[JonF]

Does a gas mix like C-75 which is 75% Argon and 25% CO2 separate in long-term storage? I have a large gas bottle that lasts a year or two and on days when I think I don't really know how to weld, I wonder if something has changed the gas mixture so I get straigt Argon? What do y'all say??

[Otto Nobedder]

(This reply is duplicated on the TIG forum.)

You would think so, but no, not really. The molecular motion (heat) that keeps it a gas keeps it pretty well diffused. CO2 is heavier than Ar, of course, so there is a variation in the ratio between the top and bottom of the cylinder, but as soon as you begin drawing gas, you begin mixing the contents of the bottle.

Consider the manufacture of these gasses. Air is cooled in stages to the liquid state of each gas to get them to condense in a fractional distillation column. This is a very energy-intensive process, yet is far more efficient than separating them by weight in a centrifuge.

I've been welding almost 30 years, and I still have off days. Some days a pipe weld looks like a "wedding band", some days more like an ugly divorce.

Steve

[JonF]

Thanks for the response, Steve. So it must be me just having an off day?

[Otto Nobedder]

If your bottle has been idle long enough for you to suspect separation, then, yes, it's possible.

We all have off days.

Steve

[kermdawg]

I read somewhere on these forums a good tip, it applied to mig gas, co2 and whatever the mix is (you can see how much i mig lol)

But disconnect the cylinder and spin it around slowly a couple times, like the guys do at the gas store when their walkin it out to your truck. Thatll mix up the gas again for ya. Dont wanna shake it or anything like that. Just gently walk it around the shop a little.

Mixed gas will seperate if its left idle long enough.

[av8r]

Otto is right. The diffusion of the gases caused by the molecular motion and the "desire" to become completely mixed (called entropy) assures that the gases remain mixed.

[Otto Nobedder]

Tell the Marine Corps to secure a building, and they will toss grenades and storm the building immediately.

Tell the Army to secure a building, they will surround the structure, lay seige, and negotiate a surrender.

Tell the Air Force to secure a building, they'll get a five-year lease and have air conditioning installed.



Steve

[jpence38]

Now that's funny right there, I don't care who you are.

[Otto Nobedder]

Some time in the next week or two, I'll post some pictures of the "cold box" I'm building for the Hemlock semiconductor plant in Clarksville, TN. I don't know how the hell they're going to ship it. Probably two 38-wheel crawlers, 7 MPH all the way. That'll give me a week off, since I'm supposed to stay here 'til it's done, and be there when it arrives.

Steve

[TheExpert]

In chemistry and chemical engineering, a separation process, or simply a separation, is any mass transfer process used to convert a mixture of substances into two or more distinct product mixtures, at least one of which is enriched in one or more of the mixture's constituents. In some cases, a separation may fully divide the mixture into its pure constituents.

[Ultralow787]

I don't know about the separation of the mixed gases once they are in the cylinder, but the explanations about molecular activity keeping the mixtures in suspension make sense to me! I did hear from some reliable experts at Lincoln Electric, that gas suppliers can and do miss-mix gases on occasion at the filling stations. The result is that a welding set-up or process that normally works well, all of a sudden goes in the toilet when a new bottle of gas is installed. I'm sure it does not happen often, but everything is possible. What do you all think?