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Negative CTE material

Posted by Hemos on from the making-things-work dept.

florescent_beige writes "An article on Yahoo talks about zirconium tungstate (ZrW2O8), a material that has a negative coefficient of thermal expansion over a wide range of temperatures. Being non-toxic, it has applications in dentistry, as well as metallurgy and optics. Johns Hopkins physicyst Collin Broholm describes the physics behind the behaviour."

5 of 23 comments (clear)

  1. Huh? by Anonymous Coward · · Score: 3, Informative

    From the article:
    "Schoolchildren learn at an early age that solids expand when they are heated and contract when cooled, like wooden doors that are more difficult to open in the summer due to swelling. "

    Um, I thought that was humidity? Wood is fibrous, I'd think what little effect temperature has on the size is nnothing compared to the sponge-like behavior of all those fiber cells.

  2. Dumb Example... by Big+Sean+O · · Score: 3, Interesting

    You're right mostly. Humidity does effect wood more. I don't think wooden doors stick in the desert.

    A better example would be running hot water over stuck jar lid. The metal expands faster than the glass.

    Kinda off-topic but not really: Water gets denser as it cools to 4 degrees C, then it expands as the temperature drops until ice forms at 0 degrees C. Ice is acutally less dense than water (which is why it floats).

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  3. Old News by GMontag451 · · Score: 3, Interesting

    So what? Good old water has a negative CTE, at least from 0 C to 4 C.

    1. Re:Old News by Raiford · · Score: 3, Informative
      Ceramic materials with negative axial CTEs have been played around with for a while. The effect that is observed with most of these so-called negative or zero CTE materials is a phenomenon known as microcracking where the material actually has a positive volumetric coefficient of expansion but the long axis contracts while the minor crystalline axis expands. The expansion of the minor axis however occurs into a void space resulting in no effective expansion.

      Zirconium Tungstate on the other hand has an intrinsic anomalous negative volumetric CTE which occurs over the temperature range from just above 0 K to 1050 K.

      This stuff is probably pretty boring to the average slashdot geek as evidenced by the absolute mighty tempest of comments generated here but if you are interested check out http://www.isis.rl.ac.uk/ISIS97/feature1.pdf

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  4. Thermal stability is not new by Rick+the+Red · · Score: 4, Insightful
    By blending materials that shrink when heated with more traditional substances that expand when heated, scientists could create a composite that neither shrinks nor expands as the temperature changes.
    Scientists could create? Engineers already have! Boeing did this when they made the framework for the Hubble space telescope, by carefully balancing the mix of carbon fibers and resins. Hubble depends on this feature. You certainly can't have the distance from the mirror to the sensors changing as it goes in and out of the Earth's shadow.

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