A Thoroughly Modern Metal

From the apex of the Washington Monument to power-distribution lines, airplanes, building surfaces, soda cans, and gum wrappers, aluminum meets the needs of people and societies around the world.

In 1884, Americans eagerly anticipated the final step in the construction of the Washington Monument in Washington, D.C.–the mounting of a small metal pyramid atop the tower’s pinnacle. Functionally, the pyramid would be a lightning rod; architecturally, it represented the monument’s crowning touch.

The engineer in charge of the project, Col. Thomas Lincoln Casey, had envisioned a pyramid made of copper, brass, or bronze plated with gleaming platinum. But Philadelphia metallurgist William Frishmuth suggested an alternative: an obscure, semiprecious metal with high electrical conductivity, very light weight, an attractive silvery sheen, and excellent corrosion resistance.

Although annual world production of this metal then amounted to less than a ton (908 kg), Casey, after inspecting samples, authorized Frishmuth to use it to fabricate a solid pyramid rising to a point nearly 9 inches (22.6 cm) above its base. The 7.6 pounds (3.45 kg) of material that went into the pyramid was worth $1.00 per ounce, nearly as much as silver. When the monument was formally dedicated on February 21, 1885, newspaper descriptions of the pinnacle pyramid–which was made of aluminum–brought that metal to the attention of many Americans for the first time.

Among the base metals that helped build modern civilization, aluminum is a decided latecomer. While copper, iron, and lead have been with us since antiquity, aluminum has been known only since the 1800s and used in quantity for just the past 60 years. Yet in that short time, it has changed everything from how we travel and transmit electricity to how we design buildings and package foods and beverages. With its use now exceeding that of all other metals except iron, aluminum has proved itself to be a metal eminently suited for a modern world.

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Abundant aluminum

In Earth’s crust, aluminum is the third most common element behind oxygen and silicon; it is the most abundant metal. A component of many minerals, rocks, soils, and clays, aluminum is always found in combination with other elements.

The ancient Greeks and Romans used alum, a naturally occurring complex aluminum sulfate, in fabric dyes and medical astringents. In the eighteenth century, French chemists named the mysterious metallic base element of alum alumine. British chemist Sir Humphrey Davy (1778–1829) renamed this yet-unseen metal “alumium” and later “aluminium.” Finally, in 1827, German chemist Friedrich Wohler chemically reduced aluminium chloride to isolate relatively pure “aluminium.” (Variant forms of the name arose early and persist to this day, as an Internet search will confirm. The American Chemical Society’s 1925 decision to use aluminum in all its publications has assured that this is the preferred term in the United States.)

Researchers found aluminum to be an easily workable, nonmagnetic, silvery- white metal. An excellent conductor of heat and electricity, it also reflects heat and light well. The lightest stable metal, it weighs just one-third as much as an equal volume of copper or iron.

Aluminum typically occurs in nature as simple or complex silicates, whose tightly bound molecular structures offer strong resistance to efforts to extract the metal from them. To this day, extracting aluminum from its one commercially valuable form, bauxite, is difficult and expensive. Bauxite, named for the French locality where it was first mined, forms when slow chemical weathering of rocks alters the contained silicates into impure, hydrated aluminum oxides.

By the 1850s, metallurgists had discovered the process for producing aluminum by first converting bauxite to aluminum oxide, or alumina, then chemically or electrolytically separating aluminum metal from oxygen. While the chemical separation process was costly and inefficient, the electrolytic process was impractical both because it required that alumina be melted at the unworkable temperature of 2,000_F (1090_C) and because electricity was then prohibitively expensive. Nevertheless, French chemists began employing experimental chemical separation methods to produce small quantities of aluminum. At the time, the metal’s few products included fine dinnerware for the French court and a crown for the king of Denmark.

Foil and aircraft

In 1886, Charles Martin Hall in the United States and Paul L.T. Heroult in France simultaneously and independently dissolved alumina in fused cryolite–the mineral form of aluminum fluoride that melts at just 1,000_F.–and electrolytically decomposed the solution to yield aluminum metal. In 1888, Hall established the Pittsburgh Reduction Company and used relatively cheap electricity from newly developed mechanical generators to produce aluminum commercially. Within five years, its output helped drop the metal’s price to 78 cents per pound.

