My vacuum system is coming together

How to get to vacuum, what the classes are, and what is needed for what job.

My vacuum system is coming together

Postby Jerry » Mon Feb 06, 2012 5:59 am

With the extra time on my hands I have finally had the chance to get my system back together. Last summer I took a lot of it apart to get it back outside of the house and took it over to a friend's shop. The other year he bought a house for his business and it came with a 1200 sq ft shop with three phase... Drool... He lets me play there.

He has a project where we need to deposit TiO on sapphire so I am getting this thing ready for coating. I really have not done anything to it since I made all the holes in the base plate in this thread:

viewtopic.php?f=12&t=44

Wow, been a year and a half!

Got everything put together. The crystal holder for the monitor, a diffuser for gas inlet, power feedthroughs, built a new rack to hold the RF power supply and other stuff. Fired it up and managed to get down to low e-5. I fired up the rag and the problem I was having before reared its ugly head again but this time it wouldn't fall for the same tricks to get it going as before. Last year I found the electronic half of the same model of RGA except in a 200AMU version with electron multiplier. I think I paid $50 for it on ebay. The electronics in the unit are basically little racks, one for input power and communications, one for I/O, and the other holds the cpu board and the main power supply. The cpu rack had the same model not he power supply board but the cpu board itself was a newer revision with a different model number. Figured I didn't have much to loose so I plugged it in and gave it a try. It worked!

Luckily whoever designed it made it so that it gets the parameter info from the rest of the unit so it shows up as it should, a 100AMU rga plus another option which I had not heard of. I got it tuned and it works. First thing I found was a pretty big air leak:

Image
IMG_1220 by macona, on Flickr

You can see the big peaks of nitrogen at 28 and 14 as well as 16 and 32 of O and O2. I brought my little tank of ballon helium over, put the RGA in leak test mode and found a leaky conflat. I think I may have tried reusing a half squished conflat here. Oh well.

After that I managed to get the system down to the mid e-6 range. Not bad for a system sitting at air for a year and a half (The DP section was still under vacuum). After:

Image
Untitled by macona, on Flickr

As you can see, it is full of water. So I took one of those Ushio Ultra High Pressure Mercury lamps and installed it hanging across the two big power feedthoughs and ran the thing off my tig welder, 40v at 6 amps. It seems like it may be an option for outgassing. If you look at the screen on the computer below you can see a yellow line. This is mass 18, H2O in a trend graph, I think 10 minutes for the width. You can see where I first turned on the lamp there is a huge spike in water vapor. At the peak is where I lowered the power on the lamp too much and it went out. It took a while to cool down enough to restrike and you can see the graph where it does and again where I shut it off. Seems to work.

Image
Untitled by macona, on Flickr

Only bad thing is it is rather bright:

Image
Untitled by macona, on Flickr

Image
Untitled by macona, on Flickr

Now I need to make the electrodes to hold the boats, figure out how to hold and heat the substrate and rig up a leak valve to let O2 in to the system. When evaporating Ti02 it decomposes and needs oxygen in the system to go back to it's transparent form.
Jerry
 
Posts: 561
Joined: Sun Jul 18, 2010 12:07 am
Location: Beaverton, OR

Re: My vacuum system is coming together

Postby Doug Coulter » Tue Feb 07, 2012 10:17 am

I've been having decent luck on leak valves with some tiny compressed air solenoid valves I've modified for the purpose (basically plug up the vent to atmosphere when in the normally closed position and use them "backwards" to get least lost volume), with a capillary on the tank side with very low lost volume. I can just pulse them till I get what I want. These have a 10-32 port, and for the capillary what's been working best is to just drill out a piece of screw stock 1/16 and stuff it full of 1/16 drill rod - it leaks around it just about the right amount. Advantage over "real" cap tubing is that if this ever gets plugged, you can just pull the rod back out.

Nice mass spec photos! My cheap one went haywire and the spectrum looks all folded up. Going to have to look into what went wrong there, probably something with the drives for the rods.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: My vacuum system is coming together

Postby Jerry » Tue Feb 07, 2012 10:00 pm

I have a Vacoa brand leaak valve that should work. It came out of a spares box from some defunct along the line.

Need to order some VCR seals too. Used all the ones I had stashed and forgot to get more.
Jerry
 
Posts: 561
Joined: Sun Jul 18, 2010 12:07 am
Location: Beaverton, OR


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