligand shell of a nanoparticle give rise to a significant degree of anisotropy in effective pair interactions for low grafting densities [B. Bozorgui, D. Meng, S. K. Kumar, C. Chakravarty, and A. Cacciuto, Nano Lett. 13, 2732 (2013)]. Here, we examine the corresponding fluctuation-driven anisotropy for gold nanocrystals densely passivated with short ligands. In particular, we consider gold nanocrystals capped by alkylthiols, both in vacuum and in ethane solvent at high density. As in the preceding study, we show that the anisotropy in the nanoparticle pair potential can be quantified by an angle-dependent correction term to themore » isotropic potential of mean force (PMF). We find that the anisotropy of the ligand shells is distance dependent, and strongly influenced by ligand interdigitation effects as well as expulsion of ligand chains from the interparticle region at short distances. Such fluctuation-driven anisotropy can be significant for alkylthiol-coated gold nanoparticles, specially for longer chain lengths, under good solvent conditions. The consequences of such anisotropy for self-assembly, specially as a function of grafting density, solvent quality and at interfaces, should provide some interesting insights in future work. Our results clearly show that an isotropic two-body PMF cannot adequately describe the thermodynamics and assembly behavior of nanoparticles in this dense grafting regime and inclusion of anisotropic effects, as well as possibly many-body interactions, is necessary. Extensions of this approach to other passivated nanoparticle systems and implications for self-assembly are considered.« less

Cortical cell and neuron density estimates in one chimpanzee hemisphere.

PubMed

Collins, Christine E; Turner, Emily C; Sawyer, Eva Kille; Reed, Jamie L; Young, Nicole A; Flaherty, David K; Kaas, Jon H

2016-01-19

The density of cells and neurons in the neocortex of many mammals varies across cortical areas and regions. This variability is, perhaps, most pronounced in primates. Nonuniformity in the composition of cortex suggests regions of the cortex have different specializations. Specifically, regions with densely packed neurons contain smaller neurons that are activated by relatively few inputs, thereby preserving information, whereas regions that are less densely packed have larger neurons that have more integrative functions. Here we present the numbers of cells and neurons for 742 discrete locations across the neocortex in a chimpanzee. Using isotropic fractionation and flow fractionation methods for cell and neuron counts, we estimate that neocortex of one hemisphere contains 9.5 billion cells and 3.7 billion neurons. Primary visual cortex occupies 35 cm(2) of surface, 10% of the total, and contains 737 million densely packed neurons, 20% of the total neurons contained within the hemisphere. Other areas of high neuron packing include secondary visual areas, somatosensory cortex, and prefrontal granular cortex. Areas of low levels of neuron packing density include motor and premotor cortex. These values reflect those obtained from more limited samples of cortex in humans and other primates.

Mass-produced multi-walled carbon nanotubes as catalyst supports for direct methanol fuel cells.

PubMed

Jang, In Young; Park, Ki Chul; Jung, Yong Chae; Lee, Sun Hyung; Song, Sung Moo; Muramatsu, Hiroyuki; Kim, Yong Jung; Endo, Morinobu

2011-01-01

Commercially mass-produced multi-walled carbon nanotubes, i.e., VGNF (Showa Denko Co.), were applied to support materials for platinum-ruthenium (PtRu) nanoparticles as anode catalysts for direct methanol fuel cells. The original VGNFs are composed of high-crystalline graphitic shells, which hinder the favorable surface deposition of the PtRu nanoparticles that are formed via borohydride reduction. The chemical treatment of VGNFs with potassium hydroxide (KOH), however, enables highly dispersed and dense deposition of PtRu nanoparticles on the VGNF surface. This capability becomes more remarkable depending on the KOH amount. The electrochemical evaluation of the PtRu-deposited VGNF catalysts showed enhanced active surface areas and methanol oxidation, due to the high dispersion and dense deposition of the PtRu nanoparticles. The improvement of the surface deposition states of the PtRu nanoparticles was significantly due to the high surface area and mesorporous surface structure of the KOH-activated VGNFs.

Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO2 Coating Deposited on Graphite for Supercapacitor

PubMed Central

Huang, Wenxin; Xu, Yunhe

2017-01-01

The nucleation and growth mechanisms of porous MnO2 coating deposited on graphite in MnSO4 solution were investigated in detail by cyclic voltammetry, chronoamperometry and scanning electron microscopy. The electrochemical properties of honeycomb-like MnO2 were evaluated by cycle voltammetry and galvanostatic charge-discharge. Results indicated that MnO2 was synthesized by the following steps: Mn2+→Mn3++e−, Mn3++2H2O→MnOOH+3H+, and MnOOH→MnO2+H++e−. The deposition of MnO2 was divided into four stages. A short incubation period (approximately 1.5 s) was observed, prior to nucleation. The decreasing trend of the current slowed as time increased due to nucleation and MnO2 growth in the second stage. A huge number of nuclei were formed by instantaneous nucleation, and these nuclei grew and connected with one another at an exceedingly short time (0.5 s). In the third stage, the gaps in-between initial graphite flakes were filled with MnO2 until the morphology of the flakes gradually became similar to that of the MnO2-deposited layer. In the fourth stage, the graphite electrode was covered completely with a thick and dense layer of MnO2 deposits. All MnO2 electrodes at different deposition times obtained nearly the same specific capacitance of approximately 186 F/g, thus indicating that the specific capacitance of the electrodes is not related with deposition time. PMID:29048377

Electrically activated artificial muscles made with liquid crystal elastomers

NASA Astrophysics Data System (ADS)

Shahinpoor, Mohsen

2000-06-01

Composites of monodomain nematic liquid crystal elastomers and a conducting material distributed within their network are shown to exhibit large deformations, i.e. contraction, expansion, bending with strains of over 200% and appreciable force, by Joule heating through electrical activation. The electrical activation of the conducting material induces a rapid Joule heating in the sample leading to a nematic to isotropic phase transition where the elastomer of dimensions 32 mm x 7 mm x 0.4 mm contracted in less than a second. The cooling process, isotropic to nematic transition where the elastomer expands back to its original length, was slow and took 8 seconds. The material studied here is a highly novel liquid crystalline co-elastomer, invented and developed by Heino Finkelmann and co-workers at Albert-Ludwigs-Universitaet in Freiburg, Germany. The material is such that in which the mesogenic units are in both the side chains and the main chains of the elastomer. This co-elastomer was then mechanically loaded to induce a uniaxial network anisotropy before the cross-linking reaction was completed. These samples were then made into a composite with a conducting material such as dispersed silver particles or graphite fibers. The final samples was capable of undergoing more than 200% reversible strain in a few seconds.

Perspective of Muon Production Target at J-PARC MLF MUSE

NASA Astrophysics Data System (ADS)

Makimura, Shunsuke; Matoba, Shiro; Kawamura, Naritoshi; Matsuzawa, Yukihiro; Tabe, Masato; Aoyagi, Hiroyuki; Kondo, Hiroto; Kobayashi, Yasuo; Fujimori, Hiroshi; Ikedo, Yutaka; Kadono, Ryosuke; Koda, Akihiro; Kojima, Kenji M.; Miyake, Yasuhiro; Nakamura, Jumpei G.; Oishi, Yu; Okabe, Hirotaka; Shimomura, Koichiro; Strasser, Patrick

A pulsed muon beam with unprecedented intensity will be generated by a 3-GeV 333-microA proton beam on a muon target made of 20-mm thick isotropic graphite at J-PARC MLF MUSE (Muon Science Establishment). The first muon beam was successfully generated on September 26th, 2008. Gradually upgrading the beam intensity, continuous 300-kW proton beam has been operated by a fixed target method without replacements till June of 2014. However, the lifetime of the fixed target was anticipated to be less than 1 year by the proton-irradiation damage of the graphite through 1-MW beam operation. To extend the lifetime, a muon rotating target, in which the radiation damage is distributed to a wider area, was installed in September of 2014, and continuous and stable operation has been successfully performed. Because the muon target becomes highly radioactive by the proton irradiation, the maintenance is conducted by remote handling in the Hot cell. In September of 2015, a scraper No. 1 to collimate the proton beam scattered by the target was replaced for further high-power beam operation. Recently, new developments on monitoring and maintenance of the muon target for higher power operation are in progress. In this article, perspective of muon production target at J-PARC MLF MUSE will be described.

Effect of dropped plies on the strength of graphite-epoxy laminates

NASA Technical Reports Server (NTRS)

Curry, James M.; Johnson, Eric R.; Starnes, James H., Jr.

1987-01-01

The reduction in the compressive and tensile strengths of graphite-epoxy laminates with thickness discontinuities due to dropped plies was studied by experiment and analysis. The specimens were fabricated with all the dropped plies lumped together in the center of a sixteen-ply quasi-isotropic layup, such that one surface was flat and the slope of the opposite surface changed abruptly at the dropped ply location to accommodate the thickness change. Even though the thick and thin sections are symmetrically laminated, there exists bending-extension coupling due to the geometric eccentricity of the middle planes of the thick and thin sections. Experiments were conducted on fifty-four specimens that differed in the configuration of the dropped plies only. The strength of a laminate with dropped plies is less than the strength of its thin section, and the compressive strength of a laminate with dropped plies is less than its tensile strength. The reduction in strength is directly related to the axial stiffness change between the thick and thin sections. To examine the mechanism of failure, the three-dimensional state of stress in the dropped ply region was evaluated by the finite element method. A tensile interlaminar criterion predicted the correct location of failure, but underestimated the failure load.

Predictions of Poisson's ratio in cross-ply laminates containing matrix cracks and delaminations

NASA Technical Reports Server (NTRS)

Harris, Charles E.; Allen, David H.; Nottorf, Eric W.

1989-01-01

A damage-dependent constitutive model for laminated composites has been developed for the combined damage modes of matrix cracks and delaminations. The model is based on the concept of continuum damage mechanics and uses second-order tensor valued internal state variables to represent each mode of damage. The internal state variables are defined as the local volume average of the relative crack face displacements. Since the local volume for delaminations is specified at the laminate level, the constitutive model takes the form of laminate analysis equations modified by the internal state variables. Model implementation is demonstrated for the laminate engineering modulus E(x) and Poisson's ratio nu(xy) of quasi-isotropic and cross-ply laminates. The model predictions are in close agreement to experimental results obtained for graphite/epoxy laminates.

Transverse kinetics of a charged drop in an external electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bondarenko, S.; Komoshvili, K.

2016-01-22

We investigate a non-equilibrium behavior of a small, dense and charged drop in the transverse plane. A collective motion of the drop’s particles with constant entropy is described. Namely, we solve Vlasov’s equation with non-isotropic initial conditions. Thereby a non-equilibrium distribution function of the process of the droplet evolution in the transverse plane is calculated. An external electric field is included in the initial conditions of the equation that affects on the form of the obtained solution. Applicability of the results to the description of initial states of quark-gluon plasma is also discussed.

The Use of Pristine and Intercalated Graphite Fiber Composites as Buss Bars in Lead-Acid Batteries

NASA Technical Reports Server (NTRS)

Opaluch, Amanda M.

2004-01-01

This study was conducted as a part of the Firefly Energy Space Act Agreement project to investigate the possible use of composite materials in lead acid batteries. Specifically, it examined the use of intercalated graphite composites as buss bars. Currently, buss bars of these batteries are made of lead, a material that is problematic for several reasons. Over time, the lead is subject to both corrosion at the positive plate and sulfation at the negative plate, resulting in decreased battery life. In addition, the weight and size of the lead buss bars make for a heavy and cumbersome battery that is undesirable. Functionality and practicality of lead buss bars is adequate at best; consequently, investigation of more efficient composite materials would be advantageous. Practically speaking, graphite composites have a low density that is nearly one fourth that of its lead counterpart. A battery made of less dense materials would be more attractive to the consumer and the producer because it would be light and convenient. More importantly, low weight would be especially beneficial because it would result in greater overall power density of the battery. In addition to power density, use of graphite composite materials can also increase the life of the battery. From a functional standpoint, corrosion and sulfation at the positive and negative plates are major obstacles when considering how to extend battery life. Neither of these reactions are a factor when graphite composites replace lead parts because graphite is chemically non-reactive with the electrolyte within the battery. Without the problem of corrosion or sulfation, battery life expectancy can be almost doubled. The replacement of lead battery parts with composite materials is also more environmentally favorable because of easy disposal of organic materials. For this study, both pristine and bromine intercalated single-ply graphite fiber composites were created. The composites were fabricated in such a way as to facilitate their use in a 3" x 1/2" buss bar test cell. The prime objective of this investigation was to examine the effectiveness of a variety of graphite composite materials to act as buss bars and carry the current to and from the positive and negative battery plates. This energy transfer can be maximized by use of materials with high conductivity to minimize the buss resistance. Electrical conductivity of composites was measured using both a contactless eddy current probe and a four point measurement. In addition, the stability of these materials at battery-use conditions was characterized.

Theoretical Study of Diamond-Like Carbons and Nucleation of Diamond

NASA Astrophysics Data System (ADS)

Lee, Choon-Heung

Different forms of amorphous carbon and hydrocarbons with varying elastic and optical properties, hardness, density and hydrogen content exist depending on the preparation technique. The structure can vary from graphitic to diamond -like, i.e., from mainly threefold coordinated to mainly four-fold coordinated. In order to study the properties of such materials, microscopic models must be developed. These studies include the modelling of crosslinked defective graphite, diamond nucleation along the graphite edges, and diamond-like carbons. Tamor's proposed structure for diamondlike carbon consists of crosslinked graphitic regions. We studied a concrete realization of this model in which the cross -links are produced by shortening the interplanar bond lengths. The model study was accomplished with a pure rhombohedral graphite cell. For this study we used a semi-empirical potential based on Tersoff's environment-dependent potential which contains angular terms. It is enhanced by a long-range potential which describes the interplanar interactions. We found a configuration corresponding to a local minimum. More general features such as the randomness of the distribution of cross-links are needed for a realistic model. A model study of diamond/graphite interfaces was motivated by recent observations by Li and Angus. They observed a significant enhancement of diamond nucleation on the graphite edge planes with the preferential orientation relationship: {0001} _{g} | {111 }_{d}, < 1120 >_{g} | < 101>_{d}. Two possible interface structures were studied using the Tersoff potential. We found that the models have comparable low interface energies even if they contain some dangling bonds. Moreover, lower interface energies were found when the dangling bonds of the non-bonded diamond layer were satisfied with hydrogen. We have proposed a growth mechanism based on this study. Finally, we constructed realistic models of dense amorphous carbon. The WWW (introduced earlier for a-Si by Wooten, Winer and Weaire) model was the starting structure. The effects of clustering of the threefold coordinated atoms in pairs, chains, or graphitic (planar hexagonal clusters) were studied. The resulting models were relaxed using the Tersoff potential. Their electronic structures were studied using an empirical tight-binding scheme with parameters adjusted to reproduce the diamond and graphite band-structures. The models were found to have densities of ~ 3 g/cm^3 and bulk moduli of ~3.1 Mbar. Localized dangling bonds and pi - pi^* states were found within the wide gap of the WWW model consistent with optical gaps of the order of 0.5-2 eV. Hydrogen atoms were introduced to remove some of the dangling bonds. The models were found to account for the essential features of ion-beam deposited amorphous carbon and hydrogenated amorphous carbon.

Imaging Galactic Dark Matter with High-Energy Cosmic Neutrinos

NASA Astrophysics Data System (ADS)

Argüelles, Carlos A.; Kheirandish, Ali; Vincent, Aaron C.

2017-11-01

We show that the high-energy cosmic neutrinos seen by the IceCube Neutrino Observatory can be used to probe interactions between neutrinos and the dark sector that cannot be reached by current cosmological methods. The origin of the observed neutrinos is still unknown, and their arrival directions are compatible with an isotropic distribution. This observation, together with dedicated studies of Galactic plane correlations, suggests a predominantly extragalactic origin. Interactions between this isotropic extragalactic flux and the dense dark matter (DM) bulge of the Milky Way would thus lead to an observable imprint on the distribution, which would be seen by IceCube as (i) slightly suppressed fluxes at energies below a PeV and (ii) a deficit of events in the direction of the Galactic center. We perform an extended unbinned likelihood analysis using the four-year high-energy starting event data set to constrain the strength of DM-neutrino interactions for two model classes. We find that, in spite of low statistics, IceCube can probe regions of the parameter space inaccessible to current cosmological methods.

Imaging Galactic Dark Matter with High-Energy Cosmic Neutrinos.

PubMed

Argüelles, Carlos A; Kheirandish, Ali; Vincent, Aaron C

2017-11-17

We show that the high-energy cosmic neutrinos seen by the IceCube Neutrino Observatory can be used to probe interactions between neutrinos and the dark sector that cannot be reached by current cosmological methods. The origin of the observed neutrinos is still unknown, and their arrival directions are compatible with an isotropic distribution. This observation, together with dedicated studies of Galactic plane correlations, suggests a predominantly extragalactic origin. Interactions between this isotropic extragalactic flux and the dense dark matter (DM) bulge of the Milky Way would thus lead to an observable imprint on the distribution, which would be seen by IceCube as (i) slightly suppressed fluxes at energies below a PeV and (ii) a deficit of events in the direction of the Galactic center. We perform an extended unbinned likelihood analysis using the four-year high-energy starting event data set to constrain the strength of DM-neutrino interactions for two model classes. We find that, in spite of low statistics, IceCube can probe regions of the parameter space inaccessible to current cosmological methods.

Novel green nano composites films fabricated by indigenously synthesized graphene oxide and chitosan.

PubMed

Khan, Younus H; Islam, Atif; Sarwar, Afsheen; Gull, Nafisa; Khan, Shahzad M; Munawar, Muhammad A; Zia, Saba; Sabir, Aneela; Shafiq, Muhammad; Jamil, Tahir

2016-08-01

Graphene oxide (GO) was indigenously synthesized from graphite using standard Hummers method. Chitosan-graphene oxide green composite films were fabricated by mixing aqueous solution of chitosan and GO using dilute acetic acid as a solvent for chitosan. Chitosan of different viscosity and calculated molecular weight was used keeping amount of GO constant in each composite film. The structural properties, thermal stability and mechanical properties of the composite films were investigated using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and tensile test. FTIR studies revealed the successful synthesis of GO from graphite powder and it was confirmed that homogenous blending of chitosan and GO was promising due to oxygenated functional groups on the surface of GO. XRD indicated effective conversion of graphite to GO as its strong peak observed at 11.06° as compared to pristine graphite which appeared at 26°. Moreover, mechanical analysis confirmed the effect of molecular weight on the mechanical properties of chitosan-GO composites showing that higher molecular weight chitosan composite (GOCC-1000) showed best strength (higher than 3GPa) compared to other composite films. Thermal stability of GOCC-1000 was enhanced for which residual content increased up to 56% as compared to the thermal stability of GOCC-200 whose residue was restricted to only 24%. The morphological analysis of the composites sheets by SEM was smooth having dense structure and showed excellent interaction, miscibility, compatibility and dispersion of GO with chitosan. The prepared composite films find their applications as biomaterials in different biomedical fields. Copyright © 2016 Elsevier Ltd. All rights reserved.

Hard convex lens-shaped particles: Densest-known packings and phase behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cinacchi, Giorgio, E-mail: giorgio.cinacchi@uam.es; Torquato, Salvatore, E-mail: torquato@princeton.edu

2015-12-14

By using theoretical methods and Monte Carlo simulations, this work investigates dense ordered packings and equilibrium phase behavior (from the low-density isotropic fluid regime to the high-density crystalline solid regime) of monodisperse systems of hard convex lens-shaped particles as defined by the volume common to two intersecting congruent spheres. We show that, while the overall similarity of their shape to that of hard oblate ellipsoids is reflected in a qualitatively similar phase diagram, differences are more pronounced in the high-density crystal phase up to the densest-known packings determined here. In contrast to those non-(Bravais)-lattice two-particle basis crystals that are themore » densest-known packings of hard (oblate) ellipsoids, hard convex lens-shaped particles pack more densely in two types of degenerate crystalline structures: (i) non-(Bravais)-lattice two-particle basis body-centered-orthorhombic-like crystals and (ii) (Bravais) lattice monoclinic crystals. By stacking at will, regularly or irregularly, laminae of these two crystals, infinitely degenerate, generally non-periodic in the stacking direction, dense packings can be constructed that are consistent with recent organizing principles. While deferring the assessment of which of these dense ordered structures is thermodynamically stable in the high-density crystalline solid regime, the degeneracy of their densest-known packings strongly suggests that colloidal convex lens-shaped particles could be better glass formers than colloidal spheres because of the additional rotational degrees of freedom.« less

Demixing in simple dipolar mixtures: Integral equation versus density functional results

NASA Astrophysics Data System (ADS)

Range, Gabriel M.; Klapp, Sabine H. L.

2004-09-01

Using reference hypernetted chain (RHNC) integral equations and density functional theory in the modified mean-field (MMF) approximation we investigate the phase behavior of binary mixtures of dipolar hard spheres. The two species ( A and B ) differ only in their dipole moments mA and mB , and the central question investigated is under which conditions these asymmetric mixtures can exhibit demixing phase transitions in the fluid phase regime. Results from our two theoretical approaches turn out to strongly differ. Within the RHNC (which we apply to the isotropic high-temperature phase) demixing does indeed occur for dense systems with small interaction parameters Γ=mB2/mA2 . This result generalizes previously reported observations on demixing in mixtures of dipolar and neutral hard spheres (Γ=0) to the case of true dipolar hard sphere mixtures. The RHNC approach also indicates that these demixed fluid phases are isotropic at temperatures accessible by the theory, whereas isotropic-to-ferroelectric transitions occur only at larger Γ . The MMF theory, on the other hand, yields a different picture in which demixing occurs in combination with spontaneous ferroelectricity at all Γ considered. This discrepancy underlines the relevance of correlational effects for the existence of demixing transitions in dipolar systems without dispersive interactions. Indeed, supplementing the dipolar interactions by small, asymmetric amounts of van der Waals-like interactions (and thereby supporting the systems tendency to demix) one finally reaches good agreement between MMF and RHNC results.

C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit

NASA Astrophysics Data System (ADS)

Martz, Pierre; Cathelineau, Michel; Mercadier, Julien; Boiron, Marie-Christine; Jaguin, Justine; Tarantola, Alexandre; Demacon, Mickael; Gerbeaud, Olivier; Quirt, David; Doney, Amber; Ledru, Patrick

2017-12-01

Graphitic shear zones are spatially associated with unconformity-related uranium deposits that are located around the unconformity between the strata of the Paleo- to Mesoproterozoic Athabasca Basin (Saskatchewan, Canada) and its underlying Archean to Paleoproterozoic basement. The present study focuses on basement-hosted ductile-brittle graphitic shear zones near the Cigar Lake U deposit, one of the largest unconformity-related U deposits. The goal of the study is to decipher the pre-Athabasca Basin fluid migration history recorded within such structures and its potential role on the formation of such exceptional deposit. Dominantly C-O-H(-N) metamorphic fluids have been trapped in Fluid Inclusion Planes (FIPs) in magmatic quartz within ductile-brittle graphitic shear zones active during retrograde metamorphism associated with the formation of the Wollaston-Mudjatik Transition Zone (WMTZ) between ca. 1805 and 1720 Ma. Such fluids show a compositional evolution along the retrograde path, from a dense and pure CO2 fluid during the earliest stages, through a lower density CO2 ± CH4-N2 (± H2O) fluid and, finally, to a very low density CH4-N2 fluid. Statistical study of the orientation, distribution, proportion, and chemical characterization of the FIPs shows that: i) CO2 (δ13CCO2 around - 9‰ PDB) from decarbonation reactions and/or partial water-metamorphic graphite equilibrium initially migrated regionally and pervasively under lithostatic conditions at about 500 to 800 °C and 150 to 300 MPa. Such P-T conditions attest to a high geothermal gradient of around 60 to 90 °C/km, probably related to rapid exhumation of the basement or a large-scale heat source. ii) Later brittle reactivation of the shear zone at around 450 °C and 25-50 MPa favored circulation of CO2-CH4-N2(± H2O) fluids in equilibrium with metamorphic graphite (δ13CCO2 around - 14‰) under hydrostatic conditions and only within the shear zones. Cooling of these fluids and the water uptake linked to fluid-basement rock reactions led to the precipitation at around 450 °C of poorly-crystallized hydrothermal graphite. This graphite presents isotopic (δ13C - 30 to - 26‰ PDB) and morphological differences from the high-T metamorphic graphite (> 600 °C, - 29 to - 20‰ δ13C) derived from metamorphism of C-rich sedimentary material. The brittle structural reactivation and the related fluid migration and graphite precipitation were specifically focused within the shear zones and related damage zones. The brittle reactivation produced major changes in the petro-physical, mineralogical, and chemical characteristics of the structures and their damage zones. It especially increased the fracture paleoporosity and rock weakness toward the fault cores. These major late metamorphic modifications of the graphitic shear zones were likely key parameters favoring the enhanced reactivity of these basement zones under tectonic stress following deposition of the Athabasca Basin, and so controlled basinal brine movement at the basin/basement interface related to the formation of the unconformity-related uranium deposits. This relationship consequently readily explains the specific spatial relationships between unconformity-related U deposits and the ductile-brittle graphitic shear zones.

A comparison of mechanical properties of some foams and honeycombs

NASA Technical Reports Server (NTRS)

Bhat, Balakrishna T.; Wang, T. G.

1990-01-01

A comparative study is conducted of the mechanical properties of foam-core and honeycomb-core sandwich panels, using a normalizing procedure based on common properties of cellular solids and related properties of dense solids. Seven different honeycombs and closed-foam cells are discussed; of these, three are commercial Al alloy honeycombs, one is an Al-alloy foam, and two are polymeric foams. It is concluded that ideal, closed-cell foams may furnish compressive strengths which while isotropic can be fully comparable to the compressive strengths of honeycombs in the thickness direction. The shear strength of ideal closed-cell foams may be superior to the shear strength of honeycombs.

Analysis of granular flow in a pebble-bed nuclear reactor.

PubMed

Rycroft, Chris H; Grest, Gary S; Landry, James W; Bazant, Martin Z

2006-08-01

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6-cm-diam spheres draining in a cylindrical vessel of diameter 3.5m and height 10 m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma

PubMed Central

Vesel, Alenka; Eleršič, Kristina; Modic, Martina; Junkar, Ita; Mozetič, Miran

2014-01-01

Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely covered with nanocones. The size of the nanocones strongly depended on treatment time. The optimal results in terms of material hemocompatibility were obtained after treatment with oxygen plasma for 15 s, when both the nanotopography and wettability were the most favorable, since marked reduction in adhesion and activation of platelets was observed on this surface. At prolonged treatment times, the rich surface topography was lost and thus also its antithrombogenic properties. Chemical composition of the surface was always more or less the same, regardless of its morphology and height of the nanocones. Namely, on all plasma treated samples, only a few atomic percent of oxygen was found, meaning that plasma caused mostly etching, leading to changes in the surface morphology. This indicates that the main preventing mechanism against platelets adhesion was the right surface morphology. PMID:28788553

Inert gas rejection device for zinc-halogen battery systems

DOEpatents

Hammond, Michael J.; Arendell, Mark W.

1981-01-01

An electrolytic cell for separating chlorine gas from other (foreign) gases, having an anode, a cathode assembly, an aqueous electrolyte, a housing, and a constant voltage power supply. The cathode assembly is generally comprised of a dense graphite electrode having a winding channel formed in the face opposing the anode, a gas impermeable (but liquid permeable) membrane sealed into the side of the cathode electrode over the channel, and a packing of graphite particles contained in the channel of the cathode electrode. The housing separates and parallelly aligns the anode and cathode assembly, and provides a hermetic seal for the cell. In operation, a stream of chlorine and foreign gases enters the cell at the beginning of the cathode electrode channel. The chlorine gas is dissolved into the electrolyte and electrochemically reduced into chloride ions. The chloride ions disfuse through the gas impermeable membrane, and are electrochemically oxidized at the anode into purified chlorine gas. The foreign gases do not participate in the above electrochemical reactions, and are vented from the cell at the end of the cathode electrode channel.

Quaternary FeCoNiMn-Based Nanocarbon Electrocatalysts for Bifunctional Oxygen Reduction and Evolution: Promotional Role of Mn Doping in Stabilizing Carbon

DOE PAGES

Gupta, Shiva; Zhao, Shuai; Wang, Xiao Xia; ...

2017-10-31

The intrinsic instability of carbon largely limits its use for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as a bifunctional catalyst in reversible fuel cells or water electrolyzers. In this paper, we discovered that Mn doping has a promotional role in stabilizing nanocarbon catalysts for the ORR/OER in alkaline media. Stable nanocarbon composites are derived from an inexpensive carbon/nitrogen precursor (i.e., dicyandiamide) and quaternary FeCoNiMn alloy via a template-free carbonization process. In addition to FeCoNiMn metal alloys/oxides, the carbon composites comprise substantial carbon tube forests growing on a thick and dense graphitic substrate. The dense carbon substratemore » with high degree of graphitization results from Mn doping, while active nitrogen-doped carbon tubes stem from FeCoNi. Catalyst structures and performance are greatly dependent on the doping content of Mn. Various accelerated stress tests (AST) and life tests verify the encouraging ORR/OER stability of the nanocarbon composite catalyst with optimal Mn doping. Extensive characterization before and after ASTs elucidates the mechanism of stability enhancement resulting from Mn doping, which is attributed to (i) hybrid carbon nanostructures with enhanced resistance to oxidation and (ii) the in situ formation of the β-MnO 2 and FeCoNi-based oxides capable of preventing carbon corrosion and promoting activity. Note that the improvement in stability due to Mn doping is accompanied by a slight activity loss due to a decrease in surface area. Finally, this work provides a strategy to stabilize carbon catalysts by appropriately integrating transition metals and engineering carbon structures.« less

Quaternary FeCoNiMn-Based Nanocarbon Electrocatalysts for Bifunctional Oxygen Reduction and Evolution: Promotional Role of Mn Doping in Stabilizing Carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Shiva; Zhao, Shuai; Wang, Xiao Xia

The intrinsic instability of carbon largely limits its use for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as a bifunctional catalyst in reversible fuel cells or water electrolyzers. In this paper, we discovered that Mn doping has a promotional role in stabilizing nanocarbon catalysts for the ORR/OER in alkaline media. Stable nanocarbon composites are derived from an inexpensive carbon/nitrogen precursor (i.e., dicyandiamide) and quaternary FeCoNiMn alloy via a template-free carbonization process. In addition to FeCoNiMn metal alloys/oxides, the carbon composites comprise substantial carbon tube forests growing on a thick and dense graphitic substrate. The dense carbon substratemore » with high degree of graphitization results from Mn doping, while active nitrogen-doped carbon tubes stem from FeCoNi. Catalyst structures and performance are greatly dependent on the doping content of Mn. Various accelerated stress tests (AST) and life tests verify the encouraging ORR/OER stability of the nanocarbon composite catalyst with optimal Mn doping. Extensive characterization before and after ASTs elucidates the mechanism of stability enhancement resulting from Mn doping, which is attributed to (i) hybrid carbon nanostructures with enhanced resistance to oxidation and (ii) the in situ formation of the β-MnO 2 and FeCoNi-based oxides capable of preventing carbon corrosion and promoting activity. Note that the improvement in stability due to Mn doping is accompanied by a slight activity loss due to a decrease in surface area. Finally, this work provides a strategy to stabilize carbon catalysts by appropriately integrating transition metals and engineering carbon structures.« less

VERY LARGE INTERSTELLAR GRAINS AS EVIDENCED BY THE MID-INFRARED EXTINCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shu; Jiang, B. W.; Li, Aigen, E-mail: shuwang@mail.bnu.edu.cn, E-mail: bjiang@bnu.edu.cn, E-mail: wanshu@missouri.edu, E-mail: lia@missouri.edu

The sizes of interstellar grains are widely distributed, ranging from a few angstroms to a few micrometers. The ultraviolet (UV) and optical extinction constrains the dust in the size range of a couple hundredths of micrometers to several submicrometers. The near and mid infrared (IR) emission constrains the nanometer-sized grains and angstrom-sized very large molecules. However, the quantity and size distribution of micrometer-sized grains remain unknown because they are gray in the UV/optical extinction and they are too cold and emit too little in the IR to be detected by IRAS, Spitzer, or Herschel. In this work, we employ themore » ∼3–8 μm mid-IR extinction, which is flat in both diffuse and dense regions to constrain the quantity, size, and composition of the μm-sized grain component. We find that, together with nano- and submicron-sized silicate and graphite (as well as polycyclic aromatic hydrocarbons), μm-sized graphite grains with C/H ≈ 137 ppm and a mean size of ∼1.2 μm closely fit the observed interstellar extinction of the Galactic diffuse interstellar medium from the far-UV to the mid-IR, as well as the near-IR to millimeter thermal emission obtained by COBE/DIRBE, COBE/FIRAS, and Planck up to λ ≲ 1000 μm. The μm-sized graphite component accounts for ∼14.6% of the total dust mass and ∼2.5% of the total IR emission.« less

Using Spin to Understand the Formation of LIGO and Virgo’s Black Holes

NASA Astrophysics Data System (ADS)

Farr, Ben; Holz, Daniel E.; Farr, Will M.

2018-02-01

With the growing number of binary black hole (BBH) mergers detected by the Advanced LIGO and Virgo detectors, it is becoming possible to constrain the properties of the underlying population and better understand the formation of these systems. Black hole (BH) spin orientations are one of the cleanest discriminators of formation history, with BHs in dynamically formed binaries in dense stellar environments expected to have spins distributed isotropically, in contrast to isolated populations where stellar evolution is expected to induce spins preferentially aligned with the orbital angular momentum. In this work, we propose a simple, model-agnostic approach to characterizing the spin properties of LIGO/Virgo’s BBH population. Using measurements of the effective spin of the binaries, we introduce a simple parameter to quantify the fraction of the population that is isotropically distributed, regardless of the spin magnitude distribution of the population. Once the orientation characteristics of the population have been determined, we show how measurements of effective spin can be used to directly constrain the BH spin magnitude distribution. We find that most effective spin measurements are too small to be informative, with the first four events showing a slight preference for a population with alignment, with an odds ratio of 1.2. We argue that it will be possible to distinguish symmetric and anti-symmetric populations at high confidence with tens of additional detections, although mixed populations may take significantly longer to disentangle. We also derive BH spin magnitude distributions from LIGO’s first four BBHs under the assumption of aligned or isotropic populations.

From intermediate anisotropic to isotropic friction at large strain rates to account for viscosity thickening in polymer solutions

NASA Astrophysics Data System (ADS)

Stephanou, Pavlos S.; Kröger, Martin

2018-05-01

The steady-state extensional viscosity of dense polymeric liquids in elongational flows is known to be peculiar in the sense that for entangled polymer melts it monotonically decreases—whereas for concentrated polymer solutions it increases—with increasing strain rate beyond the inverse Rouse time. To shed light on this issue, we solve the kinetic theory model for concentrated polymer solutions and entangled melts proposed by Curtiss and Bird, also known as the tumbling-snake model, supplemented by a variable link tension coefficient that we relate to the uniaxial nematic order parameter of the polymer. As a result, the friction tensor is increasingly becoming isotropic at large strain rates as the polymer concentration decreases, and the model is seen to capture the experimentally observed behavior. Additional refinements may supplement the present model to capture very strong flows. We furthermore derive analytic expressions for small rates and the linear viscoelastic behavior. This work builds upon our earlier work on the use of the tumbling-snake model under shear and demonstrates its capacity to improve our microscopic understanding of the rheology of entangled polymer melts and concentrated polymer solutions.

Anisotropic Rayleigh-wave Phase-velocity Maps in Northern Vietnam

NASA Astrophysics Data System (ADS)

Zhao, L.; Legendre, C. P.; Huang, W.; Huang, B.

2013-12-01

Northern Vietnam is the location of both the Song Ma Complex, the suture between the Indochina and South China Blocks, and the southern end of the giant Red River Shear Zone. Lithospheric structure provides important clues to the evolutions of the tectonic boundary zone and the interaction between the Indochina and South China Blocks. During 2006-2008, an array of 24 broadband stations were deployed in northern Vietnam in a collaborative project between the Institute of Geophysics of the Vietnam Academy of Science and Technology and the Institute of Earth Sciences of Academic Sinica in Taiwan. In this study, we use Rayleigh waveforms recorded at those stations from globally distributed earthquakes to construct the regional isotropic and azimuthally anisotropic phase velocity maps. Rayleigh-wave dispersion curves in the period range of 10-200 sec are obtained manually by the two-station method using vertical-component broadband waveforms. The dispersion curves along the densely distributed crossing paths are inverted via the LSQR algorithm for the isotropic and azimuthally anisotropic phase-velocity maps at a number of periods. Results will be compared with previous studies in this region based on body-wave traveltimes, SKS splitting observations and receiver functions, and with the tectonic features observed in the region.

Patterned forests of vertically-aligned multiwalled carbon nanotubes using metal salt catalyst solutions.

PubMed

Garrett, David J; Flavel, Benjamin S; Baronian, Keith H R; Downard, Alison J

2013-01-01

A simple method for producing patterned forests of multiwalled carbon nanotubes (MWCNTs) is described. An aqueous metal salt solution is spin-coated onto a substrate patterned with photoresist by standard methods. The photoresist is removed by acetone washing leaving the acetone-insoluble catalyst pattern on the substrate. Dense forests of vertically aligned (VA) MWCNTs are grown on the patterned catalyst layers by chemical vapour deposition. The procedures have been demonstrated by growing MWCNT forests on two substrates: silicon and conducting graphitic carbon films. The forests adhere strongly to the substrates and when grown directly on carbon film, offer a simple method of preparing MWCNT electrodes.

Bias-induced conformational switching of supramolecular networks of trimesic acid at the solid-liquid interface

NASA Astrophysics Data System (ADS)

Ubink, J.; Enache, M.; Stöhr, M.

2018-05-01

Using the tip of a scanning tunneling microscope, an electric field-induced reversible phase transition between two planar porous structures ("chickenwire" and "flower") of trimesic acid was accomplished at the nonanoic acid/highly oriented pyrolytic graphite interface. The chickenwire structure was exclusively observed for negative sample bias, while for positive sample bias only the more densely packed flower structure was found. We suggest that the slightly negatively charged carboxyl groups of the trimesic acid molecule are the determining factor for this observation: their adsorption behavior varies with the sample bias and is thus responsible for the switching behavior.

Microscale Heat Conduction Models and Doppler Feedback

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hawari, Ayman I.; Ougouag, Abderrafi

2015-01-22

The objective of this project is to establish an approach for providing the fundamental input that is needed to estimate the magnitude and time-dependence of the Doppler feedback mechanism in Very High Temperature reactors. This mechanism is the foremost contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic (TRISO) coated particles. Therefore, its correct prediction is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat deposition, heat transfer and temperaturemore » rise must be correctly predicted. To achieve the above objective, this project will explore an approach that accounts for lattice effects as well as local temperature variations and the correct definition of temperature and related local effects.« less

Diffusivities of Ag, Cs, Sr, and Kr in TRISO fuel particles and graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collin, Blaise Paul

Tri-structural isotropic (TRISO) coated particles have been developed and studied since the late 1950s when the concept of coated particles was invented by Roy Huddle of the United Kingdom Atomic Energy Authority. Several decades of work by half a dozen countries on fission product transport in TRISO fuel through numerous irradiation and heating experiments have led to several recommendations of transport data and to the adoption of various sets of diffusion coefficients. In 1997, the International Atomic Energy Agency (IAEA) gathered all these historical results and issued a technical document (TECDOC-978 [IAEA]) that summarizes these sets of recommended diffusion coefficients.more » Table 1 shows the reference literature articles for the diffusivities that have historically been recommended by the American and German TRISO fuel development programs and that are summarized in the IAEA report (see section 7 for full references of these articles).« less

On the fractography of overload, stress corrosion, and cyclic fatigue failures in pyrolytic-carbon materials used in prosthetic heart-valve devices.

PubMed

Ritchie, R O; Dauskardt, R H; Pennisi, F J

1992-01-01

A scanning electron microscopy study is reported of the nature and morphology of fracture surfaces in pyrocarbons commonly used for the manufacture of mechanical heart-valve prostheses. Specifically, silicon-alloyed low-temperature-isotropic (LTI)-pyrolytic carbon is examined, both as a coating on graphite and as a monolithic material, following overload, stress corrosion (static fatigue), and cyclic fatigue failures in a simulated physiological environment of 37 degrees C Ringer's solution. It is found that, in contrast to most metallic materials yet in keeping with many ceramics, there are no distinct fracture morphologies in pyro-carbons which are characteristic of a specific mode of loading; fracture surfaces appear to be identical for both catastrophic and subcritical crack growth under either sustained or cyclic loading. We conclude that caution should be used in assigning the likely cause of failure of pyrolytic carbon heart-valve components using fractographic examination.

Parametric Study on the Response of Compression-Loaded Composite Shells With Geometric and Material Imperfections

NASA Technical Reports Server (NTRS)

Hilburger, Mark W.; Starnes, James H., Jr.

2004-01-01

The results of a parametric study of the effects of initial imperfections on the buckling and postbuckling response of three unstiffened thinwalled compression-loaded graphite-epoxy cylindrical shells with different orthotropic and quasi-isotropic shell-wall laminates are presented. The imperfections considered include initial geometric shell-wall midsurface imperfections, shell-wall thickness variations, local shell-wall ply-gaps associated with the fabrication process, shell-end geometric imperfections, nonuniform applied end loads, and variations in the boundary conditions including the effects of elastic boundary conditions. A high-fidelity nonlinear shell analysis procedure that accurately accounts for the effects of these imperfections on the nonlinear responses and buckling loads of the shells is described. The analysis procedure includes a nonlinear static analysis that predicts stable response characteristics of the shells and a nonlinear transient analysis that predicts unstable response characteristics.

Direct observation of impact propagation and absorption in dense colloidal monolayers

NASA Astrophysics Data System (ADS)

Buttinoni, Ivo; Cha, Jinwoong; Lin, Wei-Hsun; Job, Stéphane; Daraio, Chiara; Isa, Lucio

2017-11-01

Dense colloidal suspensions can propagate and absorb large mechanical stresses, including impacts and shocks. The wave transport stems from the delicate interplay between the spatial arrangement of the structural units and solvent-mediated effects. For dynamic microscopic systems, elastic deformations of the colloids are usually disregarded due to the damping imposed by the surrounding fluid. Here, we study the propagation of localized mechanical pulses in aqueous monolayers of micron-sized particles of controlled microstructure. We generate extreme localized deformation rates by exciting a target particle via pulsed-laser ablation. In crystalline monolayers, stress propagation fronts take place, where fast-moving particles (V approximately a few meters per second) are aligned along the symmetry axes of the lattice. Conversely, more viscous solvents and disordered structures lead to faster and isotropic energy absorption. Our results demonstrate the accessibility of a regime where elastic collisions also become relevant for suspensions of microscopic particles, behaving as “billiard balls” in a liquid, in analogy with regular packings of macroscopic spheres. We furthermore quantify the scattering of an impact as a function of the local structural disorder.

Direct observation of impact propagation and absorption in dense colloidal monolayers

PubMed Central

Cha, Jinwoong; Lin, Wei-Hsun; Job, Stéphane; Daraio, Chiara

2017-01-01

Dense colloidal suspensions can propagate and absorb large mechanical stresses, including impacts and shocks. The wave transport stems from the delicate interplay between the spatial arrangement of the structural units and solvent-mediated effects. For dynamic microscopic systems, elastic deformations of the colloids are usually disregarded due to the damping imposed by the surrounding fluid. Here, we study the propagation of localized mechanical pulses in aqueous monolayers of micron-sized particles of controlled microstructure. We generate extreme localized deformation rates by exciting a target particle via pulsed-laser ablation. In crystalline monolayers, stress propagation fronts take place, where fast-moving particles (V approximately a few meters per second) are aligned along the symmetry axes of the lattice. Conversely, more viscous solvents and disordered structures lead to faster and isotropic energy absorption. Our results demonstrate the accessibility of a regime where elastic collisions also become relevant for suspensions of microscopic particles, behaving as “billiard balls” in a liquid, in analogy with regular packings of macroscopic spheres. We furthermore quantify the scattering of an impact as a function of the local structural disorder. PMID:29087329

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerczak, Tyler J.; Smith, Kurt R.; Petrie, Christian M.

Tristructural-isotropic (TRISO)–coated particle fuel is a promising advanced fuel concept consisting of a spherical fuel kernel made of uranium oxide and uranium carbide, surrounded by a porous carbonaceous buffer layer and successive layers of dense inner pyrolytic carbon (IPyC), silicon carbide (SiC) deposited by chemical vapor , and dense outer pyrolytic carbon (OPyC). This fuel concept is being considered for advanced reactor applications such as high temperature gas-cooled reactors (HTGRs) and molten salt reactors (MSRs), as well as for accident-tolerant fuel for light water reactors (LWRs). Development and implementation of TRISO fuel for these reactor concepts support the US Departmentmore » of Energy (DOE) Office of Nuclear Energy mission to promote safe, reliable nuclear energy that is sustainable and environmentally friendly. During operation, the SiC layer serves as the primary barrier to metallic fission products and actinides not retained in the kernel. It has been observed that certain fission products are released from TRISO fuel during operation, notably, Ag, Eu, and Sr [1]. Release of these radioisotopes causes safety and maintenance concerns.« less

Acceptance Test Data for BWXT Coated Particle Batch 93164A Defective IPyC Fraction and Pyrocarbon Anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmreich, Grant W.; Hunn, John D.; Skitt, Darren J.

