Aluminum

The metallic element aluminum is the third most plentiful element in the earth's crust, comprising 8% of the planet's soil and rocks (oxygen and silicon make up 47% and 28%, respectively). In nature, aluminum is found only in chemical compounds with other elements such as sulphur, silicon, and oxygen. Pure, metallic aluminum can be economically produced only from aluminum oxide ore.

Metallic aluminum has many properties that make it useful in a wide range of applications. It is lightweight, strong, nonmagnetic, and nontoxic. It conducts heat and electricity and reflects heat and light. It is strong but easily workable, and it retains its strength under extreme cold without becoming brittle. The surface of aluminum quickly oxidizes to form an invisible barrier to corrosion. Furthermore, aluminum can easily and economically be recycled into new products.

Background

Aluminum compounds have proven useful for thousands of years. Around 5000 b.c., Persian potters made their strongest vessels from clay that contained aluminum oxide. Ancient Egyptians and Babylonians used aluminum compounds in fabric dyes, cosmetics, and medicines. However, it was not until the early nineteenth century that aluminum was identified as an element and isolated as a pure metal. The difficulty of extracting aluminum from its natural compounds kept the metal rare for many years; half a century after its discovery, it was still as rare and valuable as silver.

In 1886, two 22-year-old scientists independently developed a smelting process that made economical mass production of aluminum possible. Known as the Hall-Heroult process after its American and French inventors, the process is still the primary method of aluminum production today. The Bayer process for refining aluminum ore, developed in 1888 by an Austrian chemist, also contributed significantly to the economical mass production of aluminum.

In 1884, 125 lb (60 kg) of aluminum was produced in the United States, and it sold for about the same unit price as silver. In 1995, U.S. plants produced 7.8 billion lb (3.6 million metric tons) of aluminum, and the price of silver was seventy-five times as much as the price of aluminum.

Raw Materials

Aluminum compounds occur in all types of clay, but the ore that is most useful for producing pure aluminum is bauxite. Bauxite consists of 45-60% aluminum oxide, along with various impurities such as sand, iron, and other metals. Although some bauxite deposits are hard rock, most consist of relatively soft dirt that is easily dug from open-pit mines. Australia produces more than one-third of the world's supply of bauxite. It takes about 4 lb (2 kg) of bauxite to produce 1 lb (0.5 kg) of aluminum metal.

Caustic soda (sodium hydroxide) is used to dissolve the aluminum compounds found in the bauxite, separating them from the impurities. Depending on the composition of the bauxite ore, relatively small amounts of other chemicals may be used in the extraction of aluminum. Starch, lime, and sodium sulphide are some examples.

Cryolite, a chemical compound composed of sodium, aluminum, and fluorine, is used as the electrolyte (current-conducting medium) in the smelting operation. Naturally occurring cryolite was once mined in Greenland, but the compound is now produced synthetically for use in the production of aluminum. Aluminum fluoride is added to lower the melting point of the electrolyte solution.

The other major ingredient used in the smelting operation is carbon. Carbon electrodes transmit the electric current through the electrolyte. During the smelting operation, some of the carbon is consumed as it combines with oxygen to form carbon dioxide. In fact, about half a pound (0.2 kg) of carbon is used for every pound (2.2 kg) of aluminum produced. Some of the carbon used in aluminum smelting is a byproduct of oil refining; additional carbon is obtained from coal.

Because aluminum smelting involves passing an electric current through a molten electrolyte, it requires large amounts of electrical energy. On average, production of 2 lb (1 kg) of aluminum requires 15 kilowatt-hours (kWh) of energy. The cost of electricity represents about one-third of the cost of smelting aluminum.

The Manufacturing
Process

Aluminum manufacture is accomplished in two phases: the Bayer process of refining the bauxite ore to obtain aluminum oxide, and the Hall-Heroult process of smelting the aluminum oxide to release pure aluminum.

