Resurrecting quasicrystals: Findings make an exotic material
commercially viable
Self-healing phenomenon could reduce defects that rendered quasicrystals impractical

Date:
October 11, 2021
Source:
University of Michigan
Summary:
A class of materials that once looked as if it might revolutionize
everything from solar cells to frying pans -- but fell out of favor
in the early 2000s -- could be poised for commercial resurrection,
new findings suggest.



FULL STORY ==========================================================================
A class of materials that once looked as if it might revolutionize
everything from solar cells to frying pans -- but fell out of favor
in the early 2000s - - could be poised for commercial resurrection,
findings from a University of Michigan-led research team suggest.


========================================================================== Published in Nature Communications, the study demonstrates a way to make
much larger quasicrystals than were possible before, without the defects
that plagued past manufacturers and led quasicrystals to be dismissed
as an intellectual curiosity.

"One reason why industry gave up on quasicrystals is because they're full
of defects," said Ashwin Shahani, U-M assistant professor of materials
science and engineering and chemical engineering and a corresponding
author on the paper.

"But we're hoping to bring quasicrystals back into the mainstream. And
this work hints that it can be done." Quasicrystals, which have the
ordered structure but not the repeating patterns of ordinary crystals,
can be manufactured with a range of alluring properties.

They can be ultra-hard or super-slippery. They can absorb heat and light
in unusual ways and exhibit exotic electrical properties, among a host
of other possibilities.

But the manufacturers who first commercialized the material soon
discovered a problem -- tiny cracks between crystals, called grain
boundaries, that invite corrosion, rendering quasicrystals susceptible
to failure. Commercial development of quasicrystals has been mostly
shelved ever since.

But new findings from Shahani's team show that, under certain conditions,
small quasicrystals can collide and meld together, forming a single large crystal with none of the grain boundary imperfections found in groups of smaller crystals. Shahani explains that the phenomenon came as a surprise during an experiment designed to observe the formation of the material.



==========================================================================
"It looks like the crystals are healing themselves after collision, transforming one type of defect into another type that eventually
disappears altogether," he said. "It's extraordinary, given that
quasicrystals lack periodicity." The crystals start as pencil-like
solids measuring a fraction of a millimeter, suspended in a molten
mixture of aluminum, cobalt and nickel, which the team can observe
in real time and in 3D using X-ray tomography. As the mixture cools,
the tiny crystals collide with each other and meld together, ultimately morphing into a single large quasicrystal that's several times larger
than the constituent quasicrystals.

After observing the process at Argonne National Laboratory, the team
replicated it virtually with computer simulations. By running each
simulation under slightly different conditions, they were able to identify
the exact conditions under which the tiny crystals will meld into larger
ones. They found, for example, that the tiny pencil-like crystals must
face each other within a certain range of alignment in order to collide
and coalesce. The simulations were conducted in the lab of Sharon Glotzer,
the John Werner Cahn Distinguished University Professor of Engineering
and a corresponding author on the paper.

"It's exciting when both experiments and simulations can observe the same phenomena happening on the same length and time scales," Glotzer said.

"Simulations can see details of the crystallization process that
experiments can't quite see, and vice versa, so that only together can
we fully understand what's happening." While commercialization of the technology is likely years off, the simulation data could ultimately prove useful in developing a process to efficiently produce large quasicrystals
in production-scale quantities. Shahani anticipates the use of sintering,
a well-known industrial process where materials are melded together
using heat and pressure. It's a far-off goal, but Shahani says the new
study opens a new avenue of research that could one day make it happen.

For now, Shahani and Glotzer are working together to understand more
about quasicrystal defects, including how they form, move and evolve.

The research was supported by the U.S. Department of Energy, Office of
Science, Office of Basic Energy Science, Award number DE-SC0019118.

Glotzer is also the Anthony C. Lembke Department Chair of Chemical
Engineering, Stuart W. Churchill Collegiate Professor of Chemical
Engineering, and a professor of materials science and engineering and macromolecular science and engineering.

========================================================================== Story Source: Materials provided by University_of_Michigan. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Insung Han, Kelly L. Wang, Andrew T. Cadotte, Zhucong Xi, Hadi
Parsamehr,
Xianghui Xiao, Sharon C. Glotzer, Ashwin J. Shahani. Formation of
a single quasicrystal upon collision of multiple grains. Nature
Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-26070-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211011091303.htm

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