Alloys — Chemistry, 11–13 years
How mixing metals, or a metal with a small amount of another element, can improve its properties.
What an alloy is
An alloy is a solid material made by combining a metal with one or more other elements. The different-sized atoms can make it harder, stronger or less likely to bend than the pure metal, while it still behaves like a useful metal.
Why make alloys
Pure metals often have a useful property but also a weakness: copper conducts electricity well but is quite soft, and iron is strong but can be brittle or rust. Making an alloy lets people tune the material for a particular job instead of accepting one metal’s limits.
From iron to steel
Start with iron, which is strong but can bend or rust in ways that limit its uses. Add a small amount of carbon and form steel: the carbon atoms fit among the iron atoms and make the structure harder. Different amounts and treatments give steels suited to bridges, tools or cutlery.
An alloy is not just a mixture you can see
It is reasonable to think an alloy must show separate pieces of each material, like sand mixed with beads. In an alloy, the components are melted and spread through one solid structure, so you usually cannot pick them apart by hand, even though their atoms are not all identical.
Alloys around us
Stainless steel is used for sinks, pans and medical tools because it is strong and resists corrosion better than ordinary iron. Brass, made mainly from copper and zinc, is useful for taps and musical instruments because it is workable, tough and gives a clear sound.
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