Showing papers on "Graphite published in 1984"
TL;DR: In this paper, a supersonic beam of carbon clusters is generated using graphite as the substrate, and carbon clusters Cn for n=1−190 have been produced having a distinctly bimodal cluster size distribution: (i) both even and odd clusters for Cn, 1≤n≤30; and (ii) only even clusters C2n, 20−n−90.
Abstract: Laser vaporization of a substrate within the throat of a pulsed nozzle is used to generate a supersonic beam of carbon clusters. The neutral cluster beam is probed downstream by UV laser photoionization with time‐of‐flight mass analysis of the resulting photoions. Using graphite as the substrate, carbon clusters Cn for n=1–190 have been produced having a distinctly bimodal cluster size distribution: (i) Both even and odd clusters for Cn, 1≤n≤30; and (ii) only even clusters C2n, 20≤n≤90. The nature of the bimodal distribution, and the intensity alterations in the observed C+n signals are interpreted on the basis of cluster formation and stability arguments. Ionizing laser power dependences taken at several different photon energies are used to roughly bracket the carbon cluster ionization potentials, and, at high laser intensity, to observe the onset of multiphoton fragmentation. By treating the graphite rod with KOH, a greatly altered carbon cluster distribution with mixed carbon/potassium clusters of for...
782 citations
01 Nov 1984-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, two catalytic processes have been explored for the preparation of suitable samples for use in 14C measurements on an accelerator mass spectrometer, and a sample preparation system using this reaction has been built.
Abstract: Two catalytic processes have been explored for the preparation of suitable samples for use in 14C measurements on an accelerator mass spectrometer. A heavy hydrocarbon was condensed from C2H2 using AlBr3 as a catalyst. This process had low isotopic fractionation, and the carbon ion beam obtainable was 60–70% that from graphite. In the second process, iron powder was used to produce graphite directly from CO2 and H2 at 600 °C. A sample preparation system using this reaction has been built. The carbon product produces exceptionally intense, long-lived ion beams. The process introduces little 14C background, and has no observed memory effects.
613 citations
TL;DR: In this paper, the effective mass-approximation differential equations appropriate for impurities in a graphite host are constructed and are used to solve self-consistently for the screening response surrounding a single intercalant atom.
Abstract: The effective-mass-approximation differential equations appropriate for impurities in a graphite host are constructed and are used to solve self-consistently for the screening response surrounding a single intercalant atom. The screening cloud is found to have a very slow algebraic decay with a characteristic length of 3.8 \AA{} in the case studied. This rather long length is due to both the semimetallic and the two-dimensional character of graphite. A Thomas-Fermi description of screening is found to be adequate, but a linear-response theory is not. From these results we conclude that the transferred charge in alkali-metal---graphite intercalation compounds is distributed nearly homogeneously on a carbon plane. We discuss recent theoretical and experimental work in light of these results.
610 citations
TL;DR: The real and imaginary parts of the complex index of refraction of a hydrogenated amorphous carbon (a•C:H) film have been determined for photon energies between 145 and 49 eV from measurements of reflectance R and transmittance T.
Abstract: The real and imaginary parts, n and k, of the complex index of refraction of a hydrogenated amorphous carbon (a‐C:H) film have been determined for photon energies between 145 and 49 eV from measurements of reflectance R and transmittance T Both n and k, and consequently e1 and e2 (the real and imaginary parts of the dielectric constant), show a considerable variation with subsequent annealing of the a‐C:H film up to Ta=750 °C, with the most rapid changes occurring for Ta=450 °C and above The optical gap Eopt is observed to decrease from 22 eV to 0 as the film is annealed, signaling the development of graphitic short range order in the film Using an effective medium approximation to model the optical properties of the film, we find that the as‐deposited film contains amorphous diamond‐like, graphitic, and polymeric components With annealing, the amorphous diamond‐like and polymeric components decrease, the amorphous graphitic component grows, and a void component appears We discuss the local order
281 citations
TL;DR: In this article, the graphitic phases of C and Si were studied with the use of the pseudopotential local density functional approach, and good agreement with experiment was obtained for the in-plane lattice constant, interlayer spacing, isotropic bulk modulus, and graphite-diamond structural energy difference.
