Atomic Number: 13
Atomic Weight: 26.981538
Family: Boron Family
CAS RN: 7429-90-5
Description: Silvery, light weight, non-magnetic, non-sparking, malleable metal.
State (25°C): Solid
Oxidation states: +3
Molar Volume: 9.99 cm3/mole
Valence Electrons: 3p1
|Boiling Point: 2740°K, 2467°C, 4473°F
Melting Point: 933.4°K, 660.25°C, 1220.45°F
Electrons Energy Level: 2, 8, 3
Isotopes: 15 + 1 Stable
Heat of Vaporization: 293.4 kJ/mol
Heat of Fusion: 10.79 kJ/mol
Density: 2.702 g/cm3 @ 300°K
Specific Heat: 0.9 J/g°K
Atomic Radius: 1.82Å
Ionic Radius: 0.535Å
Electronegativity: 1.61 (Pauling); 1.47 (Allrod Rochow)
Vapor Pressure: 2.42E-06 Pa @ 660.25°C
Aluminum ranks third on the list of the ten most abundant elements in the earth's
crust, while its oxide is fourth among the ten most common compounds in the crust. It is
the most abundant metal on the planet.
The ancient Greeks and Romans used Aluminum salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. In 1761 Gutyon de Morveau suggested calling the base alum alumine. In 1807 or 1808, Humphry Davy identified the existence of a metal base of alum, which he at first named alumium and later aluminum.
Soft, lightweight and silvery, its existence was proposed by Antoine Lavoisier in 1787. Friedrich Wohler is generally credited with isolating aluminum (Latin alumen, alum) in 1827 by mixing anhydrous Aluminum Chloride with Potassium. The metal, however, had indeed been produced for the first time two years earlier but in an impure form by the Danish physicist and chemist Hans Christian Ørsted in 1825. Therefore, Ørsted can also be listed as the discoverer of the metal. Further, Pierre Berthier discovered Aluminum in Bauxite Ore and successfully extracted it. The Frenchman Henri Saint-Claire Deville improved Wöhler's method in 1846 and described his improvements in a book in 1859, chief among these being the substitution of Sodium for the considerably more expensive Potassium.
1s2 2s2p6 3s2p1
The ancient Greeks and Romans used Aluminum salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic.
Alchemical Symbol, Aluminum
In 1761 Gutyon de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first named alumium and later aluminum.
Friedrich Wohler is generally credited with isolating aluminum (Latin alumen, alum) in 1827 by mixing anhydrous Aluminum Chloride with Potassium. The metal, however, had indeed been produced for the first time two years earlier but in an impure form by the Danish physicist and chemist Hans Christian Ørsted. Therefore, Ørsted can also be listed as the discoverer of the metal. Further, Pierre Berthier discovered Aluminum in Bauxite Ore and successfully extracted it. The Frenchman Henri Saint-Claire Deville improved Wöhler's method in 1846 and described his improvements in a book in 1859, chief among these being the substitution of Sodium for the considerably more expensive Potassium.
Aluminum was selected as the material to be used for the apex of the Washington Monument, at a time when one ounce (30 grams) cost twice the daily wages of a common worker in the project; aluminium was a semiprecious metal at that time.
The American Charles Martin Hall of Oberline, Ohio applied for a patent (400655) in 1886 for an electrolytic process to extract Aluminum using the same technique that was independently being developed by the Frenchman Paul Heroult in Europe. The invention of the Hall-Heroult Process in 1886 made extracting Aluminum from minerals cheaper, and is now the principal method in common use throughout the world. The Hall-Heroult process cannot produce Super Purity Aluminium directly. Upon approval of his patent in 1889, Hall, with the financial backing of Alfred E. Hunt of Pittsburgh, PA, started the Pittsburgh Reduction Company, renamed to Aluminum Company of America in 1907, later shortened to Alcoa.
Germany became the world leader in Aluminum production soon after Adolf Hitler's rise to power. By 1942, however, new hydroelectric power projects such as the Grand Coulee Dam gave the United States something Nazi Germany could not hope to compete with, namely the capability of producing enough Aluminum to manufacture sixty thousand warplanes in four years.
