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Author: Subject: Fluorine in quartz?
sbreheny
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[*] posted on 23-10-2014 at 21:51


I will try some UV absorption experiments when I receive the ampoules. I may also see if I can use RF or induction to make a plasma inside the ampoule.

Of course, I don't have Astatine or Darmstadtium, but I think I'm doing pretty well.

Right now, I have, in pure form, samples of everything up to Bismuth except for F, Br, Rb, Cs, Tc, and Thallium. I have the full set of Lanthanides except Promethium. I have sealed samples of liquid Cl. I also have a small amount of pure Thorium metal and quite a few grams of (depleted) Uranium metal. I have some Radium watch hands as Ra samples.

I was even able to get a very tiny amount of Tc99 as Sodium Pertechnetate. It's a few milliliters of solution from a medical Tc99m generator which long since decayed to simple Tc99, before I obtained it. Based on radiation measurements, it seems to contain about 50 ng, which is several typical doses.

I plan on obtaining samples of the remaining ones up to Bi. It sure would be nice to have elemental F2 - otherwise I'll have to cop out and have a compound for F.
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[*] posted on 23-10-2014 at 22:26


Sounds like a good collection.
You know that Br is pretty easy to synthesise?
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sbreheny
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[*] posted on 23-10-2014 at 22:34


Quote: Originally posted by j_sum1  
Sounds like a good collection.
You know that Br is pretty easy to synthesise?


Thanks! Yes - I have made Br before by oxidizing NaBr, but I didn't remove the water to purify it - I just rendered it safe using thiosulfate. All of the other samples I purchased. I am leaving Br as the one that I will make and contribute to the collection :)
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[*] posted on 24-10-2014 at 00:51


I do a simple displacement passing Cl2 through bromide salt. It can even be done with dry crystals but the yield is lower since the Br2 sticks to the solid.
Still you get high purity bromine with minimal equipment requirements, low expense and little fuss.
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[*] posted on 24-10-2014 at 00:53


Not sure what you mean by rendering safe with thiosulfate. That will reduce back to Br- which is not what you want.
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[*] posted on 24-10-2014 at 04:55


J_sum1: I think he means rendered safe to dispose of - pouring straight Br2 down the drain seems like an ill advised decision!



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[*] posted on 24-10-2014 at 05:44


Quote: Originally posted by Arcuritech  
J_sum1: I think he means rendered safe to dispose of - pouring straight Br2 down the drain seems like an ill advised decision!


Yes, exactly. I didn't have the time/means then to purify the bromine water and I wanted to dispose of it safely.
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[*] posted on 24-10-2014 at 06:10


Shameless plug: Try the electrolytic method! Here's my video on it: https://www.youtube.com/watch?v=NKjyM2AkZSY

One of the most fun experiments I've done (except for the smell). I wanted to avoid distillation to cut down on fumes, plus this was a novel method that nobody else at the time had a video of. Also, you generally want to avoid chlorine because it can form interhalogens that are very difficult to remove and lower the purity of your product.
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Dan Vizine
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[*] posted on 24-10-2014 at 06:34


Quote: Originally posted by j_sum1  
I do a simple displacement passing Cl2 through bromide salt. It can even be done with dry crystals but the yield is lower since the Br2 sticks to the solid.
Still you get high purity bromine with minimal equipment requirements, low expense and little fuss.


Don't you run the risk of interhalogens? Perhaps a better solution is using NaBr + H2SO4 + KMnO4.
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[*] posted on 24-10-2014 at 06:48


Quote: Originally posted by Arcuritech  
Quote: Originally posted by Dan Vizine  


...It won't work because you have no way to make gas tight seals between the salt and the metal tube that won't be attacked by the halogen.[/rquote]

What about an o-ring made of teflon or another fluorinated polymer?

Even the idea of creating a direct bond between the Ni and the CaF2 isn't so inconceivable because the nickel withstands attack by F2 by the formation of a NiF2 passivation coating on contact. That layer could be affixed to the the CaF2 using a lower melting fluoride salt as a "solder".

*edited to remove typo*

[Edited on 2014-10-24 by Arcuritech]


...It won't work because you have no way to make gas tight seals between the salt and the metal tube that won't be attacked by the halogen.


