by Vaclav Smil
FIGURE 4.11. Illustrations of aluminum reduction process in Hall’s two U.S. patents (400,664 on the left, 400,766 on the right) granted on April 2, 1889. In both images, A is a crucible, B a furnace, and C the positive and D the negative electrode. The first patent proposed K2Al2F8 as the electrolyte; the second one, Na2Al2F8.
A new plant at New Kensington near Pittsburgh reached output of 900 kg/day by 1894, and in the same year an even larger facility was built at Niagara Falls to use the inexpensive electricity from what was at that time the world’s largest hydro station. In 1907, the Pittsburgh Reduction Co. was renamed Aluminum Company of America, and Alcoa, now a multinational corporation with operation in 39 countries, remains the metal’s largest global producer (Alcoa 2003). Canada’s first plant, the precursor of today’s large multinational Aluminum Company of Canada (Alcan), was built in 1901.
Similarities between Hall’s and Héroult’s independent specifications are striking. Heéroult, who conducted his experiments on the premises of his father’s small tannery and who did not rely on batteries but on a small steam-powered Gramme dynamo to produce a more powerful current, described his invention as a “process for the production of aluminium alloys by the heating and electrolytic action of an electric current on the oxide of aluminium, Al2O3, and the metal with which the aluminium shall be alloyed” (cited in Borchers 1904:127). Like Hall, he also made a provision for external heating of the electrolytic vessel, and his aluminum furnace also had carbon lining and a carbon anode. Héroult’s technique was commercialized for the first time in 1888 by the Aluminium Industrie Aktiengesselschaft in Neuhausen in Switzerland and by the Socieétée Electromeétallurgique Francçaise (Ristori 1911). Larger works, using inexpensive hydroelectricity, were soon established in France, Scotland, Italy, and Norway.
Mature Hall-Héroult Process
More than a century after its discovery, the Hall-Héroult process remains the foundation of the world’s aluminum industry. Nothing can change the facts that the abundant Al2O3 is nonconducting and that molten cryolite, in which it gets dissolved, is an excellent conductor and hence a perfect medium for performing electrochemical separation. Heat required to keep the cryolite molten comes from the electrolyte’s resistance and not from any external source; during the electrolysis, graphite is consumed at the anode with the release of CO2 while liquid aluminum is formed at the cathode and collects conveniently at the bottom of the electrolytic vessel, where it is protected from reoxidation, because its density is greater than that of the supernatant molten cryolite.
Another important step toward cheaper aluminum that took place in 1888 and on which we continue to rely more than a century later was Karl Joseph Bayer’s (1847-1904) patenting of an improved process for alumina production. After washed bauxite is ground and dissolved in NaOH, insoluble compounds of iron, silicon, and titanium are removed by settling, and fine particles of alumina are added to the solution to precipitate the compound, which is then calcined (converted to an oxide by heating) and shipped as a white powder of pure Al2O3 (IAI 2000). Typically, 4-5 t of bauxite will produce 2 t of alumina, which will yield 1 t of the metal.
FIGURE 4.12. Increasing cell size (indicated by highter current) and declining energy cost of the Hall-Héroult aluminum production, 1888–2000. Based on Beck (2001).
As so many other late 19th-century innovations, the electrolytic process was greatly scaled up while its energy consumption fell considerably. During the 20th century, average cell size in Hall-Héroult plants had doubled every 18 years while energy use decreased by nearly half between 1888 and 1914 and then dropped by nearly as much by 1980 (Beck 2001; figure 4.12). By 1900 the worldwide output of aluminum reached 8,000 t, and its price fell by more than 95% compared to the cost in 1885 (Borchers 1904). By 1913 its global production was 65,000 t, and the demand rose to nearly 700,000 t by the end of WII. By the end of the 20th century, annual global output of aluminum from the primary electrolysis of alumina surpassed 20 Mt and was about 50% higher than the worldwide smelting of copper (IAI 2003). The metal is produced both in pure (99.8%) form and as various alloys, and most of it is sent for final processing in rolls of specified thickness.
