Sciencemadness Discussion Board

Creating eutectics

helzblack - 11-10-2024 at 11:02

So I have never made an eutectic salt. I want to make the salt-potassium chloride eutectic.

Do I have to mix them forcefully with a mortar? Dissolve them and then evaporate the water?

How is the eutectic made, it is supposed to melt at around 600C

Rainwater - 11-10-2024 at 13:41

What other compound are you mixing with the KCl?
To the best of my knowledge, KCl will decrease the melting point of water and a few other organic solvents
It will decrease the melting point of calcium chloride when mixed to a ratio of 70% KCl
(going off memory here, lots of crc errors)
https://www.sciencedirect.com/science/article/abs/pii/S09270...

[Edited on 12-10-2024 by Rainwater]

Fulmen - 11-10-2024 at 23:21

You need to melt them together. Once one of the components melts the others will start dissolving into it. Finely ground and mixed materials will probably melt faster, but not at a lower temperature.

helzblack - 12-10-2024 at 05:45

@Rainwater Salt and Potassium Chloride
NaCL and KCL

chornedsnorkack - 12-10-2024 at 07:05

Quote: Originally posted by Fulmen  
You need to melt them together. Once one of the components melts the others will start dissolving into it. Finely ground and mixed materials will probably melt faster, but not at a lower temperature.

Is it so? Compare water and salts. The eutectic is -21 for NaCl, lower for some other salts. If solid NaCl and solid water are brought to contact at say -10 degrees, will solid-solid contact initiate melt formation, or will there be no reaction till they are warmed to 0 degrees?

Fulmen - 12-10-2024 at 08:25

Fair point. As you come close to the melting points there is bound to be some interaction. So in theory you should be able to form the eutectic slightly below the melting point. But it's going to be a slow process compared to melting the ingredients together.

[Edited on 12-10-24 by Fulmen]

Deathunter88 - 12-10-2024 at 08:32

Quote: Originally posted by chornedsnorkack  
Quote: Originally posted by Fulmen  
You need to melt them together. Once one of the components melts the others will start dissolving into it. Finely ground and mixed materials will probably melt faster, but not at a lower temperature.

Is it so? Compare water and salts. The eutectic is -21 for NaCl, lower for some other salts. If solid NaCl and solid water are brought to contact at say -10 degrees, will solid-solid contact initiate melt formation, or will there be no reaction till they are warmed to 0 degrees?


Yes the solid water would melt - this is precisely how road salt works to melt snow and ice.

Bedlasky - 12-10-2024 at 17:22

Awesome eutectic is LiCl-KCl. 41,8 mol % KCl, 58,2 mol % LiCl (anhydrous). Mixture melt at 352 °C, which is very low for ionic chloride mixture.

DraconicAcid - 12-10-2024 at 17:49

Quote: Originally posted by Bedlasky  
Awesome eutectic is LiCl-KCl. 41,8 mol % KCl, 58,2 mol % LiCl (anhydrous). Mixture melt at 352 °C, which is very low for ionic chloride mixture.

Molten lithium salts will weaken glass. You get slow ion exchange which makes the glass very brittle.

knowledgevschaos - 13-10-2024 at 02:06

Phase diagrams are super useful for this kind of thing.
This website has a great article on how they work. Although it's specialized for the alloys of metals, everything should still apply for eutectic salts.

Fulmen - 13-10-2024 at 12:10

The KCl/NaCl eutectic is pretty underwhelming (650/800C). Adding MgCl2 can drop it under 500C, I'm going to try that as a flux for molten aluminum in a future project.

If you're just after cool eutectics I would study the K/Na/CaNO3-system. The constituent salts melt from 300-550C, the eutectics go down to 160C.

Rainwater - 13-10-2024 at 12:52

Quote: Originally posted by Fulmen  
K/Na/CaNO3-system.

I accidentally mixed sodium and potassium metal. It was not nice.
It is very unpleasant to depose.
1 drop of water into the alloy was too explosive, so i thought to drip the mix into an extreme excess of water. It worked great until it didn't
Eat through a ptfe stopcock in a seperation funnel and leaked out very, very fast, instantly ignited my table, bucket, grass. Big booms and puffs, flashes, and pops.
1 of 5 stars will not repeat.

Leftovers turned yellow, poked with a stick from far away. Instant pops.
Wear ear protection
3 of 5 stars would recommend to a friend.

Sir_Gawain - 13-10-2024 at 14:14

I think he’s referring to a mixture of all three nitrates. Not elemental Na/K.

Morgan - 13-10-2024 at 17:16

When doing some experiments/toying with solid rock salt, I thought it would be nice to make my own solid rock salt, but the melting point is annoyingly high. I was able to melt or glaze the surface of some table salt with a simple torch but beyond that of course it's more effort to melt it so the idea of a eutectic appealed to me. It would be nice if a eutectic could retain or improve the high thermal expansion property of rock salt.
When the physicist John Tyndall was studying the Trevelyan Rocker, on this topic, of all the minerals he experimented with, he found rock salt to be the best. "I scarcely know a substance, metallic or non-metallic, with which vibrations can be obtained with greater ease and certainty than with this mineral."

A few random experiments tried with salt.
https://www.youtube.com/watch?v=jlD1EGEieC0
https://www.youtube.com/watch?v=5bu01y_6LJU
https://www.youtube.com/watch?v=Yet6p4ja7qQ
https://www.engineeringtoolbox.com/linear-expansion-coeffici...

One curious tidbit if anyone knows, is it possible that this very tiny spark from this tiny hot brass fitting was caused by an electrostatic discharge when set upon the salt? It occurs at the the 10 second mark and it's very faint. I haven't been able to reproduce it, hoping to amplify it if possible.
https://www.youtube.com/watch?v=i-7kbkVx8bI

Fulmen - 14-10-2024 at 02:19

Quote: Originally posted by Sir_Gawain  
I think he’s referring to a mixture of all three nitrates.

You are correct, my apologies for the confusion. It is of course KNO3/NaNO3/Ca(NO3)2. NaK is pretty cool, but not really suited for amateurs. And combining it with nitrates sounds like a bad day in the lab for everyone.

[Edited on 14-10-24 by Fulmen]

helzblack - 15-10-2024 at 04:12

Quote: Originally posted by Fulmen  
The KCl/NaCl eutectic is pretty underwhelming (650/800C). Adding MgCl2 can drop it under 500C, I'm going to try that as a flux for molten aluminum in a future project.

If you're just after cool eutectics I would study the K/Na/CaNO3-system. The constituent salts melt from 300-550C, the eutectics go down to 160C.


And how do you plan to mix them to make the eutectic? Mortar and pestle? I have heard that it must be forcefully and intimately mixed, hence why I am asking if this is correct?

[Edited on 15-10-2024 by helzblack]

chornedsnorkack - 15-10-2024 at 04:24

I am unsure that a double eutectic needs forceful mixing. A triple eutectic might.