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Forces exerted by the expansion of freezing water
- Thread starter scott916
- Start date
That is -as it turns out- very, very complicated.
First of all, there are many types of ice; even if you only study single crystals there are still several possible phases and which phase the water freezes into depends on pressure and temperature. As far as I remember all phases will occupcy a larger volume than the corresponing weight of water but I am not sure that is true for all pressures.
I'm not really sure, but I think it CAN "freeze" into a different crystal structure. I know that in research labs they have observed and characterized several different "ices", or crystalline solid forms of water. They form at certain combinations of pressure and temperature. That is, at temperatures lower than 32F (or 0C) and MUCH higher pressures than normal atmospheric pressure. In these forms the water molecules are arranged in a different way from what we normally see as ice, and many of them pack the water molecules together more tightly than our "ice", so it is denser.
Years ago in grad school I met a man who worked in this field. When I asked what might be the practical use of such information, he said people who explore for natural gas deposits in the Arctic were interested because some gas is trapped in wierd ice forms under tremendous pressure miles down from the surface. They are called ice/gas clathrates, with gas molecules occupying the small spaces between water molecules in the crystal.
Years ago in grad school I met a man who worked in this field. When I asked what might be the practical use of such information, he said people who explore for natural gas deposits in the Arctic were interested because some gas is trapped in wierd ice forms under tremendous pressure miles down from the surface. They are called ice/gas clathrates, with gas molecules occupying the small spaces between water molecules in the crystal.
That's it exactly.
I happen to work in a high-pressure mineral physics lab right now. We're usually dealing with pressures around .4-10GPa, in a temperature range between 20-400 C. You can see water do all sorts of cool things in this regime. Unfortunately, the experiments we do are supposed to be in liquid phase water, so if it freezes we screwed up.😛
But if you're not careful cranking up the pressure, you'll see the whole thing go to crystals, and the boundaries start shifting due to Ostwald ripening (where bigger crystals grow and smaller crystals shrink).
JustAnAverageGuy
Diamond Member
Now the question becomes what if said container were unbreakable? 😉
Is there such an ice structure that occupies less/same space as regular water?
- JaAG
Is there such an ice structure that occupies less/same space as regular water?
- JaAG
MetalStorm
Member
If the water is cooled to freezing point, and then pressurised, it will remain as water, even at say -200C it is possible to still have liquid water so long as it is under very high pressure.
Think of it like this, when ice skating, the reason you have so little friction is because you are actually running on a very thin layer or water, not on the ice its self. When your blade runs over the ice, the pressure melts the ice and it resolidifies again after the blade has past. This obviously means if you were to cool the ice enough, the pressure induced by the blade would be unable to change the phase of the ice and it would be like walking on concrete with ice skates.
Think of it like this, when ice skating, the reason you have so little friction is because you are actually running on a very thin layer or water, not on the ice its self. When your blade runs over the ice, the pressure melts the ice and it resolidifies again after the blade has past. This obviously means if you were to cool the ice enough, the pressure induced by the blade would be unable to change the phase of the ice and it would be like walking on concrete with ice skates.
That's simply not true. At -200C and high pressure, you may not have Ice 1, but you certainly won't have liquid water. Look at the phase diagram that Gibsons posted. It's true that you can get pretty far into the metastable regime in some cases, but certainly not all the way down to -200C.
MetalStorm
Member
Fair play, I didn't really look at that table, so -200C was a bit of a guess really.
Living here in the land of -60F winter temperatures, I can safely say that there is very little in the everyday world that is made of metal, hard plastic, ceramic, or any other common material that will survive being frozen with water in it with no damage. Engine blocks, water pipes, pop bottles, pumps, valves, and just about everything else you can think of bursts with alarming regularity. I have seen hydraulic cylinders contaminated with water, capable of withstanding thousands of PSI pressures with the ends pushed out. This is one of natures irresistable forces.
DrPizza
Administrator Elite Member Goat Whisperer
Re: skating on a thin layer of water that forms under the pressure from the skates -
That's what I was taught in middle or high school... But, I recall reading more than once that it's not quite true; and also recall that the exact mechanisms involved aren't completely understood.
That's what I was taught in middle or high school... But, I recall reading more than once that it's not quite true; and also recall that the exact mechanisms involved aren't completely understood.
Ice skating can become labored when the ice temperature becomes very low. The NHL facilities try to maintain the ice surface temperature between 24F and 26F. At -60F skating on ice resembles skating on concrete. On the other hand driving a car becomes much less chancy on a -60F icy roadway.
Nope. It's a matter of heat flow and temperature gradients. The ice on top of the water is exposed to the air. Assuming air temperature is below 32F (or 0C), heat will flow from ice to air and keep the ice surface cold enough to stay frozen. But at the lake bottom there is also a flow of heat from the underlying soil into the water. As long as the soil temperature is above 0C, heat will flow from the soil into the water to try to keep the water at or above 0C. So the water near the bottom remains liquid because it has a constant supply of heat to maintain its temperature. Because there is a temperature gradient (warmer at the bottom, colder at the surface), somewhere in the middle of the lake depth there is a point where the heat flow from soil through water to ice and up to the surface just manages to hit the magic temperature of 0C. At that point there is a dynamic equlibrium in which H2O molecules convert from liquid water to solid ice and back again. At lower depths (and marginally higher temperatures) you see liquid water. But higher (and marginally lower temperatures) you see ice.
imported_Wilco
Junior Member
While that helps, the main reason is that Water gets less dense from 4-0 degrees C. Usually materials get more dense as their temperature decreases, which means in liquids you generally find the coldest liquid at the bottom. However with water over this small temperature range it becomes less dense, so the cold water (being cooled by the air) stays on the surface. Causing it to freeze across the top. This creates a barrier to more heat escaping from the water below (which is also warmed by the soil at its edges, as noted above), thus slowing down the freezing of the water below it substantially.
This change in density (less dense means increase volume, causing thermal strain if this volume is constrained) is also why water turning to ice breaks engine blocks, and and structures in general.
Pressure does affect phase change (e.g. Boiling / Freezing points). Increased pressure lowers the freezing point, and would help, but I think the density change is the main reason.
Btw, water is not incompressible, nothing is actually incompressible, its just trying to compress water takes a huge amount of force (pressure). However water compressibility has to be taken into account in some circumstances. If you filled an unbreakable container with water and froze it, the water would just be under a huge amount of strain.
This change in density (less dense means increase volume, causing thermal strain if this volume is constrained) is also why water turning to ice breaks engine blocks, and and structures in general.
Pressure does affect phase change (e.g. Boiling / Freezing points). Increased pressure lowers the freezing point, and would help, but I think the density change is the main reason.
Btw, water is not incompressible, nothing is actually incompressible, its just trying to compress water takes a huge amount of force (pressure). However water compressibility has to be taken into account in some circumstances. If you filled an unbreakable container with water and froze it, the water would just be under a huge amount of strain.
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