How does a Helium / Argon MIX stay mixed?

# Thread: How does a Helium / Argon MIX stay mixed?

1. WeldingWeb Journeyman
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## How does a Helium / Argon MIX stay mixed?

Argon is one of the heaviest gasses. Helium is one of the lightest. They wouldn't mix out of the bottle (think of the lengths we go to when backing up a weld with argon). So how are they a mixture in a bottle? Surely the take-off valve at the top sucks the helium first? Or is there something i don't know about the bottles it comes in?

2. ## Re: How does a Helium / Argon MIX stay mixed?

How does the air we breath stay mixed?

ponder...

3. WeldingWeb Journeyman
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## Re: How does a Helium / Argon MIX stay mixed?

Okay, I looked into it a bit. (Following a lead in a comment by Fred S in another thread, about the entropy of mixing.)
The reason that it _seems_ to be that they would separate is because of a (my) poor understanding of what mixing means. It's not about combining, aggitating, or stirring things that want to be apart. More like a physics thing, with ideal gas laws etc. In fact that impetus to be separate because of one being lighter actually doesn't factor into it.
The absolute simplest explanation is that once they're mixed, it would take energy to separate them, and there's nowhere that energy is coming from.
The next level explanation involves imagining opening a valve between bottles of argon and helium. Soon as you do, there's 'new' room for the argon in the helium bottle, and 'new' room for helium in the argon bottle, so they spread out to occupy that space. And it would take 'convincing' to get all the atoms of one gas to squeeze back into only one bottle, or indeed one section of a closed system (important to remember it's a closed system and the rules are different). Gravity just doesn't have that kind of energy. It can slow things from mixing when out of a bottle. But once mixed inside a bottle there's no going back.

4. ## Re: How does a Helium / Argon MIX stay mixed?

You nailed it. It's not like water and oil that naturally repel each other but as you discovered they are "mixed" to begin with and must be separated "by force".

I was going to say because the guy filling the cylinder tells them to but . . .

5. ## Re: How does a Helium / Argon MIX stay mixed?

Originally Posted by Reseda luteola
Argon is one of the heaviest gasses. Helium is one of the lightest. They wouldn't mix out of the bottle (think of the lengths we go to when backing up a weld with argon). So how are they a mixture in a bottle? Surely the take-off valve at the top sucks the helium first? Or is there something i don't know about the bottles it comes in?
just shake the cylinder before use, all the ones on the welding trucks get mixed as they drive and hit bumps..........................yeah that sounds good..

6. ## Re: How does a Helium / Argon MIX stay mixed?

Originally Posted by Hobbytime
just shake the cylinder before use, all the ones on the welding trucks get mixed as they drive and hit bumps..........................yeah that sounds good..
Either that or just roll them around on the shop floor to remix the gases!

7. ## Re: How does a Helium / Argon MIX stay mixed?

There is a LOT of empty space between molecules. They bop around amongst themselves and never notice the other guys. Compress them to about the density of people living in Hong Kong and you might see some action.

8. WeldingWeb Apprentice
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## Re: How does a Helium / Argon MIX stay mixed?

Originally Posted by Reseda luteola
The absolute simplest explanation is that once they're mixed, it would take energy to separate them, and there's nowhere that energy is coming from.
Unfortunately, that is completely wrong. There is a lot of energy in the system, with the energy of each atom a constant times the absolute temperature (room temperature is approximately 300 Kelvin).

This thermal energy results in the argon atoms moving at nearly 1000 mph, and the helium atoms moving ~2.5x faster. Although gravity acts on both types of atoms, the force of gravity is weak compared with this thermal energy. Under the effect of gravity alone the argon would sink to the bottom of the bottle because it is heavier than helium and the gravitational force is proportional to mass. However, each argon (and helium) atom is bombarded by 1000 mph argon atoms (and 2500 mph helium atoms) that hit it from all sides so frequently that it only moves a few micro-inches after a hit before it's hit again. Since the forces from those constant, random impacts is so much larger than that of gravity the atoms remain mixed.

9. ## Re: How does a Helium / Argon MIX stay mixed?

Originally Posted by MCTig
...atom is bombarded by 1000 mph argon atoms (and 2500 mph helium atoms) that hit it from all sides so frequently that it only moves a few micro-inches after a hit before it's hit again. Since the forces from those constant, random impacts is so much larger than that of gravity the atoms remain mixed.
That statement makes me think that the gas would never cool down after being compressed.

10. WeldingWeb Craftsman
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## Re: How does a Helium / Argon MIX stay mixed?

Originally Posted by Brainfarth
That statement makes me think that the gas would never cool down after being compressed.
The gases are moving that fast because they're at room temperature. When they're compressed and heated they're moving even faster!!! When they hit the sides of the relatively cold container, they give off more heat than they receive (bounce back with less speed). Eventually they'll slow down to the speeds at room temperature.

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## Re: How does a Helium / Argon MIX stay mixed?

It seems I managed to pay attention in grade eight when "Brownian motion" was explained. As a result my little mind never worries about gases mixing.

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