Cathodic protection

PPonte

The science of cathodic protection (CP) was born in 1824, when Sir Humphrey Davy made a presentation to the Royal Society of London: "The rapid decay of the copper sheeting on His Majesty's ships of war, and the uncertainty of the time of its duration, have long attracted the attention of those persons most concerned in the naval interest of the count. ... I entered into an experimental investigation upon copper. In pursuing this investigation, I have ascertained many facts ... to illustrate some obscure parts of electrochemical science... seem to offer important application." Davy succeeded in protecting copper against corrosion from seawater by the use of iron anodes.

What did iron do to protect copper?

1. I know it has a stronger reductive power than copper, which means it has more tendency to oxidize.

Question: So, iron reduces O₂ and H₂O instead of copper? Or does it also reduce the copper that oxidized?

Could someone explain me what really happens?

Hootenanny

Basically, the process is know as sacrificial protection. It is used on oil rigs were they bolt blocks of magnesium to the steel structure. Iron is more reactive than copper (greater reducing power) and is so oxidised in preference to the copper. The iron need not completely cover the copper, it only need tobe in contact with it so that it can transfer its electrons. A google for "sacrificial protection" will probably yield all the information you required.

PPonte

Thank you, Hootenanny! To know the precise words is essential to search in google. I did find very useful information with "sacrificial protection".

Hootenanny

Quote by PPonte

Thank you, Hootenanny! To know the precise words is essential to search in google. I did find very useful information with "sacrificial protection".

My pleasure

mrjeffy321

I have also heard to called "Sacrificial Anode".

A similar method can be used to protect metal pipes buried in the ground from corrosion. Lets say you have an Iron pipe which would normally rust/corrode away when burried underground and exposed to the elements. In order to keep from having to constantly dig up and replace piping all the time, you can electrically connect a sacrificial anode made of some more reactive metal than Iron to the pipe (say Magnesium). Doing this will cause the Mg to corrose away before the Iron pipe begins to rust.

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PPonte	Thank you, Hootenanny! To know the precise words is essential to search in google. I did find very useful information with "sacrificial protection".