PEEK in Vacuum Systems

I don't have any first-hand knowledge, but from the wiki article " It is one of the few plastics compatible with ultra-high vacuum applications"

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Hi Nigh,

PEEK is typically used in HPLC applications and can withstand high pressures (according to thickness of the tubing, etc.). It has very low out-gasing - brittleness/mechanical strength would depend primarily on temperature (which is?).

Depending on how the parts are used - do they have constant wear/motion against other parts, or are they fittings that, once in place only need to be disconnected once in a while?

I have used PEEK tubing and fittings for HPLC and never saw any friability in the screw parts of the fittings or in the tubing.

Remember, total vacuum is only -14.7psig!

Mike

I've used glass filled PEK (PEEK's brother) in high temp/pressure (135C, 15Kpsi) applications and it has held up well for short term use. Long term we had issues with cold flow (relatively speaking), but it had the advantage that it didn't shatter internally if you happened to drop one while installing it like the Glass to Metal Hermetic ones did. Green Tweed made them for us. We eventually had to phase them out because our units had to withstand pressure/temp for decades and they really only lasted a year or two. but if you can live with that, or if your application isn't as severe, you are probably fine with that choice. 1 Bar should be a piece of cake.

I'm using PEEK in a UHV chamber now. I've even accidentally sputtered YBCO with a few superconductors onto the PEEK. (Sputtered YBCO makes everything so shiny. ) Now this chamber should not reach the high temperatures that are acceptable for a glass ceramic, but that is the one attribute that I would be concerned with replacing ceramics with PEEK. I cannot vouch for its "long term" performance. This experiment is still being developed.

Some good comments, thanks for that. The application is static with no heavy loads. It could sometimes be heated to maybe 200°C but that would be only occasionally. Working temperature is lab type ambient. I think we will buy some & machine it to see how it is. We can put it under vacuum but can obviously only look at short term performance.

I've personally used residual gas analyzers and metal sputtering systems with PEEK parts in hard vaccum as you've indicated, but 200 degrees C would be too high for that material - it'll fail at around 175 C. Look into plastics such as vespel, ultem, torlon, or teflon depending on your particular needs.

The glass transition temperature is in the range of 143C. The melting point is approximately 343C. So it really depends upon the application and what loads would be placed on the part at 200C. The temperature at which it will "fail", or even what is considered a "failure" is very application specific.

I would recommend going to the website of a PEEK supplier and reviewing their property data. They have a lot of data available and also a lot of application specific information.