DC-Arc discharge

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... 

Ahmad B, Riaz M, Ahmad M et al (2008) Synthesis and characterization of higher fullerene (C84) in dc arc discharge using Cu as a catalyst. Mater Lett 62 3367-3369... 

Metallofullerenes can be synthesized typically in two ways similar to the s)mthesis of empty fullerenes, which involves the generation of a carbon-rich vapor or plasma in He or Ar gas atmosphere. The two methods have been routinely used to date for preparing macroscopic amounts of metallofullerenes the high-temperature laser vaporization or "laser-furnace method (Chai et al., 1991 Haufler et al., 1991 Ying et al., 1994) and the standard direct current (DC) arc discharge method (Haufler et al., 1990). Both methods simultaneously generate a mixture of hollow fullerenes (Ceo, C70, C76, C78, Cs4,...) together with metallofullerenes. The production of metallofullerenes can be followed by procedures to extract from soot and to separate/purify the metallofullerenes from the hollow fullerenes (see Sections 2.2, 3.1, and 3.2). 

Figure 4 represents a third-generation large-scale DC arc discharge apparatus for the production of metallofullerenes developed and installed at Nagoya (Dennis and Shinohara, 1998 Nakane et al., 1997 Shinohara, 1998, 2000 Shinohara et al., 1996a). The arc generator consists... 

FIGURE 4 A cross-sectional view of the third-generation DC arc discharge apparatus (in Nagoya University) with an anaerobic collection and sampling mechanism. The produced metallofullerene-containing soot is effectively trapped by the liquid N2 trap installed in the center of the collection chamber. Typical arc discharge conditions 40-100 Torr He flow, 300-500 A, and 25-30 V. 

Methods used to synthesize fullerenes are also adopted for metallofullerene production. Because metal sources are necessary for producing EMFs, only laser ablation [60] and DC arc-discharge [6] are effective methods. 

Lian, Y. R, Shi, Z.J., Zhou, X.H. etal. (2000) High-yield preparation of endohedral metallofullerenes by an improved DC arc-discharge method. Carbon, 38, 2117-2121. 

A common DC glow discharge PACVD system may be varied by operating the plasma at higher pressures and powers at which a DC arc discharge between the electrodes can be produced. In 1988, Kurihara et al.t l first reported the use of the DC plasma arc-jet CVD method, in which... 

DC Arc Plasma Jet Gas Stabilized Arc DC arc discharge formed between nonsample electrodes in flowing gas streams of argon or helium. Sample introduced separately. liquids, powders 1500-3500... 

The spectra of DC-arc discharges are considerably different from those observed for flames and sparks. Because of the high temperature of the arc column, sufficient energy is available to populate higher atomic states. A complex spectrum, generally composed of neutral-atom and ion emission, results. 

A feature common to all these DC plasma sources is the DC arc discharge. The discharge is stabilized in various ways or transferred away from the arc column to produce a flame-like appearance (plasmajet). DC plasmas are divided into two groups (i) current carrying DC plasmas, and (ii) current free DC plasmas or plasmajets. 

The only effective methods for producing endohedral metallofullerenes are laser ablation and DC arc discharge, techniques that are similar to the production of fullerenes. The DC arc method has become more popular because the laser ablation method has low yields and is costly. 

The DC arc technique is carried out in a water-cooled chamber with a graphite cathode and a graphite anode that has been doped with the desired metal and a catalyst in the presence of a gas, usually helium. One reason for the lack of transition-metal endohedral fullerenes can be attributed to the difficulty of current DC arc-discharge methods to cause encapsulation of transition metals in fullerenes, for which the reason remains unclear. For this reason, transition metals are... 

The major products formed by DC arc discharge are empty fullerenes, with the endohedral fullerenes composing only about 1% of the raw soot. For this reason, better extraction methods are always being sought. Sublimation is a fairly efficient metiiod for extraction and is a solventless technique. Nevertheless, file most popular method for extraction of endohedral fiiUerenes is solvent extraction. Some popular solvents for extraction are xylene, carbon disulfide, and toluene. The efficiency of this method is not great because about half of the endohedral fiillerenes remain in the extracted residue, which needs further processing with other solvents. Extraction of trimetallic nitride endohedral fiillerenes has a higher efficiency because of increased solubility in common solvents. 

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