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Phase diagram of oxygen

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LAN_403

magnet18

Sat Jul 23 2011, 05:45AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Hey, does anyone know where I can find a phase diagram for oxygen with some level of detail to it? Google is letting me down.

OR, if anyone happens to just know this kind of stuff, what pressure would I have to get oxygen to in order to liquefy it with dry ice?

Dr. ISOTOP

Sat Jul 23 2011, 07:43AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

T_c for oxygen is 154K and dry ice is ~200K, so it will never liquefy.

Ash Small

Sat Jul 23 2011, 09:02AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
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"Oxygen becomes a liquid at temperatures below its boiling point of -183 C and takes on a pale blue color weighing 1.14 times the weight of water. When the temperature of liquid oxygen is greater then -118.6 C, the liquid will return back into a gas regardless of the pressure exerted on it. This is known as the critical temperature. 1 Liter of liquid oxygen provides 860 Liters of gas."

magnet18

Sat Jul 23 2011, 02:46PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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bwang wrote ...

T_c for oxygen is 154K and dry ice is ~200K, so it will never liquefy.

it will if you pressurize it

magnet18

Sat Jul 23 2011, 02:49PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Ash Small wrote ...

"Oxygen becomes a liquid at temperatures below its boiling point of -183Ã¯Â¿Â½C and takes on a pale blue color weighing 1.14 times the weight of water. When the temperature of liquid oxygen is greater then -118.6Ã¯Â¿Â½C, the liquid will return back into a gas regardless of the pressure exerted on it. This is known as the critical temperature. 1 Liter of liquid oxygen provides 860 Liters of gas."

but oxygen also has a critical pressure at which it will liquify at standard temperature,

Bored Chemist

Sat Jul 23 2011, 04:25PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

magnet18 wrote ...

but oxygen also has a critical pressure at which it will liquify at standard temperature,

No, it will not.
That's the whole point of a critical temperature.
Above the critical temperature, no matter how high the pressure, it will not form a liquid.

magnet18

Mon Jul 25 2011, 02:57PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Doh,
I feel dumb now, it would go to supercritical phase, wouldn't it.
hmm... maybe I could place the dry ice in alcohol to cool the alcohol beyond the 198K where dry ice sublimates... but everything would bank on the dry ice having an internal temperature below 154k

klugesmith

Wed Jul 27 2011, 10:04PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

If you want to liquefy air or O2 at home, the dry ice & alcohol might be a good start.
Decades ago they talked about this sort of stuff in the Amateur Science column in Scientific American.

I haven't run the numbers, but I bet one can reach 77K with a single expansion stage and regenerative cooling. Google the invention of liquid air machines (mid to late 19th century?).
Here's a starting point:

1. Compress a flow of air or O2 to high pressure, or draw it from a high pressure tank. (Well respecting the hazards of mechanical and pyro explosions. It would be safer to start with gaseous N2 ).

2. Run it through high pressure tube immersed in ice water (optional), then dry ice/alcohol, so you have high pressure gas (or supercritical fluid) at 195K.

3. Then the high pressure tube runs -inside- a low pressure tube, all coiled in a well insulated enclosure. The outer tube carries cold gas flowing in the opposite direction, and the pair form a counterflow heat exchanger.

4. The high pressure tube ends at a flow-limiting orifice, porous plug, or length of capillary tubing. When the gas is cold enough before the expansion, some may liquefy. What doesn't liquefy and drip into the collecting flask is made to return through the outer tube. (Think about a loose-fitting 1-hole stopper made of nonflammable thermal insulating material).

Of course it's trivial to make LO2 if you have a source of GO2 and plenty of LN2.

magnet18

Thu Jul 28 2011, 02:14AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Posts: 624

Awesome, so I just need an old air conditioner, and pipe.
Lots of pipe.

Bored Chemist

Thu Jul 28 2011, 11:26AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

You probably need a rather better pump than the one in an air conditioner.

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