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September
17, 2001
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Cool Stuff
| What
Am I? |
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You can freeze
ice cream instantly with me. You can use me to create the
fog you need for movie special effects. I come in handy if
you're preserving animal cells or performing precision surgery.
I can help you turn a humble metal into a superconductor of
electricity. In the future, I might even replace gasoline
as the fuel for your car. Nitrogen gas is in abundant supply in the air around you; 74% of Earth's atmosphere is made up of nitrogen molecules. If you've got enough refrigeration power, you can cool down nitrogen gas and condense it — in other words, turn it into a liquid. So, how cold does it need to be to convert nitrogen gas to its liquid form? Nitrogen changes from a gas to a liquid at a temperature of -320 ºF. This makes liquid nitrogen an exceptionally cold substance — almost as cold as the surface of the planet Pluto in the farthest corner of our solar system. It sounds like science fiction, but this freezing substance is actually being used by people every day. Good Chills A familiar application of coldness is refrigeration for preserving food. But the extreme cold of liquid nitrogen is exploited in numerous other ways. Nitrogen gas is inert, which means it won't readily react
with other substances. Similarly, you can immerse things in
liquid nitrogen and it won't react with them. Here are some
of the common uses of liquid nitrogen. |
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Cryogenics |
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Stop the Molecules! The bottom of the cryogenics temperature range, -459.67 ºF, is known as "absolute zero." (We rounded it to -460 ºF above.) In theory, this is the lowest possible temperature that can be reached! But how can there be a limit to coldness? It's all a function of the motion of atoms and molecules. The temperature of a substance is related to the motion of the molecules in the substance. Absolute zero is believed to be the point at which molecular motion in objects comes as close as theoretically possible to stopping completely. This is of special interest to scientists looking for ways of conducting electricity efficiently. |
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The Cool Electric Highway To avoid wasting electrical energy, it needs to be channeled efficiently. In other words, the electrons flowing through a wire should be allowed to pass through with a minimal amount of resistance. If the atoms and molecules in a wire have almost stopped moving, such as in extremely cold conditions, then they will offer little resistance to electricity passing through. In effect, they become what scientists call "superconductors." Scientists have discovered that when some metals and metal compounds are cooled to an extremely low temperature, such as that of liquid nitrogen, they conduct electricity with incredible efficiency. But don't expect to see super-cold cables and appliances in your home anytime soon. The process of cooling substances to the point where they become superconductors is very costly. So far, this process can only be used for specialized scientific purposes. Scientists hope that they can find materials that become superconducting at higher temperatures — temperatures that are more practical for everyday use. |
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