Sciencemadness Discussion Board - Apparatus for generating HF

Apparatus for generating HF

Upsilon - 15-9-2015 at 15:17

I ordered some CaF₂ because it was easily the cheapest fluoride salt I could find. However, it is insoluble in water and I need to find a way to make other fluoride salts out of it. The only way I can think of is to treat it with sulfuric acid, generating HF gas which I can then bubble into a solution of a carbonate salt. However I do not want to do this with my glassware, since HF will attack it. I am thinking of using discarded plastic water bottles and rubber/vinyl hose. Will these be ok for this process? And which is more ideal for the hose - rubber or vinyl?

crazyboy - 15-9-2015 at 15:29

This is a really bad idea, please do not do this. HF is very toxic, this reaction takes place at elevated temperatures that will melt the plastic. Even professional chemists avoid gaseous HF whenever possible.

Bert - 15-9-2015 at 15:31

I would not do this thing until and unless you research the history of famous 18th-19th century chemists injured and KILLED while attempting to work with Flourine compounds, working to isolate elemental Flourine.

Google "Flourine martyrs".

Quote:

Humphry Davy of England: poisoned, recovered. George and Thomas Knox of Ireland: both poisoned, one bedridden 3 years, recovered. P. Louyet of Belgium: poisoned, died. Jerome Nickels of Nancy, France: poisoned, died. George Gore of England: fluorine / hydrogen explosion, narrowly escaped injury. Henri Moissan of France: poisoned several times, success, but shortened life.

After doing that research, you will find out which common, ductile, easily worked metal may become coated with a layer of fluoride and be useful for the endeavor.

Please have a friend knowledgable of chemistry advised of your work, asked to check on you occasionally and directed to post your lab notes here in the case of your untimely death.

Not being facetious, we will want to know. Might save some other amateur's life-

[Edited on 15-9-2015 by Bert]

Cou - 15-9-2015 at 15:31

wtf do not mess with hydrogen fluoride unless you want death

Hawkguy - 15-9-2015 at 15:32

Actually this takes place at like room temperature. You'll need Teflon or PTFE or something, for the apparatus and also for a container. Actually, the receiving flask has to be Teflon I think.

Upsilon - 15-9-2015 at 15:37

Looks like this isn't going to be an option then. Is there anything else I can do with this calcium fluoride to convert it to other fluoride salts, like NaF?

j_sum1 - 15-9-2015 at 15:47

I have a question and a comment.

What do you actually need the fluoride salt for anyway?
If it was me, I would simply buy what I needed in this case. Everything that I know about HF and fluoride salts in general indicates that it is not something to be trifled with.

Upsilon - 15-9-2015 at 15:56

Quote: Originally posted by j_sum1

I have a question and a comment.

What do you actually need the fluoride salt for anyway?
If it was me, I would simply buy what I needed in this case. Everything that I know about HF and fluoride salts in general indicates that it is not something to be trifled with.

I don't necessarily have an actual need for them, per se, but it would be cool to have them. Kind of like element collecting. And I could possibly find a use for a water-soluble fluoride salt in the future.

Texium - 15-9-2015 at 20:51

Sodium fluoride is quite cheap from Seattle Pottery Supply. Much better to buy some from there rather than dealing with hydrofluoric acid, nevermind gaseous HF. Especially when you are not well equipped or very experienced and only want it because it would be "cool to have."

violet sin - 15-9-2015 at 20:57

that is pretty freaking affordable

http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?S...

Upsilon - 15-9-2015 at 21:08

Quote: Originally posted by violet sin

that is pretty freaking affordable

http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?S...

Dangit, I really need to start looking closer at these small pottery stores.

woelen - 16-9-2015 at 03:53

If you want soluble fluoride salts, then NaF also is not the best choice. It is soluble in water, but only quite sparingly. A better choice would be KF, KHF2 or NH4HF2. The latter two are available from eBay for cheap.

But keep in mind, fluoride salts also are quite dangerous and they attack glass as well, albeit less energetically than HF. If you get a solution of ANY fluoride on your skin, IMMEDIATELY wash it away, even if it is just "plain" sodium fluoride or ammonium bifluoride. Playing with fluorides is not like playing with the other halides, they are much much more dangerous.

