Arc-discharge

The arc discharge is commonly used to volatilize and ionize thermally intractable inorganic materials such as bone or pottery so that a mass spectrum of the constituent elements can be obtained. 

The exact conditions of gas pressure, current flow, and applied voltage under which the discharge occurs determine if it is of the corona, plasma, or arc type. The color of the emitted light may also change, depending not only on the type of gas used but also on whether it is a corona, plasma, or arc discharge. 

Thus, either the emitted light or the ions formed can be used to examine samples. For example, the mass spectrometric ionization technique of atmospheric-pressure chemical ionization (APCI) utilizes a corona discharge to enhance the number of ions formed. Carbon arc discharges have been used to generate ions of otherwise analytically intractable inorganic substances, with the ions being examined by mass spectrometry. 

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... 

Carbon tubules (or nanotubes) are a new form of elemental carbon recently isolated from the soot obtained during the arc-discharge synthesis of fuller-enes[I]. High-resolution electron micrographs do not favor a scroll-like heUcal structure, but rather concentric tubular shells of 2 to 50 layers, with tips closed by curved, cone-shaped, or even polygonal caps. Later work[2] has shown the possibility of obtaining singleshell seamless nanotubes. 

Graphite was tised as substrate for the deposition of carbon vapor. Prior to the tube and cone studies, this substrate was studied by us carefully by STM because it may exhibit anomalotis behavior w ith unusual periodic surface structures[9,10]. In particular, the cluster-substrate interaction w as investigated IJ. At low submonolayer coverages, small clusters and islands are observed. These tend to have linear struc-tures[12j. Much higher coverages are required for the synthesis of nanotubes and nanocones. In addition, the carbon vapor has to be very hot, typically >3000°C. We note that the production of nanotubes by arc discharge occurs also at an intense heat (of the plasma in the arc) of >3000°C. 

In a common method for the production of tubular carbon fibers, the growth is initiated by submicrometer size catalytic metal particles[19]. Tube growth out of a graphite rod during arc-discharge might also be related to nanoparticle-like seeds present... 

During the last years, several authors have reported the production of carbon nanotubes by the catalytic decomposition of hydrocarbons in the presence of metals[l-5]. More recently, carbon nanotubes were also found as by-products of arc-discharge[6] and hydrocarbon flame[7] production of fullerenes. 

In this article, we describe and summarize our studies on the structural, magnetic,and transport properties of buckytubes. In addition, we describe how a conventional arc discharge can be modified into a stable glow discharge for the efficient synthesis of well-aligned buckytubes. 

Fig. 9. Photographs of the cro.s.s-.section of the deposited rods photos (a) and (b) were taken from deposited rods produced by the glow discharge and by the conventional arc discharge, respectively.

The electric arc is the easiest and most frequently used experiment to produce onion-like particles. A dc arc-discharge is used to generate a carbon deposit on the negative electrode following the procedure for... 

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