Cleaning the Chamber 3

[Jake Wells]

I get these IPA pads from first aid kits and store them in a drawer for medical emergencies if i accidently cut myself. But i rembered chris bradley recomended using IPA and a lint free rag ( My rag is 100% cotton) to clean the chamber. Could thes alcohol pads be used to clean the chambber?

[John Futter]

YES

[Jake Wells]

can ipa outgas in a vacuum

[Jerry Biehler]

Not really, it will go away pretty fast but I dont know what makes up the other 30% of what is in there.

[Richard Hull]

I tend to use "everclear", 90% ethyl, from the booze store. You can make it "absolute" with copper sulfate crystals heated to whiteness in an oven if you are after 0% contaminants. I do this for drying microscope specimens. Everclear is usually good enough for vacuum component cleaning; the other 10% is always water. With 70% isopropyl, you just don't know what the other 30% of the stuff is, but I would imagine water.

Richard Hull

[Dennis P Brown]

Most commercial alcohol pads are 30% liquid water; as Mr. Hull says, even the 190 proof alcohol has water and needs to have a drying agent added to further reduce the water content. Liquid water is not exactly what you want to add in any vacuum system so I'd avoid most of those things unless absolutely needed. Air, with its trace of water vapor is bad enough but pumping does get rid of it (heating even faster as disused in the recent posts). That all said, cleaning a vacuum system isn't normally needed unless you know oil vapor has accumulated (these oils aren't the issue but they do absorb water and other gasses. Baking would do a lot for those issues, too.) But if your mechanical oil pump has a trap and you use a cold trap on any diffusion pump this shouldn't be a problem. With a turbo, even less likely. The best test is out gassing by your system (not to be confused with very small leaks. They behave very differently than out gassing.) If out gassing isn't an issue, why contaminate your chamber at all by wiping it down?

[Jake Wells]

I already cleaned the chamber with the ipa pads. I am in trouble with water and will be outgasing. Or am i fine?

[Dennis P Brown]

Don't worry; some out gassing will occur due to the water but will quickly be removed by pumping. All I'm trying to get at is that cleaning a vacuum system that is just pumped out for a plasma is generally not useful because it becomes ultra clean by the plasma. That is, the plasma will clean the surfaces very well of water and organics. Of course, before striking the plasma the water vapor will out gas from the walls every time after the chamber has been opened to the air. No big deal.
There are times someone can/should clean a chamber but those times are rare and special. A fusor should generally not need any cleaning except if oil vapor back flow is a constant issue.

[Richard Hull]

I have used plasma cleaning for years.

When first running after a long time, I turn on the forepump, open the gas ballast wide open and wait until the foreline is near 15 microns. (This normally takes about 20 minutes). This rids the forepump of most water in the oil I then close the gas ballast and open all valves right up to and including the fusor.

I then start a hard, hot plasma at about 50 microns. (Note: opening all the other valves causes the forline TC gauge to rise to high pressures and the process starts anew for the diff pump and fusor) I force the plasma to draw about 20-30ma regardless of voltage. I up the voltage as needed to maintain at least 20ma until the foreline TC gauge and the fusor chamber Barocell agree in the range of 10-15 microns which is the norm for a long running, bottom to my forepump. By this time the fusor chamber is almost too hot to touch. (plasma dissapation and electron bombardment of the shell).

I then close the fusor chamber valve and start the diff pump heater and cooling fan. I have a temperature gauge on the boiler and as the temperature rises so does the foreline pressure due to water vapor and other volitiles leaving the diff pump oil. (This can be as high as 20+ microns!) As the temperature approaches the full operating temp of the oil to start through the jets, but before any significant pressure drop occurs below the normal "hot" bottoming of about 12 microns, I quickly open the fusor chamber valve. Most of the time I open the valve just before the boiler hits 100 deg C., as my diff pump drops the 12 micron chamber pressure like a stone at about 110 deg. C. As this temperature is reached it is natural for all plasma to cease as it can't be maintained at any voltage. Turn all power to the fusor off at this time.

This warrants that most of the water vapor is sent out of the system and that the water vapor and light volatiles don't back flow into the fusor.

There is an art to not fouling a long dormant fusor and plasma cleaning is just part of it.

Richard Hull

[David Kunkle]

I already cleaned the chamber with the ipa pads. I am in trouble with water and will be outgasing. Or am i fine?

Seems to me that the H2O adsorbed onto the chamber walls will be in a state of equilibrium with the atmosphere given the humidity and temperature. If you clean the chamber with a solvent with some percent of water, the solvent will evaporate quickly leaving a layer of water on the walls as opposed to just adsorbed molecules of H2O. The layer of water will also evaporate relatively quickly- leaving the walls back in their state of equilibrium with adsorbed water molecules. My guess is you won't see any difference in pumping time- as long as the layer of water has a reasonable period of time to dry before sealing it up again.

Maybe a good high school science fair project? Test the above by measuring the time it takes to get the fusor down to its max vacuum level after exposure to atmosphere and after being wiped down with various solvents like IPA, ethanol, straight water.

[Chris Bradley]

Water is, itself, a good solvent for many things. There is no issue with using 70% IPA and then doing a plasma clean. You should want to do a plasma clean anyway, it will break down all of those solvents, and any other greasy/oily droplets that might've found their way onto surfaces, and is a standard way for cleaning items in a clean lab (you wash in solvent, then plasma clean the item).

IPA's ~70% water content serves the medical application where the water content causes the skin pores to open up to assist cleaning the skin.

The principal reason for not using a lint cloth for cleaning is that you can get fibres across the vacuum connections, which may create leaks. I use 'regular' IPA wipes you get for industrial purposes and you pull 6" squares of the stuff from the top of a cylindrical dispenser. (I generally buy out-of-date stuff that may have dried up a little - no problem, just open the top and spray in a load of IPA!) These are 'lint free' but still tend to be a little fibrous, so after cleaning with that I will wipe down the seals with 1mm packing foam that I have sprayed IPA on to.

Cheap as chips.

Then to plasma clean you want to run around 100 to 1000 microns at 1000V with minimum current to get a glow discharge (AC is better, RF induction is what the lab plasma cleaners use) and leave it like that for 10 minutes or so, then switch off the plasma and pump down to sub micron for a few hours.

You will never get rid of all the adsorbed water before you close the chamber up, so there is little point in trying beyond ensuring it appearing visibly dry. Just plasma clean, and pump!