The Statue of Liberty
The Statue of Liberty was first assembled in Paris in 1884, then disassembled and reassembled in the United States at what is now called Liberty Island. Beginning in July 1981, a series of inspections was conducted by the National Park Service and by an International team of engineers and architects. Over a dozen problem areas needing attention were identified:
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Rust stains on the exterior copper skin |
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Severe corrosion of some small areas of the copper skin |
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Deterioration of the torch |
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Degradation in the crown area and spikes |
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Structural concerns in the shoulder of the torch arm |
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Corrosion of the iron armature |
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Paint peeling on the interior copper skin and support structure |
The problem that most necessitated the restoration of the Statue of Liberty was galvanic corrosion of the iron armature in contact with the copper skin. Galvanic corrosion occurs when dissimilar metals are in electrical contact in the same electrolyte. The difference in electrochemical potential between the dissimilar metals (iron and copper) is the driving force for electrolysis, whereby the armature, forming horizontal anodes at an accelerated rate. The iron armature, forming horizontal and vertical ribs against the copper skin, and the attachment mechanism, whereby copper saddles (which are flush riveted to the copper skin) surround the iron armature, provided a configuration conducive to galvanic corrosion.
Since all of the iron armature was interconnected, only one location of physical contact to the copper skin was necessary to provide electrical continuity to the copper throughout the Statue. The designers of the Statue had tried to prevent this galvanic coupling by insulating the two materials with asbestos cloths soaked in shellac. This was only a temporary barrier that became porous with age and provided electrolytic continuity by wicking and capillary action.
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