What Happens When Water Freezes in a Box So Strong It Can’t Expand?

>We currently know of 15 different "solid phases" [...]

>The form you're likely most familiar with is Hexagonal Ice [...]. If you keep lowering the temperature of Hexagonal ice, it eventually becomes Cubic Ice; tweak the temperature and pressure further and you can create Ice II, Ice III all the way up to Ice XV.

I've counted 16.

What I keep wondering is how long these various exotic forms of ice survive outside the conditions in which they were created. If XV quickly changes back into regular ice this is a cool but seemingly impractical topic of research.

I don't see that it's necessarily impractical. We still have a lot to learn about why various materials behave the way they do. Examining corner cases and weirdness is often informative.

Ice exerts 45,000 lb pressure as it freezes! SO James Watt was 'all wet' when he invented the steam engine. He should have invented the 'ice engine'.

>It is theorized that at pressures somewhere between 1.55-5.62 terapascals ice will become metallic.