During a maintenance check in the 1980’s, it was discovered that the Statue of Liberty had a serious case of Galvanic Corrosion. The structure’s internal wrought iron support system was rusting over because the insulating layer of shellac between the iron and copper had failed. After a labor-intensive restoration that required complete disassembly Lady Liberty was good as new.

This type of Corrosion can happen to any application with two dissimilar metals. To help you avoid galvanic corrosion in your next multi-Metal application, here’s what you need to know:

What is galvanic corrosion?
Galvanic corrosion is an electrochemical reaction that occurs when two dissimilar metals make contact in the presence of an electrolyte like sulfuric acid or sodium acetate.

It’s similar to the way a battery works: the presence of an electrolyte allows a conductive path to form between the two metals. This path allows for metallic ions to migrate from the anode (positively charged metal) to the cathode (negatively charged metal), thus weakening the anode and making it more susceptible to rust.

Why does galvanic corrosion occur?
Galvanic corrosion occurs because each metal has its own electrical conductivity potential. It’s this difference in electrode potential that drives the corrosive attack on the positively charged metal (anode), forcing it to dissolve into the electrolyte.

Which factors contribute galvanic corrosion?
Different metals react differently to natural elements and to the environment they’re ultimately installed in. For example, steel becomes less resistant to corrosion-causing electrolytes when it’s installed in a high temperature or high humidity environment.

Concrete is also a big consideration when it comes to galvanic corrosion. The sodium acetate  that’s used to seal concrete and protect it from weathering elements can cause galvanic corrosion in metals installed in or around it.

What are the best methods for preventing galvanic corrosion?
In order to prevent galvanic corrosion from becoming an issue, you’ll need to separate the metals electrically using non-conductive materials. This stops ion migration and keeps each metal intact. Here’s what you can do:

• Separate metals with an insulator like plastic
• Use water-repellent compounds like grease to prevent contact with electrolytes
• Consider electroplating–this uses noble metals that resist corrosion better.
• Apply cathodic protection
• For aluminum and copper, apply antioxidant paste

Alternatively, you can also choose metals with similar electrode potentials if appropriate for you application. You can also check out this galvanic corrosion chart to see which metals are most susceptible to it:

If you need further information about the corrosive properties of the metals we use in our products, please give us a call at (631) 750-3000.