Interlayer Spacing Of Graphite Research Articles

Multiwalled carbon nanotubes with bamboo-like structure and effects of heat treatment

Microstructures of bamboo-like multiwalled carbon nanotubes prepared by pyrolysis of Ni-phthalocyanine are studied by high-resolution transmission electron microscopy. The intershell spacings of graphitic shells in these nanotubes are estimated. From pristine nanotubes with a tube diameter of 40–260 nm, the spacing values of 0.339–0.342 nm are obtained almost independent of their tube diameters. However, after heat treatment at 2800 °C they are reduced to a value equivalent to the interlayer spacing of graphite, and tube walls with a clear polygonal cross section come to be observed. The heat treatment of samples is also a very useful method to prepare metal-free nanotubes. The bamboo-like graphitic shells are interpreted to be determined by a cone-shaped Ni nanoparticle included at the base of the multiwalled carbon nanotube.

Carbon Structures Prepared from Molten Aromatic Hydrocarbons

Carbon structures were produced by melting aromatic hydrocarbons in mixtures of fine metal and metal-salt powders and were investigated by electron microscopy. Depending on the preparation conditions, the products contained various amounts of amorphous and microcrystalline carbon, diamond, and tubular structures, including carbon nanotubes 50 to 400 nm in diameter, resulting from the rolling of graphitic layers. The separation between graphitic layers in the nanotubes is much larger than the interlayer spacing in crystalline graphite.

Molecular Dynamics Study of Graphite/Electrolyte Interfaces

Molecular dynamics simulations of graphite-electrolyte interfaces are performed on 3D unit cells with periodic boundary conditions at lithium concentrations between 0 and 17% in the carbon phase. The liquid electrolyte consists of a mixture of cyclic carbonates and Staging phenomena, structural changes in the modeled graphite systems, charge distribution on the atoms, and lithium-ion diffusion coefficients are evaluated as a function of lithium concentration in the solid phase. Transitions between ordered carbon structures are detected in the model systems. Repulsive lithium-lithium interlayer interactions are predominant during the intercalation process. Calculated solid phase diffusion coefficients of lithium ions for a state of charge between 0 and 17% are in the range to The maximum increase of graphite interlayer spacing found when the lithium ions are intercalated varies from 6 to 10% depending on the degree of intercalation. An electrostatic double layer is formed between the solid and the electrolyte phase; the average charge at each side of the solid/liquid interface is strongly dependent on the composition and electronic properties of the electrolyte. © 2001 The Electrochemical Society. All rights reserved.

The Effect of Organic Solvent on the Anionic Polymerization in the Interlayer Spacing of Graphite

KC24 was allowed to react with the unsaturated hydrocarbon-organic solvent mixtures. Isoprene molecules were introduced into the interlayer of KC24 and polymerized, whereupon organic solvents such as cyclohexane, n-hexane or 2, 5-dimethyltetrahydrofuran was incorporated into the polyisoprene. On the other hand, the polymerization of styrene in the interlayer spacing of graphite was carried out without the incorporation of n-hexane or 2, 5-dimethyltetrahydrofuran. This is explained on the basis of the low affinity of aromatic styrene for aliphatic solvents. The polymerization of styrene was not observed in the presence of cyclohexane, which is attributed to a low reactivity of styrene to polymerize in the interlayer spacing of graphite.

Hexagonal or Quasi Two-Dimensional Palladium Nanoparticles—Tested at the Heck Reaction

This paper deals with the occurrence of quasi two-dimensional palladium nanoparticles (hcp structure, 53 nm in average lateral dimension, approx. 37 wt% Pd) encapsulated into graphite. Microphotographs showed that the nanoparticles occurred in the interlayer spacing of graphite. Raman spectroscopy of Pd–graphite showed absolutely no charge-transfer interaction between Pd nanoparticles and the carbon lattice. The Pd nanoparticles proved to be active catalysts for the Heck reaction. In this test reaction a halobenzene reacts with styrene to form diphenylethene (stilbene). Although no interaction between nanoparticles and the carbon lattice occurs, the nanoparticles remain inside the carbon lattice after the Heck reaction. They could be not washed out; therefore, the catalyst is stable.

