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Re: Yet more: diffusion pumps
At 10:07 AM 2/1/96 -1000, you wrote:
> >I do believe there some point of decreasing returns.
>
>
>
How bout some increasing returns.....In all the diagrams for pumping &
bombarding setups I fail to see vacume traps in the systems. I was a
chemistry major in college and worked for three years doing reasearch
in organo-metallic chemistry. In my reasearch I had to perform reactions
in either a vacume or in an inert (and bone dry) atmosphere of argon. I
learned how to make vacume manifolds (with the old silicone grease stopcocks)
out of pyrex. I made alot of vacume traps, we allways had one in-line (before)
the vacume pump to trap any liquid's like acetone, water, benzene etc. The
traps increased pumping efficency, eliminated pump oil contamination and
were just generally a good idea. We cooled the traps in dewar flasks full
of a mixture of ethyl alchol and dry ice. We used merc. maniometers and
not once in the three years did I see any merc. contaminated pumps, etc.
(See the Ace Glass catalog for "ready made" traps)
The traps are a necessity if using a diffusion pump to prevent pump oil
oxidation and contamination. The fellow who had to rinse out salt water
filled tubes before repairing and pumping sure needed one (if he did not
have one already). We used to repeatdly open our manifolds to the atmosphere,
or attach vessels that needed to be pumped down and the pumps (welch) allways
performed great (and rapidly).
We also did not use diffusion pumps, if we needed a really "clean" atmosphere
of argon, we would pump the system, then fill with dry argon then re-pump (this
second pumping removed traces of H2O & O2 with the argon) & re-fill with dry
argon. Each pumping and re-filling will get you closer to a "pure" atmosphere
of argon, eventually removing all traces of contaminants (or at least getting
them down to undetectable levels).
Just .02 from a old chem head. (please excuse the spelling, I'll leave that
to the english & humanities majors!)