Until well into the 20th century, new steel alloys were concocted mainly by trial-and-error cookery, but steelmakers at least had the advantage of long experience—3 millennia of it, in fact. That wasn't the case with aluminum, the third most common element in Earth's crust, yet never seen in pure form until 1825. It was heralded as a marvel—light, silvery, resistant to corrosion—but the metal was so difficult to separate from its ore that it remained a rarity until the late 19th century, when a young American, Charles Martin Hall, found that electricity could pull aluminum atoms apart from tight-clinging oxygen partners. Extensive use was still blocked by the metal's softness, limiting it to such applications as jewelry and tableware. But in 1906 a German metallurgist named Alfred Wilm, by happy chance, discovered a strengthening method. He made an alloy of aluminum with a small amount of copper and heated it to a high temperature, then quickly cooled it. At first the aluminum was even softer than before, but within a few days it became remarkably strong, a change caused by the formation of minute copper-rich particles in the alloy, called precipitation hardening. This lightweight material became invaluable in aviation and other transportation applications. In recent decades other high performance metals have found important roles in aircraft. Titanium, first isolated in 1910 but not produced in significant quantities until the 1950s, is one of them. It is not only light and resistant to corrosion but also can endure intense heat, a requirement for the skin of planes traveling at several times the speed of sound. But even titanium can't withstand conditions inside the turbine of a jet engine, where temperatures may be well above 2,000° F. Turbine blades are instead made of nickel- and cobalt-based materials known as superalloys, which remain strong in fierce heat while spinning at tremendous speed. To ensure they have the maximum possible resistance to high-temperature deformation, the most advanced of these blades are grown from molten metal as single crystals in ceramic molds.
Another major category of high performance materials is that of synthetic polymers, commonly known as plastics. Unknown before the 20th century, they are now ubiquitous and immensely varied. The first of the breed was created in 1907 by a Belgium-born chemist named Leo Baekeland. Working in a suburb of New York City, he spent years experimenting with mixtures of phenol (a distillate of coal tar) and formaldehyde (a wood-alcohol distillate). Eventually he discovered that, under controlled heat and pressure, the two liquids would react to yield a thick brownish resin. Further heating of the resin produced a powder, which became a useful varnish if dissolved in alcohol. And if the powder was remelted in a mold, it rapidly hardened and held its shape. Bakelite, as the hard plastic was called, was an excellent electrical insulator. It was tough; it wouldn't burn; it didn't crack or fade; and it was unaffected by most solvents. By the 1920s the translucent, amber-colored plastic was everywhere—in pipe stems and toothbrushes, billiard balls and fountain pens, combs and ashtrays. It was "the material of a thousand purposes," Time magazine said. Another major category of high performance materials is that of synthetic polymers, commonly known as plastics. Unknown before the 20th century, they are now ubiquitous and immensely varied. The first of the breed was created in 1907 by a Belgium-born chemist named Leo Baekeland. Working in a suburb of New York City, he spent years experimenting with mixtures of phenol (a distillate of coal tar) and formaldehyde (a wood-alcohol distillate). Eventually he discovered that, under controlled heat and pressure, the two liquids would react to yield a thick brownish resin. Further heating of the resin produced a powder, which became a useful varnish if dissolved in alcohol. And if the powder was remelted in a mold, it rapidly hardened and held its shape. Bakelite, as the hard plastic was called, was an excellent electrical insulator. It was tough; it wouldn't burn; it didn't crack or fade; and it was unaffected by most solvents. By the 1920s the translucent, amber-colored plastic was everywhere—in pipe stems and toothbrushes, billiard balls and fountain pens, combs and ashtrays. It was "the material of a thousand purposes," Time magazine said. Other synthetic polymers soon emerged from research laboratories in the United States and Europe. Polyvinyl chloride, useful for adhesives or in hardened sheets, appeared in 1926. Polystyrene, which yielded very lightweight foams, was introduced in 1930. A few years later came a glass substitute, chemically known as polymethyl methacrylate but sold under the name of Plexiglas. During this period of plastics pioneering, many chemists were convinced that the new materials were composed of small molecules of the sort familiar to their science. A German researcher named Hermann Staudinger had a very different vision, however. Polymers, he said, were made up of extremely long molecules comprising thousands of subunits linked together in various ways by chemical bonding between carbon atoms. His insight, ultimately honored with a Nobel Prize, won general acceptance by the mid-1930s and gave new momentum to the polymer hunt.
A leader of that effort was Wallace Carothers, a young chemist at E. I. du Pont de Nemours & Company. In 1930 he and his research team created neoprene, a synthetic rubber that was more resistant to corrosive chemicals than vulcanized natural rubber. The team then began trying to develop a synthetic fiber from organic building blocks that would bond in the same way amino acids join up to form the protein molecules in silk. The payoff came in 1934 when one of the researchers dipped a rod into a beaker full of syrupy melt. When he pulled the rod out, a thread of the viscous substance came with it, and the stretching and subsequent curing of the strand transformed it into a substance of remarkable strength and elasticity. This was nylon, soon produced in quantity for stockings, toothbrush bristles, and such wartime uses as parachute cloth, ropes, and reinforcement for tires. Because of its low friction and high resistance to wear, nylon also proved valuable for gears, rollers, fasteners, and zippers. The menu of valuable polymers continued to grow steadily. Polyethylenes, suitable for making bottles, appeared in 1939. Polyester fibers, destined to be a staple of the apparel industry, arrived in 1941. A vinyl-based transparent film called Saran, useful for wrapping food, was developed in 1943. Dacron, whose applications ranged from upholstery to grafts to repair blood vessels, hit the market in 1953. Lycra spandex fiber that could stretch as much as five times its length without permanent deformation was introduced in 1958. Kevlar, a fiber five times stronger than steel on a density-adjusted basis, was launched in 1973. By 1979 the annual production volume of polymers surpassed that of all metals combined. A famously pithy bit of career advice in The Graduate, a late 1960s film, summed up the situation well: when the hero asks someone about promising fields for employment, he is told simply, "plastics."
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