Using materials

• Corrosion is the destruction of materials by chemical reactions with substances in the environment.
• Both air and water are necessary for iron to rust.
• Carbon fibre and fibreglass are examples of composites.
• Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement.
• Examples of composites include bricks and pottery, both of which are very hard but very brittle.
• Corrosion can be prevented by applying a coating that acts as a barrier, such as greasing, painting or electroplating.
• Aluminium has an oxide coating that protects the metal from further corrosion.
• Some coatings are reactive and contain a more reactive metal to provide sacrificial protection.
• Zinc is used to galvanise iron.
• Sacrificial protection works by the more reactive metal donating electrons to any ions of the other metal that may have formed so they don’t corrode.
• Most metals in everyday uses are alloys.
• Pure copper, gold, iron and aluminium are all too soft for everyday uses and so are mixed with small amounts of similar metals to make them harder for everyday use.
• Gold in jewellery is usually an alloy with silver, copper and zinc and the gold purity is measured in carats.
• Bronze is an alloy of copper and tin - used in electrical connectors.
• Brass is an alloy of copper and zinc - used for tools.
• Steels are alloys since they use mixtures of carbon and iron.
• Some steels contain other metals.
• Alloys can be designed to specific uses.
• Properties of polymers depend on the monomers they are made from and the conditions under which they are made.
• Thermosoftening polymers are easily separated and melted by heat due to weak intermolecular forces between the chains.
• Aluminium alloys are low density and used for aircraft.
• Clay ceramics, including pottery and bricks, are made by shaping wet clay and then heating in a furnace.
• Low-carbon steels are easily shaped and used for sheeting.
• High carbon steels are hard and used for cutting tools.
• Soda-lime glass is made by heating a mixture of sand, sodium carbonate, and limestone.
• High density polyethene has higher forces of attraction, a higher melting point.
• Thermosetting polymers consist of polymer chains that cross-link, preventing them from melting when heated.
• Low density polyethene has weaker forces of attraction, a low melting point, and is soft.
• Borosilicate glass is made from sand and boron trioxide and melts at higher temperatures than soda-lime glass.
• Stainless steels (containing chromium and nickel) are resistant to corrosion and used for cutlery.