The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is alumium, which Humphry Davy employed in 1808 for the metal he was trying to isolate electrolytically from the mineral alumina. The citation is from his journal Philosophical Transactions: "Had I been so fortunate as..to have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium."
By 1812, Davy had settled on aluminum, which, as other sources note, matches its Latin root. He wrote in the journal Chemical Philosophy: "As yet Aluminum has not been obtained in a perfectly free state." But the same year, an anonymous contributor to the Quarterly Review, British political-literary journal, objected to aluminum and proposed the name aluminium, "for so we shall take the liberty of writing the word, in preference to aluminum, which has a less classical sound."
The -ium suffix had the advantage of conforming to the precedent set in other newly discovered elements of the period: Potassium, Sodium, Magnesium, Calcium, and Strontium (all of which Davy had isolated himself). Nevertheless, -um spellings for elements were not unknown at the time, as for example Platinum, known to Europeans since the 16th century, Molybdenum, discovered in 1778, and Tantalum, discovered in 1802.
Americans adopted -ium for most of the 19th century, with aluminium appearing in Webster's Dictionary of 1828. In 1892, however, Charles Martin Hall used the -um spelling in an advertising handbill for his new electrolytic method of producing the metal, despite his constant use of the -ium spelling in all the patents he filed between 1886 and 1903. It has consequently been suggested that the spelling on the flier was a simple spelling mistake. Hall's domination of production of the metal ensured that the spelling aluminum became the standard in North America; the Webster Unabridged Dictionary of 1913, though, continued to use the -ium version.
In 1926, the American Chemical Society officially decided to use aluminum in its publications; American dictionaries typically label the spelling aluminium as a British variant.
In the UK and other countries using British spelling, only aluminium is used. In the United States, the spelling aluminium is largely unknown, and the spelling aluminum predominates. The Canadian Oxford Dictionary prefers aluminum.
In other English-speaking countries, the spellings (and associated pronunciations) aluminium and aluminum are both in common use in scientific and nonscientific contexts. The spelling in virtually all other languages is analogous to the -ium ending.
The International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990, but three years later recognized aluminum as an acceptable variant. Hence their periodic table includes both, but places aluminium first. IUPAC officially prefers the use of aluminium in its internal publications, although several IUPAC publications use the spelling aluminum.
Aluminum is a soft, lightweight metal with normally a dull silvery appearance caused by a thin layer of oxidation that forms quickly when the metal is exposed to air. Aluminum Oxide, Al2O3, has a higher melting point than pure Aluminum. Aluminum is nontoxic (as the metal), nonmagnetic, and nonsparking. It has a tensile strength of about 49 megapascals (MPa) in a pure state and 400 MPa as an alloy. Aluminum is about one-third as dense as steel or Copper, it is malleable, ductile, and easily machined and cast. It has excellent corrosion resistance and durability because of the protective oxide layer.
Aluminum is one of the few metals which retains full silvery reflectance, even in finely powdered form, which makes it a very important component of silver paints.
Aluminum mirror finish has the highest reflectance of any metal in the 200400 nm (UV) and the 300010000 nm (far IR) regions, while in the 400700 nm visible range it is slightly outdone by Silver and in the 7003000 (near IR) by Silver, Gold, and Copper. It is the second-most malleable metal (after Gold) and the sixth-most ductile. Aluminum is a good thermal and electrical conductor. Aluminum is capable of being a superconductor, with a superconducting critical temperature of 1.2oKelvin.
Aluminum is found primarily in Bauxiite Ore and is remarkable for its ability to resist corrosion (due to the phenomenon of passivation) and its light weight. The metal is used in many industries to manufacture a large variety of products and is very important to the world economy. Structural components made from Aluminum and its alloys are vital to the aerospace industry and very important in other areas of transportation and building.
As the Metal
Whether measured in terms of quantity or value, the global use of Aluminum exceeds that of any other metal except Iron, and it is important in virtually all segments of the world economy.
