Iron (Fe)
For all it short comings, iron is the most used and cheapest
metal. It started its dominance of technology around 1000 BC, ending
the mighty Bronze Age and has maintained that dominance ever since.
By all accounts, iron should be the metal of last choice for most applications:
- it is dense and heavy
- it corrodes, rusting quickly in air and water
- it is very rare as natural metal and difficult to extract form
its ore
Why use iron?
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There is plenty of iron which
can be found in an ore state and makes up 5% of the Earth's crust
and is second in abundance only to aluminium. Australia has great
mountains of iron ore, such as Mt. Tom Price and Mt Newman in
Western Australia.
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Abundance of iron
Iron
is the chief constituent of the Earth's core and is the most abundant
element in the Earth, making up 35% by mass. It is also found in the
Sun and other stars. The only free iron found naturally on Earth comes
from meteorites. Before man discovered how to extract iron from its
ore, the only iron available for use by man was that which fell to Earth
as meteorites.
Iron was the original "star metal" and was
much prized for its hardness. One way of determining whether people
have lived in an area in the past is to look for meteorites: if you
do not find any there is a good chance that ancient man got to them
first.
Metal iron is extracted by smelting the ore with carbon
(coke) and limestone. This is not an easy process and requires high
temperatures. The first iron was probably produced in a pottery kiln
as the result of heating red ochre glaze. See Production
of iron for more information.
The average human body contains about 4.5g of iron,
mostly in the form of haemoglobin in our blood.
Properties and uses
Pure iron itself is rarely used as it is too soft and prone to rusting.
Iron is more commonly alloyed with carbon to form steel which although
less malleable than iron, is stronger and less prone to rusting. Mixed
with other metals a whole range of steels can be produced: Stainless
steel which is highly resistant to corrosion through to mild steels,
used to make steel plate and cast iron. Cast iron is actually is a form
of steel which, although brittle is cheap to produce and can be cast
easily.
Although iron reacts with water, acids and is heavy,
hard to produce and rusts quickly, iron is the most used metal. It all
comes down to money. It is cheap and we have a lot of it! The built-in
redundancy of iron also sells a lot more cars, bridges and train tracks.
In fact, protecting iron and steel against corrosion and replacing rusted
structures is a very big industry.
The future of iron
Iron will probably still dominate our building and transport technologies
in the foreseeable future, but the new space age materials such as aluminium,
plastics, ceramics, carbon composites and alloys will take over many
of the present uses of iron and steel. The future of iron is in new
alloys and combined with other materials to give strength and resistance
to rusting.
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