Inexpensive electrolytic aluminum was a novelty that had to take away market shares from established metals and create entirely new uses (Devine 1990a). During the early 1890s, the metal’s main use was for deoxidation of steel, but a much larger market soon emerged with aluminum’s use for cooking utensils, and then with parts for bicycles, cameras, cars, and many other manufactures. No machine is more unimaginable without aluminum and its alloys than the modern aircraft: steel alloys are the quintessential material in land and sea transport, but they are too heavy to be used for anything but some special parts in aircraft.
Aluminum bodies began displacing wood and cloth in aircraft construction during the late 1920s, after the mid-1930s demand for the metal was driven mainly by the need for large numbers of military planes (Hoff 1946). After WWII the market for aluminum alloys expanded rapidly with the large-scale adoption of military jet airplanes during the late 1940s and of commercial jets during the late 1950s. High-strength aluminum alloys (mainly alloy 7075 made with copper and zinc) make up 70–80% of the total airframe mass of modern commercial planes, which means that for the Boeing 747, this metal adds up to more than 100 t per plane (figure 4.13). The rest is accounted for by steel alloys, titanium alloys (in engines, landing gear) and, increasingly, composite materials (CETS 1993). Space flight and Earth-orbiting satellites have been another important market for such alloys.
The metal’s light weight and resistance to corrosion also guaranteed its expanding uses in construction (from window and door frames to roofing and cladding), and aluminum extrusions are widely used in railroad rolling stock (large hopper cars that carry bulk loads), in automobiles and trucks (in 2000 a typical sedan contained twice as much Al, mostly in its engine, as it did in 1990), in both recreational boats and commercial shipping, and in food preparation (cooking and table utensils) and packaging (ubiquitous pop and beer cans, foils). And aluminum wires, supported by steel towers, are now the principal long-distance carriers of both HVAC and HVDC.
The Hall-Héroult process is not without its problems. Even after all those efficiency gains, it is still highly energy intensive: in 2002, primary aluminum production in the United States averaged about 15.2 MWh of electricity per ton of the metal (IAI 2003), or about 55 GJ/t. Adding the inevitable electricity losses in generation and transmission and energy costs of bauxite mining, production of alumina and electrodes, and the casting of the smelted metal raises the total rate to almost 200 GJ/t, and well above that for less efficient producers. This is an order of magnitude more than producing steel from blast-furnace smelted pig iron (EIA 2000). But as there are no obvious alternatives, it is safe to conclude that our reliance on those two great 1888 commercial innovations in metal industry—Bayer’s production of alumina and Hall-Héroult’s electrolysis of the mixture of cryolite and alumina—will continue well into the 21st century.
FIGURE 4.13. The Boeing 747, the largest passenger aircraft of the late 20th century whose construction requires more than 100 t of aluminum alloys. Photo from author’s collection.
New Syntheses
Even reasonably well-informed people do not usually mention explosives when asked to list remarkable innovations that helped to create, rather than to imperil, the modern world. While it is an indisputable historic fact that the immense increase in human destructive power attributable to more powerful explosives has been one of the key reasons behind inflicting greater losses in successive large-scale military conflicts, the constructive power of modern explosives has received a disproportionately small amount of attention. Yet their constant use is irreplaceable not only in construction projects but also in destruction of old buildings and concrete and steel objects and, above all, in ore and coal mining. How many Americans would even guess that during the late 1990s coal extraction (mostly in surface mines) accounted for 6
7% of all industrial explosives used annually in the United States (Kramer 1997)?
There was only a brief delay between the patenting of the first modern explosive and its widespread use. Dynamite patents were granted to Alfred Nobel (1833–1896; figure 4.14) in 1867 (G.B. Patent 1345) and in 1868 (U.S. Patent 78,317), and by 1873 the explosive was such a great commercial success that he could settle in Paris in a luxurious residence at 59 Avenue Malakoff, where a huge crystal chandelier in his large winter garden lit his prize orchids and where a pair of Russian horses was waiting to take his carriage for a ride in the nearby Bois de Boulogne (Fant 1993). In contrast, the first new synthetic materials—nitrocellulose-based Parke-sine (1862) and Xylonite (1870) used for combs, shirt collars, billiard balls, and knife handles—made little commercial difference after their introduction. And the first commercial product made from the first successful thermoset plastic—a Bakelite gear-lever knob for a Rolls Royce—was introduced only in 1916, nearly a decade after Leo Baekeland filed his patent for producing the substance (Bijker 1995).
