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How Negative Thermal Expansion Works
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."
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.
"When you sit with a nice girl for two hours, it seems like two minutes. When you sit on a hot stove for two minutes, it
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...
"The object of war is not to die for your country, but to make the other bastard die for his." - Patton
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.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!
Clockmakers have used such a material for a long time; it's a complex alloy called invar. 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.
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?
"The object of war is not to die for your country, but to make the other bastard die for his." - Patton
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.
Most materials do the same. There are very few liquids that don't subliminate in a vacum.
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
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 for a long time. Measurement stability requires such properties. And such rods are still used today in less critical areas.
Back on the original topic, any unusual property of materials is bound to find an application.
Shouldn't we just call it "thermal contraction"?
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...