Cryogenics: Uses and Abuses

[Swany]

Air is a good thing. It allows us to breath. However, air isn't supposed to be a liquid, that is silly! Nitrogen and oxygen are symmetic molecules, (N2, triple bond; O2 double bond) and thus contain no dipole movement or seperation of charges and thus no attractive forces between seperate molecules and thus cannot be liquified, or solidified!

 

Well..... thank goodness for London dispersion forces, a division pf Van der Waals forces. Essentially, electrons may be concentrated on one side of the molecule at a time, and thus a temporary seperation of charge ensues and thus the gas can be liquified providing the kinetic/thermal energy is very low, and/or it is pressurized. VdW forces are not nearly as strong as ionic interactions, hydrogen bonding, dipole bonding, etc and thus these gasses have a very low BP. Low specific heat capacities are also a mixed blessing.

 

So, there is your introduction if you wanted one. Or else, I just wasted a minute or three of your life as you had to read it.

 

In order to get liquid gasses, one needs:

1) A supplier

2) A dewar flask/tank

 

Liquid nitrogen and other gasses are used more than you may think, hospitals use lN2 for various reasons, welders, and other people. Dewars can be found on eBay for fairly low prices; new ones take a triple digit figure of US dollars. I borrowed mine from a welder/farmer friend, and it appears to be a Cold War relic. It is ugly, ugly, and old. However, it holds an estimated 5-10l of liquid nitrogen, so hooray for that.

 

Now, what to do with liquid nitrogen? All sorts of fun can be had! Google the liedenfrost (sp) effect for an interesting explination of some behavior. Imagine dropping water on a hot frying pan, the globs kind of dance around not really touching the pan, this is why you can pour lN2 over your hand, but not stick your hand in it! You can even put some in your mouth and then blow it out in a spectacular plume of smoke.

 

Frozen stuff tends to be very hard/brittle.

 

Physical data for nitrogen:

Melting point 63.34 K

Boiling point 77.4 K

Heat of fusion 0.3604 kJ/mol

Heat of vaporization 2.7928 kJ/mol

Specific heat 1.04J/g degC

 

So, I am planning to liquify Cl2, NH3, O2, solidify Hg and note properties, supercool Mg and see if it will be very brittle, drop burning Mg in it, perhaps stick a salute in a cup of it, freeze baby seals, then club them... ideas please!

 

EDIT: And, the first video is..... a friend smashing a semi-frozen marshmallow and playing with frozen mercury! No sound, small file: http://www.apcforum.net/files/hgln2.wmv

 

Request expirements and I will attempt to get pictures/video of all of the afore mentioned expirements.

[lacrima97]

You know how in the Terminator 2 movie, how they spill LN2 on the T1000, and he falls down and shatters?

 

If you took, say, a metal pipe, would it have the same effect?, or is that just movie entertainment.

[Rogue Chemist]

No effect, unless the metals crystal structure radically changes at low temps.

[dragonman586]

If the pipe is heated and rapidly cooled by something I'm not even sure if it has to be heated much. I think it will work.

[Douchermann]

Swanny, hydrogen. You can do it, cool it with the LN2, followed by applying pressure. Oh and get some pictures of liquid oxygen, that stuff looks cool.

How about N2O, or even NO2... its green muahaha. And if you're daring enough, try Fluorine

There are so many gasses that you could liquidfy and solidify with this, try some acid gasses like HCl. I think liquifying/solidifying chlorine would be a good idea. Make benzyl chloride production a hell of a lot easier.

 

-Freeze a frisbee

-freeze a sock and beat someone with it

-Do the old hammering a nail with a banana trick

-Freeze a tennis ball and serve it up to someone

-Styrofoam (not only will it be messy, it'll hurt)

 

I'm sure you'll think of some good ones.

[Mumbles]

If I'm not mistaken, styrofoam crumples in LN2. When I worked at the lab we did this thing where we froze some onions, and smashed it with a hammer. It sounded like glass. Other than that, we threw some on the floor and it rolls around on it's own pocket of gases, that is cool.