MrHomeScientist - 16-9-2015 at 06:06

I have some ammonium bifluoride (bought from eBay) and I can say that this is by far the most dangerous chemical I own. I used it in my synthesis of NdF3, and the whole time my nerves were on edge. I donned all my safety gear, plus some extra precautions, and moved very slowly and deliberately. Fluoride is an insidious poison - very small amounts will kill you, and burns may not be painful until a day after a spill (so you may not realize it until it's too late). I bought calcium gluconate gel (also from eBay) and I keep this nearby to my bifluoride in case of emergencies. If you buy a soluble fluoride salt, also buy this gel. It's expensive, but your life is worth $50. If a spill occurs, wash it off immediately, apply the gel generously, and go to the hospital. We can't stress enough the dangers of this chemical.

Taking that into account, I'd avoid working with soluble fluorides until you have a real need for them.

battoussai114 - 16-9-2015 at 06:22

Anything that contains fluorine (and isn't teflon) is a big nope for me. Way too dangerous for my home lab and, in fact, even here at the university I study there aren't many researchers willing to work with HF or Fluorine.

Quote: Originally posted by MrHomeScientist

I have some ammonium bifluoride (bought from eBay) and I can say that this is by far the most dangerous chemical I own. I used it in my synthesis of NdF3, and the whole time my nerves were on edge. I donned all my safety gear, plus some extra precautions, and moved very slowly and deliberately. Fluoride is an insidious poison - very small amounts will kill you, and burns may not be painful until a day after a spill (so you may not realize it until it's too late). I bought calcium gluconate gel (also from eBay) and I keep this nearby to my bifluoride in case of emergencies. If you buy a soluble fluoride salt, also buy this gel. It's expensive, but your life is worth $50. If a spill occurs, wash it off immediately, apply the gel generously, and go to the hospital. We can't stress enough the dangers of this chemical.

Taking that into account, I'd avoid working with soluble fluorides until you have a real need for them.

Isn't it necessary to inject the gluconate bellow the place were the fluoride got you? Or is it HF that require it?

MrHomeScientist - 16-9-2015 at 09:41

The stuff I have is a tube of gel, applied topically. It's called Calgonate: http://www.calgonate.com/calgonate_gel.php
That page also has handy application instructions.

ave369 - 16-9-2015 at 10:18

I have a small jar of sodium fluoride sitting on the shelf in my reagent cabinet. I didn't buy it specifically, I've bought a chemistry set with it included. It sits there and does nothing, because I stay away from experimenting with this thing unless it's absolutely necessary.

That chemistry set described experiments with fluorides and HF for schoolchildren. One is making a mixture of NaF and oxalic acid and using it to etch glass. The other is a modified version of the "fake blood" trick: after the "blood" (iron thiocyanate complex) shows up, apply a cotton ball wetted in a solution of NaF to your arm to make the blood vanish.

Fluoride.
For schoolchildren.
On the skin, Carl!

... on the other hand, maybe we Russians are just hardier and more resistant to all kinds of shit...

[Edited on 16-9-2015 by ave369]

Upsilon - 16-9-2015 at 14:08

Alright all, you've successfully talked me out of this (for the time being, anyway). I suppose my calcium fluoride is just going to sit around for a while. No big deal, I bought 2 pounds for a measly $3.

Little_Ghost_again - 16-9-2015 at 14:18

Quote: Originally posted by Upsilon

Alright all, you've successfully talked me out of this (for the time being, anyway). I suppose my calcium fluoride is just going to sit around for a while. No big deal, I bought 2 pounds for a measly $3.

First the good news, well done for actually listening as many dont but we rarely get any more posts from them.

Now the bad news, because you listened you are unlikely to be winning the Darwin prize this month

.

Playing with that stuff is a bit like trying to find out what 1Kg of Arsenic taste like.

Maybe the Calcium Fluoride is cool enough for now

careysub - 16-9-2015 at 18:53

This reminds me of the "sand gas" (silicon tetrafluoride) thread(s):

http://www.sciencemadness.org/talk/viewthread.php?tid=8
http://www.sciencemadness.org/talk/viewthread.php?tid=22494

"Thrilling Stunts with a Glass Eating Chemical!" Popular Science proclaimed in January 1938.

mayko - 16-9-2015 at 19:22

This account of an HF burn helped spark my morbid fascination with fluorine (the chlorine trifluoride entry in Merck also contributed)

Quote:

The side of the bottle carried the warning CAUTION: DO NOT USE WITHOUT GLOVES. William didn’t read that bit, however, and he removed the cap from the bottle, spilled some liquid onto a rag, and began rubbing it into his stained coat. But as the stain began to fade, his right hand, the hand he was using to apply the liquid, began to hurt. After 20 minutes the pain was so intense that he had to stop. Within 40 minutes he could no longer move his fingers. Frightened and in terrible pain, he managed to drive himself to our emergency room. Fortunately, he brought the rust remover with him. While William writhed in agony, I took a close look at his right hand. Except for some mild swelling of the fingertips, it looked just like his left hand. But if I even gently pressed on his fingernails, he grimaced and begged for a painkiller.

