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Heat Transfer

  1. Apr 17, 2008 #1
    Does anybody know why thorium is better than uranium as far as heat transfer is concerned?
     
  2. jcsd
  3. Apr 18, 2008 #2

    Astronuc

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    Staff: Mentor

    Thermal conductivity of Th is 54 W/m-K, and the of U is 27 W/m-K. I believe this is a room temperature.

    Th has slightly lower atomic mass than U do it would offer less resistance to phonon conduction.

    Th-Th bond length = 359.5 pm
    U-U bond length = 277 pm

    But -

    http://www.webelements.com/webelements/elements/text/Th/xtal.html
    Space group: Fm-3m (Space group number: 225)
    Structure: ccp (cubic close-packed)
    Cell parameters:
    a: 508.42 pm
    b: 508.42 pm
    c: 508.42 pm
    α: 90.000°
    β: 90.000°
    γ: 90.000°

    http://www.webelements.com/webelements/elements/text/U/xtal.html
    Space group: Cmcm (Space group number: 63)
    Structure: orthorhombic
    Cell parameters:
    a: 285.37 pm
    b: 586.95 pm
    c: 495.48 pm
    α: 90.000°
    β: 90.000°
    γ: 90.000°

    I suspect that the orthorhombic crystal with different lengths in all three dimensions plays the biggest role in the lower thermal conductivity of U as compare to Th, which has a closed packed cubic structure.
     
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