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.