The Bayer process

• 1 First, the bauxite ore is mechanically crushed. Then, the crushed ore is mixed with caustic soda and processed in a grinding mill to produce a slurry (a watery suspension) containing very fine particles of ore.
• 2 The slurry is pumped into a digester, a tank that functions like a pressure cooker. The slurry is heated to 230-520°F (110-270°C) under a pressure of 50 lb/in² (340 kPa). These conditions are maintained for a time ranging from half an hour to several hours. Additional caustic soda may be added to ensure that all aluminum-containing compounds are dissolved.
• 3 The hot slurry, which is now a sodium aluminate solution, passes through a series of flash tanks that reduce the pressure and recover heat that can be reused in the refining process.
• 4 The slurry is pumped into a settling tank. As the slurry rests in this tank, impurities that will not dissolve in the caustic soda settle to the bottom of the vessel. One manufacturer compares this process to fine sand settling to the bottom of a glass of sugar water; the sugar does not settle out because it is dissolved in the water, just as the aluminum in the settling tank remains dissolved in the caustic soda. The residue (called "red mud") that accumulates in the bottom of the tank consists of fine sand, iron oxide, and oxides of trace elements like titanium.
• 5 After the impurities have settled out, the remaining liquid, which looks somewhat like coffee, is pumped through a series of cloth filters. Any fine particles of impurities that remain in the solution are trapped by the filters. This material is washed to recover alumina and caustic soda that can be reused.
• 6 The filtered liquid is pumped through a series of six-story-tall precipitation tanks. Seed crystals of alumina hydrate (alumina bonded to water molecules) are added through the top of each tank. The seed crystals grow as they settle through the liquid and dissolved alumina attaches to them.
• 7 The crystals precipitate (settle to the bottom of the tank) and are removed. After washing, they are transferred to a kiln for calcining (heating to release the water molecules that are chemically bonded to the alumina molecules). A screw conveyor moves a continuous stream of crystals into a rotating, cylindrical kiln that is tilted to allow gravity to move the material through it. A temperature of 2,000° F (1,100° C) drives off the water molecules, leaving anhydrous (waterless) alumina crystals. After leaving the kiln, the crystals pass through a cooler.

The Hall-Heroult process

Smelting of alumina into metallic aluminum takes place in a steel vat called a reduction pot. The bottom of the pot is lined with carbon, which acts as one electrode (conductor of electric current) of the system. The opposite electrodes consist of a set of carbon rods suspended above the pot; they are lowered into an electrolyte solution and held about 1.5 in (3.8 cm) above the surface of the molten aluminum that accumulates on the floor of the pot. Reduction pots are arranged in rows (potlines) consisting of 50-200 pots that are connected in series to form an electric circuit. Each potline can produce 66,000-110,000 tons (60,000-100,000 metric tons) of aluminum per year. A typical smelting plant consists of two or three potlines.

• 8 Within the reduction pot, alumina crystals are dissolved in molten cryolite at a temperature of 1,760-1,780° F (960-970° C) to form an electrolyte solution that will conduct electricity from the carbon rods to the carbon-lined bed of the pot. A direct current (4-6 volts and 100,000-230,000 amperes) is passed through the solution. The resulting reaction breaks the bonds between the aluminum and oxygen atoms in the alumina molecules. The oxygen that is released is attracted to the carbon rods, where it forms carbon dioxide. The freed aluminum atoms settle to the bottom of the pot as molten metal.

  The smelting process is a continuous one, with more alumina being added to the cryolite solution to replace the decomposed compound. A constant electric current is maintained. Heat generated by the flow of electricity at the bottom electrode keeps the contents of the pot in a liquid state, but a crust tends to form atop the molten electrolyte. Periodically, the crust is broken to allow more alumina to be added for processing. The pure molten aluminum accumulates at the bottom of the pot and is siphoned off. The pots are operated 24 hours a day, seven days a week.

• 9 A crucible is moved down the potline, collecting 9,000 lb (4,000 kg) of molten aluminum, which is 99.8% pure. The metal is transferred to a holding furnace and then cast (poured into molds) as ingots. One common technique is to pour the molten aluminum into a long, horizontal mold. As the metal moves through the mold, the exterior is cooled with water, causing the aluminum to solidify. The solid shaft emerges from the far end of the mold, where it is sawed at appropriate intervals to form ingots of the desired length. Like the smelting process itself, this casting process is also continuous.

Byproducts/Waste

Alumina, the intermediate substance that is produced by the Bayer process and that constitutes the raw material for the Hall-Heroult process, is also a useful final product. It is a white, powdery substance with a consistency that ranges from that of talcum powder to that of granulated sugar. It can be used in a wide range of products such as laundry detergents, toothpaste, and fluorescent light bulbs. It is an important ingredient in ceramic materials; for example, it is used to make false teeth, spark plugs, and clear ceramic windshields for military airplanes. An effective polishing compound, it is used to finish computer hard drives, among other products. Its chemical properties make it effective in many other applications, including catalytic converters and explosives. It is even used in rocket fuel—400,000 lb (180,000 kg) is consumed in every space shuttle launch. Approximately 10% of the alumina produced each year is used for applications other than making aluminum.

