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David Marx
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[*] posted on 12-9-2004 at 20:28
Sealing ampoules


Does anyone have any experience with sealing glass ampoules? I have a box of Wheaton glass pre-scored ampoules that I would like to be able to use. I have tried heating them with a standard propane torch from the hardware store and while they get soft, it takes forever and they never become soft enough to pull seal.

Any suggestions would be appreciated.




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JohnWW
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[*] posted on 12-9-2004 at 21:18


When I was doing university chemistry, one experiment in an inorganic laboratory class was the synthesis of AsCl3 (very poisonous, of course), and to do a few further experiments with it. (One such further experiment was forming its intensely blood-red complex with Fe(III), which may owe its intense color to charge-transfer in which the As is present as both (III) and (V) and the Fe is present as both (II) and (III). I note here that Fe(III) is used to remove As from drinking water as in Bangladesh.). The liquid AsCl3 made by the class (m.pt. -18ºC, b.pt. 130ºC) was distilled into special test tubes like you describe, and afterwards this was sealed into ampoules by heating the necks with a bunsen burner at maximum heat until it was sufficiently liquid to close by twisting.

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[*] posted on 12-9-2004 at 21:33


Can you get a MAPP gas torch? That's easy to find at hardware stores and should be considerably hotter than propane. You can also get small torch kits that use disposable oxygen cylinders with propane or MAPP, which should certainly be hot enough to do the job.



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Tacho
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[*] posted on 13-9-2004 at 03:47


David,

I have done quite a lot of elementary glasswork on 10mm diameter borosilicate (pyrex) glass tubes, with walls 1,5 mm thick, using a common blowtorch. I have also sealed some small ampoules some time ago using an alcohol lamp fire.

My point is: in theory, you should have no trouble softening those ampoules. Don't be offended but, are you sure you are not trying to do it in a very wrong way?
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[*] posted on 13-9-2004 at 07:44


Can I ask a really simple question: How do you avoid the sample heating up if you apply ~800 deg C to one end to seal it?
Are the tubes quite long, or is the sample bit kept in a cool envelope while heating the other end?




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[*] posted on 13-9-2004 at 08:41
Flame Temperatures


These are from John Strong's Procedures in Experimental Physics. Sorry the file is so large. 8 pages in jpegs. Normally I'd djvu them, but not set up just now.

Edit: I have posted a better quality and smaller version of this file in djvu below. Save bandwidth and use that one if possible.

[Edited on 13-9-2004 by HRH_Prince_Charles]

Attachment: proc.exp.physics.j-strong.jpg.zip (384kB)
This file has been downloaded 928 times





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Tacho
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[*] posted on 13-9-2004 at 08:48


Quote:
Originally posted by chemoleo
Can I ask a really simple question: How do you avoid the sample heating up if you apply ~800 deg C to one end to seal it?
Are the tubes quite long, or is the sample bit kept in a cool envelope while heating the other end?


Think how hard it would be to heat a sample in the bottom of a test tube pointing the bunsen's flame one inch above it.

HRH, interesting material. I love those old books.
Edit: Very interesting INDEED.

[Edited on 13-9-2004 by Tacho]
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[*] posted on 13-9-2004 at 09:43
Flame Temperatures


Glad you liked it. Takes ages to scan and format with Linux. I hate the command line.

Here's a better quality version of same scan in djvu. Smaller too. Similar to pdf but better.

Attachment: proc.exp.physics(j-strong)flames.djvu (196kB)
This file has been downloaded 676 times





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neutrino
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[*] posted on 13-9-2004 at 13:36


Usually, the tubes are thin-walled, allowing them to be heated and softened very quickly, which, along with the poor thermal conductivity of glass, keeps the temp of the sample down. If it takes a long time to heat witha propane tirch, you are doing something wrong. Capillary tubing (d = 1.8mm) melts in an alcohol burner in a matter of seconds, and I think this is around the diameter of the part of the ampuole that's heated (a thin glass tube).
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[*] posted on 13-9-2004 at 14:40


I have had some experience with homemade ampoules, I have used glass tubing from fluorescent light tubes fused at both ends.

Not that long ago, I prepared some small ampoules of crude ammonium sulfide (yep, stink bombs:D) by using thermometer outer tubes.

