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Science

How Negative Thermal Expansion Works 53

Posted by michael from the weird-science dept.
Bill Kendrick writes "Scientists at the University of California, Santa Cruz, are discovering why compounds like zirconium tungstate 'are acting like they are from Bizarro world': contracting, rather than expanding, when heated. They believe it's a combination of geometrical frustration (which sounds a lot like what it is), and a 'twisting' motion of the atoms."
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How Negative Thermal Expansion Works More

How Negative Thermal Expansion Works

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  • go ahead...

    ... but what practical purposes does a material like this have? I would think a material that doesn't have ANY expansion or contraction in varied environments would be very useful, but what's usable about something that gets smaller when hotter?
    • interesting != useful
      • The parent to my original post speaks of his view that there is a lack of usefulness for this property. The article is not talking about the uses of negative thermal expansion but rather how the process works; furthermore, this article made /. because it is interesting. Therefore, being interesting is not the same thing as usefulness.

        I am not inferring that this concept is neither interesting nor useful. I can understand how my statement can be interpreted as a troll, but come on...
    • What's useful about something that gets larger when it gets hotter? Just because an application can't be thought of today doesn't mean something is useless, it just means we haven't thought of a need for it.

      • Re:Call me dumb... (Score:3, Insightful)

        by capnjack41 ( 560306 )
        What's useful about something that gets larger when it gets hotter? Just because an application can't be thought of today doesn't mean something is useless, it just means we haven't thought of a need for it.

        Seriously. "What's so useful about all these stupid electrons, anyway!"

        Why is it that very often the first response to an article about some scientific discovery/invention/whatever is "well why would this ever be useful?" Trust me, someone will find a use.

    • Re:Call me dumb... (Score:3, Insightful)

      by scheme ( 19778 )
      Suppose you wanted something that didn't expand or contract in certain temperature ranges, you might be able to combine something with negative expansion and positive expansion in a structure so that the entire structure doesn't expand or contract.

      • Re:Call me dumb... (Score:4, Interesting)

        by david.given ( 6740 ) <dg@cowlark.com> on Friday November 19, 2004 @12:01PM (#10865294) Homepage Journal
        Suppose you wanted something that didn't expand or contract in certain temperature ranges, you might be able to combine something with negative expansion and positive expansion in a structure so that the entire structure doesn't expand or contract.

        Clockmakers have used such a material for a long time; it's a complex alloy called invar [orologeria.com]. The linked article gives the composition of one type of invar, which has an expansion coefficient of 1.6 ppm. This means that a bar of invar ten kilometres long that heats up by one kelvin will get longer by 1.6cm. That's pretty good. The equivalent steel bar would expand by 11cm.

        And yeah, the above figures were very nearly copied verbatim from the article; read it if you're interested.

        • Clockmakers have used such a material for a long time; it's a complex alloy called invar.

          While invar is useful, it just has a small (and controllable, through different alloying) coefficient. It's used many times to put metal through glass becaue they tune it to have the same thermal expansion as the glass. Therefore you can have a gas-tight glass container with metal coming out of it (used mostly for phototubes).

          The "controllable" nature is the most important - in most situations you just want a matched

      • Suppose you wanted something that didn't expand or contract in certain temperature ranges

        No supposition required. A physical metal rod was the official definition of the meter [wikipedia.org] for a long time. Measurement stability requires such properties. And such rods are still used today [nist.gov] in less critical areas.

        Back on the original topic, any unusual property of materials is bound to find an application.

    • Re:Call me dumb... (Score:4, Informative)

      by MindStalker ( 22827 ) <mindstalker AT gmail DOT com> on Friday November 19, 2004 @11:03AM (#10864586) Journal
      RTFL. They said the theoretical right mix of expanding and contracting elements which would produce zero change is what the ultimatly are wanting to develop. This is the first material that contracts over large temperature ranges, so it may be perfect for such a mix. Obviously they are still working on it.
    • Actually - I'm an idiot... The last paragraph:

      "If you could create the right mix of materials to neutralize thermal expansion, that would be quite a significant technological advance," Schlesinger said.

      THAT is how it would be useful...
    • Take something that expands. Add to the end of it a bit of the right size that contracts. Voila, you have something whose net length remains constant.

      Oh yeah, almost forgot, you're dumb.

    • Duh? [pgo-online.com]

    • Re:Call me dumb... (Score:4, Interesting)

      by Profane MuthaFucka ( 574406 ) <busheatskok@gmail.com> on Friday November 19, 2004 @11:13AM (#10864696) Homepage Journal
      Bronze expands as it cools, and in a mold it will therefore fill all the little details. This is why you have statues made of bronze.

      Plaster of Paris expands slightly as it sets, and then contracts again. This is also why people use plaster to cast things.
    • Ok, you asked for it. You are dumb. And I'm an insensative clod.)

      Now that that is out of the way thing about this. If you are sending a vehicle that needs to remain air tight into a very hot environment this property would be ideal. The vehicle seals would become more functional rather then breaking down. The trick would be maintaining enough functional space inside the vehicle as well as maintaining the relative shape through the constriction.

    • I think its useful aswell if it just contracts when getting hotter, coolant systems for example came into my mind by the first glance...
    • Heat-shrink tubing, baby. Of course, that's not a reversible contraction (it doesn't then get larger--at least appreciably--when the termperature it lowered again). But there are several materials (rubber bands) which also have this property and are quite useful.
      In the case of long-chain molecules (think latex), the free energy (F=U-TS, where T is the temperature, S is the entropy, and U is the thermal energy of the system) is minimized when the entropy is *decreased* by stretching them out, thus aligni
    • If water didn't get smaller when it melted then we'd probably all be dead. I'm sure there are some other ones too though.

