Redox Corrosion: Explaining HMS Alarm's Surprising Results

[futb0l]

Anyways, can anyone help me with this question..

In 1763, the British Admirality covered wooden ship HMS Alarm with copper sheeting to protect it from marine worms. This was sucessful but, they reported: '... we were surprised to perceive the effect of the copper had upon iron where the two metals touched... the nails and staples... were found dissolved into a rusty paste.' Briefly explain this occurrence and how it might have been prevented.

This should be easy for you guys...

I know that both the metals undergo wet corrosion, but I don't know anything about the effect on having the two metals in contact.

 

[Nate810]

This phenomenon is known as galvanic corrosion. It occurs when two different metals are in contact with each other in an electrolyte, such as saltwater. In this case, the copper sheeting and iron nails and staples created a "battery" which caused an electric current to flow between the metals. This caused the iron to corrode much faster than it would have otherwise. To prevent this, they should have used some form of insulation, such as a rubber pad or coating, between the copper and the iron. This would have prevented the flow of electricity and the accelerated corrosion.

 

[quicknote]

Redox corrosion, also known as galvanic corrosion, is a type of corrosion that occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte (such as seawater). In this case, the copper sheeting on the HMS Alarm acted as the anode and the iron nails and staples acted as the cathode.

When two dissimilar metals are in contact, an electrochemical reaction occurs where the more reactive metal (iron in this case) loses electrons and undergoes oxidation, while the less reactive metal (copper) gains electrons and undergoes reduction. This leads to the corrosion of the more reactive metal (iron) while the less reactive metal (copper) remains protected.

To prevent this type of corrosion, the two metals should be electrically isolated from each other, either by using a non-conductive material between them or by using a sacrificial anode (a more reactive metal that will corrode instead of the protected metal). In this case, the British Admirality could have used zinc or magnesium as a sacrificial anode to protect the iron nails and staples from corrosion.

In addition, proper design and maintenance of the copper sheeting could have also prevented this type of corrosion. For example, ensuring that there are no gaps or cracks in the copper sheeting and regularly inspecting and replacing damaged areas can help prevent the electrolyte (seawater) from coming into contact with the iron nails and staples.

In conclusion, the surprising results observed on HMS Alarm were due to redox corrosion, where the copper sheeting acted as an anode and the iron nails and staples acted as a cathode. This could have been prevented by using proper isolation techniques or sacrificial anodes, as well as regular maintenance and inspections.