Institute of Materials Research
Functional Material Systems

Functional Materials

Research on functional materials

Nano-porous gold

Nano-porous gold could be used as a sensor. Photo: HZG

Aircraft fuselage, cars chassis, computer casings – in all of these cases, materials are used to provide shape, stability and strength. But there are also materials that can take on specific functions, such as lighting up, measuring or even repairing themselves. The Helmholtz-Zentrum Geesthacht is working on these functional materials within the scope of various projects.

Thus HZG experts are involved in the “Tailor-made Multi-scale Materials Systems” Colloborative Research Centres (CRC), together with experts from the Hamburg University of Technology and the University of Hamburg. They are focusing on materials that show a fundamentally different structure to standard materials.

Multi-scale systems

A metal, for example, is generally made of crystallites in the micrometre range. The new materials, on the other hand, generally have a tiny nano-structure – basic elements one-millionth of a millimetre in size. These nano building blocks together form larger units. These units, in turn, form even larger conglomerates, of which the actual material consists. As the inner structures extend over several size scales, these are called multi-scale systems and are generally identified by their hierarchical structure.

Metalle wie ein Schwamm

HZG scientist at the Nanoindenter

Photo: HZG/Christian Schmid

They are surrounded by microscopically small, soft plastic mantles. The idea behind this is that if both substances could be skilfully linked in a hierarchical structure, this would result in a material with remarkable properties: it would be hard and scratch-resistant like a ceramic, yet ductile and impact-resistant like a metal. HZG researchers are exploring such materials systems using theoretical models and sophisticated computer simulations.

Also interesting are sponge-like metal structures. They have innumerable nanometresmall pores and could be used as sensors. The principle: if a mechanical load falls on the material, then there will be an electrical change in the surface tension, which can be accurately recorded and analysed. The HZG researchers produce these metal foams using electrochemical corrosion.

First, they immerse a piece of metal such as a gold-silver alloy in an acid. Then they send an electrical current through the metal, so that the silver in the alloy corrodes out. The remaining gold forms a porous piece of metal with complex nanostructures. Larger channels are then required for the transportation of signals. A second corrosion process occurs to form these in the foam.

Self-healing materials

Symbol image aircraft

Foto: Fotolia/Paylessimages

The new sensor material could be interesting for aircraft construction. Applied as a thin layer to the aircraft skin, it could monitor the mechanical stresses of the jet during operation. As fatigue cracks can occur in high-stress areas, a particularly careful eye could be kept on these during regular inspections.

In addition, scientists are researching another innovation – materials that can heal themselves in the case of slight defects. One example are special polymer coatings for magnesium components. They contain molecules that work as nano-containers and contain a small amount of corrosion inhibitor.

Should damage occur anywhere, such as a crack on the surface, the containers would rupture and release the corrosion inhibitor – for instance, a substance that traps iron ions and thus suppresses rusting.