alvinz95
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Supercooling, Snap Freezing, Freezing Point Deppresion, etc!

Postby alvinz95 » Mon Oct 15, 2007 4:58 pm

Questions:

1. What EXACTLY is freezing point deppresion?
2. What happens to liquid crystals when the water "supercools"?
3. How do the liquid crystals "nucleate" when it starts to supercool?
4. What happens to the molecules of "supercooled" water when you "snap-freeze" them with an ice cube?
5. How did Gabriel Fahrenheit discover how to "supercool" water?
6. How does salt cool ice lower than zero degrees Celcius?

Answer ASAP.

wildfirefox
Former Expert
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Joined: Tue Oct 02, 2007 3:27 pm

Re: Supercooling, Snap Freezing, Freezing Point Deppresion,

Postby wildfirefox » Mon Oct 15, 2007 5:19 pm

alvinz95 wrote:1. What EXACTLY is freezing point deppresion?

http://en.wikipedia.org/wiki/Freezing-point_depression
alvinz95 wrote:2. What happens to liquid crystals when the water "supercools"?
3. How do the liquid crystals "nucleate" when it starts to supercool?
4. What happens to the molecules of "supercooled" water when you "snap-freeze" them with an ice cube?

Here's and example what happen to supercooling effects in water molecules:
http://www.phy.ohiou.edu/~braslavs/articles/APL264.pdf
alvinz95 wrote:5. How did Gabriel Fahrenheit discover how to "supercool" water?

This is quite easy. Go to the local library, and look up on the autobiographies of Gabriel Fahrenheit. His discoveries are discussed extensively throughout his books. Here's a shorter article about him:
http://www.bookrags.com/Gabriel_Fahrenheit
[/quote]
alvinz95 wrote:6. How does salt cool ice lower than zero degrees Celcius?

This should explain 90% of your questions up front:
http://www.natmus.dk/cons/tp/cool/suprcool.htm
[/quote]
alvinz95 wrote:Answer ASAP

A "please" would greatly boost the pleasantry and interaction between experts and students.
Those who can see that do not exist are geniuses. Those who can see what exists are brilliant. Those cannot see what exists are ignorant.
- Lao Tsu

alvinz95
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Joined: Thu Oct 11, 2007 7:00 pm

Thank you!

Postby alvinz95 » Mon Oct 15, 2007 5:25 pm

Thank you alot!

One more question: What is "equilibrium temperature"?

wildfirefox
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Re: Thank you!

Postby wildfirefox » Mon Oct 15, 2007 5:27 pm

alvinz95 wrote:One more question: What is "equilibrium temperature"?

http://www.smv.org/jims/l4.htm
Those who can see that do not exist are geniuses. Those who can see what exists are brilliant. Those cannot see what exists are ignorant.
- Lao Tsu

alvinz95
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Joined: Thu Oct 11, 2007 7:00 pm

Postby alvinz95 » Mon Oct 15, 2007 5:36 pm

Thank you very much again!

For my bibliography (interview), I need your name. So may I please have your full name? (First, Last)

wildfirefox
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Postby wildfirefox » Tue Oct 16, 2007 8:42 am

Hm..I don't think I wrote any of those articles. But as for my full name, it's Nam Nguyen
Those who can see that do not exist are geniuses. Those who can see what exists are brilliant. Those cannot see what exists are ignorant.
- Lao Tsu

ambersupercools
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Joined: Sun Nov 11, 2007 2:59 pm

snap freezing

Postby ambersupercools » Sun Nov 11, 2007 3:11 pm

I have been unable to locate an exact definition or explanation of snap freezing. I cannot seem to find any information on the steps or logistics of what occurs during the snap freezing of water. A lot of my experiment deals with how different frozen items and the sizes of these affect how quickly and how well supercooled water and other liquids will snap freeze. However, unless I can find some background information on this phenomena, all of my data will be inadmissible. Any help I can get would be appreciated, I don't want to lose this large section of my experiment.

Thanks!

Louise
Former Expert
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Joined: Mon Jan 16, 2006 2:17 pm

Re: snap freezing

Postby Louise » Sun Nov 11, 2007 3:43 pm

ambersupercools wrote:I have been unable to locate an exact definition or explanation of snap freezing. I cannot seem to find any information on the steps or logistics of what occurs during the snap freezing of water. A lot of my experiment deals with how different frozen items and the sizes of these affect how quickly and how well supercooled water and other liquids will snap freeze. However, unless I can find some background information on this phenomena, all of my data will be inadmissible. Any help I can get would be appreciated, I don't want to lose this large section of my experiment.

