Aluminium is a soft, durable, lightweight, malleable metal with
appearance ranging from silvery to dull grey, depending on
the surface roughness. Aluminium is nonmagnetic and nonsparking.
It is also insoluble in alcohol, though it can be soluble in
water in certain forms. The yield
strength of pure aluminium is 7–11 MPa,
while aluminium
alloys have yield strengths ranging from 200 MPa to 600
MPa. Aluminium has about one-third the density and stiffness of steel.
It is ductile,
and easily machined, cast,
and extruded.
Corrosion resistance can be excellent due to a thin surface
layer of aluminium
oxide that forms when the metal is exposed to air, effectively
preventing further oxidation.
The strongest aluminium alloys are less corrosion resistant
due to galvanic reactions
with alloyed copper. This corrosion resistance is also often
greatly reduced when many aqueous salts are present however,
particularly in the presence of dissimilar metals.
Aluminium atoms are arranged in a face-centered
cubic (FCC) structure. Aluminium has a stacking-fault energy
of approximately 200 mJ/m².
Aluminium is one of the few metals that retain full silvery
reflectance in finely powdered form, making it an important
component of silver paints. Aluminium mirror finish has the
highest reflectance of any metal in the 200–400 nm (UV)
and the 3000–10000 nm (far IR)
regions, while in the 400–700 nm visible range it is slightly
outdone by tin and silver and
in the 700–3000 (near IR) by silver, gold,
and copper.
Aluminium is a good thermal and electrical
conductor, by weight better than copper. Aluminium is capable
of being a superconductor,
with a superconducting critical temperature of 1.2 kelvin and
a critical magnetic field of about 100 gauss.
Recycling
Aluminium Recycling Code
Aluminium is 100% recyclable without any loss of its natural
qualities. Recovery of the metal via recycling has
become an important facet of the aluminium industry.
Recycling involves melting the scrap, a process that requires
only five percent of the energy used to produce aluminium from
ore. However, a significant part (up to 15% of the input material)
is lost as dross (ash-like
oxide).
Recycling was a low-profile activity until the late 1960s,
when the growing use of aluminium beverage cans brought it
to the public awareness.
In Europe aluminium
experiences high rates of recycling, ranging from 42% of beverage
cans, 85% of construction materials and 95% of transport vehicles.
Recycled aluminium is known as secondary aluminium, but maintains
the same physical properties as primary aluminium. Secondary
aluminium is produced in a wide range of formats and is employed
in 80% of the alloy injections. Another important use is for
extrusion. Besides being cheaper, secondary aluminium products
are as good as primary ones and may display ISO 9001 and ISO
14000 certification marks.
Some of the many uses for aluminium metal are in:
Household Aluminium foil
1. Transportation (automobiles, aircraft, trucks, railway
cars, marine vessels, bicycles etc.)
as sheet, tube, castings etc
2. Packaging (cans,
foil, etc.)
3. Construction (windows, doors, siding,
building wire, etc.)
4. Cooking
utensils.
5. Street lighting poles, sailing ship masts, Walking
poles etc
6. Outer shells of consumer electronics, also cases for equipment
eg photographic equipment.
7. Electrical transmission lines for power distribution.
8. MKM steel and Alnico magnets.
9. Super purity aluminium (SPA, 99.980% to 99.999% Al), used
in electronics and CDs.
10. Heat
sinks for electronic appliances such as transistors and CPUs.
11. Substrate material of metal-core
copper clad laminates used in high brightness LED
lighting.
12. Powdered aluminium is used in paint,
and in pyrotechnics such
as solid
rocket fuels and thermite.
13. In the blades of prop swords and knives used
in stage combat.
14. Aluminium is widely used in watch production as it provides
durability and resists tarnishing and corrosion.
