Sciencemadness Discussion Board - Ampouling gases

Ampouling gases

Upsilon - 12-10-2013 at 16:29

I want to ampoule some samples of gases for an element collection, and I am currently working on chlorine and hydrogen. First, I'd like the chlorine gas to be visible in the ampoule (the green-yellow color). Does the gas need to be pressurized to be visible or not? Also, how should I go about ampouling flammable gases like hydrogen? Obviously melting the glass shut on an open flame is a horrible idea. Should I heat the pliers to the melting temp of the glass and attempt it that way?

kristofvagyok - 12-10-2013 at 17:09

Forget ampouling hydrogen in time, before you hurt yourself seriously.

Hydrogen form explosive mixtures with air in concentrations from 1 to 99%, so it is not a really good idea what you wrote there. Also the "heat the pliers to the melting temp of the glass and attempt it that way?" is really fool idea, you will never seal an ampule on that way, especially what contains gases.

I have made ampouled liquid chlorine and a few really toxic gas (with bp 10 °C) in the past. The general method is to condense the gas in its liquid form with something cool, e.g.: dry ice-acetone, and seal the ampule under a gas what protects it from flame, argon works pretty well.

The best idea for making an ampule what contains hydrogen is: seal some fresh air in the ampule, write hydrogen on the label and try to imagine that you have it inside.

Upsilon - 12-10-2013 at 17:27

I suppose it depends on what temperature the glass melts at. If the temperature required to melt glass is close to the autoignition temperature of hydrogen (about 500C) then it truly is virtually impossible; if not it may be practical to use induction heating, offering very high temperatures with no flame.

elementcollector1 - 12-10-2013 at 17:49

There must be some way to do it. Perhaps what you could do is first glue the ampoule shut (assuming it's some sort of tube) and then seal the ampoule a little ways up from the glue? That way, the hydrogen would never contact the flame (glass's heat transmission is very poor), and you can seal the ampoule without it exploding.
I'm not sure that's foolproof, but it's a hell of a lot better than imagination.

watson.fawkes - 12-10-2013 at 17:53

In order to do this right, you need a vacuum manifold system similar to the ones that neon sign makers use. (1) Pull vacuum. (2) Introduce gas. (3) Seal. Done properly, the sealed gas and outside atmosphere never touch, eliminating any trouble with explosion. Also a good idea to fill at less that atmospheric pressure; it makes sealing easier because there's a pressure gradient from outside to inside. A hand-held crossfire torch is also a good idea.

For extra points, seal electrodes in as well and make a spectrum lamp to make the hydrogen visible.

Upsilon - 12-10-2013 at 17:55

Also, would it really be necessary to liquify the chlorine, even if I basically have a compressed cylinder of it?

elementcollector1 - 12-10-2013 at 18:04

Quote: Originally posted by Upsilon

Also, would it really be necessary to liquify the chlorine, even if I basically have a compressed cylinder of it?

Well, it does make for a better and more easily visible sample when you let it boil off to purge the ampoule...
I would not recommend a pressurized ampoule.

[Edited on 10-13-2013 by elementcollector1]

Upsilon - 12-10-2013 at 18:16

Quote: Originally posted by elementcollector1

Well, it does make for a better and more easily visible sample when you let it boil off to purge the ampoule...
I would not recommend a pressurized ampoule.

I wasn't necessarily going to pressurize the ampoule. Is chlorine gas visible to a decent extent at STP, or does condensing it really make that much of a difference? If you let it vaporize inside the ampoule, isn't that basically pressurizing it? I could condense it but I just want to know if it's worth the effort.

elementcollector1 - 12-10-2013 at 21:20

Quote: Originally posted by Upsilon

Let it vaporize while the ampoule is open. You'll lose some chlorine, but in the end you'll have an ampoule full of pure chlorine gas, which will be a very noticeable yellow-green color.

woelen - 13-10-2013 at 05:28

I ampouled chlorine gas without first making it liquid. I prepared 250 ml of pure Cl2 from TCCA and dilute HCl. This, I sucked into a syringe of 60 ml from just above the liquid. In the syringe I had a mix of CaCl2 and some P4O10. Shaking around the syringe for a few minutes makes the gas really dry.

Next, I transferred the gas to another 60 ml syringe, using a small PVC tube. Using a pasteur pipette I first pushed 5 ml of gas out of the syringe, and then I pushed the remaining 55 ml of the gas into into a 20 ml ampoule, while slowly moving the tip of the pipitte upwards. In this way, the ampoule has quite pure Cl2-gas, which is perfectly dry. I think it is at least 90% pure. I did this on a cold dry day. Next, I immediately sealed the ampoule. I put a picture of the ampoule on the wiki-page:

http://en.wikipedia.org/wiki/File:Chlorine_ampoule.jpg

As you can see, the chlorine is clearly visible.

I have done this quite a few years ago, and now the ampoule still is as good as on the day it was made.

[Edited on 13-10-13 by woelen]

Endimion17 - 13-10-2013 at 08:34

One of the most important details which woelen included is that you have to slowly remove the pipette (or a cannula) out.
First you flush out your container with the gas and then you keep adding the gas while removing the tube.

