Onion-like Particles Research Articles

Transformation of carbon nanotubes to nanoparticles by ball milling process

Carbon nanotubes were treated by high-energy ball milling processing for different milling times, and the samples were observed by HRTEM. The broken nanotubes and lots of carbon onion-like particles were obtained in the sample milled for 15 min. When the milling time was up to 60 min, carbon nanotubes turned into amorphous carbon. On the basis of HRTEM observation of carbon nanotubes and carbon nanoparticles, we discuss the possible formation mechanism of nanoparticles under the impact acting as driving force.

Macroscopic synthesis of onion-like graphitic particles

In this paper, we present a method for macroscopic synthesis of onion-like graphitic particles, which may be used to study physical properties. This method is based on annealing carbon nanotubes under high pressure. By transmission electron microscopy (TEM), the microstructure of carbon nanotubes is found to transform into quasi-spherical graphitic structures when the sample has been treated at 770 °C and 950 °C under 5.5 GPa. The high pressure assumes an important role in this transformation.

A NEW WAY OF MAKING BUCKY ONION BY THERMAL DECOMPOSITION OF SiC NANOMETER POWDERS UNDER HIGH-TEMPERATURE AND VACUUM

Bucky onions have been produced by decomposing SiC nanometer powders under high- temperature and vacuum. Transmission electron microscope and high resolution electron microscope observations show that when SiC particles decompose completely, they transform into quasi-spherical hollow carbon particles and onion-like particles composed of concentric graphitic shells. When SiC particles decompose incompletely, they become compound particles, which are composed of β-SiC in particles and of quasi-concentric graphitic shells on surface of particles. The results suggest that the traditional idea that planar graphite is the most stable form of pure carbon would then have to be seriously discussed.

An atomic force microscope study of carbon onions and related nanoparticles

Carbon onions are found along with carbon nanotubes and other carbon nanoparticles in the cathodic deposit in the arc-vaporization of graphite. Atomic force microscopy has been used to characterize these particles on the basis of their sizes and shapes. Onion-like particles have three-dimensional, near spherical structure and are distinct from two-dimensional graphitic particles. The spherical shape and height to diameter ratios obtained using atomic force microscope, afford a distinction between onion-like structures and other carbon nanoparticles.

Onion-like graphitic particles produced from diamond

Onion-like particles composed of concentric spherical graphitic shells have been obtained by irradiating diamond crystals with 200 keV electrons. The onion-like structures were found to be producible only in intense electron beams with an irradiation flux density of about 107 electrons/nm2 s or greater. The genesis of this nanostructure of carbon was suggested to follow a three-step mechanism comprising displacements, migration, and aggregation. Electrical charging and electron-beam enhanced diffusion are proposed to be central to the high rate formation. The atomic evolution in diamond-graphite transformation is also discussed in connection with a recently reported model.

Onion-like graphitic particles

Nanometric graphitic structures (fullerenes, nanotubes, bucky-onions, etc.) form in different harsh environments (electric arc, electron irradiation, plasma torch). In particular, the onion-like graphitic particles may display a wide range of structures, going from polyhedral to nearly spherical. High-resolution electron microscopy is the primary tool for studying these systems. On the basis of HREM observations, we discuss the energetics and possible formation mechanism of these multi-shell fullerenes. The better understanding of the underlying processes would allow the development of an efficient production method.

Effect of explosion conditions on the structure of detonation soots: Ultradisperse diamond and onion carbon

Detonations of a number of pure and composite explosives with the negative oxygen balance in a hermetic tank filled with inert gas (N 2, Ar) have yielded the diamond containing solid carbonaceous products (soots). The influence of detonation parameters, namely (a) the inert gas pressure in the tank decreasing the effective temperature of detonation products, and (b) the composition of explosives determining the detonation pressure and temperature, on the nature and the yield of detonation soots have been investigated by TEM, XRD, SAXS, and auger spectroscopy. The soots contain ultradisperse diamond (UDD, 20–150 Å) along with amorphous carbon (40–250 Å), graphite ribbons (with length less than 200 Å), and spheres (20–40 Å) made of concentric graphite shells (onion-like carbon, registered only in the experiments with low initial inert gas pressure). It was shown that UDD thermally transformed into onion-like carbon particles. The detonation parameters have been optimized to increase the UDD yield.

Very long graphitic nano-tubules synthesized by plasma-decomposition of benzene

Ver long (over 0.2 mm) graphitic nano-scale tubules and spherical onion-like particles were synthesized by plasma-decomposition of benzene. A new model for the tubules formation is proposed.

Formation mechanism of quasi-spherical carbon particles induced by electron bombardment

A detailed study of the transformation of graphitic structures into spherical onion-like particles under electron bombardment is presented. This evolution has been monitored up to the atomic details in a high-resolution electron microscope. The transformation from a tubular or polyhedral graphitic particle into a quasi-spherical onion is made in several steps, firstly the innermost shell collapses, then the regraphitization begins in the surface and follows towards the center by a sort of internal epitaxy.

On the 2175 A absorption band of hollow, onion-like carbon particles

view Abstract Citations (32) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the 2175 Angstrom Absorption Band of Hollow, Onion-like Carbon Particles Henrard, L. ; Lucas, A. A. ; Lambin, Ph. Abstract We present a theoretical result on the ultraviolet absorption of nanoscale graphite onions with a central void. The polarizability and the excitation cross section of particles in this geometry are obtained in the electrostatic (nonretarded) approximation and using a 'spherically uniaxial' dielectric tensor transported from planar graphite. We study the influence of the ratio r/R of the inner and outer radii on the extinction efficiency. It appears that the onion particles for r/R about 0.6 well reproduce the observed UV absorption bump of interstellar dust around 5.7 eV. We also investigate the effects of the hollow structure of the carbon particles on a second absorption peak around 18 eV. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172422 Bibcode: 1993ApJ...406...92H Keywords: Absorption Cross Sections; Fullerenes; Graphite; Interstellar Extinction; Particle Size Distribution; Ultraviolet Absorption; Absorption Spectra; Interstellar Matter; Astrophysics; ISM: DUST; EXTINCTION; ISM: MOLECULES full text sources ADS |