Aluminium - Element information, properties and uses

Aluminium - Element Information, Properties and Uses

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Chemistry in Its Element: Aluminium

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You're listening to Chemistry in its Element, brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

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Chris Smith

This week, we delve into the chemical cause of transatlantic linguistic friction. Is it an 'um' or an 'ium' at the end? It turns out us Brits might have egg on our faces along with a liberal smattering of what we call aluminium.

Kira J. Weissman

"I feel like I'm trapped in a tin box at 39,000 feet." It's a common refrain of the flying-phobic, but maybe they would find comfort in knowing that the box is actually made of aluminium—over 66,000 kg of it, if they're sitting in a jumbo jet. While lamenting one's presence in an 'aluminium box' doesn't have quite the same ring, there are several good reasons to appreciate this material. Pure aluminium is soft. However, alloying it with elements like copper, magnesium, and zinc dramatically boosts its strength while keeping it lightweight, a clear advantage when fighting gravity. These alloys, sometimes more malleable than aluminium itself, can be molded into various shapes, including the aerodynamic arcs of a plane's wings or its tubular fuselage. Whereas iron rusts when exposed to the elements, aluminium forms a thin oxide layer, protecting its surface from corrosion. With this impressive résumé, it's no surprise aluminium is found in many other vehicles, including ships, cars, trucks, trains, and bicycles.

Nature has blessed the transportation industry with vast quantities of aluminium. As the most abundant metal in the Earth's crust, it's nearly everywhere. Yet, aluminium remained undiscovered until 1808, since it is bound with oxygen and silicon into various minerals and never appears naturally in its metallic form. Sir Humphrey Davy, the Cornish chemist, called it 'aluminum,' after one of its source compounds, alum. Shortly thereafter, the International Union of Pure and Applied Chemistry (IUPAC) standardized it to the more conventional 'ium.' Oddly enough, in 1925, the American Chemical Society resurrected the original spelling, so it is the Americans, not the British, who pronounce the element's name as Davy intended.

In 1825, Danish Scientist Hans Christian Ørsted had the honor of isolating aluminium for the first time. He described it as, "a lump of metal that resembles tin in color and sheen"—not a flattering description but possibly an explanation for passengers' confusion. The challenging task of separating aluminium from its oxides ensured its temporary status as a precious metal, more valuable than gold. An aluminium bar was displayed alongside the Crown Jewels at the 1855 Paris Exhibition, and Napoleon reserved aluminium tableware for his most honored guests.

It wasn't until 1886 that Charles Martin Hall, an amateur scientist, developed the first economic means of extracting aluminium. Working with his sister in a woodshed, he dissolved aluminium oxide in molten sodium hexafluoroaluminate (commonly known as 'cryolite') and separated the aluminium and oxygen using a strong electrical current. Remarkably, Frenchman Paul Louis Toussaint Héroult discovered the same technique around the same time, leading to a patent race. Their method, known as the Hall-Héroult process, remains the primary method for producing aluminium commercially, yielding millions of tons annually from bauxite, aluminium's most plentiful ore.

By the early 1900s, aluminium had already replaced copper in electrical power lines due to its flexibility, lightweight, and lower cost, despite poorer conductivity. Aluminium alloys became a construction favorite, used in cladding, windows, gutters, door frames, and roofing. Inside homes, aluminium appears in appliances, utensils, TV aerials, and furniture. As a thin foil, aluminium excels in packaging, offering durability, impermeability, and resistance to chemical attack, making it ideal for protecting medication and candy bars. However, its most recognizable form is the aluminium beverage can. Hundreds of billions are produced annually, with naturally glossy surfaces making them attractive for branding. Though refining aluminium consumes a large portion of global electricity, recycling aluminium cans can save nearly 95% of the energy initially required to smelt the metal.

However, aluminium has a darker side. Despite its abundance, aluminium serves no known biological purpose. In its soluble +3 form, it is toxic to plants, reducing crop yields in acidic soils, which cover nearly half of arable land. Humans also ingest aluminium through air, water, and food. While naturally present in small amounts in foods, higher levels come from additives and over-the-counter antacids. Many of us apply aluminium-containing deodorants daily. Some studies suggest aluminium as a risk factor for breast cancer and Alzheimer's, although most experts are unconvinced by the evidence. Despite being a proven neurotoxin at high concentrations, primarily affecting bones and brains, more research is needed.

Chris Smith

Researcher Kira Weissman from Saarland University in Saarbrucken, Germany, shares the story of aluminium and why I haven't been pronouncing it as Humphrey Davy intended. Next week, we explore another element and its unique sound.

Brian Clegg

There aren't many elements whose names are onomatopoeic. Say oxygen or iodine, and there's no clue in the word's sound about the element. But zinc is different—zinc, zinc, zinc—you can almost hear coins falling into an old-fashioned bath. It's a hard metal. Zinc is often hidden away, stopping iron from rusting, soothing sunburn, combating dandruff, combining with copper to make brass, and keeping us healthy. Yet, we hardly notice it.

Chris Smith

You can catch up with the clink of zinc with Brian Clegg on next week's Chemistry in Its Element. I'm Chris Smith. Thank you for listening and goodbye.

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Chemistry in Its Element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in Its Element on our website at chemistryworld.org/elements.

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H.C. Ørsted Discovered Aluminium

The plaster statue of Ørsted (erected in 1885), which stands at the Oxford University Museum of Natural History. Photo: Andrew Gray / CC BY-SA 3.0

Aluminium is the most common metal in the Earth's crust, making up 8.3 percent of it, surpassing iron's 5.6 percent. The discovery of this important metal was made by H.C. Ørsted, making him the only Danish scientist to discover one of the 118 elements of the periodic table. However, when he announced "a metal lump, which in color and gloss somewhat resembles tin" in 1825, he was notably modest and did not attribute further significance to his discovery. He eventually passed his method to a young German chemist who improved it and was considered the real discoverer of aluminium for much of the century.