Although pure aluminum is not particularly strong, metallurgists soon created alloys with greatly enhanced strength and durability. As aluminum became affordable, fabricators devised casting, rolling, and forming processes to fashion the metal into such products as cookware, electric wire, and several parts for the engine used in the Wright Brothers’ first powered flight in 1903 at Kitty Hawk, North Carolina. In 1907, Hall’s rapidly growing Pittsburgh Reduction Company, which owned bauxite mines in Arkansas and aluminum smelters in New York and Canada, was renamed the Aluminum Company of America (now ALCOA). While Americans used aluminum preferentially, Europe and much of the world would continue to use Davy’s “aluminium” spelling.

Aluminum’s first major social impact came in the 1920s, when many new brands of tobacco, chewing gum, and candy products were appearing in stores. Such products had traditionally been packaged in tin and lead foils, but in 1926, Richard Samuel Reynolds, who headed the U.S. Foil Company of Louisville, Kentucky, introduced a foil made of aluminum. The foil was brilliant and eye-catching, and because it could be rolled much thinner than either tin or lead, it yielded more foil per pound of metal at less cost.

Reynolds’ new aluminum foil soon appeared as packaging for such popular products as Wrigley’s Spearmint chewing gum, Eskimo Pie ice cream sandwiches, and Camel cigarettes. Because its tight folds protected against excessive loss or gain of moisture, the foil extended the shelf life of many perishable products. That capability, together with its extremely light weight, allowed manufacturers to ship foil-wrapped tobacco and food products to distant markets, thus aiding the emergence of nationally marketed food and tobacco brands. After expanding into production of gravure-printed foil bottle labels, heat-sealed foil food bags, and easily installed, foil-laminated building insulation paper, U.S. Foil reorganized as the Reynolds Metals Company.

Aluminum’s impact on aviation was far greater. Improving the performance of early aircraft, which were built largely of wood, lacquered fabric, and baling wire, held little promise. Realizing the need for a strong, lightweight metal, aeronautical engineers began employing aluminum in airframes during the 1920s, albeit only as design afterthoughts to save weight.

In 1931, the Douglas Aircraft Company began employing aluminum much more extensively in its limited-production DC-1 and DC-2 passenger aircraft. Douglas engineers quickly refined and incorporated the best elements of those two designs into the DC-3, the first aircraft designed specifically around aluminum’s weight-saving properties. Employing a stressed, sheet- aluminum skin flush-riveted to an aluminum rib-and-spar frame, the DC-3 had a tapered fuselage, clean lines, graceful wings, and a gleaming, aerodynamically efficient surface of polished aluminum.

Thanks in large measure to lightweight aluminum, the DC-3’s large payload made it the first profitable passenger aircraft ever built. From its first flight in December 1935, the durable and reliable DC-3 opened the door to rapid advances in commercial aviation, while its streamlined appearance and gleaming aluminum skin became worldwide symbols of modernity. Yet despite the success of institutional foil and the DC-3, industry was still not using aluminum in great quantity. It remained an alternative metal, waiting for the time when worldwide demand for its unique combination of lightness and strength would make it indispensable.

Coming-of-age

In 1937, aluminum magnate Richard Samuel Reynolds, noting that Germany was buying and producing large amounts of aluminum, warned the U.S. government that the Germans were planning a fleet of high-performance military aircraft. Reynolds’ efforts to increase U.S. aluminum production capacity proved invaluable, for aluminum would contribute enormously to victory in World War II. Translating lightness and strength into speed and large bomb and armament payloads, aluminum was the most vital component of such high- performance combat aircraft as the P-51 Mustang, B-17 Flying Fortress, and B-29 Superfort.

During the mid-1930s, U.S. industry had consumed just 60,000 metric tons (132 million pounds) of aluminum each year, a level that increased more than tenfold by 1945. As aluminum helped win the war, metallurgists developed advanced alloys that further enhanced the metal’s many useful properties. As little as 1 percent copper improved machinability, while similar amounts of manganese and magnesium, respectively, produced alloys with high corrosion resistance and increased hardness. Addition of about 2 percent zinc created a high-strength alloy perfectly suited for aircraft use, while as much as 8 percent silicon produced alloys with substantially reduced melting points that lowered the cost of many fabrication and welding processes.

Meanwhile, after huge wartime production capacity had lowered its price to 20 cents per pound, aluminum was finally ready to better the lives of millions. One of its first major postwar impacts was in rural electrification, a federally backed program to bring electrical power to millions of rural U.S. residents. The program had begun in 1936 but was sidetracked by World War II.

