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Increasing melting point of Water

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ME_BOG:
Thank you for your answers.


--- Quote from: Enthalpy on December 11, 2022, 11:55:24 AM ---Some pure metals too melt more easily under pressure, or equivalently, expand when freezing

--- End quote ---
- Sadly, this does not work in my case, since all three of the metals you mentioned cost a lot (with bismuth being the cheapest at ~20$ per kg), and, to make myself clear, for the project I would ideally need two cubic meters of material, and using a metal would cost a fortune. Magnesium Chloride Hexahydrate, on the other hand, is sold for 100-150$ per metric ton.


--- Quote from: mjc123 on December 09, 2022, 07:18:27 PM ---If you heat a 10% mixture, it will start to melt at temperature D, and become completely liquid when the vertical line y = 10% crosses the thick line (what you may be thinking of as the "melting point").

--- End quote ---
- Considering this, I think my best bet is perform some tests on a small amount of Magnesium Chloride Hexahydrate in order to see whether it fulfills my needs, since I was unable to find much detailed data on it.

Is it possible to re-melt Magnesium Chloride Hexahydrate without it forming Tetrahydrate and releasing water vapor ?

Are there possibly any organic compounds which also have high friction and fusion under pressure (with melting point 20-50 degrees Celsius)?

Enthalpy:
Expansion upon freezing is a rare property. By memory, I knew only water and gallium plus few other metals. Quick googling seems to suggest that some other solvents might expand too, but I didn't find which ones. I addition, they are liquid at room temperature, so melting in the +20 to +50°C range would need a somewhat adapted molecule, which means a development effort.

A different path would try to imitate water by seeking molecules that build several hydrogen bonds, needing a less compact organization when frozen. Polyols, polyglycols, polyamines, others? With luck you stumble upon a banal existing one, if not it's a significant research effort.

Cheap 2m3 is an other extremely rare property, met essentially by ore. The cheapest processed materials cost a bit under 1$/kg, the most elementary oil derivatives do. Basic food, like sugar, falls in this price category. Even polypropylene costs a bit more presently.

Both properties from one compound is very unlikely. Try your luck searching for the cheapest mass-produced compounds like polyols and polyglycols.

Adding "high friction" won't help. Consider yourself extremely lucky if one compound fulfills the two first demands.

==========

Melting hexahydrate: the source I read contradict an other. Some tell "hexahydrate melts at +117°C upon rapid heating" and others "hexahydrate decomposes at +118°C"
https://en.wikipedia.org/wiki/Magnesium_chloride
https://de.wikipedia.org/wiki/Magnesiumchlorid

It must be possible to regenerate (rehydrate) the hexahydrate after decomposition, but not necessarily in a way that suits your application.

Worth trying? Heat the hexahydrate under pressure of liquid water (or rather of saturated water solution), hoping that the magnesium chloride retains its crystallization water then. At +117°C it's a trivial pressure. Last chance at +374°C, then you need 218 atm. An approximate formula: P~(°C/100)4.

ME_BOG:
Expansion when freezing is not that important to me. What I really need is melting under pressure, generally low friction, hardness and a melting point above room pressure.

ME_BOG:
Also, does anyone know if Lauric acid would work?

Enthalpy:

--- Quote from: ME_BOG on December 14, 2022, 03:07:03 AM ---Expansion when freezing is not that important to me. What I really need is melting under pressure [...]
--- End quote ---
It's the same. A higher pressure favors the liquid when the liquid has less volume than the solid.

This property is seriously rare. Dodecanoic acid doesn't behave like that
researchgate.net

This website of limited credibility claims acetic acid expands upon freezing
vedantu.com
but that discussion claims the pure acid doesn't
sciencemadness.org

How many such substances are known: 10? 100? If you find a longer list than the linked Wiki article, you're lucky.

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