Preventing Corrosion

Rusting is a type of corrosion and there are two main methods for preventing it:

  • Barrier methods
  • Sacrificial methods

Barrier Methods

Rusting occurs when iron reacts with oxygen and water.

an oxygen cloud + a water droplet + a piece of iron with an arrow pointing to a rusted piece of iron.

Therefore, we can prevent rusting by creating a barrier that prevents iron from coming into contact with these elements. Some common barrier methods are:

  • Paint – Suitable for large iron surfaces, such as ships
  • Grease or oil – Ideal for moving parts, such as bicycle chains
  • Plastic cover – Offers an additional protective layer

Another form of barrier protection is electroplating.

Electroplating

Electroplating is a process in which an object is coated in a thin layer of another metal to prevent it from rusting. This improves the corrosion resistance of the metal and makes it more durable.

When electroplating iron or steel, the cathode is the iron or steel object, the anode is the plating metal, and the electrolyte contains ions of the plating metal.

Sacrificial Methods

Sacrificial protection is a method that involves covering iron with a more reactive metal, such as zinc, to prevent rusting. If the zinc layer is exposed to oxygen, it will be oxidised instead of iron because it’s more reactive. This protects the iron underneath.

Unlike barrier methods, even if the zinc layer is scratched and the iron underneath is exposed, the zinc will continue to react with nearby oxygen. This is due to its higher reactivity. Therefore, zinc essentially sacrifices itself to prevent iron corrosion. This phenomenon is known as sacrificial corrosion.

  • The process of coating iron with zinc is called galvanising

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