2017-02-01

Coated particle fuel batch J52O-16-93164 was produced by Babcock and Wilcox Technologies (BWXT) for possible selection as fuel for the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program’s AGR-5/6/7 irradiation test in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR), or may be used as demonstration production-scale coated particle fuel for other experiments. The tristructural-isotropic (TRISO) coatings were deposited in a 150-mm-diameter production-scale fluidizedbed chemical vapor deposition (CVD) furnace onto 425-μm-nominal-diameter spherical kernels from BWXT lot J52L-16-69316. Each kernel contained a mixture of 15.5%-enriched uranium carbide and uranium oxide (UCO) and was coated with four consecutive CVD layers:more » a ~50% dense carbon buffer layer with 100-μm-nominal thickness, a dense inner pyrolytic carbon (IPyC) layer with 40-μm-nominal thickness, a silicon carbide (SiC) layer with 35-μm-nominal thickness, and a dense outer pyrolytic carbon (OPyC) layer with 40-μm-nominal thickness. The TRISO-coated particle batch was sieved to upgrade the particles by removing over-sized and under-sized material, and the upgraded batch was designated by appending the letter A to the end of the batch number (i.e., 93164A).« less

Three Dimensionally Interlinked, Dense, Solid Form of Single-Walled CNT Ropes

NASA Technical Reports Server (NTRS)

Smalley, Richard E.

2012-01-01

A 3D networked, dense form of single-walled carbon nanotubes (SWNT) has been made through isotropic shrinking of a gel-like SWNT-water paste by very slow evaporation. Approximately 35 g of Raw HiPco nanotubes were cleaned by the method of soft baking (250 C for 15 hours in air saturated with water vapor) in a glass beaker followed by leaching with concentrated hydrochloric acid. Typically, one liter of concentrated hydrochloric acid was added to the soft-baked voluminous mass in the same large beaker, and allowed to digest at room temperature with stirring overnight. The acid-digested SWNT slurry was filtered through a large porcelain Buchner funnel under atmospheric pressure. The slurry was continuously flushed, while still in the funnel, with a very slow but steady stream of deionized water employing a peristaltic pump. This process, referred to as gwashing, h continued until the filtrate water dripping from the Buchner funnel was clear, colorless, and neutral to a pH paper. This took about 15 liters of water to flow through the slurry over a day. At this point, the water pump was stopped and the SWNT-water slurry was allowed to drain the excess water for about 10 hours. The resulting thick paste of SWNT-neutral water was transferred to a beaker. The beaker was covered with aluminum foil with few holes and allowed to dry very slowly in a hood at room temperature. In about eight weeks, the sample gradually dried isotropically to a cylindrical dense mass referred to as a carbon nanotube block (CNB). There was no carbonaceous matter sticking to any of the glass surface where the SWNT-water paste made contact. The approximate dimensions of the cylindrical SWNT block that weighed 28 g were 1.5 in. (.3.8 cm) in diameter and 1.25 in. (.3.2 cm) in height. The bottom portion of the cylinder that was in contact with the beaker surface was slightly wider, indicating some resistance to shrinking. The cylindrical mass also consisted of several pores. The cylindrical mass was very tough and could not be broken with a small hammer using considerable force. The mass of the solid could be polished over a fine grain emery paper or even a smooth, stainless steel surface indicative of alignment at finer levels.

Development of Simultaneous Corrosion Barrier and Optimized Microstructure in FeCrAl Heat-Resistant Alloy for Energy Applications. Part II: The Optimized Creep-Resistant Microstructure

NASA Astrophysics Data System (ADS)

Pimentel, G.; Aranda, M. M.; Chao, J.; González-Carrasco, J. L.; Capdevila, C.

2015-09-01

The first part of this two-part study reported the possibility of simultaneously generating a dense, self-healing α-alumina layer by thermal oxidation and a coarse-grained microstructure with a potential goodness for high-temperature creep resistance in a FeCrAl oxide dispersion-strengthened ferritic alloy that was cold deformed after hot rolling and extrusion. In this second part, the factors affecting the formation of the coarse-grained microstructure such as strain gradients induced during the rolling process are analyzed. It is concluded that larger strain gradients lead to more refined and more isotropic grain structures.

X-ray Thomson scattering measurement of temperature in warm dense carbon

DOE PAGES

Falk, Katerina; Fryer, C. L.; Gamboa, E. J.; ...

2016-11-22

Here, a novel platform to measure the equation of state using a combination of diagnostics, where the spectrally resolved x-ray Thomson scattering (XRTS) is used to obtain accurate temperature measurements of warm dense matter (WDM) was developed for the OMEGA laser facility. OMEGA laser beams have been used to drive strong shocks in carbon targets creating WDM and generating the Ni He-alpha x-ray probe used for XRTS. Additional diagnostics including x-ray radiography, velocity interferometry and streaked optical pyrometry provided complementary measurements of density and pressure. The WDM regime of near solid density and moderate temperatures (1–100 eV) is a challengingmore » yet important area of research in inertial confinement fusion and astrophysics. This platform has been used to study off-Hugoniot states of shock-released diamond and graphite at pressures between 1 and 10 Mbar and temperatures between 5 and 15 eV as well as first x-ray Thomson scattering data from shocked low density CH foams reaching five times compression and temperatures of 20–30 eV.« less

Evolution of elastic x-ray scattering in laser-shocked warm dense lithium.

PubMed

Kugland, N L; Gregori, G; Bandyopadhyay, S; Brenner, C M; Brown, C R D; Constantin, C; Glenzer, S H; Khattak, F Y; Kritcher, A L; Niemann, C; Otten, A; Pasley, J; Pelka, A; Roth, M; Spindloe, C; Riley, D

2009-12-01

We have studied the dynamics of warm dense Li with near-elastic x-ray scattering. Li foils were heated and compressed using shock waves driven by 4-ns-long laser pulses. Separate 1-ns-long laser pulses were used to generate a bright source of 2.96 keV Cl Ly- alpha photons for x-ray scattering, and the spectrum of scattered photons was recorded at a scattering angle of 120 degrees using a highly oriented pyrolytic graphite crystal operated in the von Hamos geometry. A variable delay between the heater and backlighter laser beams measured the scattering time evolution. Comparison with radiation-hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Near-elastic scattering amplitudes have been successfully simulated using the screened one-component plasma model. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state Z[over ] and by extension to the choice of ionization model in the radiation-hydrodynamics simulations used to predict plasma properties within the shocked Li.

High speed spectral domain optical coherence tomography for retinal imaging at 500,000 A‑lines per second

PubMed Central

An, Lin; Li, Peng; Shen, Tueng T.; Wang, Ruikang

2011-01-01

We present a new development of ultrahigh speed spectral domain optical coherence tomography (SDOCT) for human retinal imaging at 850 nm central wavelength by employing two high-speed line scan CMOS cameras, each running at 250 kHz. Through precisely controlling the recording and reading time periods of the two cameras, the SDOCT system realizes an imaging speed at 500,000 A-lines per second, while maintaining both high axial resolution (~8 μm) and acceptable depth ranging (~2.5 mm). With this system, we propose two scanning protocols for human retinal imaging. The first is aimed to achieve isotropic dense sampling and fast scanning speed, enabling a 3D imaging within 0.72 sec for a region covering 4x4 mm2. In this case, the B-frame rate is 700 Hz and the isotropic dense sampling is 500 A-lines along both the fast and slow axes. This scanning protocol minimizes the motion artifacts, thus making it possible to perform two directional averaging so that the signal to noise ratio of the system is enhanced while the degradation of its resolution is minimized. The second protocol is designed to scan the retina in a large field of view, in which 1200 A-lines are captured along both the fast and slow axes, covering 10 mm2, to provide overall information about the retinal status. Because of relatively long imaging time (4 seconds for a 3D scan), the motion artifact is inevitable, making it difficult to interpret the 3D data set, particularly in a way of depth-resolved en-face fundus images. To mitigate this difficulty, we propose to use the relatively high reflecting retinal pigmented epithelium layer as the reference to flatten the original 3D data set along both the fast and slow axes. We show that the proposed system delivers superb performance for human retina imaging. PMID:22025983

High speed spectral domain optical coherence tomography for retinal imaging at 500,000 A‑lines per second.

PubMed

An, Lin; Li, Peng; Shen, Tueng T; Wang, Ruikang

2011-10-01

We present a new development of ultrahigh speed spectral domain optical coherence tomography (SDOCT) for human retinal imaging at 850 nm central wavelength by employing two high-speed line scan CMOS cameras, each running at 250 kHz. Through precisely controlling the recording and reading time periods of the two cameras, the SDOCT system realizes an imaging speed at 500,000 A-lines per second, while maintaining both high axial resolution (~8 μm) and acceptable depth ranging (~2.5 mm). With this system, we propose two scanning protocols for human retinal imaging. The first is aimed to achieve isotropic dense sampling and fast scanning speed, enabling a 3D imaging within 0.72 sec for a region covering 4x4 mm(2). In this case, the B-frame rate is 700 Hz and the isotropic dense sampling is 500 A-lines along both the fast and slow axes. This scanning protocol minimizes the motion artifacts, thus making it possible to perform two directional averaging so that the signal to noise ratio of the system is enhanced while the degradation of its resolution is minimized. The second protocol is designed to scan the retina in a large field of view, in which 1200 A-lines are captured along both the fast and slow axes, covering 10 mm(2), to provide overall information about the retinal status. Because of relatively long imaging time (4 seconds for a 3D scan), the motion artifact is inevitable, making it difficult to interpret the 3D data set, particularly in a way of depth-resolved en-face fundus images. To mitigate this difficulty, we propose to use the relatively high reflecting retinal pigmented epithelium layer as the reference to flatten the original 3D data set along both the fast and slow axes. We show that the proposed system delivers superb performance for human retina imaging.

Grain Temperature and Infrared Emission from Carbon Dust of Mixed Composition

NASA Astrophysics Data System (ADS)

Bartlett, S.; Duley, W. W.

1996-06-01

The equilibrium temperature of carbonaceous dust grains whose composition is consistent with IR spectra of diffuse cloud and dense cloud dust has been calculated using random covalent network (RCN) solutions for amorphous dust having a mixed graphite, diamond, and polymeric hydrocarbon composition. An effective medium approximation has been adopted to describe optical and thermal constants for dust compositions consistent with IR absorption spectra. A small amount of sp2 hybridized carbon in the form of aromatic rings is found to have a significant effect in reducing equilibrium temperature in dust with high diamond/polymer content. This formalism has also been used to calculate nonequilibrium emission spectra of very small grains (VSGs) subjected to stochastic heating in the interstellar radiation field. Such grains are found to emit strongly in sharp IR bands associated with C-H bonds at 3.4 μm and longer wavelengths. The effect of varying graphite/diamond/hydrocarbon composition on nonequilibrium emission by VSGs can also be described using this formalism. The ratio of emission at 12 and 25 μm is found to be high for VSGs with a large fraction of diamond or polymeric hydrocarbon but decreases dramatically for dust with a large sp2 aromatic component.

The Potential Role Played by the Fullerene-Like Structures of Interstellar Carbon Dust in the Formation of Molecular Hydrogen in Space

NASA Astrophysics Data System (ADS)

Cataldo, Franco; Iglesias-Groth, Susana

After a general introduction to the problem of formation of molecular hydrogen from atomic hydrogen in the interstellar medium and in the dense molecular clouds in particular, and after the explanation of the key role played by the surfaces on this process, it is proposed that the most suitable carbon surface for the formation of molecular hydrogen (from the radiative association process of atomic hydrogen) can be represented by carbon black rather than by graphite. Furthermore, it is proposed that the fullerene-like structures present in the carbon black graphene sheets are the reaction sites where molecular hydrogen may be formed.

Open water camouflage via 'leaky' light guides in the midwater squid Galiteuthis.

PubMed

Holt, Amanda L; Sweeney, Alison M

2016-06-01

Galiteuthis, a midwater squid, has photophores on the ventral surfaces of its eyes. These photophores emit bioluminescence to counter-illuminate the shadows cast by the eyes in downwelling sunlight, thereby hiding the eyes from upward-looking predators. The photophores consist of laminated fibre-like cells with semi-coaxial protein-dense layers around axial cytoplasm. These cells have been suggested to function as light guides: bioluminescence is an isotropic process used to hide in an anisotropic light environment, so any emission must be reshaped to be effective. We found a wide variation in cross-sectional geometries of photophore cells; some were more efficient at light guiding than others. We used a set of optical models to place these photophores in the context of the radiance where Galiteuthis lives and discovered a possible adaptive reason for this variation. In Galiteuthis's horizontal and vertical range, ocean radiance is also quite variable. For complete camouflage, photophores must reproduce this variation in radiance using an isotropic source. Our models show that variation in the geometry of the photophore light guides reproduces the predicted variation in ocean radiance experienced by this species. By selectively activating geometrically distinct populations of photophore cells, the animal may reproduce the angular distribution of light at all positions in its habitat. © 2016 The Author(s).

Acceptance Test Data for Candidate AGR-5/6/7 TRISO Particle Batches BWXT Coater Batches 93165 93172 Defective IPyC Fraction and Pyrocarbon Anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmreich, Grant W.; Hunn, John D.; Skitt, Darren J.

2017-03-01

Coated particle fuel batches J52O-16-93165, 93166, 93168, 93169, 93170, and 93172 were produced by Babcock and Wilcox Technologies (BWXT) for possible selection as fuel for the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program’s AGR-5/6/7 irradiation test in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR). Some of these batches may alternately be used as demonstration coated particle fuel for other experiments. Each batch was coated in a 150-mm-diameter production-scale fluidized-bed chemical vapor deposition (CVD) furnace. Tristructural isotropic (TRISO) coatings were deposited on 425-μm-nominal-diameter spherical kernels from BWXT lot J52R-16-69317 containing a mixture of 15.5%-enriched uranium carbide andmore » uranium oxide (UCO). The TRISO coatings consisted of four consecutive CVD layers: a ~50% dense carbon buffer layer with 100-μm-nominal thickness, a dense inner pyrolytic carbon (IPyC) layer with 40-μm-nominal thickness, a silicon carbide (SiC) layer with 35-μm-nominal thickness, and a dense outer pyrolytic carbon (OPyC) layer with 40-μmnominal thickness. The TRISO-coated particle batches were sieved to upgrade the particles by removing over-sized and under-sized material, and the upgraded batches were designated by appending the letter A to the end of the batch number (e.g., 93165A).« less

Intense ionizing radiation from laser-induced processes in ultra-dense deuterium D(-1)

NASA Astrophysics Data System (ADS)

Olofson, Frans; Holmlid, Leif

2014-09-01

Nuclear fusion in ultra-dense deuterium D(-1) has been reported from our laboratory in a few studies using pulsed lasers with energy < 0.2 J. The direct observation of massive particles with energy 1-20 MeV u-1 is conclusive proof for fusion processes, either as a cause or as a result. Continuing the step-wise approach necessary for untangling a complex problem, the high-energy photons from the laser-induced plasma are now studied. The focus is here on the photoelectrons formed. The photons penetrating a copper foil have energy > 80 keV. The total charge created is up to 2 μC or 1 × 1013 photoelectrons per laser shot at 0.13 J pulse energy, assuming isotropic photon emission. The variation of the photoelectron current with laser intensity is faster than linear for some systems, which indicates rapid approach to volume ignition. On a permanent magnet at approximately 1 T, a laser pulse-energy threshold exists for the laser-induced processes probably due to the floating of most clusters of D(-1) in the magnetic field. This Meissner effect was reported previously.

Synchrotron X-Ray Interrogation of Turbulent Gas–Liquid Mixing in Cryogenic Rocket Sprays

DOE PAGES

Radke, Christopher D.; McManamen, J. Patrick; Kastengren, Alan L.; ...

2017-07-31

The atomization and vaporization of liquid jets within turbulent gaseous flows are characterized by the mixing phenomena occurring over a wide range of spatiotemporal scales. This creates a complex, turbid medium that is not easily interrogated using conventional optical-measurement techniques. In the current study, the optically dense, multiphase flow created by a cryogenic liquid jet injected into a turbulent gaseous coflow is probed using high-speed (MHz) X-ray radiography from a focused, narrowband synchrotron source to resolve the internal cascade of scales and the evolution to isotropic, homogeneous turbulence. Changes in the spectral characteristics for different flow conditions are furthermore correlatedmore » with changes in the spatial distributions of the liquid and gas phases within the spray using simultaneous X-ray radiography and tracer (krypton) fluorescence. It is found that an increase in entrainment and mixing infers an evolution in spectral characteristics toward the well-known -5/3 law of energy dissipation in the context of the classical Kolmogorov theory. Finally, these data demonstrate the utility of the synchrotron-based X-ray radiography and fluorescence for uncovering the internal, turbulent mixing processes in multiphase and optically dense flows.« less

The role of non-ionizing radiation pressure in star formation: the stability of cores and filaments

NASA Astrophysics Data System (ADS)

Seo, Young Min; Youdin, Andrew N.

2016-09-01

Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (I.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, ˜103 cm-3, the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic centre or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.

Synchrotron X-Ray Interrogation of Turbulent Gas–Liquid Mixing in Cryogenic Rocket Sprays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radke, Christopher D.; McManamen, J. Patrick; Kastengren, Alan L.

The atomization and vaporization of liquid jets within turbulent gaseous flows are characterized by the mixing phenomena occurring over a wide range of spatiotemporal scales. This creates a complex, turbid medium that is not easily interrogated using conventional optical-measurement techniques. In the current study, the optically dense, multiphase flow created by a cryogenic liquid jet injected into a turbulent gaseous coflow is probed using high-speed (MHz) X-ray radiography from a focused, narrowband synchrotron source to resolve the internal cascade of scales and the evolution to isotropic, homogeneous turbulence. Changes in the spectral characteristics for different flow conditions are furthermore correlatedmore » with changes in the spatial distributions of the liquid and gas phases within the spray using simultaneous X-ray radiography and tracer (krypton) fluorescence. It is found that an increase in entrainment and mixing infers an evolution in spectral characteristics toward the well-known -5/3 law of energy dissipation in the context of the classical Kolmogorov theory. Finally, these data demonstrate the utility of the synchrotron-based X-ray radiography and fluorescence for uncovering the internal, turbulent mixing processes in multiphase and optically dense flows.« less

Pulsed photoinitiated fabrication of inkjet printed titanium dioxide/reduced graphene oxide nanocomposite thin films.

PubMed

Bourgeois, Briley; Luo, Sijun; Riggs, Brian; Ji, Yaping; Adireddy, Shiva; Schroder, Kurt; Farnsworth, Stan; Chrisey, Douglas; Escarra, Matthew

2018-08-03

This work reports a new technique for scalable and low-temperature processing of nanostructured TiO 2 thin films, allowing for practical manufacturing of TiO 2 -based devices such as perovskite solar cells at low-temperature or on flexible substrates. Dual layers of dense and mesoporous TiO 2 /graphitic oxide nanocomposite films are synthesized simultaneously using inkjet printing and pulsed photonic irradiation. Investigation of process parameters including precursor concentration (10-20 wt%) and exposure fluence (4.5-8.5 J cm -2 ) reveals control over crystalline quality, graphitic oxide phase, film thickness, dendrite density, and optical properties. Raman spectroscopy shows the E g peak, characteristic of anatase phase titania, increases in intensity with higher photonic irradiation fluence, suggesting increased crystallinity through higher fluence processing. Film thickness and dendrite density is shown to increase with precursor concentration in the printed ink. The dense base layer thickness was controlled between 20 and 80 nm. The refractive index of the films is determined by ellipsometry to be 1.92 ± 0.08 at 650 nm. Films exhibit an energy weighted optical transparency of 91.1%, in comparison to 91.3% of a thermally processed film, when in situ carbon materials were removed. Transmission and diffuse reflectance are used to determine optical band gaps of the films ranging from 2.98 to 3.38 eV in accordance with the photonic irradiation fluence and suggests tunability of TiO 2 phase composition. The sheet resistance of the synthesized films is measured to be 14.54 ± 1.11 Ω/□ and 28.90 ± 2.24 Ω/□ for films as-processed and after carbon removal, respectively, which is comparable to high temperature processed TiO 2 thin films. The studied electrical and optical properties of the light processed films show comparable results to traditionally processed TiO 2 while offering the distinct advantages of scalable manufacturing, low-temperature processing, simultaneous bilayer fabrication, and in situ formation of removable carbon nanocomposites.

Structure and Li+ ion transport in a mixed carbonate/LiPF6 electrolyte near graphite electrode surfaces: a molecular dynamics study.

PubMed

Boyer, Mathew J; Vilčiauskas, Linas; Hwang, Gyeong S

2016-10-12

Electrolyte and electrode materials used in lithium-ion batteries have been studied separately to a great extent, however the structural and dynamical properties of the electrolyte-electrode interface still remain largely unexplored despite its critical role in governing battery performance. Using molecular dynamics simulations, we examine the structural reorganization of solvent molecules (cyclic ethylene carbonate : linear dimethyl carbonate 1 : 1 molar ratio doped with 1 M LiPF 6 ) in the vicinity of graphite electrodes with varying surface charge densities (σ). The interfacial structure is found to be sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. We also evaluated the potential difference across the electrolyte-electrode interface, which exhibits a nearly linear variation with respect to σ up until the onset of Li + ion accumulation onto the graphite edges from the electrolyte. In addition, well-tempered metadynamics simulations are employed to predict the free-energy barriers to Li + ion transport through the relatively dense interfacial layer, along with analysis of the Li + solvation sheath structure. Quantitative analysis of the molecular arrangements at the electrolyte-electrode interface will help better understand and describe electrolyte decomposition, especially in the early stages of solid-electrolyte-interphase (SEI) formation. Moreover, the computational framework presented in this work offers a means to explore the effects of solvent composition, electrode surface modification, and operating temperature on the interfacial structure and properties, which may further assist in efforts to engineer the electrolyte-electrode interface leading to a SEI layer that optimizes battery performance.

Characterization of diamond thin films and related materials

NASA Astrophysics Data System (ADS)

McKindra, Travis Kyle

Thin carbon films including sputtered deposited graphite and CO 2 laser-assisted combustion-flame deposited graphite and diamond thin films were characterized using optical and electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Amorphous carbon thin films were deposited by DC magnetron sputtering using Ar/O2 gases. The film morphology changed with the oxygen content. The deposition rate decreased as the amount of oxygen increased due to oxygen reacting with the growing film. The use of oxygen in the working gas enhanced the crystalline nature of the films. Graphite was deposited on WC substrates by a CO2 laser-assisted O2/C2H2 combustion-flame method. Two distinct microstructural areas were observed; an inner core of dense material surrounded by an outer shell of lamellar-like material. The deposits were crystalline regardless of the laser power and deposition times of a few minutes. Diamond films were deposited by a CO2 laser-assisted O 2/C2H2/C2H4 combustion-flame method with the laser focused parallel to the substrate surface. The laser enhanced diamond growth was most pronounced when deposited with a 10.532 microm CO2 laser wavelength tuned to the CH2-wagging vibrational mode of the C2H4 molecule. Nucleation of diamond thin films deposited with and without using a CO 2 laser-assisted combustion-flame process was investigated. With no laser there was nucleation of a sub-layer of grains followed by irregular grain growth. An untuned laser wavelength yielded nucleation of a sub-layer then columnar grain growth. The 10.532 microm tuned laser wavelength caused growth of columnar grains.

Polarized micro Raman spectroscopy of bilayer graphene

NASA Astrophysics Data System (ADS)

Moon, Hyerim; Yoon, Duhee; Son, Young-Woo; Cheong, Hyeonsik

2009-03-01

The frequency of Raman 2D band of the graphite depends on the excitation laser energy. This phenomenon is explained with double resonance Raman process. In polarized micro-Raman spectroscopy of single layer graphene, Raman G band (˜1586 cm-1) is isotropic, and 2D band (˜2686 cm-1) strongly depends on relative polarizations of the incident and scattered photons. This strong polarization dependence originates from inhomogeneous optical absorption and emission mediated by resonant electron-phonon interaction. In bi-layer graphene, Raman 2D band can be decomposed into four Lorenztian peaks which can be interpreted in terms of the four transition paths in the double resonance Raman process. We investigated the polarization dependence of each Lorenztian peak in the Raman 2D band of bi-layer graphene for different excitation laser energies. Strong polarization dependence of the Raman 2D band, similar to the case of single layer graphene, is observed. The excitation energy dependence of the polarized Raman scattering is analyzed in terms of the band structure of bi-layer graphene.

Measure of displacement around holes in composite plates subjected to quasi-static compression

NASA Technical Reports Server (NTRS)

Duke, J. C., Jr.; Post, D.; Czarnek, R.; Asundi, A.

1986-01-01

Contour maps of thickness changes were obtained for three quasi-isotropic graphite-epoxy plates with central holes, loaded in compression. Thickness changes were determined for six load increments from nearly zero to within a few percent of the failure load. The largest change of thickness occurred near the hole but not at the boundary of the hole. Below 90 percent of the failure load, the thickness changes were nearly proportional to load. Irregularities of thickness changes occurred in zones of compressive stresses and they were attributed to localized fiber buckling. A new optical technique was developed to measure thickness changes with high sensitivity. It utilizes a comparatively simple means of holographic interferometry on both sides of the specimen, followed by additive moire to obtain thickness changes as the sum of the out-of-plane displacements. Sensitivity was 12.5 x 10 to the -6 power in. per fringe order. The fringe patterns represent thickness changes uniquely, even when specimen warpage and consequent out-of-plane displacements are very large.

Pitch-based carbon foam and composites and use thereof

DOEpatents

Klett, James W.; Burchell, Timothy D.; Choudhury, Ashok

2006-07-04

A thermally conductive carbon foam is provided, normally having a thermal conductivity of at least 40 W/mK. The carbon foam usually has a specific thermal conductivity, defined as the thermal conductivity divided by the density, of at least about 75 Wcm.sup.3/m.degree. Kgm. The foam also has a high specific surface area, typically at least about 6,000 m.sup.2/m.sup.3. The foam is characterized by an x-ray diffraction pattern having "doublet" 100 and 101 peaks characterized by a relative peak split factor no greater than about 0.470. The foam is graphitic and exhibits substantially isotropic thermal conductivity. The foam comprises substantially ellipsoidal pores and the mean pore diameter of such pores is preferably no greater than about 340 microns. Other materials, such as phase change materials, can be impregnated in the pores in order to impart beneficial thermal properties to the foam. Heat exchange devices and evaporatively cooled heat sinks utilizing the foams are also disclosed.

Pitch-based carbon foam and composites and uses thereof

DOEpatents

Klett, James W.; Burchell, Timothy D.; Choudhury, Ashok

2004-01-06

A thermally conductive carbon foam is provided, normally having a thermal conductivity of at least 40 W/m.multidot.K. The carbon foam usually has a specific thermal conductivity, defined as the thermal conductivity divided by the density, of at least about 75 W.multidot.cm.sup.3 /m.multidot..degree.K.multidot.gm. The foam also has a high specific surface area, typically at least about 6,000 m.sup.2 /m.sup.3. The foam is characterized by an x-ray diffraction pattern having "doublet" 100 and 101 peaks characterized by a relative peak split factor no greater than about 0.470. The foam is graphitic and exhibits substantially isotropic thermal conductivity. The foam comprises substantially ellipsoidal pores and the mean pore diameter of such pores is preferably no greater than about 340 microns. Other materials, such as phase change materials, can be impregnated in the pores in order to impart beneficial thermal properties to the foam. Heat exchange devices and evaporatively cooled heat sinks utilizing the foams are also disclosed.

A fiber-optic technique for the measurement of contact angle in a clearance-fit pin-loaded hole

NASA Technical Reports Server (NTRS)

Prabhakaran, R.; Naik, R. A.

1987-01-01

A fiber-optic technique for measuring contact angle during pin loading of a specimen is proposed. The experimental design and procedures for loading a 49.8-mm-diameter instrumented pin into an quasi-isotropic graphite-epoxy specimen are described. The optical fiber was located just above the surface of the pin outer diameter in order to obtain accurate pin-hole contact-angle measurements at increasing load levels. The movement of the optical fiber through the no-contact, contact, and no-contact regions is discussed; the photodiode output decreased monotonically as the fiber moved from the no-contact to the contact region and then decreased monotonically as the fiber moved from the contact region to the no-contact region. Variations in the contact angle measurements are examined as function of applied load level. The measurements are compared to contact angle values obtained using a finite element analysis and an electrical technique; it is determined that the data correlate well.

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

NASA Technical Reports Server (NTRS)

Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

1991-01-01

Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

Analysis of progressive damage in thin circular laminates due to static-equivalent impact loads

NASA Technical Reports Server (NTRS)

Shivakumar, K. N.; Elber, W.; Illg, W.

1983-01-01

Clamped circular graphite/epoxy plates (25.4, 38.1, and 50.8 mm radii) with an 8-ply quasi-isotropic layup were analyzed for static-equivalent impact loads using the minimum-total-potential-energy method and the von Karman strain-displacement equations. A step-by-step incremental transverse displacement procedure was used to calculate plate load and ply stresses. The ply failure region was calculated using the Tsai-Wu criterion. The corresponding failure modes (splitting and fiber failure) were determined using the maximum stress criteria. The first-failure mode was splitting and initiated first in the bottom ply. The splitting-failure thresholds were relatively low and tended to be lower for larger plates than for small plates. The splitting-damage region in each ply was elongated in its fiber direction; the bottom ply had the largest damage region. The calculated damage region for the 25.4-mm-radius plate agreed with limited static test results from the literature.

Thermometry of the system “heat-resistant sample - incident plasma stream”

NASA Astrophysics Data System (ADS)

Sargsyan, M. A.; Chinnov, V. F.; Kavyrshin, D. I.; Gadzhiev, M. Kh; Khromov, M. A.; Chistolinov, A. V.; Senchenko, V. N.

2017-11-01

To study the interacting system “heat-resistant sample - an incident plasma stream” a setup of synchronized measurement equipment was developed and tested that recorded the main parameters of such interaction. Heat resistance tests were carried out on the samples of MPG-6 grade isotropic graphite, and samples of pyrolytic graphite that were subjected to a long (60 … 100 s) exposure to nitrogen, argon and air plasma streams at atmospheric pressure. As plasma generators a series of plasma torches with a vortex stabilization of the stream and an expanding anode channels was used. The temperature and composition of the plasma in the jet and near the sample were determined using two AvaSpec2048 and AvaSpec3648 scanning optical spectrometers and the MS5402i spectrograph with the Andor matrix at its outlet. The surface temperature of the sample was determined in real time using three independent ways: two pyrometric systems - a high-speed micro-pyrometer FMP1001 and a two-position visualization of the heated sample by high-speed Motion Pro X3 and VS-FAST cameras, and the spectral analysis of the wide-range thermal radiation of the samples. The main method for determining the rate of material loss during the action of a plasma jet on it was to analyze a two-position synchronous visualization of the “jet-sample” system. When a crater was formed on the surface of the sample under the “dagger” effect of a plasma jet, a video recording system of the crater zone was used, backlit using the “laser knife” method.

Ruby and sapphire from Jegdalek, Afghanistan

USGS Publications Warehouse

Bowersox, G.W.; Foord, E.E.; Laurs, B.M.; Shigley, J.E.; Smith, C.P.

2000-01-01

This study provides detailed mining and gemological information on the Jegdalek deposit, in east-central Afghanistan, which is hosted by elongate beds of corundum-bearing marble. Some facet-grade ruby has been recovered, but most of the material consists of semitransparent pink sapphire of cabochon or carving quality. The most common internal features are dense concentrations of healed and nonhealed fracture planes and lamellar twin planes. Color zoning is common, and calcite, apatite, zircon, mica, iron sulfide minerals, graphite, rutile, aluminum hydroxide, and other minerals are also present in some samples. Although the reserves appear to be large, future potential will depend on the establishment of a stable government and the introduction of modern mining and exploration techniques. ?? 2000 Gemological Institute of America.

Group electronegativity for prediction of materials hardness.

PubMed

Li, Keyan; Yang, Peng; Niu, Lingxiao; Xue, Dongfeng

2012-06-28

We have developed a method to predict the hardness of materials containing ultrastrong anionic polyhedra, dense atomic clusters, and layers stacked through van der Waals bonds on the basis of group electronegativity. By considering these polyhedra, clusters, and layers as groups that behave as rigid unities like superatoms bonding to other atoms or groups, the hardness values of materials such as oxysalts, T-carbon, and graphite were quantitatively calculated, and the results are consistent with the available experiments. We found that the hardness of materials containing these artificial groups is determined by the bonds between the groups and other atoms or groups, rather than by the weakest bonds. This work sheds light on the nature of materials hardness and the design of novel inorganic crystal materials.

Post-mortem analysis on LiFePO4|Graphite cells describing the evolution & composition of covering layer on anode and their impact on cell performance

NASA Astrophysics Data System (ADS)

Lewerenz, Meinert; Warnecke, Alexander; Sauer, Dirk Uwe

2017-11-01

During cyclic aging of lithium-ion batteries the formation of a μm-thick covering layer on top of the anode facing the separator is found on top of the anode. In this work several post-mortem analyses of cyclic aged cylindrical LFP|Graphite cells are evaluated to give a detailed characterization of the covering layer and to find possible causes for the evolution of such a layer. The analyses of the layer with different methods return that it consists to high percentage of plated active lithium, deposited Fe and products of a solid electrolyte interphase (SEI). The deposition is located mainly in the center of the cell symmetrical to the coating direction. The origin of these depositions is assumed in locally overcharged particles, Fe deposition or inhomogeneous distribution of capacity density. As a secondary effect the deposition on one side increases the thickness locally; thereafter a pressure-induced overcharging due to charge agglomeration of the back side of the anode occurs. Finally a compact and dense covering layer in a late state of aging leads to deactivation of the covered parts of the anode and cathode due to suppressed lithium-ion conductivity. This leads to increasing slope of capacity fade and increase of internal resistance.

Recognising Axionic Dark Matter by Compton and de-Broglie Scale Modulation of Pulsar Timing

NASA Astrophysics Data System (ADS)

De Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Schive, Hsi-Yu; Lazkoz, Ruth

2017-11-01

Light Axionic Dark Matter, motivated by string theory, is increasingly favored for the "no-WIMP era". Galaxy formation is suppressed below a Jeans scale, of ≃ 10^8 M_⊙ by setting the axion mass to, m_B ˜ 10^{-22}eV, and the large dark cores of dwarf galaxies are explained as solitons on the de-Broglie scale. This is persuasive, but detection of the inherent scalar field oscillation at the Compton frequency, ω_B= (2.5 months)^{-1}(m_B/10^{-22}eV), would be definitive. By evolving the coupled Schrödinger-Poisson equation for a Bose-Einstein condensate, we predict the dark matter is fully modulated by de-Broglie interference, with a dense soliton core of size ≃ 150pc, at the Galactic center. The oscillating field pressure induces General Relativistic time dilation in proportion to the local dark matter density and pulsars within this dense core have detectably large timing residuals, of ≃ 400nsec/(m_B/10^{-22}eV). This is encouraging as many new pulsars should be discovered near the Galactic center with planned radio surveys. More generally, over the whole Galaxy, differences in dark matter density between pairs of pulsars imprints a pairwise Galactocentric signature that can be distinguished from an isotropic gravitational wave background.

Develop and test fuel cell powered on-site integrated total energy systems. Phase 3: Full-scale power plant development

NASA Technical Reports Server (NTRS)

1983-01-01

Satisfactory performance is reported for the first three 12-cell sub-stacks of the 5 kW stack rebuild. Early general conclusions are presented from an economic study. Results are reported on a successful 700-hour test of a 3-cell stack in the full-sized configuration (0.33m x 0.56m). Construction of a 5 kW equivalent methanol/steam reformer based on a commercial shell-and-tube heat exchanger was completed. Several test runs are summarized. Preliminary conclusions are presented on the technical and economic aspects of fuel cell/HVAC interaction. Physical data are presented on several dense graphite materials which are candidates for gas-distribution plates. Performance of a new cathode catalyst is reported.

Survival of carbon grains in shocks

NASA Technical Reports Server (NTRS)

Seab, C. Gregory

1990-01-01

Supernova shocks play a significant part in the life of an interstellar grain. In a typical 10 to the 9th power year lifetime, a grain will be hit by an average of 10 shocks of 100 km s(sup -1) or greater velocity, and even more shocks of lower velocity. Evaluation of the results of this frequent shock processing is complicated by a number of uncertainties, but seems to give about 10 percent destruction of silicate grains and about half that for graphite grains. Because of the frequency of shocking, the mineralogy and sizes of the grain population is predominately determined by shock processing effects, and not by the initial grain nucleation and growth environment. One consequence of the significant role played by interstellar shocks is that a certain fraction (up to 5 percent) of the carbon should be transformed into the diamond phase. Diamond transformation is observed in the laboratory at threshold shock pressures easily obtainable in grain-grain collisions in supernova shocks. Yields for transforming graphite, amorphous carbon, glassy carbon, and other nearly pure carbon solids into diamond are quite high. Impurities up to at least the 10 percent level (for oxygen) are tolerated in the process. The typical size diamond expected from shock transformation agrees well with the observed sizes in the Lewis et al. findings in meteoritic material. Isotropic anomalies already contained in the grain are likely to be retained through the conversion process, while others may be implanted by the shock if the grain is close to the supernova. The meteoritic diamonds are likely to be the results of transformation of carbon grains in grain-grain collisions in supernova shock waves.

Properties of HIPed stainless steel powder

NASA Astrophysics Data System (ADS)

Dellis, Ch.; Le Marois, G.; Gentzbittel, J. M.; Robert, G.; Moret, F.

1996-10-01

In the current design of ITER primary wall, 316LN stainless steel is the reference structural material. Austenitic stainless steel is used for water-cooling channels and structures. As material data on hot isostatic pressed (HIP) 316LN were not available in open literature and from powder producers, the main properties of unirradiated samples have been measured in CEA/CEREM. Fully dense material without any porosity is obtained when appropriate HIP parameters are applied. Microstructural examination and mechanical properties are confirmed that the HIPed 316LN material is equivalent to a very good fine-grain, isotropic and uniformly forged 316LN. Moreover, ultrasonic inspection showed that this fine and uniform microstructure produced a remarkably low noise, which allow the use of transverse waves at very high frequencies (4 MHz). Defects undetectable in forged material will be easily detected in HIPed material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahnood, Arman, E-mail: arman.ahnood@unimelb.edu.au; Ganesan, Kumaravelu; Stacey, Alastair

Beyond conventional electrically-driven neuronal stimulation methods, there is a growing interest in optically-driven approaches. In recent years, nitrogen-doped ultrananocrystalline diamond (N-UNCD) has emerged as a strong material candidate for use in electrically-driven stimulation electrodes. This work investigates the electrochemical activity of N-UNCD in response to pulsed illumination, to assess its potential for use as an optically-driven stimulation electrode. Whilst N-UNCD in the as-grown state exhibits a weak photoresponse, the oxygen plasma treated film exhibits two orders of magnitude enhancement in its sub-bandgap open circuit photovoltage response. The enhancement is attributed to the formation of a dense network of oxygen-terminated diamondmore » nanocrystals at the N-UNCD surface. Electrically connected to the N-UNCD bulk via sub-surface graphitic grain boundaries, these diamond nanocrystals introduce a semiconducting barrier between the sub-surface graphitic semimetal and the electrolyte solution, leading to a photovoltage under irradiation with wavelengths of λ = 450 nm and shorter. Within the safe optical exposure limit of 2 mW mm{sup −2}, charge injection capacity of 0.01 mC cm{sup −2} is achieved using a 15 × 15 μm electrode, meeting the requirements for extracellular and intercellular stimulation. The nanoscale nature of processes presented here along with the diamond's biocompatibility and biostability open an avenue for the use of oxygen treated N-UNCD as optically driven stimulating electrodes.« less

Transient photoresponse of nitrogen-doped ultrananocrystalline diamond electrodes in saline solution

NASA Astrophysics Data System (ADS)

Ahnood, Arman; Simonov, Alexandr N.; Laird, Jamie S.; Maturana, Matias I.; Ganesan, Kumaravelu; Stacey, Alastair; Ibbotson, Michael R.; Spiccia, Leone; Prawer, Steven

2016-03-01

Beyond conventional electrically-driven neuronal stimulation methods, there is a growing interest in optically-driven approaches. In recent years, nitrogen-doped ultrananocrystalline diamond (N-UNCD) has emerged as a strong material candidate for use in electrically-driven stimulation electrodes. This work investigates the electrochemical activity of N-UNCD in response to pulsed illumination, to assess its potential for use as an optically-driven stimulation electrode. Whilst N-UNCD in the as-grown state exhibits a weak photoresponse, the oxygen plasma treated film exhibits two orders of magnitude enhancement in its sub-bandgap open circuit photovoltage response. The enhancement is attributed to the formation of a dense network of oxygen-terminated diamond nanocrystals at the N-UNCD surface. Electrically connected to the N-UNCD bulk via sub-surface graphitic grain boundaries, these diamond nanocrystals introduce a semiconducting barrier between the sub-surface graphitic semimetal and the electrolyte solution, leading to a photovoltage under irradiation with wavelengths of λ = 450 nm and shorter. Within the safe optical exposure limit of 2 mW mm-2, charge injection capacity of 0.01 mC cm-2 is achieved using a 15 × 15 μm electrode, meeting the requirements for extracellular and intercellular stimulation. The nanoscale nature of processes presented here along with the diamond's biocompatibility and biostability open an avenue for the use of oxygen treated N-UNCD as optically driven stimulating electrodes.

Merger of Multiple Accreting Black Holes Concordant with Gravitational-wave Events

NASA Astrophysics Data System (ADS)

Tagawa, Hiromichi; Umemura, Masayuki

2018-03-01

Recently, the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) has detected black hole (BH) merger events, most of which are sourced by BHs more massive than 30 M ⊙. Especially, the observation of GW170104 suggests dynamically assembled binaries favoring a distribution of misaligned spins. It has been argued that mergers of unassociated BHs can be engendered through a chance meeting in a multiple BH system under gas-rich environments. In this paper, we consider the merger of unassociated BHs, concordant with the massive BH merger events. To that end, we simulate a multiple BH system with a post-Newtonian N-body code incorporating gas accretion and general relativistic effects. As a result, we find that gas dynamical friction effectively promotes a three-body interaction of BHs in dense gas of n gas ≳ 106 cm‑3, so that BH mergers can take place within 30 Myr. This scenario predicts an isotropic distribution of spin tilts. In the concordant models with GW150914, the masses of seed BHs are required to be ≳25 M ⊙. The potential sites of such chance meeting BH mergers are active galactic nucleus (AGN) disks and dense interstellar clouds. Assuming the LIGO O1, we roughly estimate the event rates for PopI BHs and PopIII BHs in AGN disks to be ≃1–2 yr‑1 and ≃1 yr‑1, respectively. Multiple episodes of AGNs may enhance the rates by roughly an order of magnitude. For massive PopI BHs in dense interstellar clouds the rate is ≃0.02 yr‑1. Hence, high-density AGN disks are a more plausible site for mergers of chance meeting BHs.

Shape Effect of Electrochemical Chloride Extraction in Structural Reinforced Concrete Elements Using a New Cement-Based Anodic System

PubMed Central

Carmona, Jesús; Climent, Miguel-Ángel; Antón, Carlos; de Vera, Guillem; Garcés, Pedro

2015-01-01

This article shows the research carried out by the authors focused on how the shape of structural reinforced concrete elements treated with electrochemical chloride extraction can affect the efficiency of this process. Assuming the current use of different anode systems, the present study considers the comparison of results between conventional anodes based on Ti-RuO2 wire mesh and a cement-based anodic system such as a paste of graphite-cement. Reinforced concrete elements of a meter length were molded to serve as laboratory specimens, to closely represent authentic structural supports, with circular and rectangular sections. Results confirm almost equal performances for both types of anode systems when electrochemical chloride extraction is applied to isotropic structural elements. In the case of anisotropic ones, such as rectangular sections with no uniformly distributed rebar, differences in electrical flow density were detected during the treatment. Those differences were more extreme for Ti-RuO2 mesh anode system. This particular shape effect is evidenced by obtaining the efficiencies of electrochemical chloride extraction in different points of specimens.

Using the graphene Moiré pattern for the trapping of C60 and homoepitaxy of graphene.

PubMed

Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Yang, Zhiyong; Bao, Qiaoliang; Gan, Chee Kwan; Loh, Kian Ping

2012-01-24

The graphene Moiré superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C(60) molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C(60) molecules adsorbing on the Moiré lattice freeze the molecular rotation of C(60) trapped in the valley sites, resulting in molecular alignment of all similarly trapped C(60) molecules at room temperature. The hierarchy of adsorption potential well on the Moiré lattice causes diffusion-limited dendritic growth of C(60) films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C(60) film, part of the dentritic C(60) films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature. © 2011 American Chemical Society

Inorganic nanotubes and fullerene-like nanoparticles.

PubMed

Tenne, R

2006-11-01

Although graphite, with its anisotropic two-dimensional lattice, is the stable form of carbon under ambient conditions, on nanometre length scales it forms zero- and one-dimensional structures, namely fullerenes and nanotubes, respectively. This virtue is not limited to carbon and, in recent years, fullerene-like structures and nanotubes have been made from numerous compounds with layered two-dimensional structures. Furthermore, crystalline and polycrystalline nanotubes of pure elements and compounds with quasi-isotropic (three-dimensional) unit cells have also been synthesized, usually by making use of solid templates. These findings open up vast opportunities for the synthesis and study of new kinds of nanostructures with properties that may differ significantly from the corresponding bulk materials. Various potential applications have been proposed for the inorganic nanotubes and the fullerene-like phases. Fullerene-like nanoparticles have been shown to exhibit excellent solid lubrication behaviour, suggesting many applications in, for example, the automotive and aerospace industries, home appliances, and recently for medical technology. Various other potential applications, in catalysis, rechargeable batteries, drug delivery, solar cells and electronics have also been proposed.

Failure mechanics in low-velocity impacts on thin composite plates

NASA Technical Reports Server (NTRS)

Elber, W.

1983-01-01

Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests.

Verification of an improved computational design procedure for TWT-dynamic refocuser-MDC systems with secondary electron emission losses

NASA Technical Reports Server (NTRS)

Ramins, P.; Force, D. A.; Palmer, R. W.; Dayton, J. A., Jr.; Kosmahl, H. G.