Atomic structure of monolayer graphite formed on Ni(111)

The atomic structure of monolayer graphite formed on a Ni(111) surface was investigated by means of LEED intensity analysis. We measured the I- V curves of the (1,0), (0,1) and (1,1) diffraction spots from a (1 × 1) atomic structure, and analyzed them using Van Hove's analytical program based on dynamical theory. Three different atomic structures meeting the experimental requirement of the 3m symmetry were evaluated with Pendry's reliability factor. The final best-fit structure characterized by the minimum Pendry's reliability factor of 0.22 is as follows: one carbon atom in a unit cell of the graphite overlayer is located at the on-top site of the topmost Ni atoms, while another carbon atom exists at the fcc hollow site. The spacing between the flat overlayer and the topmost Ni layer is 2.11 ± 0.07 A ̊ , which is much narrower than the interlayer spacing in bulk graphite (3.35 Å).

Fine metallic particles in graphite matrix

The reduction of metal chloride in the interlayer spacing of graphite has been a subject of interest during recent years [1-5]. However, few studies of the reaction mechanism have been described in the literature. In a previous letter [6], we discussed factors determining the size of fine metallic particles formed in the graphite matrix. Atoms of zero-valent metal generated by the reduction of metal chloride at respective sites in the graphite intercalation compound (GIC) start moving in the interlayer spacing of graphite to aggregate. The aggregate of metallic atoms also moves in the interlayer spacing of graphite and coalesces with other aggregates or metallic atoms. The activity to move decreases with increasing size. After this aggregate grows to a certain size and its spontaneous movement is restricted, its growth is carried out by coalescence with other aggregates or atoms, which can move actively due to smaller size and coalesce into this immobile aggregate. As the activity of particle precursors (i.e. metal atoms or their aggregates) to move in the graphite gallery is determined by the bulk melting point of the metal, the lower the bulk melting point, the better the chance the precursor has of growing to a great size, which explains the order of the particle size Fe < Ni < Cu. The dependence of the stage number of starting GICs on the particle size is explicable, assuming the mechanism described above. In this letter, we discuss temperature dependence on the size of fine metallic particles and the form of particles. The preparation method of stage 2 FeC13, NiC12 and CuC12 GICs was shown in the previous letter [6]. Each metal chloride GIC ( -10 rag) was immersed in 2 ml tetrahydrofuran (THF) in the presence of 50 mg naphthalene and 200 mg lithium. The mixture was sealed in a Pyrex glass tube and allowed to stand for 21 days at various temperatures: -70 °C, 0 °C, 25 °C and 50 °C. The size of metallic particles, obtained in the graphite matrix, was estimated from the line width of the X-ray diffraction (XRD) profiles, based on Scherrer's formula. The estimated size is listed in Table I. When atoms of zero-valent metal or their aggregates move in the interlayer spacing of graphite, the activity to move is expected to be

Atomic Structure of Monolayer Graphite Formed on Ni(111).

The atomic structure of monolayer graphite formed on a Ni (111) surface was investigated by means of LEED intensity analysis. We measured the I-V curves of the (1, 0), (0, 1) and (1, 1) diffraction spots from a 1×1 atomic structure, and analyzed them by using the Van Hove's analytical program based on dynamical theory. Three different atomic structures meeting the experimental requirement of the 3-m symmetry were evaluated with Pendry's reliability factor. The final best-fit structure characterized by the minimum Pendry's reliability factor of 0.22 is as follows; one carbon atom in a unit cell of the graphite overlayer is located at the on-top site of the topmost Ni atoms, while another carbon atom exists at the fcc-hollow site. The spacing between the flat overlayer and the topmost Ni layer is 2.11 ± 0.07 A, which is much narrower than the interlayer spacing in bulk graphite (3.35 A).