What about an o-ring made of teflon or another fluorinated polymer?

Even the idea of creating a direct bond between the Ni and the CaF2 isn't so inconceivable because the nickel withstands attack by F2 by the formation of a NiF2 passivation coating on contact. That layer could be affixed to the the CaF2 using a lower melting fluoride salt as a "solder".

*edited to remove typo*

**********************************************************

The lower melting fluoride salt may work as a gas tight seal. I just worry that the thermal expansion differences between a CaF2 plate and nickel would cause leakage.

The other issue is tougher. It was suggested to add F2 to the nickel tube via a connection that needs to be subsequently closed. A valve may work. There's no other way to seal it gas tight without disrupting the passivation layer, leading to failure of the metal. You can't melt it shut or hammer it shut.

Teflon and other fluorinated elastomers or plastics all have a fatal weakness. They contain C-C bonds, which fluorine will readily attack. As far as I know, CF4 is the only organic molecule regularly credited as being fluorine-proof.

[Edited on 24-10-2014 by Dan Vizine]
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[*] posted on 24-10-2014 at 07:21


What about this polymer: [OCF2]n?

The only bonds are C-F and C-O sigma bonds; of those only the C-O bond could conciveably react and the exotherm from that exchange is 127 kJ(mol-1), much less than the 358 kJ(mol-1) C-O bond energy.

And on the note of teflon: I know it will burn in fluorine if given an ignition source, however I don't think that it will react at STP. (Similar to how paper, wood, or any other cellulose based material will readily burn in oxygen - but only if heated.)

(edit) About the thermal expansion problems: I had considered this, if it was no concern you could just "weld" the NiF2 and CaF2 directly; the low-melting "solder" salt was my suggested solution o the thermal expansion issue. (/edit)

[Edited on 2014-10-24 by Arcuritech]




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[*] posted on 24-10-2014 at 08:19


You could try getting the above polymer by fluorinating paraformaldehyde. However, it could decompose to carbonyl fluoride.



As below, so above.
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[*] posted on 24-10-2014 at 08:50


Then what about this one: [OCF2CF2]n? It does have one C-C bond per monomer, but it is completely surrounded by the C-O and C-F bonds and should be geometrically shielded by them.

Additionally, [OCF2CF2]n should be softer and less stiff than [OCF2]n ((edit)which would have a high stiffness(/edit)) making it all the better as an o-ring material.

[Edited on 2014-10-24 by Arcuritech]




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[*] posted on 24-10-2014 at 09:02


Quote: Originally posted by Dan Vizine  
Quote: Originally posted by DrMario  
I can completely see the point of 1 Kg of cocaine for the druggie. I've never tried it, but I hear cocaine is lots of fun, when consumed.

Fluorine, on the other hand, is probably not much fun when consumed :D

No comments on my method? It should be able to store 100% fluorine gas, indefinitely, making said "element collector" very happy. And yet, no signs of happiness anywhere.


I do have a comment. It won't work because you have no way to make gas tight seals between the salt and the metal tube that won't be attacked by the halogen.


Holy acid-resistant-stainless-steel FORK! The ONLY comment on the method is a negative one! Luckily, a few others have at least tried to contribute to the solution. And here's another attempt at a solution of the lack of a gasket: make the gasket out of lead or copper. Or better yet, make the whole container from pure gold - very malleable and very inert to fluorine at room temperature.



[Edited on 24-10-2014 by DrMario]
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[*] posted on 24-10-2014 at 12:14


Quote: Originally posted by Arcuritech  
Then what about this one: [OCF2CF2]n? It does have one C-C bond per monomer, but it is completely surrounded by the C-O and C-F bonds and should be geometrically shielded by them.

[Edited on 2014-10-24 by Arcuritech]


The bond enthalpy for C-C is - 367 kJ/mol, for C-F - 440 kJ/mol and for F-F - 159 kJ/mol. So replacing 1 C-C with 2 C-F, even taking into account the (small) bond enthalpy of F-F, is thermodynamically favourable. Of course that doesn't mean the reaction would proceed spontaneously at RT and the shielding effect you mention may play its part. But materials that contain C-C bonds are not ideal starting points as fluorine inert materials.




