Pure iron is soft and rusts; add chromium, nickel and carbon and it becomes stainless steel for cutlery and surgical tools. An alloy is a mixture, and the atoms of the added elements are the reason it is harder and stronger.
An alloy is a mixture of a metal with other elements. Examples: brass is copper and zinc; stainless steel is iron with other elements such as chromium, nickel and carbon. Alloys can be harder and stronger than the pure metals and are used for that reason: stainless steel for cutlery because it is hard and resists rusting. Extended: in an alloy, atoms of different sizes disrupt the regular layers, so the layers cannot slide over each other as easily.
Mix in atoms of a different size in the simulator and try to slide the layers. Compare the force needed with the pure metal.
| Alloy | Made from | Use | Reason |
|---|---|---|---|
| brass | copper and zinc | musical instruments, electrical plugs | harder than copper, resists corrosion, attractive |
| stainless steel | iron, chromium, nickel, carbon | cutlery, sinks, surgical instruments | hard and resistant to rusting |
| mild steel | iron and a little carbon | car bodies, machinery | strong and malleable |
| aluminium alloys | aluminium with copper or magnesium | aircraft | strong with low density |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
An alloy is:
Which metals are mixed to make brass?
Why is stainless steel used for cutlery?
Compared with a pure metal, an alloy is usually:
Extended. The answer is in the arrangement of the atoms.
An alloy is a mixture, not a compound: the elements are not chemically combined and there is no fixed formula. And the added element need not be a metal: steel contains carbon, a non-metal.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
(Extended) Why is an alloy harder than the pure metal?
Which is an alloy that contains a non-metal?
Which element in stainless steel helps it to resist rusting?
Pure aluminium is soft. Why are aircraft made from aluminium alloys?
This skill is now recorded on your profile. Keep the chain going.