Relatively pure Aluminum is encountered only when corrosion resistance and/or workability is more important than strength or hardness. Pure Aluminum serves as an excellent reflector (approximately 99%) of visible light and a good reflector (approximately 95%) of infrared. A thin layer of Aluminum can be deposited onto a flat surface by chemical vapor deposition or chemical means to form optical coatings and mirrors. These coatings form an even thinner layer of protective Aluminum oxide that does not deteriorate, as Silver coatings do. Nearly all modern mirrors are made using a thin coating of Aluminum on the back surface of a sheet of float glass. Telescope mirrors are also made with Aluminum, but are front coated to avoid internal reflections, refraction, and transparency losses. These first surface mirrors are more susceptible to damage than household back-surface mirrors.
Pure Aluminum has a low tensile strength, but when combined with thermo-mechanical processing, Aluminum alloys display a marked improvement in mechanical properties, especially when tempered. Aluminum alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio. Aluminum readily forms alloys with many elements such as Copper, Zinc, Magnesium, Manganese and Silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to loosely as "Aluminum," are actually alloys. For example, the common Aluminum foils are alloys of 92% to 99% Aluminum.
Aluminum alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO). Selecting the right alloy for a given application entails considerations of strength, ductility, formability, weldability and corroson resistance to name a few. Aluminum is used extensively in modern aircraft due to its high strength to weight ratio.
Improper use of Aluminum may result in problems, particularly in contrast to Iron or steel, which appear "better behaved" to the intuitive designer, mechanic, or technician. The reduction by two thirds of the weight of an Aluminum part compared to a similarly sized Iron or steel part seems enormously attractive, but it must be noted that this replacement is accompanied by a reduction by two thirds in the stiffness of the part. Therefore, although direct replacement of an Iron or steel part with a duplicate made from Aluminum may still give acceptable strength to withstand peak loads, the increased flexibility will cause three times more deflection in the part.
Where failure is not an issue but excessive flex is undesirable due to requirements for precision of location, or efficiency of transmission of power, simple replacement of steel tubing with similarly sized Aluminum tubing will result in a degree of flex which is undesirable; for instance, the increased flex under operating loads caused by replacing steel bicycle frame tubing with Aluminum tubing of identical dimensions will cause misalignment of the power-train as well as absorbing the operating force. To increase the rigidity by increasing the thickness of the walls of the tubing increases the weight proportionately, so that the advantages of lighter weight are lost as the rigidity is restored.
In such cases, Aluminum may best be used by redesigning the dimension of the part to suit its characteristics; for instance making a bicycle frame of Aluminum tubing which has an oversize diameter rather than thicker walls. In this way, rigidity can be restored or even enhanced without increasing weight. The limit to this process is the increase in susceptibility to what is termed "buckling" failure, where the deviation of the force from any direction other than directly along the axis of the tubing, causes folding of the walls of the tubing.
The latest models of the Corvette automobile, among others, are a good example of redesigning parts to make best use of Aluminum's advantages. The Aluminum chassis members and suspension parts of these cars have large overall dimensions for stiffness but are lightened by reducing cross-sectional area and removing unneeded metal; as a result, they are not only equally or more durable and stiff as the usual steel parts, but they possess an airy gracefulness which most people find attractive. Similarly, Aluminum bicycle frames can be optimally designed so as to provide rigidity where required, yet exhibit some extra flexibility which functions as a natural shock-absorber for the rider.
The strength and durability of Aluminum varies widely, not only as a result of the components of the specific alloy, but also as a result of the particular manufacturing process. This variability, plus a learning-curve in employing it, has from time to time gained Aluminum a bad reputation. For instance, a high frequency of failure in many poorly-designed early Aluminum bicycle frames in the 1970s, temporarily hurt Aluminum's reputation for this use. However, the widespread use of Aluminum components in the aerospace and automotive high performance industries, where huge stresses are withstood with vanishingly small failure rates, illustrates that properly-built Aluminum bicycle components need not be intrinsically unreliable. Time and experience has subsequently proven this to be the case.