1986-01-01

A computational procedure for the design of TWT-refocuser-MDC systems was used to design a short 'dynamic' refocusing system and highly efficient four-stage depressed collector for a 200-W 8-18-GHz TWT. The computations were carried out with advanced multidimensional computer programs which model the electron beam as a series of disks of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure and refocusing section, to their points of impact in the depressed collector. Secondary emission losses in the MDC were treated semiquantitatively by injecting a representative beam of secondary electrons into the MDC analysis at the point of impact of each primary beam. A comparison of computed and measured TWT and MDC performance showed very good agreement. The electrodes of the MDC were fabricated from a particular form of isotropic graphite that was selected for its low secondary electron yield, thermal expansion characteristics, ease of machinability and vacuum properties. This MDC was tested at CW for more than 1000 h with negligible degradation in TWT and MDC performances.

Changes of composition and microstructure of joint interface of tungsten coated carbon by high heat flux

NASA Astrophysics Data System (ADS)

Tokunaga, K.; Matsubara, T.; Miyamoto, Y.; Takao, Y.; Yoshida, N.; Noda, N.; Kubota, Y.; Sogabe, T.; Kato, T.; Plöchl, L.

2000-12-01

Tungsten coatings of 0.5 and 1 mm thickness were successfully deposited by the vacuum plasma spraying (VPS) technique on carbon/carbon fiber composite (CFC), CX-2002U and isotropic fine grained graphite, IG-430U. High heat flux experiments by irradiation of electron beam with uniform profile were performed on the coated samples in order to prove the suitability and load limit of such coating materials. The cross-sectional composition and structure of the interface of VPS-W and carbon material samples were investigated. Compositional analyses showed that the Re/W multi-layer acts as diffusion barrier for carbon and suppresses tungsten carbide formation in the VPS-W layer at high temperature about 1300°C. Microstructure of the joint interface of the sample changed in the case of a peak temperature of about 2800°C. The multi-layer structure completely disappeared and compositional distribution was almost uniform in the interface of the sample after melting and resolidification. The diffusion barrier for carbon is not expected to act in this stage.

Sulfur Isotropic Studies of Archean Slate and Graywacke from Northern Minnesota: Evidence for the Existence of Sulfate Reducing Bacteria

NASA Technical Reports Server (NTRS)

Ripley, E. M.; Nicol, D. L.

1979-01-01

Sulfur isotopic studies of pyrite from metasediments in the 2.6 b.y. old Deer Lake greenstone sequence, Minnesota, were conducted in order to evaluate the possible importance of sulfate reducing bacteria in sulfide formation. Pyrite occurs as ovules up to 2 cm in diameter within graphitic slates, and as fine disseminations in metagraywacke units. SEM studies indicate the pyrite is framboidal in morphology. Delta notation values of pyrite from the Deer Lake sediments range from -2.3 to 11.1 0/00, with a peak at approximately +2 o/oo. Isotopic data is consistent with either high temperature inorganic reduction of circulating seawater sulfate, or low temperature bacterial reduction. However, the lack of sulfide bands or massive occurrences in the sediments, the restriction of pyrite mineralization to the sediments, and the absence of evidence for hot spring activity suggest that a diagenetic origin of pyrite is more feasible. Sulfide in such an environment would be produced principally by the action of sulfate reducing bacteria.

Inorganic nanotubes and fullerene-like nanoparticles

NASA Astrophysics Data System (ADS)

Tenne, R.

2006-11-01

Although graphite, with its anisotropic two-dimensional lattice, is the stable form of carbon under ambient conditions, on nanometre length scales it forms zero- and one-dimensional structures, namely fullerenes and nanotubes, respectively. This virtue is not limited to carbon and, in recent years, fullerene-like structures and nanotubes have been made from numerous compounds with layered two-dimensional structures. Furthermore, crystalline and polycrystalline nanotubes of pure elements and compounds with quasi-isotropic (three-dimensional) unit cells have also been synthesized, usually by making use of solid templates. These findings open up vast opportunities for the synthesis and study of new kinds of nanostructures with properties that may differ significantly from the corresponding bulk materials. Various potential applications have been proposed for the inorganic nanotubes and the fullerene-like phases. Fullerene-like nanoparticles have been shown to exhibit excellent solid lubrication behaviour, suggesting many applications in, for example, the automotive and aerospace industries, home appliances, and recently for medical technology. Various other potential applications, in catalysis, rechargeable batteries, drug delivery, solar cells and electronics have also been proposed.

Graphite fiber intercalation: Basic properties of copper chloride intercalated fibers

NASA Technical Reports Server (NTRS)

Jaworske, D. A.; Miller, J. D.

1986-01-01

In situ resistance measurements were used to follow the intercalation of copper chloride in pitch-based fibers. Subsequent single fiber resistivity measurements reveal a large range of resistivities, from 13 to 160 micro-ohms cm. Additional density measurements reveal a bimodal distribution of mass densities. The dense fibers have lower resistivities and correspond to the stage III compound identified by X-ray diffraction. Neither resistivity nor density correlate with diameter. Both energy dispersive spectroscopy and mass density data suggest that excess chlorine resides in the intercalated fiber, resulting in a stoichiometry of C4.9n CuCl2.5 (where n is the stage number) for the denser fibers. Finally, thermogravimetric analysis shows a 33 percent loss in mass upon heating to 700C. This loss in mass is attributed to loss of both chlorine and carbon.

Spark plasma sintering of highly dense fine-grained mineral aggregates

NASA Astrophysics Data System (ADS)

Koizumi, S.; Suzuki, T. S.; Sakka, Y.; Hiraga, T.

2017-12-01

To obtain highly dense and fine-grained mineral aggregates, which are suitable for laboratory measurements of their physical and chemical properties, we applied spark plasma sintering (SPS) to synthetic mineral powders and powders originated from naturally derived crystals. SPS is an emerging consolidation technique which has been applied to various metals and ceramics and rarely to geomaterials (e.g., Guignard et al., 2011). The technique uses spark plasma created by a pulse direct current during heat treatment of powders in a graphite die. It has been found that the technique provides better densification with little grain growth during sintering compared to a conventional sintering technique in many materials. To obtain ideal highly dense fine-grained materials, it is essential to prepare starting powders suitable for the sintering and also to find appropriate sintering conditions of applied uniaxial pressures, pulsed current patterns and heating rates. We prepared synthetic mineral powers through solid state reaction of source powders at high temperature well developed by our group (Koizumi et al. 2010). We also used jet milling at wet condition and subsequent elutriation to prepare olivine powders with sub-micron particle size and equiaxed particle shape. At heating rate of ≦10°C/min and an achievement of highest temperature of 1150°C, Fe-free olivine aggregate with average grain size of 200 nm with porosity of 0.003% was obtained. We also could obtain olivine aggregate, which was sintered from powders of Horoman peridotite, with average grain size of 500 nm and porosity of 0.2%. We will show results of other minerals including major rock forming minerals of the Earth's crust.

Single inclusion piezobarometry confirms high-temperature decompression path for Variscan granulites

NASA Astrophysics Data System (ADS)

Angel, Ross; Alvaro, Matteo; Mazzucchelli, Mattia; Nimis, Paolo; Nestola, Fabrizio

2016-04-01

The identification and chemistry of inclusions trapped in host minerals during growth of the host phase have long been used to infer P-T points on metamorphic paths. The determination of the remnant pressure on the inclusion, e.g., using data from X-ray diffractometry, birefringence analysis or Raman spectroscopy, provides an alternative method of barometry using elasticity theory. A remnant pressure in an inclusion is developed because the inclusion and the host have different thermal expansion and compressibilities, and the inclusion does not expand in response to P and T as would a free crystal. Instead it is restricted to expand only as much as the host mineral, and this constriction in volume can result in inclusions exhibiting over-pressures when the host is studied at room conditions. This concept has been known for a long time, but satisfactory quantitative modelling of inclusion-host systems based on non-linear elasticity theory and precise thermal-pressure euqations of state has only recently come available (Angel et al., 2014, 2015), even though it is still restricted to elastically isotropic minerals. No mineral is elastically isotropic, but garnets and diamond are almost so. Calculations show that diamonds trapped as inclusions in host silicates at P and T within the stability field of diamond should exhibit zero pressure when the samples are recovered to room conditions. However, some diamond inclusions in garnets in granulites are reported to exhibit significant residual overpressures (e.g., Kotková et al., 2011). This indicates that the inclusion was elastically re-equilibrated (e.g., by plastic flow in the garnet host) at high temperatures and lower pressures in the stability field of graphite, consistent also with the observed partial inversion of diamond to graphite. In this case, the elastic analysis of the diamond-in-garnet inclusions provides qualitative independent evidence that the Variscan granulites underwent pressure reduction at high temperatures. The extension of single inclusion piezobarometry to elastically anisotropic minerals will allow quantitative analysis of diamonds trapped in other minerals such as kyanite. This work was supported by ERC starting grant 307322 to Fabrizio Nestola and by the MIUR-SIR grant "MILE DEEp" (RBSI140351) to M. Alvaro. Angel R.J., Mazzucchelli M.L., Alvaro M., Nimis P. & Nestola F. (2014) Geobarometry from host-inclusion systems: the role of elastic relaxation. Am. Mineral., 99, 2146-2149. Angel R.J., Nimis P., Mazzucchelli M.L., Alvaro M. & Nestola F. (2015) How large are departures from lithostatic pressure? Constraints from host-inclusion elasticity. J. Metamorphic Geol., 33, 801-813. Kotková J, O'Brien P.J & Ziemann M.A. (2011)Diamond and coesite discovered in Saxony-type granulite: Solution to the Variscan garnet peridotite enigma. Geology, 39, 667-670.

Grain boundary crystallography in polycrystalline yttria-stabilised cubic zirconia

NASA Astrophysics Data System (ADS)

Kini, Maya K.

2018-07-01

Properties of grain boundaries such as grain boundary energy, mobility and diffusion are reported to depend strongly on their crystallography. While studies on ceramic bicrystals with low Σ misorientations have shown highly ordered structures and low energies, studies on dense polycrystalline ceramics often show the significance of grain boundary planes. In the present study, grain boundary plane distributions were studied for yttria-stabilised cubic zirconia with varying grain sizes using Electron Back Scattered Diffraction technique combined with a stereological approach. Despite nearly isotropic grain boundary plane distributions, a highly anisotropic grain boundary character distribution is observed for specific misorientations. Certain low-energy symmetric tilts such as Σ3 and Σ11 are found to occur with high frequencies across the grain size range studied, leading to an inverse correlation between GB energy and frequency of occurrence, consistent with other ceramics studied in literature.

Dynamics and Emergent Structures in Active Fluids

NASA Astrophysics Data System (ADS)

Baskaran, Aparna

2014-03-01

In this talk, we consider an active fluid of colloidal sized particles, with the primary manifestation of activity being a self-replenishing velocity along one body axis of the particle. This is a minimal model for varied systems such as bacterial colonies, cytoskeletal filament motility assays vibrated granular particles and self propelled diffusophoretic colloids, depending on the nature of interaction among the particles. Using microscopic Brownian dynamics simulations, coarse-graining using the tools of non-equilibrium statistical mechanics and analysis of macroscopic hydrodynamic theories, we characterize emergent structures seen in these systems, which are determined by the symmetry of the interactions among the active units, such as propagating density waves, dense stationary bands, asters and phase separated isotropic clusters. We identify a universal mechanism, termed ``self-regulation,'' as the underlying physics that leads to these structures in diverse systems. Support from NSF through DMR-1149266 and DMR-0820492.

Neutron angular distribution in a plasma focus obtained using nuclear track detectors.

PubMed

Castillo-Mejía, F; Herrera, J J E; Rangel, J; Golzarri, J I; Espinosa, G

2002-01-01

The dense plasma focus (DPF) is a coaxial plasma gun in which a high-density, high-temperature plasma is obtained in a focused column for a few nanoseconds. When the filling gas is deuterium, neutrons can be obtained from fusion reactions. These are partially due to a beam of deuterons which are accelerated against the background hot plasma by large electric fields originating from plasma instabilities. Due to a beam-target effect, the angular distribution of the neutron emission is anisotropic, peaked in the forward direction along the axis of the gun. The purpose of this work is to illustrate the use of CR-39 nuclear track detectors as a diagnostic tool in the determination of the time-integrated neutron angular distribution. For the case studied in this work, neutron emission is found to have a 70% contribution from isotropic radiation and a 30% contribution from anisotropic radiation.

Carbothermic Synthesis of 820 m UN Kernels: Literature Review, Thermodynamics, Analysis, and Related Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindemer, Terrence; Voit, Stewart L; Silva, Chinthaka M

2014-01-01

The U.S. Department of Energy is considering a new nuclear fuel that would be less susceptible to ruptures during a loss-of-coolant accident. The fuel would consist of tristructural isotropic coated particles with large, dense uranium nitride (UN) kernels. This effort explores many factors involved in using gel-derived uranium oxide-carbon microspheres to make large UN kernels. Analysis of recent studies with sufficient experimental details is provided. Extensive thermodynamic calculations are used to predict carbon monoxide and other pressures for several different reactions that may be involved in conversion of uranium oxides and carbides to UN. Experimentally, the method for making themore » gel-derived microspheres is described. These were used in a microbalance with an attached mass spectrometer to determine details of carbothermic conversion in argon, nitrogen, or vacuum. A quantitative model is derived from experiments for vacuum conversion to an uranium oxide-carbide kernel.« less

Particle Settling in Low Energy Turbulence

NASA Astrophysics Data System (ADS)

Allen, Rachel; MacVean, Lissa; Tse, Ian; Mazzaro, Laura; Stacey, Mark; Variano, Evan

2014-11-01

Particle settling velocities can be altered by turbulence. In turbulence, dense particles may get trapped in convergent flow regions, and falling particles may be swept towards the downward side of turbulent eddies, resulting in enhanced settling velocities. The degree of velocity enhancement may depend on the Stokes number, the Rouse number, and the turbulent Reynolds number. In a homogeneous, isotropic turbulence tank, we tested the effects of particle size and type, suspended sediment concentration, and level of turbulence on the settling velocities of particles typically found in muddy estuaries. Two Acoustic Doppler Velocimeters (ADVs), separated vertically, measured turbulent velocities and suspended sediment concentrations, which yield condition dependent settling velocities, via ∂/á C ñ ∂ t = -∂/∂ z (ws á C ñ + á w ' C ' ñ) . These results are pertinent to fine sediment transport in estuaries, where high concentrations of suspended material are transported and impacted by low energy turbulence.

Transformation of the ordered internal structures during the acceleration of fast charged particles in a dense plasma focus

NASA Astrophysics Data System (ADS)

Kubes, P.; Paduch, M.; Cikhardt, J.; Cikhardtova, B.; Klir, D.; Kravarik, J.; Rezac, K.; Zielinska, E.; Sadowski, M. J.; Szymaszek, A.; Tomaszewski, K.; Zaloga, D.

2017-07-01

The paper concerns important differences in the evolution of plasma column structures during the production of fusion neutrons in the first and subsequent neutron pulses, as observed for plasma-focus discharges performed with the deuterium filling. The first neutron pulse, of a more isotropic distribution, is usually produced during the formation of the first big plasmoid. The next neutron pulses can be generated by the fast deuterons moving dominantly in the downstream direction, at the instants of a disruption of the pinch constriction, when other plasmoids are formed during the constriction evolution. In both cases, the fusion neutrons are produced by a beam-target mechanism, and the acceleration of fast electron- and deuteron-beams can be interpreted by transformation and decay of the magnetic field associated with a filamentary structure of the current flow in the plasmoid.

Dysprosium-free melt-spun permanent magnets.

PubMed

Brown, D N; Wu, Z; He, F; Miller, D J; Herchenroeder, J W

2014-02-12

Melt-spun NdFeB powders can be formed into a number of different types of permanent magnet for a variety of applications in electronics, automotive and clean technology industries. The melt-spinning process produces flake powder with a fine uniform array of nanoscale Nd2Fe14B grains. These powders can be net-shape formed into isotropic polymer-bonded magnets or hot formed into fully dense magnets. This paper discusses the influence of heavy rare earth elements and microstructure on the magnetic performance, thermal stability and material cost of NdFeB magnets. Evidence indicates that melt-spun nanocrystalline NdFeB magnets are less dependent on heavy rare earth elements for high-temperature performance than the alternative coarser-grained sintered NdFeB magnets. In particular, hot-pressed melt-spun magnets are an attractive low-cost solution for applications that require thermal stability up to 175-200 °C.

Method for producing dustless graphite spheres from waste graphite fines

DOEpatents

Pappano, Peter J [Oak Ridge, TN; Rogers, Michael R [Clinton, TN

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.

Neutron spectra from beam-target reactions in dense Z-pinches

NASA Astrophysics Data System (ADS)

Appelbe, B.; Chittenden, J.

2015-10-01

The energy spectrum of neutrons emitted by a range of deuterium and deuterium-tritium Z-pinch devices is investigated computationally using a hybrid kinetic-MHD model. 3D MHD simulations are used to model the implosion, stagnation, and break-up of dense plasma focus devices at currents of 70 kA, 500 kA, and 2 MA and also a 15 MA gas puff. Instabilities in the MHD simulations generate large electric and magnetic fields, which accelerate ions during the stagnation and break-up phases. A kinetic model is used to calculate the trajectories of these ions and the neutron spectra produced due to the interaction of these ions with the background plasma. It is found that these beam-target neutron spectra are sensitive to the electric and magnetic fields at stagnation resulting in significant differences in the spectra emitted by each device. Most notably, magnetization of the accelerated ions causes the beam-target spectra to be isotropic for the gas puff simulations. It is also shown that beam-target spectra can have a peak intensity located at a lower energy than the peak intensity of a thermonuclear spectrum. A number of other differences in the shapes of beam-target and thermonuclear spectra are also observed for each device. Finally, significant differences between the shapes of beam-target DD and DT neutron spectra, due to differences in the reaction cross-sections, are illustrated.

Recognizing Axionic Dark Matter by Compton and de Broglie Scale Modulation of Pulsar Timing.

PubMed

De Martino, Ivan; Broadhurst, Tom; Tye, S-H Henry; Chiueh, Tzihong; Schive, Hsi-Yu; Lazkoz, Ruth

2017-12-01

Light axionic dark matter, motivated by string theory, is increasingly favored for the "no weakly interacting massive particle era". Galaxy formation is suppressed below a Jeans scale of ≃10^{8}  M_{⊙} by setting the axion mass to m_{B}∼10^{-22}  eV, and the large dark cores of dwarf galaxies are explained as solitons on the de Broglie scale. This is persuasive, but detection of the inherent scalar field oscillation at the Compton frequency ω_{B}=(2.5  months)^{-1}(m_{B}/10^{-22}  eV) would be definitive. By evolving the coupled Schrödinger-Poisson equation for a Bose-Einstein condensate, we predict the dark matter is fully modulated by de Broglie interference, with a dense soliton core of size ≃150  pc, at the Galactic center. The oscillating field pressure induces general relativistic time dilation in proportion to the local dark matter density and pulsars within this dense core have detectably large timing residuals of ≃400  nsec/(m_{B}/10^{-22}  eV). This is encouraging as many new pulsars should be discovered near the Galactic center with planned radio surveys. More generally, over the whole Galaxy, differences in dark matter density between pairs of pulsars imprints a pairwise Galactocentric signature that can be distinguished from an isotropic gravitational wave background.

FennoFlakes: a project for identifying flake graphite ores in the Fennoscandian shield and utilizing graphite in different applications

NASA Astrophysics Data System (ADS)

Palosaari, Jenny; Eklund, O.; Raunio, S.; Lindfors, T.; Latonen, R.-M.; Peltonen, J.; Smått, J.-H.; Kauppila, J.; Lund, S.; Sjöberg-Eerola, P.; Blomqvist, R.; Marmo, J.

2016-04-01

Natural graphite is a strategic mineral, since the European Commission stated (Report on critical raw materials for the EU (2014)) that graphite is one of the 20 most critical materials for the European Union. The EU consumed 13% of all flake graphite in the world but produced only 3%, which stresses the demand of the material. Flake graphite, which is a flaky version of graphite, forms under high metamorphic conditions. Flake graphite is important in different applications like batteries, carbon brushes, heat sinks etc. Graphene (a single layer of graphite) can be produced from graphite and is commonly used in many nanotechnological applications, e.g. in electronics and sensors. The steps to obtain pure graphene from graphite ore include fragmentation, flotation and exfoliation, which can be cumbersome and resulting in damaging the graphene layers. We have started a project named FennoFlakes, which is a co-operation between geologists and chemists to fill the whole value chain from graphite to graphene: 1. Exploration of graphite ores (geological and geophysical methods). 2. Petrological and geochemical analyses on the ores. 3. Development of fragmentation methods for graphite ores. 4. Chemical exfoliation of the enriched flake graphite to separate flake graphite into single and multilayer graphene. 5. Test the quality of the produced material in several high-end applications with totally environmental friendly and disposable material combinations. Preliminary results show that flake graphite in high metamorphic areas has better qualities compared to synthetic graphite produced in laboratories.

Voronoi-Tessellated Graphite Produced by Low-Temperature Catalytic Graphitization from Renewable Resources.

PubMed

Zhao, Leyi; Zhao, Xiuyun; Burke, Luke T; Bennett, J Craig; Dunlap, Richard A; Obrovac, Mark N

2017-09-11

A highly crystalline graphite powder was prepared from the low temperature (800-1000 °C) graphitization of renewable hard carbon precursors using a magnesium catalyst. The resulting graphite particles are composed of Voronoi-tessellated regions comprising irregular sheets; each Voronoi-tessellated region having a small "seed" particle located near their centroid on the surface. This suggests nucleated outward growth of graphitic carbon, which has not been previously observed. Each seed particle consists of a spheroidal graphite shell on the inside of which hexagonal graphite platelets are perpendicularly affixed. This results in a unique high surface area graphite with a high degree of graphitization that is made with renewable feedstocks at temperatures far below that conventionally used for artificial graphites. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Metal-Coated Graphite Powders on Microstructure and Properties of the Bronze-Matrix/Graphite Composites

NASA Astrophysics Data System (ADS)

Zhao, Jian-hua; Li, Pu; Tang, Qi; Zhang, Yan-qing; He, Jian-sheng; He, Ke

2017-02-01

In this study, the bronze-matrix/x-graphite (x = 0, 1, 3 and 5%) composites were fabricated by powder metallurgy route by using Cu-coated graphite, Ni-coated graphite and pure graphite, respectively. The microstructure, mechanical properties and corrosive behaviors of bronze/Cu-coated-graphite (BCG), bronze/Ni-coated-graphite (BNG) and bronze/pure-graphite (BPG) were characterized and investigated. Results show that the Cu-coated and Ni-coated graphite could definitely increase the bonding quality between the bronze matrix and graphite. In general, with the increase in graphite content in bronze-matrix/graphite composites, the friction coefficients, ultimate density and wear rates of BPG, BCG and BNG composites all went down. However, the Vickers microhardness of the BNG composite would increase as the graphite content increased, which was contrary to the BPG and BCG composites. When the graphite content was 3%, the friction coefficient of BNG composite was more stable than that of BCG and BPG composites, indicating that BNG composite had a better tribological performance than the others. Under all the values of applied loads (10, 20, 40 and 60N), the BCG and BNG composites exhibited a lower wear rate than BPG composite. What is more, the existence of nickel in graphite powders could effectively improve the corrosion resistance of the BNG composite.

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.

Method of Joining Graphite Fibers to a Substrate

NASA Technical Reports Server (NTRS)

Beringer, Durwood M. (Inventor); Caron, Mark E. (Inventor); Taddey, Edmund P. (Inventor); Gleason, Brian P. (Inventor)

2014-01-01

A method of assembling a metallic-graphite structure includes forming a wetted graphite subassembly by arranging one or more layers of graphite fiber material including a plurality of graphite fibers and applying a layer of metallization material to ends of the plurality of graphite fibers. At least one metallic substrate is secured to the wetted graphite subassembly via the layer of metallization material.

Sulfonated Holey Graphene Oxide (SHGO) Filled Sulfonated Poly(ether ether ketone) Membrane: The Role of Holes in the SHGO in Improving Its Performance as Proton Exchange Membrane for Direct Methanol Fuel Cells.

PubMed

Jiang, Zhong-Jie; Jiang, Zhongqing; Tian, Xiaoning; Luo, Lijuan; Liu, Meilin

2017-06-14

Sulfonated holey graphene oxides (SHGOs) have been synthesized by the etching of sulfonated graphene oxides with concentrated HNO 3 under the assistance of ultrasonication. These SHGOs could be used as fillers for the sulfonated aromatic poly(ether ether ketone) (SPEEK) membrane. The obtained SHGO-incorporated SPEEK membrane has a uniform and dense structure, exhibiting higher performance as proton exchange membranes (PEMs), for instance, higher proton conductivity, lower activation energy for proton conduction, and comparable methanol permeability, as compared to Nafion 112. The sulfonated graphitic structure of the SHGOs is believed to be one of the crucial factors resulting in the higher performance of the SPEEK/SHGO membrane, since it could increase the local density of the -SO 3 H groups in the membrane and induce a strong interfacial interaction between SHGO and the SPEEK matrix, which improve the proton conductivity and lower the swelling ratio of the membrane, respectively. Additionally, the proton conductivity of the membrane could be further enhanced by the presence of the holes in the graphitic planes of the SHGOs, since it provides an additional channel for transport of the protons. When used, direct methanol fuel cell with the SPEEK/SHGO membrane is found to exhibit much higher performance than that with Nafion 112, suggesting potential use of the SPEEK/SHGO membrane as the PEMs.

Complex inner core of the Earth: The last frontier of global seismology

NASA Astrophysics Data System (ADS)

Tkalčić, Hrvoje

2015-03-01

The days when the Earth's inner core (IC) was viewed as a homogeneous solid sphere surrounded by the liquid outer core (OC) are now behind us. Due to a limited number of data sampling the IC and a lack of experimentally controlled conditions in the deep Earth studies, it has been difficult to scrutinize competitive hypotheses in this active area of research. However, a number of new concepts linking IC structure and dynamics has been proposed lately to explain different types of seismological observations. A common denominator of recent observational work on the IC is increased complexity seen in IC physical properties such as its isotropic and anisotropic structure, attenuation, inner core boundary (ICB) topography, and its rotational dynamics. For example, small-scale features have been observed to exist as a widespread phenomenon in the uppermost inner core, probably superimposed on much longer-scale features. The characterization of small-scale features sheds light on the nature of the solidification process and helps in understanding seismologically observed hemispherical dichotomy of the IC. The existence of variations in the rate and level of solidification is a plausible physical outcome in an environment where vigorous compositional convection in the OC and variations in heat exchange across the ICB may control the process of crystal growth. However, further progress is hindered by the fact that the current traveltime data of PKIKP waves traversing the IC do not allow discriminating between variations in isotropic P wave velocity and velocity anisotropy. Future studies of attenuation in the IC might provide crucial information about IC structure, although another trade-off exists—that of the relative contribution of scattering versus viscoelastic attenuation and the connection with the material properties. Future installations of dense arrays, cross paths of waves that sample the IC, and corresponding array studies will be a powerful tool to image and clearly distinguish between viscoelastic and scattering attenuation, and isotropic- and anisotropic-heterogeneity related effects on traveltimes of core-sensitive body waves. This will then inevitably contribute to a better understanding of what the IC is made of, how it solidifies and how it contributes to the generation and dynamics of the geomagnetic field.

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.

High Volumetric Energy Density Asymmetric Supercapacitors Based on Well-Balanced Graphene and Graphene-MnO2 Electrodes with Densely Stacked Architectures.

PubMed

Sheng, Lizhi; Jiang, Lili; Wei, Tong; Fan, Zhuangjun

2016-10-01

The well-matched electrochemical parameters of positive and negative electrodes, such as specific capacitance, rate performance, and cycling stability, are important for obtaining high-performance asymmetric supercapacitors. Herein, a facile and cost-effective strategy is demonstrated for the fabrication of 3D densely stacked graphene (DSG) and graphene-MnO 2 (G-MnO 2 ) architectures as the electrode materials for asymmetric supercapacitors (ASCs) by using MnO 2 -intercalated graphite oxide (GO-MnO 2 ) as the precursor. DSG has a stacked graphene structure with continuous ion transport network in-between the sheets, resulting in a high volumetric capacitance of 366 F cm -3 , almost 2.5 times than that of reduced graphene oxide, as well as long cycle life (93% capacitance retention after 10 000 cycles). More importantly, almost similar electrochemical properties, such as specific capacitance, rate performance, and cycling stability, are obtained for DSG as the negative electrode and G-MnO 2 as the positive electrode. As a result, the assembled ASC delivers both ultrahigh gravimetric and volumetric energy densities of 62.4 Wh kg -1 and 54.4 Wh L -1 (based on total volume of two electrodes) in 1 m Na 2 SO 4 aqueous electrolyte, respectively, much higher than most of previously reported ASCs in aqueous electrolytes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Towards ultrahigh volumetric capacitance: graphene derived highly dense but porous carbons for supercapacitors

NASA Astrophysics Data System (ADS)

Tao, Ying; Xie, Xiaoying; Lv, Wei; Tang, Dai-Ming; Kong, Debin; Huang, Zhenghong; Nishihara, Hirotomo; Ishii, Takafumi; Li, Baohua; Golberg, Dmitri; Kang, Feiyu; Kyotani, Takashi; Yang, Quan-Hong

2013-10-01

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm-3, 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm-3, which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs.

Towards ultrahigh volumetric capacitance: graphene derived highly dense but porous carbons for supercapacitors.

PubMed

Tao, Ying; Xie, Xiaoying; Lv, Wei; Tang, Dai-Ming; Kong, Debin; Huang, Zhenghong; Nishihara, Hirotomo; Ishii, Takafumi; Li, Baohua; Golberg, Dmitri; Kang, Feiyu; Kyotani, Takashi; Yang, Quan-Hong

2013-10-17

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm(-3), 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm(-3), which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs.

On the Boundary Condition for Water at a Hydrophobic, Dense Surface

NASA Technical Reports Server (NTRS)

Walther, J. H.; Jaffe, R. L.; Werder, T.; Halicioglu, T.; Koumoutsakos, P.

2002-01-01

We study the no-slip boundary conditions for water at a hydrophobic (graphite) surface using non-equilibrium molecular-dynamics simulations. For the planar Couette flow, we find a slip length of 64 nm at 1 bar and 300 K, decreasing with increasing system pressure to a value of 31 nm at 1000 bar. Changing the properties of the interface to from hydrophobic to strongly hydrophilic reduces the slip to 14 nm. Finally, we study the flow of water past an array of carbon nanotubes mounted in an inline configuration with a spacing of 16.4 x 16.4 nm. For tube diameters of 1.25 and 2.50 nm we find drag coefficients in good agreement with the macroscopic, Navier-Stokes values. For carbon nanotubes, the no-slip condition is valid to within the definition of the position of the interface.

The action of macrosounds on graphite ore and derived products

NASA Technical Reports Server (NTRS)

Bradeteanu, C.; Dragan, O.

1974-01-01

A suspension of graphite ore, floated graphite, and the gangue left over from flotation were subjected to the action of macrosounds under determinant conditions. The following was found: (1) The graphite ore undergoes an efficient settling action. (2) The floated graphite is strongly crushed down to the dimensions of colloidal graphite. (3) The gangue left over from flotation can be further processed to recuperate graphite from its nuclei.

Graphene prepared by thermal reduction–exfoliation of graphite oxide: Effect of raw graphite particle size on the properties of graphite oxide and graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dao, Trung Dung; Jeong, Han Mo, E-mail: hmjeong@mail.ulsan.ac.kr

Highlights: • Effect of raw graphite particle size on properties of GO and graphene is reported. • Size of raw graphite affects oxidation degree and chemical structure of GO. • Highly oxidized GO results in small-sized but well-exfoliated graphene. • GO properties affect reduction degree, structure, and conductivity of graphene. - Abstract: We report the effect of raw graphite size on the properties of graphite oxide and graphene prepared by thermal reduction–exfoliation of graphite oxide. Transmission electron microscope analysis shows that the lateral size of graphene becomes smaller when smaller size graphite is used. X-ray diffraction analysis confirms that graphitemore » with smaller size is more effectively oxidized, resulting in a more effective subsequent exfoliation of the obtained graphite oxide toward graphene. X-ray photoelectron spectroscopy demonstrates that reduction of the graphite oxide derived from smaller size graphite into graphene is more efficient. However, Raman analysis suggests that the average size of the in-plane sp{sup 2}-carbon domains on graphene is smaller when smaller size graphite is used. The enhanced reduction degree and the reduced size of sp{sup 2}-carbon domains contribute contradictively to the electrical conductivity of graphene when the particle size of raw graphite reduces.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, Fei; Xu, Wu; Choi, Daiwon

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.more » 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.« less

Graphite

USGS Publications Warehouse

Robinson, Gilpin R.; Hammarstrom, Jane M.; Olson, Donald W.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Graphite is a form of pure carbon that normally occurs as black crystal flakes and masses. It has important properties, such as chemical inertness, thermal stability, high electrical conductivity, and lubricity (slipperiness) that make it suitable for many industrial applications, including electronics, lubricants, metallurgy, and steelmaking. For some of these uses, no suitable substitutes are available. Steelmaking and refractory applications in metallurgy use the largest amount of produced graphite; however, emerging technology uses in large-scale fuel cell, battery, and lightweight high-strength composite applications could substantially increase world demand for graphite.Graphite ores are classified as “amorphous” (microcrystalline), and “crystalline” (“flake” or “lump or chip”) based on the ore’s crystallinity, grain-size, and morphology. All graphite deposits mined today formed from metamorphism of carbonaceous sedimentary rocks, and the ore type is determined by the geologic setting. Thermally metamorphosed coal is the usual source of amorphous graphite. Disseminated crystalline flake graphite is mined from carbonaceous metamorphic rocks, and lump or chip graphite is mined from veins in high-grade metamorphic regions. Because graphite is chemically inert and nontoxic, the main environmental concerns associated with graphite mining are inhalation of fine-grained dusts, including silicate and sulfide mineral particles, and hydrocarbon vapors produced during the mining and processing of ore. Synthetic graphite is manufactured from hydrocarbon sources using high-temperature heat treatment, and it is more expensive to produce than natural graphite.Production of natural graphite is dominated by China, India, and Brazil, which export graphite worldwide. China provides approximately 67 percent of worldwide output of natural graphite, and, as the dominant exporter, has the ability to set world prices. China has significant graphite reserves, and China’s graphite production is expected to increase, although rising labor costs and some mine production problems are developing. China is expected to continue to be the dominant exporter for the near future. Mexico and Canada export graphite mainly to the United States, which has not had domestic production of natural graphite since the 1950s. Most graphite deposits in the United States are too small, low-grade, or remote to be of commercial value in the near future, and the likelihood of discovering larger, higher-grade, or favorably located domestic deposits is unlikely. The United States is a major producer of synthetic graphite.

Phase diagram of two-dimensional hard ellipses.

PubMed

Bautista-Carbajal, Gustavo; Odriozola, Gerardo

2014-05-28

We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [E. P. Bernard and W. Krauth, Phys. Rev. Lett. 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i.e., isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios.

Strategic graphite, a survey

USGS Publications Warehouse

Cameron, Eugene N.; Weis, Paul L.

1960-01-01

Strategic graphite consists of certain grades of lump and flake graphite for which the United States is largely or entirely dependent on sources abroad. Lump graphite of high purity, necessary in the manufacture of carbon brushes, is imported from Ceylon, where it occurs in vein deposits. Flake graphite, obtained from deposits consisting of graphite disseminated in schists and other metamorphic rocks, is an essential ingredient of crucibles used in the nonferrous metal industries and in the manufacture of lubricants and packings. High-quality flake graphite for these uses has been obtained mostly from Madagascar since World War I. Some flake graphite of strategic grade has been produced, however, from deposits in Texas, Alabama, and Pennsylvania. The development of the carbon-bonded crucible, which does not require coarse flake, should lessen the competitive advantage of the Madagascar producers of crucible flake. Graphite of various grades has been produced intermittently in the United States since 1644. The principal domestic deposits of flake graphite are in Texas, Alabama, Pennsylvania, and New York. Reserves of flake graphite in these four States are very large, but production has been sporadic and on the whole unprofitable since World War I, owing principally to competition from producers in Madagascar. Deposits in Madagascar are large and relatively high in content of flake graphite. Production costs are low and the flake produced is of high quality. Coarseness of flake and uniformity of the graphite products marketed are cited as major advantages of Madagascar flake. In addition, the usability of Madagascar flake for various purposes has been thoroughly demonstrated, whereas the usability of domestic flake for strategic purposes is still in question. Domestic graphite deposits are of five kinds: deposits consisting of graphite disseminated in metamorphosed siliceous sediments, deposits consisting of graphite disseminated in marble, deposits formed by thermal or dynamothermal metamorphism of coal beds or other highly carbonaceous sediments, vein deposits, and contact metasomatic deposits in marble. Only the first kind comprises deposits sufficiently large and rich in flake graphite to be significant potential sources of strategic grades of graphite. Vein deposits in several localities are known, but none is known to contain substantial reserves of graphite of strategic quality.Large resources of flake graphite exist in central Texas, in northeastern Alabama, in eastern Pennsylvania, and in the eastern Adirondack Mountains of New York. Tonnages available, compared with the tonnages of flake graphite consumed annually in the United States, are very large. There have been indications that flake graphite from Texas, Alabama, and Pennsylvania can be used in clay-graphite crucibles as a substitute for Madagascar flake, and one producer has made progress in establishing markets for his flake products as ingredients of lubricants. The tonnages of various commercial grades of graphite recoverable from various domestic deposits, however, have not been established; hence, the adequacy of domestic resources of graphite in a time of emergency is not known.The only vein deposits from which significant quantities of lump graphite have been produced are those of the Crystal Graphite mine, Beaverhead County, Mont. The deposits are fracture fillings in Precambrian gneiss and pegmatite. Known reserves in the deposits are small. In Texas, numerous flake-graphite deposits occur in the Precambrian Packsaddle schist in Llano and Burnet Counties. Graphite disseminated in certain parts of this formation ranges from extremely fine to medium grained. The principal producer has been the mine of the Southwestern Graphite Co., west of the town of Burnet. Substantial reserves of medium-grained graphite are present in the deposit mined by the company. In northeastern Alabama, flake-graphite deposits occur in the Ashland mica schist in two belts that trend northeastward across Clay, Goosa, and Chilton Counties. The northeastern belt has been the most productive. About 40 mines have been operated at one time or another, but only a few have been active during or since World War I. The deposits consist of flake graphite disseminated in certain zones or "leads" consisting of quartz-mica-feldspar schists and mica quartzite. Most of past production has come from the weathered upper parts of the deposits, but unweathered rock has been mined at several localities. Reserves of weathered rock containing 3 to 5 percent graphite are very large, and reserves of unweathered rock are even greater. Flake graphite deposits in Chester County, Pa., have been worked intermittently since about 1890. The deposits consist of medium- to coarse-grained graphite disseminated in certain belts of the Pickering gneiss. The most promising deposit is one worked in the Benjamin Franklin and the Eynon Just mines. Reserves of weathered rock containing 1.5 percent graphite are of moderate size; reserves of unweathered rock are large. In the eastern Adirondack Mountains in New York there are two principal kinds of flake-graphite deposits: contact-metasomatic deposits and those consisting of flake graphite disseminated in quartz schist. The contact-metasomatic deposits are small, irregular, and very erratic in graphite content. The deposits in quartz schist are very large, persistent, and uniform in grade. There are large reserves of schist containing 3 to 5 percent graphite, but the graphite is relatively fine grained.

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.

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)

AGC-2 Irradiation Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rohrbaugh, David Thomas; Windes, William; Swank, W. David

The Next Generation Nuclear Plant (NGNP) will be a helium-cooled, very high temperature reactor (VHTR) with a large graphite core. In past applications, graphite has been used effectively as a structural and moderator material in both research and commercial high temperature gas cooled reactor (HTGR) designs.[ , ] Nuclear graphite H 451, used previously in the United States for nuclear reactor graphite components, is no longer available. New nuclear graphites have been developed and are considered suitable candidates for the new NGNP reactor design. To support the design and licensing of NGNP core components within a commercial reactor, a completemore » properties database must be developed for these current grades of graphite. Quantitative data on in service material performance are required for the physical, mechanical, and thermal properties of each graphite grade with a specific emphasis on data related to the life limiting effects of irradiation creep on key physical properties of the NGNP candidate graphites. Based on experience with previous graphite core components, the phenomenon of irradiation induced creep within the graphite has been shown to be critical to the total useful lifetime of graphite components. Irradiation induced creep occurs under the simultaneous application of high temperatures, neutron irradiation, and applied stresses within the graphite components. Significant internal stresses within the graphite components can result from a second phenomenon—irradiation induced dimensional change. In this case, the graphite physically changes i.e., first shrinking and then expanding with increasing neutron dose. This disparity in material volume change can induce significant internal stresses within graphite components. Irradiation induced creep relaxes these large internal stresses, thus reducing the risk of crack formation and component failure. Obviously, higher irradiation creep levels tend to relieve more internal stress, thus allowing the components longer useful lifetimes within the core. Determining the irradiation creep rates of nuclear grade graphites is critical for determining the useful lifetime of graphite components and is a major component of the Advanced Graphite Creep (AGC) experiment.« less

Stable dispersions of polymer-coated graphitic nanoplatelets

NASA Technical Reports Server (NTRS)

Nguyen, Sonbinh T. (Inventor); Stankovich, Sasha (Inventor); Ruoff, Rodney S. (Inventor)

2011-01-01

A method of making a dispersion of reduced graphite oxide nanoplatelets involves providing a dispersion of graphite oxide nanoplatelets and reducing the graphite oxide nanoplatelets in the dispersion in the presence of a reducing agent and a polymer. The reduced graphite oxide nanoplatelets are reduced to an extent to provide a higher C/O ratio than graphite oxide. A stable dispersion having polymer-treated reduced graphite oxide nanoplatelets dispersed in a dispersing medium, such as water or organic liquid is provided. The polymer-treated, reduced graphite oxide nanoplatelets can be distributed in a polymer matrix to provide a composite material.

Structural disorder of graphite and implications for graphite thermometry

NASA Astrophysics Data System (ADS)

Kirilova, Martina; Toy, Virginia; Rooney, Jeremy S.; Giorgetti, Carolina; Gordon, Keith C.; Collettini, Cristiano; Takeshita, Toru

2018-02-01

Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite crystallinity versus other thermometers have been documented in deformed rocks. To examine the possibility of mechanical modifications of graphite structure and the potential impacts on graphite thermometry, we performed laboratory deformation experiments. We sheared highly crystalline graphite powder at normal stresses of 5 and 25 megapascal (MPa) and aseismic velocities of 1, 10 and 100 µm s-1. The degree of structural order both in the starting and resulting materials was analyzed by Raman microspectroscopy. Our results demonstrate structural disorder of graphite, manifested as changes in the Raman spectra. Microstructural observations show that brittle processes caused the documented mechanical modifications of the aggregate graphite crystallinity. We conclude that the calibrated graphite thermometer is ambiguous in active tectonic settings.

International strategic minerals inventory summary report; natural graphite

USGS Publications Warehouse

Krauss, U.H.; Schmidt, H.W.; Taylor, H.A.; Sutphin, D.M.

1989-01-01

Natural graphite is a crystalline mineral of pure carbon which normally occurs in the form of platelet-shaped crystals. It has important properties, such as chemical inertness, low thermal expansion, and lubricity, that make it almost irreplaceable for certain uses such as refractories and steelmaking. Graphite ore types are crystalline (flake and lump} or 'amorphous' (cryptocrystalline}. Refractory applications use the largest total amount of natural graphite, while the most important use of crystalline graphite is in crucibles for handling molten metals. All graphite deposits being mined today are found in the following metamorphic environments: (1) contact metamorphosed coal generally is a source of amorphous graphite; (2)disseminated crystalline flake graphite comes from syngenetic metasediments; and (3) crystalline lump graphite is found in epigenetic veins in high-grade metamorphic regions. Graphite may also occur as a trace mineral in ultrabasic rocks and pegmatites, but these are economically insignificant. The world's identified economically exploitable resources of crystalline graphite in major deposits are estimated to be about 9.7 million metric tons of concentrate. In-place resources of amorphous graphite are about 11.5 million metric tons. Of these, less than 2 percent of the crystalline ore and less than 1 percent of the amorphous ore are in western industrial countries. World mining production of natural graphite rose from 347,000 metric tons in 1973 to 659,000 metric tons in 1986, while the proportion produced by central economy countries increased from about 50 percent for the period from 1973 to 1978 to more than 64 percent in 1979 to 1986. It is estimated that crystalline flake graphite accounts for at least 180,000 metric tons of total annual world mining production of natural graphite, and amorphous graphite makes up the rest.

Transformation of graphite by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Kirilova, Matina; Toy, Virginia; Timms, Nicholas; Halfpenny, Angela; Menzies, Catriona; Craw, Dave; Rooney, Jeremy; Giorgetti, Carolina

2017-04-01

Graphite is a material with one of the lowest frictional strengths, with coefficient of friction of 0.1 and thus in natural fault zones it may act as a natural solid lubricant. Graphitization, or the transformation of organic matter (carbonaceous material, or CM) into crystalline graphite, is induced by compositional and structural changes during diagenesis and metamorphism. The supposed irreversible nature of this process has allowed the degree of graphite crystallinity to be calibrated as an indicator of the peak temperatures reached during progressive metamorphism. We examine processes of graphite emplacement and deformation in the Alpine Fault Zone, New Zealand's active continental tectonic plate boundary. Raman spectrometry indicates that graphite in the distal, amphibolite-facies Alpine Schist, which experienced peak metamorphic temperatures up to 640 ◦C, is highly crystalline and occurs mainly along grain boundaries within quartzo-feldspathic domains. The subsequent mylonitisation in the Alpine Fault Zone resulted in progressive reworking of CM under lower temperature conditions (500◦C-600◦C) in a structurally controlled environment, resulting in spatial clustering in lower-strain protomylonites, and further foliation-alignment in higher-strain mylonites. Subsequent brittle deformation of the mylonitised schists resulted in cataclasites that contain over three-fold increase in the abundance of graphite than mylonites. Furthermore, cataclasites contain graphite with two different habits: highly-crystalline, foliated forms that are inherited mylonitic graphite; and lower-crystallinity, less mature patches of finer-grained graphite. The observed graphite enrichment and the occurrence of poorly-organised graphite in the Alpine Fault cataclasites could result from: i) hydrothermal precipitation from carbon-supersaturated fluids; and/or ii) mechanical degradation by structural disordering of mylonitic graphite combined with strain-induced graphite localisation. The lack of published systematic studies of mechanical modification of the structure of graphite inhibits further conclusion to be drawn. Thus, we performed laboratory deformation experiments during which we sheared highly crystalline graphite powder at room temperature, normal stresses of 5 MPa and 25 MPa and sliding velocities of 1 µm/s, 10 µm/s and 100 µm/s. The degree of graphite crystallinity, both in the starting and resulting materials, was analysed by Raman microspectroscopy. Our results demonstrate consistent decrease of graphite crystallinity with increasing shear strain. We conclude that: i) graphite 'thermometers' are unreliable in brittely deformed rocks; ii) a shear strain calibration of graphite 'thermometers' is needed; iii) fault creep is very likely responsible for the observed structural and textural characteristics of graphite in the Alpine Fault cataclasites. Finally, to investigate the possibility of hydrothermal origin for at least some of the graphite in the Alpine Fault cataclasites we will also present synchrotron FTIR and carbon isotope analysis of the Alpine fault rocks.