The production and structure of pyrolytic carbon nanotubes (PCNTs)

The structures of pyrolytic carbon nanotubes (PCNTs), produced by thermal decomposition of hydrocarbon vapor (benzene at ca 1100°C) have been studied. Electron microscope images of the PCNTs “as-formed” and after various degrees of subsequent heat treatment are presented and discussed on the basis of elongated giant fullerene structures and a possible primary growth mechanism. The images indicate that some PCNTs show evidence of thickening due to secondary pyrolytic deposition whereas others appear to be essentially exposed nanotubes (without further carbon deposition) or have sections with negligible secondary deposition. The nanotubes appear initially to grow as ultra-thin tubes with a central hollow core (diameters ca2 nm or more). No catalytic particles are observed at the tips of the tubes shown by high resolution transmission electron microscope (HRTEM) studies to be composed of concentric graphite cylinders with consecutive radii increasing by a factor close to that of the standard graphite interlayer spacing. The further pyrolytic carbon thickening occurs at roughly the same time as longitudinal nanotube growth. This phenomenon can cause the diameters of the tubes to increase to micron sizes. Heat treatment of the “as-formed” PCNTs results in encapsulation of the hollow cores by polyhedral hemispherical fullerene-like caps. Single or multi-layered nodes are also generated, yielding “bamboo-like” structures. The PCNTs are similar to those obtained by d.c. arc techniques using graphite electrodes.

Reduction of Metal Chloride in the Interlayer Spacing of Graphite

Graphite intercalation compounds with FeCl3, NiCl2, CuCl2 and EuCl3 were immersed in lithium-naphthalene-THF mixture. All of the metal chlorides, except EuCl3, were reduced in the interlayer spacing of graphite, and fine particles of corresponding metal and lithium chloride were obtained. As the particles are protected in the graphite matrix, they are inert even in acid solution.The size of Fe, Ni, Cu and LiCl particles, obtained in the graphite matrix, were estimated from the line width of X-ray diffraction profiles. The size increases in the order Ni<Fe<Cu<LiCl, which is explained based on the mobility difference of the precursors of fine particles.

Electrochemical oxidation of graphite in an aqueous medium: intercalation of FeCl 4−

Graphite was oxidized electrochemically in an aqueous solution of 2.5 moles of FeCl 3, 1.75 moles of HCl and 6 moles of H 2O, which leads to the formation of stage n iron chloride-graphite intercalation compounds (GICs) (where n ≧ 2). The interplanar distance d i of the GIC is ~9.4 Å; this value is similar to that of the FeCl 3-GIC obtained by the vapour phase method. Mössbauer spectroscopy shows that the FeCl 4 − ion exists in the interlayer spacing of graphite. The existence of co-intercalated species is suggested by the results of elemental analysis, thermogravimetry and so on.

The structure of highly tetrahedral amorphous diamond-like carbon II. High-resolution electron microscopy

Abstract Amorphous carbon (a-C) that has been shown to be highly tetrahedral by neutron-scattering techniques is examined by high-resolution transmission electron microscopy. There are clear indications of an amorphous structure, characterized by 02 nm periodicities, and this is distinctly different from the structure seen in evaporated a-C. Thin regions, near the edges of the foil, resemble a-C, however, and show periodicities nearer to the interlayer spacing in graphite. A number of crystalline and microcrystalline inclusions that are not representative of the intrinsic structure of the material are observed, and these include some uncommon crystalline forms of carbon.

On the stability of alkali metals in the interlayer spacing of graphite

On the stability of alkali metals in the interlayer spacing of graphite

Oxidation of ionic potassium-coal adducts

The behaviour of potassium-graphite intercalation compounds (GIC) and directly prepared potassium-coal adducts (PCA) was studied during their oxidation by oxygen. The reactions were carried out in dry state or after dispersion in a solvating medium. The reaction rate in THF was found to be higher. E.s.r. data showed that the KO 2 produced in the oxidation process was in the form of a complex in the interlayer space of graphite or inserted between the parallel layers of condensed aromatic nuclei in the case of coal adducts. This state of KO 2 explains the fact that its e.s.r. signal was registered at room temperature. This work revealed an approach for the mild oxidation of PCA with a view to structural investigation of solubilized coal.

