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Plating aluminum mirrors with copper

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I am fabricating 6 inch dia. aluminum mirrors and would like to plate them with copper. I have never electroplated anything in my life before but have brushed up on my university electro chemistry. I tried a sample piece of polished aluminum with copper sulfateamazoninfo solution and a battery chargeramazoninfo but the build up was very pulpy and did not adhere to the aluminum surface, flaking off when I tried to polish it to a smooth finish.
What can I do to produce a mirror like quality smooth layer of copper over my aluminum blank?

Any and all suggestion greatly appreciated.

Thank you

Note: These mirrors will be used to reflect IR (heat) from an oven to focus the energy and may be operating at a very high temperature.

Dr. A. Dovigi
- Canada


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Dr. Dovigi:

The surface of aluminum items almost instantly oxidize, so that the surface is not active and not amenable to plating. A solution is to zincate the item first, replacing the aluminum surface with a zinc surface, which is plateable. Even then, copper is far more noble than zinc and will immersion deposit pulpy and non-adherently from a copper sulphate solution. You would need to cyanide copper plate or copper pyrophosphate plate before you do the acid copper. There is a lot to the process, and you'll need to read a few chapters on this from the plating texts before starting.

Even then I question whether you are approaching things the best way. Usually, infrared reflectors are bright dipped, anodized, and gold dyed, rather than copper plated. It's simpler, less expensive, more reliable.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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Dear Ted,

Thank you for your reply and information. I know a gold surface is a much better reflector at infrared wavelengths. The only reason for using copper was to try and keep the costs down. Being a dentist I have worked with gold foil and considered this an option to plate the finished surface of the mirror blank, but again I ran into the problem with the gold foil not adhering to the aluminum surface. Now that you have explained why (aluminum oxide coating forming)I understand why this failed as well. Can you offer any suggestions on the most cost effective way to go about plating my mirrors?

Thank you Al

Dr. A. Dovigi
- Canada


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Sir,

As an anodizer I agree with Ted........hardly any of the platers I know plate on Aluminum. We process many reflectors here with bright dip and clear and colored anodize.

David A. Kraft
- Long Island City, New York

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Thank you for your reply and information on trying to electroplate aluminum with copper and why I failed. I have also tried to coat the aluminum surface with gold foil but it failed to adhere to the surface. I understand now the oxide coating is the source of the problem.

Any suggestions on how to over come this problem and to coat the reflecting surface of my aluminum mirror with gold foil?

Thank you

Note this mirror will be operating at high temperatures, will thermal cycling pose a problem with adhesion?

Dr. A. Dovigi
- Canada


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i have a brush plating system and do gold and chrome plating of car emblems, my question is how can I gold , chrome or nickel plate aluminum emblems or motorcycle parts using a brush system.

also where may I get info on designing brush plating equipment and tank plating systems

ted izzo



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Plating on aluminum requires, as a minimum, a zincating step. Your supplier, or the brush plating suppliers listed at www.finishing.com/chemicals, can provide zincate. The actual process is to clean the aluminum, etch it with caustic, desmut with acid, zincate, cyanide copper plate, nickel plate, then gold or chrome.

I don't know of any articles that tell you how to design brush plating systems, but
- The Electroplating Engineering Handbook, edited by Larry Durney is all about designing tank plating systems, and
- Rubinstein's Electrochemical Metallizing is an encyclopedia of info about brush plating.
pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey


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All of the major brush plating vendors have methods for plating on aluminum.

At least one vendor has a procedure for plating on aluminum (simple shapes) without the zincate and claims good adhesion. You have to be quick and good to do it however.

James Watts
- Navarre, Florida

misc. plating stuff
For Sale cheap



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I am with a company active in HF PCB as electromagnetic field radiators. These boards have very few soldering points and therefore I laminated plastic substrates with aluminum foil instead of expensive copper. My idea was to plate copper 1-2 microns thick after etching off the extra aluminum on the sides of the board leads.

The etching shop that supports our R&D initially was positive about prospects to have another massive project in a little while, but after three weeks of experimenting is not giving me anything.

Meanwhile I learned of a "Aluminum Bonder" - material that allows copper built up on the brushed with it aluminum.

Will appreciate any kind of advice, offer to cooperate.

(Mr) Valery Ostrovsky
- Rosh Ha'Ayin, Israel


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Dear Mr. Ostrovsky,

Thank you for your letter.

It sounds to me that you want to make the circuit paths of a wiring board using aluminum, and you just want to plate "tabs" at the soldering points using some kind of copper plating. Using a robust activation system using a metal cleaner, then a zincate as you describe as the aluminum bonder, followed by an aluminum tolerant electroless nickel, then a electroplated copper, then electroplated tin should provide a solderable surface for your connections.

Regards,

Tom Pullizzi
Falls Township, Pennsylvania 

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