ice cubes behaviour

[murulidhara]

When we put two ice cube one above the other and press it for a few minutes they adhere together. Why it is so?

[Glider]

Forcing the ice cubes together producec heat, which melts the ice. The ice melting releases energy and the loss of energy causes the water to freeze again, welding the cubes together.

[NeonBlack]

Pressing the ice cubes together increases pressure, which lowers the melting point.

Water is one of the few substances in which the melting point decreases with higher pressure.

This is also how ice skates work. The skates distibute your weight over a small area on the ice. The high pressure melts the ice, which gives you a thin layer of water to glide on.

[swansont]

Pressing the ice cubes together increases pressure, which lowers the melting point.

Water is one of the few substances in which the melting point decreases with higher pressure.

This is also how ice skates work. The skates distibute your weight over a small area on the ice. The high pressure melts the ice, which gives you a thin layer of water to glide on.

 

That's the usual explanation, but has been shown to be wrong, as it would only work within a certain range of temperatures very near freezing. But skating routinely works at colder temperatures; it turns out that there is always some liquid present, and kinetic heating is another contributing mechanism

 

http://www.ccmr.cornell.edu/education/ask/index.html?quid=1138

NYT article

http://www.skridsko.net/klubbar/data/science.html

 

 

So if the ice cubes are colder than freezing, they can easily bond when you remove the exposed water layer, as that water then becomes solid. Some small amount of heat flows into the cubes from the liquid.

[John Cuthber]

The idea that there's always a surface layer of water is interesting. How does the water know that it's near the surface and, therefore, shouldn't freeze?

[swansont]

The idea that there's always a surface layer of water is interesting. How does the water know that it's near the surface and, therefore, shouldn't freeze?

 

You don't have anything on the other side to bond with. An individual molecule can always break free, since there will be random changes in its KE. Ice will sublimate, as anyone with a frost-free freezer can attest, so forming a liquid layer should not really be a surprise.

[Externet]

For ice cubes to stick, their mating surfaces have to be wet, and no need to press them.

 

The only place an ice cube is at 0Cº is at its surface if wet.

Inside is below zero, up to waaaay below zero. This is something usually misunderstood.

For a while I was daily buying large quantities of ice blocks to preserve seafood, and on a day I decided to ask : "What is the temperature of the ice you sell" ?

Many idiots responses at that place was 'zero degrees, of course'.

If it was 'zero degrees', it would melt in seconds.

 

Joining ice cubes freeze their wet joining surfaces as the heat at the wet surfaces is quickly drawn by the colder core of the cubes.

Miguel

[murulidhara]

thannks

[Rocket Man]

ice at 0 celcius still needs quite a bit of heat to melt, latent heat of fusion. while the pressure reduces the mp, it also squeezes liquid water out resulting in a wet boundary below zero. if the boundary is far enough below zero, the water can heat up to zero while going solid.

has anyone seen a cable supporting weights over a block of ice? the ice forms over the cable. i tried it with nichrome wire and couldn't get enough tension out of it. so it does take a LOT of pressure.

 

colder ice simply gets some water in the boundary and freezes it.

[John Cuthber]

"You don't have anything on the other side to bond with. An individual molecule can always break free, since there will be random changes in its KE. Ice will sublimate, as anyone with a frost-free freezer can attest, so forming a liquid layer should not really be a surprise."

OK, that's a molecule tick layer and I guess it could reasonable explain a layer2 molecules thick because the "next to the outside layer" layer might be affected. On the other hand, somewhere this effect has to stop or the whole sample melts.

Are we talking about a single monomolecular layer? That's not going to offer a lot of lubrication unless the surface is smooth.

What evidence is given for this liquid layer?

 

 

You can still sublime water at very low temperatures so I don't think that's relevant here.

[swansont]

What evidence is given for this liquid layer?

 

http://www.universityscience.ie/pages/scimat_Explaining_ice.php

 

"In 1996, Gabor A. Somorjai, a scientist at Lawrence Berkeley Laboratory, bombarded the surface of ice with electrons and watched how they bounced off, producing a pattern that looked at least partially liquid at temperatures down to minus 235 degrees. A couple of years later, a team of German scientists bounced helium atoms off ice and found results that corroborated the Lawrence Berkeley findings.

 

"The water layer is absolutely intrinsic to ice," Dr. Somorjai said."

[John Cuthber]

Thanks for that reference. It seems I'm not the only one who thinks a thin layer of water won't help much "In 2002, Dr. Salmeron and colleagues performed an experiment. They dragged the tip of an atomic force microscope, resembling a tiny phonograph needle, across the surface of ice.

 

"We found the friction of ice to be very high," Dr. Salmeron said. That is, ice is not really that slippery, after all.

 

Dr. Salmeron said that this finding indicates that while the top layer of ice may be liquid, it is too thin to contribute much to slipperiness except near the melting temperature. In his view, friction is the primary reason ice is slippery. (The microscope tip was so small that its friction melted only a tiny bit of water, which immediately refroze and therefore did not provide the usual lubrication, he said.)

 

Dr. Salmeron concedes, however, that he cannot definitively prove that his view is the correct one.

 

"It's amazing," he said. "We're in 2006, and we're still talking about this thing."

 

"

Well, now it's 2007 and I don't see this as fully resolved yet.

[Rocket Man]

iirc, water (all phases inclusive) is one of the most anomolous substances known.