Damage detection in composite materials using Lamb wave methods

NASA Astrophysics Data System (ADS)

Kessler, Seth S.; Spearing, S. Mark; Soutis, Constantinos

2002-04-01

Cost-effective and reliable damage detection is critical for the utilization of composite materials. This paper presents part of an experimental and analytical survey of candidate methods for in situ damage detection of composite materials. Experimental results are presented for the application of Lamb wave techniques to quasi-isotropic graphite/epoxy test specimens containing representative damage modes, including delamination, transverse ply cracks and through-holes. Linear wave scans were performed on narrow laminated specimens and sandwich beams with various cores by monitoring the transmitted waves with piezoceramic sensors. Optimal actuator and sensor configurations were devised through experimentation, and various types of driving signal were explored. These experiments provided a procedure capable of easily and accurately determining the time of flight of a Lamb wave pulse between an actuator and sensor. Lamb wave techniques provide more information about damage presence and severity than previously tested methods (frequency response techniques), and provide the possibility of determining damage location due to their local response nature. These methods may prove suitable for structural health monitoring applications since they travel long distances and can be applied with conformable piezoelectric actuators and sensors that require little power.

Thermal expansion of composites using Moire interferometry

NASA Technical Reports Server (NTRS)

Bowles, D. E.; Post, D.; Herakovich, C. T.; Tenny, D. R.

1980-01-01

An experimental technique for precise measurement of the thermal response of fiber-reinforced composite materials uses moire interferometry with fringe multiplication which yield a sensitivity of 833 nm (32.8 mu in.) per fringe. Results from the technique are compared with those obtained from electrical resistance strain gages, and also those predicted from classical lamination theory. Temperature dependent coefficients of thermal expansion for composite materials subjected to thermal cycling in the temperature range of 297 K (75 F) to 422 K (300 F) were determined for four laminate configurations (0, 90, 0/ + or - 45/90 sub s and 0/90/ + or - 45 sub s) of T300/5208 graphite epoxy, and ranged from -0.107 mu epsilon K/1 (-0.059 mu epsilon deg F/-) for the 0 laminate to 32.18 mu epsilon K/1 (17.88 mu epsilon F/1) for the 90 laminate. Moisture was found to greatly influence the thermal response of a quasi-isotropic laminate, resulting in hysteresis and residual compressive strain as the moisture content was reduced. Comparisons between moire and strain gage measurements were inconclusive with both techniques giving consistent but systematically different results. Differences of as much as 29% were observed.

Acoustic radiation damping of flat rectangular plates subjected to subsonic flows

NASA Technical Reports Server (NTRS)

Lyle, Karen Heitman

1993-01-01

The acoustic radiation damping for various isotropic and laminated composite plates and semi-infinite strips subjected to a uniform, subsonic and steady flow has been predicted. The predictions are based on the linear vibration of a flat plate. The fluid loading is characterized as the perturbation pressure derived from the linearized Bernoulli and continuity equations. Parameters varied in the analysis include Mach number, mode number and plate size, aspect ratio and mass. The predictions are compared with existing theoretical results and experimental data. The analytical results show that the fluid loading can significantly affect realistic plate responses. Generally, graphite/epoxy and carbon/carbon plates have higher acoustic radiation damping values than similar aluminum plates, except near plate divergence conditions resulting from aeroelastic instability. Universal curves are presented where the acoustic radiation damping normalized by the mass ratio is a linear function of the reduced frequency. A separate curve is required for each Mach number and plate aspect ratio. In addition, acoustic radiation damping values can be greater than or equal to the structural component of the modal critical damping ratio (assumed as 0.01) for the higher subsonic Mach numbers. New experimental data were acquired for comparison with the analytical results.

EXPLORATORY DEVELOPMENT OF GRAPHITE MATERIALS.

DTIC Science & Technology

COMPOSITE MATERIALS), (* GRAPHITE , (*FIBERS, GRAPHITE ), (*LAMINATED PLASTICS, GRAPHITE ), MOLDINGS, EXTRUSION, VACUUM, EPOXY RESINS, FILAMENTS, STRESSES, TENSILE PROPERTIES, OXIDATION, PHYSICAL PROPERTIES.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, J.X.; Wei, B.Q.; Li, D.D.

The evolution of microstructure in bainite during graphitization annealing at 680 °C of Jominy-quenched bars of an Al-Si bearing medium carbon (0.4C wt%) steel has been studied and compared with that in martensite by using light, scanning and transmission electron microscopy. The results show that the graphitization process in bainite is different from that in martensite in many aspects such as the initial carbon state, the behavior of cementite, the nucleation-growth feature and kinetics of formation of graphite spheroids during graphitization annealing, and the shape, size and distribution of these graphite spheroids. The fact that the graphitization in bainite canmore » produce more homogeneous graphite spheroids with more spherical shape and finer size in a shorter annealing time without the help of preexisting coring particles implies that bainite should be a better starting structure than martensite for making graphitic steel. - Highlights: • This article presents a microstructural characterization of formation of graphite spheroids in bainite. • Nucleation and growth characteristics of graphite spheroids formed in bainite and martensite are compared. • Bainite should be a better starting structure for making graphitic steel as results show.« less

40 CFR 436.380 - Applicability; description of the graphite subcategory.

Code of Federal Regulations, 2012 CFR

2012-07-01

... graphite subcategory. 436.380 Section 436.380 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Graphite Subcategory § 436.380 Applicability; description of the graphite subcategory. The provisions of this subpart are applicable to the mining and processing of naturally occurring graphite. ...

Impact response of graphite/epoxy fabric structures

NASA Technical Reports Server (NTRS)

Lagace, Paul A.; Kraft, Michael J.

1990-01-01

The impact damage resistance and damage tolerance of graphite/epoxy fabric plate (coupon) and cylinder structures were investigated and compared in an analytical and experimental study. Hercules A370-5H/3501-6 five-harness satin weave cloth in a quasi-isotropic (0,45)(sub s) laminate configuration was utilized. Specimens were impacted with 12.7 mm diameter steel spheres at velocities ranging from 10 m/s to 100 m/s. Damage resistance of the specimens was determined through the use of dye penetrant enhanced x-radiography, sectioning, epoxy burnoff, and visual methods. Damage tolerance of the flat plate structures was assessed in a residual tensile test while damage tolerance of the cylinder structures was assessed via pressurization tests. Impacted fabric laminates exhibited matrix crushing, fiber breakage, delamination, and fiber bundle disbonds; the latter being a unique damage mode for fabric laminates. Plate delamination and bundle disbonding was found to be more extensive around the central core area of fiber damage in the coupon specimens than in the cylinder specimens which showed a cleaner damage area due to impact. Damage resistance and damage tolerance were predicted by utilizing a five-step analysis approach previously utilized for coupon configurations. Two of the five steps were adapted to account for the effects of the structural configuration of the pressurized cylinder. The damage resistance analysis provided good correlation to the fiber damage region of both the coupon and cylinder specimens. There was little difference in the size of this region in the two specimen types. However, the analysis was not able to predict the distribution of damage through-the-thickness. This was important in assessing the damage tolerance of the cylinders. The damage tolerance analysis was able to predict the residual tensile strength of the coupons. A general methodology to predict the impact damage resistance and damage tolerance of composite structures utilizing coupon data is presented.

Method for producing thin graphite flakes with large aspect ratios

DOEpatents

Bunnell, L. Roy

1993-01-01

A method for making graphite flakes of high aspect ratio by the steps of providing a strong concentrated acid and heating the graphite in the presence of the acid for a time and at a temperature effective to intercalate the acid in the graphite; heating the intercalated graphite at a rate and to a temperature effective to exfoliate the graphite in discrete layers; subjecting the graphite layers to ultrasonic energy, mechanical shear forces, or freezing in an amount effective to separate the layes into discrete flakes.

Physical, electrochemical, and thermal properties of granulated natural graphite as anodes for Li-ion batteries.

PubMed

Jo, Yong Nam; Park, Min-Sik; Kim, Jae-Hun; Kim, Young-Jun

2013-05-01

Two different types of granulated graphites were synthesized by blending and kneading of natural graphite with pitch followed by sintering methods. The electrochemical performances of granulated graphites were investigated as anode materials for use in Li-ion batteries. The blending type granulated graphite possesses a large amount of cavities and voids, while the kneading type granulated graphite has a relatively compact microstructure, which is responsible for a high tap density. Both granulated graphites show improved the initial coulombic efficiencies as a result of decrease of surface area by the granulations. In particular, the kneading type granulated graphite exhibits an excellent rate-capability without significant capacity loss. In addition, the thermal stabilities of both granulated graphites were also improved, which could be attributed to the decrease of active surface area due to pitch coating.

Effect of Reacting Surface Density on the Overall Graphite Oxidation Rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang H. Oh; Eung Kim; Jong Lim

2009-05-01

Graphite oxidation in an air-ingress accident is presently a very important issue for the reactor safety of the very high temperature gas cooled-reactor (VHTR), the concept of the next generation nuclear plant (NGNP) because of its potential problems such as mechanical degradation of the supporting graphite in the lower plenum of the VHTR might lead to core collapse if the countermeasure is taken carefully. The oxidation process of graphite has known to be affected by various factors, including temperature, pressure, oxygen concentration, types of graphite, graphite shape and size, flow distribution, etc. However, our recent study reveals that the internalmore » pore characteristics play very important roles in the overall graphite oxidation rate. One of the main issues regarding graphite oxidation is the potential core collapse problem that may occur following the degradation of graphite mechanical strength. In analyzing this phenomenon, it is very important to understand the relationship between the degree of oxidization and strength degradation. In addition, the change of oxidation rate by graphite oxidation degree characterization by burn-off (ratio of the oxidized graphite density to the original density) should be quantified because graphite strength degradation is followed by graphite density decrease, which highly affects oxidation rates and patterns. Because the density change is proportional to the internal pore surface area, they should be quantified in advance. In order to understand the above issues, the following experiments were performed: (1)Experiment on the fracture of the oxidized graphite and validation of the previous correlations, (2) Experiment on the change of oxidation rate using graphite density and data collection, (3) Measure the BET surface area of the graphite. The experiments were performed using H451 (Great Lakes Carbon Corporation) and IG-110 (Toyo Tanso Co., Ltd) graphite. The reason for the use of those graphite materials is because their chemical and mechanical characteristics are well identified by the previous investigations, and therefore it was convenient for us to access the published data, and to apply and validate our new methodologies. This paper presents preliminary results of compressive strength vs. burn-off and surface area density vs. burn-off, which can be used for the nuclear graphite selection for the NGNP.« less

Acceptance Test Data for BWXT Coated Particle Batches 93172B and 93173B—Defective IPyC and Pyrocarbon Anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hunn, John D.; Helmreich, Grant W.; Dyer, John A.

Coated particle batches J52O-16-93172B and J52O-16-93173B were produced by Babcock and Wilcox Technologies (BWXT) as part of the production campaign for the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program’s AGR-5/6/7 irradiation test in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR), but were not used in the final fuel composite. However, these batches may be used as demonstration production-scale coated particle fuel for other experiments. Each batch was coated in a 150-mm-diameter production-scale fluidized-bed chemical vapor deposition (CVD) furnace. Tristructural isotropic (TRISO) coatings were deposited on 425-μm-nominal-diameter spherical kernels from BWXT lot J52R-16-69317 containing a mixture ofmore » 15.5%-enriched uranium carbide and uranium oxide (UCO). The TRISO coatings consisted of four consecutive CVD layers: a ~50% dense carbon buffer layer with 100-μm-nominal thickness, a dense inner pyrolytic carbon (IPyC) layer with 40-μm-nominal thickness, a silicon carbide (SiC) layer with 35-μm-nominal thickness, and a dense outer pyrolytic carbon (OPyC) layer with 40-μm-nominal thickness. The TRISO-coated particle batches were sieved to upgrade the particles by removing over-sized and under-sized material, and the upgraded batches were designated by appending the letter A to the end of the batch number (e.g., 93172A). Secondary upgrading by sieving was performed on the A-designated batches to remove particles with missing or very-thin buffer layers that were identified during previous analysis of the individual batches for defective IPyC, as reported in the acceptance test data report for the AGR-5/6/7 production batches [Hunn et al. 2017b]. The additionally-upgraded batches were designated by appending the letter B to the end of the batch number (e.g., 93172B).« less

Systems and methods for forming defects on graphitic materials and curing radiation-damaged graphitic materials

DOEpatents

Ryu, Sunmin; Brus, Louis E.; Steigerwald, Michael L.; Liu, Haitao

2012-09-25

Systems and methods are disclosed herein for forming defects on graphitic materials. The methods for forming defects include applying a radiation reactive material on a graphitic material, irradiating the applied radiation reactive material to produce a reactive species, and permitting the reactive species to react with the graphitic material to form defects. Additionally, disclosed are methods for removing defects on graphitic materials.

Graphite anode surface modification with controlled reduction of specific aryl diazonium salts for improved microbial fuel cells power output.

PubMed

Picot, Matthieu; Lapinsonnière, Laure; Rothballer, Michael; Barrière, Frédéric

2011-10-15

Graphite electrodes were modified with reduction of aryl diazonium salts and implemented as anodes in microbial fuel cells. First, reduction of 4-aminophenyl diazonium is considered using increased coulombic charge density from 16.5 to 200 mC/cm(2). This procedure introduced aryl amine functionalities at the surface which are neutral at neutral pH. These electrodes were implemented as anodes in "H" type microbial fuel cells inoculated with waste water, acetate as the substrate and using ferricyanide reduction at the cathode and a 1000 Ω external resistance. When the microbial anode had developed, the performances of the microbial fuel cells were measured under acetate saturation conditions and compared with those of control microbial fuel cells having an unmodified graphite anode. We found that the maximum power density of microbial fuel cell first increased as a function of the extent of modification, reaching an optimum after which it decreased for higher degree of surface modification, becoming even less performing than the control microbial fuel cell. Then, the effect of the introduction of charged groups at the surface was investigated at a low degree of surface modification. It was found that negatively charged groups at the surface (carboxylate) decreased microbial fuel cell power output while the introduction of positively charged groups doubled the power output. Scanning electron microscopy revealed that the microbial anode modified with positively charged groups was covered by a dense and homogeneous biofilm. Fluorescence in situ hybridization analyses showed that this biofilm consisted to a large extent of bacteria from the known electroactive Geobacter genus. In summary, the extent of modification of the anode was found to be critical for the microbial fuel cell performance. The nature of the chemical group introduced at the electrode surface was also found to significantly affect the performance of the microbial fuel cells. The method used for modification is easy to control and can be optimized and implemented for many carbon materials currently used in microbial fuel cells and other bioelectrochemical systems. Copyright © 2011 Elsevier B.V. All rights reserved.

Equivalent isotropic scattering formulation for transient short-pulse radiative transfer in anisotropic scattering planar media.

PubMed

Guo, Z; Kumar, S

2000-08-20

An isotropic scaling formulation is evaluated for transient radiative transfer in a one-dimensional planar slab subject to collimated and/or diffuse irradiation. The Monte Carlo method is used to implement the equivalent scattering and exact simulations of the transient short-pulse radiation transport through forward and backward anisotropic scattering planar media. The scaled equivalent isotropic scattering results are compared with predictions of anisotropic scattering in various problems. It is found that the equivalent isotropic scaling law is not appropriate for backward-scattering media in transient radiative transfer. Even for an optically diffuse medium, the differences in temporal transmittance and reflectance profiles between predictions of backward anisotropic scattering and equivalent isotropic scattering are large. Additionally, for both forward and backward anisotropic scattering media, the transient equivalent isotropic results are strongly affected by the change of photon flight time, owing to the change of flight direction associated with the isotropic scaling technique.

Effect of graphite target power density on tribological properties of graphite-like carbon films

NASA Astrophysics Data System (ADS)

Dong, Dan; Jiang, Bailing; Li, Hongtao; Du, Yuzhou; Yang, Chao

2018-05-01

In order to improve the tribological performance, a series of graphite-like carbon (GLC) films with different graphite target power densities were prepared by magnetron sputtering. The valence bond and microstructure of films were characterized by AFM, TEM, XPS and Raman spectra. The variation of mechanical and tribological properties with graphite target power density was analyzed. The results showed that with the increase of graphite target power density, the deposition rate and the ratio of sp2 bond increased obviously. The hardness firstly increased and then decreased with the increase of graphite target power density, whilst the friction coefficient and the specific wear rate increased slightly after a decrease with the increasing graphite target power density. The friction coefficient and the specific wear rate were the lowest when the graphite target power density was 23.3 W/cm2.

AGC 2 Irradiated Material Properties Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rohrbaugh, David Thomas

2017-05-01

The Advanced Reactor Technologies Graphite Research and Development Program is conducting an extensive graphite irradiation experiment to provide data for licensing of a high temperature reactor (HTR) design. In past applications, graphite has been used effectively as a structural and moderator material in both research and commercial high temperature gas cooled reactor designs. , Nuclear graphite H 451, used previously in the United States for nuclear reactor graphite components, is no longer available. New nuclear graphite grades have been developed and are considered suitable candidates for new HTR reactor designs. To support the design and licensing of HTR core componentsmore » within a commercial reactor, a complete properties database must be developed for these current grades of graphite. Quantitative data on in service material performance are required for the physical, mechanical, and thermal properties of each graphite grade, with a specific emphasis on data accounting for the life limiting effects of irradiation creep on key physical properties of the HTR candidate graphite grades. Further details on the research and development activities and associated rationale required to qualify nuclear grade graphite for use within the HTR are documented in the graphite technology research and development plan.« less

AGC 2 Irradiation Creep Strain Data Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Windes, William E.; Rohrbaugh, David T.; Swank, W. David

2016-08-01

The Advanced Reactor Technologies Graphite Research and Development Program is conducting an extensive graphite irradiation experiment to provide data for licensing of a high temperature reactor (HTR) design. In past applications, graphite has been used effectively as a structural and moderator material in both research and commercial high temperature gas cooled reactor designs. Nuclear graphite H-451, used previously in the United States for nuclear reactor graphite components, is no longer available. New nuclear graphite grades have been developed and are considered suitable candidates for new HTR reactor designs. To support the design and licensing of HTR core components within amore » commercial reactor, a complete properties database must be developed for these current grades of graphite. Quantitative data on in service material performance are required for the physical, mechanical, and thermal properties of each graphite grade, with a specific emphasis on data accounting for the life limiting effects of irradiation creep on key physical properties of the HTR candidate graphite grades. Further details on the research and development activities and associated rationale required to qualify nuclear grade graphite for use within the HTR are documented in the graphite technology research and development plan.« less

Preparation, quantitative surface analysis, intercalation characteristics and industrial implications of low temperature expandable graphite

NASA Astrophysics Data System (ADS)

Peng, Tiefeng; Liu, Bin; Gao, Xuechao; Luo, Liqun; Sun, Hongjuan

2018-06-01

Expandable graphite is widely used as a new functional carbon material, especially as fire-retardant; however, its practical application is limited due to the high expansion temperature. In this work, preparation process of low temperature and highly expandable graphite was studied, using natural flake graphite as raw material and KMnO4/HClO4/NH4NO3 as oxidative intercalations. The structure, morphology, functional groups and thermal properties were characterized during expanding process by Fourier transform infrared spectroscopy (FTIR), Raman spectra, thermo-gravimetry differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscope (SEM). The analysis showed that by oxidation intercalation, some oxygen-containing groups were grafted on the edge and within the graphite layer. The intercalation reagent entered the graphite layer to increase the interlayer spacing. After expansion, the original flaky expandable graphite was completely transformed into worm-like expanded graphite. The order of graphite intercalation compounds (GICs) was proposed and determined to be 3 for the prepared expandable graphite, based on quantitative XRD peak analysis. Meanwhile, the detailed intercalation mechanisms were also proposed. The comprehensive investigation paved a benchmark for the industrial application of such sulfur-free expanded graphite.

The impact of LDEF results on the space application of metal matrix composites

NASA Technical Reports Server (NTRS)

Steckel, Gary L.; Le, Tuyen D.

1993-01-01

Over 200 graphite/aluminum and graphite/magnesium composites were flown on the leading and trailing edges of LDEF on the Advanced Composites Experiment. The performance of these composites was evaluated by performing scanning electron microscopy and x-ray photoelectron spectroscopy of exposed surfaces, optical microscopy of cross sections, and on-orbit and postflight thermal expansion measurements. Graphite/aluminum and graphite/magnesium were found to be superior to graphite/polymer matrix composites in that they are inherently resistant to atomic oxygen and are less susceptible to thermal cycling induced microcracking. The surface foils on graphite/aluminum and graphite/magnesium protect the graphite fibers from atomic oxygen and from impact damage from small micrometeoroid or space debris particles. However, the surface foils were found to be susceptible to thermal fatigue cracking arising from contamination embrittlement, surface oxidation, or stress risers. Thus, the experiment reinforced requirements for carefully protecting these composites from prelaunch oxidation or corrosion, avoiding spacecraft contamination, and designing composite structures to minimize stress concentrations. On-orbit strain measurements demonstrated the importance of through-thickness thermal conductivity in composites to minimize thermal distortions arising from thermal gradients. Because of the high thermal conductivity of aluminum, thermal distortions were greatly reduced in the LDEF thermal environment for graphite/aluminum as compared to graphite/magnesium and graphite/polymer composites. The thermal expansion behavior of graphite/aluminum and graphite/magnesium was stabilized by on-orbit thermal cycling in the same manner as observed in laboratory tests.

Natural graphite demand and supply - Implications for electric vehicle battery requirements

USGS Publications Warehouse

Olson, Donald W.; Virta, Robert L.; Mahdavi, Mahbood; Sangine, Elizabeth S.; Fortier, Steven M.

2016-01-01

Electric vehicles have been promoted to reduce greenhouse gas emissions and lessen U.S. dependence on petroleum for transportation. Growth in U.S. sales of electric vehicles has been hindered by technical difficulties and the high cost of the lithium-ion batteries used to power many electric vehicles (more than 50% of the vehicle cost). Groundbreaking has begun for a lithium-ion battery factory in Nevada that, at capacity, could manufacture enough batteries to power 500,000 electric vehicles of various types and provide economies of scale to reduce the cost of batteries. Currently, primary synthetic graphite derived from petroleum coke is used in the anode of most lithium-ion batteries. An alternate may be the use of natural flake graphite, which would result in estimated graphite cost reductions of more than US$400 per vehicle at 2013 prices. Most natural flake graphite is sourced from China, the world's leading graphite producer. Sourcing natural flake graphite from deposits in North America could reduce raw material transportation costs and, given China's growing internal demand for flake graphite for its industries and ongoing environmental, labor, and mining issues, may ensure a more reliable and environmentally conscious supply of graphite. North America has flake graphite resources, and Canada is currently a producer, but most new mining projects in the United States require more than 10 yr to reach production, and demand could exceed supplies of flake graphite. Natural flake graphite may serve only to supplement synthetic graphite, at least for the short-term outlook.

Treatment of irradiated graphite from French Bugey reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, Howard; Laurent, Gerard

In 2008, following the general French plan for nuclear waste management, Electricite de France attempted to find for irradiated graphite an alternative solution to direct storage at the low-activity long-life storage center in France managed by the national agency for wastes (ANDRA). EDF management requested that its engineering arm, EDF CIDEN, study the graphite treatment alternatives to direct storage. In mid-2008, this study revealed the potential advantage for EDF to use a steam reforming process known as Thermal Organic Reduction, 'THOR' (owned by Studsvik, Inc., USA), to treat or destroy the graphite matrix and limit the quantity of secondary wastemore » to be stored. In late 2009, EDF began a test program with Studsvik to determine if the THOR steam reforming process could be used to destroy the graphite. The program also sought to determine if the graphite could be treated to release the bulk of activity while minimizing the gasification of the bulk mass of the graphite. In October 2009, tests with non-irradiated graphite were completed and demonstrated destruction of a graphite matrix by the THOR process at satisfactory rates. After gasifying the graphite, focus shifted to the effect of roasting graphite at high temperatures in inert gases with low concentrations of oxidizing gases to preferentially remove volatile radionuclides while minimizing the graphite mass loss to 5%. A radioactive graphite sleeve was imported from France to the US for these tests. Completed in April 2010, 'Phase I' of testing showed that the process removed >99% of H-3 and 46% of C-14 with <6% mass loss. Completed in September 2011, 'Phase II' testing achieved increased removals as high as 80% C-14. During Phase II, it was also discovered that roasting in a reducing atmosphere helped to limit the oxidation of the graphite. Future work seeks to explore the effects of reducing gases to limit the bulk oxidation of graphite. If the graphite could be decontaminated of long-lived radionuclides up to 95% for C-14 while minimizing mass loss to <5%, this would minimize the volume of any secondary waste streams and potentially lower the waste class of the larger bulk of graphite. Alternatively, if up to 95% decontamination of C-14 is achieved, the graphite may be completely gasified which could result in lower disposal. (authors)« less

The melting of subducted banded iron formations

NASA Astrophysics Data System (ADS)

Kang, Nathan; Schmidt, Max W.

2017-10-01

Banded iron formations (BIF) were common shelf and ocean basin sediments 3.5-1.8 Ga ago. To understand the fate of these dense rocks upon subduction, the melting relations of carbonated BIF were determined in Fe-Ca-(Mg)-Si-C-O2 at 950-1400 °C, 6 and 10 GPa, oxidizing (fO2 = hematite-magnetite, HM) and moderately reducing (fO2 ∼CO2-graphite/diamond, CCO) conditions. Solidus temperatures under oxidizing conditions are 950-1025 °C with H2O, and 1050-1150 °C anhydrous, but 250-175 °C higher at graphite saturation (values at 6-10 GPa). The combination of Fe3+ and carbonate leads to a strong melting depression. Solidus curves are steep with 17-20 °C/GPa. Near-solidus melts are ferro-carbonatites with ∼22 wt.% FeOtot, ∼48 wt% CO2 and 1-5 wt.% SiO2 at fO2 ∼ HM and ∼49 wt.% FeOtot, ∼20 wt% CO2 and 19-25 wt.% SiO2 at fO2 ∼ CCO . At elevated subduction geotherms, as likely for the Archean, C-bearing BIF could melt out all carbonate around 6 GPa. Fe-rich carbonatites would rise but stagnate gravitationally near the slab/mantle interface until they react with the mantle through Fe-Mg exchange and partial reduction. The latter would precipitate diamond and yield Fe- and C-rich mantle domains, yet, Fe-Mg is expected to diffusively re-equilibrate over Ga time scales. We propose that the oldest subduction derived diamonds stem from BIF derived melts.

Auto-assembly of nanometer thick, water soluble layers of plasmid DNA complexed with diamines and basic amino acids on graphite: Greatest DNA protection is obtained with arginine.

PubMed

Khalil, T T; Boulanouar, O; Heintz, O; Fromm, M

2017-02-01

We have investigated the ability of diamines as well as basic amino acids to condense DNA onto highly ordered pyrolytic graphite with minimum damage after re-dissolution in water. Based on a bibliographic survey we briefly summarize DNA binding properties with diamines as compared to basic amino acids. Thus, solutions of DNA complexed with these linkers were drop-cast in order to deposit ultra-thin layers on the surface of HOPG in the absence or presence of Tris buffer. Atomic Force Microscopy analyses showed that, at a fixed ligand-DNA mixing ratio of 16, the mean thickness of the layers can be statistically predicted to lie in the range 0-50nm with a maximum standard deviation ±6nm, using a simple linear law depending on the DNA concentration. The morphology of the layers appears to be ligand-dependent. While the layers containing diamines present holes, those formed in the presence of basic amino acids, except for lysine, are much more compact and dense. X-ray Photoelectron Spectroscopy measurements provide compositional information indicating that, compared to the maximum number of DNA sites to which the ligands may bind, the basic amino acids Arg and His are present in large excess. Conservation of the supercoiled topology of the DNA plasmids was studied after recovery of the complex layers in water. Remarkably, arginine has the best protection capabilities whether Tris was present or not in the initial solution. Copyright © 2016 Elsevier B.V. All rights reserved.

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.

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.

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.

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.

Morphological and optoelectronic characteristics of nanocomposites comprising graphene nanosheets and poly(3-hexylthiophene).

PubMed

Chang, Yo-Wei; Yu, Shiau-Wei; Liu, Cheng-Hao; Tsiang, Raymond Chien-Chao

2010-10-01

P3HT/graphene nanocomposite was prepared via in-situ reduction of exfoliated graphite oxide in the P3HT polymer matrix, where the exfoliated graphite oxide was formed beforehand via the oxidation of graphite via the Hummers method. The oxidation reaction not only imparts functional groups, such as C=O, C-OH, and C-O-C, to graphite but also causes exfoliation of the resulting graphite oxide. The functional groups render graphite oxide an additional, lower thermal degradation temperature (T(d)) and the exfoliation shifts the XRD pattern towards a much smaller angle. The oxidation of graphite into graphite oxide creates a pleated flaking morphology for graphite oxide as opposed to that of graphite. UV/Vis and photoluminescence (PL) spectra of P3HT/graphene nanocomposite indicate that the existence of graphene does not alter the UV/Vis and PL excitation characteristics of P3HT, and the P3HT/graphene composite has higher electron mobility, a smaller band gap and higher conductivity than the pristine P3HT.

Anisotropic magnetic particles in a magnetic field

PubMed Central

Martchenko, Ilya; Mihut, Adriana M.; Bialik, Erik; Hirt, Ann M.; Rufier, Chantal; Menzel, Andreas; Dietsch, Hervé; Linse, Per

2016-01-01

We characterize the structural properties of magnetic ellipsoidal hematite colloids with an aspect ratio ρ ≈ 2.3 using a combination of small-angle X-ray scattering and computer simulations. The evolution of the phase diagram with packing fraction φ and the strength of an applied magnetic field B is described, and the coupling between orientational order of magnetic ellipsoids and the bulk magnetic behavior of their suspension addressed. We establish quantitative structural criteria for the different phase and arrest transitions and map distinct isotropic, polarized non-nematic, and nematic phases over an extended range in the φ–B coordinates. We show that upon a rotational arrest of the ellipsoids around φ = 0.59, the bulk magnetic behavior of their suspension switches from superparamagnetic to ordered weakly ferromagnetic. If densely packed and arrested, these magnetic particles thus provide persisting remanent magnetization of the suspension. By exploring structural and magnetic properties together, we extend the often used colloid-atom analogy to the case of magnetic spins. PMID:27722439

Erasure of memory in paste by irradiation of ultrasonic waves

NASA Astrophysics Data System (ADS)

Nakahara, Akio; Yoneyama, Ryota; Ito, Maruto; Matsuo, Yousuke; Kitsunezaki, So

2017-06-01

Densely packed colloidal suspension, called paste, remembers the direction of applied forces, such as vibration and flow, and these memories kept in paste can be visualized as morphology of desiccation crack patterns. For example, when the paste remembers the direction of vibration, all primary cracks propagate in the direction perpendicular to the direction of initial vibration. On the other hand, when the paste remembers the direction of flow, all primary cracks propagate along the direction of initial flow. These results indicate that external forces imprint easy-breakable direction into paste as memories. Therefore, by controlling memories in paste, we can tune to produce various types of crack patterns, such as cellular, radial, lamellar, ring, spiral and lattice structures. Recently we have found that memories in paste can be erased by the irradiation of ultrasonic waves to paste as we obtain only isotropic and cellular crack patterns without any anisotropy related to memory effect. This method can be applied to increase the breaking strength of dried paste by homogenizing microstructure in paste.

The effects of particle loading on turbulence structure and modelling

NASA Technical Reports Server (NTRS)

Squires, Kyle D.; Eaton, J. K.

1989-01-01

The objective of the present research was to extend the Direct Numerical Simulation (DNS) approach to particle-laden turbulent flows using a simple model of particle/flow interaction. The program addressed the simplest type of flow, homogeneous, isotropic turbulence, and examined interactions between the particles and gas phase turbulence. The specific range of problems examined include those in which the particle is much smaller than the smallest length scales of the turbulence yet heavy enough to slip relative to the flow. The particle mass loading is large enough to have a significant impact on the turbulence, while the volume loading was small enough such that particle-particle interactions could be neglected. Therefore, these simulations are relevant to practical problems involving small, dense particles conveyed by turbulent gas flows at moderate loadings. A sample of the results illustrating modifications of the particle concentration field caused by the turbulence structure is presented and attenuation of turbulence by the particle cloud is also illustrated.

Graphite Sheet Coating for Improved Thermal Oxidative Stability of Carbon Fiber Reinforced/PMR-15 Composites

NASA Technical Reports Server (NTRS)

Campbell, Sandi; Papadopoulos, Demetrios; Heimann, Paula; Inghram, Linda; McCorkle, Linda

2005-01-01

Expanded graphite was compressed into graphite sheets and used as a coating for carbon fiber reinforced PMR-15 composites. BET analysis of the graphite indicated an increase in graphite pore size on compression, however the material was proven to be an effective barrier to oxygen when prepegged with PMR-15 resin. Oxygen permeability of the PMR-15/graphite was an order of magnitude lower than the compressed graphite sheet. By providing a barrier to oxygen permeation, the rate of oxidative degradation of PMR-15 was decreased. As a result, the composite thermo-oxidative stability increased by up to 25%. The addition of a graphite sheet as a top ply on the composites yielded little change in the material's flexural strength or interlaminar shear strength.

GRAFEC: A New Spanish Program to Investigate Waste Management Options for Radioactive Graphite - 12399

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marquez, Eva; Pina, Gabriel; Rodriguez, Marina

Spain has to manage about 3700 tons of irradiated graphite from the reactor Vandellos I as radioactive waste. 2700 tons are the stack of the reactor and are still in the reactor core waiting for retrieval. The rest of the quantities, 1000 tons, are the graphite sleeves which have been already retrieved from the reactor. During operation the graphite sleeves were stored in a silo and during the dismantling stage a retrieval process was carried out separating the wires from the graphite, which were crushed and introduced into 220 cubic containers of 6 m{sup 3} each and placed in interimmore » storage. The graphite is an intermediate level radioactive waste but it contains long lived radionuclides like {sup 14}C which disqualifies disposal at the low level waste repository of El Cabril. Therefore, a new project has been started in order to investigate two new options for the management of this waste type. The first one is based on a selective decontamination of {sup 14}C by thermal methods. This method is based on results obtained at the Research Centre Juelich (FZJ) in the Frame of the EC programs 'Raphael' and 'Carbowaste'. The process developed at FZJ is based on a preferential oxidation of {sup 14}C in comparison to the bulk {sup 12}C. Explanations for this effect are the inhomogeneous distribution and a weaker bounding of {sup 14}C which is not incorporated in the graphite lattice. However these investigations have only been performed with graphite from the high temperature reactor Arbeitsgemeinschaft Versuchsreaktor Juelich AVR which has been operated in a non-oxidising condition or research reactor graphite operated at room temperature. The reactor Vandellos I has been operated with CO{sub 2} as coolant and significant amounts of graphite have been already oxidised. The aim of the project is to validate whether a {sup 14}C decontamination can also been achieved with graphite from Vandellos I. A second possibility under investigation is the encapsulation of the graphite in a long term stable glass matrix. The principal applicability has been already proved by FNAG. Crushed graphite mixed with a suitable glass powder has been pressed at elevated temperature under vacuum. The vacuum is required to avoid gas enclosures in the obtained product. The obtained products, named IGM for 'Impermeable Graphite Matrix', have densities above 99% of theoretical density. The amount of glass has been chosen with respect to the pore volume of the former graphite parts. The method allows the production of encapsulated graphite without increasing the disposal volume. This paper will give a short overview of characterisation results of different irradiated graphite materials obtained at CIEMAT and in the Carbowaste project as well as the proposed methods and the actual status of the program including first results about leaching of non-radioactive IGM samples and hopefully first tendencies concerning the C-14 separation from graphite of Vandellos I by thermal treatment. Both processes, the thermal treatment as well as the IGM, have the potential to solve problems related to the management of irradiated graphite in Spain. However the methods have only been tested with different types of i-graphite and virgin graphite, respectively. Only investigations with real i-graphite from Spain will reveal whether the described methods are applicable to graphite from Vandellos I. However all partners are convinced that one of these new methods or a combination of them will lead to a feasible option to manage i-graphite in Spain on an industrial scale. (authors)« less

Research on graphite reinforced glass matrix composites

NASA Technical Reports Server (NTRS)

Bacon, J. F.; Prewo, K. M.

1977-01-01

The results of research for the origination of graphite-fiber reinforced glass matrix composites are presented. The method selected to form the composites consisted of pulling the graphite fiber through a slurry containing powdered glass, winding up the graphite fiber and the glass it picks up on a drum, drying, cutting into segments, loading the tape segment into a graphite die, and hot pressing. During the course of the work, composites were made with a variety of graphite fibers in a glass matrix.

Research on the transformation mechanism of graphite phase and microstructure in the heated region of gray cast iron by laser cladding

NASA Astrophysics Data System (ADS)

Liu, Yancong; Zhan, Xianghua; Yi, Peng; Liu, Tuo; Liu, Benliang; Wu, Qiong

2018-03-01

A double-track lap cladding experiment involving gray cast iron was established to investigate the transformation mechanism of graphite phase and microstructure in a laser cladding heated region. The graphite phase and microstructure in different heated regions were observed under a microscope, and the distribution of elements in various heated regions was analyzed using an electron probe. Results show that no graphite existed in the cladding layer and in the middle and upper parts of the binding region. Only some of the undissolved small graphite were observed at the bottom of the binding region. Except the refined graphite size, the morphological characteristics of substrate graphite and graphite in the heat-affected zone were similar. Some eutectic clusters, which grew along the direction of heat flux, were observed in the heat-affected zone whose microstructure was transformed into a mixture of austenite, needle-like martensite, and flake graphite. Needle-like martensite around graphite was fine, but this martensite became sparse and coarse when it was away from graphite. Some martensite clusters appeared in the local area near the binding region, and the carbon atoms in the substrate did not diffuse into the cladding layer through laser cladding, which only affected the bonding area and the bottom of the cladding layer.

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)

Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading. M.S. Thesis

NASA Technical Reports Server (NTRS)

Priest, Stacy Marie

1993-01-01

The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0/+/-45/90)(sub s) cylinders. This indicates that the ratios of D(sub 16) and D(sub 26) to D(sub 11), as opposed to the absolute magnitudes of D(sub 16) and D(sub 26), may be important in the failure of these cylinders and in the applicability of the methodology. Discontinuities observed in the slit tip hoop strains for all the cylinders tested indicate that subcritical damage can play an important role in the failure of tape cylinders. This role varies with layup and loading condition and is likely coupled to the effects of structural anisotropy. Biaxial failure pressures may exceed the uniaxial values because the axial stress contributes to the formation of 0 deg ply splitting (accompanied by delamination) or similar stress-mitigating subcritical damage. The failure behavior of similar cylinders can also vary as a result of differences in the role of subcritical damage as observed for the case of a biaxially loaded (90/0/+/-45)(sub s) cylinder with a 12.7 mm slit. For this case, the methodology is valid when the initial coupon and cylinder fracture modes agree. However, the methodology underpredicts the failure pressure of the cylinder when a circumferential fracture path, suggestive of a 0 deg ply split, occurs at one slit tip. Thus, the failure behavior of some tape cylinders may be highly sensitive to the initial subcritical damage mechanism. Finite element analyses are recommended to determine how structural anisotropy and axial stress modify the slit tip stress states in cylinders from those found in flat plates since similarity of these stress states is a fundamental assumption of the current predictive methodology.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferralis, N.; Diehl, R.D.; Pussi, K.

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 ismore » 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.« less

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

NASA Astrophysics Data System (ADS)

Laffont, L.; Jday, R.; Lacaze, J.

2018-04-01

Growth of graphite during solidification and high-temperature solid-state transformation has been investigated in samples cut out from a thin-wall casting which solidified partly in the stable (iron-graphite) and partly in the metastable (iron-cementite) systems. Transmission electron microscopy has been used to characterize graphite nodules in as-cast state and in samples having been fully graphitized at various temperatures in the austenite field. Nodules in the as-cast material show a twofold structure characterized by an inner zone where graphite is disoriented and an outer zone where it is well crystallized. In heat-treated samples, graphite nodules consist of well-crystallized sectors radiating from the nucleus. These observations suggest that the disoriented zone appears because of mechanical deformation when the liquid contracts during its solidification in the metastable system. During heat-treatment, the graphite in this zone recrystallizes. In turn, it can be concluded that nodular graphite growth mechanism is the same during solidification and solid-state transformation.

Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

NASA Astrophysics Data System (ADS)

Lin, Na; Jia, Zhe; Wang, Zhihui; Zhao, Hui; Ai, Guo; Song, Xiangyun; Bai, Ying; Battaglia, Vincent; Sun, Chengdong; Qiao, Juan; Wu, Kai; Liu, Gao

2017-10-01

The structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystalline graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.

Scale Properties of Anisotropic and Isotropic Turbulence in the Urban Surface Layer

NASA Astrophysics Data System (ADS)

Liu, Hao; Yuan, Renmin; Mei, Jie; Sun, Jianning; Liu, Qi; Wang, Yu

2017-11-01

The scale properties of anisotropic and isotropic turbulence in the urban surface layer are investigated. A dimensionless anisotropic tensor is introduced and the turbulent tensor anisotropic coefficient, defined as C, where C = 3d3 + 1 (d3 is the minimum eigenvalue of the tensor) is used to characterize the turbulence anisotropy or isotropy. Turbulence is isotropic when C ≈ 1, and anisotropic when C ≪ 1. Three-dimensional velocity data collected using a sonic anemometer are analyzed to obtain the anisotropic characteristics of atmospheric turbulence in the urban surface layer, and the tensor anisotropic coefficient of turbulent eddies at different spatial scales calculated. The analysis shows that C is strongly dependent on atmospheric stability ξ = (z-zd)/L_{{it{MO}}}, where z is the measurement height, zd is the displacement height, and L_{{it{MO}}} is the Obukhov length. The turbulence at a specific scale in unstable conditions (i.e., ξ < 0) is closer to isotropic than that at the same scale under stable conditions. The maximum isotropic scale of turbulence is determined based on the characteristics of the power spectrum in three directions. Turbulence does not behave isotropically when the eddy scale is greater than the maximum isotropic scale, whereas it is horizontally isotropic at relatively large scales. The maximum isotropic scale of turbulence is compared to the outer scale of temperature, which is obtained by fitting the temperature fluctuation spectrum using the von Karman turbulent model. The results show that the outer scale of temperature is greater than the maximum isotropic scale of turbulence.

Friction and wear of carbon-graphite materials for high-energy brakes

NASA Technical Reports Server (NTRS)

Bill, R. C.

1978-01-01

Caliper type brake simulation experiments were conducted on seven different carbon graphite materials formulations against a steel disk material and against a carbon graphite disk material. The effects of binder level, boron carbide (B4C) additions, SiC additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level, additions of B4C, and additions of SiC each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. The transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur.

Anti-aliasing filters for deriving high-accuracy DEMs from TLS data: A case study from Freeport, Texas

NASA Astrophysics Data System (ADS)

Xiong, L.; Wang, G.; Wessel, P.

2017-12-01

Terrestrial laser scanning (TLS), also known as ground-based Light Detection and Ranging (LiDAR), has been frequently applied to build bare-earth digital elevation models (DEMs) for high-accuracy geomorphology studies. The point clouds acquired from TLS often achieve a spatial resolution at fingerprint (e.g., 3cm×3cm) to handprint (e.g., 10cm×10cm) level. A downsampling process has to be applied to decimate the massive point clouds and obtain portable DEMs. It is well known that downsampling can result in aliasing that causes different signal components to become indistinguishable when the signal is reconstructed from the datasets with a lower sampling rate. Conventional DEMs are mainly the results of upsampling of sparse elevation measurements from land surveying, satellite remote sensing, and aerial photography. As a consequence, the effects of aliasing have not been fully investigated in the open literature of DEMs. This study aims to investigate the spatial aliasing problem and implement an anti-aliasing procedure of regridding dense TLS data. The TLS data collected in the beach and dune area near Freeport, Texas in the summer of 2015 are used for this study. The core idea of the anti-aliasing procedure is to apply a low-pass spatial filter prior to conducting downsampling. This article describes the successful use of a fourth-order Butterworth low-pass spatial filter employed in the Generic Mapping Tools (GMT) software package as anti-aliasing filters. The filter can be applied as an isotropic filter with a single cutoff wavelength or as an anisotropic filter with different cutoff wavelengths in the X and Y directions. The cutoff wavelength for the isotropic filter is recommended to be three times the grid size of the target DEM.

