Showing papers on "Graphite published in 1992"

Large-scale synthesis of carbon nanotubes

Abstract: INTEREST in carbon fibres1,2 has been stimulated greatly by the recent discovery of hollow graphitic tubules of nanometre dimensions3. There has been much speculation about the properties and potential application of these nanotubes4–8. Theoretical studies predict that their electronic properties will depend on their diameter and degree of helicity4,5. Experimental tests of these ideas has been hampered, however, by the lack of macroscopic quantities of the material. Here we report the synthesis of graphitic nanotubes in gram quantities. We use a variant of the standard arc-discharge technique for fullerene synthesis under a helium atmosphere. Under certain conditions, a carbonaceous deposit forms on one of the graphite rods, consisting of a macroscopic (diameter of about 5 mm) cylinder in which the core comprises pure nanotubes and nanoscale particles in high yield. The purity and yield depend sensitively on the gas pressure in the reaction vessel. Preliminary measurements of the conductivity of the bulk nanotube material indicate a conductivity of about 100 S cm–11.

Handbook of carbon, graphite, diamond, and fullerenes

Abstract: The performance of a single-crystal diamond detector, grown by chemical vapour deposition, as an energy (2) Pierson H. O., Handbook of Carbon, Graphite. Diamonds and Fullerenes: Processing, Properties. Applications. Handbook of carbon, graphite, diamond and fullerenes 1993 Pierson.pdf 4.72 MB Handbook of preparative inorganic chemistry 1963 Vol 1,2 Brauer.pdf. but in other areas, less-ordered graphitic or amorphous carbon shells were also Pierson, H. O. in Handbook of Carbon, Graphite, Diamond and Fullerenes:. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in Pierson, H. O. Handbook of carbon, graphite, diamonds and fullerenes:. nanotoxicity of carbon nanotubes and graphene in biomedicine. Pierson, H.O. Handbook of Carbon, Graphite, Diamond, and Fullerenes: Properties. Section 4 of the article is devoted towards discussing the role of carbon and its (7) H O Pierson, Handbook of carbon, graphite, diamonds and fullerenes:. The main forms are diamond and graphite, and they exhibit markedly di erent Books Handbook of Carbon, Graphite, Diamond and Fullerenes Properties. Four different forms of carbon namely, Graphite, Activated H. O. Pierson, Handbook of Carbon, Graphite, Diamonds and Fullerenes: Processing, Properties. The growth of multi-walled carbon nanotube (MWCNT) and carbon nano (13) H. O. Pierson, Handbook of Carbon, Graphite, Diamond and Fullerenes:.

A transferable tight-binding potential for carbon

Abstract: An interatomic potential for carbon is developed that is based on an empirical tight-binding approach. The model reproduces accurately the energy-versus-volume diagram of carbon polytypes and gives a good description of the phonons and elastic constants for carbon in the diamond and graphite structures. To test the transferability of the model to different environments further, the authors performed molecular-dynamics simulations to study the liquid phase and the properties of small carbon microclusters. The results obtained are in good agreement with those obtained from ab initio calculations.

Energetics of negatively curved graphitic carbon

Abstract: BY analogy with the positively curved carbon networks that comprise the fullerenes1–3, it has been suggested4 that negative curvature might be possible in graphitic carbon sheets, giving rise to extended structures corresponding to periodic minimal surfaces5 that divide space into two disjoint labyrinths. Whereas the positive curvature of fullerenes results from the presence of five-membered rings, negative curvature would derive from seven-membered rings. Here we present calculations of the cohesive energy and bulk moduli of two such hypothetical, negatively curved carbon networks. We find that both have a cohesive energy smaller than that of graphite but significantly greater than that of C60, even though the proportion of odd-membered rings is comparable. We therefore suggest that it is worth scrutinizing the insoluble residue generated in the carbon-arc preparation of fullerenes6 for possible evidence of fragments of negatively curved graphitic carbon.