The largest waste product generated in bauxite refining is the tailings (ore refuse) called "red mud." A refinery produces about the same amount of red mud as it does alumina (in terms of dry weight). It contains some useful substances, like iron, titanium, soda, and alumina, but no one has been able to develop an economical process for recovering them. Other than a small amount of red mud that is used commercially for coloring masonry, this is truly a waste product. Most refineries simply collect the red mud in an open pond that allows some of its moisture to evaporate; when the mud has dried to a solid enough consistency, which may take several years, it is covered with dirt or mixed with soil.

Several types of waste products are generated by decomposition of carbon electrodes during the smelting operation. Aluminum plants in the United States create significant amounts of greenhouse gases, generating about 5.5 million tons (5 million metric tons) of carbon dioxide and 3,300 tons (3,000 metric tons) of perfluorocarbons (compounds of carbon and fluorine) each year.

Approximately 120,000 tons (110,000 metric tons) of spent potlining (SPL) material is removed from aluminum reduction pots each year. Designated a hazardous material by the Environmental Protection Agency (EPA), SPL has posed a significant disposal problem for the industry. In 1996, the first in a planned series of recycling plants opened; these plants transform SPL into glass frit, an intermediate product from which glass and ceramics can be manufactured. Ultimately, the recycled SPL appears in such products as ceramic tile, glass fibers, and asphalt shingle granules.

The Future

Virtually all of the aluminum producers in the United States are members of the Voluntary Aluminum Industrial Partnership (VAIP), an organization that works closely with the EPA to find solutions to the pollution problems facing the industry. A major focus of research is the effort to develop an inert (chemically inactive) electrode material for aluminum reduction pots. A titanium-diboride-graphite compound shows significant promise. Among the benefits expected to come when this new technology is perfected are elimination of the greenhouse gas emissions and a 25% reduction in energy use during the smelting operation.

Where to Learn More

Books

Altenpohl, Dietrich. Aluminum Viewed from Within: An Introduction into the Metallurgy of Aluminum Fabrication (English translation). Dusseldorf: Aluminium-Verlag, 1982.

Russell, Allen S. "Aluminum." McGraw-Hill Encyclopedia of Science & Technology. New York: McGraw-Hill, 1997.

Periodicals

Thompson, James V. "Alumina: Simple Chemistry—Complex Plants." Engineering & Mining Journal (February 1, 1995): 42 ff.

Other

Alcoa Aluminum. http://www.alcoa.com/ (March 1999).

Reynolds Metals Company. http://www.reynoldswrap.com/gbu/bauxitealumina/ (April 1999).

—LorettaHall

Aluminum family

The aluminum family consists of elements in Group 13 of the periodic table: boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). The family is usually named after the second element, aluminum, rather than the first, boron, because boron is less typical of the family members than is aluminum. Boron is a metalloid (an element that has some of the properties of metals and some of the properties of nonmetals), while the other four members of the family are all metals.

Aluminum

Aluminum is a lightweight, silvery metal, familiar to every household in the form of pots and pans, beverage cans, and aluminum foil. It is attractive, nontoxic, corrosion-resistant, nonmagnetic, and easy to form, cast, or machine into a variety of shapes. It has a melting point of 660°C (1,220°F) and a boiling point of 2,519°C (4,566°F).

Aluminum is the third most abundant element in Earth's crust after oxygen and silicon, and it is the most abundant of all metals. It constitutes 8.1 percent of the crust by weight and 6.3 percent of all the atoms in the crust. Because it is a very active metal, aluminum is never found in its metallic form. Rather, it occurs in a wide variety of earthy and rocky minerals, including feldspar, mica, granite, and clay. Kaolin is an especially fine, white, aluminum-containing clay that is used in making porcelain.

Known as aluminium in other English-speaking countries, the element was named after the mineral alum, one of its salts that has been known for thousands of years. Alum was used by the Egyptians, Greeks, and Romans as a mordant, a chemical that helps dyes stick to cloth.