Anti-aliasing filters for deriving high-accuracy DEMs from TLS data: A case study from Freeport, Texas

NASA Astrophysics Data System (ADS)

Xiong, Lin.; Wang, Guoquan; Wessel, Paul

2017-03-01

Terrestrial laser scanning (TLS), also known as ground-based Light Detection and Ranging (LiDAR), has been frequently applied to build bare-earth digital elevation models (DEMs) for high-accuracy geomorphology studies. The point clouds acquired from TLS often achieve a spatial resolution at fingerprint (e.g., 3 cm×3 cm) to handprint (e.g., 10 cm×10 cm) level. A downsampling process has to be applied to decimate the massive point clouds and obtain manageable DEMs. It is well known that downsampling can result in aliasing that causes different signal components to become indistinguishable when the signal is reconstructed from the datasets with a lower sampling rate. Conventional DEMs are mainly the results of upsampling of sparse elevation measurements from land surveying, satellite remote sensing, and aerial photography. As a consequence, the effects of aliasing caused by downsampling have not been fully investigated in the open literature of DEMs. This study aims to investigate the spatial aliasing problem of regridding dense TLS data. The TLS data collected from the beach and dune area near Freeport, Texas in the summer of 2015 are used for this study. The core idea of the anti-aliasing procedure is to apply a low-pass spatial filter prior to conducting downsampling. This article describes the successful use of a fourth-order Butterworth low-pass spatial filter employed in the Generic Mapping Tools (GMT) software package as an anti-aliasing filter. The filter can be applied as an isotropic filter with a single cutoff wavelength or as an anisotropic filter with two different cutoff wavelengths in the X and Y directions. The cutoff wavelength for the isotropic filter is recommended to be three times the grid size of the target DEM.

Probing storm-time near-Earth magnetotail dynamics using 30 keV proton isotropic boundaries as tracers of precipitating and trapped populations

NASA Astrophysics Data System (ADS)

Ganushkina, N. Y.; Dubyagin, S.; Liemohn, M. W.

2017-12-01

The isotropic boundaries of the energetic protons, which can be routinely observed by low-altitude satellites, have been used as a tool to probe remotely the nightside magnetic configuration in the near-Earth region. The validity of this method is based on the assumption that the isotropic boundary is formed by the particle scattering on the curved field lines in the magnetotail current sheet. However recent results revealed that the wave-particle interaction process often can be responsible for the isotropic boundary formation especially during active times. Using numerous observations of the 30 keV proton isotropic boundaries and conjugated measurements of the magnetic field in the equatorial magnetosphere we demonstrate that isotropic boundary location can be used as a proxy of the magnetotail stretching even during magnetic storms. The results imply that the scattering on the curved field lines still plays major role as a mechanism of the isotropic boundary formation during storm-time. We found that the wave-particle interaction could lead to isotropic boundary formation in 15% of events. In addition, we discuss the morphology of the storm-time energetic proton precipitations.

Fluid-deposited graphitic inclusions in quartz: Comparison between KTB (German Continental Deep-Drilling) core samples and artificially reequilibrated natural inclusions

USGS Publications Warehouse

Pasteris, J.D.; Chou, I.-Ming

1998-01-01

We used Raman microsampling spectroscopy (RMS) to determine the degree of crystallinity of minute (2-15 ??m) graphite inclusions in quartz in two sets of samples: experimentally reequilibrated fluid inclusions in a natural quartz grain and biotite-bearing paragneisses from the KTB deep drillhole in SE Germany. Our sequential reequilibration experiments at 725??C on initially pure CO2 inclusions in a quartz wafer and the J. Krautheim (1993) experiments at 900-1100??C on organic compounds heated in gold or platinum capsules suggest that, at a given temperature, (1) fluid-deposited graphite will have a lower crystallinity than metamorphosed organic matter and (2) that the crystallinity of fluid-deposited graphite is affected by the composition of the fluid from which it was deposited. We determined that the precipitation of more-crystalline graphite is favored by lower fH2 (higher fO2), and that the crystallinity of graphite is established by the conditions (including gas fugacities) that pertain as the fluid first reaches graphite saturation. Graphite inclusions within quartz grains in the KTB rocks show a wide range in crystallinity index, reflecting three episodes of carbon entrapment under different metamorphic conditions. Isolated graphite inclusions have the spectral properties of totally ordered, completely crystalline graphite. Such crystallinity suggests that the graphite was incorporated from the surrounding metasedimentary rocks, which underwent metamorphism at upper amphibolite-facies conditions. Much of the fluid-deposited graphite in fluid inclusions, however, shows some spectral disorder. The properties of that graphite resemble those of experimental precipitates at temperatures in excess of 700??C and at elevated pressures, suggesting that the inclusions represent precipitates from C-O-H fluids trapped under conditions near those of peak metamorphism at the KTB site. In contrast, graphite that is intimately associated with chlorite and other (presumably low-temperature) silicates in inclusions is highly disordered and spectrally resembles kerogens. This graphite probably was deposited during later greenschist-facies retrograde metamorphism at about 400-500??C. The degree of crystallinity of fluid-deposited graphite is shown to be a much more complex function of temperature than is the crystallinity of metamorphic graphite. To some extent, experiments can provide temperature-calibration of the crystallinity index. However, the difference in time scales between experimental runs and geologic processes makes it difficult to infer specific temperatures for naturally precipitated graphite. Copyright ?? 1998 Elsevier Science Ltd.

Tubular graphite cones.

PubMed

Zhang, Guangyu; Jiang, Xin; Wang, Enge

2003-04-18

We report the synthesis of tubular graphite cones using a chemical vapor deposition method. The cones have nanometer-sized tips, micrometer-sized roots, and hollow interiors with a diameter ranging from about 2 to several tens of nanometers. The cones are composed of cylindrical graphite sheets; a continuous shortening of the graphite layers from the interior to the exterior makes them cone-shaped. All of the tubular graphite cones have a faceted morphology. The constituent graphite sheets have identical chiralities of a zigzag type across the entire diameter, imparting structural control to tubular-based carbon structures. The tubular graphite cones have potential for use as tips for scanning probe microscopy, but with greater rigidity and easier mounting than currently used carbon nanotubes.

Process for the fabrication of aluminum metallized pyrolytic graphite sputtering targets

DOEpatents

Makowiecki, D.M.; Ramsey, P.B.; Juntz, R.S.

1995-07-04

An improved method is disclosed for fabricating pyrolytic graphite sputtering targets with superior heat transfer ability, longer life, and maximum energy transmission. Anisotropic pyrolytic graphite is contoured and/or segmented to match the erosion profile of the sputter target and then oriented such that the graphite`s high thermal conductivity planes are in maximum contact with a thermally conductive metal backing. The graphite contact surface is metallized, using high rate physical vapor deposition (HRPVD), with an aluminum coating and the thermally conductive metal backing is joined to the metallized graphite target by one of four low-temperature bonding methods; liquid-metal casting, powder metallurgy compaction, eutectic brazing, and laser welding. 11 figs.

Environmentally benign graphite intercalation compound composition for exfoliated graphite, flexible graphite, and nano-scaled graphene platelets

DOEpatents

Zhamu, Aruna; Jang, Bor Z.

2014-06-17

A carboxylic-intercalated graphite compound composition for the production of exfoliated graphite, flexible graphite, or nano-scaled graphene platelets. The composition comprises a layered graphite with interlayer spaces or interstices and a carboxylic acid residing in at least one of the interstices, wherein the composition is prepared by a chemical oxidation reaction which uses a combination of a carboxylic acid and hydrogen peroxide as an intercalate source. Alternatively, the composition may be prepared by an electrochemical reaction, which uses a carboxylic acid as both an electrolyte and an intercalate source. Exfoliation of the invented composition does not release undesirable chemical contaminants into air or drainage.

Mineral resource of the month: graphite

USGS Publications Warehouse

,

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.

Nucleation and Growth of Graphite in Eutectic Spheroidal Cast Iron: Modeling and Testing

NASA Astrophysics Data System (ADS)

Carazo, Fernando D.; Dardati, Patricia M.; Celentano, Diego J.; Godoy, Luis A.

2016-06-01

A new model of graphite growth during the continuous cooling of eutectic spheroidal cast iron is presented in this paper. The model considers the nucleation and growth of graphite from pouring to room temperature. The microstructural model of solidification accounts for the eutectic as divorced and graphite growth rate as a function of carbon gradient at the liquid in contact with the graphite. In the solid state, the microstructural model takes into account three stages for graphite growth, namely (1) from the end of solidification to the upper bound of intercritical stable eutectoid, (2) during the intercritical stable eutectoid, and (3) from the lower bound of intercritical stable eutectoid to room temperature. The micro- and macrostructural models are coupled using a sequential multiscale approach. Numerical results for graphite fraction and size distribution are compared with experimental results obtained from a cylindrical cup, in which the graphite volumetric fraction and size distribution were obtained using the Schwartz-Saltykov approach. The agreements between the experimental and numerical results for the fraction of graphite and the size distribution of spheroids reveal the importance of numerical models in the prediction of the main aspects of graphite in spheroidal cast iron.

Graphitized-carbon fiber/carbon char fuel

DOEpatents

Cooper, John F [Oakland, CA

2007-08-28

A method for recovery of intact graphitic fibers from fiber/polymer composites is described. The method comprises first pyrolyzing the graphite fiber/polymer composite mixture and then separating the graphite fibers by molten salt electrochemical oxidation.

Thermodynamic Simulation of Equilibrium Composition of Reaction Products at Dehydration of a Technological Channel in a Uranium-Graphite Reactor

NASA Astrophysics Data System (ADS)

Pavliuk, A. O.; Zagumennov, V. S.; Kotlyarevskiy, S. G.; Bespala, E. V.

2018-01-01

The problems of accumulation of nuclear fuel spills in the graphite stack in the course of operation of uranium-graphite nuclear reactors are considered. The results of thermodynamic analysis of the processes in the graphite stack at dehydration of a technological channel, fuel element shell unsealing and migration of fission products, and activation of stable nuclides in structural elements of the reactor and actinides inside the graphite moderator are given. The main chemical reactions and compounds that are produced in these modes in the reactor channel during its operation and that may be hazardous after its shutdown and decommissioning are presented. Thermodynamic simulation of the equilibrium composition is performed using the specialized code TERRA. The results of thermodynamic simulation of the equilibrium composition in different cases of technological channel dehydration in the course of the reactor operation show that, if the temperature inside the active core of the nuclear reactor increases to the melting temperature of the fuel element, oxides and carbides of nuclear fuel are produced. The mathematical model of the nonstationary heat transfer in a graphite stack of a uranium-graphite reactor in the case of the technological channel dehydration is presented. The results of calculated temperature evolution at the center of the fuel element, the replaceable graphite element, the air gap, and in the surface layer of the block graphite are given. The numerical results show that, in the case of dehydration of the technological channel in the uranium-graphite reactor with metallic uranium, the main reaction product is uranium dioxide UO2 in the condensed phase. Low probability of production of pyrophoric uranium compounds (UH3) in the graphite stack is proven, which allows one to disassemble the graphite stack without the risk of spontaneous graphite ignition in the course of decommissioning of the uranium-graphite nuclear reactor.

Electrochemical treatment of evaporated residue of soak liquor generated from leather industry.

PubMed

Boopathy, R; Sekaran, G

2013-09-15

The organic and suspended solids present in soak liquor, generated from leather industry, demands treatment. The soak liquor is being segregated and evaporated in solar evaporation pans/multiple effect evaporator due to non availability of viable technology for its treatment. The residue left behind in the pans/evaporator does not carry any reuse value and also faces disposal threat due to the presence of high concentration of sodium chloride, organic and bacterial impurities. In the present investigation, the aqueous evaporated residue of soak liquor (ERSL) was treated by electrochemical oxidation. Graphite/graphite and SS304/graphite systems were used in electrochemical oxidation of organics in ERSL. Among these, graphite/graphite system was found to be effective over SS304/graphite system. Hence, the optimised conditions for the electrochemical oxidation of organics in ERSL using graphite/graphite system was evaluated by response surface methodology (RSM). The mass transport coefficient (km) was calculated based on pseudo-first order rate kinetics for both the electrode systems (graphite/graphite and SS304/graphite). The thermodynamic properties illustrated the electrochemical oxidation was exothermic and non-spontaneous in nature. The calculated specific energy consumption at the optimum current density of 50 mA cm(-2) was 0.41 kWh m(-3) for the removal of COD and 2.57 kWh m(-3) for the removal of TKN. Copyright © 2013 Elsevier B.V. All rights reserved.

AGC-2 Graphite Pre-irradiation Data Package

DOE Office of Scientific and Technical Information (OSTI.GOV)

David Swank; Joseph Lord; David Rohrbaugh

2010-08-01

The NGNP Graphite R&D program is currently establishing the safe operating envelope of graphite core components for a Very High Temperature Reactor (VHTR) design. The program is generating quantitative data necessary for predicting the behavior and operating performance of the new nuclear graphite grades. To determine the in-service behavior of the graphite for pebble bed and prismatic designs, the Advanced Graphite Creep (AGC) experiment is underway. This experiment is examining the properties and behavior of nuclear grade graphite over a large spectrum of temperatures, neutron fluences and compressive loads. Each experiment consists of over 400 graphite specimens that are characterizedmore » prior to irradiation and following irradiation. Six experiments are planned with the first, AGC-1, currently being irradiated in the Advanced Test Reactor (ATR) and pre-irradiation characterization of the second, AGC-2, completed. This data package establishes the readiness of 512 specimens for assembly into the AGC-2 capsule.« less

Preparation and Characterization of Graphite Waste/CeO2 Composites

NASA Astrophysics Data System (ADS)

Kusrini, E.; Utami, C. S.; Nasruddin; Prasetyanto, E. A.; Bawono, Aji A.

2018-03-01

In this research, the chemical modification of graphite waste with CeO2 was developed and characterized. Graphite waste was pretreated with mechanical to obtain the size 200 mesh (75 μm), and thermal methods at 110°C oven for 6 hours. Here, we demonstrate final properties of graphite before modification (GBM), activated graphite (GA) and graphite/CeO2 composite with variation of 0.5, 1 and 2 g of CeO2 (G0.5; G1; G2). The effect of CeO2 concentration was observed. The presence of cerium in modified graphite samples (G0.5; G1; G2) were analyzed using SEM-EDX. The results show that the best surface area was found in G2 is 26.82 m2/g. The presence of CeO2 onto graphite surface does not significantly increase the surface area of composites.

Monolithic porous graphitic carbons obtained through catalytic graphitization of carbon xerogels

NASA Astrophysics Data System (ADS)

Kiciński, Wojciech; Norek, Małgorzata; Bystrzejewski, Michał

2013-01-01

Pyrolysis of organic xerogels accompanied by catalytic graphitization and followed by selective-combustion purification was used to produce porous graphitic carbons. Organic gels impregnated with iron(III) chloride or nickel(II) acetate were obtained through polymerization of resorcinol and furfural. During the pyrolysis stage graphitization of the gel matrix occurs, which in turn develops mesoporosity of the obtained carbons. The evolution of the carbon into graphitic structures is strongly dependent on the concentrations of the transition metal. Pyrolysis leads to monoliths of carbon xerogel characterized by substantially enhanced mesoporosity resulting in specific surface areas up to 400 m2/g. Removal of the amorphous carbon by selective-combustion purification reduces the xerogels' mesoporosity, occasionally causing loss of their mechanical strength. The graphitized carbon xerogels were investigated by means of SEM, XRD, Raman scattering, TG-DTA and N2 physisorption. Through this procedure well graphitized carbonaceous materials can be obtained as bulk pieces.

Friction and wear of carbon-graphite materials for high energy brakes

NASA Technical Reports Server (NTRS)

Bill, R. C.

1975-01-01

Caliper-type brakes simulation experiments were conducted on seven different carbon-graphite material formulations against a steel disk material and against a carbon-graphite disk material. The effects of binder level, boron carbide (B4C) additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level and additions of B4C each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. This transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur. The exposure of the fiber structure of the cloth constituent is believed to play a role in the shear film disruption.

Cosmological models with homogeneous and isotropic spatial sections

NASA Astrophysics Data System (ADS)

Katanaev, M. O.

2017-05-01

The assumption that the universe is homogeneous and isotropic is the basis for the majority of modern cosmological models. We give an example of a metric all of whose spatial sections are spaces of constant curvature but the space-time is nevertheless not homogeneous and isotropic as a whole. We give an equivalent definition of a homogeneous and isotropic universe in terms of embedded manifolds.

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

NASA Astrophysics Data System (ADS)

Lee, Su-Yoon; Jeong, Ye-Jin; Chae, So-Ryong; Yeon, Kyeong-Ho; Lee, Yunkyu; Kim, Chan-Soo; Jeong, Nam-Jo; Park, Jin-Soo

2016-04-01

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)63-) and hexacyanoferrate(II) (i.e., Fe(CN)64-) redox couple and 1 M Na2SO4 at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current-voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil

Comparison between the Strength Levels of Baseline Nuclear-Grade Graphite and Graphite Irradiated in AGC-2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carroll, Mark Christopher

2015-07-01

This report details the initial comparison of mechanical strength properties between the cylindrical nuclear-grade graphite specimens irradiated in the second Advanced Graphite Creep (AGC-2) experiment with the established baseline, or unirradiated, mechanical properties compiled in the Baseline Graphite Characterization program. The overall comparative analysis will describe the development of an appropriate test protocol for irradiated specimens, the execution of the mechanical tests on the AGC-2 sample population, and will further discuss the data in terms of developing an accurate irradiated property distribution in the limited amount of irradiated data by leveraging the considerably larger property datasets being captured in themore » Baseline Graphite Characterization program. Integrating information on the inherent variability in nuclear-grade graphite with more complete datasets is one of the goals of the VHTR Graphite Materials program. Between “sister” specimens, or specimens with the same geometry machined from the same sub-block of graphite from which the irradiated AGC specimens were extracted, and the Baseline datasets, a comprehensive body of data will exist that can provide both a direct and indirect indication of the full irradiated property distributions that can be expected of irradiated nuclear-grade graphite while in service in a VHTR system. While the most critical data will remain the actual irradiated property measurements, expansion of this data into accurate distributions based on the inherent variability in graphite properties will be a crucial step in qualifying graphite for nuclear use as a structural material in a VHTR environment.« less

Influence of graphite-alloy interactions on corrosion of Ni-Mo-Cr alloy in molten fluorides

NASA Astrophysics Data System (ADS)

Ai, Hua; Hou, Juan; Ye, Xiang-Xi; Zeng, Chao Liu; Sun, Hua; Li, Xiaoyun; Yu, Guojun; Zhou, Xingtai; Wang, Jian-Qiang

2018-05-01

In this study, the effects of graphite-alloy interaction on corrosion of Ni-Mo-Cr alloy in molten FLiNaK salt were investigated. The corrosion tests of Ni-Mo-Cr alloys were conducted in graphite crucibles, to examine the differences of test specimens in conditions of electric contact and isolated with graphite, respectively. The corrosion attack is severer with more weight loss and deeper Cr depletion layer in samples electric contact with graphite than those isolated with graphite. The occurrence of galvanic corrosion between alloy specimens and graphite container was confirmed by electrochemical measurement. The corrosion is controlled by nonelectric transfer in isolated test while electrochemical reaction accelerated corrosion in electric contact test.

The origin of epigenetic graphite: evidence from isotopes

USGS Publications Warehouse

Weis, P.L.; Friedman, I.; Gleason, J.P.

1981-01-01

Stable carbon isotope ratios measured in syngenetic graphite, epigenetic graphite, and graphitic marble suggests that syngenetic graphite forms only by the metamorphism of carbonaceous detritus. Metamorphism of calcareous rocks with carbonaceous detritus is accompanied by an exchange of carbon between the two, which may result in large changes in isotopic composition of the non-carbonate phase but does not affect the relative proportions of the two reactants in the rock. Epigenetic graphite forms only from carbonaceous material or preexisting graphite. The reactions involved are the water gas reaction (C + H2O ??? CO + H2) at 800-900??C, and the Boudouard reaction (2CO ??? C + CO2), which probably takes place at temperatures about 50-100??C lower. ?? 1982.

Method of producing exfoliated graphite, flexible graphite, and nano-scaled graphene platelets

DOEpatents

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

2010-11-02

The present invention provides a method of exfoliating a layered material (e.g., graphite and graphite oxide) to produce nano-scaled platelets having a thickness smaller than 100 nm, typically smaller than 10 nm. The method comprises (a) dispersing particles of graphite, graphite oxide, or a non-graphite laminar compound in a liquid medium containing therein a surfactant or dispersing agent to obtain a stable suspension or slurry; and (b) exposing the suspension or slurry to ultrasonic waves at an energy level for a sufficient length of time to produce separated nano-scaled platelets. The nano-scaled platelets are candidate reinforcement fillers for polymer nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.

METHOD FOR COATING GRAPHITE WITH METALLIC CARBIDES

DOEpatents

Steinberg, M.A.

1960-03-22

A method for producing refractory coatings of metallic carbides on graphite was developed. In particular, the graphite piece to be coated is immersed in a molten solution of 4 to 5% by weight of zirconium, titanium, or niobium dissolved in tin. The solution is heated in an argon atmosphere to above 1400 deg C, whereby the refractory metal reacts with the surface of the graphite to form a layer of metalic carbide. The molten solution is cooled to 300 to 400 deg C, and the graphite piece is removed. Excess tin is wiped from the graphite, which is then heated in vacuum to above 2300 deg C. The tin vaporizes from the graphite surface, leaving the surface coated with a tenacious layer of refractory metallic carbide.

Recent Advances in Preparation, Structure, Properties and Applications of Graphite Oxide.

PubMed

Srivastava, Suneel Kumar; Pionteck, Jürgen

2015-03-01

Graphite oxide, also referred as graphitic oxide or graphitic acid, is an oxidized bulk product of graphite with a variable composition. However, it did not receive immense attention until it was identified as an important and easily obtainable precursor for the preparation of graphene. This inspired many researchers to explore facts related to graphite oxide in exploiting its fascinating features. The present article culminates up-dated review on different preparative methods, morphology and characterization of physical/chemical properties of graphite oxide by XRD, XPS, FTIR, Raman, NMR, UV-visible, and DRIFT analyses. Finally, recent developments on intercalation and applications of GO in multifaceted areas of catalysis, sensor, supercapacitors, water purification, hydrogen storage and magnetic shielding etc. has also been reviewed.

CMB-13 research on carbon and graphite

NASA Technical Reports Server (NTRS)

Smith, M. C.

1972-01-01

The research on graphite and carbon for this period is reported. Topics discussed include: effects of grinding on the Santa Marie graphites, properties and purities of coal-tar, resin-bonded graphite, carbonization of resin components, and glass-like carbon filler.

Tribological Analysis of Copper-Coated Graphite Particle-Reinforced A359 Al/5 wt.% SiC Composites

NASA Astrophysics Data System (ADS)

Lin, C. B.; Wang, T. C.; Chang, Z. C.; Chu, H. Y.

2013-01-01

Copper-coated graphite particles can be mass-produced by the cementation process using simple equipment. Graphite particulates that were coated with electroless copper and 5 wt.% SiC particulates were introduced into an aluminum alloy by compocasting to make A359 Al/5 wt.% SiC(p) composite that contained 2, 4, 6, and 8 wt.% graphite particulate composite. The effects of SiC particles, quantity of graphite particles, normal loading, sliding speed and wear debris on the coefficient of friction, and the wear rate were investigated. The results thus obtained indicate that the wear properties were improved by adding small amounts of SiC and graphite particles into the A359 Al alloy. The coefficient of friction of the A359 Al/5 wt.% SiC(p) composite that contained 6.0 wt.% graphite particulates was reduced to 0.246 and the amount of graphite film that was released on the worn surface increased with the graphite particulate content. The coefficient of friction and the wear rate were insensitive to the variation in the sliding speed and normal loading.

Preparation and characterization of copper-graphite composites by electrical explosion of wire in liquid.

PubMed

Bien, T N; Gul, W H; Bac, L H; Kim, J C

2014-11-01

Copper-graphite nanocomposites containing 5 vol.% graphite were prepared by a powder metallurgy route using an electrical wire explosion (EEW) in liquid method and spark plasma sintering (SPS) process. Graphite rods with a 0.3 mm diameter and copper wire with a 0.2 mm diameter were used as raw materials for EEWin liquid. To compare, a pure copper and copper-graphite mixture was also prepared. The fabricated graphite was in the form of a nanosheet, onto which copper particles were coated. Sintering was performed at 900 degrees C at a heating rate of 30 degrees C/min for 10 min and under a pressure of 70 MPa. The density of the sintered composite samples was measured by the Archimedes method. A wear test was performed by a ball-on-disc tribometer under dry conditions at room temperature in air. The presence of graphite effectively reduced the wear of composites. The copper-graphite nanocomposites prepared by EEW had lower wear rates than pure copper material and simple mixed copper-graphite.

Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Na; Jia, Zhe; Wang, Zhihui

Here in this paper, the structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystallinemore » graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.« less

Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

DOE PAGES

Lin, Na; Jia, Zhe; Wang, Zhihui; ...

2017-10-01

Here in this paper, the structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystallinemore » graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.« less

Study of evaporating the irradiated graphite in equilibrium low-temperature plasma

NASA Astrophysics Data System (ADS)

Bespala, E. V.; Novoselov, I. Yu.; Pavlyuk, A. O.; Kotlyarevskiy, S. G.

2018-01-01

The paper describes a problem of accumulation of irradiated graphite due to operation of uranium-graphite nuclear reactors. The main noncarbon contaminants that contribute to the overall activity of graphite elements are iso-topes 137Cs, 60Co, 90Sr, 36Cl, and 3H. A method was developed for processing of irradiated graphite ensuring the volu-metric decontamination of samples. The calculation results are presented for equilibrium composition of plasma-chemical reactions in systems "irradiated graphite-argon" and "irradiated graphite-helium" for a wide range of tem-peratures. The paper describes a developed mathematical model for the process of purification of a porous graphite surface treated by equilibrium low-temperature plasma. The simulation results are presented for the rate of sublimation of radioactive contaminants as a function of plasma temperature and plasma flow velocity when different plasma-forming gases are used. The extraction coefficient for the contaminant 137Cs from the outer side of graphite pores was calculated. The calculations demonstrated the advantages of using a lighter plasma forming gas, i.e., helium.

Hybridized polymer matrix composites

NASA Technical Reports Server (NTRS)

House, E. E.; Hoggatt, J. T.; Symonds, W. A.

1980-01-01

The extent to which graphite fibers are released from resin matrix composites that are exposed to fire and impact conditions was determined. Laboratory simulations of those conditions that could exist in the event of an aircraft crash and burn situation were evaluated. The effectiveness of various hybridizing concepts in preventing this release of graphite fibers were also evaluated. The baseline (i.e., unhybridized) laminates examined were prepared from commercially available graphite/epoxy, graphite/polyimide, and graphite/phenolic materials. Hybridizing concepts investigated included resin fillers, laminate coatings, resin blending, and mechanical interlocking of the graphite reinforcement. The baseline and hybridized laminates' mechanical properties, before and after isothermal and humidity aging, were also compared. It was found that a small amount of graphite fiber was released from the graphite/epoxy laminates during the burn and impact conditions used in this program. However, the extent to which the fibers were released is not considered a severe enough problem to preclude the use of graphite reinforced composites in civil aircraft structure. It also was found that several hybrid concepts eliminated this fiber release. Isothermal and humidity aging did not appear to alter the fiber release tendencies.

Chemical Characterization and Removal of C-14 from Irradiated Graphite-12010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cleaver, James; McCrory, Shilo; Smith, Tara E.

2012-07-01

Quantities of irradiated graphite waste are expected to drastically increase, which indicates the need for a graphite waste management strategy. Of greatest concern for long-term disposal of irradiated graphite is carbon-14 (C-14), with a half-life of 5730 years. Study of irradiated graphite from nuclear reactors indicates C-14 is concentrated on the outer 5 mm of the graphite structure. The aim of the research described here is to identify the chemical form of C-14 in irradiated graphite and develop a practical method by which C-14 can be removed. Characterization of pre- and post-irradiation graphite was conducted to determine bond type, functionalmore » groups, location and concentration of C-14 and its precursors via the use of surface sensitive characterization techniques. Because most surface C-14 originates from neutron activation of nitrogen, an understanding of nitrogen bonding to graphite may lead to a greater understanding of the formation pathway of C-14. However, no single technique provides a complete picture. Therefore, a portfolio of techniques has been developed, with each technique providing another piece to the puzzle that is the chemical nature of the C-14. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Raman Spectroscopy were used to evaluate the morphological features of graphite samples. The concentration, chemical composition, and bonding characteristics of C-14 and its precursors were determined through X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (SIMS), and Auger and Energy Dispersive X-ray Analysis Spectroscopy (EDX). High-surface-area graphite foam, POCOFoam{sup R}, was exposed to liquid nitrogen and irradiated. Characterization of this material has shown C-14 to C-12 ratios of 0.035. This information was used to optimize the thermal treatment of graphite. Thermal treatment of irradiated graphite as reported by Fachinger et al. (2007) uses naturally adsorbed oxygen complexes to gasify graphite, thus its effectiveness is highly dependent on the availability of adsorbed oxygen compounds. In research presented, the quantity and form of adsorbed oxygen complexes in pre- and post irradiated graphite was studied using SIMS and XPS. SIMS and XPS detected adsorbed oxygen compounds on both irradiated and unirradiated graphite. During thermal treatment graphite samples are heated in the presence of inert argon gas, which carries off gaseous products released during treatment. Experiments were performed at 900 deg. C and 1400 deg. C to evaluate the selective removal of C-14. (authors)« less

Estimating Effective Seismic Anisotropy Of Coal Seam Gas Reservoirs from Sonic Log Data Using Orthorhombic Buckus-style Upscaling

NASA Astrophysics Data System (ADS)

Gross, Lutz; Tyson, Stephen

2015-04-01

Fracture density and orientation are key parameters controlling productivity of coal seam gas reservoirs. Seismic anisotropy can help to identify and quantify fracture characteristics. In particular, wide offset and dense azimuthal coverage land seismic recordings offers the opportunity for recovery of anisotropy parameters. In many coal seam gas reservoirs (eg. Walloon Subgroup in the Surat Basin, Queensland, Australia (Esterle et al. 2013)) the thickness of coal-beds and interbeds (e.g mud-stone) are well below the seismic wave length (0.3-1m versus 5-15m). In these situations, the observed seismic anisotropy parameters represent effective elastic properties of the composite media formed of fractured, anisotropic coal and isotropic interbed. As a consequence observed seismic anisotropy cannot directly be linked to fracture characteristics but requires a more careful interpretation. In the paper we will discuss techniques to estimate effective seismic anisotropy parameters from well log data with the objective to improve the interpretation for the case of layered thin coal beds. In the first step we use sonic log data to reconstruct the elasticity parameters as function of depth (at the resolution of the sonic log). It is assumed that within a sample fractures are sparse, of the same size and orientation, penny-shaped and equally spaced. Following classical fracture model this can be modeled as an elastic horizontally transversely isotropic (HTI) media (Schoenberg & Sayers 1995). Under the additional assumption of dry fractures, normal and tangential fracture weakness is estimated from slow and fast shear wave velocities of the sonic log. In the second step we apply Backus-style upscaling to construct effective anisotropy parameters on an appropriate length scale. In order to honor the HTI anisotropy present at each layer we have developed a new extension of the classical Backus averaging for layered isotropic media (Backus 1962) . Our new method assumes layered HTI media with constant anisotropy orientation as recovered in the first step. It leads to an effective horizontal orthorhombic elastic model. From this model Thomsen-style anisotropy parameters are calculated to derive azimuth-dependent normal move out (NMO) velocities (see Grechka & Tsvankin 1998). In our presentation we will show results of our approach from sonic well logs in the Surat Basin to investigate the potential of reconstructing S-wave velocity anisotropy and fracture density from azimuth dependent NMO velocities profiles.

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.

RECOVERY OF VALUABLE MATERIAL FROM GRAPHITE BODIES

DOEpatents

Fromm, L.W. Jr.

1959-09-01

An electrolytic process for recovering uranium from a graphite fuel element is described. The uraniumcontaining graphite body is disposed as the anode of a cell containing a nitric acid electrolyte and a 5 amp/cm/sup 2/ current passed to induce a progressive disintegration of the graphite body. The dissolved uranium is quickly and easily separated from the resulting graphite particles by simple mechanical means, such as centrifugation, filtration, and decontamination.

Interface Character of Aluminum-Graphite Metal Matrix Composites.

DTIC Science & Technology

1983-01-27

studied included the commer- cial A/graphite composites; layered model systems on single crystal and poly- crystalline graphite substrates as well as...composition and thickness of the composite interface, and graphite crystal orientation. 3 For the model systems in this study , single crystal graphite...been reviewed by Kingcry. Segregation at surfaces in single- crystal MgO of Fe, Cr and Sc, which were Dresent in concentrations within the single- 3phase

Structure and Performance of Epoxy Resin Cladded Graphite Used as Anode

NASA Astrophysics Data System (ADS)

Zhou, Zhentao; Li, Haijun

This paper is concerning to prepare modified natural graphite which is low-cost and advanced materials used as lithium ion battery anode using the way of cladding natural graphite with epoxy resin. The results shows that the specific capacity and circular performance of the modified natural graphite, which is prepared in the range of 600°C and 1000°C, have been apparently improved compare with the not-modified natural graphite. The first reversible capacity of the modified natural graphite is 338mAh/g and maintain more than 330mAh/g after 20 charge/discharge circles.

Artificially-built solid electrolyte interphase via surface-bonded vinylene carbonate derivative on graphite by molecular layer deposition

NASA Astrophysics Data System (ADS)

Chae, Seulki; Lee, Jeong Beom; Lee, Jae Gil; Lee, Tae-jin; Soon, Jiyong; Ryu, Ji Heon; Lee, Jin Seok; Oh, Seung M.

2017-12-01

Vinylene carbonate (VC) is attached in a ring-opened form on a graphite surface by molecular layer deposition (MLD) method, and its role as a solid electrolyte interphase (SEI) former is studied. When VC is added into the electrolyte solution of a graphite/LiNi0.5Mn1.5O4 (LNMO) full-cell, it is reductively decomposed to form an effective SEI on the graphite electrode. However, VC in the electrolyte solution has serious adverse effects due to its poor stability against electrochemical oxidation on the LNMO positive electrode. A excessive acid generation as a result of VC oxidation is observed, causing metal dissolution from the LNMO electrode. The dissolved metal ions are plated on the graphite electrode to destroy the SEI layer, eventually causing serious capacity fading and poor Coulombic efficiency. The VC derivative on the graphite surface also forms an effective SEI layer on the graphite negative electrode via reductive decomposition. The detrimental effects on the LNMO positive electrode, however, can be avoided because the bonded VC derivative on the graphite surface cannot move to the LNMO electrode. Consequently, the graphite/LNMO full-cell fabricated with the VC-attached graphite outperforms the cells without VC or with VC in the electrolyte, in terms of Coulombic efficiency and capacity retention.

Micro-fabrication method of graphite mesa microdevices based on optical lithography technology

NASA Astrophysics Data System (ADS)

Zhang, Cheng; Wen, Donghui; Zhu, Huamin; Zhang, Xiaorui; Yang, Xing; Shi, Yunsheng; Zheng, Tianxiang

2017-12-01

Graphite mesa microdevices have incommensurate contact nanometer interfaces, superlubricity, high-speed self-retraction, and other characteristics, which have potential applications in high-performance oscillators and micro-scale switches, memory devices, and gyroscopes. However, the current method of fabricating graphite mesa microdevices is mainly based on high-cost, low efficiency electron beam lithography technology. In this paper, the processing technologies of graphite mesa microdevices with various shapes and sizes were investigated by a low-cost micro-fabrication method, which was mainly based on optical lithography technology. The characterization results showed that the optical lithography technology could realize a large-area of patterning on the graphite surface, and the graphite mesa microdevices, which have a regular shape, neat arrangement, and high verticality could be fabricated in large batches through optical lithography technology. The experiments and analyses showed that the graphite mesa microdevices fabricated through optical lithography technology basically have the same self-retracting characteristics as those fabricated through electron beam lithography technology, and the maximum size of the graphite mesa microdevices with self-retracting phenomenon can reach 10 µm  ×  10 µm. Therefore, the proposed method of this paper can realize the high-efficiency and low-cost processing of graphite mesa microdevices, which is significant for batch fabrication and application of graphite mesa microdevices.

Isotropic matrix elements of the collision integral for the Boltzmann equation

NASA Astrophysics Data System (ADS)

Ender, I. A.; Bakaleinikov, L. A.; Flegontova, E. Yu.; Gerasimenko, A. B.

2017-09-01

We have proposed an algorithm for constructing matrix elements of the collision integral for the nonlinear Boltzmann equation isotropic in velocities. These matrix elements have been used to start the recurrent procedure for calculating matrix elements of the velocity-nonisotropic collision integral described in our previous publication. In addition, isotropic matrix elements are of independent interest for calculating isotropic relaxation in a number of physical kinetics problems. It has been shown that the coefficients of expansion of isotropic matrix elements in Ω integrals are connected by the recurrent relations that make it possible to construct the procedure of their sequential determination.

Graphite tail powder and liquid biofertilizer as trace elements source for ground nut

NASA Astrophysics Data System (ADS)

Hindersah, Reginawanti; Setiawati, M. Rochimi; Fitriatin, B. Natalie; Suryatama, Pujawati; Asmiran, Priyanka; Panatarani, Camellia; Joni, I. Made

2018-02-01

Utilization of graphite tail waste from the mineral beneficiation processing is very important since it contain significant amount of essential minerals which are necessary for plant growth. These mineral are required in biochemical processes and mainly play an important role as cofactor in enzymatic reaction. The objective of this research is to investigate the performance of graphite tail on supporting plant growth and yield of ground nut (Arachishypogeae L.). A field experiment has been performed to test the performance of mixed graphite tail and reduced organic matter dose. The graphite tail size were reduced to various sieved size, -80 mesh, -100 mesh and -200 mesh. The experiment was setup in randomized block design with 4 treatments and 6 replications for each treatment, while the control plot is received without graphite tail. The results demonstrated that reduced organic matter along with -200 mesh tail has potentially decreased plant height at the end of vegetative growth stage, in contrast for to -80 mesh tail amendment increased individual fresh plant biomass. Statistically, there was no change of plant nodule, individual shoot fresh and dry weight, root nodule, number of pod following any mesh of graphite tail amendment. Reducing organic matter while adding graphite tail of 5% did not change bean weight in all plot. In contrast, reduced organic matter along with 80-mesh graphite tail amendment improved the nut yield per plot. This experiment suggests that graphite tail, mainly -80 mesh graphite tail can be possibly used in legume production.

40 CFR 436.380 - Applicability; description of the graphite subcategory.

Code of Federal Regulations, 2011 CFR

2011-07-01

... graphite subcategory. 436.380 Section 436.380 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS MINERAL MINING AND PROCESSING POINT SOURCE CATEGORY Graphite Subcategory § 436.380 Applicability; description of the graphite subcategory. The provisions of this subpart...

40 CFR 436.380 - Applicability; description of the graphite subcategory.

Code of Federal Regulations, 2010 CFR

2010-07-01

... graphite subcategory. 436.380 Section 436.380 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS MINERAL MINING AND PROCESSING POINT SOURCE CATEGORY Graphite Subcategory § 436.380 Applicability; description of the graphite subcategory. The provisions of this subpart...

Temperature effect of friction and wear characteristics for solid lubricating graphite

NASA Astrophysics Data System (ADS)

Kim, Yeonwook; Kim, Jaehoon

2015-03-01

Graphite is one of the effective lubricant additives due to its excellent high-temperature endurance and self-lubricating properties. In this study, wear behavior of graphite used as sealing materials to cut off hot gas is evaluated at room and elevated temperature. Wear occurs on graphite seal due to the friction of driving shaft and graphite. Thus, a reciprocating wear test to evaluate the wear generated for the graphite by means of the relative motion between a shaft material and a graphite seal was carried out. The friction coefficient and specific wear rate for the changes of applied load and sliding speed were compared under different temperature conditions considering the actual operating environment. Through SEM observation of the worn surface, the lubricating film was observed and compared with test conditions.

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.

Generation of high energetic ions from hollow cathode discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atta, M.; El Nadai, L.; Lie, Y.T.

1995-12-31

High energetic beams of ions can be produced by using the dense and highly ionized plasma that is generated by the vacuum arc. Ian G. Brown (1993) described the general features and performance characteristics of the ion sources and their use for accelerator injection and ion implantation applications. Atta, at al. (1993) found that the ratio of ion density to electron density has been decreased beside the hollow cathode at different hole diameter due to increasing the ionization degree. Here we have evaluated the ion velocity distribution F(v) = S{Upsilon}(t)/V{sup 2}, where {Upsilon}(t) is the ion flux intensity, S ismore » the distance between the hollow cathode spot and the quadrupole maps spectrometer, and V is the ion velocity. The ion energy (E=mV{sup 2}/2, in is the mass of the ion), and the ion fraction due to the total number of ions for different ion species emitted from graphite and titanium hollow cathode have been determined.« less

Towards ultrahigh volumetric capacitance: graphene derived highly dense but porous carbons for supercapacitors

PubMed Central

Tao, Ying; Xie, Xiaoying; Lv, Wei; Tang, Dai-Ming; Kong, Debin; Huang, Zhenghong; Nishihara, Hirotomo; Ishii, Takafumi; Li, Baohua; Golberg, Dmitri; Kang, Feiyu; Kyotani, Takashi; Yang, Quan-Hong

2013-01-01

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm−3, 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm−3, which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs. PMID:24131954

UO2 fuel pellets fabrication via Spark Plasma Sintering using non-standard molybdenum die

NASA Astrophysics Data System (ADS)

Papynov, E. K.; Shichalin, O. O.; Mironenko, A. Yu; Tananaev, I. G.; Avramenko, V. A.; Sergienko, V. I.

2018-02-01

The article investigates spark plasma sintering (SPS) of commercial uranium dioxide (UO2) powder of ceramic origin into highly dense fuel pellets using non-standard die instead of usual graphite die. An alternative and formerly unknown method has been suggested to fabricate UO2 fuel pellets by SPS for excluding of typical problems related to undesirable carbon diffusion. Influence of SPS parameters on chemical composition and quality of UO2 pellets has been studied. Also main advantages and drawbacks have been revealed for SPS consolidation of UO2 in non-standard molybdenum die. The method is very promising due to high quality of the final product (density 97.5-98.4% from theoretical, absence of carbon traces, mean grain size below 3 μm) and mild sintering conditions (temperature 1100 ºC, pressure 141.5 MPa, sintering time 25 min). The results are interesting for development and probable application of SPS in large-scale production of nuclear ceramic fuel.

Templated bilayer self-assembly of fully conjugated π-expanded macrocyclic oligothiophenes complexed with fullerenes

PubMed Central

Cojal González, José D.; Iyoda, Masahiko; Rabe, Jürgen P.

2017-01-01

Fully conjugated macrocyclic oligothiophenes exhibit a combination of highly attractive structural, optical and electronic properties, and multifunctional molecular thin film architectures thereof are envisioned. However, control over the self-assembly of such systems becomes increasingly challenging, the more complex the target structures are. Here we show a robust self-assembly based on hierarchical non-covalent interactions. A self-assembled monolayer of hydrogen-bonded trimesic acid at the interface between an organic solution and graphite provides host-sites for the epitaxial ordering of Saturn-like complexes of fullerenes with oligothiophene macrocycles in mono- and bilayers. STM tomography verifies the formation of the templated layers. Molecular dynamics simulations corroborate the conformational stability and assign the adsorption sites of the adlayers. Scanning tunnelling spectroscopy determines their rectification characteristics. Current–voltage characteristics reveal the modification of the rectifying properties of the macrocycles by the formation of donor–acceptor complexes in a densely packed all-self-assembled supramolecular nanostructure. PMID:28281557

Composition, structure and chemistry of interstellar dust

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M.; Allamandola, Louis J.

1986-01-01

The observational constraints on the composition of the interstellar dust are analyzed. The dust in the diffuse interstellar medium consists of a mixture of stardust (amorphous silicates, amorphous carbon, polycyclic aromatic hydrocarbons, and graphite) and interstellar medium dust (organic refractory material). Stardust seems to dominate in the local diffuse interstellar medium. Inside molecular clouds, however, icy grain mantles are also important. The structural differences between crystalline and amorphous materials, which lead to differences in the optical properties, are discussed. The astrophysical consequences are briefly examined. The physical principles of grain surface chemistry are discussed and applied to the formation of molecular hydrogen and icy grain mantles inside dense molecular clouds. Transformation of these icy grain mantles into the organic refractory dust component observed in the diffuse interstellar medium requires ultraviolet sources inside molecular clouds as well as radical diffusion promoted by transient heating of the mantle. The latter process also returns a considerable fraction of the molecules in the grain mantle to the gas phase.

Microwave plasma-assisted chemical vapor deposition of porous carbon film as supercapacitive electrodes

NASA Astrophysics Data System (ADS)

Wu, Ai-Min; Feng, Chen-Chen; Huang, Hao; Paredes Camacho, Ramon Alberto; Gao, Song; Lei, Ming-Kai; Cao, Guo-Zhong

2017-07-01

Highly porous carbon film (PCF) coated on nickel foam was prepared successfully by microwave plasma-assisted chemical vapor deposition (MPCVD) with C2H2 as carbon source and Ar as discharge gas. The PCF is uniform and dense with 3D-crosslinked nanoscale network structure possessing high degree of graphitization. When used as the electrode material in an electrochemical supercapacitor, the PCF samples verify their advantageous electrical conductivity, ion contact and electrochemical stability. The test results show that the sample prepared under 1000 W microwave power has good electrochemical performance. It displays the specific capacitance of 62.75 F/g at the current density of 2.0 A/g and retains 95% of its capacitance after 10,000 cycles at the current density of 2.0 A/g. Besides, its near-rectangular shape of the cyclic voltammograms (CV) curves exhibits typical character of an electric double-layer capacitor, which owns an enhanced ionic diffusion that can fit the requirements for energy storage applications.