Similarly, use of Aluminum in automotive applications, particularly in engine parts which must survive in difficult conditions, has benefited from development over time. An Audi engineer, in commenting about the V12 engine, producing over 500 horsepower (370 kW), of an Auto Union race car of the 1930s which was recently restored by the Audi factory, that the Aluminum alloy of which the engine was constructed would today be used only for lawn furniture and the like. Even the Aluminum cylinder heads and crankase of the Corvair, built as recently as the 1960s, earned a reputation for failure and stripping of threads in holes, even as large as spark plug holes, which is not seen in current Aluminum cylinder heads.
One important structural limitation of an Aluminum alloy is its fatigue properties. While steel has a high fatigue limit (the structure can theoretically withstand an infinite number of cyclical loadings at this stress), Aluminum's fatigue limit is near zero, meaning that it will eventually fail under even very small cyclic loadings, but for small stresses this can take an exceedingly long time.
Often, the metal's sensitivity to heat must also be considered. Even a relatively routine workshop procedure involving heating is complicated by the fact that Aluminum, unlike steel, will melt without first glowing red. Forming operations where a blow torch is used therefore requires some expertise, since no visual signs reveal how close the material is to melting.
Aluminum also is subject to internal stresses and strains when it is overheated; the tendency of the metal to creep under these stresses tends to result in delayed distortions. For instance, the warping or cracking of overheated Aluminum automobile cylinder heads is commonly observed, sometimes years later, as is the tendency of welded Aluminum bicycle frames to gradually twist out of alignment from the stresses of the welding process. Thus, the aerospace industry avoids heat altogether by joining parts with adhesives or mechanical fasteners. Adhesive bonding was used in some bicycle frames in the 1970s, with unfortunate results when the Aluminum tubing corroded slightly, loosening the adhesive and collapsing the frame.
Stresses in overheated Aluminum can be relieved by heat-treating the parts in an oven and gradually cooling it in effect annealing the stresses. Yet these parts may still become distorted, so that heat-treating of welded bicycle frames, for instance, can result in a significant fraction becoming misaligned. If the misalignment is not too severe, the cooled parts may be bent into alignment. Of course, if the frame is properly designed for rigidity, that bending will require enormous force.
Aluminum's intolerance to high temperatures has not precluded its use in rocketry; even for use in constructing combustion chambers where gases can reach 3500oK. The Agena upper stage engine used a regeneratively cooled Aluminum design for some parts of the nozzle, including the thermally critical throat region; in fact the extremely high thermal conductivity of Aluminum prevented the throat from reaching the melting point even under massive heat flux, resulting in a reliable lightweight component.
Because of its high conductivity and relatively low price compared to Copper in the 1960s, Aluminum was introduced at that time for household electrical wiring in the United States, even though many fixtures had not been designed to accept Aluminum wire. But the new use brought some problems:
All of this resulted in overheated and loose connections, and this in turn resulted in some fires. Builders then became wary of using the wire, and many jurisdictions outlawed its use in very small sizes, in new construction. Yet newer fixtures eventually were introduced with connections designed to avoid loosening and overheating. At first they were marked "Al/Cu", but they now bear a "CO/ALR" coding.
Another way to forestall the heating problem is to crimp the Aluminum wire to a short "pigtail" of Copper wire. A properly done high-pressure crimp by the proper tool is tight enough to reduce any thermal expansion of the Aluminum. Today, new alloys, designs, and methods are used for Aluminum wiring in combination with Aluminum terminations.
Production and Refinement
Although Aluminum is the most abundant metallic element in Earth's crust (believed to be 7.5% to 8.1%), it is very rare in its free form, occurring in oxygen-deficient environments such as volcanic mud, and it was once considered a precious metal more valuable than Gold. Napoleon III, Emperor of the French, is reputed to have given a banquet where the most honoured guests were given Aluminum utensils, while the other guests had to make do with Gold ones. Aluminum has been produced in commercial quantities for just over 100 years.
Aluminum is a reactive metal that is difficult to extract from ore, Aluminum Oxide, Al2O3. Direct reduction with Carbon, for example is not economically viable since Aluminum Oxide has a melting point of about 2,000°C. Therefore, it is extracted by electrolysis, that is, the Aluminum Oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the operational temperature of the reduction cells is around 950 to 980°C. Cryolite is found as a mineral in Greenland, but in industrial use it has been replaced by a synthetic substance. Cryolite is a mixture of Aluminum, Sodium, and Calcium Fluorides: (Na3AlF6). The Aluminium Oxide (a white powder) is obtained by refining Bauxite in the Bayer Process. (Previously, the Deville Process was the predominant refining technology).
