Here is a brief description of aluminum.
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Aluminum , symbol Al, is 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 (see Periodic Law). 1

Atomic Structure2

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| | |Number of Energy Levels: 3 |
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| | |First Energy Level: 2 |
| | |Second Energy Level: 8 |
| | |Third Energy Level: 3 |

Hans Christian Oersted, a 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.
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II. Properties[pic] 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 (see Welding).

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 (see Alum). 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.3

Physical properties of aluminum

• Standard state: solid at 298 K • Color: silvery
|Top of Form |Density of solid [/kg m-3]: 2700 |
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|Top of Form |Molar volume [/cm3]: 10.00 |
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|Top of Form |Electrical resistivity [/10-8 Ω m; or μΩ cm]: 2.65 |
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|Top of Form |Melting point [/K]: 933.47 [or 660.32 °C (1220.58 °F)] |
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|Top of Form |Boiling point [/K]: 2792 [or 2519 °C (4566 °F)] (liquid range: 1858.53 K) |
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Manufacturing Processes
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III. Occurrence[pic]
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.
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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.5
Metallic aluminum was first prepared by Hans Oersted, a Danish chemist, in 1825. He obtained the metal by heating dry aluminum chloride with potassium metal.
AlCl3 + 3 K [pic]Al + 3 KCl
Robert Bunsen prepared aluminum metal in the 1850s by passing an electric current though molten sodium aluminum chloride. However, because both potassium metal and electricity were quite expensive, aluminum remained a laboratory chemical until after the invention of the mechanical electrical generator. In 1886, Charles Martin Hall of Oberlin, Ohio, and Paul Héroult of France, who were both 22 years old at the time, independently discovered and patented the process in which aluminum oxide is dissolved in molten cryolite and decomposed electrolytically. The Hall-Héroult process remains the only method by which aluminum metal is produced commercially.
The first step in the commercial production of aluminum is the separation of aluminum oxide from the iron oxide in bauxite. This is accomplished by dissolving the aluminum oxide in a concentrated sodium hydroxide solution. Aluminum ions form a soluble complex ion with hydroxide ions, while iron ions do not.
Al2O3xH2O(s) + 2 OH¯(aq) [pic]2 Al(OH)4¯(aq) + (x3) H2O(l)
After the insoluble iron oxide is filtered from the solution, Al(OH)3 is precipitated from the solution by adding acid to lower the pH to about 6. Then the precipitate is heated to produce dry Al2O3 (alumina).
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|2 Al(OH)3(s) |[pic] |Al2O3(s) + 3 H2O(g) |

In the Hall-Héroult process, aluminum metal is obtained by electrolytic reduction of alumina. Pure alumina melts at over 2000°C. To produce an electrolyte at lower temperature, alumina is dissolved in molten cryolite at 1000°C. The electrolyte is placed in an iron vat lined with graphite. The vat serves as the cathode. Carbon anodes are inserted into the electrolyte from the top. The oxygen produced at the anodes reacts with them, forming carbon dioxide and carbon monoxide. Therefore, the anodes are consumed and need to be replaced periodically. Molten aluminum metal is produced at the cathode, and it sinks to the bottom of the vat. The principal cell reactions are
|cathode: |4 Al3+ + 12 e¯ |[pic] |4 Al(l) |
|anode: |6 O2¯ |[pic] |3 O2(g) + 12 e¯ |
|net: |4 Al3+ |[pic] |4 Al(l) + 3 O2(g) |

