Cylindrical quartz tube to be placed within a stainless steel socket or bore. (http://www.idealvac.com/files/images/KFSocketWeldFlageLong_Draw_1.jpg )
Quartz tube can reach relatively high temperatures (1000C). Thermal expansion of epoxy must be such that the quartz tube will not shatter due to expanding material surrounding it.
I have found two products which may work, however I am not sure if they will hold a vacuum as a barrier between 760Torr and 1e-7 Torr. I will call the supplier and ask.
(http://www.tedpella.com/technote_html/16026_16026-10_TN_V2_04172012.pdf & http://www.cotronics.com/vo/cotr/pdf/801.pdf )
Has anyone used an epoxy with the same requirements in mind?
This sounds like you should use a high temperature braze. We use cusil 65/35 which I think melts at about 1050c. It is gold copper mix. We use ramp rate of 10c per minute.
When I was at IBM we used to seal our Langmuir probes at the colleciton tip with a glass-metal seal: Pyrex-Tungsten directly works great, certainly at the probe-tip-diameter size. Coefficients of expansion are well matched (~ 4 ppm vs 4.3 ppm).
Pyrex only good up to 850C, not sure if that is the softening point or the melting point.
If you don't need the full 1000C, and trace boron sputtering is OK, then you might get away with it, and it is cheap and easy! If the metal-tube is thin then you would get away with a 6mm tube sealing too, I think. (How bad is it if it fails? )
Hey Bert,
When you say you are sealing at the collection tip, do you mean as to separate the collection are of the tungsten from the plasma with a thin layer of borosillicate? Or just the area around the tungsten while still exposing some of the tip? I've been looking into some scientific glassblowing websites and the information appears to agree with your Pyrex-Tungsten experience. That's good information to have in my back pocket.
It is cataclysmic to my turbo-pump if this were to fail. My pump rests at the bottom of my chamber. I did not design this. I had made a filter to relatively larger particles entering the TMP with some copper mesh as a precaution, while this does sacrifice the time the system needs to pump down, I'm dead in the water if my pump dies.
As of now I'm using high temperature RTV and it's working pretty well. This is for mating quartz tubes used in my Helicon array. I'm able to see pressures as low as 0.1mTorr, and once I get my ion gauge working again I should know for sure. Then I'll have to use a helium leak test to make sure all my seals are good since we just switched over to viton gaskets for our CF flanges.
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