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Helium is also used in leak detection machines. A friend of mine works for a company that makes those machines. Simplifying the process is: you fill an item wit
by pmontra 3y ago
Helium is also used in leak detection machines. A friend of mine works for a company that makes those machines. Simplifying the process is: you fill an item with helium, put it in a vacuum chamber inside the machine, a mass spectrometer checks if there is more helium than expected. If positive, there is a leak.
They use helium because it's not reactive and it's tiny but not too tiny like hydrogen, which he says it's harder to contain. I just checked and the hydrogen molecule is indeed smaller than the helium atom, 120 pm vs 140 pm van der Waals radius. Furthermore, as many candidates as helium alternatives, there is too much hydrogen around and it's not clear what the mass spectrometer is reading: a leak or some leftover from the vacuuming process?
Anyway, they were hit by the spike in helium costs years ago. Not so much to steer them and their industry to something different. Their customers need to check for leaks no matter what.
- thrdbndndn 3y agoI'd argue helium being non-reactive is 100 times more important than being larger than hydrogen in "why we choose it over hydrogen".
- exmadscientist 3y agoNot really. The transport of helium and hydrogen through potential leaking sites is just different enough that they are sensitive to different things and appropriate for different uses. So hydrogen is indeed sometimes used for leak checking. ...though the inert gases (helium, argon, various freons) being inert sure does help make them popular.
- RugnirViking 3y agoI've done some work on chemical plants with hydrogen. Through a long chain of people (I was nowhere near the actual bare metal operations) I got a very strong impression that sealing hydrogen is a pain in the ass, it makes its way through every joint and seal. I'm sure some of it is reactivity but it being tiny I think also causes it. I know some of the machines must never be turned off because the sheen created by the ongoing reaction helps to seal it
- marcosdumay 3y agoAt least, it is 100 times more important than the atomic radius to explain why it leaks more. (Or, rather, it's some number of times where people only care about the exponent.)