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Topic: Increasing melting point of Water  (Read 4889 times)

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Offline ME_BOG

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Increasing melting point of Water
« on: December 07, 2022, 09:19:44 PM »
For a project I would like to create a large amount of a substance with water-like properties (melts from pressure and has low friction) but that is solid at room temp. and atmospheric pressure. Ideally it should have a melting point between 20 and 50 degrees Celsius.

One way I've read this could be done is by mixing it with a salt past the eutectic point, for example, 90% water 10% MgCl2, according to the following graph: (mod edit: image attached).

Will this work or do I need a catalyst or something complicated for it ?

Are there any other alternatives ?
« Last Edit: December 08, 2022, 03:05:20 AM by Borek »

Offline Borek

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Re: Increasing melting point of Water
« Reply #1 on: December 09, 2022, 03:08:14 AM »
Can't think of anything that would make the idea completely off at first sight. But there are many fine prints, the only way to check if it works as expected is experimental.
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Offline mjc123

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Re: Increasing melting point of Water
« Reply #2 on: December 09, 2022, 07:18:27 PM »
It would not be solid at room temperature. Mixtures melt over a range. 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").

Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #3 on: December 11, 2022, 11:55:24 AM »
Some pure metals too melt more easily under pressure, or equivalently, expand when freezing
https://en.wikipedia.org/wiki/Category:Materials_that_expand_upon_freezing
Gallium melts in the sought temperature range. Antimony and bismuth need higher temperatures, but eutectics exist. Gallium has known alloys and eutectics (with indium, tin, or both: "galinstan") that melt more easily.
I didn't check the friction coefficient of gallium. Antimony is known to ease alloys gliding (or make it sounder).

Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #4 on: December 11, 2022, 11:58:21 AM »
Ice fusion under pressure is a common explanation for its low friction under skate blades or skis.

Experiments with gallium under proper pressure would bring more data for or against this theory.

Offline ME_BOG

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Re: Increasing melting point of Water
« Reply #5 on: December 11, 2022, 06:50:41 PM »
Thank you for your answers.

Some pure metals too melt more easily under pressure, or equivalently, expand when freezing
- 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.

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").
- 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)?

Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #6 on: December 13, 2022, 02:41:03 PM »
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.
« Last Edit: December 13, 2022, 02:58:53 PM by Enthalpy »

Offline ME_BOG

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Re: Increasing melting point of Water
« Reply #7 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, generally low friction, hardness and a melting point above room pressure.

Offline ME_BOG

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Re: Increasing melting point of Water
« Reply #8 on: December 14, 2022, 12:01:11 PM »
Also, does anyone know if Lauric acid would work?

Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #9 on: December 14, 2022, 03:11:33 PM »
Expansion when freezing is not that important to me. What I really need is melting under pressure [...]
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.

Offline ME_BOG

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Re: Increasing melting point of Water
« Reply #10 on: December 19, 2022, 05:24:40 PM »
I think that Magnesium Chloride Hexahydrate is not going to work, since its melting point is too high and even if it were to melt under pressure it would not happen at room temperature.

Something that might work is Disodium Hydrogen Phosphate Dodecahydrate (aka. Sodium Phosphate Dibasic Dodecahydrate) that has a melting point well in my desired range. I have also found a paper that states than the friction coefficient of this material in Liquid form is almost as low as that of water, also making it a good candidate of conducting further research.

I have found a russian forum where someone states that Manganese(II) Fluoride also melts under pressure (I would appreciate it if someone finds a scientific paper proving this property of MnF2).
If this were to be true, would a Hydrate of this salt also have the same property ?

Offline Borek

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Re: Increasing melting point of Water
« Reply #11 on: December 20, 2022, 03:02:33 AM »
If this were to be true, would a Hydrate of this salt also have the same property ?

Not necessarily.
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Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #12 on: December 20, 2022, 08:44:02 AM »
Can a fluoride be cheap? Affordable 2m3 is a strong constraint.

https://en.wikipedia.org/wiki/Fluorine
[Fluorine] "costs only $5–8 per kilogram as sulfur hexafluoride"

PTFE would have properties similar to the sought ones - except the price...
A bit over room temperature, it change its conformation, increasing at once its volume and friction (but this is a transition among solids, not a fusion). Slightly above that transition, pressure would reduce the friction. I suppose it takes some time.

Offline ME_BOG

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Re: Increasing melting point of Water
« Reply #13 on: December 21, 2022, 05:46:02 PM »
Can a fluoride be cheap?

Well, this Chinese supplier is apparently selling it for 50 cents a kilo.
https://www.alibaba.com/product-detail/Manganese-fluoride-CAS-7782-64-1_1600598107816.html

Offline Enthalpy

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Re: Increasing melting point of Water
« Reply #14 on: December 22, 2022, 09:17:05 AM »
My Handbook of Chem & Phys doesn't tell whether the dihydrate melts or decomposes at the alleged +58°C.
No idea if the contracts upon melting. This property is rare and I see no correlation between the anhydrous salt and the hydrate. I didn't even find this data for the anhydrous salt.

Be cautious about prices and all data indicated on Alibaba. This seller also claims "white" powder, doubtful for Mn (II).

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