Liquid Oxygen is Magnetic

August 10, 2021 10:21 PM

Liquid Oxygen is Magnetic (SLYT)
posted by jamjam (17 comments total)

W H O A
posted by rrrrrrrrrt at 11:28 PM on August 10, 2021 [2 favorites]

I have (had?) a home chemistry book from about 1900 that suggests you go to your local chemist (!) and get some liquid oxygen to do experiments with magnetism.
posted by bifurcated at 12:54 AM on August 11, 2021 [4 favorites]

Oxygen was first liquefied in 1877 by an apparatus that seemed to rely more on compression than cooling, and the Dewar flask (the shiny thing with an aluminum base and covered in blue mesh in the video) was invented in 1892.

I have a feeling a chemistry book from 1900 advising going to a local chemist to pick up some liquid oxygen might not have been referring to liquified oxygen gas, but people were very excited by the quest to liquefy "the permanent gases" back then, which ended in 1908 with the liquefaction of helium, so maybe it was.
posted by jamjam at 1:20 AM on August 11, 2021 [1 favorite]

Cryogenic gases are weird.

This reminded me of a bizarre fact about liquid hydrogen - the following is from John D. Clark's fantastic book Ignition!: An informal history of liquid rocket propellants:

Quantum mechanics had predicted that the hydrogen molecule, H₂, should appear in two forms: ortho, with the nucleii of the two atoms spinning in the same direction (parallel), and para, with the two nucleii spinning in opposite directions (antiparallel). It further predicted that at room temperature or above, three-quarters of the molecules in a mass of hydrogen should appear in the ortho form and a quarter in the para, and that at its boiling point almost all of them should appear in the para state.

But for years nobody observed this phenomenon. (The two forms should be distinguishable by their thermal conductivity.) Then, in 1927, D. M. Dennison pointed out, in the Proceedings of the Royal Society, that the transition from the ortho to the para state might be a slow process, taking, perhaps, several days, and that if the investigators waited a while before making their measurements, they might get some interesting results.

Urey, Brickwedde and others in this country, as well as Clusius and Hiller in Germany looked into the question exhaustively between 1929 and 1937, and the results were indeed interesting, and when the propellant community got around to looking them up, disconcerting. The transition was slow, and took several days at 21 K. But that didn't matter to the rocket man who merely wanted to burn the stuff. What did matter was that each mole of hydrogen (2 grams) which changed from the ortho to the para state gave off 337 calories of heat in the process. And since it takes only 219 calories to vaporize one mole of hydrogen, you were in real trouble. For if you liquefied a mass of hydrogen, getting a liquid that was still almost three quarters ortho-hydrogen, the heat of the subsequent transition of that to para-hydrogen was enough to change the whole lot right back to the gaseous state. All without the help of any heat leaking in from the outside.

Interestingly, the paramagnetism of liquid oxygen don't seem to have been a practical issue for rocketry, apparently because of the extremely high magnetic field strength needed to induce the effect.

It does mean however that you can move liquid oxygen with a magnetic pump, without any moving parts.
posted by automatronic at 4:09 AM on August 11, 2021 [9 favorites]

When the camera peers down into the dewar flask, the LOX looks clear. That's a little weird because the only time I've seen it before it was noticeably *blue*. Like, eerily pretty light blue. I thought maybe my experience was colored with impurities but wikipedia et al say that, nope, liquid and solid oxygen are both quite blue.
posted by introp at 5:43 AM on August 11, 2021

Yeah, when you use Liquid Nitrogen in a Cold Trap, which is set up to condense (usually very flammable) vapors off a chemical reaction you are exposing to high vaccuum, accidentally condensing liquid oxygen inside your cold-trap organics mixture is a shit-your-pants moment.

LO2 is a very powerful oxidant. Oxidizes things very quickly - not what you want in a lab setting with other flammables around.

Behold, some cotton wool - bye bye! . Not swanky enough for you? Perhaps quickly burining a diamond would make you happier.
posted by lalochezia at 6:53 AM on August 11, 2021 [3 favorites]

LO2 is a very powerful oxidant.

And yet, not the most powerful. There are a number of fluorides that are far more powerful oxidizers than even pure liquid oxygen itself, allowing them to set fire to things like sand, bricks, asbestos, and the ashes of stuff that any sane person would have thought burned all the way to hell already.

On this topic I highly recommend two of the classic posts from Derek Lowe's Things I Won't Work With blog, on chlorine trifluoride and dioxygen difluoride.
posted by automatronic at 7:20 AM on August 11, 2021 [3 favorites]

→ accidentally condensing liquid oxygen inside your cold-trap organics mixture

Ah, that's giving me sweaty palms at even the thought of it, because of course liquid oxygen will form peroxides with anything it touches, run away run away run away ...