In 1946, with 2.8 million U.S. farm families still lacking power, rural electrification resumed at a record pace, greatly accelerated by the use of a new, highly conductive aluminum-boron alloy. Although less conductive than copper, the alloy was so light that it could carry twice as much electricity as an equal weight of copper. With lightweight aluminum cables, power lines needed fewer costly steel support towers, making construction much cheaper and faster.

Carried on lightweight aluminum high-voltage lines, electricity raced into rural America, bringing power to 500,000 new customers in 1949 alone. Postwar rural electrification was a national economic boon, creating new jobs, expanding the market for electrical appliances, and raising the standard of living for millions. Today, aluminum lines provide affordable power to more than 1,000 electric cooperatives that serve 30 million rural Americans in 46 states. They are also vital to ongoing rural electrification programs in many Third World nations.

By 1950 aluminum had displaced copper in the conductive bases of billions of incandescent lightbulbs and fluorescent light tubes manufactured worldwide each year. It went on to become the preferred metal for home television antennas, satellite dishes, and even the power systems of modern skyscrapers.

Household aluminum foil appeared in home kitchens in 1947, when the Reynolds Metals Company introduced Reynolds Wrap. Affordable and enormously popular, the versatile foil changed kitchen practices forever by enabling homemakers to protect food from freezer burn and keep leftovers fresh.

Aluminum building products changed the look of cities and suburbs. Despite its high chemical reactivity, aluminum weathers extremely well because its corrosion product, aluminum oxide (Al2O3), binds tightly to the metal’s surface as a protective coating. This natural oxide coating is thickened and toughened when aluminum is immersed in an acid electrolyte through which electrical current is passed. The process is called anodization, and the treated aluminum is called “anodized” aluminum. Variations in the process produce permanent colors ranging from soft reds, greens, and blues to gold and even black, as well as a variety of attractive, metallic finishes such as glossy, brushed, and satin. By improving aluminum’s inherent durability and enhancing its already pleasing aesthetic qualities, anodizing suits the metal perfectly for such specialized applications as golf carts, baseball bats, boats, refrigerators, cigarette lighters, camera bodies, and automotive trim.

In the late 1950s, as annual world aluminum production soared above two million metric tons (4,400 million pounds), architects began using exterior aluminum panels on new high-rise buildings, replacing the subdued look of traditional stone or brick with that of bright, gleaming metal. Today, virtually all high-rises are clad in reflective, bright panels of rolled aluminum. By the 1960s, aluminum was also changing the look of the suburbs, as countless older, wooden suburban homes received “facelifts” with multicolor aluminum siding and windows. Its ability to reflect heat enabled aluminum siding to reduce home heating bills by reflecting inward interior heat that was otherwise lost. Conversely, the siding kept homes cooler in summer, by reflecting exterior atmospheric and solar heat.

Aluminum was the metal most responsible for the explosive postwar growth of commercial aviation. Just as in the DC-3, aluminum was a key factor in the success of the DC-6 and DC-7, Lockheed Constellation, Boeing 707, and the family of jet transports that followed. In the aerospace field, where weight is critical, exotic, ultralight aluminum alloys proved indispensable to the development of rockets, satellites, and manned spacecraft.

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A metal for the environment

In 1964, the introduction of the aluminum can revolutionized beverage marketing. Unlike the old, three-piece steel can, the 12-ounce, extrusion- pressed, aluminum can, consisting only of a seamless body and a lid, permitted 360-degree printing that enhanced consumer appeal. Aluminum cans neither rusted nor imparted undesirable tastes. Despite a thickness equal to just two magazine pages, they were durable enough to withstand extreme temperature changes and pressures of 90 pounds per square inch.

Inexpensive and easy to manufacture, aluminum cans reflected heat to keep beverages cooler than steel cans did, while their lightness slashed shipping costs. The new cans allowed beer and beverage companies to expand their markets rapidly, thus contributing heavily to the rise of national beverage brands–and subsequently to the demise of smaller regional and local beer and soft-drink producers.

But the booming popularity of the aluminum beverage can quickly created landfill and littering problems. That led to recycling, a solution that proved an economic godsend for the aluminum industry and helped open the age of public environmental awareness. Aluminum has great “sustainable recyclability,” meaning repeated recycling produces no deterioration in material performance or quality. Furthermore, recycling it is a simple remelting process requiring just 5 percent of the energy needed to produce the same amount of metal from bauxite ore.

