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Yale-Led Team Solves Half-Century Carbon-Crystal Mystery 42

Posted by timothy
from the fold-here-bend-there dept.
slew writes "Unlike its more famous carbon cousins: diamonds and fullerenes, you've probably never heard of M-Carbon, but this form of compressed graphite which is as hard as diamonds has baffled researcher for half a century. Over the past few years, many theoretical computations have suggested at least a dozen different crystal structures for this phase of carbon, but new experiments showed that only one crystal structure fits the data: M-carbon."
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Yale-Led Team Solves Half-Century Carbon-Crystal Mystery

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  • M-Carbon? (Score:5, Informative)

    by Mal-2 (675116) on Sunday July 22, 2012 @12:19PM (#40730513) Homepage Journal

    Nice of TFS to not link to anything describing M-carbon.

    Maybe this will help. [newscientist.com] Maybe it was "common knowledge", but I personally hadn't heard of the stuff till now.

  • Re:M-Carbon? (Score:5, Informative)

    by Mal-2 (675116) on Sunday July 22, 2012 @12:37PM (#40730627) Homepage Journal

    Bad form to reply to myself, but this might actually prove useful:
    A new superhard form of carbon [stonybrook.edu]

    And I'm too drunk to make the decision for y'all. It appears to me like it alternates between 7-sided and 5-sided carbon polygons, rather than the usual 6-sixed polygons in a sheet of graphene. It beats me how this would do anything but form a sheet of its own. It still seems like a two-dimensional structure, but I'm not organic chemist.

  • Re:Toughness? (Score:5, Informative)

    by blackest_k (761565) on Sunday July 22, 2012 @12:41PM (#40730651) Homepage Journal

    Hardness and toughness are pretty much opposites. when a crystal deforms it does so along slip plains and the harder something is the less available slip plans are available for the material to deform which is why diamonds are used in hardness testing (the softer the material the bigger impression the diamond makes on the material (google vickers hardness test) .

    From wikipedia
    In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing;[1] Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing. It is also defined as the resistance to fracture of a material when stressed.

    So as a Diamond is hard due to lack of available slip plains its toughness is lowered due to its inability to deform. Therefore it is unlikely that this new material will be tough. (that says nothing about tensile strength just it's ability to deal with a sharp blow).

       

  • Re:where's the info? (Score:5, Informative)

    by ceoyoyo (59147) on Sunday July 22, 2012 @01:03PM (#40730759)

    When you cold press graphite you get new forms of carbon that are not graphite and are not diamond. It damages the diamond anvils in your compression apparatus, so it seems to be as hard as diamond. But nobody could figure out what the crystal structure was, even though several theoretical structures had been proposed. These guys have shown that only one of those structures, M carbon, fits the experimental data.

  • by lessthan (977374) on Sunday July 22, 2012 @01:11PM (#40730787)

    I started Googling and what I found is that some scientists [cleantechnica.com] have been playing with graphite and compressing it. They found that, at room temperature and high pressures, graphite goes from black to colorless and becomes very hard. They lacked the ability to determine the precise structure of the super hard carbon. They just knew it wasn't diamond.

    Around the same time, some theoretical mineral physicists [stonybrook.edu] came up with some math that says that carbon can have any number of forms with different properties and configurations. These configurations were labeled with letters, lacking any pattern I can discern. (Maybe they labeled an initial list and then began disqualifying configurations?)

    The article in the summary essentially is saying that they have linked the 2 bits of data and have determined that the super hard carbon is in fact the M carbon. Nothing I have found gives us any information on the duration of the M carbon once the pressure is removed or any properties of M carbon, except that the hardness is greater than diamond's. I guess we'll have to read the paper.

  • The actual article (Score:3, Informative)

    by Anonymous Coward on Sunday July 22, 2012 @01:40PM (#40730951)

    can be found here http://www.nature.com/srep/2012/120719/srep00520/full/srep00520.html (OPEN ACCESS).

  • by vuo (156163) on Sunday July 22, 2012 @04:44PM (#40731867) Homepage
    From the original Scientific Reports article: [doi.org]

    We find the bulk modulus of M-carbon to be 365+/-38 GPa, thus is one of the stiffest materials known comparable to that of cubic-BN (387+/-4 GPa) and wurtzitic BN (375+/-9 GPa). ... M-carbon also shows anisotropic compressibilities along lattice axes: the a axis is stiffest [527+/-2 GPa] and the b [271+/-1] and c [267+/-1 GPa] axes are roughly equivalent ...

    It seems that the anisotropy does give a lower compressibility, but not dramatically more as in graphite (weaker plane compressibility is 2.7% of the stronger plane). It's also clear that the diamond in the diamond anvil cell used to make this is damaged by the material. The picture in the Yale News article is the damaged anvil, not the M-carbon. In SEM images, it doesn't look like graphite at all, but more like fused grains. Characterization and proof of structure is done by X-ray diffraction [wikipedia.org], a standard materials science method, using synchrotrons [wikipedia.org], which are giant particle accelerators, namely ALS at LBL [lbl.gov] and APS at Argonne [anl.gov].

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