Question

Why are the lower parts of ships and bridges coated with coal tar?

Answer 1

• Ships and bridges are made up of Iron.
• When a metal is exposed to the atmosphere in the presence of moisture, it reacts with Oxygen and water vapour present in the air to form its oxide which tarnishes the metal surface.
• The natural process, which converts a refined metal to a more stable form, such as its oxide, hydroxide, or sulphide is known as Corrosion.
• The process of corrosion of Iron articles in the presence of damp air is known as rusting.
• During rusting of Iron, a reddish-brown flaky layer will be formed on the surface of the Iron object which is known as rust.
• Ships and bridges are in direct contact with water. Moreover, salty water.
• The salt present in water increases the rate of rusting.
• Hence, coating with coal tar epoxy is done to prevent rusting.