FIGURE 4.14. Alfred Nobel. His wealth and fame did little to ease his near-chronic depression and feelings of worthlessness (see chapter 6). Photograph © The Nobel Foundation.
Numerous, and always only black, Bakelite moldings, sometimes elegant but more often either undistinguished or outright ugly-looking (and still too brittle)—ranging from the classic rotary telephone to cigarette holders, and from early radio dials to electric switch covers—began appearing only after WWI. So did products made of polyvinyl chloride, now one of the most commonly used plastics encountered in cable and wire insulation as well as in pipes and bottles, a polymer that was first produced in 1912. Many new plastics were introduced during the 1930s, but their widespread commercial use came only after 1950. Modern plastics are thus much less beholden to the pre-WWI period than is electricity or steel, and they fill the image of quintessential 20th-century materials. Consequently, their introduction, proliferation, and impact will be examined in this book’s companion volume.
But there is another chemical synthesis, one involving a deceptively simple reaction of two gases, whose laboratory demonstration was followed by an unusually rapid commercialization that established an entirely new industry just before the beginning of WWI. Nearly a century later this accomplishment ranks as one of the most important scientific and engineering advances of all times. As such, this process deserves closer attention, which is why this chapter closes with a fairly detailed narrative and appraisal of the Haber-Bosch synthesis of ammonia from its elements.
Powerful Explosives
Introduction of new powerful explosives during the 1860s ended more than half a millennium of gunpowder’s dominance. Clear directions for preparing different grades of gunpowder were published in China by 1040, and its European use dates to the early 14th century (Needham et al. 1986). The mixture of the three components capable of detonation typically included about 75% saltpeter (potassium nitrate, KNO3), 15% charcoal, and 10% sulfur. Rather than drawing oxygen from the surrounding air, ignited gunpowder used the element present in the saltpeter to produce a very rapid (roughly 3,000-fold) expansion of its volume in gas. Historians have paid a great deal of attention to the consequences of gunpowder use in firearms and guns (Anderson 1988), particularly to its role in creating and expanding the European empires after 1450 (Cipolla 1966; McNeill 1989).
Gunpowder’s destructive capacity was surpassed only in 1846, when Ascanio Sobrero (1812–1888), a former student of Justus von Liebig who also worked with Alfred Nobel when they both studied with Jules Pelouze in Paris in the early 1850s, created nitroglycerin. This pale yellow, oily liquid is highly explosive on rapid heating or on even a slight concussion, and it was produced by replacing all the –OH groups in glycerol—C3H5(OH)3—with –NO2 groups (Escales 1908; Marshall 1917). Glycerol, a sweet syrupy liquid, is the constituent of triglycerides, and hence it is readily derived from lipids or from fermentation of sugar; among its many commercial uses are antifreeze compounds and plasticizers. Nitroglycerol is the most common of nitroglycerin’s many synonyms, but the proper chemical designation is 1,2,3-propanetriol trinitrate (figure 4.15). The compound is best known for its use as an antianginal agent and coronary vasodilator.
After an explosion at the Torino armory, Sobrero stopped all experiments with the dangerous substance and assuaged his anxiety about discovering such a terrible compound with the thought that sooner or later some other chemist would have done it. But Sobrero did not become famous for his invention: who knows his name today besides the historians of chemistry? Enter Nobel, whose great fame does not rest on discovering a new explosive compound but, first, on a process to ignite nitroglycerine in a controllable and predictable fashion and then on the preparation and marketing of the substance in a form that is relatively safe to handle and practical to use for industrial blasting. Nobel’s nitroglycerin experiments began in 1862 when he was detonating the compound by using small amounts of black powder attached to a slow fuse. In 1863 he got his first patent for using nitroglycerin in blasting and introduced an igniter (a wooden capsule filled with black powder) to trigger the compound’s explosion.