Electron emission and plasma generation in a modulator electron gun using ferroelectric cathode

NASA Astrophysics Data System (ADS)

Chen, Shutao; Zheng, Shuxin; Zhu, Ziqiu; Dong, Xianlin; Tang, Chuanxiang

2006-10-01

Strong electron emission and dense plasma generation have been observed in a modulator electron gun with a Ba 0.67Sr 0.33TiO 3 ferroelectric cathode. Parameter of the modulator electron gun and lifetime of the ferroelectric cathode were investigated. It was shown that electron emission from Ba 0.67Sr 0.33TiO 3 cathode with a positive triggering pulse is a sort of plasma emission. Electrons were emitted by the co-effect of surface plasma and non-compensated negative polarization charges at the surface of the ferroelectric. The element analyses of the graphite collector after emission process was performed to show the ingredient of the plasma consist of Ba, Ti and Cu heavy cations of the ceramic compound and electrode. It was demonstrated the validity of the Child-Langmuir law by introducing the decrease of vacuum gap and increase of emission area caused by the expansion of the surface plasma.

Templated bilayer self-assembly of fully conjugated π-expanded macrocyclic oligothiophenes complexed with fullerenes

NASA Astrophysics Data System (ADS)

Cojal González, José D.; Iyoda, Masahiko; Rabe, Jürgen P.

2017-03-01

Fully conjugated macrocyclic oligothiophenes exhibit a combination of highly attractive structural, optical and electronic properties, and multifunctional molecular thin film architectures thereof are envisioned. However, control over the self-assembly of such systems becomes increasingly challenging, the more complex the target structures are. Here we show a robust self-assembly based on hierarchical non-covalent interactions. A self-assembled monolayer of hydrogen-bonded trimesic acid at the interface between an organic solution and graphite provides host-sites for the epitaxial ordering of Saturn-like complexes of fullerenes with oligothiophene macrocycles in mono- and bilayers. STM tomography verifies the formation of the templated layers. Molecular dynamics simulations corroborate the conformational stability and assign the adsorption sites of the adlayers. Scanning tunnelling spectroscopy determines their rectification characteristics. Current-voltage characteristics reveal the modification of the rectifying properties of the macrocycles by the formation of donor-acceptor complexes in a densely packed all-self-assembled supramolecular nanostructure.

Redox-controlled potassium intercalation into two polyaromatic hydrocarbon solids

NASA Astrophysics Data System (ADS)

Romero, F. Denis; Pitcher, M. J.; Hiley, C. I.; Whitehead, G. F. S.; Kar, S.; Ganin, A. Y.; Antypov, D.; Collins, C.; Dyer, M. S.; Klupp, G.; Colman, R. H.; Prassides, K.; Rosseinsky, M. J.

2017-07-01

Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely after reports of superconductivity in a number of potassium- and rubidium-intercalated materials. There are, however, no reported crystal structures to inform our understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K2Pentacene and K2Picene by a solid-solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, and so enables the determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, in which the cation sites are pre-defined by the host structure.

Self-induced conversion in dense neutrino gases: Pendulum in flavor space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hannestad, Steen; Max-Planck-Institut fuer Physik; Raffelt, Georg G.

Neutrino-neutrino interactions can lead to collective flavor conversion effects in supernovae and in the early universe. We demonstrate that the case of bipolar oscillations, where a dense gas of neutrinos and antineutrinos in equal numbers completely converts from one flavor to another even if the mixing angle is small, is equivalent to a pendulum in flavor space. Bipolar flavor conversion corresponds to the swinging of the pendulum, which begins in an unstable upright position (the initial flavor), and passes through momentarily the vertically downward position (the other flavor) in the course of its motion. The time scale to complete onemore » cycle of oscillation depends logarithmically on the vacuum mixing angle. Likewise, the presence of an ordinary medium can be shown analytically to contribute to a logarithmic increase in the bipolar conversion period. We further find that a more complex (and realistic) system of unequal numbers of neutrinos and antineutrinos is analogous to a spinning top subject to a torque. This analogy easily explains how such a system can oscillate in both the bipolar and the synchronized mode, depending on the neutrino density and the size of the neutrino-antineutrino asymmetry. Our simple model applies strictly only to isotropic neutrino gasses. In more general cases, and especially for neutrinos streaming from a supernova core, different modes couple to each other with unequal strength, an effect that can lead to kinematical decoherence in flavor space rather than collective oscillations. The exact circumstances under which collective oscillations occur in nonisotropic media remain to be understood.« less

Comparison of two-dimensional and three-dimensional simulations of dense nonaqueous phase liquids (DNAPLs): Migration and entrapment in a nonuniform permeability field

NASA Astrophysics Data System (ADS)

Christ, John A.; Lemke, Lawrence D.; Abriola, Linda M.

2005-01-01

The influence of reduced dimensionality (two-dimensional (2-D) versus 3-D) on predictions of dense nonaqueous phase liquid (DNAPL) infiltration and entrapment in statistically homogeneous, nonuniform permeability fields was investigated using the University of Texas Chemical Compositional Simulator (UTCHEM), a 3-D numerical multiphase simulator. Hysteretic capillary pressure-saturation and relative permeability relationships implemented in UTCHEM were benchmarked against those of another lab-tested simulator, the Michigan-Vertical and Lateral Organic Redistribution (M-VALOR). Simulation of a tetrachloroethene spill in 16 field-scale aquifer realizations generated DNAPL saturation distributions with approximately equivalent distribution metrics in two and three dimensions, with 2-D simulations generally resulting in slightly higher maximum saturations and increased vertical spreading. Variability in 2-D and 3-D distribution metrics across the set of realizations was shown to be correlated at a significance level of 95-99%. Neither spill volume nor release rate appeared to affect these conclusions. Variability in the permeability field did affect spreading metrics by increasing the horizontal spreading in 3-D more than in 2-D in more heterogeneous media simulations. The assumption of isotropic horizontal spatial statistics resulted, on average, in symmetric 3-D saturation distribution metrics in the horizontal directions. The practical implication of this study is that for statistically homogeneous, nonuniform aquifers, 2-D simulations of saturation distributions are good approximations to those obtained in 3-D. However, additional work will be needed to explore the influence of dimensionality on simulated DNAPL dissolution.

A contrastive study of three graphite anodes in the piperidinium based electrolytes for lithium ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Xiao-Tao; Wang, Chen-Yi; Gao, Kun, E-mail: gaokun0451@163.com

Graphical abstract: The fitting results of R{sub sei} and R{sub ct} of three graphite/Li cells. Besides three graphite/Li cells show the similar R{sub sei}, the NG198/Li cell demonstrates a higher R{sub ct} value in all test temperatures. Especially, the R{sub ct} at 333 K is even up to 355.8 Ω cm{sup 2}. Obviously, the narrow distribution of edge plane for NG198 caused this result, and then greatly restricts its cell capacity. By contrast, CMB with bigger specific surface area and more Li{sup +} insertion points shows lower resistance at room temperature, which should help to improve its capacity. - Highlights:more » • SEI film is closely related to graphite structures and formation temperature. • The graphite with bigger surface area and more Li{sup +} insertion points behaves better. • The graphite with narrow edge plane is uncompetitive for ionic liquid electrolyte. - Abstract: The electrochemical behaviors of natural graphite (NG198), artificial graphite (AG360) and carbon microbeads (CMB) in an ionic liquid based electrolyte are investigated by cyclic voltammetry (CV). The surface and structure of three graphite materials are characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) before and after cycling. It is found that solid electrolyte interface (SEI) is closely related to graphite structure. Benefiting from larger specific surface area and more dispersed Li{sup +} insertion points, CMB shows a better Li{sup +} insertion/de-insertion behavior than NG198 and AG360. Furthermore, electrochemical impedance spectra (EIS) prove that the SEI of different graphite electrodes has different intrinsic resistance and Li{sup +} penetrability. By comparison, CMB behaves better cell performances than AG360, while the narrow edge plane makes NG198 uncompetitive as a potential anode for the ionic liquids (ILs)-type Li-ion battery.« less

Is Water at the Graphite Interface Vapor-like or Ice-like?

PubMed

Qiu, Yuqing; Lupi, Laura; Molinero, Valeria

2018-04-05

Graphitic surfaces are the main component of soot, a major constituent of atmospheric aerosols. Experiments indicate that soots of different origins display a wide range of abilities to heterogeneously nucleate ice. The ability of pure graphite to nucleate ice in experiments, however, seems to be almost negligible. Nevertheless, molecular simulations with the monatomic water model mW with water-carbon interactions parameterized to reproduce the experimental contact angle of water on graphite predict that pure graphite nucleates ice. According to classical nucleation theory, the ability of a surface to nucleate ice is controlled by the binding free energy between ice immersed in liquid water and the surface. To establish whether the discrepancy in freezing efficiencies of graphite in mW simulations and experiments arises from the coarse resolution of the model or can be fixed by reparameterization, it is important to elucidate the contributions of the water-graphite, water-ice, and ice-water interfaces to the free energy, enthalpy, and entropy of binding for both water and the model. Here we use thermodynamic analysis and free energy calculations to determine these interfacial properties. We demonstrate that liquid water at the graphite interface is not ice-like or vapor-like: it has similar free energy, entropy, and enthalpy as water in the bulk. The thermodynamics of the water-graphite interface is well reproduced by the mW model. We find that the entropy of binding between graphite and ice is positive and dominated, in both experiments and simulations, by the favorable entropy of reducing the ice-water interface. Our analysis indicates that the discrepancy in freezing efficiencies of graphite in experiments and the simulations with mW arises from the inability of the model to simultaneously reproduce the contact angle of liquid water on graphite and the free energy of the ice-graphite interface. This transferability issue is intrinsic to the resolution of the model, and arises from its lack of rotational degrees of freedom.

47 CFR 25.204 - Power limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... communication services, the equivalent isotropically radiated power transmitted in any direction towards the... coequally with terrestrial radiocommunication services, the equivalent isotropically radiated power... restriction as to the equivalent isotropically radiated power transmitted by an earth station towards the...

47 CFR 25.204 - Power limits.

Code of Federal Regulations, 2012 CFR

2012-10-01

... communication services, the equivalent isotropically radiated power transmitted in any direction towards the... coequally with terrestrial radiocommunication services, the equivalent isotropically radiated power... restriction as to the equivalent isotropically radiated power transmitted by an earth station towards the...

47 CFR 25.204 - Power limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... communication services, the equivalent isotropically radiated power transmitted in any direction towards the... coequally with terrestrial radiocommunication services, the equivalent isotropically radiated power... restriction as to the equivalent isotropically radiated power transmitted by an earth station towards the...

Effect of friction on oxidative graphite intercalation and high-quality graphene formation.

PubMed

Seiler, Steffen; Halbig, Christian E; Grote, Fabian; Rietsch, Philipp; Börrnert, Felix; Kaiser, Ute; Meyer, Bernd; Eigler, Siegfried

2018-02-26

Oxidative wet-chemical delamination of graphene from graphite is expected to become a scalable production method. However, the formation process of the intermediate stage-1 graphite sulfate by sulfuric acid intercalation and its subsequent oxidation are poorly understood and lattice defect formation must be avoided. Here, we demonstrate film formation of micrometer-sized graphene flakes with lattice defects down to 0.02% and visualize the carbon lattice by transmission electron microscopy at atomic resolution. Interestingly, we find that only well-ordered, highly crystalline graphite delaminates into oxo-functionalized graphene, whereas other graphite grades do not form a proper stage-1 intercalate and revert back to graphite upon hydrolysis. Ab initio molecular dynamics simulations show that ideal stacking and electronic oxidation of the graphite layers significantly reduce the friction of the moving sulfuric acid molecules, thereby facilitating intercalation. Furthermore, the evaluation of the stability of oxo-species in graphite sulfate supports an oxidation mechanism that obviates intercalation of the oxidant.

Direct Preparation of Few Layer Graphene Epoxy Nanocomposites from Untreated Flake Graphite.

PubMed

Throckmorton, James; Palmese, Giuseppe

2015-07-15

The natural availability of flake graphite and the exceptional properties of graphene and graphene-polymer composites create a demand for simple, cost-effective, and scalable methods for top-down graphite exfoliation. This work presents a novel method of few layer graphite nanocomposite preparation directly from untreated flake graphite using a room temperature ionic liquid and laminar shear processing regimen. The ionic liquid serves both as a solvent and initiator for epoxy polymerization and is incorporated chemically into the matrix. This nanocomposite shows low electrical percolation (0.005 v/v) and low thickness (1-3 layers) graphite/graphene flakes by TEM. Additionally, the effect of processing conditions by rheometry and comparison with solvent-free conditions reveal the interactions between processing and matrix properties and provide insight into the theory of the chemical and physical exfoliation of graphite crystals and the resulting polymer matrix dispersion. An interaction model that correlates the interlayer shear physics of graphite flakes and processing parameters is proposed and tested.

New insights into canted spiro carbon interstitial in graphite

NASA Astrophysics Data System (ADS)

EL-Barbary, A. A.

2017-12-01

The self-interstitial carbon is the key to radiation damage in graphite moderator nuclear reactor, so an understanding of its behavior is essential for plant safety and maximized reactor lifetime. The density functional theory is applied on four different graphite unit cells, starting from of 64 carbon atoms up to 256 carbon atoms, using AIMPRO code to obtain the energetic, athermal and mechanical properties of carbon interstitial in graphite. This study presents first principles calculations of the energy of formation that prove its high barrier to athermal diffusion (1.1 eV) and the consequent large critical shear stress (39 eV-50 eV) necessary to shear graphite planes in its presence. Also, for the first time, the gamma surface of graphite in two dimensions is calculated and found to yield the critical shear stress for perfect graphite. Finally, in contrast to the extensive literature describing the interstitial of carbon in graphite as spiro interstitial, in this work the ground state of interstitial carbon is found to be canted spiro interstitial.

Adsorption behavior of bisphenol A on CTAB-modified graphite

NASA Astrophysics Data System (ADS)

Wang, Li-Cong; Ni, Xin-jiong; Cao, Yu-Hua; Cao, Guang-qun

2018-01-01

In this work, the adsorption behavior of BPA on CTAB-modified graphite was investigated thoroughly to develop a novel absorbent material. Atomic force microscopy revealed that conical admicelles formed on the surface of graphite. The surface area of graphite decreased significantly from 1.46 to 0.95 m2 g-1, which confirmed the formation of the larger size admicelle instead of the original smaller particle on the surface. CTAB concentration and incubation time affected the progress of admicelle formation on the surface of graphite. Adsolubilization is key in BPA adsorption by CTAB-modified graphite. An extraordinary cation-π electron interaction between CTAB and BPA, revealed by a red-shift in the ultraviolet spectrum, as well as a hydrophobic interaction contribute substantially to BPA adsolubilization. The equilibrium adsorption capacity of the modified graphite for BPA was 125.01 mg g-1. The adsorption kinetic curves of BPA on modified graphite were shown to follow a pseudosecond-order rate. The adsorption process was observed to be both spontaneous and exothermic complied with the Freundlich model.

Phase Structures and Magnetic Properties of Graphite Nanosheets and Ni-Graphite Nanocomposite Synthesized by Electrical Explosion of Wire in Liquid

NASA Astrophysics Data System (ADS)

Nguyen, Minh-Thuyet; Kim, Jin-Hyung; Lee, Jung-Goo; Kim, Jin-Chun

2018-03-01

The present work studied on phases and magnetic properties of graphite nanosheets and Ni-graphite nanocomposite synthesized using the electrical explosion of wire (EEW) in ethanol. X-ray diffraction and field emission scanning electron microscope were used to investigate the phases and the morphology of the nanopowders obtained. It was found that graphite nanosheets were absolutely fabricated by EEW with a thickness of 29 nm and 3 μm diameter. The as-synthesized Ni-graphite composite powders had a Ni-coating on the surfaces of graphite sheets. The hysteresis loop of the as-exploded, the hydrogen-treated composite nanopowders and the sintered samples were examined with a vibrating sample magnetometer at room temperature. The Ni-graphite composite exposed the magnetic behaviors which are attributed to Ni component. The magnetic properties of composite had the improvement from 10.2 emu/g for the as-exploded powders to 15.8 emu/g for heat-treated powders and 49.16 emu/g for sintered samples.

Quantifying microstructural dynamics and electrochemical activity of graphite and silicon-graphite lithium ion battery anodes

NASA Astrophysics Data System (ADS)

Pietsch, Patrick; Westhoff, Daniel; Feinauer, Julian; Eller, Jens; Marone, Federica; Stampanoni, Marco; Schmidt, Volker; Wood, Vanessa

2016-09-01

Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of magnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

Fire test method for graphite fiber reinforced plastics

NASA Technical Reports Server (NTRS)

Bowles, K. J.

1980-01-01

A potential problem in the use of graphite fiber reinforced resin matrix composites is the dispersal of graphite fibers during accidential fires. Airborne, electrically conductive fibers originating from the burning composites could enter and cause shorting in electrical equipment located in surrounding areas. A test method for assessing the burning characteristics of graphite fiber reinforced composites and the effectiveness of the composites in retaining the graphite fibers has been developed. The method utilizes a modified rate of heat release apparatus. The equipment and the testing procedure are described. The application of the test method to the assessment of composite materials is illustrated for two resin matrix/graphite composite systems.

Process for the fabrication of aluminum metallized pyrolytic graphite sputtering targets

DOEpatents

Makowiecki, Daniel M.; Ramsey, Philip B.; Juntz, Robert S.

1995-01-01

An improved method for fabricating pyrolytic graphite sputtering targets with superior heat transfer ability, longer life, and maximum energy transmission. Anisotropic pyrolytic graphite is contoured and/or segmented to match the erosion profile of the sputter target and then oriented such that the graphite's high thermal conductivity planes are in maximum contact with a thermally conductive metal backing. The graphite contact surface is metallized, using high rate physical vapor deposition (HRPVD), with an aluminum coating and the thermally conductive metal backing is joined to the metallized graphite target by one of four low-temperature bonding methods; liquid-metal casting, powder metallurgy compaction, eutectic brazing, and laser welding.

Arsenic Removal from Water by Adsorption on Iron-Contaminated Cryptocrystalline Graphite

NASA Astrophysics Data System (ADS)

Yang, Qiang; Yang, Lang; Song, Shaoxian; Xia, Ling

This work aimed to study the feasibility of using iron-contaminated graphite as an adsorbent for As(V) removal from water. The adsorbent was prepared by grinding graphite concentrate with steel ball. The study was performed through the measurements of adsorption capacity, BET surface area and XPS analysis. The experimental results showed that the iron-contaminated graphite exhibited significantly high adsorption capacity of As(V). The higher the iron contaminated on the graphite surface, the higher the adsorption capacity of As(V) on the material obtained. It was suggested that the ion-contaminated graphite was a good adsorbent for As(V) removal.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inam, A., E-mail: aqil.ceet@pu.edu.pk; Brydson, R., E-mail: mtlrmdb@leeds.ac.uk; Edmonds, D.V., E-mail: d.v.edmonds@leeds.ac.uk

The potential for using graphite particles as an internal lubricant during machining is considered. Graphite particles were found to form during graphitisation of experimental medium-carbon steel alloyed with Si and Al. The graphite nucleation sites were strongly influenced by the starting microstructure, whether ferrite–pearlite, bainite or martensite, as revealed by light and electron microscopy. Favourable nucleation sites in the ferrite–pearlite starting microstructure were, not unexpectedly, found to be located within pearlite colonies, no doubt due to the presence of abundant cementite as a source of carbon. In consequence, the final distribution of graphite nodules in ferrite–pearlite microstructures was less uniformmore » than for the bainite microstructure studied. In the case of martensite, this study found a predominance of nucleation at grain boundaries, again leading to less uniform graphite dispersions. - Highlights: • Metallography of formation of graphite particles in experimental carbon steel. • Potential for using graphite in steel as an internal lubricant during machining. • Microstructure features expected to influence improved machinability studied. • Influence of pre-anneal starting microstructure on graphite nucleation sites. • Influence of pre-anneal starting microstructure on graphite distribution. • Potential benefit is new free-cutting steel compositions without e.g. Pb alloying.« less

Understanding the reaction of nuclear graphite with molecular oxygen: Kinetics, transport, and structural evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kane, Joshua J.; Contescu, Cristian I.; Smith, Rebecca E.

A thorough understanding of oxidation is important when considering the health and integrity of graphite components in graphite reactors. For the next generation of graphite reactors, HTGRs specifically, an unlikely air ingress has been deemed significant enough to have made its way into the licensing applications of many international licensing bodies. While a substantial body of literature exists on nuclear graphite oxidation in the presence of molecular oxygen and significant efforts have been made to characterize oxidation kinetics of various grades, the value of existing information is somewhat limited. Often, multiple competing processes, including reaction kinetics, mass transfer, and microstructuralmore » evolution, are lumped together into a single rate expression that limits the ability to translate this information to different conditions. This article reviews the reaction of graphite with molecular oxygen in terms of the reaction kinetics, gas transport, and microstructural evolution of graphite. It also presents the foundations of a model for the graphite-molecular oxygen reaction system that is kinetically independent of graphite grade, and is capable of describing both the bulk and local oxidation rates under a wide range of conditions applicable to air-ingress.« less

Understanding the reaction of nuclear graphite with molecular oxygen: Kinetics, transport, and structural evolution

DOE PAGES

Kane, Joshua J.; Contescu, Cristian I.; Smith, Rebecca E.; ...

2017-06-08

A thorough understanding of oxidation is important when considering the health and integrity of graphite components in graphite reactors. For the next generation of graphite reactors, HTGRs specifically, an unlikely air ingress has been deemed significant enough to have made its way into the licensing applications of many international licensing bodies. While a substantial body of literature exists on nuclear graphite oxidation in the presence of molecular oxygen and significant efforts have been made to characterize oxidation kinetics of various grades, the value of existing information is somewhat limited. Often, multiple competing processes, including reaction kinetics, mass transfer, and microstructuralmore » evolution, are lumped together into a single rate expression that limits the ability to translate this information to different conditions. This article reviews the reaction of graphite with molecular oxygen in terms of the reaction kinetics, gas transport, and microstructural evolution of graphite. It also presents the foundations of a model for the graphite-molecular oxygen reaction system that is kinetically independent of graphite grade, and is capable of describing both the bulk and local oxidation rates under a wide range of conditions applicable to air-ingress.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chuang, Chihpin; Singh, Dileep; Kenesei, Peter

The size and morphology of the graphite particles play a crucial role in determining various mechanical and thermal properties of cast iron. In the present study, we utilized high-energy synchrotron X-ray tomography to perform quantitative 3D-characterization of the distribution of graphite particles in high-strength compacted graphite iron (CGI). The size, shape, and spatial connectivity of graphite were examined. The analysis reveals that the compacted graphite can grow with a coral-tree-like morphology and span several hundred microns in the iron matrix.

Preparation of pyrolytic carbon coating on graphite for inhibiting liquid fluoride salt and Xe135 penetration for molten salt breeder reactor

NASA Astrophysics Data System (ADS)

Song, Jinliang; Zhao, Yanling; He, Xiujie; Zhang, Baoliang; Xu, Li; He, Zhoutong; Zhang, DongSheng; Gao, Lina; Xia, Huihao; Zhou, Xingtai; Huai, Ping; Bai, Shuo

2015-01-01

A fixed-bed deposition method was used to prepare rough laminar pyrolytic carbon coating (RLPyC) on graphite for inhibiting liquid fluoride salt and Xe135 penetration during use in molten salt breeder reactor. The RLPyC coating possessed a graphitization degree of 44% and had good contact with graphite substrate. A high-pressure reactor was constructed to evaluate the molten salt infiltration in the isostatic graphite (IG-110, TOYO TANSO CO., LTD.) and RLPyC coated graphite under 1.01, 1.52, 3.04, 5.07 and 10.13 × 105 Pa for 12 h. Mercury injection and molten-salt infiltration experiments indicated the porosity and the salt-infiltration amount of 18.4% and 13.5 wt% under 1.52 × 105 Pa of IG-110, which was much less than 1.2% and 0.06 wt% under 10.13 × 105 Pa of the RLPyC, respectively. A vacuum device was constructed to evaluate the Xe135 penetration in the graphite. The helium diffusion coefficient of RLPyC coated graphite was 2.16 × 10-12 m2/s, much less than 1.21 × 10-6 m2/s of the graphite. Thermal cycle experiment indicated the coatings possessed excellent thermal stability. The coated graphite could effectively inhibit the liquid fluoride salt and Xe135 penetration.

Kinetics of Chronic Oxidation of NBG-17 Nuclear Graphite by Water Vapor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contescu, Cristian I; Burchell, Timothy D; Mee, Robert

2015-05-01

This report presents the results of kinetic measurements during accelerated oxidation tests of NBG-17 nuclear graphite by low concentration of water vapor and hydrogen in ultra-high purity helium. The objective is to determine the parameters in the Langmuir-Hinshelwood (L-H) equation describing the oxidation kinetics of nuclear graphite in the helium coolant of high temperature gas-cooled reactors (HTGR). Although the helium coolant chemistry is strictly controlled during normal operating conditions, trace amounts of moisture (predictably < 0.2 ppm) cannot be avoided. Prolonged exposure of graphite components to water vapor at high temperature will cause very slow (chronic) oxidation over the lifetimemore » of graphite components. This behavior must be understood and predicted for the design and safe operation of gas-cooled nuclear reactors. The results reported here show that, in general, oxidation by water of graphite NBG-17 obeys the L-H mechanism, previously documented for other graphite grades. However, the characteristic kinetic parameters that best describe oxidation rates measured for graphite NBG-17 are different than those reported previously for grades H-451 (General Atomics, 1978) and PCEA (ORNL, 2013). In some specific conditions, certain deviations from the generally accepted L-H model were observed for graphite NBG-17. This graphite is manufactured in Germany by SGL Carbon Group and is a possible candidate for the fuel elements and reflector blocks of HTGR.« less

Through-thickness thermal conductivity enhancement of graphite film/epoxy composite via short duration acidizing modification

NASA Astrophysics Data System (ADS)

Wang, Han; Wang, Shaokai; Lu, Weibang; Li, Min; Gu, Yizhou; Zhang, Yongyi; Zhang, Zuoguang

2018-06-01

Graphite films have excellent in-plane thermal conductivity but extremely low through-thickness thermal conductivity because of their intrinsic inter-layer spaces. To improve the inter-layer heat transfer of graphite films, we developed a simple interfacial modification with a short duration mixed-acid treatment. The effects of the mixture ratio of sulfuric and nitric acids and treatment time on the through-thickness thermal properties of graphite films were studied. The modification increased the through-thickness thermal conductivity by 27% and 42% for the graphite film and its composite, respectively. X-ray photoelectron spectroscopy, X-ray powder diffraction, and scanning electron microscopy results indicated that the acidification process had two competing effects: the positive contribution made by the enhanced interaction between the graphite layers induced by the functional groups and the negative effect from the destruction of the graphite layers. As a result, an optimal acidification method was found to be sulfuric/nitric acid treatment with a mixture ratio of 3:1 for 15 min. The resultant through-thickness thermal conductivity of the graphite film could be improved to 0.674 W/mK, and the corresponding graphite/epoxy composite shows a through-thickness thermal conductivity of 0.587 W/mK. This method can be directly used for graphite films and their composite fabrication to improve through-thickness thermal conductivity.

Characterization of the Intrinsic Water Wettability of Graphite Using Contact Angle Measurements: Effect of Defects on Static and Dynamic Contact Angles.

PubMed

Kozbial, Andrew; Trouba, Charlie; Liu, Haitao; Li, Lei

2017-01-31

Elucidating the intrinsic water wettability of the graphitic surface has increasingly attracted research interests, triggered by the recent finding that the well-established hydrophobicity of graphitic surfaces actually results from airborne hydrocarbon contamination. Currently, static water contact angle (WCA) is often used to characterize the intrinsic water wettability of graphitic surfaces. In the current paper, we show that because of the existence of defects, static WCA does not necessarily characterize the intrinsic water wettability. Freshly exfoliated graphite of varying qualities, characterized using atomic force microscopy and Raman spectroscopy, was studied using static, advancing, and receding WCA measurements. The results showed that graphite of different qualities (i.e., defect density) always has a similar advancing WCA, but it could have very different static and receding WCAs. This finding indicates that defects play an important role in contact angle measurements, and the static contact angle does not always represent the intrinsic water wettability of pristine graphite. On the basis of the experimental results, a qualitative model is proposed to explain the effect of defects on static, advancing, and receding contact angles. The model suggests that the advancing WCA reflects the intrinsic water wettability of pristine (defect-free) graphite. Our results showed that the advancing WCA for pristine graphite is 68.6°, which indicates that graphitic carbon is intrinsically mildly hydrophilic.

Graphite fiber reinforced thermoplastic resins

NASA Technical Reports Server (NTRS)

Navak, R. C.

1977-01-01

The results of a program designed to optimize the fabrication procedures for graphite thermoplastic composites are described. The properties of the composites as a function of temperature were measured and graphite thermoplastic fan exit guide vanes were fabricated and tested. Three thermoplastics were included in the investigation: polysulfone, polyethersulfone, and polyarylsulfone. Type HMS graphite was used as the reinforcement. Bending fatigue tests of HMS graphite/polyethersulfone demonstrated a gradual shear failure mode which resulted in a loss of stiffness in the specimens. Preliminary curves were generated to show the loss in stiffness as a function of stress and number of cycles. Fan exit guide vanes of HMS graphite polyethersulfone were satisfactorily fabricated in the final phase of the program. These were found to have stiffness and better fatigue behavior than graphite epoxy vanes which were formerly bill of material.

High efficiency of CO2-activated graphite felt as electrode for vanadium redox flow battery application

NASA Astrophysics Data System (ADS)

Chang, Yu-Chung; Chen, Jian-Yu; Kabtamu, Daniel Manaye; Lin, Guan-Yi; Hsu, Ning-Yih; Chou, Yi-Sin; Wei, Hwa-Jou; Wang, Chen-Hao

2017-10-01

A simple method for preparing CO2-activated graphite felt as an electrode in a vanadium redox flow battery (VRFB) was employed by the direct treatment in a CO2 atmosphere at a high temperature for a short period. The CO2-activated graphite felt demonstrates excellent electrochemical activity and reversibility. The VRFB using the CO2-activated graphite felts in the electrodes has coulombic, voltage, and energy efficiencies of 94.52%, 88.97%, and 84.15%, respectively, which is much higher than VRFBs using the electrodes of untreated graphite felt and N2-activated graphite felt. The efficiency enhancement was attributed to the higher number of oxygen-containing functional groups on the graphite felt that are formed during the CO2-activation, leading to improving the electrochemical behaviour of the resultant VRFB.

Influence of the Interaction Between Graphite and Polar Surfaces of ZnO on the Formation of Schottky Contact

NASA Astrophysics Data System (ADS)

Yatskiv, R.; Grym, J.

2018-03-01

We show that the interaction between graphite and polar surfaces of ZnO affects electrical properties of graphite/ZnO Schottky junctions. A strong interaction of the Zn-face with the graphite contact causes interface imperfections and results in the formation of laterally inhomogeneous Schottky contacts. On the contrary, high quality Schottky junctions form on the O-face, where the interaction is significantly weaker. Charge transport through the O-face ZnO/graphite junctions is well described by the thermionic emission model in both forward and reverse directions. We further demonstrate that the parameters of the graphite/ZnO Schottky diodes can be significantly improved when a thin layer of ZnO2 forms at the interface between graphite and ZnO after hydrogen peroxide surface treatment.

Thermophysical properties of graphite HOPG and HAPG in the solid state and under melting (from 2000 K up to 5000 K)

NASA Astrophysics Data System (ADS)

Savvatimskiy, A. I.; Onufriev, S. V.; Konyukhov, S. A.

2017-11-01

Experiments with HOPG graphite grade showed that the melting temperature of graphite equals 4800-4900 K and that the melting of graphite is possible only at elevated pressures. The data were obtained for resistivity, specific heat and input (Joule) energy up to 5000 K. HAPG (Highly Annealing Pyrolytic Graphite) is a form of highly oriented pyrolytic graphite. HAPG specimens in the form of strips (thickness 30 microns) were placed in a cell (between two plates of glass-sapphire). The specimen temperature was measured by a high speed pyrometer. The heat of fusion for both graphite grades (heated in a confined volume) was less (and specific heat - higher) than for the case with nearly free expansion. A possible reason for the observed effects is discussed in the report.

Modelling deformation and fracture of Gilsocarbon graphite subject to service environments

NASA Astrophysics Data System (ADS)

Šavija, Branko; Smith, Gillian E.; Heard, Peter J.; Sarakinou, Eleni; Darnbrough, James E.; Hallam, Keith R.; Schlangen, Erik; Flewitt, Peter E. J.

2018-02-01

Commercial graphites are used for a wide range of applications. For example, Gilsocarbon graphite is used within the reactor core of advanced gas-cooled reactors (AGRs, UK) as a moderator. In service, the mechanical properties of the graphite are changed as a result of neutron irradiation induced defects and porosity arising from radiolytic oxidation. In this paper, we discuss measurements undertaken of mechanical properties at the micro-length-scale for virgin and irradiated graphite. These data provide the necessary inputs to an experimentally-informed model that predicts the deformation and fracture properties of Gilsocarbon graphite at the centimetre length-scale, which is commensurate with laboratory test specimen data. The model predictions provide an improved understanding of how the mechanical properties and fracture characteristics of this type of graphite change as a result of exposure to the reactor service environment.

Pyrolytic graphite gauge for measuring heat flux

NASA Technical Reports Server (NTRS)

Bunker, Robert C. (Inventor); Ewing, Mark E. (Inventor); Shipley, John L. (Inventor)

2002-01-01

A gauge for measuring heat flux, especially heat flux encountered in a high temperature environment, is provided. The gauge includes at least one thermocouple and an anisotropic pyrolytic graphite body that covers at least part of, and optionally encases the thermocouple. Heat flux is incident on the anisotropic pyrolytic graphite body by arranging the gauge so that the gauge surface on which convective and radiative fluxes are incident is perpendicular to the basal planes of the pyrolytic graphite. The conductivity of the pyrolytic graphite permits energy, transferred into the pyrolytic graphite body in the form of heat flux on the incident (or facing) surface, to be quickly distributed through the entire pyrolytic graphite body, resulting in small substantially instantaneous temperature gradients. Temperature changes to the body can thereby be measured by the thermocouple, and reduced to quantify the heat flux incident to the body.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganesh, Panchapakesan; Kent, Paul R; Mochalin, Vadym N

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core ofmore » the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism

NASA Astrophysics Data System (ADS)

Ortega, L.; Millward, D.; Luque, F. J.; Barrenechea, J. F.; Beyssac, O.; Huizenga, J.-M.; Rodas, M.; Clarke, S. M.

2010-04-01

The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C-O-H fluids. The δ 13C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous metapelites of the Skiddaw Group by andesite magmas of the Borrowdale Volcanic Group. The graphite mineralization occurred as the fluids migrated upwards through normal conjugate fractures forming the main subvertical pipe-like bodies. The mineralizing fluids evolved from CO 2-CH 4-H 2O mixtures (XCO 2 = 0.6-0.8) to CH 4-H 2O mixtures. Coevally with graphite deposition, the andesite and dioritic wall rocks adjacent to the veins were intensely hydrothermally altered to a propylitic assemblage. The initial graphite precipitation was probably triggered by the earliest hydration reactions in the volcanic host rocks. During the main mineralization stage, graphite precipitated along the pipe-like bodies due to CO 2 → C + O 2. This agrees with the isotopic data which indicate that the first graphite morphologies crystallizing from the fluid (cryptocrystalline aggregates) are isotopically lighter than those crystallizing later (flakes). Late chlorite-graphite veins were formed from CH 4-enriched fluids following the reaction CH 4 + O 2 → C + 2H 2O, producing the successive precipitation of isotopically lighter graphite morphologies. Thus, as mineralization proceeded, water-generating reactions were involved in graphite precipitation, further favouring the propylitic alteration. The structural features of the pipe-like mineralized bodies as well as the isotopic homogeneity of graphite suggest that the mineralization occurred in a very short period of time.

Solid Fuel Burning in Steady, Strained, Premixed Flow Fields: The Graphite/Air/Methane System

NASA Technical Reports Server (NTRS)

Egolfopoulos, Fokion N.; Wu, Ming-Shin (Technical Monitor)

2000-01-01

A detailed numerical investigation was conducted on the simultaneous burning of laminar premixed CH4/air flames and solid graphite in a stagnation flow configuration. The graphite and methane were chosen for this model, given that they are practical fuels and their chemical kinetics are considered as the most reliable ones among solid and hydrocarbon fuels, respectively. The simulation was performed by solving the quasi-one-dimensional equations of mass, momentum, energy, and species. The GRI 2.1 scheme was used for the gas-phase kinetics, while the heterogeneous kinetics were described by a six-step mechanism including stable and radical species. The effects of the graphite surface temperature, the gas-phase equivalence ratio, and the aerodynamic strain rate on the graphite burning rate and NO, production and destruction mechanisms were assessed. Results indicate that as the graphite temperature increases, its burning rate as well as the NO, concentration increase. Furthermore, it was found that by increasing the strain rate, the graphite burning rate increases as a result of the augmented supply of the gas-phase reactants towards the surface, while the NO, concentration decreases as a result of the reduced residence time. The effect of the equivalence ratio on both the graphite burning rate and NO, concentration was found to be non-monotonic and strongly dependent on the graphite temperature. Comparisons between results obtained for a graphite and a chemically inert surface revealed that the chemical activity of the graphite surface can result to the reduction of NO through reactions of the CH3, CH2, CH, and N radicals with NO.

Unit-Sphere Multiaxial Stochastic-Strength Model Applied to Anisotropic and Composite Materials

NASA Technical Reports Server (NTRS)

Nemeth, Noel, N.

2013-01-01

Models that predict the failure probability of brittle materials under multiaxial loading have been developed by authors such as Batdorf, Evans, and Matsuo. These "unit-sphere" models assume that the strength-controlling flaws are randomly oriented, noninteracting planar microcracks of specified geometry but of variable size. This methodology has been extended to predict the multiaxial strength response of transversely isotropic brittle materials, including polymer matrix composites (PMCs), by considering (1) flaw-orientation anisotropy, whereby a preexisting microcrack has a higher likelihood of being oriented in one direction over another direction, and (2) critical strength, or K (sub Ic) orientation anisotropy, whereby the level of critical strength or fracture toughness for mode I crack propagation, K (sub Ic), changes with regard to the orientation of the microstructure. In this report, results from finite element analysis of a fiber-reinforced-matrix unit cell were used with the unit-sphere model to predict the biaxial strength response of a unidirectional PMC previously reported from the World-Wide Failure Exercise. Results for nuclear-grade graphite materials under biaxial loading are also shown for comparison. This effort was successful in predicting the multiaxial strength response for the chosen problems. Findings regarding stress-state interactions and failure modes also are provided.

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Mall, S.

1985-01-01

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg nd 45 deg interface plies. Damage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

The strength of metal matrix composites

NASA Astrophysics Data System (ADS)

Baxter, William J.

1992-11-01

There is intensive interest in metal matrix composites (MMCs) for automotive components, and the first production applications in Japan use discontinuous fibers as the reinforcements. These fibers are randomly oriented, resulting in an MMC with isotropic properties. However, there are conflicting reports on the tensile strengths attainable. In some cases, the strength increases with increasing volume fraction (V f) of fibers, while in other cases, there is little or no benefit. A simple method is proposed to calculate the strength of this type of MMC. It is shown that the fibers oriented perpendicular to the stress direction play a key role, and the strength depends upon the strength of the interfacial bond. Upper and lower limits of the composite strength are calculated. If the bond strength is larger than the matrix strength, the composite strength has a maximum value which increases with V f. If the bond strength is weaker than the matrix, the composite strength has a minimum value which is either weakly dependent or even independent of V f. These calculations are in good agreement with examples taken from the literature of aluminum composites reinforced with either A12O3, graphite, or SiC. The strength of the matrix alloy is shown to be a very important parameter: weak alloys are easily strengthened, while in certain cases, strong alloys may be weakened.

Mechanical Characterization of In and Out-of-Autoclave Cured Composite Panels for Large Launch Vehicles

NASA Technical Reports Server (NTRS)

Kellas, Sotiris; Lerch, Bradley A.; Wilmoth, Nathan

2012-01-01

Two manufacturing demonstration panels (1/16th-arc-segments of 10 m diameter cylinder) were fabricated under the composites part of the Lightweight Space Structures and Materials program. Both panels were of sandwich construction with aluminum core and 8-ply quasi-isotropic graphite/epoxy facesheets. One of the panels was constructed with in-autoclave curable unidirectional prepreg (IM7/977-3) and the second with out-of-autoclave unidirectional prepreg (T40-800B/5320-1). Following NDE inspection, each panel was divided into a number of small specimens for material property characterization and a large (0.914 m wide by 1.524 m long) panel for a buckling study. Results from the small specimen tests were used to (a) assess the fabrication quality of each 1/16th arc segment panel and (b) to develop and/or verify basic material property inputs to Finite Element analysis models. The mechanical performance of the two material systems is assessed at the coupon level by comparing average measured properties such as flatwise tension, edgewise compression, and facesheet tension. The buckling response of the 0.914 m wide by 1.524 m long panel provided a comparison between the in- and out-of autoclave systems at a larger scale.

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Mall, S.

1986-01-01

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg and 45 deg interface plies. Damaage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Effect of angle-ply orientation on compression strength of composite laminates

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeTeresa, S J; Hoppel, C P

1999-03-01

An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive strength (X{sub 1C}) of 0{degree} plies in fiber reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with the generic architecture [0{sub 2}/{+-}{theta}] (where {theta} varied between 0{degree} and 90{degree}) and for the quasi-isotropic architecture were evaluated. The effective compressive strength of the 0{degree} plies varied considerably. The results were related to the Poisson's ratios of the laminates with high Poisson's ratios leading to high transverse tensile strains in the test coupons and lower than expected strengths. Specimens with the [O{sub 2}/{+-}30] architecture had both themore » highest Poisson's ratio and the lowest calculated ply-level compression strength for the 0{degree} plies. This work has implications in the selection of composite failure criterion for compression performance, design of test coupons for acceptance testing, and the selection of laminate architectures for optimum combinations of compressive and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different laminate strengths depending on the Poisson's ratio of the laminate. This implies that the biaxial stress state in the laminate needs to be carefully considered before backing out unidirectional properties.« less

Reaction rates of graphite with ozone measured by etch decoration

NASA Technical Reports Server (NTRS)

Hennig, G. R.; Montet, G. L.

1968-01-01

Etch-decoration technique of detecting vacancies in graphite has been used to determine the reaction rates of graphite with ozone in the directions parallel and perpendicular to the layer planes. It consists essentially of peeling single atom layers off graphite crystals without affecting the remainder of the crystal.

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.

78 FR 56864 - Small Diameter Graphite Electrodes From the People's Republic of China: Affirmative Final...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-16

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... (Department) determines that imports from the People's Republic of China (PRC) of graphite electrodes... Act of 1930, as amended (the Act).\\1\\ \\1\\ See Antidumping Duty Order: Small Diameter Graphite...

New Occurrence of Shocked Graphite Aggregates at Barringer Crater

NASA Astrophysics Data System (ADS)

Miura, Y.; Noma, Y.; Iancu, O. G.

1993-07-01

High-pressure carbon minera]s are considered to be formed by solid-solid transformation under static or impact high-pressure condition, but shocked quartz aggregates of impact craters are considered to be formed by quenched accretion of various aggregates by dynamic impact process [1-3]. The main purpose of this study is to elucidate new findings and occurrences of shocked graphite (SG) aggregates [2,3] at the Barringer meteorite crater. The graphite nodule block of Barringer Crater used in this study is collected near the rim. The sample is compared with standard graphite samples of Korea, Madagascar, and artificial impact graphites. There are four different mineral aggregates of the Barringer graphite nodule sample: (1) shocked graphite-1, (2) shocked graphite-2 and hexagonal diamond in the vein, (3) shocked quartz-1 (with kamacite) in the rim, and (4) calcite in the rim (Table 1). X-ray diffraction peaks of shocked graphite reveal low X-ray intensity, high Bragg-angle shift of X-ray diffraction peak, and multiple splitting of X-ray diffraction peaks. X-ray calculated density (rho) has been determined by X-ray diffractometer by the equation of density deviation Delta rho (%) = 100 x {(rho-rho(sub)0)/rho(sub)0}, where standard density rho(sub)0 is 2.255 g/cm^3 in Korean graphite [2,3]. The high-density value of shocked graphite grain obtained in Barringer is Delta rho = +0.6 +/- 0.1%. Shocked hexagonal diamonds (chaoite) show a high value of Delta rho = +0.6 +/- 0.9%. Analytical electron microscopy data reveal three different aggregates in the graphite nodule samples (Table 1): (1) shocked graphite-1 in the matrix, which contains uniformly Fe and Ca elements formed under gas state; (2) shocked graphite-2 in the vein, where crystallized shocked graphites and hexagonal diamonds are surrounded by kamacite-rich metals formed under gas-melt states of mixed compositions from iron meteorite and target rocks; and (3) shocked quartz-1 and kamacite in the rim, where coexisted elements are supplied from kamacite, sandstone, and limestone. The shocked quartz-1 grains with high density contain Fe and Ca elements that are different from the shocked quartz-2 of pure silica [1] formed at the final stage from the Coconino sandstone. (4) Limestone in the rim is attached from Kaibab limestone. The present shocked graphites with high density are the same as artificial fine-grained shocked graphites (Delta rho = +0.7%). Table 1, which appears here in the hard copy, shows formation stages with two shocked graphites in the Barringer Crater. Formation of shocked aggregates with chemical contamination indicate dynamic accretion processes of quenching and depression at impact. The existence of two shocked graphites indicates the two formation stages of the first gas-state and the second gas-melt states with quenching processes. The origin of carbon in the shocked graphites is considered in this study to be from Kaibab limestone. References: [1] Miura Y. (1991) Shock Waves, 1, 35-41. [2] Miura Y. (1992) Proc. Shock Waves (Japan), 2, 54-57. [3] Miura Y. et al. (1993) Symp. NIPR Antarctic Meteorite (Tokyo), in press. [4] Foote A. E. (1891) Am. J. Sci., 42, 413-417. [5] Hannemann R. E. et al. (1967) Science, 155, 995-997.

