Preventing Corrosion
Chemistry: Cambridge International GCSE Supplement, topic 9.5.2
Preventing Corrosion
There are three main methods used to stop metals corroding.
Coatings
- We can prevent corrosion by applying a coating that acts as a barrier, such as greasing, painting or electroplating.
- E.g. Aluminium has an oxide coating that protects the metal from further corrosion by preventing the metal's surface coming into contact with oxygen and water.
- A disadvantage is that any damage to the coating will lead to the metal becoming exposed and so corrosion will take place.
Sacrificial method
- In the sacrificial method, a metal that requires protection will have a more reactive metal attached to it.
- The metal is attached to a more reactive metal and the more reactive metal will undergo oxidation, leaving the less reactive metal intact.
- This means that water and oxygen will stop reacting with the protected metal as they are too busy reacting with the sacrificial metal!
Galvanising
- Galvanising is a hybrid of coatings and the sacrificial method.
- The metal that needs protecting is sprayed with a more reactive metal (e.g. zinc).
- This initially acts as a coating.
- If the more reactive metal is damaged, it will continue to protect as a sacrificial metal.