I'm hoping someone can shed some light on some trouble we've had in our lab.
We often use slush baths (solvents cooled with dry ice, LN2, or LAr) to
reach specific temperatures in various analytical methods. Most recently,
we've been using iso-pentane and LN2, which lets us go down to -160C. It
worked fine for a few weeks, then we ran into trouble.
When cooling the solvent down, we could hear little "pops", almost like
popping bubble wrap. Occasionally, this would be severe enough that we
would get solvent blowing out of the dewar like a geyser.
Several changes failed to solve the problem: replacing the solvent with a
new batch out of the bottle. Changing the dewars to other clean ones.
Trying liquid argon. Trying n-pentane. In our last test, a dewar of
iso-pentane actually exploded violently, vaporizing the solvent and sending
shards of glass flying (in a closed fume hood, of course!).
Can anyone offer up an idea as to what is happening here?
Who says science isn't exciting!
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Biogeochemistry Lab (E-Hut, room 102)
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University of Victoria
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