Abstract: The graphitic phases of C and Si are studied with the use of the pseudopotential local-density-functional approach. For graphite, good agreement with experiment is obtained for the in-plane lattice constant, interlayer spacing, isotropic bulk modulus, and graphite-diamond structural energy difference. Graphitic Si has relatively weak bonding and its formation is unlikely since its energy is 0.71 eV/atom higher than the diamond phase and a large negative pressure of -69 kbar is required.
182 citations
TL;DR: In this paper, the failure characteristics of [0/90/0] and [90/ 0/90] cross-ply laminates based on statistical strength analysis were analyzed.
Abstract: This paper treats the failure characteristics of [0/90/0] and [90/0/90] cross-ply laminates based upon the statistical strength analysis. The stress redistributions at the failure of the 90 ° ply are analyzed using a shear-lag model, taking the thermal residual stresses and Poisson effect into consideration. The formulae for determining first cracking, subsequent multiple cracking and ultimate fracture are derived. The present analysis is compared with the existing experimental results for graphite/epoxy cross-ply laminates, and reasonable agreements have been obtained.
159 citations
TL;DR: In this article, it was found that graphite with organic phosphate and phosphite esters has an increased resistance to air oxidation at elevated temperatures, and that a hydrophilic residue strongly adsorbed on the graphite surface at active sites where oxidation normally occurs.
159 citations
TL;DR: In this article, a reduction in the rate of graphite oxidation in dry or moist air between 600 and 1000°C was reported. But the results were limited to aqueous solutions of boric oxide or with organo-borates.
146 citations
TL;DR: In this article, the digital difference spectrum technique in X-ray photoelectron spectroscopy has proved to be effective for the analysis of the functional groups introduced by surface oxidation treatment of carbon fibers.
133 citations
TL;DR: In this article, the effects of applied pressure on graphite and its intercalation compounds are reviewed emphasizing the relationship between structure and transport properties, and it has been recognized that high pressure plays a crucial role in the polymorphic phase transitions of graphite, notably in the graphite-diamond transformation.
Abstract: The effects of applied pressure on graphite and its intercalation compounds are reviewed emphasizing the relationship between structure and transport properties. It has long been recognized that high pressure plays a crucial role in the polymorphic phase transitions of graphite, notably in the graphite-diamond transformation. More recent studies have revealed a wealth of pressure-induced phases associated with the unusual layer-stacking (‘staging’) mechanism in the intercalation compounds of graphite. The high degree of structural anisotropy associated with staging is strongly reflected in the electronic band structure and transport properties, and in the remarkable pressure dependence of the superconducting states of some of the graphite intercalation compounds. High pressure is shown to be a valuable means not only to realize new structural phases but also to improve our understanding of the fundamental behaviour of these important materials.
125 citations
TL;DR: In this paper, the influence of graphite additions on the wear characteristics of cast Al-Si alloys, produced by compocasting followed by squeeze casting, has been assessed using a pin-on-disc wear test.
TL;DR: In this paper, Fatigue crack growth rates have been determined on standard specimens containing long cracks and on specimens containing two-dimensional short cracks (∼0.10-0.50mm).
Abstract: Fatigue crack growth rates have been determined on standard specimens containing long cracks (∼5–10mm) and on specimens containing two-dimensional short cracks (∼0.10–0.50mm). Large differences have been observed indicating that at a given stress intensity factor short cracks propagate much faster than long cracks. Mouth opening displacement measurements for both specimen geometries have shown that the crack closure effect is largely responsible for the observed effect. These results are used to rationalize the behaviour of short cracks initiated from natural sites which were either graphite nodules or microshrinkage pores. The three-dimensional aspect of these natural small cracks is analysed and discussed in detail.
TL;DR: In this article, a self-consistent local-density all-electron theory and model-potential calculations were performed on thin graphite films consisting of up to 25 atomic layers and the surface states were predicted at 3.8 eV above the Fermi energy.
Abstract: Thin graphite films consisting of up to 25 atomic layers are studied with self-consistent local-density all-electron theory and model-potential calculations. Unoccupied surface states confined in the direction of the $c$ axis are predicted at 3.8 eV above the Fermi energy. They are split off from the bulk free-electron interlayer band. These results provide a convincing interpretation of the surface states found in recent inverse photoemission experiments by Fauster et al.
