May. 06, 2024
Transcript :
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(Promo)
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 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 as well as a liberal smattering of what we call aluminium.
Kira J. Weissman
'I feel like I'm trapped in a tin box at 39000 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 - more than 66000 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 choice of material. Pure aluminium is soft. However, alloying it with elements such as such as copper, magnesium, and zinc, dramatically boosts its strength while leaving it lightweight, obviously an asset when fighting against gravity. The resulting alloys, sometimes more malleable than aluminium itself, can be moulded into a variety of shapes, including the aerodynamic arc of a plane's wings, or its tubular fuselage. And whereas iron rusts away when exposed to the elements, aluminium forms a microscopically thin oxide layer, protecting its surface from further corrosion. With this hefty CV, it's not surprising to find aluminium in many other vehicles, including ships, cars, trucks, trains and bicycles.
Happily for the transportation industry, nature has blessed us with vast quantities of aluminium. The most abundant metal in the earth's crust, it's literally everywhere. Yet aluminium remained undiscovered until 1808, as it's bound up with oxygen and silicon into hundreds of different minerals, never appearing naturally in its metallic form. Sir Humphrey Davy, the Cornish chemist who discovered the metal, called it 'aluminum', after one of its source compounds, alum. Shortly after, however, the International Union of Pure and Applied Chemistry (or IUPAC) stepped in, standardizing the suffix to the more conventional 'ium'. In a further twist to the nomenclature story, the American Chemical Society resurrected the original spelling in 1925, and so ironically it is the Americans and not the British that pronounce the element's name as Davy intended.
In 1825, the honour of isolating aluminium for the first time fell to the Danish Scientist Hans Christian Øersted. He reportedly said of his prize, 'It forms a lump of metal that resembles tin in colour and sheen" - not an overly flattering description, but possibly an explanation for airline passengers' present confusion. The difficulty of ripping aluminium from its oxides - for all early processes yielded only kilogram quantities at best - ensured its temporary status as a precious metal, more valuable even than gold. In fact, an aluminium bar held pride of place alongside the Crown Jewels at the 1855 Paris Exhibition, while Napoleon is said to have reserved aluminium tableware for only his most honoured guests.
It wasn't until 1886 that Charles Martin Hall, an uncommonly dogged, amateur scientist of 22, developed the first economic means for extracting aluminium. Working in a woodshed with his older sister as assistant, he dissolved aluminium oxide in a bath of molten sodium hexafluoroaluminate (more commonly known as 'cryolite'), and then pried the aluminium and oxygen apart using a strong electrical current. Remarkably, another 22 year-old, the Frenchman Paul Louis Toussaint Héroult, discovered exactly the same electrolytic technique at almost exactly the same time, provoking a transatlantic patent race. Their legacy, enshrined as the Hall-Héroult process, remains the primary method for producing aluminium on a commercial scale - currently million of tons every year from aluminium's most plentiful ore, bauxite.
It wasn't only the transportation industry that grasped aluminium's advantages. By the early 1900s, aluminium had already supplanted copper in electrical power lines, its flexibility, light weight and low cost more than compensating for its poorer conductivity. Aluminium alloys are a construction favourite, finding use in cladding, windows, gutters, door frames and roofing, but are just as likely to turn up inside the home: in appliances, pots and pans, utensils, TV aerials, and furniture. As a thin foil, aluminium is a packaging material par excellence, flexible and durable, impermeable to water, and resistant to chemical attack - in short, ideal for protecting a life-saving medication or your favourite candy bar. But perhaps aluminium's most recognizable incarnation is the aluminium beverage can, hundreds of billions of which are produced annually. Each can's naturally glossy surface makes as an attractive backdrop for the product name, and while its thin walls can withstand up to 90 pounds of pressure per square inch (three times that in a typical car tyre), the contents can be easily accessed with a simple pull on the tab. And although aluminium refining gobbles up a large chunk of global electricity, aluminium cans can be recycled economically and repeatedly, each time saving almost 95% of the energy required to smelt the metal in the first place.
