Galvanic Corrosion
Galvanic Corrosion in the Statue of Liberty
Introduction:
The Statue of liberty built by Gustav Eiffel and Frederic Bartholdi in 1886 was made of materials that consisted of a wrought iron framework with an outer cladding of copper attached by saddles of copper. It was pretty much anticipated that galvanic corrosion would occur so both of the metals were separated by an insulation known as “asbestos and shellac” insulation (Shellac is a natural resin that was widely used in the Victorian period as a lacquer or protective coating). However despite pre-emptive measures acidic rainwater soaked the insulation thus providing electrolytic conduction between metals which resulted in galvanic corrosion. The corrosion was detected in the 1980s when maintenance works were carried out, and it was found out that galvanic corrosion has taken place between the copper skin and the wrought iron support structure. The corrosion was so extensive that there was a concern the statue might collapse. As a result renovation works had to be done in 1986 where the wrought iron framework was replaced by stainless steel which did not corrode in the presence of copper, coated in a layer of PTFE insulation.
Problem analysis:
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. Since different metals have differing electrode potentials, when any two metals are in contact and there is an electrolyte present, then a galvanic couple is setup whereby one metal acts as a cathode and the other as an anode. The anode dissolves into the electrolyte hence resulting in corrosion and causing damage to structure
The culprit for damaging the statue of liberty is “crevice corrosion” because the corrosion only occurs at the contact patch at the junction where the two different metals meet. A crevice is then formed where the attack get concentrated making deeper
Introduction:
The Statue of liberty built by Gustav Eiffel and Frederic Bartholdi in 1886 was made of materials that consisted of a wrought iron framework with an outer cladding of copper attached by saddles of copper. It was pretty much anticipated that galvanic corrosion would occur so both of the metals were separated by an insulation known as “asbestos and shellac” insulation (Shellac is a natural resin that was widely used in the Victorian period as a lacquer or protective coating). However despite pre-emptive measures acidic rainwater soaked the insulation thus providing electrolytic conduction between metals which resulted in galvanic corrosion. The corrosion was detected in the 1980s when maintenance works were carried out, and it was found out that galvanic corrosion has taken place between the copper skin and the wrought iron support structure. The corrosion was so extensive that there was a concern the statue might collapse. As a result renovation works had to be done in 1986 where the wrought iron framework was replaced by stainless steel which did not corrode in the presence of copper, coated in a layer of PTFE insulation.
Problem analysis:
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. Since different metals have differing electrode potentials, when any two metals are in contact and there is an electrolyte present, then a galvanic couple is setup whereby one metal acts as a cathode and the other as an anode. The anode dissolves into the electrolyte hence resulting in corrosion and causing damage to structure
The culprit for damaging the statue of liberty is “crevice corrosion” because the corrosion only occurs at the contact patch at the junction where the two different metals meet. A crevice is then formed where the attack get concentrated making deeper
References: http://openlearn.open.ac.uk/mod/oucontent/view.php?id=397857&section=2.4 http://www.corrosion-doctors.org/Landmarks/Statue.htm http://en.wikipedia.org/wiki/Galvanic_corrosion#Statue_of_Liberty