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peach
Bon Vivant
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Have you looked into using degassing tablets for the silver?
Buget Casting Supplies
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garage chemist
chemical wizard
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Thanks for the info, madscienctist. That's just what I wanted to know.
For distilling straight HF from CaF2 + H2SO4 you'd need a lead or silver retort, but if you use oleum, you can do it in glass. Isn't that fascinating?
The FSO3H could be used as a source of free HF by hydrolysis.
Conversion of CaF2 into a highly reactive HF carrier in an all-glass setup!
In order to avoid etching of the glass flask, one would have to make sure that there is enough free SO3 in the oleum to react with all the HF. So one
would have to add an excess of SO3 with the oleum to the CaF2, and collect excess SO3 as the forerun before the FSO3H product.
One thing is worrying me, and that is the compound pyrosulfuryl fluoride S2O5F2. According to Brauer, this substance is formed from CaF2 and pure SO3
at 200°C, and is not hydrolyzed by 92% H2SO4.
It is colorless liquid boiling at 51°C, fumes only very slightly in air, and is extremely toxic in a similar way as phosgene.
Potential formation of this compound should be avoided as far as possible.
Though the desired product FSO3H is probably not much less toxic than this substance, its formation would mean an uncontrollable loss of fluoride and
SO3. It would be impossible to separate SO3 and S2O5F2 by distillation.
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Fleaker
International Hazard
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Peach,
I'm well familiar with degassing tablets, degassing alloys (think lithium phosphide), and the like.
Watson.fawkes,
Actually, the dissolved gas is oxygen. Silver has a propensity to absorb it. It's called spitting. The purer the silver, the more likely it is to
happen. When I cast a silver bar I play a slightly rich flame over the surface to slow the cooling (this precludes concentric contraction related
rings from occurring) and to ensure oxygen keeps away from the silver as it cools. If I didn't do that, the silver would have a jagged, spikey
surface. Many metals dissolve gases. Actually, I should say all metals dissolve gases (including argon) but it's the degree that the resulting
porosity can be tolerated that governs the conditions by which the metal is melted.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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plante1999
International Hazard
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des someone have thinked of a standart glass setup with 10-12 coat of silver mirror in?
I never asked for this.
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blogfast25
International Hazard
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Have we collectively forgotten the (in)famous anhydrous HF thread by kilowatt?
http://www.sciencemadness.org/talk/viewthread.php?tid=9842
… which somewhat ominously went ‘dead’ at about 17-02-08? 
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peach
Bon Vivant
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I like the PTFE still.
I am concerned by the squeezy bottle being used for dropping the sulphuric. Which will seem amusing, as I have posted photos of myself trying to use
them to generate gases. I am not concerned by the plastic, but by the way in which it's connected together; and by an addition funnel being used in
the first place. Mine featured an equalising arm and some attempt at controlling the flow. And the worst that'd come from mine going wrong (which
happened) was a mess, as opposed to HF. There would be essentially zero control over the flow with that single, tapless, tube into the bottle. It's
only going to make things harder and more likely to go wrong if a big squirt of it goes in whilst the still is hot.
I dread to think of the possibilities if it was squeezed in by hand whilst the thing was in an oil bath. Wooooosh! Cough cough!
| Quote: | | For one thing, this isn't an uncontrolled reaction |
Where's the control on an unequalised, tapless dropping funnel?
| Quote: | | do you think I am just dumping a bunch of sulfuric acid and fluorspar together in a bucket and cooking it in my back yard? |
That'd be safer, dumping it all in at the start.
There are also some odd things going on with the temperatures and such. E.g. acid is being added whilst it's hot, rather than cold, and the
temperature it's being run at is quite a lot below the point where it would need to be to produce much in a short time.
I think it's doable. Well, I know it is looking at that lead pipe method and hearing about people making it. But that dropping of acid whilst hot
should have been ruled out from the start. Never mind doing it sans equalising arm or tap.
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Formatik
National Hazard
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Registered: 25-3-2008
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There is some information on HF handling materials and preparation, and some info on super acids (fluorosulfonic acid) here that may be of some interest, including a declassified document on the corrosive action of some super acid mixtures.
Note that the one declassified has some of the same data from the article below. Magic acid (HSO3F with SbF5) also does not attack common glass at any
significant rate even at higher temperatures. Some magic acid that is. It will dissolve candles, but not glass.
Attachment: magicacidmetalcorrosion.pdf (51kB)
This file has been downloaded 1204 times
[Edited on 28-2-2011 by Formatik]
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Formatik
National Hazard
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Some great information here on fluorosulfuric acid concerning preparation and properties from Gmelin. In there is also some information on
disulfuryl fluoride, and also from Inorganic Synthesis. Disulfuryl fluoride is made from heating CaF2 and an excess of SO3 at 100 to 300 C as stated
in Gmelin about a JACS article. With toxicity like phosgene, this is serious stuff now.
Some properties on fluorosulfuric acid from Gmelin, I'm sure some of you were itching to know: at normal temperatures it is a thin, colorless liquid
that fumes in air. It has a weakly pungent odor. On dry skin, it only attacks a little; it feels like a fat on contact and then does not have the
strongly vesicant properties of HF. Rubber, wood, cork, sealing wax and similar materials are easily, to some extent immediately decomposed.
[Edited on 1-3-2011 by Formatik]
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Formatik
National Hazard
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New link for the files above.
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