  • Doesn't Ice contract when it is heated to melting? That's why ice floats. (and why we're here today)
    • Yes, but its over a very small temperature range, past that it expands into steam. This material contracts over a fairly large temperature range.
  • I think this is the most bizzarre of all!

    h2o also contracts when heated above its melting point.

    Is this solely due to air and crystalisation upon freezing or does put h2o do this in a vacuum?

    Who knows! not me! I never lost control...
    • Is this solely due to air and crystalisation upon freezing or does put h2o do this in a vacuum?

      I believe this is due to the directional hydrogen bonds formed by water when it is frozen. The crystalline structure that accomodates the angles of these hydrogen bonds is less dense than the randomly packed configuration that the water molecules can assume once they have significant kinetic energy to break the hydrogen bonds, i.e. the ice melts.

      I would also like to point out that if you try to melt ice in a

      • Re:Ice ice baby (Score:3, Interesting)

        by over_exposed ( 623791 )
        Not that I don't believe you, I'd just like to see some evidence of water-ice sublimating... any linkage or a reasonable scientific explanation?

        • Re:Ice ice baby (Score:3, Informative)

          by jericho4.0 ( 565125 )
          Phase diagram of water [lsbu.ac.uk]

          Most materials do the same. There are very few liquids that don't subliminate in a vacum.

        • I probably should not respond to a guy who does not even bother to use google, but here goes:

          Look at this page [uiuc.edu]. This is not complex stuff. I remember this from high school chemistry. The diagram on the bottom shows water. Plug in your temperature and pressure, and look to see where you are at (solid, liquid, gas). Below approximately 0.01 atmospheres, water can go directly from liquid to a gas. In fact, at such low pressures, you cannot have liquid water at all!
        • There is a P-T diagram of water here: http://www.tpub.com/content/doe/h1012v1/css/h1012v 1_68.htm [tpub.com] The diagram describes how the phase of the water depends on the pressure and temperature. You can see that at pressure below the "triple point" of water that it can exist as only a solid or a gas. This diagram is actually a little off because the boundary between the liquid and solid phase should have a negative slope rather than being straight up and down.

          Carbon dioxide is an example of a substance that e

        • Here's a simple experiment to prove water-ice sublimates. Look in the back of your freezer at those ice cubes you made in April and never used. Remember how when you first made them they filled the whole tray? Now they are much smaller. There's the proof. Overtime the ice sublimates.
        • Others have provided links to scientific documentation about water sublimating, but I'd just like to point out the practical application which is probably documented somewhere in your kitchen.

          Anything which has been "freeze dried" has been done so through sublimation. They freeze the food rock-solid and put it in a vacuum. The water sublimates into gas and gets pumped off. *POOF!* Bone-dry food with no heat damage and no shriveling.

          -
      • That is why melting points are given at sea level pressure right? They change as pressure drops - does it boil into a gas? explode? shrink down?

        interesting to know, I think space stations expose waste to the vacuum which 'dries' it before it is expelled (or retained, keep space tidy!)

    • Re:Ice ice baby (Score:1, Flamebait)

      by blahlemon ( 638963 )
      It's not bizarre, it's just further proof of intelligent design over random chance in creation. Consider this:

      If water didn't have the property of ice expanding as it cools then life in the rivers and streams would be decimated in the winter where it gets cold enough to form ice.

      Such care and consideration for such a vital part of our lives. Water that is. Oh, sorry, I forgot, that's just the luck of random chance. Silly me.

      • Of course we exist in the only world where it is possible for us to exist. Anything else would be silly indeed.

        That's a beautiful reductio ad absurdum of that argument for "intelligent design." At first I thought you were sincere, but your argument is actually a perfect description of the anthropic principle.
      • If water didn't have this property we'd live somewhere where water didn't freeze - silly.

      • Re:Ice ice baby (Score:1, Insightful)

        by Anonymous Coward
        Yea. And what if it the universal constants were different? Life as we know it wouldn't exist, and the other (example) sentient rock-sucking tentaclies who did exist because of it would be saying the same bloody thing: "thank Bog he picked out conditions that were just right for us!"

        If no worlds in some alternate universe could ever support life, then no one would be around to discuss it.

        My point? A random dice roll of universal constants is as good as any other: not lucky, not special.
      • Not to be too picky, but your .sig should use the word "than" where you used the word "then".
      • Yes true, I agree, and to all the posts (which I think might be realted to the sentient rock-sucking tentaclies mentioned below! - obtuse? your reply was, I couldnt make head nor tail of it! volve it somewhat, until it can hold a knife and fork, and then maybe I will read it!) below, I say - forget something as blunt as chemistry or genetics, go lower, think about the colour green, and then decide about intelligent design.

        people who talk about random chance do so [on topic as well] on thin ice, lies upon h
  • Shouldn't we just call it "thermal contraction"?
  • You can make a wheel out of coat hangers, and make the spokes out of rubber bands stretched between the rim and the hub Then you support the wheel on a horizontal axle so it looks like a ferris wheel and shine an incandescent lamp on one side so that it gets hotter than the other side. The rubber bands contract as they heat and expand as they cool and the wheel turns. It's cool.
    • You can make a wheel out of coat hangers, and make the spokes out of rubber bands stretched between the rim and the hub Then you support the wheel on a horizontal axle so it looks like a ferris wheel and shine an incandescent lamp on one side so that it gets hotter than the other side. The rubber bands contract as they heat and expand as they cool and the wheel turns. It's cool.

      So we could use this material to generate energy from heat.
  • "geometrical frustration (which sounds a lot like what it is)"

    Maybe that's why it's called geometrical frustration.

    Walking up stairs (which sounds a lot like what it is)!

  • Plutonium has several solid phases, and IIRC 1 or 2 have a negative coefficient of expansion.

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