DT wrote:
Actually quite real.
Nitrogen supercools tarmac.
Oxygen condenses on tarmac, soaks in.
Tarmac goes boom as it warms up, or a fly lands on it.



Interesting, although I don't recall any warnings about this in all my years of
working with cryogenics, though. LN2 isn't all that much colder than the
condensation temperature of oxygen (-270 F) but if the tarmac got to full LN2
temp (-320 F) it could work. Certainly LN2 doesn't cause oxygen to condense
appreciably in typical lab conditions.


We made experimental quantities of LOX with just LN2 in our lab, to demonstrate
the paramagnetic effect of LOX. I think we just filled a thin-walled metal
container (part of a nitrogen trap) with a couple hundred cc's of LN2, and
placed an insulated container below it to catch anything that dripped off.
We then poured the captured liquid off, and it was repelled by a magnet.
It was also clearly a blue color.

I have a friend who works on medical MRI magnets. When they have a magnet
quench, it blows the burst diaphragm. The liquid helium is almost immediately
vaporized, although you could arque that there are structures inside the
magnet that would still be near 4 K. Condensation of Oxygen in the
opened dewar is a serious safety problem, and they have to use vacuum pumps
with special silicone oil, as the pumping of gases containing too much
oxygen can cause a truly spectacular explosion of petroleum-based oil
in vacuum pumps.

Jon