High strength through hierarchy EurekAlert! Science News

The research group will present their findings in the current issue of the journal Science.

When the Eiffel Tower was founded in 1889, it was seen as a technical wonder. The elegant and delicate arrangement of large and small iron girders provided remarkable durability and ensured that it was the tallest building in the world at the time with a long bullet. Experts call the engineering method of open range of larger behavior by smaller ones “hierarchy”. For several years now, materials science researchers have tried to transfer this efficient approach to the microstructure of interior materials, for example by using 3D printers capable of re-engineering collection structures. -reproduction on a micrometer scale.

To date, the hopes of creating a new generation of robust lightweight building materials have not been met. One of the reasons: “A 3D printer can only print about ten miles of transport and that will take hours,” according to Professor Jörg Weißmüller of the Institute of Materials Mechanics at HZG, co. the author of the current publication. “For practical applications, this is not an operational option.”

Corroding away money

Nevertheless, his team is pursuing an even more ambitious goal. The vision: If behavior could be strengthened by shrinking to a few nanometers in diameter, they could form the basis for a new type of material – particularly lightweight and at the same time strong. However, this type of material had to have trillions of carriers, far beyond the capacity of even the most intriguing printer. “That’s why we have to deceive nature into making these kinds of products for us, just by self-organization,” Weißmüller’s colleague, Dr. Shan Shi, lead author of the study explains.

As a starting point, the team used 93% silver and 7% gold. This alloy is immersed in dilute sulfuric acid, dispersing about half of the silver. As a result, the remaining material rearranges itself, creating a delicate network of nanoscale liquids. After that, the material undergoes heat treatment at several hundred degrees. “This coarsens the network to a beam size of 150 nanometers while maintaining the original architecture,” Shi explains.

During the final step, acid re-emerges. It is used to wash out the rest of the silver, leaving only a gold carrier with an average pore size of 15 nanometers. The result is a hierarchically structured material with two completely different bearing sizes, unlike the Eiffel Tower. Due to its open network structure, this new material absorbs 80 to 90% air, giving a density of just 10 to 20% of the hard metal.

Incredibly light, incredibly strong

The research group then tested the mechanical properties of their millimeter-sized samples. “Despite the low density of this material, it exhibits extremely high values ​​for key mechanical parameters such as strength and elastic modulus,” Jörg Weißmüller is pleased to report. “We’ve removed a lot of the mass and left very little, but the material is much stronger than it has been so far.” This, he said, demonstrates for the first time that a ranking structure can be beneficial not only for macroscopic engineering collection structures such as the Eiffel Tower, but also for lightweight network materials.

The new material is not yet suitable for applications in lightweight construction – gold is just too expensive, too heavy and too soft for that reason. However, the design approach of the new HZG materials could be shifted to other more technologically relevant metals such as aluminum, magnesium or titanium. The researchers will then face another challenge then: Until now, they have only been able to make small millimeter-sized samples. “But it seems that it is entirely possible to make wires or even sheets full of metal with our process,” Weißmüller hopes. “At that point the material becomes interesting in real-world situations, for example, in new concepts for lighter and therefore more energy efficient vehicles. ”

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