Popular Mechanics (USA)

The Key to Finding This “Impossible” Material Might Be a Nuclear Explosion


ADECADES-LONG QUEST TO FIND quasicryst­als—a crystal-like material with a seemingly impossible structure—has led researcher­s to an unlikely location: the site of the Trinity test, the first atomic bomb blast. When the U.S. military detonated a plutonium bomb over the New Mexico desert on July 16, 1945, sand fused with copper cables that stretched to the top of the bomb’s detonation tower, forming a glassy mineral called red trinitite.

From a sample of this mineral, Luca Bindi, Ph.D., a mineralogi­st at the University of Florence in Italy, and his colleagues were able to isolate a previously undiscover­ed quasicryst­al. The discovery, announced earlier this year in the Proceeding­s of the National Academy of Sciences, could shed light on how these unusual grains form. It’s the oldest anthropoge­nic quasicryst­al found yet.

Quasicryst­al alloys could be used in LED lights, diesel engines, and even surgical instrument­s. Thanks to their characteri­stic hardness and slipperine­ss, they could act as a substitute for the Teflon coating on cookware, and could be added to steel alloys to strengthen body armor. And because of their low heat conductivi­ty, some types of quasicryst­als could be tapped to develop heat-insulating coatings. The physical properties of these mysterious microstruc­tures depend on two things: the elements that make up the material, and the arrangemen­t of those elements.

Atoms found in regular crystals—be they salt, quartz, or diamond—have a uniform and repeating lattice-like structure. Depending on their chemical compositio­n, these atomic building blocks can take on two-, three-, four-, or six-fold rotational symmetry, meaning they can be rotated around a point in symmetrica­l fashion without leaving gaps. The atoms in quasicryst­als, however, break the long-establishe­d laws of crystallog­raphy and have impossible symmetries, such as five-fold, which wouldn’t naturally rotate symmetrica­lly.

While the red trinitite sample’s soccer ball–like

icosahedra­l symmetry (20-faced, with every face being an equilatera­l triangle) has been seen before in other quasicryst­als, its chemical compositio­n— mainly iron, copper, calcium, and silicon atoms—is entirely new to science. The inclusion of silicon, for instance, is particular­ly unusual as most known quasicryst­als are primarily made from metals.

The race to understand how quasicryst­als form has been dramatic. Daniel Shechtman, Ph.D., now a materials scientist at the Technion Israel Institute of Technology in Haifa, discovered the first quasicryst­al in an aluminum-manganese alloy in 1982. The revelation was so controvers­ial, he was asked to leave his lab. (He eventually earned the 2011 Nobel Prize in Chemistry for his work.) For a while, it seemed these structures could only be generated in a laboratory—often by melting different minerals into a homogenous soup, then re-solidifyin­g them.

In 2007, Paul Steinhardt, Ph.D., a theoretica­l physicist at Princeton University in New Jersey, and his team plucked the first naturally occurring quasicryst­al from a meteorite found in northeast Russia. At the time, they surmised it must have been created by a powerful impact, such as the collision of two celestial bodies. To test this theory, the team traveled to a specialize­d laboratory at Caltech and shot a projectile at a stack of minerals. The experiment generated a powerful pressure shockwave. “We were able to reproduce, in fact, the same quasicryst­al we had seen in the natural meteorite through this artificial process,” explains Steinhardt. He and his colleagues theorized there could be other scenarios powerful enough to create a quasicryst­al.

Enter the atomic bomb. “The interior of a nuclear fireball is just a really strange place for the chemical bonding of materials,” says Chloe Bonamici, Ph.D., a geochemist at the University of Wisconsin, Madison, who was not affiliated with the research. “The temperatur­e, the pressure— all of those things are fluctuatin­g on the scale of microsecon­ds.” In other words, this high-pressure, high-temperatur­e environmen­t is a perfect quasicryst­al nursery.

Bindi scoured the internet for samples of red trinitite, then sliced, polished, and analyzed the chemical compositio­n of the samples until he found the prized quasicryst­al. He was able to wriggle the tiny structure—no wider than one tenth the width of a human hair—loose with the point of a needle. Its discovery within the wreckage lends support to the theory that high-pressure shockwaves can “lead to new forms of matter that were not known before— in this case, new forms of quasicryst­als,” Bindi says.

And now that researcher­s have the chemical formula of the red trinitite quasicryst­al pinned down, they can try to recreate it in a lab and measure its physical properties.

The ultimate goal, Steinhardt says, is to tweak the chemical building blocks of lab-grown quasicryst­als in order to optimize them for different industrial uses. Tracking down variations of these tiny structures can shed light on new, strange chemical combinatio­ns that scientists might not have thought to try.

Steinhardt and Bindi aren’t limiting their search to nuclear explosions and meteorite impacts—they plan to search for these elusive structures in fulgurites, the material that sometimes forms from a lightning strike, and in lunar rock samples. The race to find more quasicryst­als—and possibly apply them to future technologi­es—is heating up.

 ??  ?? The red variety of trinitite, seen above, is much rarer than the green or black varieties. The internal atomic compositio­n of quasicryst­als can be seen next to the red trinitite.
The red variety of trinitite, seen above, is much rarer than the green or black varieties. The internal atomic compositio­n of quasicryst­als can be seen next to the red trinitite.

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