hard anodized aluminum in high-vacuum?

[Trix4kids]

I am trying to use a linear guide for a door in a vacuum chamber. It is aluminum with a clear hard anodize surface. The pressure of the chamber will be 3x10-5 Torr and Temp. will be 150F. I was told not to use anodized aluminum because of its porosity but it doesn't make much sense to me. I believe the guide should be fine in the chamber. Any comments?

 

[Trix4kids]

By the way, the guide is .25x.75x72". Will this cause high outgassing and why?

 

[IRstuff]

That's probably correct.

Anodic and chemical treatments tend to "mess up" the native surface of the aluminum at the molecular level. This tends to create more sites for trapping atmospheric gases thereby making it harder to pump down and potentially resulting in more outgassing.

TTFN

 

[JimMetalsCeramics]

The porosity will create virtual leaks. The entrapped gasses will slowing outgas as you pump down. This might make achieving high vacuum take longer.

 

[vacuumsage]

jimmetalsceramics and irstuff are quite right, but you are only attempting to get down to 3X10-5, and that is not very difficult, especially if you have a big enough pump. If you haven't bought your linear guide yet though you might want to consider finding something else. It's better in the long run. Try

http://www.nor-cal.com

for vacuum parts, or

http://www.lesker.com

may have some alternatives.

 

[garyjMRC]

I have a similar problem, I'm planning on putting an anodized aluminum structure in a high-vac chamber. I've been told (but seen no proof) that the problem I'll have is that the water vapor that gets trapped in the surface pores will carry off the Nickel Acetate sealant and coat other surfaces in the chamber. Has anyone run into this before?

 

[vacuumsage]

I don't know about carrying off the sealant, that doesn't sound too plausible, but if you are in aerospace and this is a coating application, you run a very high chance that the outgassing water vapour (and there will be plenty of that if you are trying to get below 2.0X10-5 torr) will either slow down your pumping time very dramatically, or even worse will contaminate any films you might be trying to deposit. Your best bet is to make any structure out of 6061 aluminum, which is easy to clean, machine and all that, or even better stainless steel (304 is often the alloy of choice).