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kilowatt
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Just to make you sleep better, I will put a stopper that vents into an alkaline scrubber on the collection bottle.
The mind cannot decide the truth; it can only find the truth.
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MagicJigPipe
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Also, that way you should be able to tell if any HF is not being condensed by measuring the pH (or BP if the concentration is high enough) of the
"scrubber".
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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carbonic
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Good deal. And I will think twice before harassing a fellow scientist. I wish you well in your endeavor. MJP has a good point about measuring the
pH of the scrubber. If you keep it lightly alkaline it might be easier to tell if only small quantity of HF is output. Or use carbonate, and the
fizzing would be easily detected.
One last thing - a long tube to the scrubber (or check valve) will prevent the possibility of suck-back into your condenser bottle.
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kilowatt
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I have a little check valve thingy, I was just going to use that to prevent suckback.
The mind cannot decide the truth; it can only find the truth.
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ScienceGeek
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What would be better than a slightly alkaline solution with some Phenolphthalein?
(Don't say pH- meter) 
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dann2
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I took the following from Industrial Electrochemical processes.
It is somewhat off topic here but I cannot fine an F making thread.
Dann2
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-jeffB
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Whoa. I don't think I'm quite ready for a fluorine cell in my garage, but that photo is... compelling. 
What is "the electrolyte" in this prep? I can't imagine it would be the usual fluorspar-in-HF, given that there's a burner under the can!
I wonder what counts as "high permeability carbon", too. I'm picturing drilling a hole into a charcoal briquette...
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DJF90
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I'm thinking that the carbon "sponge" that results from the reaction between conc. sulphuric acid and sucrose (ordinary sugar) could be applied here.
IIRC the carbon that i saw produced was very porous.
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kilowatt
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Off subject, but not a big deal I guess. Fluorine is prepared industrially (and I believe Moissan used basically the same method) with electrolysis
of anhydrous HF with a little KHF2 dissolved in there for conduction, in a nickel cell with iridium anode. This is carried out at like -50°C to
minimize corrosion. Many of the earlier chemists who attempted to isolate fluorine were killed or blinded.
Edit: Here is the new modification of the rig. It contains about 2/3 mole of premixed CaF2 and H2SO4 (both low grade). Right now I have the oil
bath running at about 180°C and I am getting distillate coming over slowly. The scrubber I am using contains saturated sodium bicarbonate at the top
of the vessel, with the tube coming in through that and not dipping down to the bottom. This it cannot suck back.
[Edited on 11-3-2008 by kilowatt]
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MagicJigPipe
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Are you getting bubbles or acid in your scrubber solution (is the pH going down?). If not I would raise the temp a little since the distillate is
coming over so slow.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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garage chemist
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BTW, you can also use lead as the retort construction material, e.g. bend a piece of lead sheet into a tube form and solder it shut.
However, the solder has to be tin-free.
Lead is only attacked superficially by HF and H2SO4 due the formation of sparingly soluble PbF2 and PbSO4.
It is not resistant against very hot concentrated H2SO4 however, so there must not be an excess of H2SO4 in your reaction mix.
Its suitability as a retort material is mentioned in several old chemistry texts that I've read.
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kilowatt
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Well I did finally get most of my yield (no way to measure exactly though) at 200°C, but a larger retort would be nice.
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garage chemist
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Your crude HF is also far from being anhydrous, but I think you already know that. Does it fume in air?
True anhydrous HF is prepared by heating dry KF*HF at 500°C in a retort made of copper. Brauer gives a procedure.
Copper and iron are resistant against HF of more than 60% concentration.
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kilowatt
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It does fume strongly in air (regardless of temperature), and yes I realize it is not quite anhydrous. I don't need it to be anhydrous for what I'm
doing, but I do need to redistill it yet to increase purity. Couldn't I dehydrate it with concentrated sulfuric if I wanted it anhydrous?
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garage chemist
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Yes, that should surely work.
Be careful with the heat of hydration of the H2SO4, it could cause the HF to boil.
Excellent work with the HF, BTW. It's always great to hear about amateur chemists who manage to safely conduct experiments often considered too
dangerous to do at home.
With anhydrous HF, you could make the KF*3HF electrolyte (mp. 66°C) for a fluorine cell operating at 80-100°C.
According to Brauer (which contains a very good section about selfmade fluorine cells), Nickel is a suitable anode material for a low- powered
fluorine cell, and iron, steel and copper can be used for the cell body, cathode and fluorine pipe.
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MagicJigPipe
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Wait, I thought F2 synthesis was frowned upon by the "home chemistry society". I got flamed for even mentioning that I wanted to try it some
day.
Now that I think about it, the "Home Chemistry Society" sounds like an organization that should exsist. That would be GREEEEAAT!!! In the words of
Tony the Tiger.
[Edited on 17-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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kilowatt
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| Quote: |
With anhydrous HF, you could make the KF*3HF electrolyte (mp. 66°C) for a fluorine cell operating at 80-100°C. |
I thought fluorine cells operated at around -50°C to minimize corrosion and contained only a small amount of KHF2 as a conductant, certainly not a
high molar ratio like that. Anyways I am not remotely set up to do such a thing soon, and have no immediate use for fluorine, but maybe someday.
About the flaming, recall I got flamed by one person in this thread just for setting up a small HF generator in my back yard, so it really depends who
you ask. There are many opinions regarding what is safe and what is not is for all "home chemists" but really the only limitation is what equipment
you have and whether or not you know what you're doing. At least both hydrogen fluoride and fluorine generation are "stable" reactions that do not
carry a risk of a explosion or thermal runaway.
The mind cannot decide the truth; it can only find the truth.
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garage chemist
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No, all of todays fluorine cells operate at about 100°C, the -50°C one was Moissans setup which used a platinum U-tube as the cell body, which is
slowly attacked by the fluorine even at this temperature.
The replacement of platinum by more suitable materials like Nickel, Monel and copper allowed the use of a KF*2-3HF melt instead of liquid HF with a
small amount of KF in it.
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