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Science

Negative CTE material 23

Posted by Hemos 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."
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Negative CTE material More

Negative CTE material

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  • Huh? (Score:3, Informative)

    by Anonymous Coward on Thursday September 26, 2002 @01:53PM (#4337900)
    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.

    • Dumb Example... (Score:3, Interesting)

      by Big Sean O ( 317186 )
      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).
      • >A better example would be running hot water over stuck jar lid. The metal expands faster than the glass.

        U know I have done that many times, but never thought as to why it works. For some reason I thought that the heat from the water loosened/melted whatever was sticking the jar and lid together.

        So don't make lids out of this stuff!
      • You're right mostly. Humidity does effect wood more. I don't think wooden doors stick in the desert.

        Shit, Ive lived in california all my life (desert) and I didnt know doors COULD stick :)

        • Shit, Ive lived in california all my life (desert) and I didnt know doors COULD stick :)

          You must live in a newer house, the house I live in has one door that sticks like mad, though its more from the ground shifting durning earthquakes, than it is from humidity/heat.
          Another fun demonstartion of termal expantion is the old ball and ring trick. You have a ball that is just slighty too big to fit through a ring, you heat the ring and the ball, then try passing the ball through the ring again, and bingo it goes through. Of course, its a bit eaiser if they are of different materials, and the ring has a higher rate of expansion.

  • error in article. (Score:2, Interesting)

    by nickbrown ( 213260 )
    You need to change the second link in the article to include the shrink tag.
    Thus;
    http://www.jhu.edu/~jhumag/0299web/tech.html#shrin king

  • Old News (Score:3, Interesting)

    by GMontag451 ( 230904 ) on Thursday September 26, 2002 @02:52PM (#4338460) Homepage
    So what? Good old water has a negative CTE, at least from 0 C to 4 C.
    • Yeah, but you can't cook in a pot made of water. You should be able to mix this stuff up in a ceramic in the right proportions and have a ceramic that just doesn't crack at all- period. oven->ice water no problem!

      By all accounts it's non toxic too. What a great material!

    • Re:Old News (Score:3, Informative)

      by Raiford ( 599622 )
      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 [rl.ac.uk]

  • Come on, you mean to tell me that nobody cares about zirconium tungstate? And you call yourselves geeks? Mirconium tungstate has always been a big part of my life.

  • Thermal stability is not new (Score:4, Insightful)

    by Rick the Red ( 307103 ) <Rick.The.Red@nOsPaM.gmail.com> on Thursday September 26, 2002 @04:22PM (#4339199) Journal
    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.

    • 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.

  • Hot/Cold (Score:2, Interesting)

    by ktulus cry ( 607800 )
    Alright, so now plates will explode when they go from hot to cold instead, and fillings will crack when you eat ice cream instead of drinking coffee. Does zirconium tungstate also expand/contract LESS during a temperature change? The article on Yahoo failed to mention it's response to decrease in temperature. Also - a VERY common of use of heat-shrinking material - heat-shrink tubing, its used in electrical work very frequently. Some of that stuff shrinks to a quarter of its original diameter or less.

    • Re:Hot/Cold (Score:1, Informative)

      by Anonymous Coward
      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.

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