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Is there any material in the world which cools when it is heated?

  1. Jan 26, 2013 #1
    Is there any material in the world which cools when it is heated?
     
    Last edited by a moderator: Feb 4, 2013
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  3. Jan 26, 2013 #2

    phinds

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    Re: Material

    Wouldn't that be a contradiction in terms? Do you understand what it means for something to be heated? That is, what happens to the molecules that make up the substance?
     
  4. Jan 26, 2013 #3

    ZapperZ

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    Re: Material

    When you ask something like this, it now matters on what exactly is meant by the things you use in your question, i.e. your question requires a clearer explanation.

    As phinds has stated, "heating" and "cooling" have specific meanings. If you heat something, by definition, its temperature is increasing since you detect it. So you're asking if by increasing its temperature, you can lower it. As you can tell, it doesn't make much sense.

    Now, if you're asking "If I supply energy to a material, can it be cooled down?", then that's different, because that is a more general. I can supply energy to a material in a number of ways, including via supplying heat energy. However, this is not the only means. I can, for example, shoot light at the material.

    Now, if we do that, there are, under certain situations, a material can cool down even when energy is supplied to it.

    http://physicsworld.com/cws/article/news/2012/jan/31/heating-cools-a-semiconductor

    Note, however, that there's a whole bunch of "gymnastics" that is associated with this process.

    In any case, this is another example where, what you are asking matters in how we are able to answer. As I've stated many times in this forum, often times, the question is as important as the answer.

    Zz.
     
    Last edited by a moderator: Jan 27, 2013
  5. Jan 26, 2013 #4
    Re: New Material

    I do not believe there is any physical material that has a negative heat capacity.

    Black holes have a negative heat capacity but that's not materials science, that's astrophysics.
     
  6. Jan 26, 2013 #5

    mfb

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    Re: New Material

    If "heated" means "increases its temperature" and "cools" means "reduced its temperature", this is impossible.

    There are materials which can go from a positive to a negative temperature if you increase their energy. But this is not cooling, they are hotter than before afterwards.

    Stars, similar to black holes, can decrease their temperature if you increase their energy.
     
  7. Jan 27, 2013 #6
    Re: New Material cools when heated

    My question was like when a material is exposed to sunlight it gets heated and if there is a material which cools when exposed to sunlight?
     
  8. Jan 27, 2013 #7

    I like Serena

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    Re: New Material cools when heated

    I'm wondering if it's possible to freeze a material that is in a certain phase into an unstable equilibrium.
    Then, if it is heated, it may suddenly make a phase transition, causing temperature to go down paradoxically.
     
    Last edited: Jan 27, 2013
  9. Jan 27, 2013 #8
    Re: New Material cools when heated

    Look for the laser cooling, on the first thoughts it sounds counter-intuitive, but it really happens.
     
  10. Jan 27, 2013 #9

    rollingstein

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    Re: New Material cools when heated

    One way to cheat is have the material do work. You can then make it cool even on supplying heat I suppose. But, yes, that's cheating.

    OTOH in the absence of Work\:

    ΔU=Q

    So, you'd need a system where U was not a monotonically increasing function of T, I suppose. I've never seen that but not sure if it is absolutely forbidden.

    Wonder what happens in a black hole that people mentioned.
     
  11. Jan 27, 2013 #10

    rollingstein

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    Re: New Material

    Even assuming a positive heat capacity how does dU/dT always remain positive? Say the eq. below:

    641f642d229c418dd834725c6781514c.png

    For simplicity assume P=const. so we only have the first term in the above equation. If Cp was ever less than αPV then wouldn't dU/dT become negative? Is there any reason why Cp always greater than αPV?
     
    Last edited by a moderator: Apr 27, 2017
  12. Jan 27, 2013 #11

    rollingstein

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    Re: New Material cools when heated

    I'm coming up with more possibilities; don't know if they make sense:

    (1) What about a material that had an endothermic reactive transformation that needed heat input to get it going?

    (2) What about something with a very large temperature coefficient of expansion?
     
  13. Jan 27, 2013 #12
    Re: New Material cools when heated

    http://www.aip.org/pnu/2001/split/524-2.html [Broken]
    This link says negative heat capacity is possible
     
    Last edited by a moderator: May 6, 2017
  14. Jan 27, 2013 #13

    ZapperZ

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    Re: New Material cools when heated

    1. Again, this is similar to the point that I made above.

    2. Did you just found this, or did you know about this when you first created this thread? If it is the former, why didn't you do a search first?
    https://www.physicsforums.com/blog.php?b=3588 [Broken]

    If it is the latter, why didn't you cite the source to help clarify what you were looking for?

    Zz.
     
    Last edited by a moderator: May 6, 2017
  15. Jan 27, 2013 #14
    Re: New Material cools when heated

    I just wanted a material and not a cluster of atoms. I knew about this link earlier, all I wanted was to know about a material with negative heat capacity which would be available quite easily.
     
  16. Jan 27, 2013 #15

    ZapperZ

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    Re: New Material cools when heated

    Usually, something with that exotic of a behavior are seldom "available quite easily".

    Zz.
     
  17. Mar 24, 2013 #16
    That's basically what precipitation hardening does. Take an alloy with a maximum solubility that decreases linearly with temperature, and quench it from liquid phase. Then you take the quenched system and reheat to some temperature below the solvus, where you hold for a predetermined (by TTT) time, and cool to room temperature. Now you have a metastable material that is out of equilibrium.
    If reheated and activation energy for diffusion of solute is exceeded, you will have a transformation occur which changes your material properties.
    Diffusion is temperature dependent though, so you will have an overall decrease in this transformation as temperature decreases.
     
    Last edited: Mar 24, 2013
  18. Mar 24, 2013 #17

    DrDu

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    It's a thermodynamic stability condition that C_P and C_V are positive.
     
  19. Apr 9, 2013 #18
    Basically you need a phase change that is delayed. A material that is in a solid state (say) at a temperature at which it should be liquid. Heating it up further can force the material to start melting which will cool it down to its melting point fairly rapidly. Maybe.
     
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