My university has a sputtering machine which is this crazy expensive piece of equipment that has to have a really strong vacuum pump and wacky copper seals and if it loses power for even a minute it has to spend 16 hours pumping it’s vacuum back down.
I know people talk about how a perfect vacuum is like near impossible, but why? We can pressurize things really easily, like air soft co2 canisters or compressed air, which is way above 1 atmosphere in pressure, so why is going below 1 atmosphere so hard? I feel dumb asking this as a senior mechanical engineering student but like I have no clue lol.
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There are many reasons. You have problems with off gassing for example, at low pressures things do not tend to stay solid and will start evaporate, including a lot of rubbers and plastic. But the main issue with very high vacuums is that the air stops behaving like a gas and more like individual particles. You can imagine pulling back a piston in a vacuum chamber, the place previously occupied by the piston will be free of any air molecules even though there is a few random stray molecules in the rest of the chamber. You have to wait for these molecules to bounce around and enter the new volume. Depending on the size of the opening and the pressure inside the chamber this may take minutes for the pressure to equalize. There is just nothing to push the air into the new void.
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