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The molecular force of water expansion

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IamSmooth

Mon Apr 30 2007, 02:40AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Water expands when it freezes. If I am correct, I think it has maximum expansion at 4 C. Anyway, does anyone know how much force freezing water generates? If I filled a strong cylinder with water, placed a force gauge at the top and began to freeze the liquid, how much force can it exert?

ragnar

Mon Apr 30 2007, 03:48AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Freezing water can exert an unbelievable amount of force on any vessel it is contained in. You've probably shattered a glass vessel by absent-mindedly putting it in the freezer at some point.

Filling a hollow metal vessel with water and dropping it into liquid nitrogen... 'tis like a bomb going off.

Bored Chemist

Mon Apr 30 2007, 05:48AM

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"'tis like a bomb going off."
Where does the stored energy come from?

Bjørn

Mon Apr 30 2007, 05:54AM

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You get minimum expansion (maximum density) at 4 deg C. I have seen someone running a small car on freezing water that compressed oil to very high pressures. If you google phase diagrams for water you will find some details, for example the freezing point changes when the pressure increases.

IamSmooth

Mon Apr 30 2007, 01:23PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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The question is, however, does anyone actually know the force it can exert? There has to be a limit.

Dr. Shark

Mon Apr 30 2007, 02:18PM

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The number depends on the ambient temperature.

shows that within certain limits you can sqeeze ice into water, and that ice can take denser structures that the normal modification.

To find the exact pressure you can generate at a fixed temperature would probably require a constant volume P-T diagram which a quick google search does not turn up. Maybe bored chemist knows more?

IamSmooth

Mon Apr 30 2007, 04:32PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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According to the graph 2 kbar should revert ice to water until -20C. This is about 2000 atmospheres which is quite a force. Still, someone must have done a constant volume/pressure curve for water as the temperature is dropped below freezing.

Swany

Fri Jun 01 2007, 05:36PM

Registered Member #261 Joined: Mon Feb 27 2006, 12:34AM
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There is a limit, if you look at a phase diagram containing various forms of ice, ice I (the sort we know, ~0.92g/cc) is the least prevelent. In General Chemistry by Pauling, there is such a diagram and it shows about 9 types of solid water, ice I is the only with a density of <1g/cc. This thread is long dead, but under varying amounts of pressure and temp, other ice forms will prevail and there will be no exerted force.

Bored Chemist

Sat Jun 02 2007, 03:50PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
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I on't have the data to hand but I remeber seeing an article in a journal using this as a means to generate gigh pressures with no real moving parts (except the water) 2 vessels made of thick stainless stell conected together and filled with water. Freeze the water in one and the expanding ice forces water out of the cooled vessel into the other one raisind the pressure. The authors pointed out that if you got the cooled vessel cold enough the ice contracted (and/or changed phase) so there was a limit to how high a pressure you could achieve; they counted this as an advantage on safety grounds. IIRC dry ice was cold enough to do the job

Shaun

Thu Jun 21 2007, 04:37AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

This how ice skates work, by pressing ice into a thin layer of water, but i'm sure I can't possibly be the only one to know that.

I once heard of a case where burglars stole all the money from an outdoor ATM by filling it with water thru its various slots on a cold night via a small van-mounted pump. The water began to cool, expanded, and broke various bolts and welds holding the device together. They either pried it open or it fell apart, and they were able to get their [soaking wet] cash out.

I don't know if this is true or not; and i would think they would have to seal a lot of leaks as i'm sure those things arent watertight.

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