Using resources

• Melting point - the temperature at which a solid melts into a liquid
• Conductivity - how well a material conducts electricity
• Strength - the ability of a material to resist an applied force
• Hardness - how well a material can resist being scratched or indented
• Brittleness - how easily a material breaks when a force it applied
• Stiffness - how well a material can resist bending 
• Ceramics are hard to define, but are basically a group of hard, brittle, heat-resistant, and corrosion-resistant materials.
• Making ceramics: They are made by shaping and then firing a non-metallic material, such as clay, at a high temperature.
• Two main groups of ceramics are clay ceramics and glass.
• Clay ceramics include brick, china and porcelain. 
• Clay ceramics are made by shaping wet clay while it's soft and then heating it to a high temperature in a furnace, which causes it to harden.
• Clay ceramics have a high compressive strength, which is why bricks can be used for building.
• Most of the glass we use is soda-lime glass. This is made by melting a mixture of sand (silicon oxide), sodium carbonate, and limestone, then allowing the molten liquid to cool and solidify.
• Borosilicate glass is made by heating sand with boron trioxide.
• Borosilicate glass has a much higher melting point than soda-lime glass.
• Glass is transparent, strong and a good thermal insulator, which makes it useful for windows.
• A composite material consists of two or more materials with different properties, that have been combined to produce a material with more desirable properties.
• Composites are made from the reinforcement - often long solid fibres or fragments and the matrix - which binds the reinforcement together. Usually something that starts soft and then hardens.
• Polymers are large molecules of high relative molecular mass and are made by linking together large numbers of smaller molecules called monomers.
• The properties of a polymer depend on the monomers from which it was made and the conditions of the chemical reaction. 
• Generally, polymers are flexible, easily shaped, and good insulators of heat and electricity.
• Poly(ethene) is one of the most common polymers and comes in two main forms: low-density poly(ethene) (LDPE) and high-density poly(ethene) (HDPE). 
• LDPE - low-density poly(ethene)

  1. Conditions: Moderate temperatures, high pressure, catalyst 
  2. Properties: More flexible but weaker
  3. Uses: Carrier bags
• HDPE - high-density poly(ethene)

  1. Conditions: Low temperature/pressure, catalyst
  2. Properties: More rigid but stronger
  3. Uses: Drainpipes
• Thermosoftening polymers are made from lots of polymer chains, held together by weak intermolecular forces. These break easily when heated, causing the polymer to melt. It can then be remoulded into a different shape and will harden again when cooled.
• Thermosetting polymers are made from lots of polymer chains, held together by strong covalent bonds. These require lots of energy to break, so don’t soften when heated. These polymers are hard, strong and rigid.
• Metals are generally malleable, ductile, good conductors of heat and electricity, and have high melting and boiling points
• Alloys on the other hand, which are metals with atoms of another element mixed in, are much stronger (no longer malleable).

  This makes them useful for purposes where they might be put under stress - like in buildings. 
• Corrosion is the process by which metals are slowly broken down by reacting with substances in their environment
• Rusting is the corrosion of iron
• Iron + oxygen + water ➔ hydrated iron (III) oxide
• During the process of rusting, iron undergoes the following half equation:

  Fe ➔ Fe3+ + 3e-

  Fe has been oxidised
• The half equation for the reduction of oxygen. 

  O2 + 4e- ➔ 2O2-
• The rusting of iron involves both oxidation and reduction. This means that it is considered a redox reaction.
• The aluminium oxide forms a protective layer, preventing further oxidation so it doesn't break down as it corrodes
• barrier methods coat the iron in something to prevent the oxygen and water from touching the iron 
• Barrier methods: Paint the iron (this works for large pieces of iron like ships)

  Oil or grease it (this works when the object has moving parts, like a bike chain)

  Electroplating (using electrolysis to cover the metal in another metal)
• Sacrificial methods: Adding a more reactive metal to the iron, so that metal reacts with oxygen instead 
• 1. Galvanising can prevent iron from rusting. It involves coating the iron in a thin layer of zinc.
  2. The layer acts as a physical barrier to prevent water or oxygen from reaching the iron (barrier method).
  3. If the zinc gets scratched though, then the zinc will still react with any nearby oxygen as it is more reactive than iron (sacrificial method). 
• Sustainable development is an approach to human and economic development that meets the needs of the present generations, without compromising the ability of future generations to meet their own needs.