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Author: Subject: How do I seal a glass ampoule in inert atmosphere?
rasiel
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[*] posted on 8-2-2016 at 18:50
How do I seal a glass ampoule in inert atmosphere?


Hey everyone,

What is the most practical way of sealing off a test tube inside a glove box filled with argon? Can't really use a torch in there ;-)

Thanks for any tips!

Ras
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[*] posted on 8-2-2016 at 18:58


Welcome to the forum!

"Storage of air sensitive compounds. The most straightforward method to store air and moisture
sensitive compounds is to keep them inside a glovebox. However, one has to take into account that the
compounds inside a glovebox are protected from air and moisture, but not from other compounds that
are being used inside. A fail-safe storage method is to isolate a compound in an ampoule and to seal this
ampoule under a protective atmosphere or under vacuum using a blowtorch.
When transferring a solid into an ampoule, it often happens, that part of the material will end up stuck
to the glass wall. This will frustrate sealing of the ampoule, as the hot flame of the blowtorch will burn
the compound and thus prevent proper sealing. Therefore, it is recommended to clean the glass wall.
When sealing compounds in an ampoule under inert atmosphere, it is necessary to do so using an
outflow of the protective gas (i.e. take the stopper off). In the case that an ampoule will be sealed while
the ampoule is closed off, expansion of the protective gas as a result of heating the gas will cause the
ampoule to burst open."

Read more here




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[*] posted on 8-2-2016 at 19:30


Low tech method -- to be used when no glovebox is available. Method will be improved if you have access to a glovebox.

Put sample in the ampoule.
If necessary, use a flame to narrow the opening until nearly closed. (Needed if you are using a test tube or something wide for an ampoule.)
Flood the ampoule with argon. (Even easier with a glovebox.)
Stopper the ampoule. (Remove from glovebox.)
Seal with a flame as normal.




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rasiel
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[*] posted on 8-2-2016 at 21:53


Thanks for the responses. Having here at home a DIY glovebox I'd love to try the first option but despite the PDF I'm not sure on the mechanics of how this is actually done. Obviously the torch needs a supply of oxygen from outside - or possibly rig it up so that the tip is firing through a port hole while the rest of the torch is outside. But both cases seem really awkward.

In the meantime I could try the low tech method. It should work for the stuff that doesn't oxidize too readily.

Thanks again!

Ras
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[*] posted on 8-2-2016 at 22:19


I have not had too much experience with this and I really don't have a way of testing my result. But it hasn't been too difficult. I have a cylinder of argon and can feed the gas into the bottom of the ampoule using a pasteur pipette. I can then remove the pipette quickly and put a stopper in. I suppose I could do it in a zip-lock plastic bag to lessen the amount of air that is able to get in before stoppering.

Once the ampoule has a stopper in it then I can flame-seal the ampoule at leisure.




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[*] posted on 9-2-2016 at 02:58


I've just been doing a bit of this myself - and am pretty pleased with the technique I came up with ...much as j_sum1 suggests ..I seal one end of a glass tube that is quite a bit longer than I need, pop it in a glovebox (if necessary), place the sample in, squirt a bit of argon in, then stuff the end with cotton wool. Finally I remove the tube from the glovebox, then, moving quickly, with a torch heat the middle between the cotton wool and sample and seal it, discarding the cotton wool end.

I got my argon from a bottle shop - its for keeping wine, and came in a can with a thin rubber tube that I can place deep in the unsealed ampule so as to be sure to displace all the existing atmosphere. If I stuff the wool around the rubber tube while its still in the ampule I can actually skip the whole glovebox altogether.


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[*] posted on 9-2-2016 at 03:23


I use the "low tech method" and also freezing the compound inside the ampoule, in order to reduce flame issues with some solvents.
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[*] posted on 9-2-2016 at 13:19


Ok, I think I understand the method pretty well now.... and it would work too except I don't have ampoules but rather test tubes. Anyone have any tips of closing off a 12mm neck by the fire of a propane torch?

I have argon and can flood the tubes straight in as you guys describe.

