What is the sealing mechanism of UHV view ports & electrical interconnects?

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Discussion Overview

The discussion centers on the sealing mechanisms used for ultra-high vacuum (UHV) view ports and electrical interconnects/feedthroughs. Participants explore the materials and techniques involved in achieving effective UHV seals, including the challenges of maintaining electrical insulation while preventing outgassing.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • Some participants propose that knife edges on flanges with maleable gaskets, like copper, are commonly used for UHV chamber environments.
  • There is a question about whether UHV view ports utilize the same sealing mechanism as flanges, specifically regarding the use of knife edges on quartz windows and gaskets between mating surfaces.
  • Concerns are raised about how electrical interconnects/feedthroughs are sealed to maintain UHV while ensuring electrical insulation, with suggestions of using ceramics or high-purity polymers like polyimide.
  • One participant mentions that electrical feedthroughs use ceramics bonded to metal surfaces, which are then welded into the chamber using vacuum-compatible techniques.
  • It is noted that obtaining materials with similar coefficients of thermal expansion is critical to prevent seal failure during heating for de-gassing.

Areas of Agreement / Disagreement

Participants express varying views on the specific materials and methods used for sealing UHV view ports and electrical feedthroughs. There is no consensus on the best practices or materials, and the discussion remains unresolved regarding the optimal approaches.

Contextual Notes

Participants highlight the importance of thermal expansion compatibility in sealing materials, indicating that dissimilar coefficients can lead to bond failure, particularly during temperature changes.

Questii
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Knife edges on the edges of flanges with a maleable material gasket like copper is often used for creating UHV chamber environments.

For UHV view ports, typically say quartz or some other material, how is the UHV seal accomplished?

Is it the same mechanism? E.g. knife edges machined on quartz windows and then encapsulated by two UHV chamber 'rings/flange cover' with a gasket inbetween the two mating surfaces?

What about electrical interconnects/feedthroughs? How do you seal them to create UHV (and still create electrical insulation because UHV chambers are often metal and you can't generally use polymers because of outgasing)? Do they use ceramics between the metal connects and the chamber or high purity polymers/epoxy like polyimide?

How is the UHV seal maintained for electrical feedthroughs also?
 
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Questii said:
Knife edges on the edges of flanges with a maleable material gasket like copper is often used for creating UHV chamber environments.

For UHV view ports, typically say quartz or some other material, how is the UHV seal accomplished?

Is it the same mechanism? E.g. knife edges machined on quartz windows and then encapsulated by two UHV chamber 'rings/flange cover' with a gasket inbetween the two mating surfaces?

What about electrical interconnects/feedthroughs? How do you seal them to create UHV (and still create electrical insulation because UHV chambers are often metal and you can't generally use polymers because of outgasing)? Do they use ceramics between the metal connects and the chamber or high purity polymers/epoxy like polyimide?

How is the UHV seal maintained for electrical feedthroughs also?
http://en.m.wikipedia.org/wiki/Glass-to-metal_seal

browsing through these vacuum system
Threads, I found this unanswered question, and thought I would contribute information I found on Wikipedia
 
Electrical feedthroughs use ceramics bonded to a metal surface which is then welded into the chamber using vacuum compatible techniques.

The ceramic-metal bonding is similar to glass-metal bonding.

Obtaining materials with similar coefficients of thermal expansion is mandatory, or else the seal will fail when the chamber is heated for de-gassing.

You can find more details here: http://www.mdcvacuum.com/DisplayContentPage.aspx?d=MDC&cc=33c1ded3-4381-4d1b-8eed-bd5622ccaa5f
and here: http://mpfpi.com/
 
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Obtaining materials with similar coefficients of thermal expansion is mandatory, or else the seal will fail when the chamber is heated...

yes and I understand similar coefficient of thermal expansion is required simply for the manufacturing process.

Dissimilar cte will cause the bond to fail as the newly fabricated part cools(!