In 1970, the drive to recycle aluminum beverage cans brought metal recycling directly to the consumer for the first time. The public’s willingness to recycle exceeded all expectations and even became something of a social phenomenon, as churches, schools, clubs, sandlot baseball teams, and Boy Scout and Girl Scout groups all successfully turned to can collecting as a fund-raiser.

The recycling of aluminum cans, now an industry in itself, consists of a national network of 10,000 buyback locations cooperating with 8,000 city or county curbside-collection services. A remarkable 65 percent of the billions of cans produced each year are recycled. That amounts to 848,000 metric tons (1,865 million pounds) of aluminum worth $1.3 billion–and an annual saving of energy equal to that needed to power Pittsburgh for six years. The recycling of aluminum cans has also heightened public interest in the environment and in recycling such materials as glass, plastics, and paper.

In the early 1970s, when new government regulations mandated the manufacture of less polluting, more fuel-efficient automobiles, aluminum made compliance easier. Increased use of lightweight aluminum helped automakers to reduce overall vehicle weight, thus permitting the use of smaller, cleaner-burning engines to boost fuel economy without compromising vehicle performance.

With one-third the density of steel, aluminum automobile components are 1.5 times thicker than steel versions, yet weigh half as much. They also absorb twice the energy as the same weight of steel and help reduce noise and vibration. While aluminum constitutes 10 percent of the overall weight of the average new automobile, it represents 50 percent of a vehicle’s eventual scrap value. More than 70 percent of all automotive aluminum is now obtained from recycled metal.

Aluminum also plays a big role in commercial ground transportation and shipping. It is employed extensively in buses, trucks, and rail locomotives and cars, where reduced weight saves energy and lowers travel and shipping costs.

Lightweight metal, heavyweight industry

Today, a global industry employing nearly a million people produces 22 million metric tons (48.4 billion pounds) of primary aluminum (aluminum produced from ore) worth $34 billion each year. This process begins with the annual mining of 125 million metric tons (275 billion pounds) of bauxite ore. Australia accounts for one-third of world bauxite production, followed by Guinea, Brazil, Jamaica, and China.

The United States is the leading importer of both bauxite and alumina and also the top producer of aluminum metal, ahead of Russia, Canada, and Australia. The U.S. aluminum industry, comprising 23 primary plants that produce 3.7 million metric tons (8 billion pounds) of aluminum each year, employs 143,000 people who share a $4.8 billion payroll. The industry also produces 3.4 million metric tons (7.5 billion pounds) of secondary, or recycled, aluminum.

Annual U.S. demand for aluminum now tops 7 million metric tons (15.4 billion pounds)–about 54 pounds (24.5 kilograms) for every citizen. One- third goes to the transportation industry for the manufacture of automobiles, buses, trucks, railcars, aircraft, and aerospace vehicles. Container and packaging manufacturers account for 21 percent of domestic aluminum demand, while the building and construction market takes another 13.2 percent. Smaller markets include the manufacturers of consumer durables and electrical wire, cables, and fixtures. The United States exports 12 percent of its annual aluminum output, in both ingot and fabricated forms, mainly to Canada, Japan, and Mexico.

Aluminum production has also mandated expansion of the electricity generating industry. Electrolytic production of primary aluminum, among the most electrically intensive of all mineral-extraction operations, requires about 15,000 kilowatt-hours per ton (908 kg) of metal. The annual worldwide production of primary aluminum requires 250 billion kilowatt- hours of electricity–about 2 percent of the entire global output of electrical power.

At the current rate of mining, the world’s bauxite ore reserves are sufficient to last more than 150 years, and future technologies may make it possible to economically extract aluminum from a host of nonbauxitic materials, including common clay. Aluminum’s natural abundance, together with ongoing research and increasingly efficient recycling, assures that the metal will affect our lives even more in the future.

More than a century has passed since that little pyramid of gleaming aluminum was mounted atop the Washington Monument. During that time, aluminum has completed the enormous transition from an obscure, costly element to the world’s second most utilized metal. Along the way, it has changed the lives of countless people for the better, proving that it is truly a metal for a modern world.n

lance writer residing in Leadville, Colorado.