FIGURE 4.15. Structures of 1,2,3-propanetriol trinitrate (nitroglycerine), ammonium picrate (2,4,6-trinitrophenol ammonium salt, C6H6N4O7), cyclonite (hexahydro-i,3,5-trinitro-i,3,5-triazine, C6H6N6O6), and TNT (i-methyl-2,4,6-trinitrobenzene, C7H5N3O6).
In November of the same year he invented dynamite, a new explosive that, to quote his U.S. Patent 78,317 granted on May 26, 1868 (Nobel 1868:i),
consists in forming out of two ingredients long known, viz. the explosive substance nitro-glycerine, and an inexplosive porous substance, hereafter specified, a composition which, without losing the great explosive power of nitro-glycerine, is very much altered as to its explosive and other properties, and which, at the same time, is free from any quality which will decompose, destroy, or injure the nitro-glycerine, or its explosiveness.
Nobel decided to give this combination a new name, dynamite, “not to hide its nature, but to emphasize its explosive traits in the new form; these are so different that a new name is truly called for” (cited in Fant 1993:94). Nobel’s dynamite was made with highly porous Kieselguhr, a mineral that was readily available along the banks of the Elbe and the Alster (the Elbe’s small northern tributary) near Hamburg, where Nobel moved from Sweden in 1865. The mineral is diatomaceous earth formed of siliceous shells of unicellular microscopic diatoms, aquatic protists found in both fresh and marine waters that often display nearly perfect radial symmetry. Diatomaceous earth—also used as an insulator, as abrasive in metal polishes, an ingredient in toothpaste, to clarify liquids, and as a filler for paper, paints, and detergents—can absorb about three times its mass of nitroglycerine.
A mixture of 25% diatomaceous earth and 75% nitroglycerine produces a reddish yellow, crumbly mass of plastic grains that is slightly compressible and safe from detonation by ordinary shocks (Shankster 1940). The explosive has been usually sold pressed into cartridges enclosed in waxed paper wrappers. Today’s standard dynamite composition is basically the same as Nobel’s ratio: 75% nitroglycerol, 24.5% diatomaceous earth, and 0.5% sodium carbonate, the last compound being added in order to neutralize any acidity that might be formed by the decomposition of nitroglycerin. Nobel returned to complete the invention in 1866, when he came up with a detonator, without which the new explosive would be nearly impossible to use. This igniter was a metal capsule filled with Hg(CNO)2 (mercury fulminate): a strong shock produced by this primary explosive, rather than high heat, set off the nitroglycerin.
The Nobel igniter, patented in 1867, opened the way for widespread use of dynamite, making it one more critically important item to mark the beginning of the Age of Synergy, whose ethos Nobel embodied as much as did Edison, Hall, Parsons, or Daimler: he wanted to see his inventions commercialized and diffused as rapidly as possible. By 1870 he had five nitroglycerine factories in Europe, established the first dynam
ite factory in Paulilles in southern France in 1871, and watched the explosive conquer the blasting market worldwide. By 1873 there were 15 dynamite factories in Europe and North America, and between 1871 and 1874 the total output of the explosive had quadrupled to just more than 3,000 t. As the most powerful explosive yet available—its velocity of detonation is as much as 6,800 m/s, compared to less than 400 m/s for gunpowder (Johansson and Persson 1970)—the compound was more effective in breaking rocks apart rather than just displacing them. Consequently, blasting for mining operations, railroad construction, and other building projects became not only safer but also more efficient and less expensive.
Nobel had tried unsuccessfully to gelatinize nitroglycerin already in 1866, and he finally succeeded in 1875 by preparing a gelatinous dynamite, the combination of nitroglycerine (about 92%) and nitrocellulose (cotton treated with nitric acid, also known as nitrocotton or gun cotton). This tough yet plastic and water-resistant compound became the explosive of choice for packing boreholes in rock-blasting operations. Cheaper ammonium nitrate was later used to replace a relatively large share of nitroglycerin and to produce many kinds of plastic and semiplastic ammonia gelatin dynamites of different explosive intensity. These substances contain 50–70% explosive gelatin (a mixture of nitroglycerine and nitrocotton), 24–45% ammonium nitrate, and 2–5% wood pulp (Shankster 1940).