by Nate Burgess Monday, October 26, 2015
Compared to gold, silver, lead and copper — metals that people have extracted, refined and used for millennia — aluminum is a relative newcomer. Pure aluminum was more valuable than gold when it was first discovered in the early 19th century. It graced the fine china of Napoleon III and was displayed next to the French Crown Jewels at the 1855 Paris Exhibition. Today, aluminum is cheap and plentiful, used in everyday products ranging from soda cans to jets. The transformation of the metal from unknown material to rare metal to ubiquity in fewer than two centuries is due to two pivotal discoveries: an abundant aluminum ore — bauxite — and a process of refining this ore using electricity.
The discovery of bauxite occurred near Les Baux, France, an ancient village near the Mediterranean Sea named for, and carved from, a rocky outcrop. On March 23, 1821, a geologist named Pierre Berthier discovered a reddish, clay-like material. He found that the substance, later named bauxite after the village, consisted of about 50 percent aluminum oxide. Berthier did not realize it at the time, but he had discovered today’s most commonly used aluminum ore — the source of more than 99 percent of industrial aluminum.
About the time Berthier discovered bauxite, European scientists were just beginning to understand the properties of aluminum. They had long theorized that the metal existed within many natural compounds, but they had never seen the metal separately in a pure form. In 1825, four years after Berthier discovered bauxite, Dutch chemist Christian Oersted managed to obtain a lump of impure but recognizable aluminum metal by reacting aluminum chloride with potassium.
Between 1827 and 1845, German chemist Frederick Wohler improved upon Oersted’s method, extracting a pure version of aluminum. Wohler also documented many of the metal’s physical properties; he found that aluminum was light, malleable and conducted electricity. Because the process was so energy intensive and the required materials were so expensive, aluminum was initially more valuable than metals like gold and platinum. In 1854, French chemist Henri Sainte-Claire Deville created the first commercial process for extracting aluminum from aluminum chloride.
Pure aluminum had its coming-out party at the Paris Exposition Universelle of 1855. At this point, Deville could only produce small amounts of aluminum — enough to make bars and small items. At the exposition, Deville’s bars were a sensation, billed as “silver from clay” and displayed next to the French Crown Jewels.
One reason the aluminum got this place of honor was because Emperor Napoleon III had provided financial support for Deville’s research. Napoleon, the nephew of Napoleon Bonaparte, had been elected president of France in 1848 and then launched a coup in 1851 to retain control of the French government after the end of his four-year term. The new dictator hoped the metal might have military uses, or could at least bring glory to France.
Napoleon approved imperial eagles made of aluminum to adorn French battle flags. He also used it personally. In 1856, Napoleon commissioned an aluminum baby rattle for his son, the newborn prince, Eugene Louis Jean Joseph. In 1858, a silversmith named Charles Christofle presented Napoleon with a large aluminum centerpiece commemorating his patronage of Deville. The emperor even provided aluminum cutlery for his most honored guests at state dinner parties.
Deville soon learned to substitute less expensive sodium for potassium in his aluminum extraction process, and the price of production fell steadily. Additionally, other manufacturers in Europe figured out how to extract the metal and began to produce aluminum too. By 1865, the price of aluminum had fallen by 90 percent. Over the next 20 years, interest in the metal spread throughout Europe and beyond. Eventually the new metal found its way to the United States — and even gained a prominent position atop the Washington Monument.
Construction on the Washington Monument, which had been first proposed in 1783 by the U.S. Continental Congress, finally began in 1848 and was finished by 1884. The last phase of construction was to cast a small metal pyramid at the top of the obelisk. This object was supposed to act as a lightning conductor between the tip of the monument and a series of internal lightning rods. Copper, bronze or brass plated with platinum were the original preferences for the pyramid. However, William Frishmuth, who was contracted to cast the pyramid, knew of Deville’s method of extracting aluminum, and in fact, he was the only person in the United States at that time producing the metal. Frishmuth asked if he could try making the pyramid out of the still relatively unknown metal. Because aluminum was known to conduct electricity relatively well, was corrosion resistant, and was unlikely to stain the structure’s marble, the monument’s engineers agreed.
Even though the metal’s cost had fallen greatly by 1884, it was still equal in value to silver. And Deville’s method still required very large amounts of energy to convert ore into aluminum, so it remained a precious commodity. Engineers were chagrined, therefore, when Frishmuth’s aluminum pyramid ended up costing more than three times the cost estimate for a pyramid made of copper, bronze or brass.
After negotiation, the builders of the monument went ahead and placed the pyramid in December 1884. The aluminum pyramid was the last and crowning achievement of the age of aluminum as a precious metal. The process of producing the metal, along with its price and applications, would change dramatically in a couple of years.
In 1886, scientists Charles Hall and Paul Louis Toussaint Heroult, working independently, invented a new process of extracting aluminum that became the standard model for producing the metal in the 20th century. In the Hall-Heroult process, aluminum oxide is mixed into molten cryolite, a sodium aluminum fluoride. It is then passed through an electric current, which causes pure aluminum to precipitate. Other electrolytic methods had been explored with less success, but the Hall-Heroult model proved economical because of a commercial electrical generator invented by Zenobe Gramme in the previous decade. Finally, people had an inexpensive source of energy sufficient to unlock pure aluminum from aluminum oxide — the compound found in Berthier’s ore, bauxite.
Complementing this discovery, in 1887 Russian chemist Karl Bayer invented a method to extract aluminum oxide from bauxite. Bayer wanted to come up with an efficient way of providing aluminum oxide to the textile industry, which used the compound to dye fabric. Bayer’s method dissolved aluminum oxide from the ore, leaving as byproducts the silica, iron oxide and titanium dioxide also found in bauxite. In 1888, Hall established the first factory producing aluminum using the Hall-Heroult process, and later the Bayer method was added to efficiently produce commercial quantities of aluminum oxide. Hall’s company is now known as Alcoa.
By the 20th century, the modern aluminum industry was born. Though technology has changed and the process has been intensely researched, streamlined and updated, the basic flow of aluminum manufacturing has remained the same. Bauxite is mined, converted into aluminum oxide using the Bayer process, and then aluminum is extracted from this oxide through the Hall-Heroult process. The French sources of bauxite were eventually depleted; the majority of the ore today comes from Australia, Brazil, China, India and Jamaica.
Aluminum is now inexpensive and used by people across the world every day. We drink soda from aluminum cans, we drive cars and bicycles with aluminum components, we fly in airplanes with aluminum skin. However, the aluminum industry has continued to look for new and more efficient ways to produce the metal. The major expense of producing aluminum continues to be the great quantity of energy required to unlock aluminum from its natural compounds. Recycling helps because aluminum can be recycled with much less energy than it takes to extract it from its natural ores, and little of the metal is lost in the process.
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