Free Term Papers and Essays
Aluminum, symbol Al, the most abundant metallic element in the earth\'s
crust. The atomic number of aluminum is 13; the element is in group 13 (IIIa) of
the periodic table.
Hans Christian Orstead, Danish chemist, first isolated
aluminum in 1825, using a chemical process involving potassium amalgam. Between
1827 and 1845, Friedrich Wöhler, a German chemist, improved Oersted\'s process
by using metallic potassium. He was the first to measure the specific gravity of
aluminum and show its lightness. In 1854 Henri Sainte-Claire Deville, in France,
obtained the metal by reducing aluminum chloride with sodium. Aided by the
financial backing of Napoleon III, Deville established a large-scale
experimental plant and displayed pure aluminum at the Paris Exposition of 1855.
Aluminum is a lightweight, silvery metal. The atomic weight of aluminum is
26.9815; the element melts at 660° C (1220° F), boils at 2467° C (4473° F), and
has a specific gravity of 2.7. Aluminum is a strongly electropositive metal and
extremely reactive. In contact with air, aluminum rapidly becomes covered with a
tough, transparent layer of aluminum oxide that resists further corrosive
action. For this reason, materials made of aluminum do not tarnish or rust. The
metal reduces many other metallic compounds to their base metals. For example,
when thermite (a mixture of powdered iron oxide and aluminum) is heated, the
aluminum rapidly removes the oxygen from the iron; the heat of the reaction is
sufficient to melt the iron. This phenomenon is used in the thermite process for
welding iron .
The oxide of aluminum is amphoteric—showing both acidic and
basic properties. The most important compounds include the oxide, hydroxide,
sulfate, and mixed sulfate compounds. Anhydrous aluminum chloride is important
in the oil and synthetic-chemical industries. Many gemstones—ruby and sapphire,
for example—consist mainly of crystalline aluminum oxide.
Aluminum is
the most abundant metallic constituent in the crust of the earth; only the
nonmetals oxygen and silicon are more abundant. Aluminum is never found as a
free metal; commonly as aluminum silicate or as a silicate of aluminum mixed
with other metals such as sodium, potassium, iron, calcium, and magnesium. These
silicates are not useful ores, for it is chemically difficult, and therefore an
expensive process, to extract aluminum from them. bauxite an impure hydrated
aluminum oxide, is the commercial source of aluminum and its compounds.
In
1886 Charles Martin Hall in the United States and Paul L. T. Héroult in France
independently and almost simultaneously discovered that alumina or aluminum
oxide, would dissolve in fused cryolite (Na3AlF6) and could then be decomposed
electrolytically to a crude molten metal. A low-cost technique, the Hall-Héroult
process, is still the major method used for the commercial production of
aluminum, although new methods are under study. The purity of the product has
been increased until a commercially pure ingot is 99.5 percent pure aluminum; it
can be further refined to 99.99 percent.
A given volume of aluminum weighs
less than one-third as much as the same volume of steel. The only lighter metals
are lithium, beryllium, and magnesium. Its high strength-to-weight ratio makes
aluminum useful in the construction of aircraft, railroad cars, and automobiles,
and for other applications in which mobility and energy conservation are
important. Because of its high heat conductivity, aluminum is used in cooking
utensils and the pistons of internal-combustion engines. Aluminum has only 63
percent of the electrical conductance of copper for wire of a given size, but it
weighs less than half as much. An aluminum wire of comparable conductance to a
copper wire is thicker but still lighter than the copper. Weight is particularly
important in long-distance, high-voltage power transmission, and aluminum
conductors are now used to transmit electricity at 700,000 V or more.
The
metal is becoming increasingly important architecturally, for both structural
and ornamental purposes. Aluminum siding, storm windows, and foil make excellent
insulators. The metal is also used as a material in low-temperature nuclear
reactors because it absorbs relatively few neutrons. Aluminum becomes stronger
and retains its toughness as it gets colder and is therefore used at cryogenic
temperatures. Aluminum foil 0.018 cm (0.007 in) thick, now a common household
convenience, protects food and other perishable items from spoilage. Because of
its light weight, ease of forming, and compatibility with foods and beverages,
aluminum is widely used for containers, flexible packages, and easy-to-open
bottles and cans. The recycling of such containers is an increasingly important
energy-conservation measure. Aluminum\'s resistance to corrosion in salt water
also makes it useful in boat hulls and various aquatic devices.
A wide
variety of coating alloys and wrought alloys can be prepared that give the metal
greater strength, castability, or resistance to corrosion or high temperatures.
Some new alloys can be used as armor plate for tanks, personnel carriers, and
other military vehicles.
A given volume of aluminum weighs less than
one-third as much as the same volume of steel. The only lighter metals are
lithium, beryllium, and magnesium. Its high strength-to-weight ratio makes
aluminum useful in the construction of aircraft, railroad cars, and automobiles,
and for other applications in which mobility and energy conservation are
important. Because of its high heat conductivity, aluminum is used in cooking
utensils and the pistons of internal-combustion engines. Aluminum has only 63
percent of the electrical conductance of copper for wire of a given size, but it
weighs less than half as much. An aluminum wire of comparable conductance to a
copper wire is thicker but still lighter than the copper. Weight is particularly
important in long-distance, high-voltage power transmission, and aluminum
conductors are now used to transmit electricity at 700,000 V or more.
The
metal is becoming increasingly important architecturally, for both structural
and ornamental purposes. Aluminum siding, storm windows, and foil make excellent
insulators. The metal is also used as a material in low-temperature nuclear
reactors because it absorbs relatively few neutrons. Aluminum becomes stronger
and retains its toughness as it gets colder and is therefore used at cryogenic
temperatures. Aluminum foil 0.018 cm (0.007 in) thick, now a common household
convenience, protects food and other perishable items from spoilage. Because of
its light weight, ease of forming, and compatibility with foods and beverages,
aluminum is widely used for containers, flexible packages, and easy-to-open
bottles and cans. The recycling of such containers is an increasingly important
energy-conservation measure. Aluminum\'s resistance to corrosion in salt water
also makes it useful in boat hulls and various aquatic devices.
A wide
variety of coating alloys and wrought alloys can be prepared that give the metal
greater strength, castability, or resistance to corrosion or high temperatures.
Some new alloys can be used as armor plate for tanks, personnel carriers, and
other military vehicles.
In 1886 the world production of aluminum was less
than 45 kg (less than 100 lb), and its price was more than $11 per kg (more than
$5 per lb). In 1989, by contrast, the estimated world production of primary
aluminum was 18 million metric tons and an estimated 4 million metric tons was
produced in the United States alone, whereas the price of aluminum was less than
$2 per kg. U.S. consumption, by major markets, consisted of containers and
packaging, 31 percent; building and construction, 20 percent; transportation, 24
percent; electric equipment, 10 percent; consumer durables, 9 percent; and
miscellaneous, 6 percent. In 1989, recycled aluminum accounted for over 20
percent of total aluminum consumption in the United States.