MrHomeScientist - 17-9-2015 at 06:28

Something you can do with calcium fluoride is use it as a flux in thermite reactions, to promote metal/slag separation and increase your yield! Here's my page on various titanium thermites I tried using CaF2: http://thehomescientist.blogspot.com/2012/09/titanium-thermi...

My procedure was from blogfast's experiments (I think he actually invented this process), which I link to at the top of my page.

Upsilon - 18-9-2015 at 10:57

So I have another dilemma that may involve HF - trying to make titanium dioxide useful (basically I need to dissolve it). I've been doing some research and it's apparently extremely difficult to do. So far I have found several possibilities, but I need help choosing the most effective method:

1) Concentrated hydrofluoric acid. This one is pretty much a "no"

2) Concentrated nitric acid with a small amount of HF. This one is a possibility; I could have everything I need in a single vessel that I can just leave by itself and have the reaction go. By that I mean putting the titanium dioxide, nitric acid, calcium fluoride, and sulfuric acid all together with a heat source. The HF will be generated and immediately reacted with no dangerous intermediate steps. Of course I would stay back from the vessel.

3) Hot concentrated sulfuric acid. I read that this reaction occurs very slowly but it does occur. Not completely sure if it is valid or not.

4) Dissolving in molten sodium bisulfate. This looks like the most appealing to me, since sodium bisulfate melts at quite a low temperature, but I'm not sure of the extent to which it will actually dissolve.

I am also open to any ideas others may have.

[Edited on 18-9-2015 by Upsilon]

battoussai114 - 18-9-2015 at 11:48

Oxalic Acid under UV should dissolve it. Worth noting that I only read the abstract.

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Upsilon - 18-9-2015 at 12:09

Quote: Originally posted by battoussai114

Oxalic Acid under UV should dissolve it. Worth noting that I only read the abstract.

Looks promising, though I do not currently have a powerful source of UV light. That's assuming that sunlight or a common blacklight aren't enough to make it work.

careysub - 18-9-2015 at 12:14

One might contemplate using CaF2 in one-pot syntheses where HF is produced and consumed in situ, with suitable precautions to dowse residual HF in the flask, and traps to prevent its escape as vapor.

Of course many of the products you might prepare this way are typically volatile fluorides (SiF4, BF3) that may hydrolyze releasing HF again. SiF4 does in part, at any rate.

Volatile fluorides are just bad news (not even Teflon is safe, if pyrolyzed).

blogfast25 - 18-9-2015 at 12:45

Quote: Originally posted by Upsilon

4) Dissolving in molten sodium bisulfate. This looks like the most appealing to me, since sodium bisulfate melts at quite a low temperature, but I'm not sure of the extent to which it will actually dissolve.

Fusion of TiO2 with excess NaHSO4 works but can take a while.

Fusion of TiO2 with excess KOH gives potassium titanate. Hydrolysis of the titanate with water gives insoluble 'Ti(OH)4' but when freshly precipitated this 'titanic acid' dissolves easily in 37 % HCl or 50 % H2SO4.

[Edited on 18-9-2015 by blogfast25]

Upsilon - 18-9-2015 at 13:23

Quote: Originally posted by blogfast25

Quote: Originally posted by Upsilon

That would require significant temperatures, no? And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing.

blogfast25 - 18-9-2015 at 13:48

Quote: Originally posted by Upsilon

That would require significant temperatures, no? And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing.

Melting points only. Of course you need steel (better even nickel) to fuse with KOH.

ave369 - 18-9-2015 at 14:16

Quote: Originally posted by Upsilon

And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing.

They do, but, apparently, their effect on porcelain is negligible (I've melted KOH in porcelain crucibles without damage to them). My only case of ruining a porcelain crucible was when I was scraping fused pyrosulfate from it too vigorously.

