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topic 11816

Optical matt-black finish on aluminium


(2001)

We are building a satellite (a student project, as follow-on to SUNSAT 1,) and have problems in obtaining a matt-black finish on some of the aluminium (7075) parts of a telescope (lens mounting rings and baffle).

Lord Corp. Aeroglaze Z306 will work for the baffle, but the mechanical engineers would like to Anodize some of the internal parts of the telescope, as they are scared that Z306 might outgas, and being close to the CCD, might condense on it. The baffle, being an open structure, can vent to the 'outside' and even if some (however little) condensation does take place on the exterior first lens element, is would not be on a focused surface (as would be the case with the CCD).

The problem is how to obtain a matt-black, non-reflective anodize surface. The normal dyes used to color anodize Al. Black is organic, which is likely to outgas and might not be stable under UV exposure.

Do you have any experience or suggestions in this regard?

Kind regards,

Francois Strumpfer
electronics systems lab. - Stellenbosch (near Cape Town), South Africa


(2001)

Dear Francois,

There are dyes that are commercially available that have excellent lightfastness characteristics. There are also inorganic dyes that are available in black. As for your requirement for a matte finish, this can be achieved by using a proper etch prior to anodizing. If there is a specific reflectivity requirement, then I would suggest processing some test panels prior to actual production.

Best of luck.

Ira Donovan, M.S.F.
Kansas City, Missouri


(2001)

Hi,

We once did some satellite bits for a space telescope.

We used nickel acetate dip then ammonium sulfide to convert the nickel to nickel sulfide.

It works but take my advice and do not try this method, the hydrogen sulfide gas is toxic and the stuff of stink bombs.

As it worked out the parts never got to space due to the rocket having the wrong control system and was blown up.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


(2001)

Dear Francois,

I would suggest using the two step (non fade) inorganic black anodize or the Type II black anodize finish. Are there specific reflectivity and emissivity requirements? If so, you should run some test panels and check the optical readings. We at Highland have plated and anodized baffles, propulsion systems, field rings, field stops, etc.. We helped many engineers, like yourself, achieve the right amount of thermal control. We have optical instruments in house that can take the reflectivity and the emissivity readings. Depending on the process and the material, you can achieve anywhere from 0.05 - 0.3 reflectivity and 0.85 to 0.9 emissivity reading. Let us know if we can help. You can email me or call me.

Best Regards,

Andrew Boussarath
- Los Angeles, California, USA



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