Formation Of Carbon Structures Research Articles

Formation of core-shell structures upon methane decomposition on metal-carbon composites with cobalt nanoparticles encapsulated into a porous carbon matrix

A method for the synthesis of core-shell structures during methane decomposition in a cobalt-carbon composite with metal particles uniformly dispersed in its bulk is proposed. These composites are obtained by the low-temperature formation of carbon structures based on reactive conjugated polymers obtained by the dehydrochlorination of chlorine-containing carbon-chain polymers. Eelectron microscopy studies show the formation of structures containing 10–50 graphene layers closely packed around a metal core with an interlayer distance of 0.34–0.35 nm.

Thermodynamics and kinetics of carbon deposits on cobalt: a combined density functional theory and kinetic Monte Carlo study.

We have built a lattice gas model for cobalt-carbon interaction to investigate the thermodynamics and kinetics of carbon deposition on Co(0001) surfaces. The formation of carbon structures on cobalt is considered to be one of the causes of deactivation of a cobalt Fischer-Tropsch (FT) catalyst. The formation of graphene - the most thermodynamically stable phase under FT conditions - is kinetically inhibited during the first 30 hours of exposure of the surface to carbon, while the build-up of surface carbide is the fastest reaction. Our simulations clearly show that the kinetics of carbon deposition is the result of two competing effects: a fast subsurface diffusion and a slower surface diffusion to form a carbon-carbon bond.

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C60 and C70 fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp2 bond hybridization under hydrothermal conditions was proposed.

Release of a diamond-like film on a nickel surface irradiated simultaneously with carbon ions and electrons

Nickel samples at temperatures of 300–1000°C have been irradiated simultaneously with 10-to 30-keV C+ ions and 1-to 5-keV electrons. The release of implanted carbon atoms on the surface of a sample with the formation of a transparent carbon film with the prevailing sp3 hybridization has been observed. The thickness of the film is several tens of nanometers. The formation of films is attributed to the acceleration of the formation of carbon structures in samples irradiated by accelerated electrons.

Formation of carbon structures upon decomposition of organic molecules on the surface of a dielectric under the action of IR femtosecond laser radiation

The formation of carbon structures as a result of decomposition of some organic molecules on the surface of metal fluorides (without molecular decay in a gas) exposed to IR femtosecond laser radiation with a wavelength of 3.3–5.4 μm is revealed. The determining influence of the laser pulse intensity on the efficiency of the decomposition process has been ascertained. A possible mechanism of the decomposition of molecules on the surface and of the growth of carbon structures has been proposed.

SR XRF study of natural micro- and nanostructured carbon from igneous rocks

Carbon micro- and nanoscale structures formed during the consolidation of magmatic rocks is investigated. They are very similar to nanoscale carbon structures synthesized in a laboratory. A wide range of elements (Fe, K, Ti, V, Cr, Mn, Ni, Pt, Zn, Ga, Ge, Br, Sr, Zr, and Pb) are identified by XRF analysis in natural globules of graphite containing micro- and nanoscale structures. Some of these elements are thought to be natural catalysts in the formation of carbon structures by chemical vapor phase deposition (CCVD); the rest (rare-earth and noble metals) are considered to be useful as indicators of host rock mineralization.

Synthesis and characterization of carbon nanospheres obtained by microwave radiation

Carbon microparticles mixed with 10wt.% zinc oxide microparticles were irradiated with microwaves in a vacuum. Characterization was made by X-ray diffraction, scanning and transmission electron microscopy and Raman spectroscopy. The micrographs showed that a morphological transformation occurred with the formation of carbon structures in the shape of micrometric spheres. High resolution transmission electron microscopy showed that for a reaction time of 3.5min, carbon nanospheres were obtained with an average diameter less than 35nm with zinc oxide nanoparticles of 4nm diameter inside them.

Formation of Carbon Structures on Stepped and Chiral Surfaces

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Formation of sub-micron size carbon structures by plasma jets emitted from a pulsed capillary discharge

We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (100) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300–1000nm spectrometer. The OES results show the presence of H, CH and C2 Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures.

Synthesis and Characterization of Carbon Nanostructures as Catalyst Support for PEMFCs

A detailed procedure for synthesis, characterization, and possibility of carbon nanostructures (CNS) as support for catalysts in polymer electrolyte membrane fuel cells (PEMFCs) is presented. The fabrication process is two-staged ballmilling of carbon graphite in the presence of hydrogen and transition metals (Fe, Co) followed by heating of the milled carbon initially in an argon atmosphere. The milling induces amorphous forms of carbon and metal, as well as C-H bonds. During the second stage, the production of methane by catalytic reaction of the bonded carbon and hydrogen is first observed, followed by the formation of metallic nanocrystals, and, finally, the formation of carbon structures on the metallic nanocrystals at a temperature of . Subsequently, metals and carbon nanoparticles are removed from the as-prepared sample. The purified samples are platinized after surface treatment by either air or chemical oxidation. Material characterization results obtained by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectrocopy, and atomic adsorption spectroscopy are presented. In addition, we also report their measured electrical conductivity, specific surface, and porosity. The real electrochemical active surface area was evaluated by cyclic voltammetry on a thin porous coated electrode.