There is, however, a darker side to this shiny metal. Despite its abundance in Nature, aluminium is not known to serve any useful purpose for living cells. Yet in its soluble, +3 form, aluminium is toxic to plants. Release of Al3+ from its minerals is accelerated in the acidic soils which comprise almost half of arable land on the planet, making aluminium a major culprit in reducing crop yields. Humans don't require aluminium, and yet it enters our bodies every day - it's in the air we breathe, the water we drink, and the food we eat. While small amounts of aluminium are normally present in foods, we are responsible for the major sources of dietary aluminium: food additives, such as leavening, emulsifying and colouring agents. Swallowing over-the-counter antacids can raise intake levels by several thousand-fold. And many of us apply aluminium-containing deodorants directly to our skin every day. What's worrying about all this is that several studies have implicated aluminium as a risk factor for both breast cancer and Alzheimer's disease. While most experts remain unconvinced by the evidence, aluminium at high concentrations is a proven neurotoxin, primarily effecting bone and brain. So, until more research is done, the jury will remain out. Now, perhaps that IS something to trouble your mind on your next long haul flight.
Chris Smith
Researcher Kira Weissman from Saarland University in Saarbruken, Germany with the story of Aluminium and why I haven't been saying it in the way that Humphrey David intended. Next week, talking of the way the elements sound, what about this one.
Brian Clegg
There aren't many elements with names that are onomatopoeic. Say oxygen or iodine and there is no clue in the sound of the word to the nature of the element, but zinc is different - zinc, zinc, zinc, you can almost hear a set of coins falling into an old fashioned bath. It just has to be a hard metal. In use, zinc is often hidden away, almost secretive. It stops iron rusting, sooths sunburn, keeps dandruff at bay, combines with copper to make a very familiar gold coloured alloy and keeps us alive but we hardly notice it.
Chris Smith
And 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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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 and thus surpassing iron’s 5.6 percent.
The discovery of the important metal was made by H.C. Ørsted, who is thus the only Danish scientist to have discovered one of the 118 elements of the periodic table.
However, when in 1825 he announced, ‘a metal lump, which in colour and gloss somewhat resembles tin’, he was strikingly modest and did not attribute any further significance to his discovery.
In fact, he gave it away to a young German chemist who improved Ørsted's method and was considered the real discoverer of aluminium for the best part of a century.
What did Ørsted find in 1825? And why did he lose interest in a discovery whose significance can be equated with his discovery of electromagnetism?
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In the early 1800s, chemists knew that certain types of clay soil contained a metallic substance that the Englishman Humphry Davy suggested calling 'aluminum' in 1808, but which others called 'aluminium'.
Davy had electrically isolated the metals sodium, potassium and calcium, and he hoped to similarly isolate aluminium from the clay soil.
However, neither his nor anyone else's attempts succeeded, so the metal remained unknown until Ørsted found a way at the end of 1824.
Ørsted had just set up a new chemical laboratory in the courtyard at Studiestræde 6, and here he found a new method of producing water-free aluminium chloride (AlCl3) from the aluminium oxide (Al2O3) that is so richly found in clay soil.
Here, he realised that the water-free chloride could be reduced to the metal by heating it with potassium.
The experiments he carried out actually resulted in a lump of aluminium, even if it was impure.
Ørsted announced his discovery to The Royal Danish Society of Sciences and Letters on February 18th, 1825, and shortly after in Dansk Litteraturtidende, a Danish journal.
At a Society meeting on April 8th that same year, he presented a sample of the new metal.
The discovery was also mentioned in international journals, but without receiving much attention, and without Ørsted himself seeking to promote his discovery.
On the contrary, he only commented on it briefly without later returning to the new element and its properties.
In his 1828 autobiography, he described his method with a single sentence.
From our perspective, Ørsted's lack of interest was peculiar, but neither he nor anyone else could have predicted the impact the metal would later have.
For the Danish name, Ørsted proposed the hopeless 'Leerær', where ‘leer’ refers to the Danish word for clay and 'ær' refers to an old Danish word for metal, while for an international name, he coined the Latin derived 'argillium'.
Ørsted's synthesis of water-free aluminium chloride (AlCl3), as reproduced in a Danish textbook from 1853.
None of the names caught on, because the chemists preferred the already known aluminium.
The reason for Ørsted's inaction was probably quite banal, namely that his teaching and numerous other administrative and organisational activities did not give him the time to explore the new metal himself.
In 1824, he founded The Society for the Dissemination of Natural Science, and this work took up a considerable amount of his time and energy.
In addition, he was working on plans that, in 1829, resulted in the creation of Polyteknisk Læreanstalt, which was a polytechnic and the precursor to the current Technical University of Denmark, DTU.
Ørsted had to prioritise his tasks, and aluminium was not high on the list.
In Copenhagen during September 1827, Ørsted met the 27-year-old German chemist Friedrich Wöhler, whom he told about his experiments with the metal from clay soil.
