NANOTECHNOLOGY: THE KEY TO A NEW ERA
Aircraft that can change their shape or miniaturised submarines that can seek out and destroy cancer cells within the human body. The visions associated with nanotechnology among the public are as breathtaking as they are utopian. At EADS Innovation Works, research work in nanotechnology is already much more than pure fantasy.
The nano-revolution is already taking shape in the EADS Innovation Works laboratories at Ottobrunn and Suresnes. Here, EADS researchers are working on a wide range of projects and studies related to nanotechnology. One of these deals with the manufacture of polymer components. Adding nanoparticles to synthetic resin can improve its material properties to a previously unimagined extent. “The initial results we achieved together with the University of Lyon using the clay-like mineral montmorillonite were very promising,” reports researcher Stephane Bechtel.
“The revolution in the laboratories is already taking shape”
Introducing a mere 5% of nanoparticle additives, instead of the usual 50 to 100 parts in the case of conventional particles, also brings about a huge reduction in fire risk. For fire-endangered standard thermoplastics, it could even be possible to meet the stringent specifications demanded of materials used in aircraft interiors more cheaply and effectively than with the costly special polymers currently used for this purpose.
But one has to keep in mind that in nanotechnology it is often not enough to just mix the nanoparticles with the base material. In order to maximise the effect, the morphology – the dispersion and orientation – of the nanoparticles is the crucial step.
“CNTs promise to increase the damage tolerance of composites”
This is also true for carbon-fibre reinforced resins, where nanotechnology is the logical link between the sub-nano-sized atoms of the resin and the micron-sized fibres. The introduction of such composite materials to replace aluminium alloys for structural applications in aerospace products (aircraft, helicopters, launchers, missiles…) was a continuous revolution starting many decades ago. The main advantages are possible weight savings and better corrosion resistance with improved fatigue behaviour compared to aluminium alloys.
“Self-healing coatings are a longer-term application”
The introduction of nanotechnologies in these composite materials promised many advantages some years ago. For example, it could be shown – also for carbonfibre reinforced epoxy resins – that the addition of only 2.5 wt% nano-clays significantly increases fire resistance – without affecting other properties such as mechanical strength. This increased FST resistance was achieved by actually aligning these nanoparticles to form a ceramic fire barrier within the epoxy matrix.
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“After several years of research, the main advantages that composites could benefit from with the introduction of nanotechnologies are expected to be the increased electrical conductivity of organic matrix composites and improved delamination properties, mainly thanks to carbon nanotubes (CNTs),” states Jacques Cinquin, EADS CNT Technology Supporter.
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Interlaminar delamination is the main damage mode for composites under low energy impact. CNTs promise to increase this damage tolerance. “The main hurdle to overcome is to align the single nanotubes perpendicular to the fibre plies,” says Hans Luinge, Innovation Works researcher from Ottobrunn. Only then can the full benefit of the extraordinary material properties of carbon nanotubes be expected. So a rethink of the processing conditions is needed.
EADS researchers are also working on nanostructured metals, particularly aluminium and titanium alloys, since these offer both improved mechanical properties and high resistance to corrosion. “Traditional metallurgy seeks to find the best compromise, although a gain in one particular direction ultimately leads to a loss in others.
However, alloys that have been reinforced with nanoparticles make it possible to achieve improvements in all directions,” says Ottobrunn researcher Achim Schoberth. “We’re currently researching this new generation of materials in Suresnes, under contract to the European Space Agency, among others,” adds his colleague Sophie Gourdet.
The most advanced today are certainly nanoapplications in the sector of coating technology. Thus easy-to-clean surfaces reduce the use of cleaning agents, which are necessary but sometimes ecologically problematic, and shorten cleaning times.
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In some cases, non-soiling or self-cleaning coatings are the precondition for introducing new aerodynamic concepts designed to reduce the air resistance and thus the fuel consumption of aircraft.
A nanotechnology approach also helps to avoid or at least reduce the use in aircraft manufacture of substances harmful to the environment and to health. One example is the replacement of preliminary treatments and coatings containing chromates. Other ideas taken from nanotechnology include the nano-encapsulation of corrosion inhibitors and layer deposition by means of sol-gel technology (on this topic, see also High Flyer no. 1-2006 “A raincoat for aircraft”). Applications that are still a longer way off include large-area layer systems that can detect certain effects that damage aircraft structures.
Self-healing coatings are another possible, but certainly rather longer-term application of nanotechnology, just like the actuator surfaces used to influence flow properties over aerodynamic surfaces, for example. Using a combination of different sensors to detect smouldering gases before a fire actually breaks out represents a significant improvement. The sensors consist of metal oxides with a nano-granular structure. Their large surface area allows them to function as finely calibrated gas sensors. In the field of nanoelectronics, as in other nano-related activities, researchers are continuously keeping an eye on the applications of the latest technologies to the aerospace industry.
“While we are still working to expand our knowledge base in certain areas of nanotechnology, progress in some fields has already advanced to a point at which implementation would be feasible,” says Matthias Geistbeck, the contact person for nanotechnology at EADS Innovation Works. Several EADS business units have also expressed early interest in targeted product applications based on this key 21st century technology.
Christian Wimmer
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