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5 Presentation Transcript

  • 1. Types of Structure
    • When a liquid cools it solidifies
    • The resulting solid may have an orderly structure CRYSTALLINE or POLY-CRYSTALLINE
    Orderly ‘Crystalline’ Structure Shows some irregularity or ‘Poly-Crystalline’ Structure
  • 2. Cooling and Crystal Size
    • Quick cooling results in _________ crystals
    • Slow cooling results in ________ crystals
    SMALL LARGE
  • 3. Non-Crystalline Structures
    • If no orderly structure is present, this is called AMORPHOUS.
    • It is a random structure and this gives it different properties – but what are they..?
  • 4. Amorphous Structures
    • Molecules are arranged randomly – but some regions align…
      • For plastics this gives them extensibility (non reversible)
      • For elastic behaviour in things like rubber, the molecules rotate. This is reversible
  • 5. Plastic behaviour of partly amorphous structure
  • 6. Modelling Amorphous Structures
    • Use spaghetti to model amorphous structures
    • Does a yoghurt pot give any indication that it is made of long chain molecules?
  • 7. Elastic (e.g. Rubber)
  • 8. Young’s Modulus – Amorphous Structures
    • Draw the graph that you think you would get for Stress/Strain for a rubber band
    Strain Stress
  • 9. Young’s Modulus – Amorphous Structures
    • Draw the graph that you think you would get for Stress/Strain for a rubber band
    Strain Stress Molecules ‘lining up’ Molecules fully extended – Less flexible
  • 10. Making Rubber Stiffer
    • Why is some rubber stiffer than other rubber?
    • Would you use the same type of rubber for a car tyre as for a pencil eraser?
  • 11. Vulcanisation
  • 12. Types of Rubber
    • Natural Rubber Vulcanised Rubber
    Stretched Vulcanised Rubber