Alloys as Useful Materials (AQA GCSE Chemistry)
Revision Note
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Alloys
An alloy is a mixture of two or more metals or metal with a non-metal such as carbon
Steel is made from iron and carbon
Alloys often have properties that can be very different from the metals they contain
They can be stronger and harder
They are resistance to corrosion or extreme temperatures
These enhanced properties can make alloys more useful than pure metals
Alloys are harder than pure metals because:
Alloys contain atoms of different sizes
This distorts the regular arrangements of atoms
So it is more difficult for the layers of atoms to slide over each other,
Alloy structure
The regular arrangement of a metal lattice structure is distorted in alloys
Copper Alloys
Bronze is an alloy made of copper and tin
It is harder than copper and is used to make ornaments and medals
Brass is a common example of an alloy which contains copper and zinc.
It is decorative and corrosion resistant and is used for low friction ornamental purposes such as plumbing and carpentry fittings
Gold Alloys
Gold alloys are usually made with silver copper and zinc
They are used to make jewellery
Carats are used to express the purity of gold jewellery.
Pure gold with nothing else added is said to be 24 carat
A 12 carat piece of gold jewellery therefore contains 50% gold
For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams
Steel Alloys
Steels are alloys of iron that contain specific amounts of carbon and other metals
High carbon steel is strong but brittle
Low carbon steel is softer and more easily shaped
Stainless steels (steel containing chromium and nickel) are hard and resistant to corrosion
Aluminium Alloys
Aluminium is mixed with copper, manganese and silicon for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium
As well as being lighter and stronger, it is also more corrosion resistant than aluminium
Examiner Tips and Tricks
Alloys are mixtures of substances, they are not chemically combined and an alloy is not a compound.
Properties & uses of alloys
Uses of alloys
Alloy | Composition | Use |
---|---|---|
High carbon steel | Iron and carbon | Cutting tools (very hard, but also brittle) |
Low carbon steel | Iron and carbon | Building frames, cookware, car bodies (Softer and more easily shaped) |
Stainless steel | Iron, chromium and nickel | Cookware, cutlery, car bodies |
Bronze | Copper and tin | Ornaments and medals |
Brass | Copper and zinc | Plumping and carpentry |
Magnalium | Aluminium and magnesium | Aircraft construction and production of fireworks (more stable than pure magnesium but still burns brightly) |
Examiner Tips and Tricks
The composition of alloys can be carefully controlled to ensure the finished alloys have desired characteristics for particular uses.
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