Tribological properties of metal matrix-graphite particle composites

Abstract: The tribological behaviour of metal matrix composites containing graphite particles is reviewed. After outlining the processes for the synthesis of these composites, present theoretical understanding pertaining to the friction and wear; of composites in the presence of a thin lubricating film is described. The experimental results show that friction and wear rate in metal matrix—graphite particle composites are significantly reduced compared with those in matrix alloys, as a result of the incorporation of graphite particles. When the graphite content of metal matrix composites exceeds about 20 vol.-%, the friction coefficient approaches that of pure graphite and becomes independent of the matrix alloy. This is an indication of effective intervention of a thin film of graphite between the matrix and the counterface. Initially during sliding, the film of graphite is not present but it forms as a result of surface and subsurface deformation resulting in transfer of graphite to the tribosurface. A dyn...

First-principles study of the electronic properties of simple hexagonal graphite

Abstract: The electronic properties of simple hexagonal graphite have been studied in the framework of the density-functional technique, using nonlocal ionic pseudopotentials and a large number of plane waves. This work leads to a first-step qualitative understanding of the electronic properties of nonperiodic structures such as pregraphitic and disordered carbons (turbostratic graphite), which are composed of periodic regions of simple hexagonal graphite surrounded by domains of the usual (Bernal) form of graphite. Particular attention has been paid to the comparison with the properties of the Bernal graphite. The valence charge density, the density of states, the band structure, as well as a description of the electronic energies at the Fermi level are provided. The latter is parametrized by a tight-binding model, and compared to the Slonczewski-Weiss-McClure model of Bernal graphite electronic energies. The Fermi surface is calculated and an exchange of hole and electron pockets between these two forms of graphite is observed. The behavior of electronic energies under pressure, and the associated deformation potentials, are also studied.

High-pressure in situ x-ray-diffraction study of the phase transformation from graphite to hexagonal diamond at room temperature.

Abstract: High-pressure in situ x-ray diffraction was carried out to clarify the nature of the pressure-induced phase transformation in graphite at room temperature. The combined use of a Drickamer-type high-pressure apparatus with sintered diamond as an anvil material and very intense x rays from synchrotron radiation made it possible to obtain high-quality x-ray-diffraction data, as well as information on the orientation relation, for this phase transformation. It was found that the transition starts at 14 GPa at room temperature, although this onset pressure is sensitive to the nature of the sample and of the applied pressure. X-ray-diffraction profiles obtained on the high-pressure phase are well explained by the hexagonal diamond structure, but the observed c/a ratio is slightly larger than that of ideal packing. The observed orientation relation satisfies the previously proposed martensitic transition mechanism from graphite to hexagonal diamond. But this hexagonal diamond formed at room temperature is unquenchable upon the release of pressure, and how it differs from the quenched phase formed under high pressure and temperature remains to be clarified.

Molecular dynamics simulations of ordered alkane chains physisorbed on graphite

Abstract: Scanning tunneling microscopy (STM) studies at the interface between the basal plane of graphite and organic solutions or melts of long chain alkanes and alkyl derivatives reveal that the molecules order in lamellae with the main molecular axes oriented parallel to the substrate. Here we employ molecular dynamics (MD) simulations to obtain more details on the molecular order and dynamics within the alkane lamellae as a function of density. We find that the orientation of the molecular carbon zigzag planes relative to the graphite is governed by a subtle interplay of packing and entropic effects. In addition, we consider multiple layer adsorption and investigate the rapid loss of order with increasing distance from the interface. Finally, we study the diffusive behavior of an isolated long chain alkane, C350H702, on graphite, which is of interest in the context of STM imaging of isolated macromolecules at interfaces. The sensitive dependence on atomic parameters renders MD simulations a valuable complement...

Energetics of interplanar binding in graphite

Abstract: Results of an ab initio density-functional study of interlayer binding in graphite are presented. We obtain good agreement with experimental results for the equilibrium c-axis lattice parameter, exfoliation energy, and uniaxial compressibility for this highly anisotropic material. We also present the calculated band structure of graphite