At intervals, a plug is removed from the vat and the molten aluminum is drained. The heat required to keep the mixture molten is provided by resistive heating of the electrolyte by the current passing through the cell. Typical cells use a potential of 4 to 5 volts and a current of 100,000 amperes. 6
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The method of obtaining aluminum metal by the electrolysis of alumina dissolved in cryolite was discovered in 1886 by Hall in the U.S. and at about the same time by Heroult in France. Cryolite, a natural ore found in Greenland, is no longer widely used in commercial production, but has been replaced by an artificial mixture of sodium, aluminum, and calcium fluorides.
Aluminum can now be produced from clay, but the process is not economically feasible at present. Aluminum is the most abundant metal to be found in the earth's crust (8.1%), but is never found free in nature. In addition to the minerals mentioned above, it is found in granite and in many other common minerals. 7 Aluminum ore, most commonly bauxite, is plentiful and occurs mainly in tropical and sub-tropical areas: Africa, West Indies, South America and Australia. There are also some deposits in Europe. Bauxite is refined into aluminum oxide trihydrate (alumina) and then electrolytically reduced into metallic aluminum. Primary aluminum production facilities are located all over the world, often in areas where there are abundant supplies of inexpensive energy, such as hydroelectric power. Two to three tons of bauxite is required to produce one ton of alumina and two tons of alumina are required to produce one ton of aluminum metal. The basis for all modern primary aluminum-smelting plants is the Hall-Héroult Process, invented in 1886. Alumina is dissolved in an electrolytic bath of molten cryolite (sodium aluminum fluoride) within a large carbon or graphite lined steel container known as a "pot". An electric current is passed through the electrolyte at low voltage, but very high current, typically 150,000 amperes. The electric current flows between a carbon anode (positive), made of petroleum coke and pitch, and a cathode (negative), formed by the thick carbon or graphite lining of the pot.
Molten aluminum is deposited at the bottom of the pot and is siphoned off periodically, taken to a holding furnace, often but not always blended to an alloy specification, cleaned and then generally cast.
A typical aluminum smelter consists of around 300 pots. These will produce some 125,000 tons of aluminum annually. However, some of the latest generation of smelters is in the 350-400,000 ton range.
On average, around the world, it takes some 15.7 kWh of electricity to produce one kilogram of aluminum from alumina. Design and process improvements have progressively reduced this figure from about 21kWh in the 1950's.
Smelter Energy Use Aluminum is formed at about 900°C, but once formed has a melting point of only 660°C. In some smelters this spare heat is used to melt recycled metal.

Recycled aluminum requires only 5 per cent of the energy required to make "new" aluminum. Blending recycled metal with new metal allows considerable energy savings, as well as the efficient use of process heat. There is no difference between primary and recycled aluminum in terms of quality or properties.
Aluminum smelting is energy intensive, which is why the world's smelters are located in areas which have access to abundant power resources (hydro-electric, natural gas, coal or nuclear). Many locations are remote and the electricity is generated specifically for the aluminum plant.
The smelting process is continuous. A smelter cannot easily be stopped and restarted. If production is interrupted by a power supply failure of more than four hours, the metal in the pots will solidify, often requiring an expensive rebuilding process.
From time to time individual pot linings reach the end of their useful life and the pots are then taken out of service and relined. Most smelters produce aluminum of 99.7% purity, which is acceptable for most applications. However, super purity aluminum (99.99%) is used for some special applications, typically those where high ductility or conductivity is required. The marginal difference in the purities of smelter grade aluminum and super purity aluminum results in significant changes in the properties of the metal.8 La Grande Baie Smelter in Quebec, Canada [pic]
IV. Uses[pic]
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 lightweight, 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. 9
These alloys are of vital importance in the construction of modern aircraft and rockets. Aluminum, evaporated in a vacuum, forms a highly reflective coating for both visible light and radiant heat. These coatings soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. They are used to coat telescope mirrors and to make decorative paper, packages, and toys. 10

[pic]Economics

V. Production
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. 11
Aluminum can be alloyed with other materials to make an array of metals with different properties. The main alloying ingredients are iron, silicon, zinc, copper and magnesium. Other materials are also used.
Aluminum can be rolled into plate, sheets, or wafer thin foils the thickness of a human hair. The rolling process changes the characteristics of the metal, making it less brittle and more ductile.
Aluminum can be cast into an infinite variety of shapes. The statue of Eros in London's Piccadilly Circus erected in 1893 is cast aluminum.
Aluminum can be extruded by heating it to around 500ºC and pushing it through a die at great pressure to form intricate shapes and sections.
Aluminum can be forged by hammering to make stress-bearing parts for aircraft and internal combustion engines.
Aluminum can be joined by welding, adhesive bonding, riveting or screwing. It can be formed by bending or superplastic molding. It can be milled or turned on a lathe.
The properties of the metal can be modified through heat treatment or mechanical working.
The appearance can be modified by surface treatments such as anodising or powder coating.
Aluminum powder, flake and paste are formed by blowing gas under pressure at molten aluminum. This process forms droplets of different sizes. These aluminum products are used in explosives, rocket fuel, metallurgy, chemicals, inks, and decorative materials.
Aluminum Chemicals are important in water treatment, papermaking, fire retardants, fillers and pharmaceuticals. 12