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Gold Coating for high IR reflectance

Q. I need to coats some complex machined parts (aluminum) with a plating that will have a very high reflectance in the near IR spectrum (0.95 or better). Gold is an excellent reflector at the wavelengths I'm interested in so what I am considering doings is applying a gold plating over a Ni plating. However I want the reflected light to be diffuse so I have been experimenting with lightly bead blasting the aluminum prior to plating.

This coating has to last for several years (in a dry, clean slightly elevated temperature ~40-50 °C environment) and changes in its reflectance over this is unwanted.

I know I can achieve the finish I want in the as plated condition but I don't know what it will look like in a couple of years. Can anyone point out possible pitfalls to this approach, am I likely to see a deterioration in the finish over time?

Michael Martin
Quebec Canada

A. Hi Michael,

I don't have the specific information you need but we plate a lot of optics for NASA and various DOD agencies and what you are doing is a standard procedure for fabricating their grazing incidence X-ray mirrors. If their was a better method or material I think they would be using it. Gold is pretty inert in most environments.

Rick Richardson, MSF
Dayton, Ohio

A. Blasting the aluminum surface may set up stresses in the skin of the component. This may result in adhesion problem. Just dull soft nickel and dull soft gold should give the desired diffusing surface.

Yashawant Deval
electroplating shop - Pune, Maharashtra, India

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