Outgassing of anodized aluminum 2

[SachaChou]

Can anyone supply any data on the chemical composition of outgassing products from anodized aluminum?

 

[nairbo]

SachaChou~

A bit confused do you mean during anodising or during subsequent processing ??

Regards Nairbo

 

[kenvlach]

Details on the anodizing would help:
Anodize solution (boric, chromic, oxalic, phosphoric, sulfuric, mixture, other…)?
Dyed (organic, metallic) or non-dyed?
Seal type (DI, steam, dichromate, Ni acetate, fluoride, other) and temperature, or unsealed?
What temperature and vacuum are you outgassing at?

In any event, I would only expect a little water vapor up to ~150^oC.

I haven’t seen data for vacuum applications, but there is quite a bit on the lighfastness of various dyes (sealed) and some on the temperature stability, so maybe this will help.
At 200^oC, you might see breakdown products of some of the less stable organic & organometallic dyes. Some dyes are pretty complex (C, H, N, O, S, metal); I wouldn’t guess at possible decomposition products.
The most stable organic & organometallic dyes will last up to 300^oC. Possibly, some seal components would react with dye and water molecules within the pores and give additional reaction products.
Some metallic/inorganic dyes are stable to the melting point of aluminum.

 

[SachaChou]

Unfortunately I am not producing the anodized coating so I do not know the nature of the treatment used to produce it. I am using parts that have a black dyed anodized coating. I am concerned that there may be outgassing of volatile chemicals from the anodize process (at room temperature and atmospheric pressure) into an enclosed volume, harming the product within. I am concerned about ppm levels of acidic, organic or similar compounds that may be released from the surface. anyone have any data?

 

[kenvlach]

"at room temperature and atmospheric pressure" (with some humidity) you shouldn't have a problem. The pores and surface of anodic coating (almost entirely aluminum oxide) are sealed with an aluminum hydroxide known as boehmite. The boehmite is highly stable at room T, and if baked, it would only give off water vapor, anyway.

I found a mention of anodized aluminum oxygen regulators being used in the medical industry (i.e., for breathing), and statements that undyed anodize is acceptable to the FDA.

http://www.finishing.com/108/81.html

To alleviate worries, I suggest running all the anodized aluminum parts through a steam autoclave.

 

[usjbh]

Organic dyes are typically used for most color anodizing and usually processed per MIL-A-8625D Type II (sulfuric). There are at least six or more different black dyes that can be specified for black color anodizing. Contact Orco for more information about your actual application to determine if the right dye is used by your supplier

http://www.organicdye.com/anodizing.asp

Most performance measures for color anodizing are for U.V. stability rather than outgassing. I suspect outgassing could be a problem for color anodized parts exposed in high vacuum and definitely for high intensity U.V. light environments. Stability is based on not only which dye is used but also with the anodized thickness and sealing method, both of which can be managed somewhat with the specification. Your concern about ppm levels can only be satisfied by testing in the extreme conditions of exposure and collecting sample that can be analyzed using Mass Spectrometric analysis. PPB levels should be easily detected.
When we have a critical application area, clear Type II anodizing or MIL-A-8625D Type I (chromic or Type III hardcoating)is usually specified. Color anodizing is usually treated as a decorative element and as such could pose potential problems only when it detracts from appearance or contaminates a sensitive environment.