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[*] posted on 24-10-2014 at 12:52


Good point blogfast25.

While CF4 is the only thermodynamically stable C-F compound. There are kinetically "stable" compounds at rt. I just looked it up and PTFE is, in fact, rated as good (as opposed to excellent) in terms of resistance to fluorine.

For the type of seal you propose, however, Teflon would be poor as it is subject to cold flow. You need resilience in a gasket seal like this. An elastomer, Kalrez, may work. But I didn't check.

[Edited on 24-10-2014 by Dan Vizine]
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[*] posted on 24-10-2014 at 14:01


Quote: Originally posted by Dan Vizine  
For the type of seal you propose, however, Teflon would be poor as it is subject to cold flow. You need resilience in a gasket seal like this. An elastomer, Kalrez, may work. But I didn't check.

[Edited on 24-10-2014 by Dan Vizine]


In that case the C-O-C containing compounds I suggested earlier may prove useful! That structure is what renders polyoxymethylene so much stronger than polyethylene after all.




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[*] posted on 24-10-2014 at 14:15


But the thing that matters in a gas tight seal is more about resilience and less about strength near atmospheric pressure. The Kalrez is springy, not real strong. It is the most chemically resistant elastomer that I know of commercially. One tiny O-ring about a quarter inch in diameter was $20, 20 years ago. I don't know if price has gone up or down since then.
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[*] posted on 24-10-2014 at 20:43


Thinking about it more cold flow would't be a problem if the fluorine was held at the same pressure as the outside air ~103,000 Pa. There would be no internal pressure compelling the elastomer to deform.



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[*] posted on 24-10-2014 at 21:00


It isn't the internal pressure. A Teflon gasket that starts out in compression to make a gas tight seal will flow to relieve the axial compression needed to seal it into the end of the tube.
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[*] posted on 25-10-2014 at 04:49


Quote: Originally posted by Dan Vizine  
The Kalrez is springy, not real strong. It is the most chemically resistant elastomer that I know of commercially. One tiny O-ring about a quarter inch in diameter was $20, 20 years ago. I don't know if price has gone up or down since then.


It's a rather lazy elastomer and not all that springy either. But it's crosslinked so it doesn't really cold flow. And it's not strong either but for static seals that hardly matters.

Pricy? I bet that size is now about $50.

And yes, I don't think there is a more chemically resistant elastomer than FFKM.




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[*] posted on 27-10-2014 at 11:53


Quote: Originally posted by DrMario  
Quote: Originally posted by Dan Vizine  
Quote: Originally posted by DrMario  
I can completely see the point of 1 Kg of cocaine for the druggie. I've never tried it, but I hear cocaine is lots of fun, when consumed.

Fluorine, on the other hand, is probably not much fun when consumed :D

No comments on my method? It should be able to store 100% fluorine gas, indefinitely, making said "element collector" very happy. And yet, no signs of happiness anywhere.


I do have a comment. It won't work because you have no way to make gas tight seals between the salt and the metal tube that won't be attacked by the halogen.


Holy acid-resistant-stainless-steel FORK! The ONLY comment on the method is a negative one! Luckily, a few others have at least tried to contribute to the solution. And here's another attempt at a solution of the lack of a gasket: make the gasket out of lead or copper. Or better yet, make the whole container from pure gold - very malleable and very inert to fluorine at room temperature.



[Edited on 24-10-2014 by DrMario]


But the most compelling reason this idea won't work, and why all commercial F2 samples are sealed ampoules, is because of diffusion.

All O-ring seals leak. You simply cannot make a gas-tight O-ring and you never will be able to, until the mating surfaces of the O-ring and what it mates to are smooth on an order comparable to the diameter of an F2 molecule, which will still be never.

To a gas molecule, the spaces between the O-ring and the metal will look like a convoluted tunnel system. Trust me, I know what I'm talking about here, this is my business.

This is also why lithium in a bottle with threaded seals, even under oil, will inevitably darken. You have a driving force due to concentration differences inside and outside and a difficult, but eminently doable, pathway to fix this (from the point of view of a gas molecule).

[Edited on 27-10-2014 by Dan Vizine]
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