Properties and uses. Pure aluminum is relatively soft and not the strongest of metals. When melted together with other elements such as copper, manganese, silicon, magnesium, and zinc, however, it forms alloys (a substance composed of two or more metals or of a metal and a nonmetal) with a wide range of useful properties. Aluminum alloys are used in airplanes, highway signs, bridges, storage tanks, and buildings. The world's tallest buildings, the World Trade Center towers in New York, are covered with aluminum. Aluminum is being used more and more in automobiles because it is only one-third as heavy as steel and therefore decreases fuel consumption.

In spite of the fact that aluminum is chemically very active, it does not corrode in moist air the way iron does. Instead, it quickly forms a thin, hard coating of aluminum oxide. Unlike iron oxide or rust, which flakes off, the aluminum oxide sticks tightly to the metal and protects it from further oxidation. The oxide coating is so thin that it is transparent, so the aluminum retains its silvery metallic appearance. Sea water, however, will corrode aluminum unless it has been given an unusually thick coating of oxide by the anodizing process. (During the anodizing process, a piece of aluminum is oxidized in order to create on its surface a coating of aluminum oxide, which is able to take dyes, unlike plain aluminum.)

When aluminum is heated to high temperatures in a vacuum, it evaporates and condenses onto any nearby cool surface such as glass or plastic. When evaporated onto glass, it makes a very good mirror. Aluminum has largely replaced silver in the production of mirrors because it does not tarnish and turn black as silver does when exposed to impure air. Many food-packaging materials and shiny plastic novelties are made of paper or plastic with an evaporated coating of bright aluminum. The silver-colored helium balloons popular at birthday parties are made of a tough plastic called Mylar™, covered with a thin, evaporated coating of aluminum metal.

Aluminum is one of the best conductors of electricity, with a conductivity about 60 percent that of copper. Because it is also light in weight and highly ductile (able to be drawn out into thin wires), it is used instead of copper in almost all of the high-voltage electric transmission lines in the United States.

Aluminum is used to make kitchen pots and pans because of its high heat conductivity. It is handy as an airtight and watertight food wrapping because it is very malleable; it can be pressed between steel rollers to make foil (a thin sheet) less than one-thousandth of an inch thick. Claims are occasionally made that aluminum is toxic and that aluminum cookware is therefore dangerous, but no clear evidence for this belief has ever been found. Many widely used over-the-counter antacids contain thousands of times more aluminum (in the form of aluminum hydroxide) than a person could ever get from eating food cooked in an aluminum pot. Aluminum is the only light element that has no known physiological function in the human body.

Production. As a highly reactive metal, aluminum is very difficult to separate from other elements that are combined with it in its minerals and compounds. In spite of its great abundance on Earth, the metal itself remained unknown for centuries. In 1825, some impure aluminum metal was finally isolated by Danish physicist Hans Christian Oersted (1777–1851) by treating aluminum chloride with potassium amalgam (potassium dissolved in mercury). Then, in 1827, German chemist Hans Wöhler (1800–1882) obtained pure aluminum by the reaction of metallic potassium with aluminum chloride. He is generally given credit for the discovery of elemental aluminum.

But it was still very expensive to produce aluminum metal in any quantity, and for a long time it remained a rare and valuable metal. In 1852, aluminum was selling for about $545 a pound. The big breakthrough came in 1886, when Charles M. Hall, a 23-year-old student at Oberlin College in Ohio, and Paul L-T. Héroult, another college student in France, independently invented what is now known as the Hall or Hall-Héroult process. This process consists of dissolving alumina (aluminum oxide) in melted cryolite, a common aluminum-containing mineral, and then passing an electric current through the hot liquid. Molten aluminum metal collects at the cathode (negative electrode). Not long after the development of this process, the price of aluminum metal plummeted to about 30 cents a pound. The process used to extract aluminum from its ores today is essentially the same as that developed by Hall and Héroult 150 years ago.

Boron

Elemental boron occurs in a variety of forms, ranging from clear red crystals to a black or brown powder to a transparent black crystal that is nearly as hard as diamond. The element is never found free in nature but is extracted commercially from minerals such as borax, ulexite, colemanite, and kernite. Boron is a relatively rare element, constituting about 0.001 percent of Earth's crust. It ranks number 38 in abundance, after nitrogen, lithium, and lead, but before bromine, uranium, and tin.

Properties and uses. The physical properties of boron are somewhat difficult to determine since the element occurs in so many different forms. The melting point of its most stable form is given as 2,180°C (3,900°F) (the second highest after carbon); its boiling point is about 3,650°C (6,600°F).

