You’re as cold as ice

I was about to type the phrase “ice is cool”, but then I realised what I was saying and decided that even I can’t get away with a pun that bad. At least not at the start of a blog post…

As well as being able to keep your drinks cool on a hot day, ice is actually pretty amazing stuff. Even more amazing as it’s now been shown that there are 20 different types of ice — 15 crystalline forms alongside 5 amorphous (non-crystalline) forms. Actually, this is yet another reason why water is pretty special. Very few substances can exist in this many different solid phases.

Different types of ice crystal form according to how water molecules stack together when they solidify. This varies according to the temperature and pressure. For instance, the ice that you’d throw into a glass of iced mocha is known scientifically as ice Ih. It has a hexagonal crystal structure which makes it very low in density. Hence, it floats in your drink because it’s actually less dense than liquid water. If you were to take that same ice though, and put it in a pressure chamber, the molecules would start to become unstable in their hexagonal shape. At a certain critical pressure, the molecules would rearrange themselves and the ice would recrystallise into a different structure.

Actually, ice is capable of forming almost every type of crystal structure if you give it the right environment. Monoclinic, orthorhombic, tetragonal, cubic, hexagonal… You name it.

The newest addition to this little crystalline family though, is ice XV, first reported just last week. Thermodynamically stable at temperatures below around 130K (-143°C) and pressures of 0.8-1.5 gigapascals, it’s unlikely to be too prolific in nature. There is, however, always a chance that exotic forms of ice like this might be able to exist inside the kind of icy moons and dwarf planets that litter the outer solar system.

It was also previously predicted that ice XV would be ferroelectric — the kind of conductive material with potential uses in electronics and suchlike. As it happens, the predictions were wrong. Very wrong in fact. Ice XV is actually antiferroelectric!

It’s quite surprising when you think about it, that we’re still discovering things about something as fundamental on planet Earth as ice!

Source: arXiv Blog, arXiv.


About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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