Ion Implantation in Diamond, Graphite and Related Materials

Abstract: 1. Introduction.- 2. Carbon Materials: Graphite, Diamond and Others.- 2.1 Structure and Materials.- 2.1.1 Graphite.- 2.1.2 Graphite-Related Materials.- 2.1.3 Carbon Fibers.- 2.1.4 Glassy Carbon.- 2.1.5 Graphite Intercalation Compounds.- 2.1.6 Diamond.- 2.1.7 CVD Diamond Films.- 2.1.8 Diamond-Like Carbon Films.- 2.2 Properties of Graphite.- 2.2.1 Lattice Properties.- 2.2.2 Electronic and Transport Properties.- 2.2.3 Optical Properties.- 2.2.4 Thermal Properties.- 2.2.5 Mechanical Properties.- 2.3 Properties of Diamond.- 2.3.1 Lattice Properties.- 2.3.2 Electronic and Transport Properties.- 2.3.3 Optical Properties.- 2.3.4 Thermal Properties.- 2.3.5 Mechanical Properties.- 2.3.6 Chemical Properties.- 3. Ion Implantation.- 3.1 Energy Loss Mechanisms.- 3.2 Parameters of Implantation.- 3.2.1 Energy of Implantation.- 3.2.2 Implantation Range.- 3.2.3 Implantation Fluence (Dose) and Beam Current (Dose Rate).- 3.3 Radiation Damage.- 3.4 Energy Loss Simulations.- 4. Ion Beam Analysis Techniques.- 4.1 Rutherford Backscattering Spectroscopy.- 4.2 Nuclear Reaction Analysis.- 4.3 Particle Induced X-Ray Emission (PIXE).- 4.4 Channeling.- 4.5 Elastic Recoil Detection (ERD).- 4.6 Secondary Ion Mass Spectroscopy (SIMS).- 4.7 Channeling Studies in Graphite-Based Materials.- 4.8 Stoichiometric Characterization of GICs by RBS.- 4.9 Ion Channeling in GICs.- 5. Other Characterization Techniques.- 5.1 Raman Spectroscopy.- 5.2 Other Optical and Magneto-Optical Techniques.- 5.3 Electron Microscopies and Spectroscopies.- 5.4 X-Ray-Related Characterization Techniques.- 5.5 Electronic Transport Measurements.- 5.6 Electron Spin Resonance (ESR).- 5.7 Hyperfine Interactions.- 5.7.1 Mossbauer Spectroscopy.- 5.7.2 Perturbed Angular Correlations (PAC).- 5.8 Mechanical Properties.- 6. Implantation-Induced Modifications to Graphite.- 6.1 Lattice Damage.- 6.2 Regrowth of Ion-Implanted Graphite.- 6.3 Structural Modification.- 6.4 Modification of the Electronic Structure and Transport Properties.- 6.5 Modification of Mechanical Properties.- 6.6 Implantation with Ferromagnetic Ions.- 6.7 Implantation-Enhanced Intercalation.- 6.8 Implantation with Hydrogen and Deuterium.- 7. Implantation-Induced Modifications to Graphite-Related Materials.- 7.1 Glassy Carbon.- 7.2 Carbon Fibers.- 7.3 Disordered Graphite.- 7.4 Carbon-Based Polymers.- 8. Implantation-Induced Modifications to Diamond.- 8.1 Structural Modifications and Damage-Related Electrical Conductivity.- 8.2 Volume Expansion.- 8.3 Lattice Damage.- 8.4 Damage Annealing and Implantations at Elevated Temperatures.- 8.5 Electrical Doping.- 8.6 Impurity State Identification.- 8.7 Electronic Device Realization.- 8.8 New Materials Synthesis.- 8.9 Improving Mechanical Properties.- 9. Implantation-Induced Modifications to Diamond-Related Materials.- 9.1 Diamond-Like Carbon (a-C:H) Films.- 9.1.1 DC Conductivity.- 9.1.2 Optical Characterization.- 9.1.3 Structural Modifications and Hydrogen Loss.- 9.1.4 Attempts to Dope a-C:H by Ion-Implantation.- 9.1.5 Discussion of Implantation-Induced Effects in DLC.- 9.2 Diamond Films.- 10. Concluding Remarks.- References.

Negatively curved graphitic sheet model of amorphous carbon.

Abstract: A computational method has been developed for generating graphitic carbon structures on an arbitrary smooth surface and with a given number of carbon rings. Using both periodic and random surfaces for constraint, many extended graphitic carbon structures have been generated. The energy relative to graphite and the bulk elastic properties have been calculated. Like their periodic counterparts, the random structures are found to be exceptionally stable. Their radial distribution functions match closely those of films of amorphous carbon grown on NaCl substrates from sublimated graphite.