Chemically, boron is a fascinating element. One text on the chemical elements claims that the inorganic chemistry of boron is "more diverse and complex than that of any other element in the periodic table." The element forms five types of compounds: (1) metal borides (a metal plus boron), (2) boron hydrides (boron plus hydrogen), (3) boron trihalides (boron plus a halide; a halide is a simple halogen compound), (4) oxo compounds (boron plus complex oxygen radicals; a radical is a group of atoms that behaves as a unit in chemical reactions but is not stable except as part of the compound), and organoboron compounds (boron combined with an organic, or carbon-containing, component).

Boron itself has relatively few uses aside from its role in nuclear reactors as a neutron absorber and in alloys as a hardening agent. (Nuclear reactors are devices used to control the energy released from nuclear reactions.) It is also used in the manufacture of semiconductors. (Semiconductors are substances that conduct an electric current but do so very

poorly.) Probably its best known compound, borax, is used as a water softening agent, in the production of glasses and ceramics, and as an herbicide. A compound derived from borax—boric acid—is used as an eyewash and in the production of heat-resistant glass.

Two boron compounds of special interest are boron carbide and boron nitride. Both are used as refractories, substances that are highly resistant to heat. The melting point of boron carbide is about 2,350°C (4,230°F) and that of boron nitride, over 3,000°C (5,400°F). When boron nitride powder is compressed at very high pressures, it produces a hard crystalline material that is as hard as natural diamonds.

Gallium, indium, and thallium

For most of its history, gallium was best known for one unusual physical property: it has a melting point of 29.76°C (85.6°F), less than that of the human body. If you were to hold a lump of gallium metal in your hand, therefore, it would melt.

In spite of this fact, gallium and its compounds have traditionally had few uses—until recently. In the 1970s, a compound of gallium called gallium arsenide was found to have semiconductor properties. Gallium arsenide has also been used extensively in light-emitting diodes (LEDs), which are used in the electronic displays of calculators, watches, and CD players.

Neither indium nor thallium has many commercial applications. The former element is used largely in making alloys and in the production of transistors and photo cells. A radioactive isotope of the latter, thallium-201, is used in medical diagnostic studies, especially those involving the function of the circulatory system.

[See also Periodic table; Transistor ]

TIREMAN, LOYD S. 1896-1959

Pioneer in bilingual education

Pioneer

During the 1930s Loyd S. Tireman conducted some of the first bilingual education experiments in the United States. At the San Jose Demonstration and Experimental School in Bernalillo County, New Mexico, and later at the Nambe Community School in Nambe, New Mexico, he developed new methods of teaching reading, bicultural education, and community relations. For thirty-two years he was among the leading American educators who organized bilingual educational programs in the face of much prejudice and opposition.

Background

Tireman was born in Orchard, Iowa, in 1896. The farming community in which he was raised emphasized quality education and tied the schools closely to the local community. For Iowans of that time good schools produced good citizens, and community interest in education was high. Tireman benefited from this attention, graduating from Fayette High School in 1913 and continuing his education at Upper Iowa State University. He graduated in 1917, in time to enlist for service in World War I, after which he returned to Iowa, married, and assumed a position as school superintendent in Hanlontown, the first of several superintendencies he held. In 1924 he earned an M.A. in education from the University of Iowa at Iowa City and continued there until he was granted a Ph.D. in 1927. That year he left Iowa for a position on the faculty of the University of New Mexico at Albuquerque. New Mexico would remain his adopted and beloved home for the rest of his life.

The San Jose School

School surveys conducted during the late 1920s indicated frequent problems with reading in New Mexican schools. Especially troubling was the disparity between English-speaking and Spanish-speaking children. In the first three grades the two groups scored equally on reading exams, but after that the lack of English reading reinforcement at home for Spanish-speaking children led Hispanic children to score poorly on tests. In 1930 Tireman secured funding (no small task during the Depression) and the cooperation of the Albuquerque public schools to open an experimental school in San Jose, a Spanish-speaking district near the city. The San Jose school quickly became a model for those interested in teaching Hispanic students. Tireman constructed a curriculum familiar to a predominantly Hispanic student body from rural backgrounds. Innovative drills in reading skills, the use of peer tutoring, and the use of community resources in the classroom successfully increased student interest in the program. After he witnessed similar programs in Mexico, Tireman began classes in health and hygiene and hired a school nurse to monitor the condition of the students. Tireman also inaugurated a preschool reading program, vastly increasing student performance in the regular grades. In 1932 the San Jose school hired a Spanish instructor and made Spanish education an elective for higher grades—one of the first bilingual educational efforts in the nation. The results were encouraging, with students making advances in both Spanish and English courses. Programs developed at San Jose were quickly instituted at other New Mexico schools,

