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Specific strength exceeds diamond! Scientists design new structure of carbon

Diamonds, with their dazzling light and hard and lasting characteristics, have a very special meaning between couples. As the original stone of diamond, diamond, which is also a solid carbon material, is the hardest substance in nature and plays an extremely important role in people’s production and life.

The most important reason why diamond is polished into diamond is its hardness. It will not be scratched by anything else, and can always maintain its own gloss. In addition, it has good dispersion characteristics, which can disperse white light into a rainbow light that diffuses outward, adding its own charm.

Recently, the University of California, Irvine, together with researchers from other institutions, has designed a carbon plate-like nanostructure from the perspective of the microstructure of the material. The specific strength (strength-weight ratio) of the structure is even more More than diamonds. The research was published in the journal Nature Communications.

Jens Bauer and Cameron Crook, as the main person in charge of this study, said: “This will be a very important insight that can help change the long-standing paradigm of material structure design and can help people create Lighter, stronger, and better materials. This is needed for future technological development.”

Break through the common patterns of decades
Carbon is one of the most eye-catching elements on earth. It has allotropes with different structures and exists in nearly 90% of the known substances in our lives.

Carbon allotropes have different physical and chemical properties. In addition to the well-known diamonds, graphite, and diamonds in people’s lives, there are many well-known molecular structures in the scientific world such as C-60 (fullerene), carbon nanotubes, and graphene that have received many honors and are currently widely studied. .

This time, the research team of Bauer and Crook successfully designed and manufactured a closed-cell plate-like nano-lattice structure material with a wall thickness of about 160 nm. This carbon nanomaterial is different from the carbon structure composed of the cylindrical truss that people have seen in the past few decades. The researchers used a closely connected closed-cell plate to “subvert” the routine. “Our research is the first experimental evidence in history, verifying that the pallet structure is superior to the structure based on the beam connection in the usual sense in the past.” Ball said very confidently. Their research shows that the arrangement of the plate-like structure makes the samples prepared by it almost reach the theoretical limit of the strength and rigidity of porous materials.

They mentioned specific values ​​in the paper: the carbon nanoplate structure designed by it exceeds the average strength performance of 639% of the previous cylindrical cylindrical beam structure, and the rigidity level is also increased by 522%. “Our carbon nanoplate materials have 40% to 80% voids, which makes them as light as polymer foam. But at the same time, they are also much stronger than any metal or alloy, such as steel, and these metals It will be more than ten times its weight.” Ball explained: “In addition, the specific strength (strength-weight ratio) of carbon nanoplate lattice structure even exceeds some types of bulk diamond, and bulk diamond is The bulk material with the highest known specific strength.

New carbon nanoplate structure

The 100-micron “Great Wall” manufactured by photon 3D printing in 2015

Nanoscale Liaoning ship carrier model made by Chinese company in 2019 (from Beijing Magic Technology Nanotechnology Co., Ltd.)

Design ideas and future applications
Although the lattice based on the beam structure has been the mainstream of materials with super mechanical properties in the past 20 years, its low structural efficiency actually limits the performance of the material to a certain range of elastic modulus. The “cubic + topology” is one of several designs that have been predicted by many scientists and can reach the theoretical performance limit of porous materials.

“But it has always been theory before, and our goal is to actually produce a material that can reach the performance limit, and finally prove those theoretical prediction results that can be traced back more than ten years ago.” Jens Ball analysis said, The main reason why it has not been verified before is that the manufacturing process always faces major challenges, so in this experiment they chose the “cube + octagon” design, precisely because of its simplicity, which allows two-photon lithography And pyrolysis method to synthesize this structure becomes the most direct.

So, why is there such a big difference between the beam and the plate structure? The beam structure can be imagined where three beams of light intersect vertically to form a node. When you apply pressure to one of the beams, only the specific one is under stress, while the other two are not under any pressure.

But the plate-like structure is different. Imagine that three plates intersect to form an angle. If you push one of them in one direction, the other two plates will share the load. In simple terms, one-third of the material in the beam structure is working; and in the plate-based structure, two-thirds of the material is working.

In preparing the plate-like structure, the research team used the two-photon laser direct writing technology (or two-photon polymerization photocuring forming technology), which is often referred to as “two-photon 3D printing” (Two-photon Polymerization, TPP). The principle is that when the laser is focused on a drop of UV-sensitive liquid resin, the molecules are hit by two photons at the same time, turning the material into a solid polymer. It can process micro-nano structures with periodic arrangement very simply and conveniently.

As early as October 2015, the team of Professor Yang Guangzhong of Imperial College of Technology printed a section of the Great Wall model on a square silicon wafer with a length of only 100 μm. At the time, there was no corresponding technology in China. However, in 2019, a private company established in Beijing and engaged in the R&D and production of commercial nano-scale 3D manufacturing equipment demonstrated the nano-scale 3D lithography manufacturing system technology with independent intellectual property rights.

Nowadays, the nanoplate-like structural material prepared by the research by Bauer and Crook et al. is about 160 nm thick, which is equivalent to 1/400 of the width of human hair. “Our research includes conceptualization, manufacturing, and measurement of mechanical stability, and then uses computer simulation through finite element analysis and nano-CT scanning to analyze the observed data.” They introduced DeepTech.

However, even though “two-photon 3D printing” has great advantages in the processing of microstructures, it is not without its shortcomings. Similar to the old camera that needs film cleaning, the photosensitive material of TPP also needs to be developed and fixed, which fixes the 3D object to be printed, and the overall processing process is relatively cumbersome.

Therefore, in response to whether the research could be applied in the future, Ball said: “So far, we can only produce this material on a small scale. The next phase of the research is to find a way to expand the scale of production materials. , For example, by further developing additive manufacturing processes.”

“The application range of this structural material is very wide.” Bauer believes that in the long run, this ultra-high strength and very low mass density characteristics are very suitable for the selection of structural materials in aerospace, automotive and other fields. Of course, when the scale of production is not expanded to that extent, there may be an earlier opportunity to apply the material to micro-electromechanical devices, such as smart phone sensors, small biomedical devices or micro satellites.

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