Metal-dispersed carbon paste electrodes

Abstract: The preparation of metal-dispersed carbon paste electrodes, based on mixing an organic binder with metalized graphite, is described. Such electrodes combine the efficient electrocatalytic activity of metal microparticles with the attractive properties of carbon paste matrices. The ability to catalyze the slow electrode reactions of hydrogen or organic peroxides, hydrazine compounds, ascorbic acid, and dihydronicotinamide adenine dinucleotide is illustrated

High-pressure fluid-absent melting experiments in the presence of graphite: oxygen fugacity, ferric/ferrous ratio and dissolved CO2

Abstract: Graphite capsules are commonly used to prevent loss of iron from iron-bearing samples in high-pressure melting experiments. The graphite is not inert in such experiments and reacts with Fe 2 O 3 in the melt to form dissolved CO 2 and FeO. This equilibrium can be quantified if the activity-composition relations of CO 2 in the melt are known. The presence of graphite is shown to limit the maximum fO 2 possible, but places no limit on the minimum fO 2 . The fO 2 in the system, the ferric/ferrous ratio in the melt, and the concentration of dissolved CO 2 are proportional to the concentration of ferric iron in the starting material. The dissolved CO 2 content cannot be controlled independently of fO 2 , but for values of fO 2 appropriate to mantle melting, the amount of dissolved CO 2 can be controlled over values ranging from about 0.1 wt% to saturation

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties: IV. Mode I and Mode II Fracture Toughness of Graphite/Epoxy Composites

Abstract: To optimize the level of fiber-matrix adhesion an understanding of the relationship between fiber-matrix interfacial bond strength and the mechanical and frac ture behavior of composites is essential. This study establishes the relationship between fiber-matrix interfacial shear strength (ISS) and interlaminar fracture toughness (both Mode I and Mode II) and failure modes for graphite/epoxy composites. A well defined and characterized graphite fiber/epoxy system was chosen in which the level of adhesion be tween fiber and matrix was changed by using the same graphite fibers with different sur face treatments. These surface treatments changed the level of adhesion between the fiber and matrix thus resulting in an increase of the fiber-matrix ISS by over a factor of two while the fiber and matrix properties remained unchanged. The Mode I and Mode II tests were conducted by the double cantilever beam (DCB) and end-notch flexure (ENF) tests methods, respectively. The Mode I fracture toughness (GIC) of composi...

Direct observation of surface reactions by scanning tunneling microscopy: Ethylene→ethylidyne→carbon particles→graphite on Pt(111)

Abstract: We have used variable temperature, ultrahigh vacuum scanning tunneling microscopy (STM), in both static and time‐dependent experiments, to study the chemistry of the ethylene/Pt(111) system. Images of ethylene which exhibit long‐range order have been obtained at a sample temperature of 160 K. The conversion of ethylene to ethylidyne has been observed directly in STM images. This conversion reaction is observed to occur in a ‘‘patchy’’ manner across the surface at saturation coverage. As the reaction proceeds, well‐defined islands of unreacted ethylene continue to be clearly observed. Further dehydrogenation of the ethylidyne formed from ethylene leads to carbon containing particles dispersed randomly across the sample. After annealing the ethylidyne covered sample to 500 K, the surface is uniformly covered with carbon containing particles which exhibit a bimodal distribution of heights (one and two atomic layers) consisting of an average of ten and twenty carbon atoms, respectively. Further annealing to 7...

Effects of substrate temperature on chemical structure of amorphous carbon films

Abstract: Amorphous carbon thin films were prepared at 30, 200, and 450 °C by magnetron sputtering of a graphite target. The surface structure and chemical bonding (sp2/sp3) of the carbon films were characterized by scanning tunneling microscopy (STM) and Raman spectroscopy. STM images show that graphite microcrystallites of 20–40 A in size are present at the surfaces of all the films and the number of the microcrystallites increases with increasing substrate temperature. The microcrystallites often contain structural defects. Raman measurements show that increasing the substrate temperature results in an increase in the sp2‐bonded fraction of carbon atoms and a decrease in the microstructural defects. These results indicate that the microstructural changes are correlated with changes in the chemical bonding ratio (sp3/sp3) and no diamond microcrystallites are present in the amorphous carbon. A three‐dimensional atomic structure of the graphite microcrystallites is discussed in terms of turbostratic graphite.

Rectification of STM Current to Graphite Covered with Phthalocyanine Molecules.

