Sylvie Bonnamy

Fluorination of carbon nanotubes

Abstract Carbon nanotubes were prepared by thermal decomposition of acetylene over silica-supported cobalt catalysts. Subsequent chemical treatments with concentrated hydrofluoric acid and dilute nitric acid, respectively, eliminated the silica substrate and the remaining catalyst. The complete removal of cobalt was very difficult due to encapsulation of part of it in the shells, but a graphitization at 2800 °C eliminated the rest of cobalt and the structural defects. The reactivity of carbon nanotubes with fluorine was studied and compared to that of graphite. Important modification of the nanotubes structure was observed after reaction at high temperature as against the behaviour observed during reaction at room temperature. Compounds were analysed by means of transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy.

Electrochemical insertion of lithium in catalytic multi-walled carbon nanotubes

Electrochemical lithium insertion was studied into purified and heat-treated catalytic multi-walled carbon nanotubes. It appears that the irreversible capacity for the MWNTs is relatively large, but decreasing with annealing temperature. This clearly shows that the intrinsic entanglement and the microtexture of the nanotubes must be responsible for this drawback of any potential application as an anode. The crucial role of the charge cut-off on the «traditional» intercalation was underlined and the reversible capacity was assigned to particular Li sites by high resolution NMR spectroscopy.

Coalescence of single-walled carbon nanotubes and formation of multi-walled carbon nanotubes under high-temperature treatments

Electric arc-discharge single-wall carbon nanotubes are annealed between 1600 and 2800 °C under argon flow. Their stability and evolution are studied by coupling TEM, X-ray diffraction and Raman spectroscopy. The first modifications appear at 1800 °C with a significant decrease of the crystalline order. It is due to SWNTs coalescence leading to smaller bundles but with an increase of the tube diameters from 2 to 4 nm. From 2200 °C, SWNTs progressively disappear to the benefit of MWNTs having at first two to three carbon layers then reaching 7 nm external diameter. The possible mechanisms responsible for the SWNTs coalescence and instability and their transformation in MWNTs are discussed.

High yield of pure multiwalled carbon nanotubes from the catalytic decomposition of acetylene on in-situ formed cobalt nanoparticles.

For the first time, multiwalled carbon nanotubes (MWNTs) could be formed selectively in a high yield, free of any disordered carbon by-product, from the catalytic decomposition of acetylene at 600 degrees C on a CoxMg(1-x)O solid solution. Starting from 1 g of catalytic substrate, 4 g of pure MWNTs were obtained after its dissolution in boiling concentrated HCl, without any additional purification in strongly oxidizing medium, as is required for other methods of nanotube production. In situ reduction of CoO by dihydrogen liberated from acetylene decomposition allows highly divided metal particles to be continuously produced as synthesis proceeds. This is undoubtedly the reason for the good performance of the catalyst and for the ability to produce nanotubes in a narrow diameter range, namely from 10 to 15 nm. With the use of acetylene instead of methane, the synthesis proceeds at low temperature, which prevents the growth of carbon shells, in which the metal particles are generally embedded, decreasing their activity. Because of the very low specific surface area of the catalyst support, the amount of disordered carbon by-product formed is negligible.

Lithium interaction with carbon nanotubes

Abstract Lithium interaction with catalytic carbon nanotubes under high-pressure conditions was studied. A large amount of Li (2Li/C) reacted with the carbon nanotubes forming an intercalation compound (Ic~4.1 A) which follows from X-ray diffraction and IR spectroscopy data. We cannot exclude also the possibility of insertion of a part of Li into the channel of the nanotubes.

Mass spectrometry during C/C composite friction: carbon oxidation associated with high friction coefficient and high wear rate

Abstract The friction of C/C composites has been studied using a pin-on-disc tester equipped with a mass spectrometer allowing the gas exchange analysis in the contact. An oxidation of the contact regions and/or wear particles is detected by a release of CO 2 associated with a consumption of O 2 . It starts when a transition from low to high friction and dusting regime occurs. The water vapor role in this oxidation mechanism is more complex. The change of friction coefficient appears at a relatively low bulk temperature (

Mechanism of anisotropy occurrence in a pitch precursor of carbon fibres: Part I—Pitches A and B

Abstract Anisotropie pitch B issued from a coal tar pitch A is a mixture of isotropic phase 1 containing Brooks and Taylor mesophase spheres and an edge-to-edge type of gel 2.3. The latter is a two-phasedisperse system made of an anisotropic network 2 of carbon basic structural units (BSU), associated edge-to-edge, including isotropic microdroplets 3. The gel is quinoline soluble-toluene insoluble (QS.TI) (i.e., β resins and able to swell in tar).

Functionalization of multiwall carbon nanotubes: Properties of nanotubes-epoxy composites

Multiwall nanotubes were functionalized using plasma treatments, chemical oxidation, ball milling and thermal treatments. In optimized conditions, plasmas modify nanotubes surface chemistry with a great selectivity. Vickers microindentation and tension tests performed on epoxy resin loaded with multiwall nanotubes allow comparison of the influence of nanotubes surface chemistry and microtexture on loaded resin mechanical properties.

Electrochemical Properties of Carbon Nanotube Fluorides in a Lithium Cell System

Abstract Carbon nanotubes synthesized by decomposition of acetylene over silica-supported cobalt catalysts were fluorinated in different conditions : at room or high temperature, ca. 500°C. The electrochemical behaviour of these carbon nanotube fluorides as electrode materials in a lithium cell was investigated using a liquid electrolyte. Results are compared to those obtained with graphite fluoride compounds which present a well known high electrochemical performance.

Synergy of components in supercapacitors based on nanotube/polypyrrole composites

Multiwalled nanotubes (MWNTs) composites with electrodeposited polypyrrole (PPy) have been proposed as electrode materials for supercapacitors. The total capacitance of the nanocomposite combines a pure electrostatic attraction of ions and the electrochemical redox reactions of the -conjugated system of PPy. A synergy effect has been found between the two components of the nanocomposite. The mesoporous network of the nanotubular material supplies very good transport conditions for ions, and PPy enhances its conducting properties. A high ability of charge accumulation in such volumetric capacitor was obtained with capacitance values of 165 F/g of material.