corrosion

• corrosion


  the deterioration of a metal due to a chemical reaction in the environment
• irons corrodes...


  easily - it rusts
• rust


  the formation of reddish-brown ferric oxides on iron by low-temperature oxidation in the presence of waterr
• rusting conditions


  iron in the presence of oxygen and water, which are both present in the air
• hydrated iron(III) oxide


  chemical name for rust
• rust formation equation


  iron + oxygen + water → hydrated iron(III) oxide

  4Fe + 3O2 + 6H2O → 4Fe(OH)3
• corrosion only happens on...

  the surface of a material, where its exposed to the air
• why will all iron in an object corrode away even if it wasn't initially at the surface?

  rust is a soft crumbly solid that eventually f;ales off to leave more iron available to rust again
• why are things made from aluminium not completely destroyed by corrosion?

  because the aluminium oxide that forms when aluminium corrodes doesn't flake away but instead forms a protective layer that sticks firmly to the aluminium below and stops any further reaction from taking place
• aluminium oxide formation equation

  aluminium + oxygen → aluminium oxide

  4Al(s) + 3O₂(g) → 2Al₂O₃(s)
• how can you show that water alone will not cause corrosion?

  put an iron nail in a boiling tube with just water and the nail will not rust (the water is boiled to remove oxygen and oil is used to stop air from getting in)
• how can you show that air alone will not cause corrosion?

  put an iron nail in a boiling tube with just air and the nail will not rust (calcium chloride can be used to absorb any water from the air)
• if you put an iron nail in a boiling tube with air and water...


  it will rust
• rusting prevention methods


  coat the iron with barrier or use the sacrificial method
• painting/coating with plastic


  ideal for big and small structures alike - it can be decorative too
• electroplating


  uses electrolysis to reduce metal ions onto an iron electrode - it can be used to coat the iron with a layer of a different metal that won't be corroded away
• oiling/greasing


  has to be used when moving parts are involved, like on bike chains
• sacrificial method


  adding a more reactive metal to the iron, so that the sacrificial metal reacts with water and oxygen instead
• galvanisation


  involves coating iron or steel with a thin layer of zinc, which acts as both a physical barrier and a sacrificial metal, meaning zinc corrodes instead of the iron