what epoxy will bond tungsten to teflon without outgassing?

[apchar]

I have some thoriated tungsten rods that I need to epoxy to a block of teflon.
Let me describe the application:
It's a high power Xenon flash-lamp. It emits 100 megawatts but only for a few microseconds and only once every 5 minutes or so in a temperature controlled lab so heat shouldn't be a problem. The body of the bulb is made from teflon with a quartz window. The electrodes are 1/16 inch thoriated tungsten welding rods that poke through the teflon into the vacuum chamber. The teflon wall is about 1 inch thick. I need an airtight seal. The pulse is brief but the rods will jump when the bulb is fired so there will be brief mechanical stress. I'll try to keep the epoxy out of the chamber and it will never be exposed to the arc but it would be better if the epoxy not out-gas into the vacuum chamber. Also, it'll be bombarded by a continuous stream of alpha particles from the thorium (they are welding rods so they're only about 2% thorium.) It'd be nice if it could hold for years but tolerable if it only lasted a few months.
Can any epoxy do this?
Thanks,
Art Blair
Dept of Aeronautics
University of Washington

 

[Compositepro]

Any epoxy will be far less permeable than Teflon. I think the alpha radiation is a non-issue. The big problem is the thermal spikes and large CTE differences in materials. You will probably get better result with an interference fit between the tungsten rod and the Teflon body and using silicone vacuum grease to improve the seal.

Flash lamps are usually made from quartz tubing and use a metal to glass seal. I can't imagine that a Teflon body would maintain a vacuum without being pumped down periodically.

 

[btrueblood]

Yes, any epoxy will probably work. NASA publishes a list of low-outgassing materials approved for spacecraft use, you can also find certified low-outgassing materials from suppliers if you google the term.

Compositepro is probably right about Teflon, though I have seen it used as electrical pass-thru materials on countless vacuum chambers (all of which were typically continuously pumped).

 

[unclesyd]

I don't think that epoxy will bond with Teflon without some help by etching or using a primer. I would give Reltek a call and present you problem.

http://www.reltekllc.com/adhesives-for-teflon.htm

I would lean toward using a ceramic material to seal the feed-through Like the ones on bulbs. Sauereisen, along with others, make a variety material that will do the job.

http://www.sauereisen.com/adhesives/adhesives.aspx