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09/11/2009
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Can aluminium loaded with nanotubes offer a genuine alternative to advanced alloys and carbon composites? Justin Cunningham reports
 Nanotechnology and the production of carbon nanotubes are emerging from the laboratories and are finding real applications. Due to the materials' extraordinary length to diameter ratio, nanotubes offer quite unique properties such as superior strength and stiffness as well as being exceptional thermal and electrical conductors.
German based Bayer Material Science now produces carbon nantubes, under the brand name Baytubes, as 'an industrial process' and it plans to up production to around 200tonnes a year. It sees great potential for industrial applications by combining nanotubes with other materials.
"What is interesting is not the nanotube itself, it is what you do with them," says Patrick Thomas, chief executive of Bayer Material Science. "And when you combine nanotubes with metals, it is possibly the most interesting area."
Light metals offer the greatest potential as they are very ductile, allowing the nanotubes to be rolled in to the metal. Bayer is loading 100% aluminium with around 30 – 40% nanotubes with remarkable results. "We have found it has the same properties as very high tensile steel but weighs significantly less," says Thomas. "In some cases it is comparable to carbon composite material." Possessing the similar strength to weight properties to composites opens up a host of applications.
Composites are notoriously difficult to manufacture, are prohibitively expensive and it is a difficult material to recycle. And, Thomas says, aluminium loaded with nanotubes will be competitively priced against other metal alloys, and will not be in the same price range as carbon composites or other more exotic metals often used by in aerospace industry.
"It means aircraft manufacturers could use traditional metal processes," he says. "There is a whole generation of engineers that like to work with metals and they are very excited by this.
"We are sending lumps of machinable aluminium samples to real customers. Aircraft, cars and defence equipment manufacturers are all fascinated by this type of material. But, clearly you don't go straight in to an Airbus with a new material. It is an incremental process and at the moment the material is being used in more niche applications; there is a hierarchy of entry." However, the company is clearly setting its sights on mass market applications. For automotive applications, it is already working with two companies to use the material on engine connecting rods that are produced from a powder formed compression moulding technology. But the material could potentially be used as a like for like replacement of any aluminium part to take out weight. Engine blocks for example are another of potential.
"It also becomes interesting when you think about space frames for vehicles," says Thomas. "These are traditionally made from steel. But you could imagine having an aluminium space frame that is about a third of the weight, but equivalent in strength."
The numerous problems experienced by both Boeing and Airbus as they have increasingly sought to incorporate composite in to aircraft structures could, potentially, be put to one side in favour of a return to aluminium, a material which the industry has a long and in depth knowledge of working with.
Perhaps the biggest draw back of the material is its inability to be welded. Joining at the moment is achieved by adhesion or by mechanical means. The high temperature needed for welding would actually destroy the nanostructure. However, as Thomas says, this is a relatively recent development and the technology is at the beginning of the curve. "We still have a long way to go and there is a lot more we can do," he says.
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Author
Justin Cunningham
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