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Aluminum: It’s not just found in the refrigerator wrapped around week-old leftovers. This element is the second-most abundant metallic element in Earth’s crust after silicon. It’s used in soda cans and other packaging, in aircraft and automobiles, and even in that snazzy iPhone 6.
Aluminum’s sheer bulk — some 8 percent of the Earth’s crust by weight, according to the University of Wisconsin — makes it easy to take this metal for granted. But aluminum is lightweight (a third the weight of steel or copper, according to the U.S. Geological Survey) and easy to mold, fold and recycle. It resists corrosion and stands up to repeated use.
The funny thing about aluminum is that it shouldn’t be so useful at all. The metal actually oxidizes, or loses electrons, easily, the same type of reaction that causes iron to rust. However, unlike flakey iron oxide, the product of this reaction, aluminum oxide, sticks to the original metal, shielding it from further decay, according to the University of Wisconsin.
Aluminum forms in stars in a fusion reaction in which magnesium picks up an extra proton, according to Chemicool, a chemistry website created by David D. Hsu of the Massachusetts Institute of Technology. It isn’t found in pure form in nature, however; in the Earth’s crust, aluminum occurs most frequently as a compound called alum (potassium aluminum sulfate).
Danish chemist Hans Christian Oersted first managed to extract aluminum from alum in 1825, according to the Thomas Jefferson National Accelerator Facility. Later scientists refined the process for wresting aluminum for alum, but were unable to bring the price down to practical levels. For decades, aluminum was more highly prized than gold: Napoleon III, the first president of the French Second Republic beginning in 1848, proudly served his most honored guests using aluminum plates and cutlery, because it was such a rare metal, according to The Aluminum Association. Napoleon III also reportedly had an aluminum rattle made for his son, according to a 1911 article in Good Housekeeping Magazine.
Finally, in 1886, a French engineer named Paul Heroult and an Oberlin chemistry graduate named Charles Hall independently invented a process in which aluminum oxide is melted in cryolite (sodium aluminum fluoride) and subjected to an electric current, according to the American Chemical Society. The Hall-Heroult process is still used to produce aluminum today, along with the Bayer process, which extracts aluminum from bauxite ore, according to the ACS.
Aluminum’s only stable form is Al-27, and most isotopes have half-lives of mere milliseconds, meaning they are gone in less than a blink of an eye. But Al-26, aluminum’s longest-lasting radioactive isotope, has a half-life of about 730,000 years. This isotope is found in star-forming regions in the galaxy, according to a January 2006 study in the journal Nature. In that study, NASA researchers used detectable bursts of Al-26 to pinpoint supernovas, or star explosions. Using these Al-26 fingerprints, the scientists estimated that a supernova occurs every 50 years, on average, in the Milky Way galaxy, and that every year, seven new stars are born.
Perhaps aluminum’s most famous appearance on the recent research scene was in 2011, when it played a role in the Nobel Prize in Chemistry. The winner of the prize, materials scientist Dan Shechtman of the Technion-Israel Institute of Technology, discovered quasicrystals, molecular structures of non-repeating patterns. The material in which Shechtman discovered these quasicrystals was a mixture of manganese and aluminum.
There are hundreds of aluminum alloys, or mixes with other metals, on the market, according to Yuntian Zhu, a professor of materials and engineering science at North Carolina State University. Aluminum alone is light but weak, so other metals are added to give it more muscle.
Zhu and his colleagues took this concept to an extreme, creating aluminum as strong as steel, they reported in a paper published in the journal Nature Communications in 2010. By subjecting aluminum mixed with a little magnesium and zinc to extreme pressure, the researchers found that they could mash the grains of aluminum down to nano-size. These smaller grains allow the alloy to move, so that it doesn’t become brittle and snap like ceramic under pressure. But the movement is grudging enough that the material remains very strong.
“The nanostructure makes it very hard for dislocation to move, but at the same time, when you apply a force that is high enough, it will allow it to move,” Zhu told Live Science.
Currently, the researchers can only make small amounts of this super-strength aluminum alloy at a time, meaning commercial applications aren’t yet possible.
Meanwhile, in Oregon, researchers are using cutting-edge technology to study aqueous aluminum, or aluminum compounds formed in water, particularly aluminum oxides. Aluminum oxides are compounds that include both aluminum and oxygen.
“Aluminum oxide, especially in film form, is used in a lot of different industries,” said Douglas Keszler, the director of the Center for Sustainable Materials Chemistry at Oregon State University. These films make good scratch-resistant, corrosion-resistant barriers; aluminum oxides are also used in water treatment to precipitate out tiny particles, Keszler told Live Science.
Keszler and his team are working to analyze the ink-like solutions that can be heated and dried into aluminum oxide films.
“We don’t have the chemical techniques that allow us simultaneously, with such solutions, to identify both the composition and the structure, the molecular structure of what is in the solution,” Keszler said. “So what we’ve done is take some brand-new laser techniques and combine that with high-power computations to be able to simultaneously deduce the composition and the structure.”
Once they understand the solutions, Keszler said, the researchers can better control the process of producing the films — and learn to make them in energy-efficient ways. Right now, the team is most excited about using the films for electron tunneling. By sandwiching a very pure aluminum oxide film between two electrodes, Keszler said, the scientists are very close to getting electrons to jump from one electrode to the other without ever interacting with the film: “Essentially, instantaneous transfer from one electrode to the other,” Keszler said.
This electron-tunneling device could be used as a cheap and simple switch, Keszler said.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor’s degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.
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