Tuesday 18 February 2014

GCSE chemistry - unit 1 - alloys

Alloys

An alloy is a mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain.
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

ALLOYS ARE NOT CHEMICALLY BONDED THEY ARE JUST MIXED 

Example
Iron is produced in a blast furnace with coke, limestone and iron oxide (from iron ore) in it. The coke contains carbon which takes the oxygen away from the iron oxide to leave just iron. This is called REDUCTION (loss of oxygen)
The iron produced is called impure pig iron and has to be purified to make it stronger.
Scientist can also control the amount of carbon they put in it to form STEEL.
LOW CARBON STEEL has 0.4% carbon and is easy to shape and not as brittle (easily broken) 
HIGH CARBON STEEL has 1.5% carbon and is resistant to corrosion, is harder but is more brittle

If we mix chromium with iron however we get stainless steel which does not corrode, rust or react.

Most metals are really soft in pure form and have limited use. We add copper to gold and aluminium to make them. Iron is the exception where you can add carbon to form steel.


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