The electrolytic process replaced the Wohler Process, which involved the reduction of anhydrous Aluminum chloride with Potassium. Both of the electrodes used in the electrolysis of Aluminum Oxide are Carbon. Once the ore is in the molten state, its ions are free to move around. The reaction at the cathode the negative terminal is:
Al3+ + 3 e- Al
Here the Aluminum Ion is being reduced (electrons are added). The Aluminum metal then sinks to the bottom and is tapped off.
At the positive electrode (anode), Oxygen is formed:
2 O2- O2 + 4 e-
This Carbon anode is then oxidised by the Oxygen, releasing Carbon Dioxide. The anodes in a reduction must therefore be replaced regularly, since they are consumed in the process:
O2 + C CO2
Unlike the anodes, the cathodes are not oxidised because there is no Oxygen present at the cathode. The Carbon cathode is protected by the liquid Aluminum inside the cells. Nevertheless, cathodes do erode, mainly due to electrochemical processes. After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.
Aluminum electrolysis with the Hall-Heroult Process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologically. The world-wide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of Aluminum produced from alumina, (52 to 56 MJ/kg). The most modern smelters reach approximately 12.8 kW·h/kg (46.1 MJ/kg). Reduction line current for older technologies are typically 100 to 200 kA. State-of-the-art smelters operate with about 350 kA. Trials have been reported with 500 kA cells.
Recovery of the metal via recycling has become an important facet of the Aluminum industry. Recycling involves melting the scrap, a process that uses only five percent of the energy needed to produce Aluminum from ore. Recycling was a low-profile activity until the late 1960s, when the growing use of Aluminum beverage cans brought it to the public consciousness.
Electric power represents about 20% to 40% of the cost of producing Aluminum, depending on the location of the smelter. Smelters tend to be situated where electric power is both plentiful and inexpensive, such as South Africa, the South Island of New Zealand, Australia, the People's Republic of China, the Middle East, Russia, Quebec and British Columbia in Canada, and Iceland.
In 2004, the People's Republic of China was the top world producer of Aluminum.
Although aluminum is the most abundant metal in the Earth's crust, it is never found free in nature. All of the earth's aluminum has combined with other elements to form compounds. Two of the most common compounds are alum, such as potassium aluminum sulfate (KAl(SO4)2·12H2O), and aluminum oxide (Al2O3). About 8.2% of the earth's crust is composed of aluminum.
Oxidation State One
Oxidation State Two
Oxidation State Three
Aluminum has fifteen isotopes. Only 27Al is stable and 26Al (radioactive isotope, t1/2 = 7.2 × 105 years) occur naturally, however 27Al has a natural abundance of 100%. 26Al is produced from Argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminum isotopes have found practical application in dating marine sediment, Manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales. Cosmogenic 26Al was first applied in studies of the Moon and Meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further 26Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Possibly, the energy released by the decay of 26Al was responsible for the remelting and differentiation of some asteroids after their formation 4.6 billion years ago.
In the journal Science of January 14, 2005 it was reported that clusters of 13 Aluminum atoms (Al13) had been made to behave like an Iodine atom; and, 14 Aluminum atoms (Al14) behaved like an alkaline earth atom. The researchers also bound 12 Iodine atoms to an Al13 cluster to form a new class of polyiodide. This discovery is reported to give rise to the possibility of a new characterization of the Periodic Table: Superatoms. The research teams were led by Shiv N. Khanna (Virginia Commonwealth University) and A. Welford Castleman Jr. (Penn State University).
