corrosion and alloys

• brass - copper and zinc

  uses: hinges, electrical plugs
• gold in jewellery usually has silver, copper and zinc
• solder - lead and tin

  uses: joining metals
• bronze - copper and tin

  uses: castings and bearings
• duralumin - aluminium, copper and other metals.

  aircraft manufacture
• iron:

  steel - alloys with a mixture of iron and carbon

  low-carbon steels are easy to shape, high-carbon steels are hard to shape. stainless steels are resistant to corrosion
• corrosion - destruction of materials by chemical reactions with substances in the environment
• rusting equation


  iron + oxygen + water --> hydrated iron(III) oxide (rust)
• rusting of iron is a redox reaction. iron loses electrons when it reacts with oxygen. oxygen gains electrons when it reacts with iron.
• oil, grease and paint prevent corrosion - they keep out oxygen, water or both so rusting can't happen.
• paint is ideal for large and small structures, it is also colourful.

  oiling or greasing has to be used whne moving parts, like on bike chains.
• tin plating is when a coat of tin is applied to the objects. the tin acts as a barrier to steel, stopping water and oxygen from reaching the surface of the metal. if the tin is scratched to reveal some of the metal, it will start to corrode
• sacrificial method


  you place a more reactive metal with the metal you don't want to corrode. the water and oxygen then react with the sacrifice
• Galvanising


  a coat of zinc is put onto an iron object to prevent rusting. the zinc acts as the sacrifice.