Aerographene, a nanomaterial, is utilized to make highly strong pumps

The so-called aeromaterial "aerographene" looks like a black foam, but consists of 99.9% air and can withstand extremely high loads. Credit: Julia Siekmann, Uni Kiel
The so-called aeromaterial "aerographene" looks like a black foam, but consists of 99.9% air and can withstand extremely high loads. Credit: Julia Siekmann, Uni Kiel

Kiel led a worldwide research team that devised a novel way for producing controlled electrical explosions. In theory, just 450 grams of this material are required to raise an elephant: "Aerographene" owes its capacity to its distinctive nanostructure. It appears to be black foam, but it is actually a finely organized tubular network based on graphene with multiple voids. As a result, it is incredibly stable, conductive, and nearly as light as air. An international research team led by materials scientists from Kiel University (CAU) has made significant progress toward practical applications.

They were able to repeatedly heat and cool the aero graph and the air trapped within it to extraordinarily high temperatures in a very short amount of time. This permits smaller versions of highly strong pumps, compressed air applications, and sterilizing air filters. The study was featured on the cover of the current edition of the prestigious scientific journal Materials Today.

Rainer Adelung recalls that when these materials were originally launched, they were the lightest class of materials in the world, with a density of only 0.2 milligrams per cubic centimeter. We termed them 'aero materials since they were essentially air.

The materials, which were initially shown in 2012, were created by CAU's professor for Functional Nanomaterials in collaboration with colleagues from Hamburg University of Technology. The interesting features of aero materials sparked global attention and have subsequently been widely explored, for example, in the large European research effort "Graphene Flagship."

This new work contributes to the understanding of how aero materials might go from fundamental research to application. Together with colleagues from Technische Universität Dresden, University of Southern Denmark, University of Trento, and the Queen Mary University of London, the Kiel material scientists identified new features that would enable improvements in pneumatics, robotics, and air filter technology.

Dr. Fabian Schütt of CAU, who led and conducted the research alongside Dr. Florian Rasch, stated that due to their low density, aero materials comprised of graphene and other conductive nanomaterials can be electrically heated extraordinarily fast, with up to several hundred degrees per millisecond. The materials scientists employed the "aero graphene" aero material, which is made up of only a few layers of carbon atoms and 99.9 percent air, to accomplish this. When heated, the air contained within the material heats up fast and expands. In the event of extremely fast heating, there occurs a volume expansion, which is referred to as an "explosion." This means that we may now utilize aero graphene to create modest, reproducible explosions that do not require a chemical reaction.

This is due to the fact that aero graphene cools almost as rapidly as it heats up when the electricity is turned off. Because of its incredibly low heat capacity, it can barely hold any heat. It swiftly releases it back into the confining air via its network structure. Because of the material's quick heating and cooling, the researchers are able to launch many explosions every second, one after the other.

According to Adelung, this provides us with incredibly strong compressed air at the push of a button, without the need for compressors or gas supply.

Scientists are using this phenomenon to create novel pumps that can be precisely regulated, as well as microscopic high-performance actuators.

According to Rasch, who just finished his Ph.D. thesis on the issue, if the aero material is placed in a pressure cylinder and heated with electricity, the resultant air blast may be utilized to move items up and down in a targeted manner and multiple times per second.

The studies conducted by the two original authors, Schütt and Rasch, showed that even little amounts of aero graphene items that are many times heavier may be moved. For example, 10 milligrams of aero graphene was sufficient to raise a two-kilogram weight in a matter of milliseconds. As a result, aero graphene actuators have high power densities while retaining substantial volume changes.

Rasch claims that, unlike chemical reactions, these little electrical explosions can be precisely regulated and are also exceedingly clean. We can accurately regulate the frequency and power of the air bursts by varying the length and strength of the current supply.

They just require a modest quantity of power for this because of the extraordinary conductivity of aero materials. So far, the material has endured 100,000 cycles in Kiel trials, and a patent has already been submitted.

Adelung's research group is now developing innovative aero graphene-based air filter materials and systems in collaboration with the German aviation supplier Lufthansa Technik and sponsored by the Graphene Flagship.

According to Adelung, air currents can be steered extremely well via the material's open network structure and heated quite intensely for a short period of time. Bacteria and viruses, for example, can be filtered out of the air and destroyed in this manner. In the future, these filtration systems may be self-cleaning and require no costly maintenance.

Journal Information: Fabian Schütt et al, Electrically powered repeatable air explosions using microtubular graphene assemblies, Materials Today (2021). DOI: 10.1016/j.mattod.2021.03.010

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