10.3.1

Corrosion

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Corrosion

Corrosion describes the gradual destruction of metals because of chemical reactions between metals and the oxygen and water around them. The rusting of iron is an example of corrosion:

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Rusting reaction

  • Iron + oxygen + water → hydrated iron(III) oxide
Illustrative background for Rusting experimentIllustrative background for Rusting experiment ?? "content

Rusting experiment

  • Take a boiling tube and put an iron nail inside under three different sets of conditions and see if it rusts:
    • Only water - no rust.
    • Only air - no rust.
    • Air and water - rust.

Preventing Corrosion

There are three main methods used to stop metals corroding:

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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.
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Sacrificial method

  • In the sacrificial method, a metal that requires protection will have a more reactive metal attached to it.
  • This means that water and oxygen will stop reacting with the protected metal as they are too busy reacting with the sacrificial metal!
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Galvanising

  • Galvanising is a hybrid of coatings and the sacrificial method.
    • The metal that needs protecting is sprayed with a more reactive metal. This initially acts as a coating.
    • If the more reactive metal is damaged, it will continue to protect as a sacrificial metal.

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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