Thanks!


I'm a little unclear on what you are doing. If you are talking about freezing something using liquid nitrogen, the process is the same as any freezing. This process is controlled by the heat capacities of the materials, the surface area, and the starting temperature of the materials. This is a pretty complicated topic, and the math may be beyond your level. You can try searching using these terms and combos oft hem: heat transfer, freezing, thermodynamics. This is how many scientists would use the term "snap freezing". For example biologists snap freeze samples for preservation and further study.

Your post also mentions supercooled water, which makes me think you aren't studying what i mentioned above, but rather the effect of bringing a liquid to a temperature below its freezing point and having it remain a liquid. This has to due with the entropy cost of going from a random fluid to an organized crystal. Try searching for "supercooled" or "supercooling" and "nucleation" or "crystal nucleation". This effect is also related to superheating, where a liquid is above its boiling point but isn't boiling. In either case, adding a particle serves as a nucleation site and leads to rapid freezing or boiling.

While I normally recommend the wikipedia for questions such as these, I was really un-impressed with what what written on these topics. (For example, the articles often confused freezing quickly (like with nitrogen) with being supercooled (a liquid with temperature below the "normal" freezing point). The articles were either confusing, imprecise, or wrong. I would recommend using other sources that turn up in your search.


Louise

ambersupercools
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Joined: Sun Nov 11, 2007 2:59 pm

Postby ambersupercools » Sun Nov 11, 2007 4:40 pm

I am studying supercooling liquids, where you bring the temperature below it's freezing point and it does remain in liquid form.

As another branch on my topic I was experimenting with the effects crystal nucleation, where it does quickly turn into a solid around the point of the disturbance, or impurity in the water. I could not find a site that explained this well in detail, at least under the term of snap freezing. I might have to change the name/nature of my project to something dealing with nucleation. Also, I cannot use Wikipedia as a cited source, thanks for that though. I will look and see what I can find for nucleation and crystal nucleation that would be applicable. Thanks again.
"In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move." - Douglas Adams, The Restaurant at the End of the Universe

Louise
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Joined: Mon Jan 16, 2006 2:17 pm

Postby Louise » Sun Nov 11, 2007 5:11 pm

ambersupercools wrote:I am studying supercooling liquids, where you bring the temperature below it's freezing point and it does remain in liquid form.

This is because there is no nucleation site.

As another branch on my topic I was experimenting with the effects crystal nucleation, where it does quickly turn into a solid around the point of the disturbance, or impurity in the water. I could not find a site that

Yes, this is the flip side of supercooled liquid. You present them as two different things, but they aren't. Supercooled liquids don't have a nucleation site, the minute they do have one, they go to the appropriate phase (crystal/solid/frozen). Same with superheated liquids, which you can easily generate in a microwave.

I could not find a site that explained this well in detail, at least under the term of snap freezing


That is because it isn't 'snap freezing'. Why do you think it is? I defined snap freezing above, but I'll define it again. Snap freezing makes an item frozen "very fast". It isn't a very scientific term, since it isn't quantitative, though it is used to describe dunking a sample in a cryogenic liquid. But, nothing about snap freezing involves anything that is 'supercooled'. The cryogenic liquid is in its normal liquid phase, not in a supercooled form. The object that is frozen is frozen fast, but it is frozen, not supercooled either. Using a supercooled liquid for snap freezing would be a bad idea... suppose you wanted to snap freeze an apple. You dunk your apple in the supercooled water; immediately your apple is encased in a block of ice. You cannot get it out. Now, use liquid nitrogen. Drop the apple in. The apple freezes, some liquid nitrogen boils away, the rest stays liquid. You pull your apple out and do whatever you wanted to do with it.


Supercooling involves the creation of a metastable state. While adding a nucleation site makes it freeze "very fast" this is not usually called snap freezing. Search for "supercooled" or "supercooling" and "nucleation" or "crystal nucleation". You can also add in 'metastable state'.

Also, I cannot use Wikipedia as a cited source, thanks for that though.

I agree with that, but the wikipedia is usually a good good place to start understanding things. In this case, it is not.

Louise


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