Letter 34013

Copper vs Stainless steel tubing for vacuum equipment  

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I am building a piece of laboratory equipment which involves mixing various gases in precise quantities at low pressure (1-2 bar). Contamination in the system would be a problem. I had intended to use 1/4" stainless steel tubing for the three gas supply lines but money is in short supply so I am considering using copper tubing instead.

At this relatively low pressure, is the use of copper pipework likely to cause a contamination problem? And would it cause a problem to use fittings designed for stainless steel pipe?

John Proctor, Postgrad student
University of Manchester - Manchester, Greater Manchester, UK

If you search around, you can find small amounts of stainless tubing at an affordable price. Do not rule out junkyards or places that manufacture equipment with SS tube that might give you some "drops". A hydraulic shop might take pity on you and give you a small amount.

Now when you say "gasses", that says absolutely nothing !! You could probably get away with argon and nitrogen, but you certainly do not want to use it on oxygen and hydrogen. Similarily, you can get away with it on some organic gass and not with others.

James Watts
- Navarre, Florida

Thanks for your help.

Since posting the query, I've found the answer elsewhere. The apparatus I am building is for growing carbon nanotubes, the electronic properties of which I plan to study.

I have been told that industrial plants for the manufacture of silicon-based semiconductors do not use copper piping since the tiny amounts of copper that ended up in their semiconductors would dope them in such a disastrous way as to render them useless! Doping with tiny amounts of foreign material also has a large effect on the physics of carbon nanotubes so I definitely cannot use copper piping.

Thanks anyway,

John Proctor, Phd student
EE&E Dept, University of Manchester- Manchester, UK

John,

You can use polypro tubing and a plastic adapter into the threaded fitting on the chamber. These are a little tricky to get proper sealing but can work. Better fittings are Swagelock but expensive.

John Carlotto
Innovative Coatings, L.L.C. - E. Providence, Rhode Island, USA

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