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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."
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.
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).
My father is a blogger.
You need to change the second link in the article to include the shrink tag.n king
Thus;
http://www.jhu.edu/~jhumag/0299web/tech.html#shri
So what? Good old water has a negative CTE, at least from 0 C to 4 C.
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.
If all this should have a reason, we would be the last to know.
Carbon dioxide has a lower freezing point than water, so it comes out of solution when your soda freezes. The increased volume of the ice and the increased pressure of the CO2 can overpressurize a can.
It also has something to the thinwalling of aluminum cans. Aluminum is the most costly component to the cost of a can of coke. Packaging engineers are constantly thinking of ways to stretch more cans out of a pound of aluminum, and sometimes they get a little too thin.
Gee, I guess my biology degree, and my stint with a can manufacturing company paid off today...
My father is a blogger.
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.
If he can't even get the units correct why should we trust his explination?
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The reason food jar lids "stick" like they do is that there is a negative pressure inside the jar compared to atmospheric pressure. This is accomplished by jarring the food while it's hot. As the stuff inside the jar cools, the pressure inside the jar goes down. It's the old PV=nRT; n and V are constant in this case, R is a constant, so that as T goes down so does P. This effect has the nice attribute of inhibiting microbial nasties, leading to long shelf-life for the jarred food.