Abstract: The scanning tunneling microscope (STM) can be used to measure current-voltage characteristics on an atomic scale. The attachment of copper phthalocyanine molecules, in contrast to a variety of other molecules, to graphite changes the electrical characteristics of the STM from relatively symmetric to highly asymmetric or rectifying. Evidence is presented to show that the asymmetry arises because of the electronic energy levels of the copper phthalocyanine. The organic molecules were bonded to the graphite by an acid-base reaction that may have wide applicability.

Solvation forces near a graphite surface measured with an atomic force microscope

Abstract: Solvation force interactions in a liquid near a solid wall (graphite) were investigated using an atomic force microscope. The general features of the data show the distinctive oscillatory force curve associated with solvation forces, with a mean periodicity approximately equal to the minimum dimensions of the molecules. Moreover, the graphite surface can still be imaged with atomic resolution; which suggests that the technique can be used for the detailed study of short range forces over specific parts of various surfaces.

Grain-boundary graphite in Kapuskasing gneisses and implications for lower-crustal conductivity

Abstract: SURFACE electromagnetic measurements commonly reveal that the intermediate and lower continental crust has an appreciable electrical conductivity, much higher than that found for laboratory analogues of deep-crustal rocks or for upper-crustal rocks either formed at shallow depths or uplifted from deeper levels. Conducting films at grain boundaries are thought to play an important part in enhancing deep-crustal conductivity, with brines and graphite being the main candidates1. At present, however, there is a lack of direct evidence for such films. Frost et al.2 have reported an enhancement in conductivity of igneous lower-crustal rocks from the La ramie complex apparently owing to the presence of graphite films, but the possible role of brines was not clear from this work. Here we present a study of the grain surface composition of metamorphic (and one igneous) rocks exhumed from 20 km depth by the Kapuskasing uplift of the Canadian shield3. We expect these samples to be representative of metamorphic and igneous rocks of the deep Archaean crust. Auger spectroscopy provides evidence for graphite films at grain boundaries, which can account for the present electrical signature of the Kapuskasing crust4–6. We also detect traces of chlorine, sulphur and iron, which suggest that brines and solid conductors other than graphite may have helped to enhance the conductivity, but their abundance suggests at best a minor role relative to graphite.

On the way to fullerenes: molecular dynamics study of the curling and closure of graphitic ribbons

Abstract: Sparked by the synthetic breakthrough of Kratschmer, Huffman, and co-workers yielding macroscopic amounts of research on the fullerenes (discovered 5 years earlier3) has continued to accelerate. Despite the pace of this research, the mechanisms leading to the facile formation of highly symmetric fullerene cages in the chaotic conditions of the carbon arc remain to be ~larified."~ In this Letter, following ideas advanced by Smalley, Curl, Kroto, and co-workers,eE we use molecular dynamics (MD) simulations to study the behavior of graphitic fragments thought to condense in the cooling carbon vapor prior to fullerene formation. These fragments are treated as ribbons as an idealization of their probable low-symmetry, far-from-circular shapes. At the conditions present in the carbon arc, we find that such ribbons can exhibit large thermal fluctuations from planarity without fragmentation. These fluctuations, when sup plemented by the curvature induced by pentagons, often cause these isolated strips spontaneously to form open-ended hollow carbon structures. Once formed, these hollow structures represent good fullerene precursors. Graphitic ribbons are modeled using a bond-order type empirical hydrocarbon potentiallo which accurately predicts the bonding and energetics of solid diamond lattices and graphite sheets, as well as hydrocarbon molecules, while still allowing reactions to occur. The reactive aspect of the potential is important both to model correctly the reactive edges of these ribbons and to allow for any possible fragmentation at high temperature. Although this potential has already been shown to provide a good model for a wide variety of properties of fullerenes and related structure~,~~-~~ to assess further its reliability for the present study we examined the energetics of the inversion of the corranulene molecule (Cal0). This molecule is similar in shape to one-third of a buckminsterfullerene cluster. Recent studies have shown that corranulene can rapidly fluctuate between two curved minima at room temperature14-a behavior that is related to the ribbon motions discussed below. First principles calculations yield an energy difference between the minimum-energy curved structures and a planar intermediate of 8.8-1 1.0 kcal/mol.l5J6 Our empirical potential predicts a difference of 10.3 kcal/mol, in excellent agreement with these calculations.