TL;DR: In this paper, the hydrogenation of carbon monoxide over iron surfaces has been investigated at medium pressure (7 atm) and over the temperature range 473-578 K. This deactivation appears to be associated with the deposition of a graphitic type of surface carbon.
TL;DR: In this article, the structure of the carbon films could be classified into three types: (i) amorphous, (ii) graphite, and (iii) cubic, depending mainly on the deposition conditions.
Abstract: Diamondlike carbon films have been prepared by ionized deposition from methane gas. The film structures were examined by transmission electron microscopy, electron diffraction, and electron spectroscopy for chemical analysis techniques. It was found that the structure of the carbon films could be classified into three types: (i) amorphous, (ii) graphite, and (iii) cubic. These types depended mainly on the deposition conditions. Usually crystalline carbon films were diamond mixed with graphite showing an average grain size of several hundred angstroms. Very hard films were composed of diamond crystallites distributed in amorphous matrix.
TL;DR: By means of Penningionization electron spectroscopy, the outermost surface layer of a pentacene film on a graphite substrate (cleavage plane) was selectively observed.
Abstract: By means of Penning-ionization electron spectroscopy the outermost surface layer of a pentacene film on a graphite substrate (cleavage plane) was selectively observed. Ultraviolet photoelectron spectroscopy was also applied to observe several layers from the surface. From the analyses of the two types of spectra the subtle changes in the electronic state and the molecular orientation of the outermost layer and also those of inner layers were probed separately during the layer-by-layer epitaxial growth of the film.
TL;DR: In this article, the graphite islands are shown to be weakly bound to the iridium substrate by Van der Waals forces, and the unsaturated valence bonds at the periphery of the graphs are "lowered down" on to the metal.
TL;DR: In this article, the mass spectra of the reaction product on graphite induced by H0/D2+ irradiation was analyzed and it was concluded that the reaction by energetic hydrogen ions occurs at the inner surfaces whereas with irradiation with H 0/energetic ions CH3 is formed at the surface.
TL;DR: In this paper, mass analyzed thermal desorption spectroscopy along with surface characterization was performed by X-ray photoelectron spectrographs for the release of hydrogen, deuterium and tritium into pyrolytic graphite.
Patent•
15 Nov 1984
TL;DR: In this article, an improvement is provided for the manufacture of perhalogenated polytetrafluoroethylene (PTFE) bonded electrodes by using a non-polymeric pore-former to make the mixture more pliable and to create micropores in the electrode when the solution is removed by evaporation.
Abstract: An improvement is provided for the manufacture of perhalogenated polymer, e.g., PTFE, bonded electrodes. The formulation comprises a mixture of an active material is carbon monofluoride (otherwise known as fluorinated graphite or fluorinated carbon or CF x or (C 2 F) n ); a conductive carbon additive, such as acetylene black or graphite; and polytetrafluoroethylene (PTFE). The process comprises high shear mixing to cause the PTFE to fibrillate. The mixture is then wet with a non-polymeric pore-former to make the mixture more pliable and to create micropores in the electrode when the solution is removed by evaporation. The wet mixture is then sequentially suitably formed into a, e.g., extruded, or calendered or pressed to flatten the mixture to a thin sheet and rolled up and folded and pressed out again until a uniform sheet is obtained and the like. The resulting product affords a sheet which is relatively flexible, and stronger and allows a lower PTFE loading than has been obtained with other electrode sheet materials formed with fibrillatable polymers. The higher the PTFE content, the higher the voltage losses for the electrode.
TL;DR: In this paper, the adsorption potential of noble gases on graphite is calculated by the summation of two-body anisotropic interactions between the adatom and each carbon atom, which takes into account the graphite anisotrophy.
Abstract: The adsorption potential of noble gases on graphite is calculated. The method used is the summation of two-body anisotropic interactions between the adatom and each carbon atom, which takes into account the graphite anisotrophy. The lateral variation which results depends on the uncertain role of anisotrophy in the repulsive part of the interaction. In any case, the computed variation is of the order of twice the value computed by Steele [Surf. Sci. 36, 317 (1973)] and is widely used. Our conclusion is consistent with thermodynamic data.