Generously, he encouraged Wöhler to take over and continue the work, which he did.
In a number of important studies, Wöhler improved the method provided by Ørsted and was first to determine a number of aluminium’s properties, including its strikingly low density for a metal of just 2.7g/cm3 (by comparison, iron's density is 7.9 and lead's 11.3).
Wöhler's aluminium, however, did not look like Ørsted's at all, because it was in the form of a dark, infusible powder, while Ørsted's metal lump could be melted in a glass tube.
For such reasons, doubts were raised as to whether Ørsted's metallic substance from 1825 really was aluminium.
According to Wöhler, Ørsted's metal lump was rather aluminium-containing potassium or perhaps an alloy of the two metals. The result of Wöhler's work meant that it was he in 1827, and not Ørsted in 1825, who was given the honour of discovering the element. Ørsted raised no objections, disinterested as he was in the matter. After Ørsted's death in 1851, his crucial contribution to the history of aluminium slipped out of both chemistry and history books. When his experiments from 1825 were mentioned, they were typically described as either erroneous or as merely an incomplete anticipation of the metal.
Most agreed that it was Wöhler who had isolated aluminium as a new metal, which is why he was the real discoverer.
In 1920, the 100th anniversary of Ørsted's discovery of electromagnetism was enthusiastically celebrated. The Copenhagen meeting involved 439 researchers from the Nordic countries 'with 181 accompanying ladies', according to the meeting’s report.
The widely celebrated event had a distinctly national character, which was further enhanced by the country’s reunification in June of that year.
One of the many songs authored for the occasion included the lines, ‘he gave Denmark honour and did the whole world good / and every time the world mentions him, Denmark’s name is mentioned too’.
During the celebration, Danish chemists decided to examine whether it was the German Wöhler or the Dane Ørsted who was the rightful discoverer of aluminium.
Because Ørsted's metal lump from 1825 no longer existed, it could not be analysed. However, by closely following Ørsted's instructions, the chemists were able to reproduce the original experiment.
They established that Ørsted had, in all likelihood, found the impure aluminium metal two years before Wöhler.
As Niels Bjerrum, a prominent chemist and professor at the Royal Veterinary and Agricultural University of Denmark, concluded in a 1926 paper, 'it is time to reinstate Ørsted as the discoverer of aluminium'.
Today there is evidence that Wöhler's result contained significant amounts of potassium, while Ørsted's contained only small amounts of potassium and mercury.
None of the results were of pure aluminium, but Ørsted's from 1825 was probably purer than Wöhler's from 1827. More recently, around 1940, Ørsted's seniority in terms of discovering aluminium was recognised by the majority of chemists.
Ørsted himself would probably not have objected to sharing this honour with Wöhler, if the question would have interested him at all.
When Ørsted died in 1851, aluminium was just a scientific curiosity, but a decade later the metal could be produced in larger quantities, and, little by little, it began to provoke industrial interest.
However, it was extremely expensive and therefore mostly used for ornamental items, such as the equestrian helmet made for Frederik VII, which today can be seen at Rosenborg Castle.
It wasn't until the mid-20th century that aluminium became the basis for large scale industry of enormous proportions. Today, 65 million tonnes of pure aluminium is produced annually, which is essential for modern society.
Aluminium is used, for example, in packaging, cans and in the construction and transport industries – to take just one example, a jet aeroplane is made from around 80 percent aluminium.
While Ørsted and his generation lived in a coal and iron age, we now live in an aluminium age.
In 1850, the renowned sculptor H.W. Bissen made a bust of Ørsted, which was later reproduced in unglazed porcelain by the Royal Porcelain Factory.
Bissen's work was also the source for a model made by sculptor Mathilius Schack Elo in 1937, which was cast in aluminium on the initiative of the Nordic Aluminium Industry to highlight Ørsted's discovery of the peerless metal.
To celebrate the 200th anniversary of Ørsted's discovery of electromagnetism, researchers at DTU have recently made a digital copy of the bust consisting of no less than 150,000 data points connected in 300,000 triangles.
Using a specially designed 3D scanner, they have created a replica of the aluminium bust, albeit of the digital kind, to understand how light interacts with aluminium.
Ørsted would not have had the first idea of what is going on at DTU Compute and DTU Imaging Center, but he would surely have appreciated the result of the institution he founded almost 200 years ago.
Translated by Stuart Pethick, e-sp.dk translation services. Read the Danish Version at Videnskab.dk's Forskerzonen.
Helge Kragh's profile (KU)
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