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Galvanic Corrosion

Q. I have a concern for galvanic corrosion between a conversion coating of Aluminum and silver plated surface at the interface of a waveguide. Could you please let me know if there is a preventive method for this. Your prompt answer would be greatly appreciated.

Thank you,

T. Nguyen
- Montreal, Canada
2002

A. If it's all one piece, so there is no way to electrically isolate the two materials, I think you need to silver plate the whole thing or aluminum coat the whole thing.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

A. Aluminum and silver are a long way apart on the Electrochemical Series, even on opposite sides of Hydrogen, so that is why you have a problem. The Aluminum Chromate is slightly non-conductive, the thicker, darker, the less conductive. Properly sealed Anodizing would be 100% non-conductive.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2002

A. Sir,

Another possibility could be to encapsulate the assembly and extract humidity or any other liquid or gas to form a path for ions to migrate. I really don't know but I doubt either silver or aluminum will inter diffuse on each other in their solid state.

Guillermo Marrufo
Monterrey, NL, Mexico
2002

Q. Dear Sir ,

What is a galvanic corrosion ?

If a stainless steel flange is tightened with Galvanized bolts & nuts, what shall be the risk to SS flange? What shall deteriorate first? galvanized bolt or SS flange?

Regards

Kailash Bahuguna
EPC contractor - Baku, Azerbaijan
2005

A. Hi Kailash. A battery typically is built by putting two dissimilar metals next to each other with a salty conductive medium between them. As soon as you close a switch to provide a metallic path for electrons, through wiring and a light bulb or whatever, current begins flowing, made possible by dissolution of the less noble of the two metals of the battery.

If, in your piping system, you have two different metals and a conductive medium like water, or even moisture in the air, you have a battery. If the two metals are touching, the switch is permanently on and that battery is running. It will cause dissolution of the less noble of the two metals, which in this case is the galvanized steel bolts. First the galvanizing will go, then the steel bolts themselves will go.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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