How to supercool water?

Question

I've looked into it a little can anyone shine some light on this mystery?

Answer 1

Oh, you can find a lot of clues about this on the net, no need to ask!

Anyway... let's give it a try.

HOW? just cool it down smoothly, without perturbing it with anything (stirring or similar)... water should be free of impurities and the container should be smooth so that there are no good nucleation point for the crystallization (i.e. easy starting points for the crystal to develop)

WHY? That's what you are interested in, I guess? Ok, below the freezing temperature at a given pressure it is thermodynamically convenient to transform your bucket of water in a bucket of ice. Fine. But this cannot happen "at once" and "everywhere"... that would be a completely unlikely fluctuation... in the real world of reasonably possible things you will have to go through an intermediate condition where you have ice somewhere and water somewhere else. In fact these intermediate steps between "bucket of water" and "bucket of ice" can be thermodynamically UNconvenient. That is why water stays liquid: it is "locally" in equilibrium, a metastable equilibrium.

If you don't know about metastable equilibrium, example: this is a bit like having some water in a lake up on a mountain... of course water would prefer to flow down to the sea (its equilibrium state), but it can't because it first has to overcome the small barrier encircling the lake.

WHY UNCONVENIENT THEN? Where is the "barrier"? Well, freezing has to start somewhere... and creating a tiny bit of ice (which is "good") requires also creating an inhomogeneity and an ice-water surface (which is "bad"). All together it turns out that water->ice transition gets convenient only once you go beyond a crytical dimension of your small ice crystal... but first you have to reach that! And to do this you need a nucleation point or some sort of perturbation.

Answer 2

How To Supercool Water

Answer 3

When ice is subjected to a high pressure it liquifies. This happens under the blade of an ice skater's skates, as long as the ice isn't too cold to begin with. If the ice is too cold, more pressure is required to force the change in phase from solid to liquid.
This behavior is follows the fact that water expands when it freezes. If it's not allowed to expand, it won't freeze. It is then possible to have supercooled water by subjecting it to adequately high pressure while cooling it.

Answer 4

You can cool water down to minus 40 (this temperature is the same both Fahrenheit and Celsius) before it freezes. The secret is to keep it free of dust, bubbles or sharp jagged surfaces which would provide nuclei to allow ice crystals to start growing. And don't subject the water to mechanical shock like shaking it.