Steps to Control Rusting
The use of a metal which is less electropositive
- The plating of iron with a thin layer of a metal which is less electropositive such as tin, silver or copper will prevent the iron underneath it to react with water and air, and so prevents the iron from rusting.
- However, the rusting of iron will occur faster if the protective layer is scratched. This is because iron is more electropositive than tin, silver or copper. The plating of iron by tin is used a lot in the making of tinned food.
The use of a metal which is more electropositive
- Metals which are more electropositive are used as a sacrificial metal to prevent corrosion on metals which are less electropositive. The metal which is more electropositive corrodes and acts as the anode.
- The less electropositive acts as the cathode and is protected from corroding. This method is known as the cathode protection or electrochemical protection.
Cover by paint, oil and grease
- A layer of paint, oil/grease, or plastic that is used to cover the surface of iron from contact with air and water in the atmosphere. So, rusting can be avoided. For example,
- Protection by a layer of paint usually is used for iron and steel objects like cars, ships, bridges and other things which do not undergo friction during use.
- Protection by a layer of oil/grease is used for part of machinery that move.
- Protection by plastic is used for daily items at home like clothes hangers and fencing.
- Alloying of iron can prevent rusting. For example, when iron is alloyed with chromium and nickel to form stainless steel, the layer of chromium oxide that is hard, strong and difficult to crack on the surface of the iron alloy prevents the iron from rusting.