Arc-evaporation

In addition to diamond and amorphous films, nanostructural forms of carbon may also be formed from the vapour phase. Here, stabilisation is achieved by the formation of closed shell structures that obviate the need for surface heteroatoms to stabilise danghng bonds, as is the case for bulk crystals of diamond and graphite. The now-classical example of closed-shell stabilisation of carbon nanostructures is the formation of C o molecules and other Fullerenes by electric arc evaporation of graphite [38] (Section 2.4). 

Filled nanocapsules, as well as hollow nanoparticles, are synthesized by the dc arc-evaporation method that is commonly used to synthesize fullerenes and... 

Bamboo-shaped tubes. A carbon tube with a peculiar shape looking like bamboo, produced by the arc evaporation of nickel-loaded graphite, is shown in Fig. 8. The tube consists of a linear chain of hollow compartments that are spaced at nearly equal separation from 50 to 100 nm. The outer diameter of the bamboo tubes is about 40 nm, and the length typically several /im. One end of the tube is capped with a needle-shaped nickel particle which is in the normal fee phase, and the other end is empty. Walls of each compartment are made up by about 20 graphitic layers[34]. The shape of each compartment is quite similar to the needle-shape of the Ni particle at the tip, suggesting that the Ni particle was once at the cavities. 

Seraphin et a/. [39] reported that an arc evaporation of Fe/C composite anode also generated nanochains with similar morphology, described above. 

The PVD process by means of electric arc evaporation has attained a high degree of importance in deposition of hard layers on an industrial scale. The hardness achieved is a minimum of 2100 HV. Compare this to the standard nitriting process which provides a hardness of about 900 HV or the stelliting process which offers about 500-600 HV. Extmsion screws treaded with this special process in the tire industry have seen a much improved wear life when processing highly filled silica compounds or very hard apex compounds. 

In addition to fullerenes, many other carbon structures formed of six-, five- and seven-membered rings (predominantly six) are likely to be discovered. Special mention must be made of carbon nanotubes formed in the direct-current arc evaporation of graphite (lijima, 1991). The nanotubes are essentially made up of graphite sheets and have an inner core of around 1 nm with a variable number of graphite sheaths (Fig. 

In the course of the experiments conducted in parallel with the described method the carbon nanostructures have been produced by pyrolysis of hydrocarbons and by arc evaporation of graphite in the gas phase in order to compare physical and chemical peculiarities of the formation of nanostructures and morphology of their structure. 

The sphere-like carbon structures are formed during the arc evaporation of carbon in liquid nitrogen (Fig. 6(a)) in joint evaporation of carbon and nickel, the different structures comprising the mixture of cotton-like carbon product and nickel needle-shaped structures are fabricated (Fig. 6(b)). 

The product produced by the arc evaporation of graphite in liquid helium without additional purification contains up to 85-90% of carbon nanotubes. Such results are not always achieved using different methods for nanotubes purification (Fig. 7). 

Current fluctuations are damped by means of choking coil D connected in series. The rectifier starts operating by means of auxiliary electrode H which is connected to anode. 1, over the resistance W. When the rectifier is started it must be tilted so that the two pools of mercury accumulated at H and K merge into one. On restoring the rectifier to its normal position the pool of mercury is divided once again in two parts and gives rise to an electrical spark at the point of interruption the heat evolved by the spark causes that a certain amount of mercury, sufficient to ignite the arc, evaporates. 

The fullerenes, Cgo and C70, are produced in the laboratory by the contact arc-evaporation of 6 mm graphite rods (e.g. Johnson Matthey, spectroscopic grade) in 100 torr of helium in a water-cooled stainless steel chamber described previously [5]. The soluble material in the soot produced from the arc-evaporation is extracted with toluene using a Soxhlet apparatus. The pure fullerenes are obtained by chromatography on neutral alumina columns using hexanes as the eluant, or by the use of a simple filtration technique using charcoal-silica as the stationary phase and toluene as the eluant [5]. The fullerenes so prepared are characterized by UV/Vis spectroscopy and other techniques. FT-IR spectra of vacuum deposited fullerene films on KBr crystals also provide a means of characterization, just as do Raman spectra of films deposited on a silicon crystal. Ultraviolet and X-ray photoelectron spectra of fullerene films on... 

Graphene has been prepared by different methods pyrolysis of camphor under reducing conditions (CG), exfoliation of graphitic oxide (EG), conversion of nanodiamond (DG) and arc evaporation of SiC (SG). The samples were examined by X-ray diffraction (XRD), transmission electron microscopy, atomic force microscopy, Raman spectroscopy and magnetic measurements. Raman spectroscopy shows EG and DG to exhibit smaller in-plane crystallite sizes, but in combination with XRD results EG comes out to be better. The CG, EG and DG samples prepared by us have BET surface areas of 46,... 

Graphene was prepared by four different methods, namely the reductive pyrolysis of camphor (CG), exfoliation of graphitic oxide (EG),4 conversion of nanodiamond (DG)5 and arc evaporation of SiC (SG).6 In the first method, to prepare CG, camphor was pyrolysed over nickel particles under a reducing atmosphere. The reaction was carried out in a two-stage furnace and camphor was slowly sublimed (170 °C) by heating from the first furnace to the second furnace held at 770 °C where the... 

Composite graphite electrodes based on metal hydrides (YH3, LaH3, CeH3 and GdH3) were for the first time used in the synthesis of EMFs containing soot. The use of metal hydrides instead of metal sward afforded electrodes with metals more homogeneously distributed in a graphite rod that provided more stable electric arc evaporation of electrodes. 

The first large-scale synthesis of fullerenes was discovered in 1989 by Huffman and Kratschmer this provided a macroscopic quantity of Ceo in order to confirm the proposed icosohedral structure. Their technique consisted of the arc-evaporation of graphite electrodes via resistive heating within an atmosphere of ca. 100 atm. helium... 

Figure 6.20. Cross-section schematics of reactors used for fullerene synthesis. Shown are (a) a reduced-pressure fuel-rich pyrolytic chamber, and (b) a benchtop modified arc evaporation system. Reproduced with permission from (a) Hebgen, R Goel, A. Howard, J. B. Rainey, L. C. Vander Sande, J. B. Proc. Combust. Inst 2000,28,1397, Copyright 2000 Elsevier, and (b) Scrivens, W. A. Tour, J. A. J. Org. Chem. 1992,57, 6932. Copyright 1992 American Chemical Society.

D) N-Methyl-3,4-dihydroxy phenylalanine (IV).—In a carbon dioxide atmosphere, 12 g. (0.05 mole) of the methoxy compound is boiled gently for three hours with 24 g. of red phosphorus and a mixture of 60 cc. of acetic anhydride and 60 cc. of hydriodic acid, (sp. gr. 1.7). The phosphorus is then removed by filtration and washed with 25 cc. of 50 per cent acetic acid. The filtrates arc combined and, in a current of carbon dioxide, arc evaporated to a... 

A solution of 5 mmol of azido alkene in 5 mL of CII2C12 in a dry two-neckcd flask under Ar is cooled to 0°C, then 1.07 g (5.5 mmol) of thexylchloroborane-dimethyl sulfide complex are added slowly and the mixture is stirred for 4 h at r.t. Then 1 mL ol CH3OH is added and the mixture is further stirred for 10 min, the solvents arc evaporated under vacuum, and the residue is taken up in 10 mL of Et20. The amine hydrochloride is extracted with two 10-inL portions of 1 M HCl, then H20 is distilled under vacuum. The crystallized amine hydrochloride is purified by recrystallization. The free amine can be obtained by basic treatment and extraction with solvent. 

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