Since pressure tracks temperature, if you put a pure gas into a piston-like chamber and squeeze, you should eventually pass the critical point and obtain a superfluid. But, if you keep squeezing, would you not at some point reach some sort of inverse convergence, where the substance exists cycles between a superfluid and some odd solid phase?
ETA: nm. Ninja’d.
( * Off to find “Fat kid/Galileo/Friction” thread. Was this point raised, because I remember a lot of people into the Fat Kid-Pressure debate cited this, even if it ultimately, no matter what the cause, is minor compared to the other physics… * )
That dimple on the side of a plastic milk jug is a “freeze plug.” It’s meant to popout or the milk freezes, so the jug doesn’t split open. The term “freeze plug” comes from engines. They have plugs fitted along the sides that are meant to pop out if the liquid coolant in the engine ever freezes, so it won’t cause the engine itself to crack. If you ever owned a very old car, it might have developed a leaky freeze plug, and had to have it replaced. I had to replace them on the engine of my 1961 Ford once. It was an easy thing to do on my own, though.
I’m pretty sure compressing most normal gases will cause the gas to condense into a normal liquid, since the cylinder described will radiate heat away … the ideal gas law says that increasing pressure will increase temperature and/or reduce volume … the change in state will screw things up, but just keep squeezing … I’m sure there are gases that can be squeezed down to a normal solid, but I don’t know how common that is …
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I seem to remember a thread about freezing water in a sealed container here some time back … as I remember the consensus opinion was that eventually the water will freeze at some temperature and be under higher pressure (if the container is strong enough) … the alternative was to start at very high pressure (500 atmospheres) and then the water would freeze into a different crystal structure …
Obviously said by someone who’s never been skiing at -35C. The “slipperiness” of ice and snow is definitely inversely correlated to temperature, whatever the physical reason.
We can skip the math and just look at the picture. The freezing point decreases.
If you stay very close to 0°C, as you take heat out of the system you’ll eventually form Ice VI, which has a higher density than water. That’s approaching 3000 atmospheres though, so good luck with that rigid container 
Is Ice VI the same as “amorphous ice”? Can you explain the differences between supercooled water and glassy water?
I am not familiar with these terms and can’t do much more than quote Wikipedia at you.
But the phases of ice described in that phase diagram are all AFAIK not amorphous.
Supercooled water is liquid water at a temperature below its freezing point, 0 C. It is an unstable state and will easily freeze even if the temperature doesn’t change. Amorphous ice is as I understand it, the same as “glassy water”, and is just a form of ice without a crystalline structure. Ice VI is something completely different, one of the many crystalline phases of ice. You can see from the phase diagram that ice VI forms only at pressures of around 1 GPa and temperatures between 130 K and 350 K. At the same pressure but lower temperatures, you get ice XV. At 0 C (273 K) but pressures above 2 GPa, you get ice VII, then at about 100 GPa, ice X, and up around 200 GPa, ice XI. Learning to read a phase diagram is a lot of fun.
Are you claiming that the slipperiness of a ski on snow is also caused by pressure melting? That’s a rather astonishing claim, one that I haven’t heard before, especially since the contact area of a ski is, I would guess, at least 100 times as great as the contact area of an ice skate, and we know that the pressure of an ice skate can only increase the melting point of ice by a few degrees C at most. The paper I cited doesn’t claim that slipperiness is not related to temperature, only that the friction does not suddenly increase below -20 C at any pressure. You can see from the phase diagram that liquid water cannot exist below -20 C. Are you saying that snow loses all its slipperiness below -20 C, so that it’s like skiing on sand? And that the pressure of a ski on snow at -35 C raises the melting point of the snow by over 35 degrees?
Indeed the rather odd properties of water are crucial to allowing life to exist. It’s one of the many points which can be used to justify the weak or strong anthropic principle.
FTR, username alert above.
The phase diagram’s source page states that the “critical point and the orange line in the ice-one phase space refer to the low-density (LDA) and high-density (HDA) forms of amorphous water (ice)” so the two glassy (amorphous) states are there but I am not quite getting how to read the diagram enough to know where and what they are referencing. Hoping to be talked through.
Looking at that phase diagram informed by the article cited by them only confuses me more as it states: “glassy water - also called amorphous ice - can exist when the temperature drops below the glass transition temperature Tg (about 130 K at 1 bar)” And I don’t see anything special at those points in the diagram … most of the rest of that review is simply beyond my reading level. Like way beyond.
I appreciate the attempt at helping me. Nevertheless I get the sense that there is much more to glassy ice than “just” that. It appears to be the most common form of water in the universe and apparently has more odd features.
If anyone’s comprehension level is high enough to explain those links to me I’d be much obliged!
In the Life Science Library volume titled *Water, * somebody did something like that. A lab technician filled a little globe-shaped cast-iron container with water, screwed the top on, and set it in a large beaker half-filled with dry ice and rock salt. Then he left the room. A camera took pictures of what happened: after a short while the water froze and the container exploded–some metal fragments were embedded in a steel door 30 feet away! :eek:
On this subject I ran into [another paper](file:///Users/donseidman/Downloads/Formenti%20F%20Res%20Sports%20Med%202014.pdf) of some interest:
Water is such a freakish thing!
The impression I get is that the fluid-to-solid transition (the gaseous state is fluid) of water typically involves energy levels that allow the water molecules to align in a crystal formation. The electrons like to hang out around the O atom, creating the polarity that attracts the Hs of one water molecule to the Os of others. Hence, an amorphous state is hard to achieve in what we would call normal circumstances.
There appears to be a crystallization energy gap that must be crossed rapidly in order to get the amorphous solid, and if it is exposed to just enough heat, it will enter that gap and crystallize, because that is what it wants to do.
There is a lot of space out there, and water is an extraordinarily stable molecule, so there should be a fair bit out there. Liquid water exists in a fairly narrow P/T band, so most of the water in the universe is probably vapor or solid (here is a pretty graphic of how much water is on the earth’s surface – and a bunch of that is ice).
Water vapor in space will mostly remain vapor, floating casually about. Until it encounters a rock. Rocks out in space tend to be a bit cold, so when a rock passes into a water cloud, the water will naturally condense onto it, just like the humidity sweating down your mojito – except, being so cold, the condensation will be solid. Condensing water rapidly onto a cold thing tends to cross the crystallization threshold (this is one way they can make glassy water), so it makes sense that most of the ice in the universe would be amorphous.