 

I'd suggest the good old liquid oxygen to light you grill trick.

 

Also, while you have LN2, you should freeze N2O5, and do some nitrations. I would personally do a certain 8th nitration on a cube like molecule. Step one of course would be getting said cube molecule and the first 7 nitrations. Most people should know what I am talking about.

[lacrima97]

That would be awesome mumbles. I am thinking that the cube may be hard to find though....

[Rogue Chemist]

I have tried getting the cube. Really difficult and also really expensive.

 

EDIT: But IIRC, the less nitrated cube does not actually start with the cube.

[flint_eastwood]

Fuck the cube, make some ice cream!

Also Swany, FYI the oxygen molecule isn't a double bond, it's a single with two three electron bonds. Thats why oxygen is paramagnetic.

[asilentbob]

Bump.

 

Anyone thought of compressing gas from atmospheric pressure with like a shop compressor for instance... so it heats up... then cooling it through leading it through essentially a radiator... then a radiator submerged in dry ice/acetone... then letting it expand and hence cool even lower... taking advantage of this to cool some liquid with a really low freezing point and using it for coolant in a condenser to condense various gases? Dry ice/acetone can get to approximately -78C IIRC... and letting a gas thats at -78C and considerable pressure expand has got to get majorly cold. Plus you can re-compress this already pretty cold gas and repeat.

 

Some CONDENSING/BOILING POINTS of some possibly attainable gases:

Acetylene -84C

Ammonia -35.5C

CO2 -78.5C (sublimes, though redundant)

Ethane -88C

R-12 -29.8C

R-22 -41.2C

Nitrogen -196C

(would be amazing for a DIYer to do without specialized equipment)

Oxygen -183C

(also amazing)

Propane -43C

Chlorine -34C

HCl gas -85C

 

If the gas we were trying to liquify was under a bit of pressure too, then its boiling point would be raised... a more positive number. For instance if we were using pre-chilled oxygen in one of those disposable gas cylinders from the hardware store if we kept it under a little pressure we could perhaps get its boiling point from -183C to around -170C... More pressure and it could be significantly lower. For instance at 1atm butane boils around 2C... but at 2atm its around 19C... 3atm 30C... 4atm 42CC... 5atm 50C...

 

Some FREEZING/MELTING POINTS for various solid things that could be hoped for:

Chlorine -101.5C

Bromine -7.3C

(not hard, just never seen it solid)

Xenon -111.7C

Mercury -38.8C

Nitric acid -42C

nitrogen monoxide -163C

sulfur dioxide -75C

HCl gas -114C

[asilentbob]

Well... I ran some calculations today... and it appears that this shouldn't be too hard to anyone that has a welder, shop compressor, copper tubing, pressure gauges, good cold thermometers, vacuum gauge, brass fittings, a schrader valve or two if they don't have a shop compressor, and patience... oh and if they can get dry ice.

 

I used the combined gas law, ie (P1V1)/T1 = (P2V2)/T2.

Then i plugged in values for P1, V1, T1, and P2, V2 and solved for T2.

In all cases The volume of gas was fixed at 50L, P2 was set to 1 atm, ie atmospheric pressure. And P1 and T1 were varied.

 

So essentially your going from a compressed gas at pressure P1 and temperature T1 of 50L in volume to letting it all reach P2 (atmospheric pressure) by letting it out of a valve, keeping the same volume of 50L, and seeing what the final temperature will be. In what I'm currently envisioning the gas will be lost to the atmosphere after many heat exchangers etc. A batch process. However, one could re-use the gas repeatably with the right kind of compressor and make the system a closed loop and continuous aside from adding more dry ice. This is a bit more than i can fathom since I'm not so great with fridge compressors. (Which might not work well because the oil inside the compressor would almost defiantly freeze anyways... but it could be a good pre-chiller instead of dry ice too... depending on the oils MP.)

