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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."

4 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. 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

    --
    "player 4 hit player 1 with 0 stroms"
  3. Re:Thermal stability is not new by florescent_beige · · Score: 2, Informative
    Those zero-cte struts Boeing made use fiberous composites. Unidirectional composites expand 'normally' with increasing temperature in the fiber direction but contract in the other direction because of the poisson's effect. A multi-ply laminate with the fibers in each ply at a certain angle to the principle direction gives a nil cte in that direction, but not any other.

    That's completely different from a monolithic isotropic material thats got negative cte in all directions.

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    Equine Mammals Are Considerably Smaller
  4. Re:Hot/Cold by Anonymous Coward · · Score: 1, Informative

    Heat shrink tubing only decreases in size. One you've heated it and shrunk it, you can't get it to expand again by cooling it. Did you ever notice that it only shrinks in one direction? High tech, elegant, and useful.

    The material in the article is great because you could use it to balance expansions. That filling you were talking about would be fine if you you drank hot coffee or ate frozen ice cream (even coffee ice cream) because you could balance its expansion so that it equalled that of the tooth itself.

    For things like telescopes, a material like this could be huge because you could balance the expansion of one by the contraction of the other and keep things perfectly still. This could be a big boon to any instrumentation that requires thermal stability.