C15

• Corrosion


  the gradual wearing away of a metal element due to a chemical reaction
• Alloy


  A mixture of two or more metals
• What is needed for rusting?

  air (oxygen) and water
• Methods of preventing rusting

  Painting, greasing, electroplating
• How aluminium corrosion is prevented

  A layer of aluminium oxide forms on the surface of the metal which prevents further rusting
• Galvanising


  protecting a metal by covering it with a more reactive metal that will corrode first
• Sacrificial protection


  A more reactive metal coating gets corroded instead of the metal itself
• Composition of bronze


  copper and tin
• Composition of brass


  copper and zinc
• Composition of gold used in jewellery

  An alloy of silver, copper and zinc
• Meaning of carat


  Proportion of gold in a material
• 24 carat gold composition

  100% gold
• 18 carat gold composition

  75% gold, 25% other metals (silver, copper or zinc)
• Composition of steel


  Alloy of iron with carbon and other metals
• High carbon steel properties

  Strong but brittle
• Low carbon steel properties


  Softer and more easily shaped
• Stainless steel composition


  Iron with carbon and chromium and nickel
• Stainless steel properties


  Resistant to corrosion, hard
• Aluminium alloy properties


  low density
• Use of bronze


  Making ship propellors
• Use of brass


  Musical instruments
• Use of aluminium alloys

  Aircraft
• Use of gold alloys

  jewellery
• Use of stainless steel


  Cooking utensils
• Use of carbon steel

  Car bodies
• Difference between thermosetting and thermosoftening polymers (properties)


  Thermosoftening polymers melt when heated, thermosetting do not
• Two types of poly(ethene)

  low-density poly(ethene) and high-density poly(ethene)
• Conditions for making low-density poly(ethene)

  High pressure and a trace of oxygen
• Conditions for making high-density poly(ethene)

  catalyst, 50 degrees C, slightly raised pressure
• Difference in structure between HDPE and LDPE

  LDPE is more branched so chains do not pack as closely together, HDPE has straighter chains
• Why thermosetting polymers do not melt when heated

  Polymer chains are fixed together by strong covalent bonds (cross-links)
• Why thermosoftening polymers melt when heated

  They are made up of a web of polymer chains which are easily separated because there are no cross-links and only weak intermolecular forces
• A composite material


  A matrix or binder surrounding and binding together fibres or fragments of the other material (the reinforcement)
• Examples of composite materials

  Plywood, MDF, Concrete
• How soda-lime glass is made

  heating a mixture of sand, sodium carbonate and limestone
• How borosilicate glass is made

  heating a mixture of sand and boron trioxide
• Comparison in properties of soda-lime and borosilicate glass

  Borosilicate glass melts at higher temperatures so is used in ovenware
• How clay ceramics are made

  Shaping wet clay and heating in a furnace at 1000 C
• Clay ceramics properties


  Hard, brittle, electrical insulators
• Use of clay ceramics

  bricks, tiles, crockery