The Fascination of Technology Sustainable Lightweight construction With Magnesium And Shell Limestone

In our "Fascination Technology" section, we present impressive research and development projects to design engineers every week. Today: How ground oyster shell powder is turned into magnesium foam for vehicle construction.

Oyster shells are produced in large quantities worldwide as a waste product of the food industry. Until now, they have mostly been dumped or disposed of in bodies of water. Researchers at the Hereon Institute for Material and Process Design have now found a way to process the shells into magnesium foam as a sustainable resource. The team has stirred oyster shell powder into a magnesium-calcium alloy using a melting furnace. As the shells consist mainly of calcium carbonate (lime), the powder reacts at high temperatures to form carbon dioxide (CO₂). The gas forms bubbles that remain in the viscous melt and thus form the foam. After cooling and hardening, a metal foam with a homogeneous pore structure is formed. The resulting CO₂ remains in these pores. What is special about the new material is that it is sustainably produced, fully recyclable, ultra-light and suitable for a wide range of applications.

Closed Recycling Loop

All the raw materials used can be obtained from the sea: The mussel shell powder comes from oysters harvested from the sea for the food industry, while magnesium and calcium remain as by-products of seawater desalination. "At the end of its life, the material could be returned to the sea. It would simply dissolve in the water," says Dr. Hajo Dieringa, materials scientist at Hereon and co-author of the study. He and his colleagues tested this with artificial seawater in the laboratory. In order to investigate the material's compatibility with the marine ecosystem, the material researchers worked together with scientists from the Hereon Institute for Coastal Environmental Chemistry. Chemical analyses by coastal researcher Dr. Daniel Pröfrock show that the recycling of the magnesium foam would not have any harmful effects, for example through the release of toxicologically relevant metals that could be contained as impurities in the raw materials used. "In a genuine closed recycling loop, however, the material is more likely to be melted down and reused as a new magnesium alloy," says Dieringa.

Pore Structure Makes Material Malleable

The pore structure makes the magnesium foam very malleable and ensures that it can absorb a lot of energy. This makes it particularly suitable for lightweight components for damping vibrations or impacts, such as crumple zone parts in vehicles. "We combine technological performance with ecological responsibility, also in terms of raw material safety for critical metals such as magnesium," says Dieringa. He and his colleagues are planning further foaming tests with other alloy systems and with the addition of recycled carbon fibres to stabilize the melt. The aim is to control foaming even better and optimize the pore structure. The researchers also see future potential applications in shipbuilding, aviation and protective clothing such as safety vests or protectors, where low weight and high energy absorption capacity are crucial.

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