Steve s
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Vacuum ampoules
I know there are a few threads about this already but i didn't want to just jump onto the recently deceased Magpies one as i thought it might be a
little disrespectful so i've put this here. Feel free to move it somewhere more appropriate.
I'm currently having a go at some vacuum ampoule making, with mixed (mostly laughable) results. My plan is once i can consistently make decent
ampoules i'm going to start ampouling some of my elements.
Below is a video/method description i made that i've posted to a glass blowing FB page in the hope someone might be able to give me a few pointers,
maybe someone could too.
You can't see it in the video but i'm vacing down to 30inches/750mm Hg to clear as much air/moisture from the tube as possible then dropping down to
5inches/100mm Hg before i start heating the tube. I'm getting mixed results (even less successful attempts in pt1 and 2). Biggest concern is the
thickness (and consequent fragility) of the little bit of molten glass that gets sucked/pulled into the tube, just seems way to thin for my liking.
Please excuse (but feel free to mock, i can take it) the rather Heath Robinson set up and prototype rotating device
Opps wrong link
Here; https://www.youtube.com/watch?v=W-co7q4yArY
[Edited on 6-5-2020 by Steve s]
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Heptylene
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Oh that's a really interesting topic, I've tried myself to make vacuum ampoules and they all ended up with an ugly seal. I've seen others make them
too but they sucked equally. The only good ones I've seen are on cathode ray tubes for TVs and on vacuum tubes (triodes and such), so clearly good
seals can be made!
There's a video on youtube of a guy making nixie tubes and the seals looks pretty good.
The thickness of the sealing tube seems critical, you want something very thick and narrow (say 3 mm I.D., 2 mm wall thickness) and you want to heat
it slowly from all sides. I think your rotating jig is promising steve.
Maybe you could first make a thick and narrow neck on the tube under atmospheric pressure and then seal it under vacuum?
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Steve s
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Yes i've had some advice from the glass blowing FB (torch talk) that basically confirms all you are saying.
I'm going to revisit the constriction under atmospheric pressure approach, i did try it before but under vacuum and heat it cracked and popped, by the
sounds of it i was either letting it cool down too much and too quickly and i was using too much vac.
Smaller ID tube would be easier but some of the samples i want to seal are quite big, a chap on torch talk has recommended quartz glass as it has a
much higher melting point so would 'suck in' slower. Also and this is news to me it doesn't react with Hg to form a black film on its surface the way
soda glass does, still waiting to find out if Boro has the same reaction.
I'll check out the video 
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Herr Haber
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I've just started thinking about ampouling things I produce either for display or to store a given amount of a chemical so it is ready for use so I'm
not gonna be much help.
Not a chance I'm mocking your set up. I think it's brilliant.
While watching the video I wondered if it would help to slightly push the tube half a second when it crumples to help you make your seal before you
separate the ampoule from the leftover molten glass. It sort of works for plastics.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Steve s
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Thanks. I have to say it hasn't been mocked anywhere near as much as i thought it might be 
General consensus from most people is that it's best to pull in a restriction under atmospheric pressure then apply the vacuum and close the
constriction. But i do see where you're coming from as the resulting 'blob' might form not only a good seal but also a nice base. However someone on
Torch Talk did say that when that happens the molten glass gets pulled in and sticks to the cooler glass which can cause fault lines. Happy to give
anything a go though so will try pushing it in and melting the glass above onto/into it.
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Refinery
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Just wild thoughts, but could adding a bit more intense heat, and pulling the ampoule carefully downwards while heating in order to make the glass
stretch and collapse to a seal and then keep heating to form a round head?
I was thinking of making my own ampoules, although without vacuum, but yet to test it out.
[Edited on 11-5-2020 by Refinery]
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Chemetix
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I can give you some tips from a scientific glassblowers point of view.
The technique to make and seal an ampoule can vary with what you put in them. Solids, Liquids, powders, heat sensitive material.....But a fine tip
torch is going to be your best bet at success.
But the general technique is get the vaccuum going and then very delicately approach the constriction on one side. As it begins to pull in slightly,
withdraw the flame and let it cool a bit. Now rotate and come in at a different point and do the same. The aim of this it to form a crimp like the
peak of a scout hat with dimples being evenly spaced and only just touching.
Now aim the flame above the dimples and let the glass collapse onto the top of the dimples. Again, gentle usage of flame will stop the whole thing
collapsing in on itself. Once there is enough glass melted in to effectively seal the tube you can get the flame slightly further up from the seal hot
enough to pull off the top and melted over to form a nice domed peak. There should be no sharp angles where glass touches glass. This will be where
the glass fails due to stresses.
Hope that helps. I can do a video if there is interest.
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Steve s
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Quote: Originally posted by Refinery  | Just wild thoughts, but could adding a bit more intense heat, and pulling the ampoule carefully downwards while heating in order to make the glass
stretch and collapse to a seal and then keep heating to form a round head?
I was thinking of making my own ampoules, although without vacuum, but yet to test it out.
[Edited on 11-5-2020 by Refinery] |
When i have done this the vacuum seems to pull molten glass into the ampoule forming a concave structure of wat appears to be very thin glass. The
vacuum bit does seem to make the whole process a lot more involved.
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Steve s
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| Quote: Originally posted by Chemetix | I can give you some tips from a scientific glassblowers point of view.
The technique to make and seal an ampoule can vary with what you put in them. Solids, Liquids, powders, heat sensitive material.....But a fine tip
torch is going to be your best bet at success.
But the general technique is get the vaccuum going and then very delicately approach the constriction on one side. As it begins to pull in slightly,
withdraw the flame and let it cool a bit. Now rotate and come in at a different point and do the same. The aim of this it to form a crimp like the
peak of a scout hat with dimples being evenly spaced and only just touching.
Thanks.
I will give this a go, wat you're describing seems to be the industry standard for sealing ampoules under vacuum. I recently watch a video of a chap
sealing Rb under vacuum very nice work. I for one would certainly be interested to see how you do it. Out of interest wat sort of vacuum would you
suggest ?
Now aim the flame above the dimples and let the glass collapse onto the top of the dimples. Again, gentle usage of flame will stop the whole thing
collapsing in on itself. Once there is enough glass melted in to effectively seal the tube you can get the flame slightly further up from the seal hot
enough to pull off the top and melted over to form a nice domed peak. There should be no sharp angles where glass touches glass. This will be where
the glass fails due to stresses.
Hope that helps. I can do a video if there is interest. |
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