https://en.m.wikipedia.org/wiki/Phase_diagram

The weirder behaviors for water generally crop up when it is allowed to move around or mixes with another liquid. A fully filled container of H2O that slowly gets heated will get hotter, the increase in temperature will increase the local pressure as the water expands. The higher pressure will raise the boiling point of water depending on the strength of your container it will either explode or may eventually achieve what is called a super critical state

Steam engine boilers have been doing something similar for over a hundred years - boiling occurs when the partial pressure of a liquid exceeds ambient atmospheric pressure, so you can just jack up the pressure to force a hot liquid to not boil, and they kinda do this by themselves by simple thermal expansion in a filled closed volume.

From memory, steam engine boilers commonly operated at something like 300+°C to get sufficient working pressure for efficient operation, and there were numerous boiler explosion disasters before we worked out how to make them strong enough to withstand the insane pressure.

Conversely, if you reduce atmospheric pressure, water will boil at a lower temperature - and in fact there's heaps of videos on youtube where folk chuck a cup of water in a vacuum chamber and make it boil until it freezes from the evaporative temperature loss, and also explains why it's really difficult to make a decent cup of tea or coffee at high altitudes.

No, you'd just get hot and high pressure water until it went supercritical and there was no longer a sharp gas/water phase transition. Also, the pressure would be rapidly huge, because you're not letting the water undergo thermal expansion. Also, it would do the same thing on Earth.

Your thought is in the right direction: raising temp without increasing volume is going to raise pressure. And a higher pressure is going to mean it take more heat for water to change phase from liquid to gas. The phase diagram for water is what is important here. I think though this might be a better question for r/askscience, especially when hypothesizing an unbreakable container or an unlimited amount of heat.

Edit: Looking at other charts, there seems to be a region called supercritical fluid

This one.

Just BTW, in theory, we could use the steam transition in forming O'Neill colonies. They're still impractical today, but I have hopes. :-)

At 1 atmosphere of pressure water will boil at 100C and the boiling point goes up as pressure goes up. If you keep heating water in a confined space it won't boil as long as it remains contained. It would start making steam but the steam would make the pressure go up. As long as the container holds it will just get hotter and hotter, well in excess of 100C.

This is what happens in a pressure cooker. The pressure builds to about 2 atmosphere and the temperature of the water can climb above 100C, cooking your food faster. A pressure cooker is a very weak vessel, though, it doesn't take much to blow the lid off (don't do that). If you had a vessel with thick steel walls, like the boiler in a steam train, you can go much higher.

Just wanted to add another real world example: the coolant system in automobiles does this all the time. That system is essentially a closed loop system. The radiator cap acts as a pressure regulator, and allows fluid to expand into the coolant tank when the pressure rises high enough. The likelihood of pressure is why there are big warnings on your radiator cap telling you to not open it when the engine is hot. If you do, the pressure drops and all that really hot water inside can suddenly decide to turn into really hot steam that will then spray out at you.

Well, see, it’s like this. The water is no longer wet. It becomes what is known as dry water. Think of it as the antimatter of hydration. And thank you for your question.

also interesting enough

you can technically line a spaceship with a field bulkhead of water, provided you use hydrodynamics to circulate the water in the bulkhead containers to avoid expansion.

i digress. bulk water like this (at a width of several cm) can halt ionizing radiation by half. you can extend this with wider bulkhead containers for the ship. this in fact helps protect space vessels from ionizing radiation from solar flares etc

yes, nasa has tested the hell out of this

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It will behave the same way as water on earth, the only difference is 1bar of pressure.

With that sort of container, water would rise in pressure at an absurd level while heating (with thermal expansion), so the question would be
"will it freeze" more than "will it boil"

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Oh steam would form till the pressure got too high then BAM!

Superhot ice sounds pretty cool. How does water form a solid if there is no room to expand into the crystalline structure?

That’s how pressure cookers work. Increasing pressure raises the boiling point which allows liquid water to exist at temperatures higher than 212F

With pressure it would form ice VII as shown in the diagram you posted, that expand less than the ice we know from everyday. The elasticity of both liquid and solid water would set pressure at a fixed volume, exactly for the same reason the pressure would increase when heating.

This. Although finally the water will pass the critical point, at which a distinction between fluid and gas is impossible. So you could say, halfjokingly, that there is steam and isn't.

Actually no. There just is no space for steam to form and the container is indestructable as stated. It will heat with rising pressure until it passes the critical point. Then a distinction between fluid and gas cannot be made anymore.

Basically everyone is saying:

https://en.wikipedia.org/wiki/Critical_point_(thermodynamics)

For water that would be 374^(o)C and 218 atm

Triple point

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