Rusting and iron

• Rusting


  A brown, flaky, solid formed when iron reacts with oxygen and water
• Steel


  • An alloy of iron containing some carbon
  • Often used to construct bridges and many structures due to its strength
• Rusting


  Weakens the structure of iron and steel
• Prevention of rusting is very important economically and for safety
• Experiment to show oxygen and water are required for rusting

  1. Iron nail suspended by thread in water

  2. Boiled water in test tube 2

  3. Anhydrous calcium chloride in test tube 3
• Rusting will only occur in test tube 1 as the nail has access to both water and oxygen
• Rusting will not occur in test tube 2 as boiling removes the oxygen from the water
• Rusting will not occur in test tube 3 as anhydrous calcium chloride removes water vapour from the air
• Barrier methods to prevent rusting

  • Painting
  • Oiling or greasing
  • Plastic coating
  • Metal plating such as chromium
  • Alloying such as stainless steel
• Galvanising


  Coating iron in zinc to prevent rusting
• Sacrificial protection


  A more reactive metal is placed in contact with the iron, and the more reactive metal reacts first instead of the iron
• Metals suitable for sacrificial protection

  • Magnesium
  • Zinc
• The sacrificial metal has to be replaced as it corrodes over time
• Haematite


  The main ore of iron, containing iron oxide (Fe2O3)
• Extraction of iron from its ore in the Blast Furnace


  1. Haematite, limestone (CaCO3) and coke (C) added to the Blast Furnace

  2. Hot air blasted in at the bottom

  3. Carbon from coke burns in oxygen forming CO2

  4. CO2 reacts with more C to form CO (reducing agent)

  5. Fe2O3 reduced to Fe

  6. Limestone thermally decomposes to CaO and CO2

  7. CaO reacts with SiO2 to form CaSiO3 (slag)

  8. Molten iron and molten slag fall to the bottom, slag floats on iron
• The exhaust gases are mainly carbon dioxide and other unreactive gases from air