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Author: Subject: high temperature filter for liquid/phase separation
bdbstone
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[*] posted on 8-9-2011 at 04:59
high temperature filter for liquid/phase separation


Hello, does somebody know if filters could be used to separate different kinds of solids. Once blend is melted it could be put through "high temperature flter" which would separate liquid substance from solid substance. I was thinking it could be used to separate NaClO3 from NaCl, since NaCLO3 have a melting point of just ~250degress and NaCl way over 800 and many other mixes..

Filter paper would not work here because it's very fragile and paper have autoignition temperature of around 200 degress celsius. But I don't know about different kinds, like ceramic filter(with vacuum filtriration), and so on.. Does anybody have any experience with it?

[Edited on 8-9-2011 by bdbstone]

[Edited on 8-9-2011 by bdbstone]
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Bot0nist
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[*] posted on 8-9-2011 at 05:39


Careful with molten chlorates. They are very reactive oxidizers and can decompose explosively. Any combustible organics = whoosh! :o

Why not substitute the Na cation for K and take advantage of KClO<sub>3</sub>'s lower solubility in a recrystallization? This won't eliminate all NaCl/KCl, but will give you a relatively pure product.

[Edited on 8-9-2011 by Bot0nist]




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Dr.Bob
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[*] posted on 8-9-2011 at 09:09


Remember that chlorates decompose (even without organics) at a low temperature. My guess is that the chlorate would dissolve and then act as a flux to dissolve the chloride, thus making a molten mixture. That is common for melts like that. It is no different than the fact that almost any impurity lowers the MP of a material from its pure form. So I don't think that will work, and it is likely to cause decomposition of the mixture, perhaps in a spectacular manner.

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Neil
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[*] posted on 8-9-2011 at 13:30


Ceramic filters are sold for metal casting and what not, salts tend to flux most ceramics...

I'm with Dr.Bob - not a snow balls chance in hell that you can melt different salts and then filter them away from each other.

Try to find a phase diagram for a chloride/chlorate melt.
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fledarmus
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[*] posted on 8-9-2011 at 13:44


There is a process based on that principle used mostly for purifying semiconductor materials: Zone Melting You don't actually use a filter, you just heat the material in a very narrow band and move the band slowly down the material. The impurities stay in the melt as purer crystals form behind the heater.
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bdbstone
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[*] posted on 8-9-2011 at 19:59


Yeah, I get what Dr.Bob said that the NaCl and NaClO3 will probably melt together. I was not thinking only about NaCl and NaClO3 but any other substance, which would not react together. But I am getting why this kind of separation is not used.
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bdbstone
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[*] posted on 8-9-2011 at 20:30


x

[Edited on 9-9-2011 by bdbstone]
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Dr.Bob
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[*] posted on 9-9-2011 at 09:58


The key is to use solubility to purify the salts, which is well documented and I believe there are a number of threads on here about how to do that. Most people either go to perchlorate and then make the potassium salt. The sodium salts are not useful for very much due to their hydroscopic nature and chlorates are not very safe for use in many pyro uses. But it is neat to be able to make them and learn the chemistry behind their uses.
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Neil
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[*] posted on 9-9-2011 at 10:10


That kind of separation IS used, only it's used where it is feasible

It is just not used in the context of your question because that is infeasible.

google "liquid metal ceramic filter"
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