cleaning the chamber–advice welcomed!

[Lerner]

For the chemists out there, we have a few cleaning questions. On the one hand, we sometimes (including right now) get accidental contamination within the vacuum chamber with lubricating grease from machining that gets stuck in unseen places and is not totally cleaned before we get the pieces into the vacuum chamber. Is there any gas we could use that would clean up hydrocarbon deposits formed after the plasma interacts with the grease, which won’t harm our stainless steel vacuum chamber or our copper electrodes? If we could just have a cleaning gas, it would be much faster than opening up the chamber and taking everything apart.
Second, copper eroded from the anode gets deposited on our glass viewing windows. We can take these out easily enough but what is good to clean the copper off the glass that won’t scratch or harm the glass or the surrounding steel?

[Breakable]

I am not much of a chemist, but for the copper cleaning from glass, I would probably suggest the idea of finding a soluble salt, and then using the acid based on the oxidizer for this salt.
http://en.wikipedia.org/wiki/Solubility_table
Copper(II) bromide seems soluble.
So what about : http://en.wikipedia.org/wiki/Bromic_acid
Not sure about toxicity of these substances.

[Francisl]

If you look at the welding helmets used for arc welding, you notice that they use a clear protective cover in front of the expensive glass lenses. I suggest that you use a replaceable sacrificial clear cover that can be attached to the window.

[Francisl]

Dry ice blast cleaning is a method that might work. It is used for cleaning electrical equipment.

[dhitter]

Guess what? Ammonia which is a traditional cleaner for glass is also a copper solvent…..problem solved!?

[coffeebean]

Hello,

In my semiconductor work, we always used to bleed a bit of nitrogen between the backing mechanical pump and the high vacuum pump (turbomolecular in my case) to prevent the mechanical pump’s oil from diffusing up stream once high vacuum had been achieved. The nitrogen would provide a minimum volume of gas flowing through the backing pump preventing the oil from diffusing up.

Oxygen plasma works well on hydrocarbons, assuming your seals and copper can withstand it, aluminum does.

By the way, thank you for doing this work. I wish I could support it somehow.

Chris

[Ivy Matt]

I’m not a chemist, but my suggestion would be to avoid using anything that reacts with decaborane.

[Brian H]

That ‘dry ice blast cleaning’ isn’t effortless, but it seems to have the mojo to do the job.

[pulser]

Start here –> http://en.wikipedia.org/wiki/Parts_cleaning
Plasma based cleaning is fine for removing sub-micron layers, but not bulk contamination.

Cu etching–>
http://www.transene.com/cu_etchant.html

Put in a rotatable transparent shutter to extend time to cleaning.
Use a removable piece of glass/quartz/saphire in front of the window and clean this.

[Henning]

I’ve cross-posted this question on Talk-Polywell, and Giorgio already answered:

IR + UV lamps or Glow discharge with Argon.

See here:
http://www.vacuumlab.com/Articles/VacLab52.pdf

They could also contact directly the guys at vacuumlab.com for additional suggestions.

Keep a look on this thread, maybe more is coming in.

[Henning]

There are already some more suggestions from the Polywellers.
For the removal of copper residuals there are two suggestions:

As far as removal of the Copper from the chamber walls, a simple DC glow discharge with Ar or O2 should do the job. The glow discharge would be simple capacitive DC with the bias plate at 500 or 1000 V bias. The Ar or O2 gas flow should be at around 1-10 torr with a base pressure of 0.1 torr (need only a roughing pump).

Change to sapphire windows and scratching during cleaning becomes less of a problem. ‘Course the sapphire windows may be out-of-budget.

Alternatively, treat the glass windows as replaceable items and don’t bother cleaning them.

Sapphire windows shouldn’t be too expensive, though: http://www.sapphirewindows.com/
There are other suppliers, but this one quotes the price directly on the front page.

[Henning]

For cleaning the glass from copper, Joseph Chikva proposes to use circuit board etching technique (of course without protecting any surface for the conductive path):
http://www.talk-polywell.org/bb/viewtopic.php?t=2126&postdays=0&postorder=asc&start=388

Here it’s described how you do it step by step (without Google translation):
http://www.wikihow.com/Etch-a-Circuit-Board

BTW, he also worries about hydrocarbon contamination induced by the Mylar insulators. I just want to mention this, so in case you get more unwanted hydrocarbons, these might be the source.

[vansig]

Archeologists have begun cleaning carbon deposits off of old paintings, with pulses from a laser. could the same work for the hydrocarbon deposits?
it would seem to be optimal: http://www.sciencedirect.com/science/article/pii/S0022311510004241

Also, copper dissolves in hot concentrated sulfuric acid, which shouldn’t harm glass, but definitely will harm steel (my stainless steel sink was stained, that way).
Can the glass be removed from the supporting steel, for cleaning?

[pulser]

For a fast clean of the window, make a clip which will hold a saphire (or glass) plate in front of your existing window. Clean the Cu with HCl (obtained at Safeway to adjust pool pH). Rinse in water for 5 minutes. Put back. All done in 10 minutes and can be done in a fumehood with no exposure to fumes. Don’t care about the stainless since you remove the plate from the system or cleaning.

[delt0r]

Well the vac chambers we had, we always puled them apart and gave them a reclean. We needed 10^-8 to 10^9 torr, so even a fingerprint was a disaster. Mostly turbo pumps. We at least know of no short cuts. Oh everything was bake-able to 200C IIRC and it was days for a full pump down. But then you don’t need to go that low do you? At any rate high quality vacuum is a PITA.

[Author]

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