Sunday, January 1, 2017

High Voltage plasma cleaning.

I was wondering if it was possible to have high voltage plasma in a conductive vacuum chamber?
Seems like it is!
My previous high voltage stuff had been in the glass belljar of previous posts.
So when I started reading about plasma cleaning and surface modification, it got me wondering. 
Here is the video: 

If you are still reading, some details are: The vacuum feedthrough is a 4mm brass rod through a 7mm glass tube. Soda glass I think. Not boro' anyway. Then the threaded bit is from an old lamp fitting. I did a little work on the lathe to make the o-ring groove. All sealed up with normal(not Kwik) JB Weld.

Then it gets pushed through one of the existing electrode holes in my base plate. I know the chamber is filthy...
Strangely, I got the best ever vacuum level from my mechanical pump on this test. I got down to nearly 2x10-2( chamber pressure) normally I only get 6 or 5x10-2. Just at the edge of diffusion pump land.

Some strange thing that happened were... 
Initally the pressure began to rise when I turned on the NST and so plasma. I'd unplug and let the pressure drop again. I did this about 5 times until gradually, the pressure stopped rising. Then I was able to leave the NST on for about 5mins or more. I didn't want to over heat the electrode.

Total in plasma was probably 10 mins at 150 watts.

In the video is some poor footage of the plasma exposed surface of some acrylic and the unexposed(I peeled the plastic film back after I took it out of the chamber). One wetting well, the other, no way!
As I handled it, the grease from my fingers was busily spreading from the sides of the acrylic across the surface. It was very interesting to see the contamination spread.

 Also possibly there was a good bit of oil from the saw blade used to cut this bit of acrylic.
The other sample in the chamber was a piece of fast cast polyurethane resin. It work on that too. Over all effect seems short lived. Maybe straight under Di-water is the thing to do.

Conclusion: yes it works. 
To do: clean the pieces normally to remove most of the contaminants. Wear gloves.
Try...spontaneous bonding of very clean flat surfaces by contact.

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