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Anodizing in a vacuum chamber

Using hard anodized aluminum in certain applications in a high vacuum chamber and found that the anodized surface is porous enough to absorb moisture and affect pump down times. Currently we are specifing MIL-8625F, Type III, Class 2 .001 thick. Would would like to know if there is a "sealer" for the porous anodizing film and how is this specified?

Myron Moreno
Capital Equipment - San Jose, California, USA
2004

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Hello,

Sealing is a standard part of Type II anodizing but isn't often used for Type III because it decreases the hardness. But, if you specify on your purchase order that you want the parts sealed, your anodizer should be set up to do that. The typical sealing baths are hot water, nickel acetate, and sodium dichromate -- If it matters to you which is used, make sure to specify that as well.

Sealing hydrates the aluminum and, essentially, swells the pores closed preventing further absorption. To the best of my knowledge, none of the parts that I anodize are used in a vacuum, so I'm not sure if you will have any problems with outgassing or not.

Good luck.

Jim Gorsich
Compton, California, USA
2004

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In follow up to my earlier post, you may want to check letters 29885 and 22543.

Good luck.

Jim Gorsich
Compton, California, USA
2004