Discoveries make exotic material commercially viable

A class of materials that once seemed capable of revolutionizing everything from solar cells to frying pans, but which fell out of favor in the early 2000s, may be poised for a commercial resurrection, suggest the findings of a research team led by the University of Michigan.

Posted in Nature Communication, the study demonstrates a way to make quasicrystals much larger than before, without the flaws that plagued past manufacturers and led to dismissing quasicrystals as an intellectual curiosity.

“One of the reasons the industry has abandoned quasicrystals is that they are full of flaws,” said Ashwin Shahani, assistant professor of materials science and engineering and chemical engineering at UM. and corresponding author of the article. “But we hope to bring quasicrystals back into the mainstream. And this work suggests that it can be done.”

Quasi-crystals, which have the ordered structure but not the repeating patterns of ordinary crystals, can be made with a range of attractive properties. They can be super 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 manufacturers who first brought the material to market quickly discovered a problem: tiny cracks between crystals, called grain boundaries, which invite corrosion, making quasicrystals susceptible to rupture. Since then, the commercial development of quasicrystals has mostly been abandoned.

But new findings from Shahani’s team show that under certain conditions, small quasicrystals can collide and coalesce, forming a single large crystal without any of the grain boundary imperfections found in the smaller crystal clusters. Shahani explains that the phenomenon came as a surprise during an experiment designed to observe the formation of the material.

“It appears that the crystals heal on their own after the collision, turning one type of defect into another that eventually disappears completely,” he said. “It’s extraordinary, given that quasicrystals lack periodicity.”

The crystals start out as pencil-shaped 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 tomography. x-ray. As the mixture cools, the tiny crystals collide with each other and merge, eventually turning into a single large quasicrystal several times the size of the constituent quasicrystals.

After observing the process at the Argonne National Laboratory, the team virtually reproduced it 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 merge into larger ones. They found, for example, that tiny pencil-like crystals must face each other within a certain range of alignment to collide and merge. The simulations were carried out in the lab of Sharon Glotzer, John Werner Cahn University engineering professor and corresponding author of the article.

“It’s exciting when experiments and simulations can observe the same phenomena occurring over the same duration and the same time scales,” said Glotzer. “Simulations can see details of the crystallization process that experiments cannot quite see, and vice versa, so only together can we fully understand what is going on.”

Although the technology is likely to be commercialized years away, the simulation data may 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 fused together using heat and pressure. That’s a distant goal, but Shahani says the new study opens up a new avenue of research that may one day get there.

For now, Shahani and Glotzer are working together to better understand the flaws of quasicrystals, including how they form, move, and evolve.

The article is entitled “Formation of a single quasi-crystal during the collision of several grains”. The research team also includes the Brookhaven National Laboratory.