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Another Form of Carbon: Magnetic Nanofoam
mhh5 writes "Researchers publishing in Nature have discovered yet another form of carbon. Apparently, this stuff is temporarily magnetic after it is made (at temperatures of ~10,000 C) and is a spongy solid. So that's five (give or take one?) allotropes for carbon: amorphous, graphite, diamond, fullerenes, and nanofoam. Collect them all!"
fullerene
,one above the other. These layers 3.35A degrees apart and are held together by weak van der waals forces only.These layers can slide over one another.Thus it is very soft. Fourth electron of each c-atom forms delocalized
p-system.
n.
Any of various cagelike, hollow molecules composed of
hexagonal and pentagonal groups of atoms, and especially
those formed from carbon, that constitute the third form of
carbon after diamond and graphite.
Diamond, Graphite and Fullerene forms are crystalline, the amorphous forms are coal, coke, charcoal, lampblack, gas carbon etc.
In diamond, each C-atom is covalently bonded to four other C-atom to give a tetrahedral unit. In diamond each C-atom is sp3-hybridized.Therefore each C-atom forms four sigma bonds with neighbouringC-atoms. In diamond C-C-C bond angle is 109.5 degrees.These basic tetrahedral units unite with one another and produce a cubic unit cell.
In graphite each C-atom is covalently bonded to three C-atom to give trigonal geometry. Bond angle in graphite is 120 degrees. Each C-atom in graphite is sp2-hybridized. Three out of four valance electrons of each C-atom are used in bond formation while the forth electrons free to move in the structure of graphite. Basic trigonal units unite together to give basic hexagonal ring. In hexagonal ring C-C bond length is 1.42A degrees. In graphite these rings forms flat layers. These layers are arranged is parallel
During the irradiation of diamond by atoms, many bonds are broken, leading to point defects and eventually to clusters of defects. At a high enough irradiation dose, amorphization of the crystal structure may occur and two specific amorphous forms of carbon may appear: the tetrahedrally bonded Diamond-like Amorphous Carbon which will be denoted by ta-C and the sp^2 bonded Graphite-like Amorphous Carbon named a-C. These two structures can be distinguished clearly by their macroscopic and microscopic properties. The former material has higher density, is transparent, electrically insulating and much harder than the latter. From the microscopic point of view, the ratio of fourfold, diamond-like bonds to threefold, graphite-like bonds (sp^3/sp^2) determines the kind of structure obtained.
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The article was egregiously low on detail. (Googles a bit...) Here is a more technical article that explains the magnetism as a result of temporary unpaired electron spins (surprise!). The magnetism occurs at temperatures below 90K, so it's fairly remarkable that they can jerk this stuff from 9700K down to 90K and have it not shatter!
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That this nanofoam loses its ferromagnetism with time suggests that nanofoam is fundamentally unstable at the molecular level. Presumable its ferromagnetism is due to a separation of the electron orbits between adjacent atoms caused by being in a "foam". Like a soap or detergent foam, it presumably breaks down over time resulting in the condensation of the carbon atoms back into a normal non-magnetic separation. I haven't read the original paper so this is just an educated guess.