Science
Cars for scrap
Iron and steel rust when they come into contact with water and oxygen. They rust faster in salty water or acid rain. Aluminium, on the other hand, does not corrode easily, because its surface is protected by a layer of aluminium oxide.
Steel and aluminium have advantages and disadvantages when used to make cars, which are recycled to re-use valuable materials and cut down on waste.
Rusting
Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur. In the experiment below, the nail does not rust when air - containing oxygen - or water is not present:
Calcium chloride absorbs water in the right-hand test tube
Salt dissolved in water does not cause rusting, but it does speed it up, as does acid rain.
Aluminium does not rust - corrode. Its surface is protected by a natural layer of aluminium oxide. This prevents the metal below from coming into contact with air and oxygen.
Unlike rust, which can flake off the surface of iron and steel objects, the layer of aluminium oxide does not flake off.
Rusting - higher
Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust. Here is the word equation for the reaction:
iron + water + oxygen → hydrated iron(III) oxide
Car bodies
Steel
Most iron is converted into steel - an alloy - before being used. Compared to iron, steel is:
- harder and stronger
- less likely to corrode - rust
Iron versus aluminium
Iron and aluminium are used to build cars. They are both malleable - they can be bent or pressed into shape - and both are good electrical conductors.
A summary of the differences betwen iron and aluminium
| property | iron | aluminium |
|---|---|---|
| density | high | low |
| magnetic? | yes | no |
| corrodes easily? | yes | no |
Aluminium has some advantages over steel. Since it has a lower density than iron or steel, a car body made from aluminium will be lighter than the same car body made from steel. This results in improved fuel economy. Also, aluminium does not corrode easily, so a car body made from aluminium will corrode less, and may last longer, than one made from steel.
However, aluminium is more expensive than steel. So a car made from aluminium is likely to be more expensive than one made from steel.
Making cars and recycling them
Cars are complex machines. Many different materials are used in their manufacture.
The main materials used in the manufacture of cars
| material | typical use | reason for use |
|---|---|---|
| steel | body panels and chassis | strong and malleable |
| copper | electrical wiring | good conductor of electricity |
| aluminium | body panels and interior fittings | lightweight and rust-proof |
| glass | windows | transparent |
| plastics | body panels, lights and dashboard | tough and easily moulded to desired shape |
| fibres | seats and carpets | good heat insulators, and can be woven into fabrics |
Recycling
European Union law requires that at least 85 per cent of a car’s materials can be recycled, rising to 95 per cent by 2015. Recycling reduces the amount of waste, and the use of natural resources.
Now try a Test Bite