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Please help me with an answer to my dilemma:

Is there a liquid that could be used to fill an ice rink (non-explosive, non-poisonous, etc), and have the freezing point above 0 Celsius?

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Iron- it has a freezing point well above zero degrees. Seriously though, water is used because it is plentiful, freezing point is at a useful temperature, plumbing is already understood and simple at this temperature and it is largely safe. –  Rory Alsop Dec 15 '12 at 13:37
    
Thank you for your comment,if such a liquid exist will help me spare a lot of electricity used to freeze the water. –  Muresan Dec 16 '12 at 5:27
    
Synthetic ice technology is already in use in places such as Disneyland- but water is much likely less expensive. –  Mark Rovetta Feb 6 at 4:46
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2 Answers 2

The answer to this question is "probably not". The reason for this is quite interesting.

Ice skates have such low friction because a layer of water forms in between the ice and the blades. In order for this to happen, you need a substance that will turn from solid to liquid when it's compressed, which (according to thermodynamics) is the same thing as having a liquid that expands when it freezes. If you don't use a substance with this property then your skates are just resting on a solid surface and friction will prevent you from going anywhere.

But water is quite unusual in having this property. There are other substances that do it, but not many. The most comprehensive list I can find includes only water, silicon, gallium, antimony, bismuth and acetic acid. The metals can all be ruled out because you'd have to heat the floor up to close to their melting point. Acetic acid comes close: its melting point is $16$-$17^\circ C$, so you could in principle skate on a floor made of the stuff at only a little below room temperature. But unfortunately pure acetic acid is corrosive and has a pungent smell (it's what you can smell in vinegar, but this would be the purified version, so much more intense) so it wouldn't be suitable for a public place.

Maybe there is another molecule that has the desirable properties, but it seems kind of unlikely, because these substances are easy to spot - the solid phase floats on top of the liquid one - so if there was another one it would probably already be known.

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Thak you very much Nathaniel, perhaps a solutions, a mix of more than one liquid will have such freezing point.For me it's important to find such a liquid or mixture to spare the electricity used to freeze the ice rink. –  Muresan Dec 16 '12 at 5:30
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@Muresan the problem is that all the known substances with the expanding-on-freezing property are metals, apart from acetic acid. The list I linked to says some of bismuth's alloys also expand, so maybe you could lower its freezing point by mixing it with mercury, while still keeping the expansion property (this seems unlikely to me but I don't know enough chemistry to say for sure) - but mercury releases toxic vapour, so it wouldn't be suitable for a public place. –  Nathaniel Dec 16 '12 at 9:00
    
@Nathaniel: "you need a substance that will turn from solid to liquid when it's compressed, which (according to thermodynamics) is the same thing as having a liquid that expands when it freezes" could you point me toward some reading material on that ? –  josinalvo Dec 16 '12 at 15:26
    
@josinalvo I first learned about the layer of water in this video of Richard Feynman talking about magnets, which is worth watching. The equivalence between melting on compression and expanding on freezing is because it's a reversible transition, so the volume change has to be the same in each case - if that's the bit you want to learn more about then you'll need a good introductory textbook on chemical thermodynamics or physical chemistry, but I don't have a specific one to recommend. –  Nathaniel Dec 17 '12 at 1:56
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I wouldn't completely rule out a gallium rink. Gallium melts at 29.76 °C (85.57 °F), which is not a terribly uncomfortable temperature when resting. The problem, of course, is that skating can be strenuous, so the air would have to be cooled, not the surface, However, it's surely cheaper to cool air somewhat than to cool water to below its freezing point, and if the air outside were cool, that could substitute for air conditioning. Besides, it's quite likely that some gallium alloy could be found that would lower the melting point somewhat, while preserving the property of melting under pressure. Also, I understand that gallium is thought to be very or fairly nontoxic; I suspect that it may also be much less volatile than acetic acid near its melting point. Bismuth, at least, might be a suitable nontoxic alloy metal. (It surely is very nontoxic, since it's in Pepto-Bismol.) Of course, even a very small toxicity could make a gallium rink illegal in most countries. There are other considerations as well, such as the viscosity of liquid gallium near its melting point. I have no research to provide; I am a mathematician and computer scientist, not a physicist.

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I have a bunch of gallium because it's cool to see metal melt in your hand. Unfortunately, it doesn't behave at all like water melting and it doesn't behave like ice at all. It isn't slippery. When frozen, gallium is pretty much like any other metal and you wouldn't want to skate on a rink made out of copper / iron / zinc / lead, etc. –  Brandon Enright Feb 5 at 23:05
    
@BrandonEnright Ice isn't slippery, either, if there is no melting. It is the liquid water that forms on its surface, especially under pressure, that makes it slippery. Ice at a low enough temperature is not slippery at all. What would make gallium slippery is the liquid metal caused by the pressure of the blades. Copper, iron, zinc, and lead do NOT melt under pressure, so they certainly could not make a rink that could be skated on. Gallium might, because of the rare property it shares with ice and a few other substances, although as I said, there are other considerations. –  Stefan Burr Feb 8 at 6:41
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protected by Qmechanic Feb 5 at 22:55

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