Electrochemical preparation of the ternary graphite intercalation compound with H 2SO 4 and H 2SeO 4

Stage- n H 2SeO 4-graphite intercalation compounds (GICs) ( n = 2,3) prepared by galvanostatic oxidation of graphite in H 2SeO 4 were transferred into the electrolytic cell filled with H 2SO 4 and then continued the oxidation. From the observed electrode potential vs. electric quantity curves and the results of measured C Se atomic ratio, it was suggested that H 2SO 4 was intercalated into stage- n H 2SeO 4-GICs and the products were ternary GICs of H 2SeO 4 and H 2SO 4. When these ternary GICs were reduced electrochemically, at first H 2SO 4 was deintercalated and then H 2SeO 4 began to be released. These results may suggest that H 2SO 4 and H 2SeO 4 are intercalated in separate interlayer spaces of graphite, i.e. bi-intercalation. Intercalation of H 2SeO 4 into stage-2 H 2SO 4-GIC was also observed.

Structural and electrical properties of intercalated and ion-implanted highly ordered graphite fibers

Because of their high degree of structural order, high mechanical strength, and small diameter (\ensuremath{\sim}1 \ensuremath{\mu}m), benzene-derived graphite fibers provide an excellent host material for a structural analysis of both the intercalation and ion-implantation processes in graphite. Using the $c$-axis lattice imaging technique, with a high-resolution electron microscope, we observe well-staged intercalated regions in this fiber matrix. With regard to ion implantation, we find a distribution in the density of lattice defects with depth from the fiber surface. Ion implantation is also found to increase the graphite interlayer spacing. This information is correlated with electrical properties of these fibers.

Synthesis of gaseous hydrocarbons from carbon monoxide and hydrogen over transition metal catalysts. Part 4. The effect of pretreatment on the composition and the catalytic activity of reduced lamellar compound of graphite with ferric chloride.

A lamellar compound of graphite (LCG) with FeCl3 was treated in flowing Ar or H2 in the temperature range from 400 to 800°C. The FeCl3 in the layers was reduced to FeCl2 or to metallic Fe whose contents changed depending on the conditions of treatment. Hydrogenation of carbon monoxide was investigated at 400°C and 20atm using these LCG catalysts. Although the active site of the LCG catalyst was the metallic Fe located between the graphite layers, it was shown that the content of FeCl2 in the layers was important for controlling catalytic activity of the LCG. The catalytic activity of the LCG increased with increasing FeCl2 content up to 0.9mmol/g-catalyst. However, FeCl2 itself showed no catalytic activity at 400°C. As is known, the interlayer spacing of graphite enlarged by FeCl2 is larger than that enlarged by Fe, and the FeCl2 in the LCG catalyst probably behaves as the spacer.

The crystal and molecular structure of quaterrylene: a redetermination

The crystal structure of quaterrylene, C 40 H 20 -first studied with limited two dimensional X-ray data in 1960 - has been redetermined with three dimensional data. Some 2816 independent reflexions have been measured. Fullmatrix least-squares refinement with large matrices of up to 200 parameters has reduced Rto 4.00 % for the 1162 reflexions with intensities significantly above background and 11.04% for the total data set. Carbon atom positions were refined anisotropically and C-C distances have been determined with an estimated standard deviation of ±0.004 A. The average length of the six pen-bonds is 1.465(5) Å . These can be divided into two chemically equivalent sets with an average length of 1.467(3) Å for the four outer bonds and 1.462(6) Å for the central pair. The crystal contains dimers consisting of two centro-symmetrically related molecules separated by a mean perpendicular distance of 3.41 Å . This is smaller than the corresponding separation in a-perylene, and approaches the interlayer spacing in graphite. There are small, significant deviations from planarity in the quaterrylene molecule at least some of which seem to be related to the interactions between the two molecules of the dimer.