G. Bister

Functional groups generated by mechanical and chemical breaking of multiwall carbon nanotubes

Since the discovery of carbon nanotubes several attempts were made to modify them by various physical and chemical methods. Applying a ball-milling system mechanical cutting of nanotubes can be achieved. TEM, surface area and porosity measurements are used to follow these changes on the nanotubes. Using different reagents and methods functional groups can be generated on the nanotubes. To prove the existence of these groups infrared spectroscopy is used. Finally, it will be shown that the physical and chemical breaking processes complete each other very well.

Textural properties of raw carbon nanotubes by nitrogen adsorption and mercury porosimetry

A sample of raw material made by catalytic decomposition of methane and containing a fraction of single-wall carbon nanotubes (SWNTs) was studied. Interpretation of mercury porosimetry and nitrogen adsorption-desorption isotherms was difficult because the purity of carbon nanotubes, thermogravimetry revealed, was rather poor. Indeed, the raw material was made up by carbon soot, graphitic disordered carbon, damaged nanotubes, SWNTs and catalyst residues. The raw material was mainly microporous with some mesopores.

Large scale synthesis of carbon nanotubes and their composite materials

MgO supported transition metals are very interesting systems for possible large scale synthesis of carbon nanotubes. Indeed, the catalytic decomposition of acetylene at high temperature leads to the formation of very thin multi-wall carbon nanotubes (inner and outer diameters are in the range of 2–4 nm and 5–9 nm, respectively). The decomposition of methane, on the other hand, produces bundles and isolated single-wall nanotubes (SWNTs) of high purity. Typically, the diameters of isolated SWNTs are 1–5 nm. For the SWNTs aligned in the bundles, the diameter values vary between 0.8 and 2 nm. The samples are characterized by TEM, and HREM. The purity of the nanotubes is evaluated by PIXE (proton induced X-ray emission) and by thermal analysis. The nanotubes are cut mechanically in a ball-mill and the introduction of various functional groups is determined by XPS. Finally, homogeneous mixture of carbon nanotubes and polyacrylonitrile will be shown.

Gram scale production of singlewall carbon nanotubes by catalytic decomposition of hydrocarbons

The quality of singlewall carbon nanotubes produced by catalytic decomposition of hydrocarbons depends on the synthesis conditions but also on the scale of production. Singlewall nanotubes are produced by the decomposition of methane over cobalt based catalyst supported on magnesium oxide. The characteristics of the samples produced at different gas flows are studied by TEM, TGA, XRD, PIXE and Raman spectroscopy. A process is suggested to remove amorphous carbon and a part of the cobalt particles from the samples.

Optimization of the amount of catalyst and reaction time in single wall nanotube production

The influence of the amount of catalyst and the reaction time on the quantity and quality of catalytically grown single wall carbon nanotubes (SWNT) was investigated. The aim was to optimize some of the SWNT growth parameters using TEM and HRTEM . The thickness of catalyst layer influences the synthesis of the nanotube because the gas composi ti n can differ between top and bottom. Microscopic investigation of the grown SWNT samples showed t hat the thicker the catalyst layer the lower relative nanotube content, so the deeper pa rts of the catalyst layer are less effective. The optimum time for the reaction was found to be 10 minutes . Thi may be understood assuming that nanotube growth needs an initial incubation time while the ac ivity of the catalyst decreases steadily until the nanotube growth stops.