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Author: Subject: Questions on Eutectics
artemov
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[*] posted on 4-10-2020 at 21:46
Questions on Eutectics


Specifically, acetic acid/water eutectic.

The graph below is from this paper : https://www.tandfonline.com/doi/abs/10.1080/01496395.2012.71...
Red and blue text/lines are added by me.

Vinegar is said to have a freezing point of around -2C (Google).
I supposed the freezing point of an eutectic mixture is defined as the temperature where solids start to appear?
If I keep the mixture just slightly below its freezing point, say -2.5C, I would not expect the whole thing to freeze solid no matter how long right? It would be just a bit of ice and a very very slightly concentrated vinegar?

My fridge is about -15C. At this temp should I expect a lot more ice and a liquid mixture of about 42% acetic acid?
This YouTube video seems to show a complete freeze https://www.youtube.com/watch?v=q8yedBBScos
I thought eutectic mixture dun completely freeze until the eutectic temp, which is about -27C here?

Cheers. I am conducting an experiment in my fridge now :D

vinegar.jpg - 69kB

vinegar2.jpg - 65kB
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macckone
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[*] posted on 5-10-2020 at 12:17


Eutectics do not melt or freeze cleanly.
At the eutectic point they will freeze cleanly.
Freeze purification is an art, not a science and the product appears far from pure.
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[*] posted on 5-10-2020 at 12:31


Quote: Originally posted by artemov  

If I keep the mixture just slightly below its freezing point, say -2.5C, I would not expect the whole thing to freeze solid no matter how long right? It would be just a bit of ice and a very very slightly concentrated vinegar?


That's correct, but what you'll often find is a very slushy ice that will be very difficult to separate from the rest of the mixture.




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artemov
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[*] posted on 5-10-2020 at 20:57


Ok thanks guy.
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