Corrosion

What is corrosion?

• Corrosion is a process of formation of the compound of pure metal by the chemical reaction between the metallic surface and its environment.
  • It is an oxidation process which means it causes the lost of metal.
• This reaction degrades metallic produces leading to reduction in their thickness and also the loss of important properties such as malleability, ductility, and electrical conductivity.
• Here are some examples of corrosion.
  • The rusting of iron which becomes oxide hematite.
  • The tarnishing of silver which is converted to silver sulfide.
  • The conversion of copper which turns into green copper carbonate (malachite).

Why do metals corrode?

• Most metals tend to spontaneously react with substances in the environment.
• Metals that are very unreactive such as gold and platinum are called noble metals.

Factors Influencing Corrosion

• There are many factors that influence the development of corrosion.
• Corrosion is enhanced by the presence of:
  • Impurities
  • Air
  • Moisture
  • Electrolytes
  • Strain in Metals
    • Dents
    • Scratches

Effects of Corrosion

• Corrosion has many significant effects on metals.
  • It reduces its strength.
  • Its lifetime is reduced.
  • Metallic properties are lost.
  • Metal is wasted.

Examples of Corrosion

• Some examples of corrosion include:
  • Microbial corrosion
  • Galvanised surfaces
  • Rust
  • Gold nuggets

Rusting

• Rusting is the corrosion of iron. Rusting results in the iron object becoming weaker.
• Both oxygen (from air) and water are required from rusting.

Corrosion Reactions

Word Equations

• Metal + Oxygen → Metal Oxide
• Aluminium + Oxygen → Aluminium Oxide

Preventing Corrosion

• To prevent corrosion, the following methods can be used.
  • Painting
  • Greasing
  • Electroplating
  • Galvanising
    • Adding a more reactive layer of metal on top of the desired preserved metal.
  • Tin-Plating
  • Coating with Plastic