Carbon
The excellent work of Bui, Perron, and Read studied several process parameters pertinent to the calcination of green petroleum coke and the subsequent effect on calcined coke properties. One parameter studied was a calcination rate that was comparatively fast. Other work has shown that the calcination rate may be more important in its effect on anisotropic, or premium, coke properties that on more...
Mesophase pitch-based carbon fibers with circular and non-circular (ribbon, C-shaped) cross sections were coated with a thin, approximately 100-150 nm SiC-layer, using a CVD technique. The surface free energy of the uncoated and SiC-coated carbon fibers was determined by measuring the contact angle of a variety of liquids with known polar and dispersive components of their total surface free energy...
An experimental study was performed to determine the effect of processing conditions on the failure mechanisms and strength of 2-D carbon-carbon laminates under uniaxial compression and shear loading. Specifically, the mechanical properties are related to the size and density of material discontinuities which, in turn, depend upon the numbers of matrix impregnation and carbonization cycles, and subsequent...
Fibrous activated carbons were prepared from Kevlar (poly (p-phenylene terephthalamide)) and Nomex (poly (m-phenylene isophthalamide)) by carbonisation in nitrogen and subsequent activation in steam of carbon dioxide to varying burn-offs at 1123 K. The resultant chars were characterised by activation rate studies, scanning electron microscopy and, in the case of the Nomex chars, energy dispersive...
Highly crystallized graphite films were prepared by successive heat treatments at 3100°C for 40 minutes and then 3200°C for 23 minutes under atmospheric pressure of pure argon gas from thin carbonized polyimide films. The starting polyimide films were a commercially available Kapton and a laboratory prepared high-modulus-polymide film formed via polyamic acid gel. The crystallinity of the graphite...
Toroidal forms for graphitic carbon are classified into five possible prototypes by the ratios of their inner and outer diameters, and the height of the torus. Present status of research of helical and toroidal forms, which contain pentagons, hexagons, and heptagons of carbon atoms, are reviewed. By molecular-dynamics simulations, we studied the length and width dependence of the stability of the...
The structural, magnetic, and transport properties of bundles of buckytubes (buckybundles) have been studied. High-resolution electron microscopy (HREM) images have revealed the detailed structural properties and the growth pattern of buckytubes and their derivatives. The magnetic susceptibility of a bulk sample of buckybundles is -10.75 10 - 6 emu/g for the magnetic field parallel...
The fundamental relations governing the geometry of carbon nanotubes are reviewed, and explicit examples are presented. A framework is given for the symmetry properties of carbon nanotubes for both symmorphic and non-symmorphic tubules which have screw-axis symmetry. The implications of symmetry on the vibrational and electronic structure of 1D carbon nanotube systems are considered. The corresponding...
Macroscopic quantities of single-layer carbon nanotubes have recently been synthesized by co-condensing atomic carbon and iron group or lanthanide metal vapors in an inert gas atmosphere. The nanotubes consist solely of carbon, sp 2 -bonded as in graphene strips rolled to form closed cylinders. The structure of the nanotubes has been studied using high-resolution transmission electron microscopy...
We present experimental evidence that strongly supports the hypothesis that the electric field of the arc plasma is essential for nanotube growth in the arc by stabilizing the open tip structure against closure. By controlling the temperature and bias voltage applied to a single nanotube mounted on a macroscopic electrode, we find that the nanotube tip closes when heated to a temperature similar...
Recent developments using synthetic methods typical of fullerene production have been used to generate graphitic nanotubes with diameters on the order of fullerene diameters: carbon nanotubes. The individual hollow concentric graphitic nanotubes that comprise these fibers can be visualized as constructed from rolled-up single sheets of graphite. We discuss the use of helical symmetry for the...
This chapter discusses some aspects of the mechanical and thermal properties of carbon nanotubes. The tensile and bending stiffness constants of ideal multi-walled and single-walled carbon nanotubes are derived in terms of the known elastic properties of graphite. Tensile strengths are estimated by scaling the 20 GPa tensile strength of Bacon's graphite whiskers. The natural resonance (fundamental...
Clusters of C 6 0 and C 7 0 coated with alkali or alkaline earth metals are investigated using photo-ionization time-of-flight mass spectrometry. Intensity anomalies in the mass spectra of clusters with composition C 6 0 M x and C 7 0 M x (x = 0 500; M {Ca, Sr, Ba}) seem to be caused by the completion of distinct metal layers around...
Evidence is accumulating that carbon nanotubes are rarely as perfect as they were once thought to be. Possible defect structures can be classified into three groups: topological, rehybridization, and incomplete bonding defects. The presence and significance of these defects in carbon nanotubes are discussed. It is clear that some nanotube properties, such as their conductivity and band gap, will...
The structure of as-grown and heat-treated pyrolytic carbon nanotubes (PCNTs) produced by hydrocarbon pyrolysis are discussed on the basis of a possible growth process. The structures are compared with those of nanotubes obtained by the arc method (ACNT; arc-formed carbon nanotubes). PCNTs, with and without secondary pyrolytic deposition (which results in diameter increase) are found to form during...
Band structure calculations show that carbon nanotubes exist as either metals or semiconductors, depending on diameter and degree of helicity. When the diameters of the nanotubes become comparable to the electron wavelength, the band structure becomes noticeably one-dimensional. Scanning tunneling microscopy and spectroscopy data on nanotubes with outer diameters from 2 to 10 nm show evidence of one-dimensional...
Tubular and conical carbon shell structures can be synthesized in the vapor phase. Very hot carbon vapor, after being deposited onto highly oriented pyrolytic graphite (HOPG), forms a variety of nanostructures, in particular single-shell tubes, multishell tubes, bundles of tubes, and cones. The structures were analyzed by scanning tunneling microscopy (STM) in UHV. Atomic resolution images show...
Experimental and theoretical studies of the vibrational modes of carbon nanotubes are reviewed. The closing of a 2D graphene sheet into a tubule is found to lead to several new infrared (IR)- and Raman-active modes. The number of these modes is found to depend on the tubule symmetry and not on the diameter. Their diameter-dependent frequencies are calculated using a zone-folding model. Results...