While aluminum was discovered by Hans Christian Oersted,
Denmark, 1825 (impure form); most credit Wohler with isolating it in 1827.
Actually the ancient Greeks and Romans used alum (aluminum sulfate with
potassium) in medicine and in dying. de Morveau recognized the base in
alum in 1761 and proposed it be called alumine. Lavoisier thought
that alum was an oxide of this undiscovered metal. In 1807 Davy proposed
the name alumium for this undiscovered metal, but it wasn't until 1827
that
Wohler actually isolated aluminum, though an impure form was isolated
by Oersted two years earlier. The new metal was called aluminum.
Two years later it was changed to aluminium to conform with the "ium" in
most other elements. American Chemical Society changed the spelling back
to aluminum in 1925, which we still use. England and elsewhere in
the world
they still spell it aluminium. So if you hear someone say "al-u-min'-i-um
foil" instead of aluminum foil, you'll know where it came from.
Uses: Kitchen utensils, building decorations, electrical transmission
(not nearly as conductive as copper, but cheaper). Alloys containing
copper, magnesium, silicon, manganese and other metals are much stronger
and more durable than aluminum, making aluminum useful in the manufacture
of aircraft and rockets.
Properties of aluminum alloys: Only a small percentage of aluminum
is used in pure form. It is made into such items as electrical conductors,
jewelry, and decorative trim for appliances and cars. Almost all aluminum
is used commercially in alloy form with up to 15 percent of one or more
other elements. The chief elements are copper, magnesium, manganese,
silicon, tin, and zinc. Copper and magnesium increase the strength
and hardness of aluminum. Magnesium also makes aluminum easier to weld.
Manganese helps aluminum resist corrosion and also provides strength. Silicon
lowers the melting point of aluminum and makes it easier to cast. Tin makes
aluminum easier to shape with metalworking tools. Zinc, especially
when combined with magnesium, gives added strength. Other
elements may also be alloyed with aluminum for special purposes. These
elements include bismuth, boron, cadmium, chromium, cobalt, iron, lead,
lithium, nickel, sodium, titanium, vanadium, and zirconium.
Aluminum, with its alloys, has many valuable properties that make it
an
exceptionally useful metal. These properties include (1) light weight,
(2)
strength, (3) corrosion resistance, (4) electrical conduction, (5)
heat
conduction, and (6) light and heat reflection.
Light weight. Aluminum is one of the lightest metals. It weighs about
170
pounds per cubic foot (2,720 kilograms per cubic meter)—about a third
as much as steel. As a result, aluminum has replaced steel for many uses.
Strength. Although pure aluminum is weak, certain aluminum alloys are
as
strong as steel. Such alloys are used in airplanes and trucks, in guardrails
along highways, and in other products that require strength. Aluminum
alloys lose some strength at high temperatures. But unlike many other
metals, they get stronger at extremely low temperatures. Aluminum alloys
are widely used in equipment for processing, transporting, and storing
liquefied natural gas, which can have a temperature of -260° F
(-162°C).
Corrosion resistance. Some metals corrode (wear away) if exposed to
oxygen, water, or various chemicals. A chemical reaction occurs that
causes the metals to rust or become discolored.
Electrical conduction. Aluminum and copper are the only common metals
suitable for use as electrical conductors. Aluminum conducts electricity
about 62 percent as well as copper. But aluminum weighs a third as
much. Aluminum wire can therefore carry the same amount of electric
power as copper wire that weighs twice as much. Aluminum is more ductile
than copper, which means it can more easily be drawn into wires.
Heat conduction. The first large commercial use of aluminum was in
cookware. Aluminum cookware heats up quickly and evenly. Aluminum also
cools quickly, which helps make it popular for such items as beverage cans
and ice cube trays.
Light and heat reflection. Aluminum reflects about 80 percent of the
light
that strikes it. This property has made the metal widely used in lighting
fixtures. Aluminum also reflects heat well. Buildings with aluminum
roofs
reflect much of the sun's heat and so stay cooler in hot weather. When
fire
fighters must walk through flames, they wear special suits coated with
aluminum.
Other properties. Aluminum is nonmagnetic, which makes it valuable
for
protecting electrical equipment from magnetic interference. Aluminum
does not produce sparks when struck and can therefore be used near flammable
or explosive materials. The metal is not poisonous, and so food can be
safely wrapped in aluminum foil and cooked in aluminum pots. Aluminum can
be shaped by almost any metalworking process. It can also be bolted, glued,
riveted, soldered, welded, and otherwise joined by most methods used for
other metals. Finally, aluminum can be recycled. |
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| Chemical composition:
Al2O3
Ruby belongs to the mineral family corundum. The beauty of ruby lies
in the richness and intensity of its color. Ruby crystals are usually flat.
The finest ruby crystals are from the gem deposits of Mogok, Burma.
Small quantities of chromium give rise to the red color of ruby. |
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Chemical
composition:
Sapphire belongs to the mineral family corundum. The crystals are shaped
like barrels. They feature zones of blue to yellow color. Australia is
the most abundant source of blue and yellow sapphires. Sri Lanka
had been the supplier for blue and pink sapphires for at least 2000 years.
Tiny quantities of iron and titanium are responsible for the blue,
yellow, and green of Sapphire. |
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