The thermometers were of the mercury type, bought solely for the Hg inside, and consisted of a wider glass tube of air, with a second, inner narrow tube with the bulb of Hg/measurement scale inside.

The Hg was taken out by cracking the end in a torch etc, and the outer glass tube ground down with fine sandpaper.

It is quite easy to close these after filling, by heating to dull red heat in a propane torch jet at just below the end, then applying pressure on both sides with pre-warmed pliers to crush the glass sides together.

The ends can be carefully twisted to stress the ampoules, and when filled with ammonium sulfide, they make quite effective stink-bombs:D




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[*] posted on 13-9-2004 at 16:20


sealing ampoules. I had difficulty with these too. You can use propane torches but the placement of the ampoule in the flame jet is important.

at first I would stick the neck right into the center of the flame and it never really worked right. it took forever, my fingers got burned and was messy as hell.

Later I found out that the center of the flame is unburned vapor spewing out of the torch and was actually cooling the damn thing. Try just touching the tip of the ampoule neck to the tip of the brightest jet of the torch. Don't spin it.

It will melt suddenly and suprisingly.

If you have larger size ampoules or a delicate substance to seal into them and need a smaller, sharper, hotter flame, try those benzomatic 29.99 oxy/acetalene brazing rigs.

H Trismegistus.




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[*] posted on 13-9-2004 at 19:01


Hermes: your tip worked quite well. I had previously been trying to melt it far into the flame, the inner blue flame if you will. When I held it right in the tip of the flame without rotation it sealed in ~7 secs. Thanks!



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[*] posted on 13-9-2004 at 20:32


someone mentioned using flourescent lights...this is dangerous. the lights contain mercury vapor which is much worse than liquid mercury. be careful.
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[*] posted on 14-8-2012 at 11:43


hi,
sorry for bumping an old topic, but my bunsen (propane) doesn't get hot enough. I do however have a bottle of pure O2.
can I saftely inject pure O2 into the air intake of my bunsen?
also:what type of tweezers are best? i use surgical tweezers but they don't seem to work well :D




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Dr.Bob
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[*] posted on 14-8-2012 at 13:03


Most propane burners are not safe for mixing oxygen with propane, unless designed that way. You can buy a propane/oxygen glass blowers torch, but a Bunsen burner will likely not work safely that way, as the gases mix too soon inside the burner. A real propane/oxygen glass blowers torch has the gases mix very close to the flame, so the flame cannot go back into the torch body. On a Bunser burner, the fire will go from the top to the middle of the burner if you add oxygen, which will not work well.

I was always taught to light the propane first and then slowly add oxygen until the flame got bluer and shorter, up to a certain point. Any more oxygen that than, and it did not work as well. But, you will only need a very simple one, not the fancier ones below, but I give a few examples. But there are also fancier glass blowing torches, below are a few, but check ebay, google, and others for more.

http://www.sundanceglass.com/national8mtr.html

http://www.hubglass.com/torches.html
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[*] posted on 14-8-2012 at 13:23


so its a nono i guess. how about putting the O2 into the bottom of the flame though a metal tube?
those things are expensive! i could look for something cheaper.
though I see you point of not introducing O2 into the air intake, consider this: everything above the air intake is already an O2/propane mix, so wouldn't the fire travel down the chimney anyway? as the mix there would still be flammable.

any advise on tweezers? or is my problem only due to the torch?




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[*] posted on 14-8-2012 at 13:55


You can buy an oxygen-propane (or "MAP-Pro" propene) torch at big-box hardware stores, sold for brazing/welding/cutting. They're about $60 dollars.

It comes with a cylinder of imitation MAPP gas, a cylinder of oxygen, the torch head, and the hoses with two regulators -- one for each cylinder.

I'd recommend using it outside the first time. It's pretty beastly, relative to the propane torches most of us are used to.
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[*] posted on 14-8-2012 at 13:58


You shouldn't seal ampoules by pinching them with tweezers. That introduces stressed points in the glass and it breaks more easily. There are few techniques for sealing, depending on the width of the neck. Check out readily available, free fmameworking manuals online and practice using glass tubes.



