Carbon Vacuum chamber or epoxy

I might consider plating the chamber. Don't epoxy coat it if you are going to 10^-6 Torr range.

Epoxies all out-gas. This is the vacuum level that materials for spacecraft applications are tested at.

Maybe it wouldn't be a problem for your process, but........

This from NASA spacecraft materials document.

"The outgassing test is conducted
in a vacuum of 10-6 Torr at a temperature of 125o Centigrade with a test exposure time of 24
hours. The equipment and test procedures required to conduct the outgassing test are defined by

ASTM E-595-77/84."

They gather to outgassed materials on a 25 degree C cold plate, and weight them.

Plating sounds good, but with what? Chrome?

Are we talking infiltration from seepage thru the metal or the steel losing the carbon/impurities or ???

How is the seal designed? What material is used?

Have you determined what the material on the "white glove" actually is?

What about coating the outside? Shot peening the inside?

I am curious about this as I am planning to build a chamber.

Good questions. Carbon from the steel is not even a concern at this point, the chamber has years of backstreaming hydrocarbon build up, from a Lesker all purpose oil that turned out be very bad at backstreaming in diffusion pumps and worse it breaks down into a hydrocarbon soot. He told me he had cleaned that stuff a few weeks ago but I know that it's still their.

The other stuff caked on the forward part of the chamber is aluminum and some cobolt on the mid section of the chamber walls. I think we would see a massive improvement if we just cleaned all the soot material so that the chamber can pass the white glove inspection.

The seals are Buna o-rings. At the moment the chamber can reach 1.4*10^-5 Torr.

Shot peening?

All sputtering, CVD, etc equipment I worked are made of SS. The gaskets are also of not ordinary rubber. Hence you go for metallic coating (Electro or Electroless). Small quantity of epoxy like Araldite may be used but it is to plug small leaks, not full coating as -6 torr is high vacuum.

I agree. The only question I have at this point is; what do I plate it with?

The only thing I found that makes sense to me is chrome.

Hi,

carbon steel is a bad choice as there is inevitably some rust on clean surfaces and if not clean then some hydrocarbons. I saw new rust showing on freshly cleaned surfaces within 30 seconds!

So your idea of over-coating is quite ok.

This over-coating with low-outgassing epoxy will not seal any of the pores or through-leaks that may exist. But prevent the surface from too much water-absorption.

If staying with epoxy: look for NASA or ESA tested material with low outgassing after baking. Baking is mandatory for any good high-vacuum system.

(Glue with high temperature epoxy and some silicon-carbide fine grit (800) as filler a series of power-resistors on the outside, equal intervals of 20 cm (8 inch) if 5mm thick walls 10 cm if 10 mm thick walls of carbon-steel. Distances 3fold larger with Aluminum and 3fold smaller with stainless-steel. Heat with AC or DC to 130°C outside temperature at pump-down, switch to natural or forced cooling to obtain best vacuum. First of first pump-down: 24h heated!) At this temperature VITON is no longer a good seal material, there will be considerable leaking-through but with cooling it will be good again and then better then before.

We used Araldite 2020 because of its very low viscosity for reworking large seal surfaces: a thin layer (0.1mm) between a flexible highly polished metal-foil and aluminum chamber-walls (20 mm thickness) gave us a much better sealing surface (for a gate valve and for matching doors to chamber sides with VITON O-rings) than anything that is commercially available. The system could be pumped down to a little below 10^-6mbar in 3 hours with 200 l volume and a 450l/s turbo-molecular pump and a 4m³/h pre-pump.

I would consider: to rebuild the entire chamber with Al (we used 2017).

If not suitable then sandblast to naked surface (two steps with in-between to be cleaned sand by heating up to 600°C to crack any hydrocarbons), coat - the thinner the better with a low outgassing epoxy and cure this at the highest allowed curing temperature -( minimum 30°C above the later to be used highest outgassing temperature.) Make sure that at sandblasting the total chamber is at elevated temperature as only this will prevent any super-fast rusting.

This will give you a low corrosion surface - good for 10^-6 mbar, but any material defects will not be sealed as any epoxy is not tight at this pressure.

Have success

RHABE

I did some work for this guy in Toronto Ontario that does some aluminum deposition. I rebuilt one of there pumps and when they hooked it back up they couldn't get it to pull the vacuum needed. So anyways we went down to this place to find out what was going on with this pump. When they brought me to it (Stokes 212 piston pump with a Edwards EH500 Booster pump) I took a look at the flanges and the chamber and these guys had multi-coloured play dough covering all of the joints to try and make the system leak tight. They even had play dough on the welded seems of the chamber. I do have to say though that when I changed there gasket between the pistin pump and booster they were running were they needed to be. Play dough worked for them I just don't know how great of an idea that is. lol

Play dough, now that's an interesting solution. I prefer using JB Weld, Tor Seal or it's Loctite equivilent, which is much, much cheaper. In either case I'll keep that in mind if everything else fails.

Hi,

anything like Loctite - if this is one of the Cyanoacrylates or similar these are not a good choice as the temperature limit is much too low and the curing is often with some cracking: leaks.

Stay with high-temperature, low-outgassing epoxy!

Also change the seal-rings to Viton - most important. If no possibility then try to cool the rubber O-rings to near zero °C.

First action: as above recommended: clean carefully from any deposit.

Chrome or Nickel plating: very often (usually) has pores with entrapped electrolyte: gas, gas, gas for nearly unlimited time!

RHABE

Loctite the brand makes an epoxy product that is the equivilent of Varien Torr Seal, but cost a fraction of what Tor Seal costs. It's called Hysol 1C and 1C LV.

Thank you,

good information.

RHABE