Low temperature vapor phase digestion of graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pierce, Robert A.

2017-04-18

A method for digestion and gasification of graphite for removal from an underlying surface is described. The method can be utilized to remove graphite remnants of a formation process from the formed metal piece in a cleaning process. The method can be particularly beneficial in cleaning castings formed with graphite molding materials. The method can utilize vaporous nitric acid (HNO.sub.3) or vaporous HNO.sub.3 with air/oxygen to digest the graphite at conditions that can avoid damage to the underlying surface.

The Fracture Toughness of Nuclear Graphites Grades

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burchell, Timothy D.; Erdman, III, Donald L.; Lowden, Rick R.

2017-04-01

New measurements of graphite mode I critical stress intensity factor, KIc (commonly referred to as the fracture toughness) and the mode II critical shear stress intensity, KIIc, are reported and compared with prior data for KIc and KIIc. The new data are for graphite grades PCEA, IG-110 and 2114. Variations of KIc and acoustic emission (AE) data with graphite texture are reported and discussed. The Codes and Standards applications of fracture toughness, KIc, data are also discussed. A specified minimum value for nuclear graphite KIc is recommended.

AC induction field heating of graphite foam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klett, James W.; Rios, Orlando; Kisner, Roger

A magneto-energy apparatus includes an electromagnetic field source for generating a time-varying electromagnetic field. A graphite foam conductor is disposed within the electromagnetic field. The graphite foam when exposed to the time-varying electromagnetic field conducts an induced electric current, the electric current heating the graphite foam. An energy conversion device utilizes heat energy from the heated graphite foam to perform a heat energy consuming function. A device for heating a fluid and a method of converting energy are also disclosed.

PROCESS OF COATING GRAPHITE WITH NIOBIUM-TITANIUM CARBIDE

DOEpatents

Halden, F.A.; Smiley, W.D.; Hruz, F.M.

1961-07-01

A process of coating graphite with niobium - titanium carbide is described. It is found that the addition of more than ten percent by weight of titanium to niobium results in much greater wetting of the graphite by the niobium and a much more adherent coating. The preferred embodiment comprises contacting the graphite with a powdered alloy or mixture, degassing simultaneously the powder and the graphite, and then heating them to a high temperature to cause melting, wetting, spreading, and carburization of the niobium-titanium powder.

Carbon with Expanded and Well-Developed Graphene Planes Derived Directly from Condensed Lignin as a High-Performance Anode for Sodium-Ion Batteries.

PubMed

Yoon, Dohyeon; Hwang, Jieun; Chang, Wonyoung; Kim, Jaehoon

2018-01-10

In this study, we demonstrate that lignin, which constitutes 30-40 wt % of the terrestrial lignocellulosic biomass and is produced from second generation biofuel plants as a cheap byproduct, is an excellent precursor material for sodium-ion battery (NIB) anodes. Because it is rich in aromatic monomers that are highly cross-linked by ether and condensed bonds, the lignin material carbonized at 1300 °C (C-1300) in this study has small graphitic domains with well-developed graphene layers, a large interlayer spacing (0.403 nm), and a high micropore surface area (207.5 m 2 g -1 ). When tested as an anode in an NIB, C-1300 exhibited an initial Coulombic efficiency of 68% and a high reversible capacity of 297 mA h g -1 at 50 mA g -1 after 50 cycles. The high capacity of 199 mA h g -1 at less than 0.1 V with a flat voltage profile and an extremely low charge-discharge voltage hysteresis (<0.03 V) make C-1300 a promising energy-dense electrode material. In addition, C-1300 exhibited an excellent high-rate performance of 116 mA h g -1 at 2.5 A g -1 and showed stable cycling retention (0.2% capacity decay per cycle after 500 cycles). By comparing the properties of the lignin-derived carbon with oak sawdust-derived and sugar-derived carbons and a low-temperature carbonized sample (900 °C), the reasons for the excellent performance of C-1300 were determined to result from facilitated Na + -ion transport to the graphitic layer and the microporous regions that penetrate through the less defective and enlarged interlayer spacings.

Phase Transition of H 2 in Subnanometer Pores Observed at 75 K

DOE PAGES

Olsen, Raina J.; Gillespie, Andrew K.; Contescu, Cristian I.; ...

2017-10-30

In this paper, we report a phase transition in H 2 adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5–0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H 2 melts at 14 K in the bulk, but at 20 K on graphite because the solid H 2 is stabilized by the surface structure. Here we observe a transition at 75 Kmore » and 77–200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H 2 (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H 2 (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H 2 can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. Finally, no phase transition was observed in H 2 adsorbed in control activated carbon materials.« less

Phase Transition of H 2 in Subnanometer Pores Observed at 75 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olsen, Raina J.; Gillespie, Andrew K.; Contescu, Cristian I.

In this paper, we report a phase transition in H 2 adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5–0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H 2 melts at 14 K in the bulk, but at 20 K on graphite because the solid H 2 is stabilized by the surface structure. Here we observe a transition at 75 Kmore » and 77–200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H 2 (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H 2 (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H 2 can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. Finally, no phase transition was observed in H 2 adsorbed in control activated carbon materials.« less

Dust inflated accretion disc as the origin of the broad line region in active galactic nuclei

NASA Astrophysics Data System (ADS)

Baskin, Alexei; Laor, Ari

2018-02-01

The broad line region (BLR) in active galactic nuclei (AGNs) is composed of dense gas (˜1011 cm-3) on sub-pc scale, which absorbs about 30 per cent of the ionizing continuum. The outer size of the BLR is likely set by dust sublimation, and its density by the incident radiation pressure compression (RPC). But, what is the origin of this gas, and what sets its covering factor (CF)? Czerny & Hryniewicz (2011) suggested that the BLR is a failed dusty wind from the outer accretion disc. We explore the expected dust properties, and the implied BLR structure. We find that graphite grains sublimate only at T ≃ 2000 K at the predicted density of ˜1011 cm-3, and therefore large graphite grains (≥0.3 μm) survive down to the observed size of the BLR, RBLR. The dust opacity in the accretion disc atmosphere is ˜50 times larger than previously assumed, and leads to an inflated torus-like structure, with a predicted peak height at RBLR. The illuminated surface of this torus-like structure is a natural place for the BLR. The BLR CF is mostly set by the gas metallicity, the radiative accretion efficiency, a dynamic configuration and ablation by the incident optical-UV continuum. This model predicts that the BLR should extend inwards of RBLR to the disc radius where the surface temperature is ≃2000 K, which occurs at Rin ≃ 0.18RBLR. The value of Rin can be tested by reverberation mapping of the higher ionization lines, predicted by RPC to peak well inside RBLR. The dust inflated disc scenario can also be tested based on the predicted response of RBLR and the CF to changes in the AGN luminosity and accretion rate.

Late-time particle emission from laser-produced graphite plasma

NASA Astrophysics Data System (ADS)

Harilal, S. S.; Hassanein, A.; Polek, M.

2011-09-01

We report a late-time "fireworks-like" particle emission from laser-produced graphite plasma during its evolution. Plasmas were produced using graphite targets excited with 1064 nm Nd: yttrium aluminum garnet (YAG) laser in vacuum. The time evolution of graphite plasma was investigated using fast gated imaging and visible emission spectroscopy. The emission dynamics of plasma is rapidly changing with time and the delayed firework-like emission from the graphite target followed a black-body curve. Our studies indicated that such firework-like emission is strongly depended on target material properties and explained due to material spallation caused by overheating the trapped gases through thermal diffusion along the layer structures of graphite.

Fire test method for graphite fiber reinforced plastics

NASA Technical Reports Server (NTRS)

Bowles, K. J.

1980-01-01

A potential problem in the use of graphite fiber reinforced resin matrix composites is the dispersal of graphite fibers during accidental fires. Airborne, electrically conductive fibers originating from the burning composites could enter and cause shorting in electrical equipment located in surrounding areas. A test method for assessing the burning characteristics of graphite fiber reinforced composites and the effectiveness of the composites in retaining the graphite fibers has been developed. The method utilizes a modified Ohio State University Rate of Heat Release apparatus. The equipment and the testing procedure are described. The application of the test method to the assessment of composite materials is illustrated for two resin matrix/graphite composite systems.

Design and development of high efficiency 140W space TWT with graphite collector

NASA Astrophysics Data System (ADS)

Srivastava, V.; Purohit, G.; Sharma, R. K.; Sharma, S. M.; Bera, A.; Bhaskar, P. V.; Singh, R. R.; Prasad, K.; Kiran, V.

2008-05-01

4-stage graphite collector assembly has been designed and developed for a 140W Ku-band space TWT to achieve the collector efficiency more than 80%. The UHV compatible, high density, copper impregnated POCO graphite (DFP-1C) was used to fabricate the four collector electrodes of the 4-stage depressed collector. Copper impregnated graphite material is used for the collector electrodes because of its low secondary electron emission coefficient, high thermal and electrical conductivities, easy machining and brazing, low thermal expansion coefficient and low weight. The graphite material was characterized for the UHV compatibility. The collector electrodes were precisely fabricated by careful machining, and technology was developed for brazing of graphite electrodes with high voltage alumina insulators. Complete TWT with four-stage graphite collector was developed and 140W output power at gain more than 55 dB was achieved. The TWT was pumped from both the gun and the collector ends.

Development of design data for graphite reinforced epoxy and polyimide composites

NASA Technical Reports Server (NTRS)

Scheck, W. G.

1974-01-01

Processing techniques and design data were characterized for a graphite/epoxy composite system that is useful from 75 K to 450 K, and a graphite/polyimide composite system that is useful from 75 K to 589 K. The Monsanto 710 polyimide resin was selected as the resin to be characterized and used with the graphite fiber reinforcement. Material was purchased using the prepreg specification for the design data generation for both the HT-S/710 and HM-S/710 graphite/polyimide composite system. Lamina and laminate properties were determined at 75 K, 297 K, and 589 K. The test results obtained on the skin-stringer components proved that graphite/polyimide composites can be reliably designed and analyzed much like graphite/epoxy composites. The design data generated in the program includes the standard static mechanical properties, biaxial strain data, creep, fatigue, aging, and thick laminate data.

Chemical stabilization of graphite surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bistrika, Alexander A.; Lerner, Michael M.

Embodiments of a device, or a component of a device, including a stabilized graphite surface, methods of stabilizing graphite surfaces, and uses for the devices or components are disclosed. The device or component includes a surface comprising graphite, and a plurality of haloaryl ions and/or haloalkyl ions bound to at least a portion of the graphite. The ions may be perhaloaryl ions and/or perhaloalkyl ions. In certain embodiments, the ions are perfluorobenzenesulfonate anions. Embodiments of the device or component including stabilized graphite surfaces may maintain a steady-state oxidation or reduction surface current density after being exposed to continuous oxidation conditionsmore » for a period of at least 1-100 hours. The device or component is prepared by exposing a graphite-containing surface to an acidic aqueous solution of the ions under oxidizing conditions. The device or component can be exposed in situ to the solution.« less

Development of CIP/graphite composite additives for electromagnetic wave absorption applications

NASA Astrophysics Data System (ADS)

Woo, Soobin; Yoo, Chan-Sei; Kim, Hwijun; Lee, Mijung; Quevedo-Lopez, Manuel; Choi, Hyunjoo

2017-09-01

In this study, the electromagnetic (EM) wave absorption ability of carbonyl iron powder (CIP)/graphite composites produced by ball milling were studied in a range of 28.5 GHz to examine the effects of the morphology and volume fraction of graphite on EM wave absorption ability. The results indicated that a ball milling technique was effective in exfoliating the graphite and covering it with CIP, thereby markedly increasing the specific surface area of the hybrid powder. The increase in the surface area and hybridization with dielectric loss materials (i.e., graphite) improved EM absorbing properties of CIP in the range of S and X bands. Specifically, the CIP/graphite composite containing 3 wt% graphite exhibited electromagnetic wave absorption of -13 dB at 7 GHz, -21 dB at 5.8 GHz, and -29 dB at 4.3 GHz after 1 h, 8 h, and 16 h of milling, respectively. [Figure not available: see fulltext.

Friction and wear of metals in contact with pyrolytic graphite

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Brainard, W. A.

1975-01-01

Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments, including vacuum, oxygen, water vapor, nitrogen, and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. Auger and LEED spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.

Formation mechanism of graphite hexagonal pyramids by argon plasma etching of graphite substrates

NASA Astrophysics Data System (ADS)

Glad, X.; de Poucques, L.; Bougdira, J.

2015-12-01

A new graphite crystal morphology has been recently reported, namely the graphite hexagonal pyramids (GHPs). They are hexagonally-shaped crystals with diameters ranging from 50 to 800 nm and a constant apex angle of 40°. These nanostructures are formed from graphite substrates (flexible graphite and highly ordered pyrolytic graphite) in low pressure helicon coupling radiofrequency argon plasma at 25 eV ion energy and, purportedly, due to a physical etching process. In this paper, the occurrence of peculiar crystals is shown, presenting two hexagonal orientations obtained on both types of samples, which confirms such a formation mechanism. Moreover, by applying a pretreatment step with different time durations of inductive coupling radiofrequency argon plasma, for which the incident ion energy decreases at 12 eV, uniform coverage of the surface can be achieved with an influence on the density and size of the GHPs.

Tuning graphitic oxide for initiator- and metal-free aerobic epoxidation of linear alkenes

NASA Astrophysics Data System (ADS)

Pattisson, Samuel; Nowicka, Ewa; Gupta, Upendra N.; Shaw, Greg; Jenkins, Robert L.; Morgan, David J.; Knight, David W.; Hutchings, Graham J.

2016-09-01

Graphitic oxide has potential as a carbocatalyst for a wide range of reactions. Interest in this material has risen enormously due to it being a precursor to graphene via the chemical oxidation of graphite. Despite some studies suggesting that the chosen method of graphite oxidation can influence the physical properties of the graphitic oxide, the preparation method and extent of oxidation remain unresolved for catalytic applications. Here we show that tuning the graphitic oxide surface can be achieved by varying the amount and type of oxidant. The resulting materials differ in level of oxidation, surface oxygen content and functionality. Most importantly, we show that these graphitic oxide materials are active as unique carbocatalysts for low-temperature aerobic epoxidation of linear alkenes in the absence of initiator or metal. An optimum level of oxidation is necessary and materials produced via conventional permanganate-based methods are far from optimal.

Construction and performance evaluation of mediator-less microbial fuel cell using carbon nanotubes as an anode material.

PubMed

Roh, Sung-Hee; Kim, Sun-Il

2012-05-01

A microbial fuel cell (MFC) is a device that converts chemical energy to electrical energy using the catalytic reaction of microorganisms. We investigated the performance of mediator-less MFC with carbon nanotubes (CNTs)/graphite felt composite electrodes. The addition of CNTs to a graphite felt electrode increases the specific surface area of the electrode and enhances the charge transfer capability so as to cause considerable improvement of the electrochemical activity for the anode reaction in a MFC. The performance of the MFC using CNTs/graphite felt electrode has been compared against a plain graphite felt electrode based MFC. A CNTs/graphite felt electrode showed as high as 15% increase in the power density (252 mW/m2) compared to graphite felt electrode (214 mW/m2). The CNTs/graphite felt anode therefore offers good prospects for application in MFCs.

Method of making segmented pyrolytic graphite sputtering targets

DOEpatents

McKernan, Mark A.; Alford, Craig S.; Makowiecki, Daniel M.; Chen, Chih-Wen

1994-01-01

Anisotropic pyrolytic graphite wafers are oriented and bonded together such that the graphite's high thermal conductivity planes are maximized along the back surface of the segmented pyrolytic graphite target to allow for optimum heat conduction away from the sputter target's sputtering surface and to allow for maximum energy transmission from the target's sputtering surface.

76 FR 36092 - Small Diameter Graphite Electrodes From the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-21

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... antidumping duty order on small diameter graphite electrodes from the People's Republic of China (``PRC'') for... preliminary results of this review were published on March 7, 2011. See Small Diameter Graphite Electrodes...

77 FR 6060 - Small Diameter Graphite Electrodes from the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-07

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... Department) initiated an administrative review of the antidumping duty order on small diameter graphite... preliminary results of this review by 95 days until February 3, 2012. See Small Diameter Graphite Electrodes...

76 FR 67411 - Small Diameter Graphite Electrodes From the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-01

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... diameter graphite electrodes from the People's Republic of China (PRC) for the period February 1, 2010... Graphite, Co. The preliminary results of the review are currently due no later than October 31, 2011...

Quenchable compressed graphite synthesized from neutron-irradiated highly oriented pyrolytic graphite in high pressure treatment at 1500 °C

NASA Astrophysics Data System (ADS)

Niwase, Keisuke; Terasawa, Mititaka; Honda, Shin-ichi; Niibe, Masahito; Hisakuni, Tomohiko; Iwata, Tadao; Higo, Yuji; Hirai, Takeshi; Shinmei, Toru; Ohfuji, Hiroaki; Irifune, Tetsuo

2018-04-01

The super hard material of "compressed graphite" (CG) has been reported to be formed under compression of graphite at room temperature. However, it returns to graphite under decompression. Neutron-irradiated graphite, on the other hand, is a unique material for the synthesis of a new carbon phase, as reported by the formation of an amorphous diamond by shock compression. Here, we investigate the change of structure of highly oriented pyrolytic graphite (HOPG) irradiated with neutrons to a fluence of 1.4 × 1024 n/m2 under static pressure. The neutron-irradiated HOPG sample was compressed to 15 GPa at room temperature and then the temperature was increased up to 1500 °C. X-ray diffraction, high-resolution transmission electron microscopy on the recovered sample clearly showed the formation of a significant amount of quenchable-CG with ordinary graphite. Formation of hexagonal and cubic diamonds was also confirmed. The effect of irradiation-induced defects on the synthesis of quenchable-CG under high pressure and high temperature treatment was discussed.

A Study on Effect of Graphite Particles on Tensile, Hardness and Machinability of Aluminium 8011 Matrix Material

NASA Astrophysics Data System (ADS)

Latha Shankar, B.; Anil, K. C.; Karabasappagol, Prasann J.

2016-09-01

Industrial application point of view, metal matrix composites in general and Aluminium alloy matrix composites in particular are ideal candidates because of their favourable engineering properties. Being lightweight Aluminium matrix composites are widely used in aircraft, defence and automotive industries. In this work Aluminium 8011 metal matrix was reinforced with fine Graphite particles of 50 μm. developed by two-step Stir casting method. Graphite weight %was varied in the range 2, 4, 6 and 8%. Uniform dispersion of graphite particle is examined under optical microscope. Tensile test coupons were prepared as per standard to determine % of elongation and tensile strength for various % of graphite particle. Hardness of developed composite for various % of graphite particle and Machinability parameters were also studied for effect on surface finish. It was observed that with increase of weight percentage of Graphite particles up to 8% in Aluminium 8011 alloy matrix there was increase in tensile strength, decrease in % of elongation with increase in hardness. Machinability study revealed that, there was decrease in surface roughness with increase in Graphite content.

Enhancement of oxidation resistance of graphite foams by polymer derived-silicon carbide coating for concentrated solar power applications

DOE PAGES

Kim, T.; Singh, D.; Singh, M.

2015-05-01

Graphite foam with extremely high thermal conductivity has been investigated to enhance heat transfer of latent heat thermal energy storage (LHTES) systems. However, the use of graphite foam for elevated temperature applications (>600 °C) is limited due to poor oxidation resistance of graphite. In the present study, oxidation resistance of graphite foam coated with silicon carbide (SiC) was investigated. A pre-ceramic polymer derived coating (PDC) method was used to form a SiC coating on the graphite foams. Post coating deposition, the samples were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The oxidation resistance of PDC-SiC coating was quantifiedmore » by measuring the weight of the samples at several measuring points. The experiments were conducted under static argon atmosphere in a furnace. After the experiments, oxidation rates (%/hour) were calculated to predict the lifetime of the graphite foams. The experimental results showed that the PDC-SiC coating could prevent the oxidation of graphite foam under static argon atmosphere up to 900 °C.« less

Effects of sequential treatment with fluorine and bromine on graphite fibers

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh; Stahl, Mark; Maciag, Carolyn; Slabe, Melissa

1987-01-01

Three pitch based graphite fibers with different degrees of graphitization and one polyacryonitrile (PAN) based carbon fiber from Amoco Corporation were treated with 1 atm, room temperature fluorine gas for 90 hrs. Fluorination resulted in higher electrical conductivity for all pitch fibers. Further bromination after ambient condition defluorination resulted in further increases in electrical defluorination conductivity for less graphitized, less structurally ordered pitch fibers (P-55) which contain about 3% fluorine by weight before bromination. This product can be stable in 200 C air, or 100% humidity at 60 C. Due to its low cost, this less graphitized fiber may be useful for industrial application, such as airfoil deicer materials. The same bromination process, however, resulted in conductivity decreases for fluorine rich, more graphitized, structurally oriented pitch fibers (P-100 and P-75). Such decreases in electrical conductivity were partially reversed by heating the fibers at 185 C in air. Differential scanning calorimetric (DSC) data indicated that the more graphitized fibers (P-100) contained BrF3, whereas the less graphitized fibers (P-55) did not.

Approaches to Deal with Irradiated Graphite in Russia - Proposal for New IAEA CRP on Graphite Waste Management - 12364

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kascheev, Vladimir; Poluektov, Pavel; Ustinov, Oleg

The problems of spent reactor graphite are being shown, the options of its disposal is considered. Burning method is selected as the most efficient and waste-free. It is made a comparison of amounts of {sup 14}C that entering the environment in a natural way during the operation of nuclear power plants (NPPs) and as a result of the proposed burning of spent reactor graphite. It is shown the possibility of burning graphite with the arrival of {sup 14}C into the atmosphere within the maximum allowable emissions. This paper analyzes the different ways of spent reactor graphite treatment. It is shownmore » the possibility of its reprocessing by burning method in the air flow. It is estimated the effect of this technology to the overall radiation environment and compared its contribution to the general background radiation due to cosmic radiation and NPPs emission. It is estimated the maximum permissible speeds of burning reactor graphite (for example, RBMK graphite) for areas with different conditions of agricultural activities. (authors)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng

An electrically conductive laminate composition for fuel cell flow field plate or bipolar plate applications. The laminate composition comprises at least a thin metal sheet having two opposed exterior surfaces and a first exfoliated graphite composite sheet bonded to the first of the two exterior surfaces of the metal sheet wherein the exfoliated graphite composite sheet comprises: (a) expanded or exfoliated graphite and (b) a binder or matrix material to bond the expanded graphite for forming a cohered sheet, wherein the binder or matrix material is between 3% and 60% by weight based on the total weight of the firstmore » exfoliated graphite composite sheet. Preferably, the first exfoliated graphite composite sheet further comprises particles of non-expandable graphite or carbon in the amount of between 3% and 60% by weight based on the total weight of the non-expandable particles and the expanded graphite. Further preferably, the laminate comprises a second exfoliated graphite composite sheet bonded to the second surface of the metal sheet to form a three-layer laminate. Surface flow channels and other desired geometric features can be built onto the exterior surfaces of the laminate to form a flow field plate or bipolar plate. The resulting laminate has an exceptionally high thickness-direction conductivity and excellent resistance to gas permeation.« less

Mineralogical and isotopic characterization of graphite deposits from the Anatectic Complex of Toledo, central Spain

NASA Astrophysics Data System (ADS)

Martín-Méndez, Iván; Boixereu, Ester; Villaseca, Carlos

2016-06-01

Graphite is found dispersed in high-grade metapelitic rocks of the Anatectic Complex of Toledo (ACT) and was mined during the mid twentieth century in places where it has been concentrated (Guadamur and la Puebla de Montalbán mines). Some samples from these mines show variable but significant alteration intensity, reaching very low-T hydrothermal (supergene) conditions for some samples from the waste heap of the Guadamur site (<100 °C and 1 kbar). Micro-Raman and XRD data indicate that all the studied ACT graphite is of high crystallinity irrespective of the degree of hydrothermal alteration. Chemical differences were obtained for graphite δ13C composition. ACT granulitic graphite shows δ13CPDB values in the range of -20.5 to -27.8 ‰, indicating a biogenic origin. Interaction of graphite with hydrothermal fluids does not modify isotopic compositions even in the most transformed samples from mining sites. The different isotopic signatures of graphite from the mining sites reflect its contrasted primary carbon source. The high crystallinity of studied graphite makes this area of central Spain suitable for graphitic exploration and its potential exploitation, due to the low carbon content required for its viability and its strategic applications in advanced technologies, such as graphene synthesis.

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.

Formation, characterization, and dynamics of onion-like carbon structures for electrical energy storage from nanodiamonds using reactive force fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganesh, P.; Kent, P. R. C.; Mochalin, V.

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbonnanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core of themore » nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbonnanostructure appears, with a shell-shell spacing of about ~3.4 Å for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large (~29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

Formation, characterization and dynamics of onion like carbon structures from nanodiamonds using reactive force-fields for electrical energy storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kent, Paul R

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core ofmore » the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

The First Discovery of Presolar Graphite Grains from the Highly Reducing Qingzhen (EH3) Meteorite

NASA Astrophysics Data System (ADS)

Xu, Yuchen; Lin, Yangting; Zhang, Jianchao; Hao, Jialong

2016-07-01

Presolar graphite grains have been extensively studied, but are limited in carbonaceous chondrites, particularly in Murchison (CM2) and Orgueil (CI1), which sampled materials from the oxidizing regions in the solar nebula. Here, we report the first discovery of presolar graphite grains from the Qingzhen (EH3) enstatite chondrite which formed under a highly reducing condition. Eighteen presolar graphite grains were identified by C-isotope mapping of the low-density fraction (1.75-1.85 g cm-3) from Qingzhen acid residue. Another 58 graphite spherules were found in different areas of the same sample mount using a scanning electron microscope and were classified into three morphologies, including cauliflower, onion, and cauliflower-onion. The Raman spectra of these spherules vary from ordered, disordered, and glassy to kerogen-like, suggestive of a wide range of thermal metamorphisms. NanoSIMS analysis of the C- and Si-isotopes of these graphite spherules confirmed 23 presolar grains. The other 35 graphite spherules have no significant isotopic anomalies, but they share similar morphologies and Raman spectra with the presolar ones. Another three grains were identified during NanoSIMS analysis. Of all the 44 presolar graphite grains identified, six grains show 28Si-excesses, suggestive of supernovae origins, and four grains are 12C- and 29,30Si-rich, consistent with low-metallicity asymptotic giant branch star origins. Another two graphite spherules have extremely low 12C/13C ratios with marginal solar Si-isotopes. The morphologies, Raman spectra, and C- and Si-isotopic distributions of the presolar graphite grains from the Qingzhen enstatite chondrite are similar to those of the low-density fractions from Murchison carbonaceous chondrites. This study suggests a homogeneous distribution of presolar graphite grains in the solar nebula.

Density functional theory study the effects of oxygen-containing functional groups on oxygen molecules and oxygen atoms adsorbed on carbonaceous materials.

PubMed

Qi, Xuejun; Song, Wenwu; Shi, Jianwei

2017-01-01

Density functional theory was used to study the effects of different types of oxygen-containing functional groups on the adsorption of oxygen molecules and single active oxygen atoms on carbonaceous materials. During gasification or combustion reactions of carbonaceous materials, oxygen-containing functional groups such as hydroxyl(-OH), carbonyl(-CO), quinone(-O), and carboxyl(-COOH) are often present on the edge of graphite and can affect graphite's chemical properties. When oxygen-containing functional groups appear on a graphite surface, the oxygen molecules are strongly adsorbed onto the surface to form a four-member ring structure. At the same time, the O-O bond is greatly weakened and easily broken. The adsorption energy value indicates that the adsorption of oxygen molecules changes from physisorption to chemisorption for oxygen-containing functional groups on the edge of a graphite surface. In addition, our results indicate that the adsorption energy depends on the type of oxygen-containing functional group. When a single active oxygen atom is adsorbed on the bridge site of graphite, it gives rise to a stable epoxy structure. Epoxy can cause deformation of the graphite lattice due to the transition of graphite from sp2 to sp3 after the addition of an oxygen atom. For quinone group on the edge of graphite, oxygen atoms react with carbon atoms to form the precursor of CO2. Similarly, the single active oxygen atoms of carbonyl groups can interact with edge carbon atoms to form the precursor of CO2. The results show that oxygen-containing functional groups on graphite surfaces enhance the activity of graphite, which promotes adsorption on the graphite surface.

Ultrastructural and geochemical characterization of Archean-Paleoproterozoic graphite particles: implications for recognizing traces of life in highly metamorphosed rocks.

PubMed

Schiffbauer, James D; Yin, Leiming; Bodnar, Robert J; Kaufman, Alan J; Meng, Fanwei; Hu, Jie; Shen, Bing; Yuan, Xunlai; Bao, Huiming; Xiao, Shuhai

2007-08-01

Abundant graphite particles occur in amphibolite-grade quartzite of the Archean-Paleoproterozoic Wutai Metamorphic Complex in the Wutaishan area of North China. Petrographic thin section observations suggest that the graphite particles occur within and between quartzite clasts and are heterogeneous in origin. Using HF maceration techniques, the Wutai graphite particles were extracted for further investigation. Laser Raman spectroscopic analysis of a population of extracted graphite discs indicated that they experienced a maximum metamorphic temperature of 513 +/- 50 degrees C, which is consistent with the metamorphic grade of the host rock and supports their indigenicity. Scanning and transmission electron microscopy revealed that the particles bear morphological features (such as hexagonal sheets of graphite crystals) related to metamorphism and crystal growth, but a small fraction of them (graphite discs) are characterized by a circular morphology, distinct marginal concentric folds, surficial wrinkles, and complex nanostructures. Ion microprobe analysis of individual graphite discs showed that their carbon isotope compositions range from -7.4 per thousand to -35.9 per thousand V-PDB (Vienna Pee Dee Belemnite), with an average of -20.3 per thousand, which is comparable to bulk analysis of extracted carbonaceous material. The range of their size, ultrastructures, and isotopic signatures suggests that the morphology and geochemistry of the Wutai graphite discs were overprinted by metamorphism and their ultimate carbon source probably had diverse origins that included abiotic processes. We considered both biotic and abiotic origins of the carbon source and graphite disc morphologies and cannot falsify the possibility that some circular graphite discs characterized by marginal folds and surficial wrinkles represent deflated, compressed, and subsequently graphitized organic-walled vesicles. Together with reports by other authors of acanthomorphic acritarchs from greenschist-amphibolite-grade metamorphic rocks, this study suggests that it is worthwhile to examine carbonaceous materials preserved in highly metamorphosed rocks for possible evidence of ancient life.

Synthesis of soluble graphite and graphene.

PubMed

Kelly, K F; Billups, W E

2013-01-15

Because of graphene's anticipated applications in electronics and its thermal, mechanical, and optical properties, many scientists and engineers are interested in this material. Graphene is an isolated layer of the π-stacked hexagonal allotrope of carbon known as graphite. The interlayer cohesive energy of graphite, or exfoliation energy, that results from van der Waals attractions over the interlayer spacing distance of 3.34 Å (61 meV/C atom) is many times weaker than the intralayer covalent bonding. Since graphene itself does not occur naturally, scientists and engineers are still learning how to isolate and manipulate individual layers of graphene. Some researchers have relied on the physical separation of the sheets, a process that can sometimes be as simple as peeling of sheets from crystalline graphite using Scotch tape. Other researchers have taken an ensemble approach, where they exploit the chemical conversion of graphite to the individual layers. The typical intermediary state is graphite oxide, which is often produced using strong oxidants under acidic conditions. Structurally, researchers hypothesize that acidic functional groups functionalize the oxidized material at the edges and a network of epoxy groups cover the sp(2)-bonded carbon network. The exfoliated material formed under these conditions can be used to form dispersions that are usually unstable. However, more importantly, irreversible defects form in the basal plane during oxidation and remain even after reduction of graphite oxide back to graphene-like material. As part of our interest in the dissolution of carbon nanomaterials, we have explored the derivatization of graphite following the same procedures that preserve the sp(2) bonding and the associated unique physical and electronic properties in the chemical processing of single-walled carbon nanotubes. In this Account, we describe efficient routes to exfoliate graphite either into graphitic nanoparticles or into graphene without resorting to oxidation. Our exfoliation process involves the intercalation of lithium into bulk graphite to yield graphene sheets reduced by the lithium. We can alkylate the resulting graphite salt reductively using solubilizing dodecyl groups. By probe microscopy, we show that these groups are attached covalently only at the graphitic edges.

Ion irradiation to simulate neutron irradiation in model graphites: Consequences for nuclear graphite

NASA Astrophysics Data System (ADS)

Galy, N.; Toulhoat, N.; Moncoffre, N.; Pipon, Y.; Bérerd, N.; Ammar, M. R.; Simon, P.; Deldicque, D.; Sainsot, P.

2017-10-01

Due to its excellent moderator and reflector qualities, graphite was used in CO2-cooled nuclear reactors such as UNGG (Uranium Naturel-Graphite-Gaz). Neutron irradiation of graphite resulted in the production of 14C which is a key issue radionuclide for the management of the irradiated graphite waste. In order to elucidate the impact of neutron irradiation on 14C behavior, we carried out a systematic investigation of irradiation and its synergistic effects with temperature in Highly Oriented Pyrolitic Graphite (HOPG) model graphite used to simulate the coke grains of nuclear graphite. We used 13C implantation in order to simulate 14C displaced from its original structural site through recoil. The collision of the impinging neutrons with the graphite matrix carbon atoms induces mainly ballistic damage. However, a part of the recoil carbon atom energy is also transferred to the graphite lattice through electronic excitation. The effects of the different irradiation regimes in synergy with temperature were simulated using ion irradiation by varying Sn(nuclear)/Se(electronic) stopping power. Thus, the samples were irradiated with different ions of different energies. The structure modifications were followed by High Resolution Transmission Electron Microscopy (HRTEM) and Raman microspectrometry. The results show that temperature generally counteracts the disordering effects of irradiation but the achieved reordering level strongly depends on the initial structural state of the graphite matrix. Thus, extrapolating to reactor conditions, for an initially highly disordered structure, irradiation at reactor temperatures (200 - 500 °C) should induce almost no change of the initial structure. On the contrary, when the structure is initially less disordered, there should be a "zoning" of the reordering: In "cold" high flux irradiated zones where the ballistic damage is important, the structure should be poorly reordered; In "hot" low flux irradiated zones where the ballistic impact is lower and can therefore be counteracted by temperature, a better reordering of the structure should be achieved. Concerning 14C, except when located close to open pores where it can be removed through radiolytic corrosion, it tends to stabilize in the graphite matrix into sp2 or sp3 structures with variable proportions depending on the irradiation conditions.

Wear mechanisms in hybrid composites of Graphite-20 Pct SiC in A356 Aluminum Alloy (Al-7 Pct Si-0.3 Pct Mg)

NASA Astrophysics Data System (ADS)

Ames, W.; Alpas, A. T.

1995-01-01

The wear behavior of A356 aluminum alloy (Al-7 Pct Si-0.3 Pct Mg) matrix composites reinforced with 20 vol Pct SiC particles and 3 or 10 vol Pct graphite was investigated. These hybrid composites represent the merging of two philosophies in tribological material design: soft-particle lubrication by graphite and hard-particle reinforcement by carbide particles. The wear tests were performed using a block-on-ring (SAE 52100 steel) wear machine under dry sliding conditions within a load range of 1 to 441 N. The microstructural and compositional changes that took place during wear were characterized using scanning electron microscopy (SEM), Auger electron spectroscopy (AES), energy-dispersive X-ray spectroscopy (EDXA), and X-ray diffractometry (XRD). The wear resistance of 3 Pct graphite-20 Pct SiC-A356 hybrid composite was comparable to 20 Pct SiC-A356 without graphite at low and medium loads. At loads below 20 N, both hybrid and 20 Pct SiC-A356 composites without graphite demonstrated wear rates up to 10 times lower than the unreinforced A356 alloy due to the load-carrying capacity of SiC particles. The wear resistance of 3 Pct graphite 20 Pct SiC-A356 was 1 to 2 times higher than 10 Pct graphite-containing hybrid composites at high loads. However, graphite addition reduced the counterface wear. The unreinforced A356 and 20 Pct SiC-A356 showed a transition from mild to severe wear at 95 N and 225 N, respectively. Hybrid composites with 3 Pct and 10 Pct graphite did not show such a transition over the entire load range, indicating that graphite improved the seizure resistance of the composites. Tribolayers, mainly consisting of a compacted mixture of graphite, iron oxides, and aluminum, were generated on the surfaces of the hybrid composites. In the hybrid composites, the elimination of the severe wear (and hence the improvement in seizure resistance) was attributed to the reduction in friction-induced surface heating due to the presence of graphite- and iron-oxide-containing tribolayers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carroll, Mark C.

High-purity graphite is the core structural material of choice in the Very High Temperature Reactor (VHTR) design, a graphite-moderated, helium-cooled configuration capable of producing thermal energy for power generation as well as process heat for industrial applications that require temperatures higher than the outlet temperatures of present nuclear reactors. The Baseline Graphite Characterization Program is establishing accurate as-manufactured mechanical and physical property distributions in nuclear-grade graphites by providing comprehensive data that captures the level of variation in measured values. In addition to providing a thorough comparison between these values in different graphite grades, the program is also carefully tracking individualmore » specimen source, position, and orientation information in order to provide comparisons both in specific properties and in the associated variability between different lots, different billets, and different positions from within a single billet. This report is a preliminary comparison between each of the grades of graphite that are considered “candidate” grades from four major international graphite producers. These particular grades (NBG-18, NBG-17, PCEA, IG-110, and 2114) are the major focus of the evaluations presently underway on irradiated graphite properties through the series of Advanced Graphite Creep (AGC) experiments. NBG-18, a medium-grain pitch coke graphite from SGL from which billets are formed via vibration molding, was the favored structural material in the pebble-bed configuration. NBG-17 graphite from SGL is essentially NBG-18 with the grain size reduced by a factor of two. PCEA, petroleum coke graphite from GrafTech with a similar grain size to NBG-17, is formed via an extrusion process and was initially considered the favored grade for the prismatic layout. IG-110 and 2114, from Toyo Tanso and Mersen (formerly Carbone Lorraine), respectively, are fine-grain grades produced via an isomolding process. An analysis of the comparison between each of these grades will include not only the differences in fundamental and statistically-significant individual strength levels, but also the differences in the overall variability in properties within each of the grades that will ultimately provide the basis for predicting in-service performance. The comparative performance of the different types of nuclear-grade graphites will naturally continue to evolve as thousands more specimens are fully characterized with regard to strength, physical properties, and thermal performance from the numerous grades of graphite being evaluated.« less

Isotropic source terms of San Jacinto fault zone earthquakes based on waveform inversions with a generalized CAP method

NASA Astrophysics Data System (ADS)

Ross, Z. E.; Ben-Zion, Y.; Zhu, L.

2015-02-01

We analyse source tensor properties of seven Mw > 4.2 earthquakes in the complex trifurcation area of the San Jacinto Fault Zone, CA, with a focus on isotropic radiation that may be produced by rock damage in the source volumes. The earthquake mechanisms are derived with generalized `Cut and Paste' (gCAP) inversions of three-component waveforms typically recorded by >70 stations at regional distances. The gCAP method includes parameters ζ and χ representing, respectively, the relative strength of the isotropic and CLVD source terms. The possible errors in the isotropic and CLVD components due to station variability is quantified with bootstrap resampling for each event. The results indicate statistically significant explosive isotropic components for at least six of the events, corresponding to ˜0.4-8 per cent of the total potency/moment of the sources. In contrast, the CLVD components for most events are not found to be statistically significant. Trade-off and correlation between the isotropic and CLVD components are studied using synthetic tests with realistic station configurations. The associated uncertainties are found to be generally smaller than the observed isotropic components. Two different tests with velocity model perturbation are conducted to quantify the uncertainty due to inaccuracies in the Green's functions. Applications of the Mann-Whitney U test indicate statistically significant explosive isotropic terms for most events consistent with brittle damage production at the source.

Method of making segmented pyrolytic graphite sputtering targets

DOEpatents

McKernan, M.A.; Alford, C.S.; Makowiecki, D.M.; Chen, C.W.

1994-02-08

Anisotropic pyrolytic graphite wafers are oriented and bonded together such that the graphite's high thermal conductivity planes are maximized along the back surface of the segmented pyrolytic graphite target to allow for optimum heat conduction away from the sputter target's sputtering surface and to allow for maximum energy transmission from the target's sputtering surface. 2 figures.

Applications Of Graphite Fluoride Fibers In Outer Space

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheng; Long, Martin; Dever, Therese

1993-01-01

Report characterizes graphite fluoride fibers made from commercially available graphitized carbon fibers and discusses some potential applications of graphite fluoride fibers in outer space. Applications include heat-sinking printed-circuit boards, solar concentrators, and absorption of radar waves. Other applications based on exploitation of increased resistance to degradation by atomic oxygen, present in low orbits around Earth.

Separation medium containing thermally exfoliated graphite oxide

NASA Technical Reports Server (NTRS)

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

2012-01-01

A separation medium, such as a chromatography filling or packing, containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m.sup.2/g to 2600 m.sup.2/g, wherein the thermally exfoliated graphite oxide has a surface that has been at least partially functionalized.

Hybridized polymer matrix composite

NASA Technical Reports Server (NTRS)

Stern, B. A.; Visser, T.

1981-01-01

Under certain conditions of combined fire and impact, graphite fibers are released to the atmosphere by graphite fiber composites. The retention of graphite fibers in these situations is investigated. Hybrid combinations of graphite tape and cloth, glass cloth, and resin additives are studied with resin systems. Polyimide resins form the most resistant composites and resins based on simple novolac epoxies the least resistant of those tested. Great improvement in the containment of the fibers is obtained in using graphite/glass hybrids, and nearly complete prevention of individual fiber release is made possible by the use of resin additives.

Method of fabricating graphite for use as a skeletal prosthesis and product thereof

DOEpatents

Eatherly, Walter P.; Robbins, J. M.; Rosson, Sr., David E.

1978-01-01

A method for producing porous graphite for use as bone replacement with a structure for osteon penetration. Graphite is produced with ordered circular pores of 100 to 1000 microns in diameter covering at least 25% of the exposed surfaces. A cylindrical fiber is coated with a carbon flour-pitch mix and is then wound on a bobbin in a predetermined manner. The product of winding is dried, pressed, carbonized, and then graphitized. The fibers are removed either chemically or by volatilization during carbonization or graphitization.

Infrared signal generation from AC induction field heating of graphite foam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klett, James W.; Rios, Orlando

A magneto-energy apparatus includes an electromagnetic field source for generating a time-varying electromagnetic field. A graphite foam conductor is disposed within the electromagnetic field. The graphite foam when exposed to the time-varying electromagnetic field conducts an induced electric current, the electric current heating the graphite foam to produce light. An energy conversion device utilizes light energy from the heated graphite foam to perform a light energy consuming function. A device for producing light and a method of converting energy are also disclosed.

Effect of fluroine content, atmosphere, and burnishing technique on the lubricating properties of graphite fluoride

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1974-01-01

Eight different graphite fluoride compounds with fluorine to carbon ratios varying from x = 0.25 to 1.1 were evaluated as burnished films in order to determine the effect of fluorine content on the solid lubricant properties of graphite fluoride. For comparison, similar experiments were conducted on graphite burnished films. It was found that even a small amount of fluorine in graphite fluoride (CF0.25)n improved the lubricating properties of graphite. However, such factors as burnishing atmosphere, burnishing technique, test atmosphere, and specimen temperature affected the results as much as varying the fluorine to carbon ratio of the compound. Best life was found for films that were machined burnished in moist air and tested in moist air.

Graphite fluoride lubrication: The effect of fluorine content, atmosphere, and burnishing technique

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1975-01-01

Eight different graphite fluoride compounds with fluorine to carbon ratios varying from x = 0.25 to 1.1 were evaluated as burnished films in order to determine the effect of fluorine content on the solid lubricant properties of graphite fluoride. For comparison, similar experiments were conducted on graphite burnished films. It was found that even a small amount of fluorine in graphite fluoride (CF sub 0.25) sub n improved the lubricating properties of graphite. Such factors as burnishing atmosphere, burnishing technique, test atmosphere, and specimen temperature affected the results as much as varying the fluorine to carbon ratio of the compound. Best life was found for films that were machine-burnished in moist air and tested in moist air.

Synthesis of graphene nanoflakes by grinding natural graphite together with NaCl in a planetary ball mill

NASA Astrophysics Data System (ADS)

Alinejad, Babak; Mahmoodi, Korosh

Natural graphite is a soft material that conventional milling methods fail to grind into nanoparticles. We found that adding NaCl into graphite during milling allows obtaining graphene nanoflakes of about 50×200nm2 as evidenced by Transmission Electron Microscope (TEM). NaCl particles are substantially brittle and harder than graphite, serving as milling agents by both helping to chop graphite into smaller pieces and preventing graphite particles from agglomeration. After milling, NaCl can be easily washed away by water. Probable mechanism for exfoliation of graphene during the modified ball milling may be explained by NaCl and graphene slipping or sliding against and over each other, exfoliating the graphene particles into thin layers.

Scaling effects in the static and dynamic response of graphite-epoxy beam-columns. Ph.D. Thesis - Virginia Polytechnic Inst. and State Univ.

NASA Technical Reports Server (NTRS)

Jackson, Karen E.