 

The below table was made by simply solving the equation with different P1 and T1 values. Ideal gas behavior is assumed. In practice bone dry air would be used and can be assumed to be around 80/20-85/15 N2/O2. Will this be gas still at -78C and 6.8 or more atmospheres? Good question. I think so.

 

Recall:

K=C+273.15

1atm = 14.7psi

0 K = Absolute zero

*Shop compressors = ~50 to 300psi at anywhere from a few ml to 100+ gallons.

*Scuba tanks = 2700 to 4400psi typical fill at 3L to 18L

**quantity of gas = volume x pressure

***so 3L * 200bar (3000psi) = 600L of air at atmospheric pressure.

*Nitrogen paintball tanks = ~3000 to 5000psi at about 45-90cubic inches. Generally regulated to 450-800psi output.

 

I could not get the table to format correctly so that it would be easy to read, so i am attaching it as a HTML document. Check it out.

 

Something doesn't seem quite right. Between the values at 5000psi, from -87C it should be lower than from -50C... Yet its not... I probably messed up rounding with the sig.figs a bit... Also i think something about the volume is kinda screwy... but we have to remember that we are assuming ideal gas here.

 

Anyways... as you can see... the higher pressure you start from the lower the temperature of the gas will be at 1atm... However there are diminishing returns the higher the pressure and hence closer to absolute zero you can get.

 

 

@STP

Helium boils at 4.22 K (-268.93 C)

Hydrogen BP is 20.28 K (-252.87 C)

Neon 27.07 K (-246.08 C)

Nitrogen 77.36 K (-195.79 C)

Argon 87.30 K (-185.85 C)

Oxygen 90.20 K (-182.95 C)

Krypton 119.93 K (-153.22 C)

Xenon 165.03 K (-108.12 C)

 

Methane through butane both frozen and liquid are possible.

Also acetone, toluene, diethyl ether, carbon disulfide,

chloroform, ethyl acetate, THF, CH2Cl2, MEK, nitromethane,

isopropanol, ammonia, ethanol, methyl alcohol, formaldehyde,

and certainly diesel, kerosene, petroleum ether, naphtha,

are mostly liquids as is and ammonia and formaldehyde shouldn't be hard to liquify if not outright freeze solid.

 

Possible problems:

*Gases straying from ideal behavior... But if one is really going to go through all the trouble to try this, they would research a shit load and be equipped with phase change diagrams for air, N2, O2, etc... So they should be able to figure that all out...

*Condensation of water/ice/CO2... Though CO2 shouldn't be much of a problem since there isn't a ton of it in our atmosphere... plus it could be removed via NaOH or something.

*Embrittlement of cold pressure container/lines.

*Glycerin that is often in pressure gauges freezes at only 18 C.

*Taking temperature readings. I don't know about you, but i don't have super low temp thermometers on hand. On could be made using some liquid that isn't going to freeze anytime soon with a capilary tube since liquid volumes expand with heat and contract with cold. Or you could use a thermocouple probably. But im not handy with that stuff unfourtunatly. You could use samples of liquids sealed in ampules. For instance butane, acetone, water, MEK, isopropanol, and ethanol. You could also have a glass vials or something with nearly pure gases in them at a known pressure to measure the temp based on boiling/condensing point... like butane, propane, ammonia, oxygen, argon, CO2, etc... but this would be harder... Also one could obtain samples of superconducting materials and use them and strong magnets to determine approximate temps when really cold.

*It would be extremely wise to hydrostaticly test the vessel. http://en.wikipedia.org/wiki/Hydrostatic_test And a visual inspection and making sure that all parts are sealed throughly.

 

Edit: Haha forgot to format the attachment... fixed it, should display properly now.

 

Edit2: An example:

Container of 100psi gas at 0 C...

(P1V1)/T1 = (P2V2)/T2

(6.8atm * 1 L) / 273.15K = (1atm * 1 L) / T2...

Solving for T2 gets us 40.2 K... This equals -233 C...

 

So basicly just putting a container at 100psi in your freezer for a while...

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