GCSE Chemistry · AQA 8462 · Topic 4.10.3
Using materials
Key points
- Corrosion is the destruction of a material by chemical reaction with substances in the environment. Rusting needs both air (oxygen) and water.
- Corrosion is prevented by barriers (paint, oil, plastic coating, electroplating) or sacrificial protection: a more reactive metal such as zinc corrodes instead (galvanising).
- Alloys: bronze is copper and tin; brass is copper and zinc; gold for jewellery is alloyed with silver, copper and zinc (purity in carats, 24 carat = 100%); steels are iron with carbon and/or other metals; aluminium alloys have low density.
- Soda-lime glass is made by heating sand, sodium carbonate and limestone; borosilicate glass melts at higher temperatures. Clay ceramics (pottery, bricks) are shaped wet then heated in a furnace.
- Polymer properties depend on monomers and conditions: low density and high density poly(ethene) differ. Thermosoftening polymers melt when heated; thermosetting polymers have cross-links and do not melt.
- Composites have a reinforcement (fibres or fragments) in a matrix or binder, e.g. fibreglass, carbon fibre and concrete.
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Choosing the right material for a job means knowing how materials behave. This sub-topic covers corrosion and how to stop it, alloys, glass and ceramics, polymers, and composites.
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