Thanks all y'all's :-)

Ras
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[*] posted on 9-2-2016 at 13:25


To give an idea of what I'm trying to accomplish, here is an "ampoule" of the sort I'm trying to make. It's just glass tubing sealed off on both sides with the sample inside, in this case mercury.

hgampoule.jpg - 147kB
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[*] posted on 9-2-2016 at 14:16


How did you seal it and how do you plan to recover the Hg without having glass bits in it? Most ampules are twisted into a point at the top end, which can easily be snapped off. The design you have shown would be better for an something that is not intended to be removed, like for an element collection.



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[*] posted on 9-2-2016 at 14:24


I use test tubes for ampoules quite often.
You can pre-narrow them if needed.
They usually taper to a point but if you are careful you can get a blunt end and you can make it rounder by pressing on something.
Making an ampoule that is nearly full is harder because the heating is closer to your sample. I suspect that the one shown was done with solid mercury.

Oh, and pulling is better than twisting for a nice-looking seal.




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[*] posted on 9-2-2016 at 15:08


The mercury ampoule is not my creation, it's what I'm trying to replicate and reverse engineer. And, yes, it is actually for an element collection so a one way trip :-)

I did just try sealing with a torch and it's just a mess. I can get the edges soft but any pressure to bend it in results in little cracks along the edges or the softened glass to stick to the tool I'm using to push. That's with regular glass, borosilicate might be much more resistant to cracking but that much harder to melt. In the end, the bigger question is whether there's a better method for sealing wide neck glass than filling with argon. I now have a good handle on that last part at least.

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[*] posted on 9-2-2016 at 15:58


I use a butane torch similar to this one.
BP90055036-black.jpg-SPOTWF-product.jpg - 28kB
It is up to the job, but only just. Take your time to fully heat the test tube -- rotating so that it heats evenly in the area where you want it. Do not attempt to put any pressure on the glass until it begins to sag under its own weight. Then pull gently to narrow. Don't try to bend or twist.

For mercury, I would create a narrow neck and let the glass cool. Then I would put the mercury in. I probably would not be so ambitious to put too much in but leave a decent space in the ampoule. Then (if possible) chill the Hg to freezing. Next put Ar in and stopper it. Finally sealing off the narrow neck in a flame can be done quite quickly. For a nice finish I would continue to heat after it has sealed and then round off the end.

There is no substitute for practice. But by the time you have ruined a dozen or so test tubes you will have a better feel for how the glass behaves in your flame.

[edit] smallifying image

[Edited on 10-2-2016 by j_sum1]

[Edited on 10-2-2016 by j_sum1]




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[*] posted on 9-2-2016 at 16:36


Thank you! Very informative. Off to the garage after I'm done with this post!

In the case of mercury no need for argon since it's air stable. I want to do this for other elements that aren't. Like this calcium below; to transfer it from a huge ampoule into little ones each holding what looks and feels like metal popcorn.



calcium.jpg - 145kB
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[*] posted on 9-2-2016 at 21:03


One of my suppliers sells equipment that use IR. It's made to bend twist and form your own glassware without a flame.

Wanna bend a glass rod, a pipette, a test tube? That would be my choice.
I was looking into it because this equipment car reach temperatures far beyond a normal heating plate / mantle AND can be used as such for distillations that need really hot temperatures.
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[*] posted on 10-2-2016 at 00:59


Well, that sounds wonderful. What is IR? Whar is this tech, whar?
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[*] posted on 10-2-2016 at 06:06


Infra Red.
This supplier supplies anything from glassware to autoclaves big enough for hospitals etc.
I guess I saw this in one of the older catalogues along other Equipment to sterilize by heat.

But basically, it was a heating resistance with a "grate" or I dont know how to describe what was on top except is was purposedly made so you could put your pipette or you glass rod Inside and then wait for it to be hot enough to do all the bending or clamping needed.
I mostly remembered it because this item was more or less "cheap" when compared to all the other stuff they sold.
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[*] posted on 10-2-2016 at 07:17


This is an example of a IR heat gun.

This sounds similar to what Haber is talking about; however, I am unsure that even with localized heating, it would be capable of reaching the temperatures needed to seal a borosil ampule.

I highly doubt it would work, but I just thought I'd share.

imgres-2.jpg - 5kB




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[*] posted on 10-2-2016 at 11:21


A heat gun is usefull in many other occasions but that not what I was thinking about :)

I found a website with the description of the electric burner I had in mind in English:
http://www.dutscher-scientific.co.uk/frontoffice/product?pro...

I hope this helps !
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