Alloys

Alloys and Recycling Learning objectives: •Pupils know pure metals are normally too soft and malleable to be useful. •Pupils can model the behaviour of alloys through particle diagrams. •Pupils can describe the advantages of alloys. •Pupils know that metals can be recycled and that this is advantageous for the environment.

Homework Revise – test next Wednesday on all the work you have done this year. Last years GCSE exam. • Multiple choice – this doesn’t mean its easy! We will also have a quizdom quiz!

What's wrong with pure metals? • In metals – Atoms sit very close to their neighbours. – Atoms are neatly arranged.

What's wrong with pure metals? • This causes a problem if a force is applied to the metal. • The atoms are so neatly arranged they can slide past each other.

• This makes pieces of metal too malleable (bendy) and soft to be any real use. • Yesterday we looked at steel. What did steel contain that pure iron doesn’t?

Adding carbon to pure iron The carbon atoms ‘mess-up’ the neat arrangement, so the atoms cannot slide over each other so easily.

Activity - Explain the properties of pig iron and mild steel. • Pig iron contains 4% carbon – This means the neat arrangement of atoms is so ‘messed-up’, the metal will snap if we apply a force – we call this brittle.

• Mild steel contains 0.2% carbon – The neat arrangement is only slightly ‘messed-up’, so the metal has a combination of strength and malleability (bendiness).

Everyday metals are usually alloys: Brass – about 70% copper, 30% zinc Used in – Musical instruments - has good acoustic properties – Coins – must be hard and resist corrosion – Electrical plugs – good conductor – contains copper

Everyday metals are usually alloys: Gold – purity measured in carats (max 24 = pure) • 18 carat gold - 18/24 = 75% gold - 6/24 = 25% copper Used for jewellery because it is hard and resists corrosion.

Designing Alloys We can combine two metals with desirable behaviour and create an alloy that has a combination of their properties. Smart alloys – These are a special example that will return to their original shape after being bent (e.g. memory frame glasses).