materials - metal, glass

• Metal oxidation in air

  Metals react with oxygen and form metal oxides
• Formation of sodium oxide

  sodium + oxygen → sodium oxide, 4Na(s) + O2(g) → 2Na2O(s)
• Gold and other very unreactive metals do not oxidise in air at all
• Corrosion

  Metal continues to oxidise, becomes weaker over time, eventually all of it may become metal oxide
• Rusting


  Occurs when iron or steel reacts with oxygen and water, iron + oxygen + water → hydrated iron(III) oxide
• Hydrated iron(III) oxide is the orange-brown substance seen on the surface of rusty objects
• An iron or steel object only rusts if oxygen and water are present
• Prevention of rusting


  Keeping oxygen or water away from the iron or steel
• Methods of rust prevention


  • Excluding oxygen by storing the metal in an atmosphere of unreactive nitrogen or argon
  • Using a desiccant to absorb water vapour
  • Creating physical barriers to oxygen and water such as painting, oiling and greasing, coating with plastic
• Electroplating


  Using electrolysis to put a thin layer of a metal on the object
• Example of electroplating

  • Steel cutlery electroplated with silver using a silver anode and silver nitrate solution
• Electroplating improves the corrosion resistance of metal objects
• Sacrificial protection


  Protecting iron from rusting by placing it in contact with a more reactive metal, such as zinc
• The more reactive metal oxidises more readily than iron, sacrificing itself while the iron does not rust
• Once the sacrificial metal has corroded away, it can simply be replaced
• When iron is coated in zinc, the process is called galvanisation. The zinc layer stops oxygen and water reaching the iron. Zinc acts as a sacrificial metal, even if the zinc layer is scratched
• Alloys

  • Bronze
  • Brass
  • Jewellery gold
  • High carbon steel
  • Low carbon steel
  • Stainless steel
  • Aluminium alloys
• Bronze


  Copper and tin
• Bronze, Gold


  • Resistant to corrosion
• Brass

  Copper and zinc
• Brass

  • Very hard but workable
• Jewellery gold

  Mostly gold with copper, silver and zinc added
• Jewellery gold

  • Lustrous, corrosion resistant, hardness depends on carat
• High carbon steel

  Iron with 1-2% carbon
• High carbon steel


  • Strong but brittle
• Low carbon steel


  Iron with less than 1% carbon
• Low carbon steel


  • Soft, easy to shape
• Stainless steel

  Iron with chromium and nickel
• Stainless steel

  • Resistant to corrosion, hard
• Aluminium alloys

  Over 300 alloys available
• Aluminium alloys

  • Low density, properties depend on composition
• Bronze was the first alloy invented (c.f. bronze age)
• Uses of alloys


  • Statues, decorative items, ship propellers
  • Door fittings, taps, musical instruments
  • Jewellery
  • Cutting tools, metal presses
  • Extensive use in manufacture: cars, machinery, ships, containers, structural steel
  • Cutlery, plumbing
  • Aircraft, military uses
• Polymers are made from monomers
• Polymer properties


  Depend on the monomer it is made from and the conditions under which it was made
• Low density poly(ethene)


  Chains have branches which prevents them packing together neatly
• Thermosoftening polymers

  Melt when heated
• Thermosetting polymers

  Do not melt when heated
• Corrosion


  The process by which metals are slowly broken down by reacting with substances in their environment
• Rusting

  Iron reacting with oxygen and water from the environment to form hydrated iron oxide (rust)