1990-01-01

Scale model technology represents one method of investigating the behavior of advanced, weight-efficient composite structures under a variety of loading conditions. It is necessary, however, to understand the limitations involved in testing scale model structures before the technique can be fully utilized. These limitations, or scaling effects, are characterized. in the large deflection response and failure of composite beams. Scale model beams were loaded with an eccentric axial compressive load designed to produce large bending deflections and global failure. A dimensional analysis was performed on the composite beam-column loading configuration to determine a model law governing the system response. An experimental program was developed to validate the model law under both static and dynamic loading conditions. Laminate stacking sequences including unidirectional, angle ply, cross ply, and quasi-isotropic were tested to examine a diversity of composite response and failure modes. The model beams were loaded under scaled test conditions until catastrophic failure. A large deflection beam solution was developed to compare with the static experimental results and to analyze beam failure. Also, the finite element code DYCAST (DYnamic Crash Analysis of STructure) was used to model both the static and impulsive beam response. Static test results indicate that the unidirectional and cross ply beam responses scale as predicted by the model law, even under severe deformations. In general, failure modes were consistent between scale models within a laminate family; however, a significant scale effect was observed in strength. The scale effect in strength which was evident in the static tests was also observed in the dynamic tests. Scaling of load and strain time histories between the scale model beams and the prototypes was excellent for the unidirectional beams, but inconsistent results were obtained for the angle ply, cross ply, and quasi-isotropic beams. Results show that valuable information can be obtained from testing on scale model composite structures, especially in the linear elastic response region. However, due to scaling effects in the strength behavior of composite laminates, caution must be used in extrapolating data taken from a scale model test when that test involves failure of the structure.

HF/H2O2 treated graphite felt as the positive electrode for vanadium redox flow battery

NASA Astrophysics Data System (ADS)

He, Zhangxing; Jiang, Yingqiao; Meng, Wei; Jiang, Fengyun; Zhou, Huizhu; Li, Yuehua; Zhu, Jing; Wang, Ling; Dai, Lei

2017-11-01

In order to improve the electrochemical performance of the positive graphite felt electrode in vanadium flow redox battery, a novel method is developed to effectively modify the graphite felt by combination of etching of HF and oxidation of H2O2. After the etching of HF for the graphite felt at ambient temperature, abundant oxygen-containing functional groups were further introduced on the surface of graphite felt by hydrothermal treatment using H2O2 as oxidant. Benefiting from the surface etching and introduction of functional groups, mass transfer and electrode process can be improved significantly on the surface of graphite felt. VO2+/VO2+ redox reaction on the graphite felt modified by HF and H2O2 jointly (denote: GF-HF/H2O2) exhibits superior electrochemical kinetics in comparison with the graphite felt modified by single HF or H2O2 treatment. The cell using GF-HF/H2O2 as the positive electrode was assembled and its electrochemical properties were evaluated. The increase of energy efficiency of 4.1% for GF-HF/H2O2 at a current density of 50 mA cm-2 was obtained compared with the pristine graphite felt. The cell using GF-HF/H2O2 also demonstrated higher discharge capacity. Our study revealed that HF/H2O2 treatment is an efficient method to enhance the electrochemical performance of graphite felt, further improving the comprehensive energy storage performance of the vanadium flow redox battery.

X-ray Analysis of Defects and Anomalies in AGR-5/6/7 TRISO Particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmreich, Grant W.; Hunn, John D.; Skitt, Darren J.

2017-06-01

Coated particle fuel batches J52O-16-93164, 93165, 93166, 93168, 93169, 93170, and 93172 were produced by Babcock and Wilcox Technologies (BWXT) for possible selection as fuel for the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program’s AGR-5/6/7 irradiation test in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR), or may be used for other tests. Each batch was coated in a 150-mm-diameter production-scale fluidized-bed chemical vapor deposition (CVD) furnace. Tristructural isotropic (TRISO) coatings were deposited on 425-μm-nominal-diameter spherical kernels from BWXT lot J52R-16-69317 containing a mixture of 15.4%-enriched uranium carbide and uranium oxide (UCO), with the exception of Batchmore » 93164, which used similar kernels from BWXT lot J52L-16-69316. The TRISO-coatings consisted of a ~50% dense carbon buffer layer with 100-μmnominal thickness, a dense inner pyrolytic carbon (IPyC) layer with 40-μm-nominal thickness, a silicon carbide (SiC) layer with 35-μm-nominal thickness, and a dense outer pyrolytic carbon (OPyC) layer with 40-μm-nominal thickness. Each coated particle batch was sieved to upgrade the particles by removing over-sized and under-sized material, and the upgraded batch was designated by appending the letter A to the end of the batch number (e.g., 93164A). Secondary upgrading by sieving was performed on the upgraded batches to remove specific anomalies identified during analysis for Defective IPyC, and the upgraded batches were designated by appending the letter B to the end of the batch number (e.g., 93165B). Following this secondary upgrading, coated particle composite J52R-16-98005 was produced by BWXT as fuel for the AGR Program’s AGR-5/6/7 irradiation test in the INL ATR. This composite was comprised of coated particle fuel batches J52O-16-93165B, 93168B, 93169B, and 93170B.« less

Acceptance Test Data for the AGR-5/6/7 Irradiation Test Fuel Composite Defective IPyC Fraction and Pyrocarbon Anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmreich, Grant W.; Hunn, John D.; Skitt, Darren J.

Coated particle composite J52R-16-98005 was produced by Babcock and Wilcox Technologies (BWXT) as fuel for the Advanced Gas Reactor Fuel Development and Qualification (AGR) Program’s AGR-5/6/7 irradiation test in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR). This composite was comprised of four coated particle fuel batches J52O-16-93165B (26%), 93168B (26%), 93169B (24%), and 93170B (24%), chosen based on the Quality Control (QC) data acquired for each individual candidate AGR-5/6/7 batch. Each batch was coated in a 150-mm-diameter production-scale fluidized-bed chemical vapor deposition (CVD) furnace. Tristructural isotropic (TRISO) coatings were deposited on 425-μm-nominal-diameter spherical kernels from BWXT Lot J52R-16-69317more » containing a mixture of 15.5%-enriched uranium carbide and uranium oxide (UCO). The TRISO coatings consisted of four consecutive CVD layers: a ~50% dense carbon buffer layer with 100-μm-nominal thickness, a dense inner pyrolytic carbon (IPyC) layer with 40-μm-nominal thickness, a silicon carbide (SiC) layer with 35-μm-nominal thickness, and a dense outer pyrolytic carbon (OPyC) layer with 40-μm-nominal thickness. The TRISO-coated particle batches were sieved to upgrade the particles by removing over-sized and under-sized material, and the upgraded batches were designated by appending the letter A to the end of the batch number (e.g., 93165A). Secondary upgrading by sieving was performed on the A-designated batches to remove particles with missing or very-thin buffer layers that were identified during previous analysis of the individual batches for defective IPyC, as reported in the acceptance test data report for the AGR-5/6/7 production batches [Hunn et al. 2017]. The additionally-upgraded batches were designated by appending the letter B to the end of the batch number (e.g., 93165B).« less

Approximate isotropic cloak for the Maxwell equations

NASA Astrophysics Data System (ADS)

Ghosh, Tuhin; Tarikere, Ashwin

2018-05-01

We construct a regular isotropic approximate cloak for the Maxwell system of equations. The method of transformation optics has enabled the design of electromagnetic parameters that cloak a region from external observation. However, these constructions are singular and anisotropic, making practical implementation difficult. Thus, regular approximations to these cloaks have been constructed that cloak a given region to any desired degree of accuracy. In this paper, we show how to construct isotropic approximations to these regularized cloaks using homogenization techniques so that one obtains cloaking of arbitrary accuracy with regular and isotropic parameters.

Sudden Relaminarization and Lifetimes in Forced Isotropic Turbulence.

PubMed

Linkmann, Moritz F; Morozov, Alexander

2015-09-25

We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from a chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase superexponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.

Analytical close-to-source investigation for an isotropic point source in an unbounded, anisotropically scattering medium

NASA Astrophysics Data System (ADS)

Rinzema, Kees; ten Bosch, Jaap J.; Ferwerda, Hedzer A.; Hoenders, Bernhard J.

1995-01-01

The diffusion approximation, which is often used to describe the propagation of light in biological tissues, is only good at a sufficient distance from sources and boundaries. Light- tissue interaction is however most intense in the region close to the source. It would therefore be interesting to study this region more closely. Although scattering in biological tissues is predominantly forward peaked, explicit solutions to the transport equation have only been obtained in the case of isotropic scattering. Particularly, for the case of an isotropic point source in an unbounded, isotropically scattering medium the solution is well known. We show that this problem can also be solved analytically if the scattering is no longer isotropic, while everything else remains the same.

Estimation of transversely isotropic material properties from magnetic resonance elastography using the optimised virtual fields method.

PubMed

Miller, Renee; Kolipaka, Arunark; Nash, Martyn P; Young, Alistair A

2018-03-12

Magnetic resonance elastography (MRE) has been used to estimate isotropic myocardial stiffness. However, anisotropic stiffness estimates may give insight into structural changes that occur in the myocardium as a result of pathologies such as diastolic heart failure. The virtual fields method (VFM) has been proposed for estimating material stiffness from image data. This study applied the optimised VFM to identify transversely isotropic material properties from both simulated harmonic displacements in a left ventricular (LV) model with a fibre field measured from histology as well as isotropic phantom MRE data. Two material model formulations were implemented, estimating either 3 or 5 material properties. The 3-parameter formulation writes the transversely isotropic constitutive relation in a way that dissociates the bulk modulus from other parameters. Accurate identification of transversely isotropic material properties in the LV model was shown to be dependent on the loading condition applied, amount of Gaussian noise in the signal, and frequency of excitation. Parameter sensitivity values showed that shear moduli are less sensitive to noise than the other parameters. This preliminary investigation showed the feasibility and limitations of using the VFM to identify transversely isotropic material properties from MRE images of a phantom as well as simulated harmonic displacements in an LV geometry. Copyright © 2018 John Wiley & Sons, Ltd.

Selecting the Best Graphite for Long-Life, High-Energy Li-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Chengyu; Wood, Marissa; David, Lamuel Abraham

Here, most lithium-ion batteries still rely on intercalation-type graphite materials for anodes, so it is important to consider their role in full cells for applications in electric vehicles. Here, we systematically evaluate the chemical and physical properties of six commercially-available natural and synthetic graphites to establish which factors have the greatest impact on the cycling stability of full cells with nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes. Electrochemical data and post-mortem characterization explain the origin of capacity fade. The NMC811 cathode shows large irreversible capacity loss and impedance growth, accounting for much of full cell degradation. However, six graphite anodes demonstrate significant differencesmore » with respect to structural change, surface area, impedance growth, and SEI chemistry, which impact overall capacity retention. We found long cycle life correlated most strongly with stable graphite crystallite size. In addition, graphites with lower surface area generally had higher coulombic efficiencies during formation cycles, which led to more stable long-term cycling. The best graphite screened here enables a capacity retention around 90% in full pouch cells over extensive long-term cycling compared to only 82% for cells with the lowest performing graphite. The results show that optimal graphite selection improves cycling stability of high energy lithium-ion cells.« less

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

NASA Astrophysics Data System (ADS)

Johns, Steve; Shin, Wontak; Kane, Joshua J.; Windes, William E.; Ubic, Rick; Karthik, Chinnathambi

2018-07-01

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. To ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ∼60 μm. Discs 3 mm in diameter were then oxidized at temperatures between 575 °C and 625 °C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575 °C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.

Comparison of reduction products from graphite oxide and graphene oxide for anode applications in lithium-ion batteries and sodium-ion batteries.

PubMed

Sun, Yige; Tang, Jie; Zhang, Kun; Yuan, Jinshi; Li, Jing; Zhu, Da-Ming; Ozawa, Kiyoshi; Qin, Lu-Chang

2017-02-16

Hydrazine-reduced graphite oxide and graphene oxide were synthesized to compare their performances as anode materials in lithium-ion batteries and sodium-ion batteries. Reduced graphite oxide inherits the layer structure of graphite, with an average spacing between neighboring layers (d-spacing) of 0.374 nm; this exceeds the d-spacing of graphite (0.335 nm). The larger d-spacing provides wider channels for transporting lithium ions and sodium ions in the material. We showed that reduced graphite oxide as an anode in lithium-ion batteries can reach a specific capacity of 917 mA h g -1 , which is about three times of 372 mA h g -1 , the value expected for the LiC 6 structures on the electrode. This increase is consistent with the wider d-spacing, which enhances lithium intercalation and de-intercalation on the electrodes. The electrochemical performance of the lithium-ion batteries and sodium-ion batteries with reduced graphite oxide anodes show a noticeable improvement compared to those with reduced graphene oxide anodes. This improvement indicates that reduced graphite oxide, with larger interlayer spacing, has fewer defects and is thus more stable. In summary, we found that reduced graphite oxide may be a more favorable form of graphene for the fabrication of electrodes for lithium-ion and sodium-ion batteries and other energy storage devices.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johns, Steve; Shin, Wontak; Kane, Joshua J.

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

Carbon isotope geochemistry of graphite vein deposits from New Hampshire, U.S.A.

NASA Astrophysics Data System (ADS)

Rumble, Douglas, III; Hoering, Thomas C.

1986-06-01

Graphite veins of hydrothermal origin occur throughout central New Hampshire. Veins truncate sillimanite-grade, metasedimentary rocks of Early Devonian-Silurian age and range in size from microscopic to meters in thickness. In addition to graphite, veins may contain quartz, tourmaline, ilmenite, rutile, sillimanite, muscovite or chlorite. Vein mineralogy is generally compatible with wall rock mineral assemblages. Mineralization structures include wall-rock alteration zones, coxcomb graphite crystals on vein walls, and botryoidal, concentrically layered graphite-silicate nodules. The δ13C values of graphite in 14 deposits studied range from - 28%. (PDB) to - 9%. Veins whose textures give evidence of a single stage of mineralization have a narrow range of δ13C values (± 0.2%.). Other veins record successive episodes of graphite precipitation and have ranges of 3-6%. In one sample, adjacent layers of graphite differ by 3%. The wide range of δ13C may be explained by mixing carbon from two crustal reservoirs: biogenic, reduced carbon and carbonate. Precipitation of graphite results from mixing two or more aqueous fluids with different CO 2/CH 4 ratios. Parental fluids are produced by devolatilization during metamorphism. Water-rich fluids with CH4 > CO2 and low δ13C are derived from pelites that contained organic matter; whereas fluids with CO2 > CH4 and high δ13C come from siliceous carbonates.

Selecting the Best Graphite for Long-Life, High-Energy Li-Ion Batteries

DOE PAGES

Mao, Chengyu; Wood, Marissa; David, Lamuel Abraham; ...

2018-06-16

Here, most lithium-ion batteries still rely on intercalation-type graphite materials for anodes, so it is important to consider their role in full cells for applications in electric vehicles. Here, we systematically evaluate the chemical and physical properties of six commercially-available natural and synthetic graphites to establish which factors have the greatest impact on the cycling stability of full cells with nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes. Electrochemical data and post-mortem characterization explain the origin of capacity fade. The NMC811 cathode shows large irreversible capacity loss and impedance growth, accounting for much of full cell degradation. However, six graphite anodes demonstrate significant differencesmore » with respect to structural change, surface area, impedance growth, and SEI chemistry, which impact overall capacity retention. We found long cycle life correlated most strongly with stable graphite crystallite size. In addition, graphites with lower surface area generally had higher coulombic efficiencies during formation cycles, which led to more stable long-term cycling. The best graphite screened here enables a capacity retention around 90% in full pouch cells over extensive long-term cycling compared to only 82% for cells with the lowest performing graphite. The results show that optimal graphite selection improves cycling stability of high energy lithium-ion cells.« less

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE PAGES

Johns, Steve; Shin, Wontak; Kane, Joshua J.; ...

2018-04-03

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

One-step solvothermal synthesis of magnetic Fe3O4-graphite composite for Fenton-like degradation of levofloxacin.

PubMed

Wang, Long; Zhao, Qi; Hou, Juan; Yan, Jin; Zhang, Fengshuang; Zhao, Jiahui; Ding, Hong; Li, Yi; Ding, Lan

2016-01-01

A novel Fe3O4-graphite composite was prepared, characterized, and investigated as a heterogeneous Fenton-like catalyst for the degradation of levofloxacin (LEV) in an aqueous solution. The results revealed that the Fe3O4-graphite composite exhibited excellent properties for the degradation and mineralization of LEV, achieving a nearly complete degradation of 50 mg L(-1) LEV in 15 min and 48% of total organic carbon removal in 60 min under optimal conditions. A large electronic conjugation structure exists in graphite, which may lead to the fast production of •OH radical species because of the easy reduction of Fe(III) to Fe(II). In addition, we observed that the graphite can degrade LEV in the presence of H2O2. Therefore, the synergistic results of the graphite structure and Fe3O4 magnetic nanoparticles (MNPs) may contribute to the high catalytic activity of the Fe3O4-graphite composite. Compared with pure Fe3O4 MNPs, lesser iron leaching of the Fe3O4-graphite composite was observed during the degradation of LEV. The degradation efficiency of LEV remained approximately 80% at the fifth recycling run, which indicates that the Fe3O4-graphite composite has potential applications in water treatment for removing organic pollutants.

Surface-reconstructed graphite nanofibers as a support for cathode catalysts of fuel cells.

PubMed

Gan, Lin; Du, Hongda; Li, Baohua; Kang, Feiyu

2011-04-07

Graphite nanofibers (GNFs), on which surface graphite edges were reconstructed into nano-loops, were explored as a cathode catalyst support for fuel cells. The high degree of graphitization, as well as the surface-reconstructed nano-loops that possess topological defects for uniform metal deposition, resulted in an improved performance of the GNF-supported Pt catalyst.

Preparation of graphite dispersed copper composite with intruding graphite particles in copper plate

NASA Astrophysics Data System (ADS)

Noor, Abdul Muizz Mohd; Ishikawa, Yoshikazu; Yokoyama, Seiji

2017-01-01

In this study, it was attempted that copper-graphite composite was prepared locally on the surface of a copper plate with using a spot welding machine. Experiments were carried out with changing the compressive load, the repetition number of the compression and the electrical current in order to study the effect of them on carbon content and Vickers hardness on the copper plate surface. When the graphite was pushed into copper plate only with the compressive load, the composite was mainly hardened by the work hardening. The Vickers hardness increased linearly with an increase in the carbon content. When an electrical current was energized through the composite at the compression, the copper around the graphite particles were heated to the temperature above approximately 2100 K and melted. The graphite particles partially or entirely dissolved into the melt. The graphite particles were precipitated from the melt under solidification. In addition, this high temperature caused the improvement of wetting of copper to graphite. This high temperature caused the annealing, and reduced the Vickers hardness. Even in this case, the Vickers hardness increased with an increase in the carbon content. This resulted from the dispersion hardening.

[Raman spectrum of nano-graphite synthesized by explosive detonation].

PubMed

Wen, Chao; Li, Xun; Sun, De-Yu; Guan, Jin-Qing; Liu, Xiao-Xin; Lin, Ying-Rui; Tang, Shi-Ying; Zhou, Gang; Lin, Jun-De; Jin, Zhi-Hao

2005-01-01

The nano-graphite powder synthesized by the detonation of explosives with negative oxygen balance is a new powder material with potential applications. In this work, the preparation of nano-graphite powder in steel chamber by pure TNT (trinitrotoluene) explosives has been introduced. In the synthesis process, the protective gases in the steel chamber are N2, CO2 and Ar, and the pressure is 0.25-2 atm. Raman spectrum of the nano-graphite was measured. The characteristic Raman band assigned to sp2 of graphite has been observed at about 1 585 cm(-1) with half-peak width of 22 cm(-1). The peak shifted to a higher frequency by 5 cm(-1) compared with that of bulk graphite. The authors explain this blue shift phenomenon by size effect. The average size of nanographite from Raman measurement is 2.97-3.97 nm. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to measure the structure and particle size of the nano-graphite. The crystallite size of nano-graphite estimated from XRD andTEM are 2.58 nm (acid untreated) and 1.86 nm (acid treated) respectively, which is in accord with the results of the measurement approximately.

Influence of solvent species on the charge-discharge characteristics of a natural graphite electrode

NASA Astrophysics Data System (ADS)

Fujimoto, Masahisa; Shoji, Yoshihiro; Kida, Yoshinori; Ohshita, Ryuji; Nohma, Toshiyuki; Nishio, Koji

The charge-discharge characteristics of a natural graphite electrode are examined in a mixed solvent composed of ethylene carbonate (EC) and propylene carbonate (PC). The characteristics are influenced largely by the solvent species. Natural graphite electrode displays good charge-discharge characteristics in an electrolyte containing EC with a high volume fraction. In an electrolyte containing PC, however, the electrode cannot be charged and the solvent is decomposed. X-ray photoelectron spectroscopy is used to obtain information about the surface of natural graphite. A thin LiF layer, the decomposition product of lithium hexafluorophosphate (LiPF 6), is formed on the surface of the natural graphite charged to 0.5 V (vs. Li/Li +) in an electrolyte containing a high volume fraction of EC. On the other hand, LiF and a carbonate compound are formed in the bulk and on the surface of natural graphite when the volume fraction of PC is high. These results suggest that the thin LiF layer, which is produced at a potential higher than 0.5 V (vs. Li/Li +) on the surface of natural graphite, enables the lithium ions to intercalate into the natural graphite without further decomposition of the electrolyte.

Phonon-assisted indirect transitions in angle-resolved photoemission spectra of graphite and graphene

NASA Astrophysics Data System (ADS)

Ayria, Pourya; Tanaka, Shin-ichiro; Nugraha, Ahmad R. T.; Dresselhaus, Mildred S.; Saito, Riichiro

2016-08-01

Indirect transitions of electrons in graphene and graphite are investigated by means of angle-resolved photoemission spectroscopy (ARPES) with several different incident photon energies and light polarizations. The theoretical calculations of the indirect transition for graphene and for a single crystal of graphite are compared with the experimental measurements for highly-oriented pyrolytic graphite and a single crystal of graphite. The dispersion relations for the transverse optical (TO) and the out-of-plane longitudinal acoustic (ZA) phonon modes of graphite and the TO phonon mode of graphene can be extracted from the inelastic ARPES intensity. We find that the TO phonon mode for k points along the Γ -K and K -M -K' directions in the Brillouin zone can be observed in the ARPES spectra of graphite and graphene by using a photon energy ≈11.1 eV. The relevant mechanism in the ARPES process for this case is the resonant indirect transition. On the other hand, the ZA phonon mode of graphite can be observed by using a photon energy ≈6.3 eV through a nonresonant indirect transition, while the ZA phonon mode of graphene within the same mechanism should not be observed.

Decolorizing of azo dye Reactive red 24 aqueous solution using exfoliated graphite and H2O2 under ultrasound irradiation.

PubMed

Li, Mei; Li, Ji-Tai; Sun, Han-Wen

2008-07-01

At its natural pH (6.95), the decolorization of Reactive red 24 in ultrasound, ultrasound/H2O2, exfoliated graphite, ultrasound/exfoliated graphite, exfoliated graphite/H2O2 and ultrasound/exfoliated graphite/H2O2 systems were compared. An enhancement was observed for the decolorization in ultrasound/exfoliated graphite/H2O2 system. The effect of solution pH, H2O2 and exfoliated graphite dosages, and temperature on the decolorization of Reactive red 24 was investigated. The sonochemical treatment in combination with exfoliated graphite/H2O2 showed a synergistic effect for the decolorization of Reactive red 24. The results indicated that under proper conditions, there was a possibility to remove Reactive red 24 very efficient from aqueous solution. The decolorization of other azo dyes (Reactive red 2, Methyl orange, Acid red 1, Acid red 73, Acid red 249, Acid orange 7, Acid blue 113, Acid brown 75, Acid green 20, Acid yellow 42, Acid mordant brown 33, Acid mordant yellow 10 and Direct green 1) was also investigated, at their natural pH.

Structural features of the adsorption layer of pentacene on the graphite surface and the PMMA/graphite hybrid surface

NASA Astrophysics Data System (ADS)

Fadeeva, A. I.; Gorbunov, V. A.; Litunenko, T. A.

2017-08-01

Using the molecular dynamics and the Monte Carlo methods, we have studied the structural features and growth mechanism of the pentacene film on graphite and polymethylmethacrylate /graphite surfaces. Monolayer capacity and molecular area, optimal angles between the pentacene molecules and graphite and PMMA/graphite surfaces as well as the characteristic angles between the neighboring pentacene molecules in the adsorption layer were estimated. It is shown that the orientation of the pentacene molecules in the film is determined by a number of factors, including the surface concentration of the molecules, relief of the surface, presence or absence of the polymer layer and its thickness. The pentacene molecules adsorbed on the graphite surface keep a horizontal position relative to the long axis at any surface coverage/thickness of the film. In the presence of the PMMA layer on the graphite, the increase of the number of pentacene molecules as well as the thickness of the PMMA layer induce the change of molecular orientation from predominantly horizontal to vertical one. The reason for such behavior is supposed to be the roughness of the PMMA surface.

Anode performance of boron-doped graphites prepared from shot and sponge cokes

NASA Astrophysics Data System (ADS)

Liu, Tao; Luo, Ruiying; Yoon, Seong-Ho; Mochida, Isao

The structures and anode performances of graphitized pristine and boron-doped shot and sponge cokes have been comparatively studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and galvanostatic measurement. The results show that high degree of graphitization can be obtained by the substituted boron atom in the carbon lattice, and boron in the resultant boron-doped graphites mainly exist in the form of boron carbide and boron substituted in the carbon lattice. Both of boron-doped graphites from shot and sponge cokes obtain discharge capacity of 350 mAh g -1 and coulombic efficiency above 90%. Apart from commonly observed discharge plateau for graphite, boron-doped samples in this study also show a small plateau at ca. 0.06 V. This phenomenon can be explained that Li ion stores in the site to be void-like spaces that are produced by "molecular bridging" between the edge sites of graphene layer stack with a release of boron atoms substituted at the edge of graphene layer. The effect of the amount of boron dopant and graphitization temperature on the anode performance of boron-doped graphite are also investigated in this paper.

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%. Copyright © 2016 Elsevier Ltd. All rights reserved.

Catalytic Graphitization of Coal-Based Carbon Materials with Light Rare Earth Elements.

PubMed

Wang, Rongyan; Lu, Guimin; Qiao, Wenming; Yu, Jianguo

2016-08-30

The catalytic graphitization mechanism of coal-based carbon materials with light rare earth elements was investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy. The interface between light rare earth elements and carbon materials was carefully observed, and two routes of rare earth elements catalyzing the carbon materials were found: dissolution-precipitation and carbide formation-decomposition. These two simultaneous processes certainly accelerate the catalytic graphitization of carbon materials, and light rare earth elements exert significant influence on the microstructure and thermal conductivity of graphite. Moreover, by virtue of praseodymium (Pr), it was found that a highly crystallographic orientation of graphite was induced and formed, which was reasonably attributed to the similar arrangements of the planes perpendicular to (001) in both graphite and Pr crystals. The interface between Pr and carbon was found to be an important factor for the orientation of graphite structure.

Fabrication of TREAT Fuel with Increased Graphite Loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luther, Erik Paul; Leckie, Rafael M.; Dombrowski, David E.

2014-02-05

As part of the feasibility study exploring the replacement of the HEU fuel core of the TREAT reactor at Idaho National Laboratory with LEU fuel, this study demonstrates that it is possible to increase the graphite content of extruded fuel by reformulation. The extrusion process was use to fabricate the “upgrade” core1 for the TREAT reactor. The graphite content achieved is determined by calculation and has not been measured by any analytical method. In conjunction, a technique, Raman Spectroscopy, has been investigated for measuring the graphite content. This method shows some promise in differentiating between carbon and graphite; however, standardsmore » that would allow the technique to be calibrated to quantify the graphite concentration have yet to be fabricated. Continued research into Raman Spectroscopy is on going. As part of this study, cracking of graphite extrusions due to volatile evolution during heat treatment has been largely eliminated. Continued research to optimize this extrusion method is required.« less

Comparison of the tribological properties of fluorinated cokes and graphites

NASA Technical Reports Server (NTRS)

Fusaro, Robert L.

1988-01-01

The friction, wear, endurance life, and surface morphology of rubbed (burnished) fluorinated graphite and fluorinated coke materials were studied. Two different coke powders, a graphitic carbon powder, and a graphite powder were fluorinated and then tribologically investigated. In addition, one of the coke powders was reduced in size before fluorinating to evaluate the effect of a finer particle size on the tribological properties. For comparison, graphite and coke powders which were not fluorinated were also tribologically evaluated. Elemental analysis by emission spectroscopy was performed on each sample to determine the impurity content and X-ray diffraction analysis was performed to determine the crystallinity. Coke was found to have very little lubricating ability, but fluorinated coke did possess good lubricating properties. However, the fluorinated graphite and fluorinated graphitic carbon (which gave equivalent results) gave superior results to those obtained with the fluorinated cokes. No tribological benefit was found for using small versus a larger particle size of coke, at least when evaluated as a rubbed film.

Comparison of the tribological properties of fluorinated cokes and graphites

NASA Technical Reports Server (NTRS)

Fusaro, Robert L.

1987-01-01

The friction, wear, endurance life, and surface morphology of rubbed (burnished) fluorinated graphite and fluorinated coke materials were studied. Two different coke powders, a graphitic carbon powder, and a graphite powder were fluorinated and then tribologically investigated. In addition, one of the coke powders was reduced in size before fluorinating to evaluate the effect of a finer particle size on the tribological properties. For comparison, graphite and coke powders which were not fluorinated were also tribologically evaluated. Elemental analysis by emission spectroscopy was performed on each sample to determine the impurity content and X-ray diffraction analysis was performed to determine the crystallinity. Coke was found to have very little lubricating ability, but fluorinated coke did possess good lubricating properties. However, the fluorinated graphite and fluorinated graphitic carbon (which gave equivalent results) gave superior results to those obtained with the fluorinated cokes. No tribological benefit was found for using small versus a larger particle size of coke, at least when evaluated as a rubbed film.

ICP-MS measurement of iodine diffusion in IG-110 graphite for HTGR/VHTR

NASA Astrophysics Data System (ADS)

Carter, L. M.; Brockman, J. D.; Robertson, J. D.; Loyalka, S. K.

2016-05-01

Graphite functions as a structural material and as a barrier to fission product release in HTGR/VHTR designs, and elucidation of transport parameters for fission products in reactor-grade graphite is thus required for reactor source terms calculations. We measured iodine diffusion in spheres of IG-110 graphite using a release method based on Fickain diffusion kinetics. Two sources of iodine were loaded into the graphite spheres; molecular iodine (I2) and cesium iodide (CsI). Measurements of the diffusion coefficient were made over a temperature range of 873-1293 K. We have obtained the following Arrhenius expressions for iodine diffusion:DI , CsI infused =(6 ×10-12 2/s) exp(30,000 J/mol RT) And,DI , I2 infused =(4 ×10-10 m2/s) exp(-11,000 J/mol RT ) The results indicate that iodine diffusion in IG-110 graphite is not well-described by Fickan diffusion kinetics. To our knowledge, these are the first measurements of iodine diffusion in IG-110 graphite.

High temperature gas-cooled reactor (HTGR) graphite pebble fuel: Review of technologies for reprocessing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mcwilliams, A. J.

2015-09-08

This report reviews literature on reprocessing high temperature gas-cooled reactor graphite fuel components. A basic review of the various fuel components used in the pebble bed type reactors is provided along with a survey of synthesis methods for the fabrication of the fuel components. Several disposal options are considered for the graphite pebble fuel elements including the storage of intact pebbles, volume reduction by separating the graphite from fuel kernels, and complete processing of the pebbles for waste storage. Existing methods for graphite removal are presented and generally consist of mechanical separation techniques such as crushing and grinding chemical techniquesmore » through the use of acid digestion and oxidation. Potential methods for reprocessing the graphite pebbles include improvements to existing methods and novel technologies that have not previously been investigated for nuclear graphite waste applications. The best overall method will be dependent on the desired final waste form and needs to factor in the technical efficiency, political concerns, cost, and implementation.« less

Measurement of the cleavage energy of graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wen; Dai, Shuyang; Li, Xide

Here, the basal plane cleavage energy (CE) of graphite is a key material parameter for understanding many of the unusual properties of graphite, graphene and carbon nanotubes. Nonetheless, a wide range of values for the CE has been reported and no consensus has yet emerged. Here we report the first direct, accurate experimental measurement of the CE of graphite using a novel method based on the self-retraction phenomenon in graphite. The measured value, 0.37±0.01 J m –2 for the incommensurate state of bicrystal graphite, is nearly invariant with respect to temperature (22 °C≤T≤198 °C) and bicrystal twist angle, and insensitivemore » to impurities from the atmosphere. The CE for the ideal ABAB graphite stacking, 0.39±0.02 J m –2, is calculated based on a combination of the measured CE and a theoretical calculation. These experimental measurements are also ideal for use in evaluating the efficacy of competing theoretical approaches.« less

Measurement of the cleavage energy of graphite

DOE PAGES

Wang, Wen; Dai, Shuyang; Li, Xide; ...

2015-08-28

Here, the basal plane cleavage energy (CE) of graphite is a key material parameter for understanding many of the unusual properties of graphite, graphene and carbon nanotubes. Nonetheless, a wide range of values for the CE has been reported and no consensus has yet emerged. Here we report the first direct, accurate experimental measurement of the CE of graphite using a novel method based on the self-retraction phenomenon in graphite. The measured value, 0.37±0.01 J m –2 for the incommensurate state of bicrystal graphite, is nearly invariant with respect to temperature (22 °C≤T≤198 °C) and bicrystal twist angle, and insensitivemore » to impurities from the atmosphere. The CE for the ideal ABAB graphite stacking, 0.39±0.02 J m –2, is calculated based on a combination of the measured CE and a theoretical calculation. These experimental measurements are also ideal for use in evaluating the efficacy of competing theoretical approaches.« less

Significance of Graphitic Surfaces in Aurodicyanide Adsorption by Activated Carbon: Experimental and Computational Approach

NASA Astrophysics Data System (ADS)

Bhattacharyya, Dhiman; Depci, Tolga; Prisbrey, Keith; Miller, Jan D.

Despite tremendous developments in industrial use of activated carbon (AC) for gold adsorption, specific aurodicyanide [Au(CN)2-] adsorption sites on the carbon have intrigued researchers. The graphitic structure of AC has been well established. Previously radiochemical and now, XPS and Raman characterizations have demonstrated higher site-specific gold adsorption on graphitic edges. Morphological characterizations have revealed the presence of slit-pores (5-10 Å). Molecular-dynamics-simulation (MDS) performed on graphitic slit-pores illustrated gold-cyanide ion-pair preferentially adsorbs on edges. Ab-initio simulations predicted lower barrier for electron sharing in pores with aurodic yanide, indicating tighter bonding than graphitic surface and was well supported by Gibbs energy calculations too. Interaction energy as function of the separation distance indicated tighter bonding of gold cyanide to the graphite edges than water molecules. Selective adsorption of aurodicyanide ion-pair seems to be related to low polarity of gold complex and its accommodation at graphitic edges.

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.

Effect of High Energy Radiation on Mechanical Properties of Graphite Fiber Reinforced Composites. M.S. Thesis

NASA Technical Reports Server (NTRS)

Naranong, N.

1980-01-01

The flexural strength and average modulus of graphite fiber reinforced composites were tested before and after exposure to 0.5 Mev electron radiation and 1.33 Mev gamma radiation by using a three point bending test (ASTM D-790). The irradiation was conducted on vacuum treated samples. Graphite fiber/epoxy (T300/5208), graphite fiber/polyimide (C6000/PMR 15) and graphite fiber/polysulfone (C6000/P1700) composites after being irradiated with 0.5 Mev electron radiation in vacuum up to 5000 Mrad, show increases in stress and modulus of approximately 12% compared with the controls. Graphite fiber/epoxy (T300/5208 and AS/3501-6), after being irradiated with 1.33 Mev gamma radiation up to 360 Mrads, show increases in stress and modulus of approximately 6% at 167 Mrad compared with the controls. Results suggest that the graphite fiber composites studied should withstand the high energy radiation in a space environment for a considerable time, e.g., over 30 years.

Investigations on Mechanical Behaviour of Micro Graphite Particulates Reinforced Al-7Si Alloy Composites

NASA Astrophysics Data System (ADS)

Nagaraj, N.; Mahendra, K. V.; Nagaral, Madeva

2018-02-01

Micro particulates reinforced metal matrix composites are finding wide range of applications in automotive and sports equipment manufacturing industries. In the present study, an attempt has been made to develop Al-7Si-micro graphite particulates reinforced composites by using liquid melt method. 3 and 6 wt. % of micro graphite particulates were added to the Al-7Si base matrix. Microstructural characterization was done by using scanning electron microscope and energy dispersive spectroscope. Mechanical behaviour of Al-7Si-3 and 6 wt. % composites were evaluated as per ASTM standards. Scanning electron micrographs revealed the uniform distribution of micro graphite particulates in the Al-7Si alloy matrix. EDS analysis confirmed the presence of B and C elements in graphite reinforced composites. Further, it was noted that ultimate tensile and yield strength of Al-7Si alloy increased with the addition of 3 and 6wt. % of graphite particulates. Hardness of graphite reinforced composites was lesser than the base matrix.

Effect of Graphite Concentration on Shear-Wave Speed in Gelatin-Based Tissue-Mimicking Phantoms

PubMed Central

Anderson, Pamela G.; Rouze, Ned C.; Palmeri, Mark L.

2011-01-01

Elasticity-based imaging modalities are becoming popular diagnostic tools in clinical practice. Gelatin-based, tissue mimicking phantoms that contain graphite as the acoustic scattering material are commonly used in testing and validating elasticity-imaging methods to quantify tissue stiffness. The gelatin bloom strength and concentration are used to control phantom stiffness. While it is known that graphite concentration can be modulated to control acoustic attenuation, the impact of graphite concentrationon phantom elasticity has not been characterized in these gelatin phantoms. This work investigates the impact of graphite concentration on phantom shear stiffness as characterized by shear-wave speed measurements using impulsive acoustic-radiation-force excitations. Phantom shear-wave speed increased by 0.83 (m/s)/(dB/(cm MHz)) when increasing the attenuation coefficient slope of the phantom material through increasing graphite concentration. Therefore, gelatin-phantom stiffness can be affected by the conventional ways that attenuation is modulated through graphite concentration in these phantoms. PMID:21710828

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.

The Nature of Metastable AA’ Graphite: Low Dimensional Nano- and Single-Crystalline Forms

PubMed Central

Lee, Jae-Kap; Kim, Jin-Gyu; Hembram, K. P. S. S.; Kim, Yong-Il; Min, Bong-Ki; Park, Yeseul; Lee, Jeon-Kook; Moon, Dong Ju; Lee, Wooyoung; Lee, Sang-Gil; John, Phillip

2016-01-01

Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior. PMID:28000780

Effect of airborne contaminants on the wettability of supported graphene and graphite

NASA Astrophysics Data System (ADS)

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P.; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

Low-temperature method of producing nano-scaled graphene platelets and their nanocomposites

DOEpatents

Zhamu, Aruna [Centerville, OH; Shi, Jinjun [Columbus, OH; Guo, Jiusheng [Centerville, OH; Jang, Bor Z [Centerville, OH

2012-03-13

A method of exfoliating a layered material to produce separated nano-scaled platelets having a thickness smaller than 100 nm. The method comprises: (a) providing a graphite intercalation compound comprising a layered graphite containing expandable species residing in an interlayer space of the layered graphite; (b) exposing the graphite intercalation compound to an exfoliation temperature lower than 650.degree. C. for a duration of time sufficient to at least partially exfoliate the layered graphite without incurring a significant level of oxidation; and (c) subjecting the at least partially exfoliated graphite to a mechanical shearing treatment to produce separated platelets. The method can further include a step of dispersing the platelets in a polymer or monomer solution or suspension as a precursor step to nanocomposite fabrication.

Effect of airborne contaminants on the wettability of supported graphene and graphite.

PubMed

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

Potassium-Based Dual Ion Battery with Dual-Graphite Electrode.

PubMed

Fan, Ling; Liu, Qian; Chen, Suhua; Lin, Kairui; Xu, Zhi; Lu, Bingan

2017-08-01

A potassium ion battery has potential applications for large scale electric energy storage systems due to the abundance and low cost of potassium resources. Dual graphite batteries, with graphite as both anode and cathode, eliminate the use of transition metal compounds and greatly lower the overall cost. Herein, combining the merits of the potassium ion battery and dual graphite battery, a potassium-based dual ion battery with dual-graphite electrode is developed. It delivers a reversible capacity of 62 mA h g -1 and medium discharge voltage of ≈3.96 V. The intercalation/deintercalation mechanism of K + and PF 6 - into/from graphite is proposed and discussed in detail, with various characterizations to support. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Graphite as a Biomarker in Rocks of the 3.8 Ga Isua Supracrustal Belt

NASA Astrophysics Data System (ADS)

Lepland, A.; van Zuilen, M.; Layne, G. D.; Arrhenius, G.

2002-12-01

Recent petrographic and isotopic studies of graphite and apatite in supracrustal rocks from the 3.8 Ga Isua belt (ISB) in southern West Greenland [1, 2] have shown inconsistencies in interpreting traces of life in the earliest terrestrial sediment record. Isotopically light graphitic carbon, suggestive of a bioorganic origin, has been previously reported from the carbonate-rich Isua rocks [3, 4] that at the time were recognized as sedimentary deposits. However, these carbonate-rich rocks, that provided the basis for original biologic interpretations, have been shown to have a metasomatic origin [5] not sedimentary as previously believed. This protolith reinterpretation has highlighted the need for assessment of graphite genesis and related isotopic systematics when using graphite as an ancient biomarker. We have, for this purpose, studied graphite in a suite of samples from the ISB including metacarbonates, turbidites, cherts and banded iron formations (BIFs). Graphite is relatively abundant (0.1-2 wt. %) in metacarbonate samples, while the abundances of reduced carbon in metasedimentary BIFs and metacherts are below 100 ppm. Petrographic analyses show that graphite in metacarbonates typically associates with Fe-bearing carbonate and magnetite. This mineral association indicates graphite formation in Isua metacarbonates by thermal-metamorphic reduction of carbonate ion, in which the carbonate ion is reduced to form graphite and ferrous iron is oxidized to form magnetite. Carbon isotopic compositions of graphite (δ13C ca. -2 per mil) and associated Fe-carbonate (δ13C ca. -6 per mil) indicate isotopic equilibrium between these two phases at ca. 500 C, consistent with the metamorphic history of the ISB. Stepped-combustion experiments undertaken on Isua BIFs and metacherts reveal that these sediments contain virtually no graphite, and the small amount of reduced carbon found there represents recent organic contamination. Our stepped-combustion-mass-spectrometry data demonstrate that previous isotopic results on graphite deficient Isua rocks obtained by single step combustion are unreliable. The proposed biologic significance of graphite occurring as inclusions in apatite [4] in Isua rocks is not supported by our findings because such graphite-apatite association can only be found in biologically irrelevant metacarbonate rocks. The isotopic systematics of the epigenetic processes responsible for formation of isotopically light graphite enclosed in apatite crystals [4] will be discussed, integrating new ion microprobe isotope data on graphite in apatite and other mineral phases occurring in Isua metacarbonates. References: [1] van Zuilen, M., Lepland, A. and Arrhenius, G., 2002. Reassessing the evidence for the earliest traces of life. Nature 418: 627-630. [2] Lepland, A., Arrhenius, G. and Cornell, D. in press. Apatite in early Archean Isua supracrustal rocks, southern West Greenland: its origin, association with graphite and potential as a biomarker. Precam. Res. [3] Schidlowski, M., 1988. A 3,800-million-year isotopic record of life from carbon in sedimentary rocks. Nature 333: 313-318. [4] Mojzsis, S.J., Arrhenius, G., McKeegan, K.D., Harrison, T.M., Nutman, A.P. and Friend, C.R.L., 1996. Evidence for life on Earth before 3800 million years ago. Nature 384: 55-59. [5] Rosing, M.T., Rose, N.M., Bridgwater, D. and Thomsen, H.S., 1996. Earliest part of Earth's stratigraphic record: a reappraisal of the >3.7 Ga Isua (Greenland) supracrustal sequence. Geol. 24: 43-46.

Ultra-widefield retinal MHz-OCT imaging with up to 100 degrees viewing angle.

PubMed

Kolb, Jan Philip; Klein, Thomas; Kufner, Corinna L; Wieser, Wolfgang; Neubauer, Aljoscha S; Huber, Robert

2015-05-01

We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85° FOV as well as with 100° and stitching of five 60° images to a 100° mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85° and 100° single volume images, but not in the mosaic. Our results suggest that 100° FOV OCT is possible with current swept source OCT technology.

Ultra-widefield retinal MHz-OCT imaging with up to 100 degrees viewing angle

PubMed Central

Kolb, Jan Philip; Klein, Thomas; Kufner, Corinna L.; Wieser, Wolfgang; Neubauer, Aljoscha S.; Huber, Robert

2015-01-01

We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85° FOV as well as with 100° and stitching of five 60° images to a 100° mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85° and 100° single volume images, but not in the mosaic. Our results suggest that 100° FOV OCT is possible with current swept source OCT technology. PMID:26137363

Preparation of UC0.07-0.10N0.90-0.93 spheres for TRISO coated fuel particles

NASA Astrophysics Data System (ADS)

Hunt, R. D.; Silva, C. M.; Lindemer, T. B.; Johnson, J. A.; Collins, J. L.

2014-05-01

The US Department of Energy is considering a new nuclear fuel that would be less susceptible to ruptures during a loss-of-coolant accident. The fuel would consist of tristructural isotropic coated particles with dense uranium nitride (UN) kernels with diameters of 650 or 800 μm. The objectives of this effort are to make uranium oxide microspheres with adequately dispersed carbon nanoparticles and to convert these microspheres into UN spheres, which could be then sintered into kernels. Recent improvements to the internal gelation process were successfully applied to the production of uranium gel spheres with different concentrations of carbon black. After the spheres were washed and dried, a simple two-step heat profile was used to produce porous microspheres with a chemical composition of UC0.07-0.10N0.90-0.93. The first step involved heating the microspheres to 2023 K in a vacuum, and in the second step, the microspheres were held at 1873 K for 6 h in flowing nitrogen.