Negative CTE material

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."

Comments

Huh?

[Anonymous Coward]

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.

Re:Old News

[Raiford]

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

Re:Thermal stability is not new

[florescent_beige]

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.