Arc discharge processes

Finally, significant amounts of single shell carbon nanotubes were obtained by adding metal catalysts such as Co, Fe, or Ni [15] [34] to the plasma arc process. The addition of metal catalysts seems to facilitate a controlled process by a VLS phase transformation. For example, the addition of cobalt was achieved with a modified positive carbon rod (electrode) into which a hole had been drilled that was filled with cobalt powder [34]. 

Single shell carbon nanotubes were produced in over 70 percent yields by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200°C [12] [81]. No multishell nanotubes were detected in the VLS process. X-ray diffraction and electron microscopy showed that the single shell nanotubes have uniform diameters and self-organize into metallic ropes (mats or arrays) of 100-500 nanotubes having a single-rope resistivity of 10 ohm-cm at 300 K. The particulate mixed-metal Ni-Co catalyst exists at the live end of the growing nanotube and leaves the end by evaporation. 

Even more perfect single wall (or shell) carbon nanotubes were reported by a scaled-up version [81] of the laser oven method described above [12]. This process yields a nearly endless, highly tangled raw nanotube material. It is purified in nitric acid and the resulting nanotube ropes, non-woven mats, or bucky paper can be cut into individual intermediate length (100-300 nm) macromolecules for further evaluation [81]. This method, which yields potentially endless nanotubes, will also be discussed in Chapter 3, which deals with continuous or potentially continuous fibers from the vapor phase. 

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FuUerenes can be made by either combustion or pyrolysis of aromatic hydrocarbons but are mostly prepared in arc-discharge processes. They have been studied extensively, and in fact, their studies developed into a new branch of organic... 

Application of composite electrodes in the arc discharge process is a well-known route to metallofullerenes [1], To prepare electrodes, a graphite rod is used to be coaxially drilled, stuffed with mixture of metal oxide, graphite powder and thermosetting resin then annealed under vacuum at ca. 2000°C. Such procedure seems to be laborious whereas the yield of metallofullerenes is low [2]. To increase the yield, composite electrodes structure was varied [2] and new equipment was... 

The composite electrode was prepared from 100x4x6 graphite rods. Lanthanum carbonate was applied to the rod surface from aqueous suspension, dried at room temperature, mounted into a reactor (Fig. 1) and kept for 8-10 h in residual gas (10 2 Pa) and helium under DC of 50-70 A. To perform arc discharge process helium pressure, voltage and DC were maintained within the ranges of 2 104-3 104 Pa, 20-25 V and 100-150 A, respectively. 

The formation mechanism of EMFs remains unclear. Informative results concerning the interactions between the encaged metals and the fullerene cage in isolated EMFs have been obtained, but many mysteries remain in the early stage of the arc-discharge process. Disclosure of these mysteries is helpful to increase the production yield and broaden the applications of EMFs. 

Certain nanotubes have been observed to form more frequently than others in the arc discharge process. In general, armchair-SWNTs grow better than zig-zag or chiral species. On one hand, this is due to the extraordinary thermodynamic... 

Lee G, Kim WY. Effect of powder synthesis atmosphere on the characteristics of iron nanopowder in a plasma arc discharge process. Metals Mater Int 2005 11(2) 177-81. 

Optimization of the arc discharge process parameters makes it possibie to improve the carbon nanotubes produced by specifically controlling the four characteristic regions and the purity level (as shown by the SEM micrograph in panel b) of the nanomaterials. ... 

The time scale is not fast (each synthesis requires at least one hour and the quantities of carbon nanotubes produced are much less than by the laser ablation and arc discharge processes, which are, in addition, faster than CVD. In this case the industrialization of the method involves different aspects regarding, principally, the alignment and density defects). 

Optical laser micrographs showing the 3D morphologies of the four characteristic regions present on the cathode surface after the arc discharge process. ... 

During arc discharge process, carbon atoms are evaporated by plasma of helium gas ignited by high currents passed through... 

Later, TEM study of the morphology of the carbon microtubules synthesized by arc discharge process revealed that there were many variations in shape, especially near the tips of... 

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