TL;DR: In this article, the authors considered the range over which a catalyst support can be expected to influence the electron density of states of a metal particle and showed that the effect of the support on catalyst reactivity is vanishingly small.
TL;DR: In this paper, it was found that the different valency states of selenium are not stabilized to the same extent by frequently applied matrix modifiers like nickel or copper, which may explain pre-atomization losses and high characteristic mass data reported previously.
TL;DR: In this article, a mechanism of formation of diamond is proposed which relies on a solid-vapor-liquid-solid (SVLS) sequence of phase transformations, and the experimental results were found to be in reasonable agreement with the proposed SVLS model.
Abstract: Different aspects of phase‐transition processes in carbon in dynamic conditions were studied. Samples of graphite/metal mixtures have been recovered and analyzed after exposure to the combined action of high temperature and pressure pulses generated by a unique flash‐heating hemispherical implosion system. Transmission electron microscopy together with x‐ray and electron diffraction examinations proved the existence of diamond, different forms of graphite, and carbynes in the samples. A mechanism of formation of diamond is proposed which relies on a solid‐vapor‐liquid‐solid (SVLS) sequence of phase transformations. The experimental results were found to be in reasonable agreement with the proposed SVLS model. A tetragonally crystallized diamondlike carbon phase ( p‐diamond) was identified in the course of the work as well as a new linear carbon polymorph (Carbon‐XIV).
TL;DR: In this paper, the integral and differential properties of adsorption of CO on exfoliated graphite (Grafoil) have been obtained and subjected to relatively simple analysis.
Abstract: Heats of adsorption, heat capacities and isotherms have been measured for CO adsorbed on exfoliated graphite (Grafoil) over a wide range of temperature and for surface coverages up to 1·2 monolayers. Both integral and differential properties have been obtained and are subjected to relatively simple analysis. From a comparison of the results with similar ones for N2 adsorption, some conclusions can be drawn about the phase diagram for adsorbed CO and about the character of the adsorption. The relative behaviour of the two gases is explicable in terms of dispersion interactions. Simulation calculations of the integral heat of adsorption of CO are made as a function of surface coverage.
TL;DR: An a-C:H film was prepared for the first time by H2 gas reactive rf-sputtering of a graphite target onto low temperature (room temperature ~150°C) substrate as mentioned in this paper.
Abstract: An a-C:H film was prepared for the first time by H2 gas reactive rf-sputtering of a graphite target onto low temperature (room temperature ~150°C) substrate. This film has a uniform amorphous structure and an H-atom ratio of 0.8 H/C; its electrical resistivity was 106~1012 Ωcm. Vickers' hardness number of the film was 1000~2000. IR, Raman and ESCA spectra showed that the bonding between the neighbouring C-atoms was for the most part by sp3 bond, and that sp2 bond was rare. Approximately 200 A of diamond grains were observed by TEM in annealed film at 1000°C, and verified by electron diffraction pattern.
Patent•
14 Aug 1984TL;DR: In this article, a radar attenuating composition or paint is prepared by uniformly mixing thin conducting fibers such as stainless steel fibers or carbon or graphite into a standard camouflage-type paint.
Abstract: A radar attenuating composition is described for which incident microwave diation is absorbed and/or scattered, causing a significant decrease in retroreflectance of the object to which the composition is applied, that is, a reduction in the radar cross-section of the object. The radar attenuating composition or paint is prepared by uniformly mixing thin conducting fibers such as stainless steel fibers or carbon or graphite into a standard camouflage-type paint. The fibers act as electric dipole segments. The purpose of the countermeasure paint of the present invention is to reduce the amount of microwave radiation reflected back by a target to the receiver, i.e. reducing the amount of retroreflection.
TL;DR: In this article, the etch decoration/transmission electron microscopy has been employed to study the catalysis of the carbon-oxygen reaction by seven group VB and VIB metal carbides and oxides.
TL;DR: The discharge reaction mechanism of graphite fluoride-lithium batteries utilizing a 1M LiClO 4 -propylene carbonate (PC) system was studied by means of X-ray diffraction, ESCA, NMR and transmission electron microscopy, differential thermal analyses and thermal gravimetry as discussed by the authors.