Sustainable lightweight construction with magnesium and seashell

For the first time, researchers at Helmholtz-Zentrum Hereon have produced a magnesium foam made entirely from natural marine raw materials. No toxic additives are required for its production.

Ground oyster shell powder from the food industry serves as the blowing agent. The foam has a wide range of applications in automotive manufacturing and is fully recyclable. The researchers recently presented their innovation in the journal Discover Materials.

Waste product becomes a sustainable resource

Oyster shells are generated in large quantities worldwide as a waste product of the food industry. Until now, they have mostly been landfilled or disposed of in waters. Researchers at the Hereon Institute of Material and Process Design have now found a way to use the shells as a sustainable resource.

The team mixed oyster shell powder into a magnesium-calcium alloy using a melting furnace. Because the shells consist mainly of calcium carbonate (limestone), the powder reacts at high temperatures to form carbon dioxide. The gas forms bubbles that remain in the viscous melt, thereby creating the foam.

After cooling and hardening, a metal foam with a homogeneous pore structure is formed. The CO₂ produced remains trapped in these pores. What makes this new material special is that it is sustainably produced, fully recyclable, ultra-lightweight, and suitable for a wide variety of applications.

Closed-loop recycling

The material concept supports a sustainable circular economy. All raw materials used can be sourced from the ocean: the shell powder comes from oysters harvested from the sea for the food industry, while magnesium and calcium are byproducts of seawater desalination. "At the end of its life, the material could be returned to the ocean. It would simply dissolve in the water," says Dr. Hajo Dieringa, a materials scientist at Hereon and co-author of the study. He and his colleagues have tested this using artificial seawater in the laboratory.

To investigate the material's compatibility with the marine ecosystem, the materials researchers collaborated with scientists from the Hereon Institute of Coastal Environmental Chemistry. Chemical analyses by coastal researcher Dr. Daniel Pröfrock show that returning the magnesium foam would not result in any harmful effects, such as the release of toxicologically relevant metals that might be present as impurities in the raw materials used. "In a real closed-loop recycling system, the material is typically melted down and reused as a new magnesium alloy," says Dieringa.

Elasticity Thanks to Porous Structure

The porous structure gives magnesium foam unique properties. It makes the material highly formable and ensures that it can absorb a great amount of energy. This makes it particularly suitable for lightweight components designed to dampen vibrations or impacts, such as crumple zone parts in vehicles.

"We combine technological performance with environmental responsibility, including in terms of securing a supply of critical metals like magnesium," says Dieringa. He and his colleagues plan to conduct further foaming experiments in the future using other alloy systems and by adding recycled carbon fibers to stabilize the melt. This should allow for even better control of foam formation and optimization of the porous structure. The researchers also see future applications in shipbuilding, aviation, or protective clothing such as safety vests or protectors, where low weight and high energy absorption capacity are crucial.

» Original publication

Source: Helmholtz-Zentrum Hereon