Chapter 15: Modern Metals
aluminium | aluminium
oxide | U3O8
Aluminium
 Aluminium
is a metal element, symbol Al, atomic number 13.
Aluminium is used more than any metal except iron. Aluminium is the most
abundant metal element in Earth's crust (8.16% by mass), and is only exceeded
by the non-metals oxygen and silicon.
| Aluminium attribute |
Makes it suitable for |
| Light weight metal - can be made very strong by processing and by
alloying |
Aeroplanes.
Vehicles and vehicle parts, such as the bonnet on some new Subaru
cars, and alloy wheels. (Note that true "mag wheels" are
magnesium, not aluminium, and weigh even less than aluminium alloy
wheels.)
Construction, eg window frames. |
| Soft |
|
| Malleable (can be made into thin sheets) |
Aluminium foil, which has replaced tin foil in common usage such
as cooking.
Drink cans. |
| Ductile |
Wire. |
| Very electrically conductive - 4th behind silver, copper, and gold
(in that order). The next most conductive element is tungsten, which
is almost exactly half as conductive as Al. |
Wire, electronics, electrical transmission lines.
Copper is more conductive than aluminium but also heavier and more
expensive. |
| Very thermally conductive - 5th behind diamond (carbon), and once
again, silver, copper, and gold (in that order). |
Cookware.
Heatsinks. |
Excellent reflector of visible light - about 99%
Good reflector of infrared - about 95% |
Mirrors (by vacuum deposition). Such mirrors will not deteriorate
like silver mirrors will.
CDs and DVDs (super purity aluminium, at up to 99.999%). |
| Reactive |
Pyrotechnics.
Thermite.
Although aluminium is quite reactive it forms a protective oxide
coating, which stops further corrosion. Mercury and some other chemicals
remove the oxide coating, which is why mercury is not allowed on
aeroplanes, which are made mostly of aluminium. |
Antiperspirants use one of a family of aluminium compounds called
aluminium chlorohydrates to clog sweat glands, normally Al2Cl(OH)5.
Water purification uses other aluminium chlorohydrates, particularly
Al12Cl12(OH)24 due to the pH of that
molecule.
Production of aluminium became easy after
electrolysis was discovered, and the price of aluminium decreased
hugely. However, according to Wikipedia it was once considered
a precious metal more valuable than gold. Napoleon III, Emperor
of France, is reputed to have given a banquet where the most honoured
guests were given aluminium utensils, while the other guests had
to make do with gold ones.
Recycling aluminium (eg, melting down old drink cans) uses
only 5% the electriciy that smelting new aluminium from ore does.
New Zealand has an aluminium smelter at Tiwai
Point at the entrance to Bluff Harbour. From their web site:
At 99.98% pure, NZAS produces the highest purity aluminium in
the world. Most of the aluminium it produces is exported, with
Japan and Korea the biggest buyers. In 2004, NZAS generated a
total export revenue of NZ$1 billion.
Warning: Their "Operation" info page has a 5MB mugshot
of their boss on it. Grrr. I've told them about the problem and
two weeks later they still haven't done anything about it. |
|
 |
Spelling of this metal's name basically depends on country. The
New Zealand spelling is aluminium. For historical reasons the American
spelling is aluminum (with the emphasis on the second syllable instead
of the third). Humphrey Davy used alumium in 1808, and aluminum
in 1812, but in the same year the Brits figured out that aluminium
matched many other elements and they thought it sounded more classical.
Wikipedia says In 1926, the American Chemical Society officially decided
to use aluminum in its publications ... The International Union of Pure
and Applied Chemistry (IUPAC) adopted aluminium as the standard international
name for the element in 1990.
Aluminium oxide
Aluminium
oxide or alumina (Al2O3) makes up 15.41% of
the mass of Earth's crust. See the table under Earth's
crust on the chapter 14 page. It is
normally found as bauxite,
a red-coloured ore that gives outback Australia its characteristic colour.
Bauxite is made of a mix of Al2O3, Fe2O3
(rust), and SiO2.
Aluminium oxide is found in crystaline form naturally as corundum (rubies
and sapphires), emery, and is used in glass making. The colour in rubies
(red) and sapphires (other colours) come from impurities - for example
chromium, which gives a red colour. (A Cr3+ ion replaces the
occasional aluminium ion.) Some watches have sapphire watch glasses. Because
of their hardness they are very resistant to scratches. Corundum is used
in industry as an abrasive.
Lasers can be made using rubies and sapphires. The first laser
made (in the early 1960s) used a ruby. Synthetic ruby and sapphire are
used in lasers for the production of coherent light.
U3O8
Triuranium octaoxide (U3O8) has a molar mass of
842.1g/mol (or a molecular mass of about 842 atomic mass units). It has
a density of 8.3 g/cm3. Also called uranite. It is a green
to black, odourless solid, and is the most stable of the uranium oxides.
The yellow uranium oxide mentioned in the book is UO3, and
a black oxide also exists, UO2, which is also called pitchblende.
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