Helium fullerene

It may be of interest that the helium-fullerene complex is in fact a natural product. It has been detected in distant stars, where it has existed in large tonnage amounts for millions of years. This recalls to mind the fact that helium was discovered in the sun (by the presence of intense lines in the visible spectrum). This fact was indicated by the name chosen for it, which is from the Greek word helios, meaning sun. It was only later discovered to exist in Earth s crust. 

The possibility that an even larger impact caused the P T extinction received support when Becker and Poreda found that helium and argon atoms were present in the inner cores of some of the fullerenes from the P T boundary sediments (The cover of this book shows a helium atom inside a mol ecule of Ceo) What is special about the fullerene trapped atoms is that the mixtures of both helium and argon isotopes resemble extraterrestrial isotopic mixtures more than earthly ones The He/ He ratio in the P T boundary fullerenes for example is 50 times larger than the natural abundance ratio... 

What a storyi Fullerenes formed during the ex plosion of a star travel through interstellar space as passengers on a comet or asteroid that eventually smashes into Earth Some of the fullerenes carry pas sengers themselves—atoms of helium and argon from the dying star The fullerenes and the noble gas atoms silently wait for 251 million years to tell us where they came from and what happened when they got here... 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

Now and then, projectiles from outer space cause excitement and surprises, as in January 2000, when a meteorite impacted the frozen surface of Lake Targish in Canada. It was a new type of C-chondrite with a carbon concentration of 4-5%, and probably came from a D-type asteroid (Hiroi et al., 2001). More exact analysis of the Targish meteorite showed the presence of a series of mono- and dicarboxylic acids as well as aliphatic and aromatic hydrocarbons (Pizzarello et al., 2001). Aromatic compounds and fullerenes were detected in the insoluble fraction from the extraction this contained planetary helium and argon, i.e., the 3He/36Ar ratio was... 

Arc discharge [25] is initially used for producing C60 fullerenes. Nanotubes are produced by arc vaporization of two carbon rods placed in a chamber that is filled with low pressure inert gas (helium, argon). The composition of the graphite anode determines the type of CNTs produced. A pure graphite anode produce preferably MWNT while catalyst (Fe, Co, Ni, Y or Mo) doped graphite anode produces mainly SWNT. This technique normally produces a complex mixture of components, and requires further purification to separate the CNTs from the soot and the residual catalytic metals present in the crude product. 

T. Jarrosson, G.-W. Wang, M. D. Bartberger, G. Schick, M. Saunders, R. J. Cross, K. N. Hock, Y. Rubin, Insertion of Helium and Molecular Hydrogen Inside an Open Fullerene , manuscript in preparation. 

Figure 1.4 IR-spectra of soot particles produced by evaporation of graphite under different helium quenching gas pressures. The occurrence of the four additional sharp peaks at elevated helium pressures turned out to originate from [60-/h]fullerene (Cgo) [20].

Figure 1.7 Dependence of the fullerene yield on the helium gas pressure in the fullerene generator.

Fullerenes can also be produced by direct inductive heating of a carbon sample held in a boron nitride support [43]. Evaporation at 2700 °C in a helium atmosphere affords fullerene-containing soot that is collected on the cold Pyrex glass of the reaction tube. This method allows a continuous operation by keeping the graphite... 

One of the aspects that has been of interest is the incorporation of an external atom in the spheroidal cavity. A variety of metal atoms can, in principle, be trapped in this cavity. Some of the studies have claimed that it is possible to push atoms such as lanthanum, iron and helium inside the spheroidal cavity of CgQ and other fullerenes. Substitution of the carbon in CgQ by boron and nitrogen has been attempted. Interestingly, nitrogen not only substitutes for carbon in the cage but also adds on to Cgo and C-iq. 

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