|Al26||25.9869||7.17E 5 years|
|Aluminum is a neurotoxin that alters the function of the blood-brain barrier. It is one of the few abundant elements that appears to have no beneficial function to living cells.|
A small percent of people are allergic to it they experience contact dermatitis from any form of it: an itchy rash from using styptic or antiperspirant products, digestive disorders and inability to absorb nutrients from eating food cooked in Aluminum pans, and vomiting and other symptoms of poisoning from ingesting such products as Amphojel, and Maalox (antacids). In other people, Aluminum is not considered as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts. The use of Aluminum cookware, popular because of its corrosion resistance and good heat conduction, has not been shown to lead to Aluminum toxicity in general. Excessive consumption of antacids containing Aluminum compounds and excessive use of Aluminum-containing antiperspirants are more likely causes of toxicity. In research published in the Journal of Applied Toxicology, Dr. Philippa D. Darby of the University of Reading has shown that Aluminum salts increase estrogen-related gene expression in human brest cancer cells grown in the laboratory. These salts' estrogen-like effects have lead to their classification as a metalloestrogen.
It has been suggested that Aluminum is a cause of Alzheimer's Disease, as some brain plaques have been found to contain the metal. Research in this area has been inconclusive; Aluminum accumulation may be a consequence of the Alzheimer's damage, not the cause. In any event, if there is any toxicity of Aluminum it must be via a very specific mechanism, since total human exposure to the element in the form of naturally occurring clay in soil and dust is enormously large over a lifetime.
Mercury applied to the surface of an Aluminum alloy can damage the protective oxide surface film. This may cause further corrosion and weakening of the structure. For this reason, mercury thermometers are not allowed on many airliners, as Aluminum is used in many aircraft structures.
|Powdered Aluminum can react with Fe2O3 to form Fe and Al2O3. This mixture is known as thermite, which burns with a high energy output. Thermite can be produced inadvertently during grinding operations, but the high ignition temperature makes incidents unlikely in most workshop environments.|
Aluminum and Plants (Phytoremediation)
Aluminum is primary among the factors that contribute to the loss of plant production on acid soils. Although it is generally harmless to plant growth in pH-neutral soils, the concentration in acid soils of toxic Al3+ cation increases and disturbs root growth and function.
Wheat's adaption to allow Aluminum tolerance is such that the Aluminum induces a release of organic compounds that bind to the harmful Aluminum cations. Sorghum is believed to have the same tolerance mechanism. The first gene for Aluminum tolerance has been identified in wheat. A group in the US Department of Agriculture showed that sorghum's Aluminum tolerance is controlled by a single gene, as for wheat. This is not the case in all plants.
Atomic Radius (Å): 1.82Å
Electrochemical Equivalents: 0.33556 g/amp-hr
Atomic Mass Average: 26.98154
(L. alumen, alum) The ancient Greeks and Romans used alum in medicine as an astringent, and as a mordant in dyeing. In 1761 de Morveau proposed the name alumine for the base in alum, and Lavoisier, in 1787, thought this to be the oxide of a still undiscovered metal. Wohler is generally credited with having isolated the metal in 1827, although an impure form was prepared by Oersted two years earlier. In 1807, Davy proposed the name alumium for the metal, undiscovered at that time, and later agreed to change it to aluminum. Shortly thereafter, the name aluminium was adopted to conform with the "ium" ending of most elements, and this spelling is now in use elsewhere in the world. Aluminium was also the accepted spelling in the U.S. until 1925, at which time the American Chemical Society officially decided to use the name aluminum thereafter in their publications. 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. Pure aluminum, a silvery-white metal, possesses many desirable characteristics. It is light, it is nonmagnetic and nonsparking, stands second among metals in the scale of malleability, and sixth in ductility. It is extensively used for kitchen utensils, outside building decoration, and in thousands of industrial applications where a strong, light, easily constructed material is needed. Although its electrical conductivity is only about 60% that of copper, it is used in electrical transmission lines because of its light weight. Pure aluminum is soft and lacks strength, but it can be alloyed with small amounts of copper, magnesium, silicon, manganese, and other elements to impart a variety of useful properties. 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 coating soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. They have found application in coatings for telescope mirrors, in making decorative paper, packages, toys, and in many other uses. The compounds of greatest importance are aluminum oxide, the sulfate, and the soluble sulfate with potassium (alum). The oxide, alumina, occurs naturally as ruby, sapphire, corundum, and emery, and is used in glassmaking and refractories. Synthetic ruby and sapphire have found application in the construction of lasers for producing coherent light.
Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond