Aluminum: Common Metal, Uncommon Past
Now ubiquitous and vital to modern life, aluminum was once more expensive than gold, locked away in its ore without a commercially viable method to release it.
In the mid-1800s aluminum was more valuable than gold. Napoléon III’s most important guests were given aluminum cutlery, while those less worthy dined with mere silver; fashionable and wealthy women wore jewelry crafted of aluminum. Today aluminum is a critical component of modern life, found in airplanes, automobiles, soft drink cans, construction materials, cooking equipment, guardrails, and countless other products. The difference between scarcity and abundance (and between obscurity and ubiquity) of this metal depended solely on scientists’ ability to find the way to release it—the third most common element in the earth’s crust by weight—from its ore.
The most familiar story of the first extraction of aluminum is that the youthful Ohioan Charles Martin Hall developed aluminum’s electrolytic extraction process in his family’s woodshed in 1886, patented the invention, helped found the company that would later become Alcoa, and died a rich man. A more complicated version reveals that Paul Héroult developed a similar process in France at the same time. In reality both Héroult and Hall were participants in a much larger program of aluminum research that started in the 1850s and lasted until 1903, when the last major patent dispute was settled. By then Alcoa was the undisputed world leader in aluminum production, and Hall himself was a multimillionaire. But neither Hall nor Héroult operated in a vacuum—their nearly simultaneous discovery of a process for aluminum extraction built on several decades’ worth of electrochemistry and, indeed, centuries’ worth of knowledge on the nature of metals.
While aluminum metal is a recent discovery, its compounds were fairly common in various industries throughout history. Alum (aluminum potassium sulfate, KAl(SO4)2), was best known as a dye fixer (or mordant) first developed in Egypt over 5,000 years ago, and clays containing aluminum silicates appear to have been favored by contemporary Persian potters for their strength. Anhydrous aluminum sulfate (Al2(SO4)3) was used by the ancient Greeks as an astringent to stanch wounds—a use that continues to this day in styptic pencils.
Electrolysis, a process central to the modern history of aluminum, has its roots in the early 19th century. In 1800 the Italian Alessandro Volta invented the “pile” battery, which provided the source of stored power that pioneering Englishmen William Nicholson and Anthony Carlisle used to break a compound (water) into its constitutive elements through a process known as electrolysis. Generally defined, the process involves applying live electrodes to a liquid containing the compound to be electrolyzed. The negative electrode in electrolysis, the cathode, naturally attracts positive ions, which take on electrons; the positive electrode, the anode, attracts negatively charged ions. When water is subjected to electrolysis, hydrogen gas is produced at the cathode and oxygen is released at the anode.
The remarkable Cornish chemist Humphry Davy also started experiments in electrolysis in 1800. He struggled to isolate metals by putting a current through solutions of their alkali salts, which did nothing more than free hydrogen. But he met with much better results when he started to electrolyze molten compounds, first isolating potassium from potash and sodium from table salt in 1807. The following year Davy used electrolysis to produce elemental calcium, strontium, barium, and magnesium before capping off his remarkable string of success with the identification and naming of aluminum. He did not actually isolate aluminum; rather, as Norman C. Craig, professor emeritus of chemistry at Oberlin College, explains, “Davy had learned enough about compounds of other metals to conclude from the composition of aluminum compounds that they contained a new metal, aluminum.” He first called the metal alumium, although it has evolved to aluminium in most English-speaking countries, and to aluminum in the United States. One of early chemistry’s true geniuses, Davy was knighted and received a baronetcy in 1812 and became president of the Royal Society in 1820. (The society has awarded an annual “Davy Medal” in his honor since 1877.) Nevertheless, his repeated attempts to isolate aluminum metal met with no success before his death in 1829.
The honor of first producing elemental aluminum went instead to Hans Christian Ørsted, a professor at the University of Copenhagen, who in 1825 produced a tiny amount of the metal by rapidly heating aluminum chloride (AlCl3) with potassium amalgam (an alloy of potassium and mercury) and then distilling off the mercury. Unfortunately, Ørsted’s process produced too little aluminum to perform even the most basic analysis, and his experiment was difficult to reproduce. The German chemist Friedrich Wöhler tried again in 1827, one year before he pioneered the field of organic chemistry by synthesizing urea. While his aluminum experiment did not produce the lump metal he desired, he did obtain an impure aluminum powder after substituting metallic potassium for Ørsted’s potassium amalgam. And there the matter rested until 1845, when Wöhler produced “gray metallic powder . . . [with] small tin-white globules [of aluminum], some as large as pins’ heads,” by heating potassium and aluminum chloride together in a closed system, thereby excluding the moisture that had been perting aluminum into aluminum hydroxide (Al(OH)3).
To Electrolysis and Back Again
By the mid-1850s battery technology had improved in output and reliability to the point that the first electrolytic production of aluminum was possible. Aided by this advance, and foreshadowing Hall’s and Héroult’s twinned, simultaneous discovery 32 years later, the first electrolysis of aluminum was also developed independently by two parties.
The first researcher to claim to produce elemental aluminum by electrolysis was the German Robert Wilhelm von Bunsen, who by coincidence had taken Wöhler’s place as a chemistry teacher at the Higher Polytechnic School at Kassel in 1836. A man of wide-ranging interests, Bunsen ultimately became famous for developing the spectroscope and for the use of iron-oxide hydrate as an antidote to arsenic poisoning. (Curiously, he did not invent the burner that carries his name; that was the work of his assistant Peter Desaga, who improved on a design by Michael Faraday.) In 1841 Bunsen improved on an 1839 battery design by William Robert Grove, who a few years later also produced the first hydrogen-oxygen fuel cell. Bunsen lowered the cost of Grove’s battery by replacing the platinum cathode with a more cost-effective carbon one inside the battery itself. With these batteries he started experimenting with electrolysis, producing pure chromium, magnesium, manganese, sodium, barium, calcium, and lithium, in addition to very small amounts of what he believed to be aluminum in 1854. But he then moved on to other areas of interest, publishing his important paper on emission spectroscopy in 1860.
The second person to experimentally reduce aluminum ions to metal by electrolysis was the Antilles-born Frenchman Henri Sainte-Claire Deville, who presented his findings on electrolytic production to the French Académie des Sciences in 1854, a week after Bunsen published his results. His work attracted the attention of Napoléon III, then titled “Emperor of the French,” who was interested in the metal as a source of military armor. With Napoléon III’s mandate, Deville quickly realized that the cost of zinc for anodes in the Bunsen cells he used was too high to efficiently produce aluminum through electrolysis. Instead he lowered the cost by returning to chemical methods, replacing Wöhler’s potassium with sodium—that is, AlCl3 + 3Na → Al + 3NaCl. Through this process he was able to obtain enough aluminum to produce marble-sized blobs. In 1855 he displayed an ingot of comparatively pure aluminum at the World’s Fair in Paris, to great popular interest. Because the Deville process was deemed “good enough,” most scientists then set aside experiments on electrolytic production of aluminum.
Deville made good use of Napoléon III’s money over the next few years, founding an aluminum production facility in Paris in 1856 before moving it to Nanterre in 1857. In 1858 he patented a method for making the extraction of alumina (Al2O3) from mineral bauxite more cost-effective. These efforts introduced aluminum to the world by lowering its price to a level that allowed ordinary people to afford aluminum jewelry. (The 1859 price for a pound of aluminum was around $17, about the same as silver.) His 1859 book, De l’Aluminium, ses Propriétés, sa Fabrication et ses Applications (On aluminum, its properties, its production, and its applications), was the first to describe the metal fully, sparking the research that would lead to Hall’s and Héroult’s famous discoveries.
Aluminum largely remained a curiosity for the next 20 years, in part because the metal produced by the Deville process was notoriously difficult to work with. The typical sample was only about 97% pure, with at least 1% each of iron and silicon introduced by impurities in the apparatus and starting materials. With low demand there was little economic reason to build aluminum plants. Production worldwide in 1869 was only about 2 metric tons. Fifteen years later, when a 6-pound aluminum cap was famously placed on the Washington Monument, world production had increased to only 3.6 metric tons—compared with the 2,834 metric tons of silver that were produced that year. Only 112 pounds of aluminum was produced in the United States, virtually all by a Philadelphia immigrant named William Frishmuth who had studied with Wöhler in Germany. The bulk of the remainder came from France, Germany, and England.
A big hurdle to achieving lower-cost aluminum production was the lack of a good power source. Even if someone developed an advantageous electrochemical reaction, it needed to be sufficiently strong, sustainable, and economical. The growth of reliable, commercial electric dynamos in the last third of the 19th century meant that reliable electrical power would be available wherever mechanical energy existed, and it returned attention to the possibilities of an economical electrolytic process for aluminum. Improvements demonstrated by Zénobe Gramme in 1871 increased the dynamo’s voltage and made the current more consistent and predictable.
This was the world in which Charles Hall entered his second year at Oberlin College and Frenchman Paul Louis-Toussaint Héroult started preparatory school before entering mining college. Both were 18 years old in 1881. Although they ultimately shared the same idea, the two couldn’t have been more different.
Charles Martin Hall
Charles Martin Hall was born on 6 December 1863, in Thompson, Ohio, where his father was a Congregational minister. When he was nine they moved 75 miles to Oberlin, Ohio, a town renowned for its college, music conservatory, and status as a terminus of the Underground Railroad. His mother and father had graduated from Oberlin College, and in turn he and his six siblings all graduated from it as well.
Hall had taken an early interest in chemistry, spending his teenage years experimenting with minerals and chemicals in his family’s house and eventually going to the college to further his studies. His professor of chemistry was Frank Jewett, who as a student in Germany in the early 1870s had gained an interest in aluminum from discussions with Friedrich Wöhler. Legend has it that Jewett, who had been named professor of chemistry and mineralogy at Oberlin in 1880, passed around a lump of aluminum in class, stating that “any person who discovers a process by which aluminum can be made on a commercial scale will bless humanity and make a fortune for himself.” Hall, who already had an interest in aluminum before entering college, allegedly told a classmate, “I’m going for that metal.”
Hall made good on this promise shortly after graduating, working partly in Jewett’s college lab and partly in his family’s woodshed. Like many 19th-century scientists, he fabricated much of his own equipment and synthesized some of his own chemicals. When his first attempts at creating an improved chemical process to extract aluminum failed, Hall had to use numerous Bunsen batteries with carbon cathodes to effect electrolysis. But first he had to find appropriate starting materials.
For an aluminum source he precipitated alumina by mixing the common household products alum with washing soda (sodium carbonate, Na2CO3) and drying the filtered results. Finding a solvent that would liquefy the mixture and make it more amenable to electrolysis turned out to be a bit more difficult. Hall tried fluorspar (calcium fluoride), potassium fluoride, sodium fluoride, magnesium fluoride, and aluminum fluoride, all to no avail. Then on 9 February 1886 Hall discovered that cryolite (sodium hexafluoroaluminate, Na3AlF6), once heated beyond its melting point of 1,000ºC with his gasoline-powered furnace, dissolved alumina like sugar in coffee.
From there the experiments were effected at a lightning-quick pace. A week after Hall’s first electrolytic attempts failed (probably owing to contamination by silicates in the clay crucible), he produced his first pieces of metallic aluminum on 23 February 1886 and filed for a patent on 9 July, using the following reaction:
2Al2O3 + 3C → 4Al + 3CO2
Where at the cathode we have: Al3+(melt) + 3e- → Al(l)
And at the anode: 2O2-(melt) + C(s) → CO2(g) + 4e-
Hall’s French counterpart, Paul Louis-Toussaint Héroult, was born on 10 April 1863 in the small Normandy town of Thury-Harcourt. Indeed, the two were a study in contrasts. Whereas Hall was the child of learned, college-educated parents, Héroult’s father ran a tannery and had at one time been a laborer at a Deville-process aluminum plant; whereas Hall was known as a quiet, obedient, studious child, Héroult was sent to a series of boarding schools, possibly in part to tame his rebelliousness. He read Deville’s famous book about aluminum while at Sainte-Barbe Academy in Gentilly (near Paris) and became obsessed with the subject.
In 1882 Héroult entered the École des Mines in Paris. But there he apparently neglected his other studies while chasing his aluminum dreams, for he was failing his courses and was asked to leave after only a few months. (Héroult himself later claimed he was ejected because he threw a wet sponge that hit the dean.) So while Hall was continuing his studies with Professor Jewett, Héroult found himself in the army until his honorable discharge in 1884.
Héroult’s father died suddenly in 1885, leaving the 22-year-old Paul in possession of the family tannery, including its steam engine. Paul seized the opportunity to continue his experiments with aluminum and persuaded some friends from the École des Mines to join him. But first he convinced his mother to give him 50,000 francs for a 400-amp, 30-volt dynamo—no small amount at a time when a kilogram of meat was 2 francs and red wine half a franc per liter. Like Hall, he ultimately decided on molten cryolite as a solvent and made his first extraction on an unrecorded date. But two dates are certain: Héroult preceded Hall in filing his patent on 23 April 1886 in France and on 22 May 1886 in the United States.
Sharing an Achievement
Fortunately the two innovators were ultimately able to come to an amicable understanding; Héroult held the earlier patent, but since Hall had demonstrated his process in February of 1886 in Oberlin, Hall’s work took precedence. Today their invention is known as the Hall-Héroult process, and they were friendly enough for Héroult to deliver a warm speech about Hall’s contributions at the ceremony in which the latter received his Perkin Medal in 1911.
In the end it was Charles Hall’s entrepreneurial spirit, coupled with persistence and some lucky breaks, that made him the big winner in the aluminum game. His first, unsuccessful attempts to commercialize his process included a stint at the Lockport, New York, plant of the Cowles Electric Smelting and Aluminum Company that would later lead to a contentious patent dispute. Eventually Hall found a backer in Captain Alfred Epher Hunt (of no relation to contemporaneous Bethlehem Steel Corporation founder Alfred Hunt), who with coinvestors provided $20,000 to build a pilot plant in Pittsburgh. That partnership would lead to the formation of the Pittsburgh Reduction Company, which in 1907 became the Aluminum Company of America, and under its current name of Alcoa is the world’s largest producer of aluminum.
Héroult’s life after the discovery continued to contrast with Hall’s. While Hall dedicated himself single-mindedly to the aluminum industry, Héroult took a greater interest in aluminum alloys and eventually moved on to other industries. Unlike Hall, who remained single and childless until his death, Héroult married twice and fathered five children. While Hall’s main pleasures outside the lab were reading, playing the piano, his family, and Oberlin college, Héroult enjoyed overseeing grand engineering tasks. Hall’s further patents were firmly in the field of aluminum production, but Héroult developed several non-aluminum inventions, such as a helicopter prototype and the “hydroslip, a sort of boat on runners, lifted by four propulsive vanes,” designed with American inventor Cooper Hewitt. Today he is perhaps most famous for inventing the electric arc furnace, still in use for steel recycling. Hall died of leukemia in Florida; Héroult died of typhoid fever and cirrhosis shortly after moving to a 100-foot yacht in the Mediterranean. And just as they shared a birth year and discovery year, they were joined together in year of their death—1914. Héroult lived only eight days longer than Hall.
Legacy of the Aluminum Innovation
At the time of the innovation by Hall and Héroult, the price of aluminum had dropped to less than $6 per pound, thanks in part to Hamilton Castner’s 1884 improved electrolytic process to produce sodium, necessary for the Deville process. But at that price aluminum was still much too expensive to be considered for the uses for which we now know it. The company Hall helped found drove the price down to below $1 per pound by 1891, and when a lightweight aluminum crankcase for their engine enabled the Wright Brothers to take their famous first flight, the metal was about $0.30 per pound.
The story of aluminum highlights how one scientific refinement enables another, which enables another, continuing in a chain until a discovery like the Hall-Héroult process becomes inevitable. Bunsen could have successfully used electrolysis to produce aluminum over 40 years earlier; after all, Hall used the same basic power source that Bunsen had. But until Deville’s chemical process proved the market and electric dynamos provided a path to commercialization, economically speaking, aluminum production seemed like folly. The fact that cryolite dissolves alumina had actually been discovered by Deville in 1859, but other details on, for example, mixture heating and construction of the reactive electrode came later.
One can only wonder what piece now missing from the world’s panoply of technologies and materials will unlock the next bonanza—and those who believe there are no such riches left need only look at the fairly recent example of titanium for proof otherwise: the metal was first extracted in 1910, commercialized in 1946, and only made widespread through a process developed in 1996. From the example of aluminum’s success it is important to note that Hall and Héroult are not lone geniuses, as popular as that image is. Rather, aluminum’s story teaches us that success stands on the shoulders of failure, and that previously discarded ideas can lead to new discoveries—like lead into gold.
The author wishes to thank Norman C. Craig for his assistance with this article.