What did Ørsted find in 1825? Why did he lose interest in a discovery as significant as electromagnetism?

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Hidden in the Clay

In the early 1800s, chemists knew that certain clay soils contained a metallic substance. Englishman Humphry Davy suggested calling it 'aluminum' in 1808, but others called it 'aluminium.' Davy had electrically isolated sodium, potassium, and calcium and hoped to similarly isolate aluminium from clay. However, his and others' attempts failed, leaving the metal unknown until Ørsted found a way in late 1824.

Ørsted had just set up a new chemical laboratory in the courtyard at Studiestræde 6, where he developed a new method to produce water-free aluminium chloride (AlCl3) from aluminium oxide (Al2O3) found abundantly in clay. He realized that the water-free chloride could be reduced to metal by heating it with potassium. His experiments resulted in a lump of aluminium, albeit impure.

Clay-Metal?

Ørsted announced his discovery to The Royal Danish Society of Sciences and Letters on February 18, 1825, and shortly after in Dansk Litteraturtidende, a Danish journal. At a Society meeting on April 8 of that year, he presented a sample of the new metal. The discovery was mentioned in international journals but without much attention, and Ørsted himself did not promote his discovery. He only commented on it briefly without further exploring the new element and its properties. In his 1828 autobiography, he described his method in a single sentence.

From our perspective, Ørsted's lack of interest was peculiar. Neither he nor anyone else could predict the metal's future impact. Ørsted proposed the Danish name 'Leerær,' combining the Danish word for clay and an old word for metal. For an international name, he coined 'argillium.' None of these names caught on as chemists preferred the already known 'aluminium.'

Busy Life of the Researcher Overshadowed the Magnitude of the Discovery

Ørsted's lack of action was likely due to his busy schedule. His teaching and numerous administrative and organizational activities left him little time to explore the new metal. In 1824, he founded The Society for the Dissemination of Natural Science, which occupied much of his time and energy. He was also working on plans that resulted in the creation of Polyteknisk Læreanstalt in 1829, the precursor to the Technical University of Denmark (DTU). Aluminium was not high on his list of priorities.

From Ørsted to Wöhler

In September 1827, Ørsted met 27-year-old German chemist Friedrich Wöhler in Copenhagen and shared his experiments with the metal from clay soil. Ørsted encouraged Wöhler to continue the work, which he did. Wöhler improved Ørsted's method and was the first to determine many of aluminium's properties, including its low density for a metal, only 2.7g/cm3 (compared to iron's 7.9 and lead's 11.3).

Wöhler's aluminium didn't resemble Ørsted's; it was a dark, infusible powder, while Ørsted's metal lump could be melted in a glass tube. Doubts arose whether Ørsted's substance was aluminium. Wöhler argued Ørsted's lump was aluminium-containing potassium or an alloy of both metals. Thus, Wöhler was credited with discovering the element in 1827, not Ørsted in 1825. Ørsted, uninterested, raised no objections. His contribution to aluminium history faded from chemistry books after his death in 1851, often described as erroneous or incomplete. Most agreed Wöhler isolated aluminium, making him the real discoverer.

A Patriotic Metal

In 1920, the 100th anniversary of Ørsted's electromagnetism discovery was celebrated. The Copenhagen meeting involved numerous researchers and their families. The event had a national character, enhanced by the country's reunification. During the celebration, Danish chemists decided to investigate whether Ørsted or Wöhler was the rightful discoverer of aluminium. By replicating Ørsted's original experiment, they established that he likely found impure aluminium two years before Wöhler. Niels Bjerrum, a prominent Danish chemist, concluded in 1926 that Ørsted should be reinstated as the discoverer of aluminium.

Ørsted Would Probably Have Liked to Share the Honour

Today, evidence suggests Wöhler's result contained significant potassium, while Ørsted's contained small amounts of potassium and mercury. Neither had pure aluminium, but Ørsted's was probably purer. Around 1940, Ørsted's seniority in discovering aluminium was recognized by most chemists. Ørsted himself would likely have shared the honour with Wöhler if it had interested him.

The Age of Aluminium

When Ørsted died in 1851, aluminium was just a scientific curiosity. A decade later, it could be produced in larger quantities and began to garner industrial interest. Initially expensive, it was used for ornamental items like Frederik VII's equestrian helmet, displayed at Rosenborg Castle. By the mid-20th century, aluminium became the basis for large-scale industry. Today, 65 million tonnes of pure aluminium are produced annually, essential for modern society. Aluminium is used in packaging, cans, and the construction and transport industries. A jet airplane, for example, is made from around 80 percent aluminium. While Ørsted lived in a coal and iron age, we now live in an aluminium age.

Bissen's Bust - Now in Digital Form

In 1850, renowned sculptor H.W. Bissen made a bust of Ørsted, later reproduced in unglazed porcelain by the Royal Porcelain Factory. Bissen's work inspired a 1937 model by Mathilius Schack Elo, cast in aluminium to highlight Ørsted's discovery of the metal. To celebrate the 200th anniversary of Ørsted's electromagnetism discovery, researchers at DTU created a digital copy of the bust, consisting of 150,000 data points connected in 300,000 triangles. Using a specially designed 3D scanner, they replicated the aluminium bust digitally to understand how light interacts with aluminium. Ørsted might not have understood the modern technology but would have appreciated the results from the institution he founded nearly 200 years ago.

Translated by Stuart Pethick, e-sp.dk translation services. Read the Danish version at Videnskab.dk's Forskerzonen.

Reference

Helge Kragh's profile (KU)

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