Researchers at the University of the Saarland have succeeded in producing a metal foam that is extremely light and airy and at the same time withstands high loads.
The close-up makes the structure of a bone clear. It serves as a model for metal foams.
Photo: Eranicle / Panthermedia.com
The principle of metal foams is not new. These porous materials are made of metals and look like a sponge. The airy construction makes them very light. However, producing them is extremely laborious and therefore expensive. Moreover, they are only suitable for a few applications because they are relatively soft and yielding. A good example is aluminum, which today is considered the most foamed metal. “That’s why metal foams have not been successful on the market so far,” says materials scientist Stefan Diebels, Professor of Engineering Mechanics at the University of Saarland. His team has now found a way to modify the metal foams so that a new material has emerged from them: still light but extremely stable.
Instruments for coating: Anode cage and galvanic bath
In principle, bones are the model for metal foams. Because these have to be light so that humans and animals do not have to carry too heavy on them. At the same time, it is their job to survive permanent loads and shocks. This works because their inner structure consists of a framework of fine trabeculae, between which there are cavities. These reduce the weight, while the shell is again hard to ensure a basic strength. Metal foams look very similar, yet they do not have the same properties because the trabeculae themselves are too yielding. The Saarland scientists have managed to change exactly that. Diebels and materials researcher Anne Jung have coated every single trabecula with a patented process and reinforced it in this way. The cavities have remained, which is why the weight is still very low.
The known aluminum foams serve as the framework. For the coating, the researchers use a galvanic bath in which electricity is used to apply the reinforcing material very thinly. Namely, the biggest problem was to distribute the stabilizing layer deep and above all evenly inside the foam. “The metal foam acts like a Faraday cage,” says Anne Jung. Its interior is surrounded by conductive material all around, therefore electricity along with the coating to be applied is dissipated on the outside and does not run through it. Jung therefore developed a special anode cage to circumvent this effect. This makes it possible to uniformly coat the foam nanocrystalline. “The patented process also works industrially on large-area foams,” she says. “The resulting metal foams have a low density and large surface area with a small volume. In relation to their weight, they are extremely stiff and strong, “adds Diebels.
Use for lightweight or soundproofing
According to the researchers, the material produced in this way is so stable that It could be used as a mobile bulkhead to intercept shockwaves during explosions. For example, when exploding under water, it could intercept sound and pressure waves and protect vulnerable marine inhabitants from the consequences. “Above all, however, we are thinking of less spectacular applications such as lightweight construction,” says Jung. For example, it would be possible to use the new metal foam for load-bearing parts in cars and airplanes. “They can be installed as a rigid brace of the body and at the same time take over the function of the impact protection. They absorb a lot of energy and absorb the force of an impact when some of the pore layers break. “
Further applications for the versatile foam are conceivable. Since he was also very resistant to heat, he could serve as a heat shield. He was also ideal for vibration damping or as electromagnetic shielding. Architects can use it for soundproof cladding or as a design element with additional benefits. The versatility of the material is also related to the ability of scientists to modify it according to their needs. They vary the coating, its thickness or the pore size and thus achieve different properties. For example, a coating of nickel ensures high stability, while copper conducts heat, silver has an antibacterial effect, and gold is interesting for decorative purposes.
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