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Creating a Home-made Vacuum Chamber

  1. Jul 9, 2014 #1
    Hello all,

    I was wondering a way to make a simple vacuum chamber with a relatively small volume (probably won't need to be bigger than 300mL at best) from some common materials. I have access to common glassware (beakers, although not sure if they can withstand the pressure), and ideally I would like another sealed opening in addition to the one that would provide the suction for the vacuum. Any ideas?

    Thank you.
     
  2. jcsd
  3. Jul 9, 2014 #2

    Simon Bridge

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    You need to specify how good-a vacuum you want.
    The way to think about this is that you are building a container with a very low pressure inside.
    The limiting factor will be the pump/method you use to reduce the pressure.
     
  4. Jul 9, 2014 #3
    I just need a good enough vacuum to avoid potential oxidation of a material with a pretty low surface area.
     
  5. Jul 9, 2014 #4

    Simon Bridge

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    For a material like an iron nail, just putting calcium carbonate in a (sealed) jar with the object is usually good enough for that.
     
  6. Jul 10, 2014 #5
    If all you want to do is prevent oxidation, why not just fill the vessel with N2? No oxygen, no oxidation.
     
  7. Jul 10, 2014 #6

    UltrafastPED

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    What is the material? If you know the material, you can look up the required vacuum.

    Or consider the other suggestions made here.

    For example, a clean silicon surface requires 10^-11 torr if you want it to stay clean for about a day.
    For hygroscopic materials, 10^-5 torr is usually good enough.

    PS: I wouldn't use a beaker; they are not designed properly. However, an old TV/CRT tube will withstand 10^-10 torr and more.
     
  8. Jul 10, 2014 #7

    PhysicoRaj

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    Creating vaccum might be just easier for the OP than filling N2. You can easily get a vaccum pump or calcium carbide as simon has suggested. Handling N2 may not be easier/economical for the OP.
     
  9. Jul 10, 2014 #8

    Simon Bridge

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    I think the query re needing a vacuum to prevent oxydation is a fair one.

    Note: Calcium Carbide is quite different from Calcium Carbonate.
    Both will absorb water - which is quite enough to stop, say, iron rusting - but the carbide will give off ascetylene as a result, and can self ignite so I suggested the carbonate. Less exciting I know but still...

    Without knowing the material I don't think we can say much more.
     
  10. Jul 10, 2014 #9

    sophiecentaur

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    How about a cylinder of Party Balloon Gas? That's mostly Helium and would be a pretty inert atmosphere for your Zinc etc.. That stuff is available everywhere these days.
     
  11. Jul 10, 2014 #10

    f95toli

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    Balloon gas can be quite contaminated (sometimes balloon gas is actually "dirty" gas that has been used for other purposes); I would certainly not assume that it is dry. It would probably be better to get a small cylinder with dry nitrogen (which is frequently used in labs for cleaning)

    Also, "not oxidize" is a very difficult concept, what kind of vacuum you need certainly depends on the material. most metals will inevitably end up having at least a few monolayers of oxide on the surface unless your vacuum is VERY good (ultra-high vacuum).
    That said, if your only goal is to avoid rust the requirements are of course much less severe.
     
  12. Jul 10, 2014 #11

    sophiecentaur

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    So we shouldn't play at making Donald Duck noises with it then? That's useful information for the next kid's party I go to - I can be Mr Miseryguts again. :grumpy:
     
  13. Jul 10, 2014 #12

    mfb

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    In a chemical sense, air is "dirty" as well - nitrogen, oxygen, argon, H2O, CO2 and various other gases mixed with dust, pollens and other stuff.
    I don't know what can be in that helium.

    You can get rid of oxygen by chemical reactions ("burning things"), if those reaction products are not an issue.
     
  14. Jul 10, 2014 #13

    AlephZero

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    I wouldn't use any "home made" construction for a vacuum chamber, especially if made from glass. It's not worth the risk of injury caused by implosion. Atmospheric pressure doesn't sound much if you think of it as "15 pounds per square inch". Converting that into "about 1 ton per square foot" might give it a more realistic "scare factor level".

    Trying to use something like a TV tube, your first problem is to get inside the tube without shattering it. The second problem is re-sealing it and restoring the vacuum!

    The difference in stresses in the chamber between a vacuum of 10^-5 torr and 10^-10 torr are negligible - not a factor of 10^5!
     
  15. Jul 10, 2014 #14

    sophiecentaur

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    It actually boils down to Energy, rather than pressure. The Volume of the container governs how much energy would be involved in any implosion. Your average round bottomed flask is quite strong enough to support a vacuum (the extra bit of a torr makes little difference*). A container with a flat bottom (beaker??) might not be so robust.
    It is a good idea to wrap transparent tape round any glass vessel that is likely to break dramatically.
    But if the aim is to prevent chemical 'corrosion', the better alternative would certainly be to use an inert gas at ambient pressure.

    *The problem with a high vacuum is not the 'danger'; it's just maintaining it and eliminating leaks.
     
  16. Jul 10, 2014 #15

    rcgldr

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    Try doing a web search for vacuum tube kits with pumps. These are educational kits, used to create vacuum tubes for audio / ham like applications. Generally two pumps are used in series to produce low enough pressure, and a kit would include a glass container meant to be used for such a purpose, so it should be safe if used properly. I recall seeing such a kit at a ham radio shop decades ago. I don't recall how the tube was sealed after being evacuated. I think it just rested on a rubber pad after evacuation, with a rubber cork that the wiring went through at the top. My guess is that the rubber cork included a port with a valve like mechanism for evacuation.
     
  17. Jul 11, 2014 #16

    f95toli

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    Many applications of helium involve pumps, and these pumps are -in general- not dry. Hence, if the gas is "recycled" it is very possible that it will contain quite a lot of hydrocarbons from pump oil; sometimes you can actually smell it (smells a bit like burned pop-corn) meaning the concentration can be quite high.
    But yes, air is of course dirty as well; but I think the idea here is to use some sort of purge gas and then you want that gas to at least be dry (free of water) and reasonably free from things like methane etc. Dry high-purity nitrogen is readily available and not very expensive,
    Another option would be argon which is also very common since it is used for TIG welding.
     
  18. Oct 30, 2015 #17
    I also need a relatively small chamber for a low grade vacuum of around 1 torr. The size may be up to one half liter. My thought is to machine some acrylic blocks with one screwing into another for some length. One piece acts as a piston which screws into the larger chamber. Then, with a valve on one end to eliminate air when the piston is completely screwed in, I can unscrew the piston to leave an evacuated space. Acrylic is so I can see inside. Does this hand operated pump sound feasible?
    Thanks.
     
  19. Oct 30, 2015 #18

    sophiecentaur

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    The force needed would be the pressure difference times the area of the piston. Double it, to be realistic and you can work out if you can provide that force with your bare hands. Levers are a good way of helping our feeble human muscles.
     
  20. Oct 30, 2015 #19
    Thanks. I think it will work then since I envisioned using perhaps a crowbar to turn the piston as well as the fact that screw threads themselves act like a leverage system. Yes, I think it might hold a decent vacuum. Thanks again.
     
  21. Oct 31, 2015 #20

    Simon Bridge

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    Historically, quite a poor vaccuum was able to keep hemispherical shells together against carthorses pulling.
    Best do the calculation...
     
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