Talk:Amorphous ice

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I merged these 5 articles into one because they were redundant and having separate articles was stupid, but then I googled and realized all the content was just cut-and-pasted from http://www.lsbu.ac.uk/water/amorph.html. I'm working on writing some original content (at Amorphous ice/Temp) now. —Keenan Pepper 16:14, 3 October 2005 (UTC)

Contents 1 Creation of amorphous ice at home 2 Relevance 3 Units 4 Density 5 Info request

[edit] Creation of amorphous ice at home

It happens from time to time glass/bottle of water to be found liquid-like if left outdoors when temperature moves from above 0 to below 0 C. On first touch, bottle suddenly freezes. We were explained that this is because water acquired same structure as glass (i.e. Amorphous ice), and then it changed to real cristal-ice. But as I read this article, this does not match -- amorphous ice requires sudden, not slow temperature change. Could someone explain me mentioned phenomenon? Saigon from europe 15:15, 7 October 2005 (UTC)

This sounds like supercooling to me. If you carefully cool water in a smooth container to below its freezing point but above its glass transition temperature, it will remain liquid. A supercooled liquid will crystallize suddenly if it's disturbed and heat up in the process (heat of fusion). Amorphous ice is what you get if you continue cooling it past the glass transition temperature of water (which is difficult to measure but it's definitely colder than it ever gets outdoors). Because it gets easier to crystallize as the temperature decreases, it's practically impossible to reach the glass transition temperature unless you do it really fast, hence the difficulty of making amorphous ice. —Keenan Pepper 16:24, 7 October 2005 (UTC)

Thanks for the explanation :) Saigon from europe 21:29, 9 October 2005 (UTC)

[edit] Relevance

Is there any utility to amorphous glass, or is it solely a curiosity? Perhaps this ice has some interesting properties? All I really know at this point is its definition and how to make it.

Amorphous glass or amorphous ice? All glass is an amorphous solid, as far as I know... so its utility is for things like Window and Eyeglasses.

I don't know if amorphous ice has any utility. :) --Syrthiss 19:47, 7 October 2005 (UTC)

And if you would like to make sinking ice cubes this might help... --Mac Davis 12:51, 8 October 2005 (UTC)

The interest in amorphous ice has something to do with the density anomaly of liquid water, ie that liquid water expands upon cooling below 4 C. Some theories of liquid water structure and dynamics postulate liquid water as a mixture of low- and high-density phases that are very intimately mixed. If the boundary between these two phases is extended into the supercooled region of the phase diagram, there should be (at least) two corresponding amorphous "phases". However, since amorphous solids are nonergodic systems, it is difficult to defend "HDA" and "LDA" as strictly analogous to the liquid. Regardless, there is great interest and effort ongoing to understand the properties of liquid water since it is such an important solvent. The amorphous solid phases of water continue to inform our general understanding of this material.

An interesting aside is that a few other materials, such as SiO2 and GeO2, show similar density anomalies in their liquids, and polyamorphism in their vitreous solids. Having worked with VHDA and HDA, I can testify that sinking ice cubes can be more conveniently created from deuterium oxide :) Robby.hart 04:29, 31 January 2006 (UTC)

[edit] Units

I've just gone ahead and changed the units to something more sensible (Kelvins, with Celcius and Fahrenheit in parentheses). Also fixed botched conversion from GPa to kilobars --Sander Pronk 21:11, 7 October 2005 (UTC)

[edit] Density

Does anybody know the actual densities of low and high density amorphous ice?

LDA, 0.94 g cm^-3

HDA, 1.17 g cm^-3

VHDA, 1.26 g cm^-3

What I don't understand is how the denisties are less than that of normal liquid water, which is 1 g/cm^3. Ice Ih would be denser, and common sense tells us amorphous ice is even denser. --Mac Davis 07:54, 8 October 2005 (UTC)

Well, water is an odd substance. Normal water ice (ala Ice cubes) is less dense than liquid water. I don't know the density of normal water ice, but I would suspect maybe 0.9. --Syrthiss 13:49, 8 October 2005 (UTC)

Sorry, I really do know that ice is less dense than water. The ice article, puts it at 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature.

"Liquid water is most dense, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the temperature drops to 0 °C."

So, it is not that difficult to understand why solid ice is less dense, because there is so much empty space in between the hexagonal crystals of ice Ih. But amorphous ice has no crystals, and that would mean there as not as much empty space, therefore the density is greater. The density is much less though, why? --Mac Davis 07:54, 9 October 2005 (UTC)

Structurally, amorphous solids are generally no different from liquids: looking at snapshots of configurations of molecules it's almost impossible to tell the two apart. The dynamics obviously differ a lot. Water molecules have this weird property that they prefer to sit edge-on (see Hydrogen bond).

If all molecules take on such an edge-on position, like they do in most ice forms, they effectively lower the density compared to a situation where the molecules are just packed together. In liquid water, most, but not all, molecules have this edge-on configuration: there is some disorder. The higher the temperature, the more disorder there is, but also the more energy the molecules have to push each other away (see Thermal expansion. And the lower the temperature, the more the water molecules like to sit edge-on putting each other a bit further away than close packing. In between the two extremes there is a balance where the molecules have enough energy to sometimes sit close-packed, but not enough energy to push each other away and expand the system. This balance is maximized at 4 °C, and therefore the density is maximal at that temperature. This is why low density amorphous ice has a lower density than water at 4 °C. High density amporphous ice is formed at very high pressure, counteracting thermal expansion and therefore has higher density. --Sander Pronk 20:29, 24 October 2005 (UTC)

[edit] Info request

"Once formed VHDA is more stable than either HDA or LDA and can retain its structure for months at normal atmospheric pressure"

This needs a temperature context as wel

And a referenceJohn Loveday 17:27, 14 June 2006 (UTC)

Also, do any of these forms of ice exist naturally on earth (e.g. deep in polar icecaps)? - MPF 19:24, 19 December 2005 (UTC)

No the temperatures are too low John Loveday 17:27, 14 June 2006 (UTC)

We need a reference other than "liquid nitrogen temperatures" in this para Ry Jones 19:12, 24 November 2006 (UTC)