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Pyro
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[*] posted on 14-8-2012 at 16:55


oh, ok. do i need special tweezers to pull them though? or is any pair fine?
over here the only possibility is an oxy- acetylene torch, costs about 350$, maybe i should invest in one, might come in handy on my boat. so no bunsen?
are MAPP's worse than oxy-acetylene? ive worked with those, but dont own one :(

[Edited on 15-8-2012 by Pyro]




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[*] posted on 15-8-2012 at 08:54


Quote: Originally posted by Pyro  
[...] my bunsen (propane) doesn't get hot enough. I do however have a bottle of pure O2.
can I saftely inject pure O2 into the air intake of my bunsen?
also:what type of tweezers are best? i use surgical tweezers but they don't seem to work well :D
If you're sealing flint glass ampoules, you don't need to use pure O2; the right air-fueled torch works fine. One popular one is called the "Hot Head" (search for it; lots of vendors). It's about 40 USD and screws right to the top of disposable gas bottles. Works with propane and hotter fuel gases.

You don't need tweezers at all, actually. Use negative pressure, that is, atmospheric pressure pushing on molten glass to a (partial) vacuum within the ampoule. Draw a vacuum with any old device, even a rubber bulb with a one-way valve or a vacuum cleaner. You're not looking for high vacuum, but just some differential pressure. Molten glass will draw toward itself and join, making a solid bead. Practice first.

As to the comments on torches. There are two basic kinds of O2 torches: premix and surface mix. The big fat glass working torches you see in artistic glass are usually surface mix, but you don't need anything nearly that large for sealing ampoules. Premix torches are also called injection torches, because they use a gas injector in a mixing chamber within the torch body. There are welding torches that are injector-style, but your garden variety oxy-acetylene one isn't. If looking at industrial-style torches, there are injection torches specifically designed for scrap cutting that use propane as a fuel, which is more cost-effective than acetylene in this application. The National 3A & 3B hand-held torches are injection-type, and perfectly suitable for small bench work. Custom holders for them can convert them into a bench torch.
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[*] posted on 15-8-2012 at 09:56


I've found for small glass work, propane torches don't work well, but a butane torch of the same size does.
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[*] posted on 15-8-2012 at 10:38


Here's a good advice. Never extend necks of larger ampoules and then immediately start sealing them. The air inside is hot and as it cools down, its volume is being reduced. If you seal the neck and it's still soft, atmosphere will crush it and you'll get a wrinkled seal which is stressed and breaks quite easy. The thinner the walls, the worse the crushing is.
Make a neck, let it cool, fill the ampoule, extend the neck, let it cool, seal the neck.
If you're ampouling a liquid (particulary highly volatile ones, like dichloromethane) you can make a long, narrow neck at the beggining, so you can skip the extending.

Of course, depending on the contents and their volume, you might want to modify the process. For example, if it's something very volatile, you can hold the lower part in an ice bath, etc.

Avoid pinching the glass with tweezers. That's just introducing stress by force and by relatively cold metal (if you heat it, glass sticks to it like chewing gum).

Buy a load of tubes, download a flameworking manual and practice, practice, practice.

[Edited on 15-8-2012 by Endimion17]




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[*] posted on 15-8-2012 at 11:53


i've been practicing with my bunsen as it is on my ampules (got 288 of em anyway), i can seal about half of them, the others tend to break, i am looking for a better burner.
thanks for all the help, any more will be very appreciated




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[*] posted on 15-8-2012 at 23:03


You indeed need a hot burner. I use a propane torch with a blue roaring flame and I heat the top of the ampoule until it comes very soft and starts glowing orange. At that moment, while the top of the ampoule still is in the blue flame, I take a metal clamp and gently press the top of the ampoule with the clamp, such that it becomes flat. In that way, the top is closed at once. Then I keep the top in the flame for a little longer, such that it becomes nice and smooth. After this I allow the top to cool down (which takes several minutes).

My success rate is appr. 80% and the seal is reliable.




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[*] posted on 16-8-2012 at 11:44
Oxygen source


Search on "oxygen concentrator, refurbished" at Google shopping. The bottom end is around $200 US.

The usual figure of merit is 5 LPM at 90%+ purity, plenty for a small oxy-propane/whatever glassblowers torch.
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