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  1. #1
    Join Date
    Sep 2007
    Valley City, ND

    Default Back purging with Argon

    Hi gang:
    I was approached with a TIG welding project of welding a bottom drain plug on a New Aluminum Gas tank on a Hot Rod project. It has a bottom plug already welded on it already, but he wants another. It is a round cylinder type tank with a vented gas cap on top.
    I would like to purge the tank with 100% argon before I tig the bottom 3/8" drain plug coupler.
    My question is this: Is argon heavier than air? Do I remove the top or bottom port while purging?
    Anyone who has any similar situations??? I plan on using my 200Dx with 2% Thoriated and 4043 filler. Any input?

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  2. #2
    Join Date
    Feb 2004
    Boulder, Colorado


    Here is a link to the Periodic Table. It provide alot of information regarding chemical and physical properties of elements.

    In regards to mass, the table is laid out so that the lightest elements are on top and they get progressively heavier as you go down the list.

  3. #3
    Join Date
    Aug 2007
    Central Fla.


    Remove the top plug. Argon is heavier than air.

  4. #4
    Join Date
    Feb 2010

    Default Yep, it's heavier than air

    Like GTA-SPEC said,

    You'll see, if using the periodic table, that Argon is heavier than air,

    Air is more or less composed of 78% Nitrogen, 20% oxygen, 0-4% water vapour, 0.9% Argon, and tiny fractions of other elements....(by volume)

    To see how you can tell, check out that periodic table and look up the atomic "weight" which, in practical terms represents the mass of one mole of that element...(a "mole" = a term similar to a "dozen" but it represents ((6,02210 to the power of 23)) atoms of the particular element you are measuring)..

    for example 1 mole of hydrogen "weighs" 1.008 grams.
    So... one mole of Argon, weighs 39.9 grams

    while one mol of atmospheric (2 atoms together) Nitrogen
    = N2 =28.0 grams of N2/mol x 78% = 21.84 grams
    + 1 mole of oxygen
    x 2 because it's 02 in air =32.0 grams 02/mol x 20% = 6.4 grams

    without getting into molar volumes of gases..., you see that for the same number of atoms of Argon and for the same number of molecules of atmospheric Nitrogen, Argon has almost twice the mass of Nitrogen.

    So, in theory, air should rise to the top as Argon sinks oil always finds its way on top of water.

    I would think you should remove the top plug to let air rise to the top and out.

    pardon the lengthy explanation!

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