Of course, it's important to prepare the container first. The opening should be narrowed down, so that the sealing operation is fast and the gas can't come out easily.

Hydrogen can be ampouled easily by skilled people. The problem is that the skill exceeds the average skill of a lab worker.

woelen - 13-10-2013 at 10:49

In the same way I also ampouled NO2. This also works quite well. It works especially well, when the gas is much more dense than air. Cl2 is a good example, vapor of Br2 also works perfectly well and even NO2 still works quite well.

I see no point in ampouling H2 or any other colorless gas. You could as well have plain air in the ampoule. But if you really want to ampoule H2, then use the same technique, but keep the ampoule with the gas upside down as long as it is not yet sealed (H2 is less dense than air).

Upsilon - 16-10-2013 at 12:05

What about fluorine? I realize that it will eat through basically any kind of glass, but would a protective layer of fluorinated material form after enough exposure? Would it be practical to periodically expose an ampoule to fluorine, and after a while seal pure fluorine in there?

Sublimatus - 16-10-2013 at 12:12

Scroll down to "Real visible fluorine." here:

http://periodictable.com/Elements/009/index.html

Quote:

Real visible fluorine. I used to think that there was no known transparent container that could contain fluorine without getting eaten by it. Then I got this email: Now, respectfully, I must take up a little bit of a qualm with your claim in fluorine...You mention that "There is no transparent container that will hold it." Granted that is true if you're talking a "forever" time scale, but I strongly believe on a "realistic" scale (a few decades) it can be done...albeit with some difficulty and great time placed into it. The way best to do it is first to get yourself a pure, single-crystal quartz tube...Now that means one with an extremely high amount of surface Si-O-Si bonds and VERY few Si-OH endcaps. The best way to do this is to take the inside portion of the quartz tube and silylate it. Then anneal it at the highest possible temperature that your annealing oven can stand...This will drive off essentially ALLLLLLL the Si-OH end caps. Because remember, the real killer in fluorine gas for Si-O's is not the fluorine, but the OH's and their ability to start a chain reaction with small amounts of HF in the fluorine gas. So, the first thing you need to do is get rid of the Si-OH's which that should take care of as best as possible. Now, being absolutely certain that your quartz tube is flamed and ultra-dry, there's another step...There was a fluorocarbon grease that DuPont made many years ago that was ultra-high-purity completely fluorinated, medium-high mol.weight fluorocarbon grease (like a lower-molecular weight Teflon)...Take that stuff and literally melt it into the tube...It's clear and translucent and won't affect the optics after the next step...So then take a high temperature vacuum oven and turn the tube upside down and melt the grease back out...What this does is leave a verrrrry thin, essentially invisible layer of fluorocarbon grease layer on the inside of the tube. This layer acts as a secondary "buffer" layer to the quartz. So IF there are any Si-OH's left on your quartz, they are difficult to get at by the fluorine gas because the fluorine gas has a difficult time penetrating the grease...This step will add years to your fluorine gas display. Then the more difficult thing to do is to make sure the quartz tube has a high-purity Teflon screw-top stopper to it so that it can seal ultra-tightly. (again, pure fluorine gas without any water/HF in it may "trade" fluorines with Teflon, but you still have Teflon; same goes for the grease, the grease may "trade" fluorines as we've seen in some isotopic studies, but it remains a carbon-fluorine bond). Then you should get a sacrificial vacuum line (kind of expensive, but it'll just be fogged up after you're done though it's best to throw it away because the integrity will be damaged) and run your fluorine gas THROUGH A LIQUID NITROGEN FILLED TRAP into your evacuated quartz tube. This is the most important AND DANGEROUS step. This step is the most important because ALLLLL commercial fluorine sources have either water or HF in them. The water and HF are what will start the "chain reaction" of eating away at things. And all it takes are a few atoms of these to get it started...But the N2(l) will definitely remove ALL of them...But the fluorine gas will still have a small amount of volatility to it so as to fill your quartz tube with approximately a quarter-atmosphere of pure F2. Now if you do anything with fluorine and leave ANY HF or H2O in it, fuggetaboutit...You'll get your stuff eaten away promptly. You won't get a full atmosphere of fluorine in your quartz sample tube like I said, but it will be enough to see under the right light and circumstances. And 50 years from now those one or two atoms of HF and H2O that are left in there will eventually have done enough damage to destroy your sample tube, but I don't plan on worrying about it 50 years from now. Sorry if that bored you...But I do say it with utmost respect...I spent 10 years fiddling and trying to perfect the best way to get a fluorine sample, and that's the best way I could get it...So, methinks there are ways to store fluorine safely in a visible specimen tube; it just takes a great amount of patience, diligence, safety-thoughts and equipment.

elementcollector1 - 23-4-2014 at 09:43

So, now that I have a confirmed vacuum of over 25 in. Hg, could I ampoule hydrogen with no fear of explosion or other catastrophic failures? Of course, I still have to figure out a method for connecting an ampoule to the vacuum setup in such a manner that it can be sealed easily. Unfortunately, my blowtorch is very... unsubtle with its flame; the required working surface of the glass to seal is usually about a quarter inch or so, and anything around that for about a half inch is also very hot. I might use a sacrificial rubber stopper, but something more permanent would be good. Again, I have these ampoules.