kovar vs Tungsten

[elizabeth]

Hello everyone,
quick question. I have made a pyrex chamber with two elecrodes on the ends, when a charge was applied it looks like the tungsten oxidized after 4 tests of 5 minutes each? It looks black and the helium turned to a red plasma. What do you think about Kovar. I got two elecrodes graded to pyrex and I think I will have them put into the ends insrtead of the tungeston which also had a littel urnamiun glass. It is for a science project for school.
Elizabeth

[TeleMad]

Are you trying to construct a light bulb from scratch? In a typical tungsten filament light bulb, the glass bulb is under vacuum to make the tungsten filament last longer.

[GAHD]

Yes, you can also fill the tube with various noble gasses to different effects.

But please, explain the experiment furthur, with whatever visual aids you can. It sounds interesting.

[elizabeth]

Hi again,
I had a pyrex tube made with electrodes on each end. On the side of the tube in the center there is a germanium viewing window and on the other side is a steel plate both are 2" in diameter. with each gas I tested it was taken down to 0Torr and then back up to 7 Torr with the gas put in. I tried argon Neon and Helium. I viewed with an infrared imager to see if plasma obstructed viewing. Not much difference. Got any ideas of another type of gas to use? I am hoping that changoing the electrodes will help. The plasma on the last test, the Helium started to spiral around the tube. pretty cool. but it was red note yelloow like I thought it was supposed to be. Oxidation of the electrodes or maybe the RTV that I gluesd the germanium and steel on with???
Elizabeth

[GAHD]

well I know a He-Ne mixture is used in red lazer tubes, so I'd assume helium glows read.

Try Xenon?

[C1ay]

Originally Posted by elizabeth

Hello everyone,
quick question. I have made a pyrex chamber with two elecrodes on the ends, when a charge was applied it looks like the tungsten oxidized after 4 tests of 5 minutes each? It looks black and the helium turned to a red plasma. What do you think about Kovar. I got two elecrodes graded to pyrex and I think I will have them put into the ends insrtead of the tungeston which also had a littel urnamiun glass. It is for a science project for school.
Elizabeth

It sounds like you are having a problem with the evacuation in removing all of the oxygen. Earlier in life I worked on vacuum furnaces which had to be oxygen free in operation. To achieve this we had to not only evacute the chamber, we found it necessary to post flow a quantity of nitrogen thru the chamber to displace any remaing molecules of oxygen. We then evacuated the nitrogen and backfilled with helium to check for leaks with a spectrometer. Your problem with oxidation should subside when your procedure is effective at removing all of the oxygen. Perhaps my past experience will help. Good luck.