This prevents water or oxygen reaching the iron. However, this is only a temporary step since paint can flake off and grease can be rubbed off quite easily. Bikes are often painted of greased to prevent rust, since this is the cheapest method of prevention.
Plastic is cheap and acts as a cover for the iron, for instance, it stops water or oxygen reaching the metal surface. Garden chairs are often made from iron coated in plastic.
This involves the iron been covered, usually in the form of a paint, by zinc. Since zinc is more reactive than iron, air and water react with the zinc rather than the iron. Outside structures, such as bridges are often galvanised.
4. Chromium plating
Works for the same reason as galvanising. Chromium is a more reactive metal than iron. Car bumpers are often chrome-plated.
Both chromium plating and galvanising are examples of sacrificial protection. Zinc and chromium are sacrificed for the iron.
Many metals are found in the Earth's crust as ores. An ore is usually a compound of the metal mixed with impurities. When the metal is dug up, a method must be used to separate the metal from the rest of the ore. This is called extracting the metal.
The method of extraction depends on how reactive the metal is. The more reactive the metal, the more difficult it is to extract from its compound.
Electrolysis is the most powerful extraction method. But it takes a lot of electricity and that makes it expensive. Hence, electrolysis is only used for the most reactive metals.
Metals are non-renewable resources. This means once dug up it cannot be replaced. Hence, the supply will eventually run out.
For example: it is expected that tin will run out within the next 15 years and copper in the next 40 years! Therefore,the recycling of these two useful metals and others such as iron and aluminium is most important.
In recycling, metals are melted down before reshaping into their new use. However, this can be costly. Recycling companies will only recycle if it is economical!
Metals often appear in the Earth's crust as an ore. An ore is the metal
usually in the form of a compound, most commonly an oxide. When the ore is
dug up, and decomposed to the metal alone, we call this extracting.
The more reactive a metal the more difficult to extract.
Unreactive metals, such as gold and silver can be found as pure elements in
the Earth's crust.
There are different methods of extraction:
Heating with carbon monoxide.
Roasting in air.
Metals are a non-renewable resource. Hence, it is important to recycle
Aluminium is extracted from the ore bauxite, using electrolysis. At
the cathode, aluminium is formed and at the anode oxygen gas forms.
Aluminium has many useful properties:
Good conductor of heat and electricity.
Malleable and ductile.
Iron is extracted from the ore haematite (iron oxide) using a blast furnace.
Cast iron and steel are two useful by-products from the extraction of iron.
The corrosion of iron and steel is called rusting.
Rusting of iron occurs if both water and oxygen (usually from the air)
To help prevent rust, several methods may be