Arc Discharge Methods

Abstract—Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated. 

Fig. 11. The loss of carbon rapidly increases with the increase of temperature. Heating of the catalysts in open air for 30 minutes at 973 K leads to the total elimination of carbon from the surface. The gasification of amorphous carbon proceeds more rapidly than that of filaments. The tubules obtained after oxidation of carbon-deposited catalysts during 30 minutes at 873 K are almost free from amorphous carbon. The process of gasification of nanotubules on the surface of the catalyst is easier in comparison with the oxidation of nanotubes containing soot obtained by the arc-discharge method[28, 29]. This can be easily explained, in agreement with Ref [30], by the surface activation of oxygen of the gaseous phase on Co-Si02 catalyst.

The characteristics of nanotubules obtained by catalytic reaction are better controlled than in the arc-discharge method. By varying the active particles on the surface of the catalyst the nanotubule diameters can be adjusted. The length of the tubules is... 

Laser-ablation method shown in Fig. 3 was used when Cgo was first discovered in 1985 [15]. This method has also been applied for the synthesis of CNT, but length of MWCNT is much shorter than that by arc-discharge method [17]. Therefore, this method does not seem adequate to the synthesis of MWCNT. However, in the synthesis of SWCNT described later (Sec. 3.1.2), marvelously high yield has been obtained by this method. Hence, laser-ablation method has become another important technology in this respect. 

MWCNT synthesized by catalytic decomposition of hydrocarbon does not contain nanoparticle nor amorphous carbon and hence this method is suitable for mass production. The shape of MWCNT thus produced, however, is not straight more often than that synthesized by arc-discharge method. This differenee could be aseribed to the strueture without pentagons nor heptagons in graphene sheet of the MWCNT synthesized by the catalytic decomposition of hydrocarbon, which would affect its electric conductivity and electron emission. 

MWCNT was first discovered by arc-discharge method of pure carbon and successive discovery of SWCNT was also based on the same method in which carbon is co-evaporated with metallic element. Optimisation of such metallic catalyst has recently been performed. Although these electric arc methods can produce gram quantity of MWCNT and SWCNT, the raw product requires rather tedious purification process. 

The laser-ablation method can produce SWCNT under co-evaporation of metals like in the electric arc-discharge method. As metallic catalyst Fe, Co or Ni plays the important role and their combination or addition of the third element such as Y produces SWCNT in an efficient manner. But it is still difficult in the laser-ablation method to produce gram quantity of SWCNT. Nonetheless, remarkable progress in the research of physical properties has been achieved in thus synthesized SWCNT. 

An MWCNT has inner concentric tube(s) with smaller diameter(s) inside its hollow, and it is normally prepared in the carbon electrode of the arc-discharging method or by chemical vapour deposition method (see Chaps. 2 and 12). Influence of such inner tubes on the most outer layer in MWCNT is of interest with respect to electronic similarity of MWCNT and SWCNT. 

Crude CNTs containing nanoparticles are produced by the arc-discharge method [8]. Although the quantitative value of CNTs cannot be determined because of the unknown amounts of nanoparticles, the whole susceptibility and spin susceptibility of the crude CNTs are reported by a number of researchers. 

Optimisation of SWCNT production has been attempted within the framework of the arc-discharge method in which anode and cathode were made of graphite rods, a hole in the anode being filled with metal catalysts such as Y (1 at.%) and Ni (4.2 at.%) [7]. A dense collar deposit (ca. 20% of the total mass of graphite rod) formed around the eathode under He (ca. 500 Torr), with 30 V and 100 A de eurrent. It was eonfirmed that this optimal eollar eontained large amounts of SWCNT bundles eonsisting of (10, 10) SWCNTs (diameter 1.4 nm). Such morphology resembles that produced by the laser ablation teehnique [4,5]. 

By the template technique using anodic oxide films and pyrolytic carbon deposition, one can prepare monodisperse carbon tubes. Since the length and the inner diameter of the channels in an anodic oxide film can easily be controlled by changing the anodic oxidation period and the current density during the oxidation, respectively, it is possible to control the length and the diameter of the carbon tubes. Furthermore, by changing the carbon deposition period, the wall thickness of the carbon tubes is controllable. This template method makes it possible to produce only carbon tubes that are not capped at both ends. Various features of the template method are summarized in Table 10.1.1 in comparison with the conventional arc-discharge method. 

Metal Filling in Carbon Nanotubes Prepared by Arc-Discharge Method... 

A Co/Ni alloy is the next active catalyst among the binary combinations within the iron-group metals in the arc discharge method (51). Laser vaporization of metal/ carbon composite in argon atmosphere at high temperature (1200°C) can also produce SWNTs (41). Guo et al. (41) reported that the Co/Ni alloy was the most effectual, with a yield of 50-90% in the laser ablation method. 

The typical voltammetric curve for a solution of SWNTs in organic solvents displays a continuum of diffusion-controlled current, with onset, in both the negative and the positive potential region, that depends on the nanotube average diameter and ultimately on the NT preparation technique. In fact, SWNTs prepared according to the arc-discharge method display an anticipated onset with respect to HiPco ones... 

For the analysis of NCM electrical resistance the NCM samples obtained by the arc-discharge method were taken. A part of the samples was subjected to thermochemical treatment in order to change its structure and phase composition. The X-ray diffraction analysis and TEM were used to characterize the structure and morphology NCM [3], The structure and phase composition of each sample are described in Table 1. Evidently, the ratio of ordered (CNT) to disordered phase contents increases from sample I to sample V. Besides the particles of nanographite were found in two last samples. 

In an earlier publication we showed that fullerene may be synthesized not only under low pressure conditions, but under atmospheric pressure as well [4]. In this work we present the result of fullerene synthesis by the arc discharge method under atmospheric pressure in which currents of different frequencies are applied. 

We could solubilize purified single-walled carbon nanotubes (SWNTs)11 in the fluorous medium by reacting them with heptadecafluoroundecylamine. For this purpose, we first prepared SWNTs by the arc discharge method and purified them by HNO3 and FL treatment.11 To solubilize the nanotubes, 1.5 mg of SWNTs, 22 uL of the heptadecafluoroundecylamine (SWNTs/amine = 2 1), and 3 mL of perfluorohexanne were sealed in a 7 mL Teflon-lined stainless steel autoclave and heated at 130 °C for 48 h. This process produced a clear solution of SWNTs in perfluorohexane, as can be seen from Figure 5a. 

Figure 1. TEM images of (a) as-synthesized SWNTs obtained by the arc-discharge method, (b) after acid treatment, (c) after first hydrogen treatment, and (d) after the second hydrogen treatment.

One major issue of the nanotube elaboration processes is to produce nanotubes with controlled dimensions (diameter, length) and without byproducts (catalytic residues, other carbonaceous particles). This is nearly achieved with processes such as catalytic chemical vapour decomposition using supported catalysts. However, the arc discharge method remains the most common one and is perhaps the easiest way to produce the large quantities of nanotubes required for the elaboration of composites (49). The dimensions of... 

Fullerenes (Q0) Carbon, but only the water-soluble derivatives of Cm used in pharmacy C60 obtained by arc discharge method using graphite electrodes or in a benzene flame, water-soluble Cm derivatives obtained by acid processing followed by conjugation with drugs 38,56... 

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