[Edited on 18-9-2015 by ave369]

Upsilon - 18-9-2015 at 16:25

Quote: Originally posted by ave369

Quote: Originally posted by Upsilon

And don't molten hydroxides dissolve glass? In that case I would need to find a suitable vessel for such a thing.

Sounds good then. I'd like to note that I mixed some titanium dioxide and highly concentrated KOH solution for the fun of it, and it has been mildly fizzing for hours now. Not really sure what it means but I'll let it keep going.

blogfast25 - 18-9-2015 at 17:34

Quote: Originally posted by Upsilon

I tried that years ago with 50 % NaOH and it didn't put a dent in the TiO2. Let me know what you find.

[Edited on 19-9-2015 by blogfast25]

Upsilon - 18-9-2015 at 17:44

Forgot to mention that I squirted some weak hydrogen peroxide in there as well. It only seems to fizz when I stir it so it's probably just the peroxide decomposing.

Upsilon - 22-9-2015 at 08:41

Ok, so my little beaker of titanium dioxide and potassium hydroxide has been sitting for several days now. I still saw solid titanium dioxide at the bottom so I figured I should just pull the plug and free up a beaker. Upon adding concentrated HCl to the mixture to neutralize the KOH, however, it bubbled extremely violently. This is not typical of a regular strong base-strong acid reaction. What's happening here?

ave369 - 22-9-2015 at 10:44

Maybe the heating up caused by neutralization kicked hydrogen chloride from the solution. Highly concentrated HCl releases the gas even on slight heating.

Upsilon - 24-9-2015 at 18:32

Quote: Originally posted by ave369

Maybe the heating up caused by neutralization kicked hydrogen chloride from the solution. Highly concentrated HCl releases the gas even on slight heating.

Possibly. I ended up dumping it out. I think I'm going to try fusion with sodium bisulfate first; I think it's a good idea to try something easier before I dive into using molten KOH. What's the reaction that goes on with molten bisulfate?

woelen - 24-9-2015 at 22:47

Quote: Originally posted by Upsilon

[...]Upon adding concentrated HCl to the mixture to neutralize the KOH, however, it bubbled extremely violently. This is not typical of a regular strong base-strong acid reaction. What's happening here?

This certainly is not due to HCl bubbling out of solution. Even if it heats up you won't get enough free HCl (remember, most of it is neutralized by the KOH) to bubble out of solution. Even 30% HCl requires near boiling temperatures for loss of HCl and even then, it contains a lot of water vapor as well.

What actually happened is that the KOH-solution absorbed CO2 from the air. If it is allowed to stand in a beaker for several days, even if this beaker is loosely covered, then it can pick up considerable amounts of CO2. Hydroxide in aqueous solution is very eager to pick up CO2:

2OH(-) + CO2 --> CO3(2-) + H2O

So, your solution of KOH turns into a solution of K2CO3.

If you add acid to such a solution, then the carbonate is converted to carbonic acid, which in turn decomposes to water and CO2:

CO3(2-) + 2H(+) --> H2CO3 --> H2O + CO2

Upsilon - 25-9-2015 at 08:31

Quote: Originally posted by woelen

Quote: Originally posted by Upsilon

That's it, then. It was definitely sitting uncovered for several days. Thanks for the explanation.

MeshPL - 26-9-2015 at 23:04

In my school I saw a video of glass etching. What they did, is they poured H2SO4 on NaF and put a glass plate on that container so that HF fumes (

) can etch it. So they let HF fumes into the air. And it wasn't inside glovebox. Maybe not even in fumehood. And it was video by our chemistry book publisher. Without a single warning of how gaseous HF dangerous is.

DFliyerz - 27-9-2015 at 11:36

I love living right near Seattle, I was able to go there in person and buy a whole bunch of chemicals that would have been a pain to get elsewhere.

chloric1 - 24-12-2015 at 09:49

Quote: Originally posted by DFliyerz

I love living right near Seattle, I was able to go there in person and buy a whole bunch of chemicals that would have been a pain to get elsewhere.

Considering the low cost of their chemicals, it still advantageous for me even though I am just under 2000 miles from Seattle pottery supply. The low prices more than compensate for transcontinental shipping. Customer service is above par as well.

DFliyerz - 24-12-2015 at 21:49

Quote: Originally posted by chloric1

When I went there they said that they get a lot of chemistry hobbyists buying stuff from them, and that some of their sales staff actually used to work in pyrotechnics.