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about superheating and supercooling....

if superheated/cooled water is exposed to exaggerated temperatures, like 1 million° celcius or to the very depths of coldness, does it still stays in liquid form? in other words, is there a limit to superheating/cooling?

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Superheating would be limited by the ability of your container to hold pressure. If you could successfully heat and contain liquid water that is heated to 1,000,000 + celcius, you can have superheated liquid water at that temperature. Of course, at some point you're going to melt your container and you're about to have a big mess. As for supercooling, I think I recall someone researching the properties of water and discussing this. Water solidifies and crystalizes at 0 celsius. But I believe there was a temperature much lower where water can solidify without the crystalization, forming a much denser type of ice that doesn't float. Don't take my word on that, as I'm not entirely sure of the details and I can't even recall where I got the idea from.
frollard8 years ago
I believe you would not possibly get superheated water, you'd have steam, and then superheated steam. At a million degrees it would easily disassociate back to elements. There becomes a point at which even supercooling in perfect circumstances cannot go below a certain temperature. Near absolute zero, there is almost NO motion in the molecules - and you'd not find a liquid in this state.
necropolian (author)  frollard8 years ago
i never heard of superheated steam... isn't superheating/cooling only possible on a liquid? the only thing i can think of that will happen if you would warm up steam, is that the steam becomes an ionized gas. plasma!
Superheating steam reduces the liklihood of any of the water becoming liquid again. Below 'superheated' its willing to condense with very little physical change - superheated steam is 'dry' - per-se. http://en.wikipedia.org/wiki/Superheater (refers to locomotive steam engines/boiler turbines etc)
Superheated steam is 'the number of degrees above its saturation temperature/pressure'.

Superheated water, at ambient temperature and pressure is possible as well where water is heated without being disturbed and no nucleation sites = no boiling. http://en.wikipedia.org/wiki/Superheating
Except 3He, of course :-)
but 3He isn't supercooled (past its freezing point but still liquid) at that temperature, its just super-duper-cold :D

it must solidify eventually.
You're right that 3He isn't supercooled.
However, If you keep things at ambient pressure (which is what I'm assuming, since you never brought up the full 2D phase diagram :-), then 3He doesn't solidify, even at absolute zero. It's a fermion (1 p + 2 n + 2 e means a net spin 1/2), and the exclusion principle is enough to keep it from crystallizing at any temperature. Weird, but true. At sufficiently high pressure, it does form a solid.
Thanks, learn something new all the time :D
Generally speaking, you can be fairly sure that water at 1 million Celsius is a mixture of oxygen and hydrogen plasma and that water near absolute zero is a Bose-Einstein condensate. (A water molecule is a boson, right, kelseymh?.)

First, keep in mind that temperature is a property of a large group of molecules, not any one molecule. In a container of room-temperature water, for example, there might be just by chance a few molecules moving with a speed typical of ones ready to boil, or a few moving with a speed typical of water molecules that are about to freeze.

To understand how water behaves, you'd need to look at a phase diagram to locate the triple point and where it transitions from one state to another. At extremes of pressure and temperature, the distinctions between states of matter become somewhat blurred.

At normal air pressure, liquid can be gradually supercooled only so far before it freezes into a solid crystal all at once, homogeneous nucleation. But if you cool it by millions of degrees per second, water solidifies into a glass (a non-crystalline solid). Superheating likewise has limits.

Also, water is weird. Water molecules are so sticky that their situation is particularly complicated. Water superheated as a result of pressure has some especially odd and useful properties.