What rusting needs and how to prevent it including sacrificial protection, the common alloys and their uses, and ceramics, composites and the two types of polymer. Chemistry only content.
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1.What is corrosion?
The destruction of materials by chemical reactions with substances in the environment.
2.What is rusting?
The corrosion of iron and steel.
3.What two substances are needed for iron to rust?
Air, specifically oxygen, and water. Both must be present.
4.How would you show both are needed?
Set up three tubes: one with iron in air and water, one with water but no air, and one with air but no water. Only the first rusts.
5.How is the water removed in a control experiment?
By using a drying agent such as calcium chloride and sealing the tube.
6.How is the air removed in a control experiment?
By using boiled water, which has had the dissolved air driven out, and covering it with a layer of oil.
7.Name two barrier methods of preventing corrosion.
Painting, greasing, or coating with a polymer or another metal by electroplating.
8.How do barrier methods work?
They stop air and water reaching the surface of the metal.
9.What is sacrificial protection?
Coating or attaching a more reactive metal, which corrodes in place of the metal being protected.
10.Which metal is commonly used for sacrificial protection of iron?
Zinc.
11.What is galvanising?
Coating iron or steel with zinc, which acts as both a barrier and sacrificial protection.
12.Why does zinc protect iron even if the coating is scratched?
Zinc is more reactive than iron, so it corrodes in preference and the iron is left unaffected.
13.Why does aluminium not corrode away completely?
It forms a thin oxide layer on its surface that protects the metal underneath.
14.What is bronze made from?
Copper and tin.
15.What is brass made from?
Copper and zinc.
16.What is 18 carat gold?
Gold alloyed with other metals, containing 18 parts gold out of 24, so 75 per cent gold.
17.Compare low carbon and high carbon steel.
Low carbon steel is softer and more easily shaped. High carbon steel is much harder but more brittle.
18.What is stainless steel and what is it used for?
Steel alloyed with chromium and nickel. It is hard and resists corrosion, so it is used for cutlery and equipment.
19.Why are aluminium alloys used in aircraft?
They have a low density but are strong enough for the purpose.
20.How is soda-lime glass made?
By heating a mixture of sand, sodium carbonate and limestone until it melts, then cooling it.
21.How does borosilicate glass differ?
It is made from sand and boron trioxide and melts at a higher temperature, so it withstands heating better.
22.How are clay ceramics made?
Wet clay is shaped and then fired at a high temperature in a furnace.
23.What is a composite made of?
Fibres or fragments of one material, held together by a matrix or binder of another.
24.Give an example of a composite and its components.
Reinforced concrete, which is concrete with steel bars inside it, or fibreglass, which is glass fibres in a polymer.
25.What is a thermosoftening polymer?
One made of individual polymer chains held by weak intermolecular forces, so it melts when heated and can be reshaped.
26.What is a thermosetting polymer?
One where the chains are joined by strong cross links, so it does not melt when heated.
27.Why does high density poly(ethene) differ from low density?
Different catalysts and reaction conditions are used, which change how the chains pack together and so change the properties.
28.Why do properties of a material determine its use?
A material is chosen because its particular combination of strength, density, cost and resistance suits the job it has to do.
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