Problems

Tireman's greatest problem with the San Jose school was not with the students, but with other educators. During the 1930s the majority of educators believed that African Americans, Hispanic Americans, and Native Americans were racially inferior to whites and incapable of anything but the most rudimentary learning. To such educators, developing curricular programs especially for Spanish American and Native American students was a waste of time and money. These educators argued that the function of the school was to assimilate nonwhite cultures to a standard set by whites, and Tireman's attempts to provide special programs for Spanish speakers was viewed as corrupting educational standards. On the other hand local Hispanic politicians feuding with white authorities and the local police viewed the San Jose school as a form of white cultural colonization and often opposed Tireman. To meet the objections of these two groups of critics, Tireman became something of a politician and began a teacher-training program at San Jose designed to recruit new instructors to his cause. The strain of such varied efforts was telling on Tireman personally. By 1938, with funding running out, he wrapped up his participation with the school and moved on to a new project, a new experimental school in Nambe, a village in northern New Mexico,

The Nambe Community School

Nambe was a primarily Spanish-speaking agricultural town with a strong tradition of communal action. It had suffered badly during the Depression, but Cyrus McCormick Jr., the heir to the International Harvester fortune, had moved near Nambe in the early 1930s and decided to fund a school based on the example set by San Jose. Tireman headed the new school. As in San Jose, he immediately abandoned the standard curriculum designed for white, eastern students and built a curriculum accessible to the experience of Hispanic, western children. Community problems determined the curriculum at the school; the school in turn acted as a center for improving the health and wellbeing of the community. With help from several New Deal agencies, the Nambe school also taught the adults of the community scientific farming techniques. As they had at San Jose, teachers at Nambe took their students on "walks" through the community, using the town and its problems as the basis for instruction. Public health, animal husbandry, and agricultural science joined mathematics and reading as standard parts of the curriculum. Again, however, the Nambe school encountered the same criticisms raised against San Jose—from professional educators who believed that Spanish-based and community-based curriculum was soft and undemanding and from Spanish-speaking parents who often objected to ideas introduced by teachers from a white, urban culture. World War II redirected much of the community and educational support for the experiment toward the war effort, and in 1942 the school closed.

Later Career

Tireman continued as an educational reformer throughout World War II and the postwar period, traveling to South America and around the United States advising governments on educational reform. The Office of Inter-American Affairs sent him to Bolivia after the war to help reorganize that nation's schools. In 1950 Tireman curtailed many of his public activities because he was suffering from heart disease and leukemia. He died on 25 October 1959.

Source;

David L. Bachelor, Educational Reform in New Mexico; Tireman, San Jose, and Nambe' (Albuquerque: University of New Mexico Press, 1991).

Aluminum

melting point: 660.32°C
boiling point: 2,519°C
density: 2.70 g/cm³
most common ions: Al³⁺

Aluminum is a silvery-white metallic element discovered in 1825 by Danish chemist Hans Christian Ørsted. It is the most abundant metal found in Earth's crust, comprising 8.3 percent of the crust's total weight. Its content in seawater, however, is as low as 0.01 gram per metric ton (0.01 part per million). The key isotope of aluminum is ²⁷Al with a natural abundance of 100 percent, but seven other isotopes are known, one of which is used as a radioactive tracer (²⁶Al).

Aluminum is not found in its metallic state in nature; it is usually found as silicate, oxide, or hydrated oxide (bauxite). Its extraction from ore is difficult and expensive; aluminum is therefore commonly recycled, the energy of recycling being a mere 5 percent of the energy needed to extract the metal.

Aluminum is lightweight, ductile , and easily machined. It is protected by an oxide film from reacting with air and water, and is therefore rust-resistant. It is one of the lightest metals but is quite tough and most helpful in metallurgy , transportation (e.g., aircraft, automobiles, railroad cars, and boats), and architecture (e.g., window frames and decorative ornaments). It is also used in the manufacture of cooking gear because it is a good conductor of heat. Aluminum foils as thin as 0.18 millimeter (0.007 inch) are a household convenience, protecting food from spoiling and providing insulation. Aluminum-made beverage cans are widely manufactured; more than 100 billion are produced each year. The average human body contains about 35 milligrams (0.0012 ounce) of aluminum, but no known biological role has been established for it; it is, however, suspected to be a factor in the development of Alzheimer's disease.

see also Electrochemistry.