The bit in Ignition! where they discuss an oxidizer that will happily burn sand and how they'd deal with it if there was a leak (“be somewhere else that isn't on fire, hopefully” is a fair summary).
posted by scruss at 9:17 AM on August 11, 2021

Ignition! is such an amazing book.
posted by curious nu at 10:59 AM on August 11, 2021

Liquid oxygen is also very pretty in zero-G.

Some of the SpaceX rockets have had a camera looking down in the top of the LOX tank, on which you can see the liquid disappearing down into the engine, then floating up into weightless blobs once the engine cuts out.

Fun fact: because of this, if you want to restart a liquid fueled rocket in space, you need a separate thruster system to accelerate it forwards slightly, so that the liquid plops down into the bottom of the tank where the fuel pumps can get at it.
posted by automatronic at 11:53 AM on August 11, 2021 [2 favorites]

LO2 is a very powerful oxidant.

I was a little nervous about the arc flash on that knife switch...I've never worked with LOX (and only very rarely with any kind of liquefied gas) but I'd nope right out of the opportunity to pour LOX on something that might burn when there's sparking going on nearby.
posted by spacewrench at 12:03 PM on August 11, 2021 [1 favorite]

Quantum mechanics had predicted that the hydrogen molecule, H2, should appear in two forms: ortho, with the nucleii of the two atoms spinning in the same direction (parallel), and para, with the two nucleii spinning in opposite directions (antiparallel). It further predicted that at room temperature or above, three-quarters of the molecules in a mass of hydrogen should appear in the ortho form and a quarter in the para, and that at its boiling point almost all of them should appear in the para state.
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For if you liquefied a mass of hydrogen, getting a liquid that was still almost three quarters ortho-hydrogen, the heat of the subsequent transition of that to para-hydrogen was enough to change the whole lot right back to the gaseous state. All without the help of any heat leaking in from the outside.

The ortho form of hydrogen is the metastable excited state which makes the hydrogen maser possible, and also the source of the 21 cm line in the emission spectrum of hydrogen as it decays into the para form.

Would there be any point in gently irradiating gaseous hydrogen with 21 cm microwaves at some late point in the liquefaction process in hopes of getting relatively ortho free liquid hydrogen which couldn't boil itself away?
posted by jamjam at 2:16 PM on August 11, 2021

I got that wrong; how embarrassing. The ortho and para transitions are NOT the source of the H-maser. It's the electron and proton spins.

Very kind of you people not to point that out, but the truth must be served
posted by jamjam at 4:40 PM on August 11, 2021 [3 favorites]

Would there be any point in gently irradiating gaseous hydrogen with 21 cm microwaves at some late point in the liquefaction process in hopes of getting relatively ortho free liquid hydrogen which couldn't boil itself away?

There's no need - catalysts were a better solution:

The answer to the problem was obvious — find a catalyst that will speed up the transition, so that the evolved heat can be disposed of during the cooling and liquefaction process and won't appear later to give you trouble; and through the 50's, several men were looking for such a thing. P. L. Barrick, working at the University of Colorado and at the Bureau of Standards at Boulder, Colorado, came up with the first one to be used on a large scale — hydrated ferric oxide. Since then several other catalytic materials have been found — palladium-silver alloys, ruthenium, and what not, several of them much more efficient than the ferric oxide — and the ortho-para problem can be filed and forgotten.

posted by automatronic at 4:43 PM on August 11, 2021 [1 favorite]

Thank you, automatronic.

This is by no means a sufficient excuse, but the city of Seattle is currently shaking my house apart with a tunnel boring machine on the street behind it.
posted by jamjam at 4:55 PM on August 11, 2021

“Hydrated ferric oxide” is more commonly known as “rust.”

My thesis experiment had a 17 liter liquid hydrogen volume. It took two days to fill with liquid, and another two days to convert to parahydrogen, even with the catalyst. The rocket people only cared about the heat of the conversion, since their goal was to store the hydrogen until they could set it on fire. But for us the extra angular momentum in the orthohydrogen allowed it to interact with neutrons, so we needed to convert it all to para. For spontaneous conversion the rate goes like the square of the ortho concentration, so even slower than an exponential.

The ortho-para division in hydrogen was historically the first evidence that protons, like electrons, obey the “exclusion principle.” Molecular nitrogen also has and ortho-para division, but because the nitrogen nucleus has spin “one” instead of spin “half,” ortho-nitrogen is the more populated species at both low and high temperatures. The rotational states of nitrogen aren't a factor in its liquefaction the way they are for hydrogen. And oxygen nuclei are spinless; liquid oxygen’s magnetism is an electronic phenomenon.

This is a neat demo. The fact that I didn’t get antsy about the spark from the switch next to the liquid oxygen tells me that I’ve been away from the lab for too long.
posted by fantabulous timewaster at 11:49 AM on August 12, 2021 [3 favorites]

“Hydrated ferric oxide” is more commonly known as “rust.”

Indeed - I wonder if they discovered the catalyst effect by storing LH₂ in a rusty tank.
posted by automatronic at 5:46 PM on August 12, 2021