Alloys as Useful Materials (AQA GCSE Chemistry)

• 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

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)