Jean-Claude Bünzli

Bibliography

Altenpohl, Dietrich G., and Kaufman, J. G. (1998). ALUMINUM: Technology, Applications, and Environment (A Profile of a Modern Metal, Sixth edition). Washington, DC: Minerals, Metals and Materials Society.

Farndon, John (2001). Aluminum. Tarrytown, NY: Benchmark Books.

aluminium (aluminum) The third most abundant element in the earth's crust (after oxygen and silicon) but with no known biological function. Present in small amounts in many foods but only a small proportion is absorbed. Aluminium salts are found in the abnormal nerve tangles in the brain in Alzheimer's disease, and it has been suggested that aluminium poisoning may be a factor in the development of the disease, although there is little evidence.

Aluminium is used in cooking vessels (the first aluminium saucepan was produced in Cleveland Ohio by Henry Avery in 1890) and as foil for wrapping food, as well as in cans and tubes. Aluminium cans were first used for food and beverages in 1960; tab‐opening aluminium cans for beverages first introduced 1962. It is a soft flexible metal, resistant to oxidation and deterioration, although it is dissolved by alkalis. The ‘silver’ beads used to decorate confectionery are coated with either silver foil or an alloy of aluminium and copper.

Baking powders containing sodium aluminium sulphate as the acid agent were used at one time (alum baking powders), and aluminium hydroxide and silicates are commonly used in antacid medications.

aluminium (symbol Al) Metallic silvery white element of group III of the periodic table. It is the most common metal in the Earth's crust; the chief ore is bauxite from which the metal is extracted by electrolysis. Alloyed with other metals, it is used extensively in machined and moulded articles, particularly where lightness is important, such as aircraft. It is protected from oxidation (corrosion) by a thin, natural layer of oxide. Properties: at.no. 13; r.a.m. 26.98; r.d. 2.69; m.p. 660.2°C (1220.38°F); b.p. 1800°C (3272°F); most common isotope Al²⁷. Aluminium was first isolated in 1825 in an impure form by Danish physicist Hans Christian Oersted. See also anodizing

aluminium XIX. alt. (after potassium, sodium, etc.) of aluminum, H. Davy's modification (1812) of the form first suggested by him, viz. alumium (1808). Aluminum (now U.S.) is parallel to alumina (XVIII), modL. formation on the type of magnesia, potassa, soda for the ‘earth of alum’, aluminium oxide. f. L. alūmen, alūmin- ALUM.
So aluminous (F. alumineux) XVI.

aluminium •columbium •erbium, terbium, ytterbium •scandium • compendium •palladium, radium, stadium, vanadium •medium, tedium •cryptosporidium, cymbidium, idiom, iridium, rubidium •indium •exordium, Gordium, rutherfordium •odeum, odium, plasmodium, podium, sodium •allium, gallium, pallium, thallium, valium •berkelium, epithelium, helium, nobelium, Sealyham •beryllium, cilium, psyllium, trillium •linoleum, petroleum •thulium • cadmium •epithalamium, prothalamium •gelsemium, premium •chromium, encomium •holmium • fermium •biennium, millennium •cranium, geranium, germanium, Herculaneum, titanium, uranium •helenium, proscenium, rhenium, ruthenium, selenium •actinium, aluminium, condominium, delphinium •ammonium, euphonium, harmonium, pandemonium, pelargonium, plutonium, polonium, zirconium •neptunium •europium, opium •aquarium, armamentarium, barium, caldarium, cinerarium, columbarium, dolphinarium, frigidarium, herbarium, honorarium, planetarium, rosarium, sanitarium, solarium, sudarium, tepidarium, terrarium, vivarium •atrium •delirium, Miriam •equilibrium, Librium •yttrium •auditorium, ciborium, conservatorium, crematorium, emporium, moratorium, sanatorium, scriptorium, sudatorium, vomitorium •opprobrium •cerium, imperium, magisterium •curium, tellurium •potassium • axiom • calcium •francium • lawrencium • americium •Latium, solatium •lutetium, technetium •Byzantium • strontium • consortium •protium • promethium • lithium •alluvium, effluvium •requiem • colloquium • gymnasium •caesium (US cesium), magnesium, trapezium •Elysium • symposium