Chemical Forums
Specialty Chemistry Forums => Materials and Nanochemistry forum => Topic started by: ME_BOG on December 07, 2022, 09:19:44 PM
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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 ?
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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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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").
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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).
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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.
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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)?
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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.
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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.
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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.
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Also, does anyone know if Lauric acid would work?
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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 (https://www.researchgate.net/figure/Lauric-acid-thermophysical-properties-30-31_tbl1_339488189)
This website of limited credibility claims acetic acid expands upon freezing
vedantu.com (https://www.vedantu.com/question-answer/true-or-false-water-contracts-on-freezing-class-11-chemistry-cbse-5fbababeffe88b10a64a0b0b)
but that discussion claims the pure acid doesn't
sciencemadness.org (https://www.sciencemadness.org/talk/viewthread.php?tid=31917)
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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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 ?
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If this were to be true, would a Hydrate of this salt also have the same property ?
Not necessarily.
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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.
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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
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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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Some salts must shrink when losing crystallization water at heat (I mean, less hydrated salt + separate water taking less volume than the more hydrated salt). But where to find such a data, or a salt with such a property, no idea. From the densities of the salt with more or less crystal water, but searching that way takes unmanageable time.
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Do you know anything about the hydrates of Disodium Hydrogen Phosphate?
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Enthalpy, from the website www.sigmaaldrich.com I have discovered that the Heptahydrate of Disodium Hydrogen Phosphate has a density of 1.68 g/cm3 while the Dodecahydrate has a density of 1.52 g/cm3.
What does this tell me ?
Edit: I am interested in the possibility of using the Dodecahydrate because it has a melting point of approximately 35 degrees Celsius.
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Na2HPO4 weighs 141.96 g/mol.
Na2HPO4 ° 7H2O weighs 268.07g/mol. 1mol occupies 159.57cm3.
5 additional mol of H2O not bound with the crystal occupy 90.53cm3.
The total is 250.1cm3.
Na2HPO4 ° 12H2O weighs 358.15g/mol. 1mol occupies 235.63cm3.
Separating the water increases the volume. Not the sought direction.
You could check the accuracy of the densities. I'm not sure neither that good crystals create under your conditions, especially if they don't have time.
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Ok thanks,
I still think it is worth a shot to try it out if i can get my hands on some of the material without having to pay an awful lot for it.
What I believe could potentially happen is that, instead of separating the water, the Dodecahydrate simply melts under the pressure (and I was unable to find any densities for it at different temperatures).
Another idea I recently had was to use an inorganic acid, like 85% phosphoric acid, however, I was sadly unable to find any phase diagrams or density/temperature data for it. What I also couldn't find was the hardness of it (although I assume that there is a decent chance the crystals will be hard). If anyone has any data on phosphoric acid I would appreciate you posting it.