C2: Material choices

C2: Material choices

1. Measuring the properties of materials

   • Materials like plastics, fibres and rubber have many different properties. All these need to be considered when choosing them for a job.
   • Some properties are melting point, strength, stifness, hardness and density.
   • Materials vary slightly, so they need to be measured many times to establish the range, eliminate outliers, find the mean, and estimate the true value.

2. Natural and synthetic materials

   • Synthetic polymers are man-made materials from the Earth's crust. Examples are: plastics from crude oil; aluminium metal from bauxite ore.
   • Natural polymers come from living things. Examples are: cotton from plants; silk from animals; limestone and iron ore from the Earth's crust.
   • Synthetic materials are alternatives to using natural materials. They include: plastic washing up bowls instead of metal or ceramic bowls; neoprene wetsuits instead of rubber ones; kevlar body armour instead of metal plates.

3. Separating crude oil

   • Crude oil is made of hydrocarbon chains of varying lengths.
   • Crude oil is separated by fractional distillation into fractions.
   • Larger hydrocarbons have more attractive forces between the molecules, so more energy is needed to separate them, resulting in higher boiling points.
   • Each fraction contains a small range if molecules sizes of similar boiling points.
   • Different fractions are used mainly as lubricants, with a small amount used for raw materials, to make materials like plastics.

4. Nanotechnology

   • Nanotechnology involves very small structures up to 100nm in size. They occur naturally, by accident, and by deisgn.
   • Nanoparticles have different properties compared to larger partciles of the same material. one key factor is their larger surface area compared to thier volume.
   • Carbon nanoparticles can be used to strnghten sports equipment and body armour. Silver nanoparticles give fibres antibacterial properties.
   • The health effects of using nanoparticles are unknown as they have not been around very long.

5. Plastics

   • The strength, stiffness and hardness of a plastic links to the amounts of energy needed to separate the molecules chains.
   • Small molecules called monomers can join together to make polymers.
   • Polymer strength depends on chain length, cross linking, plasticisers and increased crystanllinity.