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Helium at 0K?

  1. Oct 29, 2012 #1
    What prevents helium from becoming solid at normal atmospheric pressure? All other elements are solid at 0K, why does helium stay a superfluid liquid?
  2. jcsd
  3. Oct 30, 2012 #2
    Well first let me say that 0k (absolute 0 or -273C) cannot be reached (ever) due to many factors (including Heisenberg Uncertainty) but I will try to answer your question anyway.
    Helium's freezing point is 1k ( and 25 atmospheric pressures) so it WILL become solid at that temp. and that pressure (but never at normal atmospheric pressure) but the superfluid state you are talking about happens at around 2.17 K. (For He3 this is around 3.1 K)

    As to WHY it doesn't freeze?
    As wiki puts it: This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) and about 25 bar (2.5 MPa) of pressure.
    Last edited: Oct 30, 2012
  4. Oct 30, 2012 #3
    The ground state (In QM) is basically the lowest possible energy state a system may have.

    Also, please keep in mind 0K is a impossibly low temperature to achieve in any system.
  5. Oct 31, 2012 #4
    Roughly the same reason why metals remain conductive at absolute zero. The energy minima at the crystal nodes are so shallow that zero point movements break down the framework.

    All other elements, including neon and hydrogen, have sufficiently deep energy minima to have ground states in solid crystal form.
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