Cathodic Protection: Understanding the Science Behind It

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In summary, the science of cathodic protection (CP) was developed in 1824 by Sir Humphrey Davy as a means to protect copper against corrosion from seawater. This process, known as sacrificial protection, involves the use of iron anodes which have a stronger reductive power than copper, causing them to oxidize in preference to the copper. This method can also be used for protecting metal pipes buried in the ground by connecting a more reactive metal, such as magnesium, to the pipe to corrode in its place.
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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?
 
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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.
 
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  • #3
Thank you, Hootenanny! To know the precise words is essential to search in google. I did find very useful information with "sacrificial protection". :approve:
 
  • #4
PPonte said:
Thank you, Hootenanny! To know the precise words is essential to search in google. I did find very useful information with "sacrificial protection". :approve:

My pleasure :biggrin:
 
  • #5
I have also heard to called "Sacrificial Anode".

A similar method can be used to protect metal pipes buried in the ground from corrosion. Let's 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.
 

1. What is cathodic protection?

Cathodic protection is a technique used to prevent corrosion of metal structures by making them the cathode of an electrochemical cell. This is achieved by applying a direct current to the metal surface, which causes a flow of electrons from the anode (a sacrificial metal) to the cathode, protecting the structure from corrosion.

2. How does cathodic protection work?

Cathodic protection works by creating a more negative potential on the metal surface, making it the cathode in an electrochemical cell. This is achieved by connecting the metal structure to a power source, such as a rectifier, which directs a direct current to the structure. This current causes a flow of electrons from the anode, which is typically a more reactive metal, to the cathode, thus protecting the structure from corrosion.

3. What are the types of cathodic protection?

There are two main types of cathodic protection: galvanic (also known as sacrificial) and impressed current. Galvanic protection uses a sacrificial anode made of a more reactive metal, such as zinc or magnesium, which corrodes instead of the protected structure. Impressed current protection uses an external power source, such as a rectifier, to direct a current to the structure.

4. When is cathodic protection used?

Cathodic protection is used to prevent corrosion in various industries, including oil and gas, transportation, and marine. It is also used to protect underground and underwater metal structures, such as pipelines, tanks, and ships. It is typically used in areas where traditional methods of corrosion prevention, such as coatings, are not feasible or effective.

5. What are the benefits of cathodic protection?

Cathodic protection offers several benefits, including cost-effectiveness, ease of installation, and long-term protection. It can also be used in conjunction with other corrosion prevention methods, such as coatings, to provide additional protection. Additionally, cathodic protection is environmentally friendly, as it does not require the use of harmful chemicals or materials.

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