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Carbon at very low temperatures

  1. Jan 8, 2008 #1
    Has study or experimentation been done on chemically and isotopically pure carbon at very low temperatures? Thanks, Rich Peterson
     
  2. jcsd
  3. Jan 8, 2008 #2

    mgb_phys

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    Probably - most things have.
    It has a useful engineering property. It's thermal conductivity drops suddenly below about 15K. You use it as a thermal short on liquid Helium cooled instruments, it gives you a thermal path to get the cold in during pre-cooling but then 'disconnects' to give good insulation once you are cold.
     
  4. Jan 10, 2008 #3
    Thanks
     
  5. Jan 10, 2008 #4

    Gokul43201

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    Moreover, charcoal sorption pumps are routinely used to get to temperatures below 1K. Adsorption energies and kinetics for different elements/compounds at various temperatures would definitely have been well studied. At temperatures above 1K, carbon-glass RTDs are widely used for thermometry in magnetic fields. Lots of good reasons to study carbon at low temperatures.

    But as mgb said above, it doesn't matter that there be reasons - it would have been studied nevertheless.
     
  6. Jan 11, 2008 #5
    In laser spectroscopy, crystals emit shorter bandwidths at very low temperatures. So their radiation has sharper peaks. Carbon might have similar properties if it has any spectroscopic use.
     
  7. Jan 11, 2008 #6

    Gokul43201

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    How is this different from garden variety thermal broadening that is seen in virtually every spectrum of any material?
     
  8. Jan 11, 2008 #7
    I am not sure, since I studied the laser crystals many years ago. We cooled them to liquid Helium temperatures, and just noticed the emission peaks became very sharp.

    We would use the 514nm Argon, and the crystals would emit in the IR. We weren't interested in the broadening, but more the narrowing of the emission cross-section.
     
  9. Jan 11, 2008 #8

    Gokul43201

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    Unless I'm misunderstanding you completely, this is perfectly natural behavior that is not characteristic of your specific material. Take a look at the temperature dependence of any photoluminescence spectrum, or x-ray diffraction/fluorescence spectra, or spin resonance spectra, etc.
     
  10. Jan 12, 2008 #9
    somewhere i read carbon conducts electricity at some specific temperature....is it true?
     
  11. Jan 17, 2008 #10
    Yep, different forms of pure carbon also exhibit different properties of conductivity. Specifically, graphite is a good conductor, which becomes even better when made into different structures such as fullerines. Diamond is a good insulator unless mixxed in with some other element (such as blue diamond, a semiconductor).

    A quick word as to why, graphite is sp2 hybridized which allows for the movement of electrons, while diamond is sp3. The pi bond is graphite covers multiple atoms and allows for delocalization of electrons. I won't go into too much detail, since this information is something I'd expect you can find in lots of introductory books on quantum mechanics or nanotechnology.

    Lots of work is being done on superconductivity in carbon nanostructures, a quick search on arxiv and you can probably find some of the more interesting papers and something a bit more advanced. Will post more on this subject when I have more time.
     
    Last edited: Jan 17, 2008
  12. Jan 17, 2008 #11
    hi thanks..for making me to remember these nice details..
     
  13. Jan 18, 2008 #12
    It's cool, sometimes the simplest stuff is the easiest to forget :redface:
     
  14. Feb 9, 2008 #13
    I often forget to put on my shoes before going to work :P
     
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