Amal Esawi, a mechanical engineering professor at The American University in Cairo (AUC), is investigating a new way to make aluminium strong, but still lightweight through the application of carbon nanotubes.
“What I’m looking for is the production of aluminium reinforced by carbon nanotubes through conventional low cost material processing techniques such as extrusion and powder metallurgy,” said Esawi, whose work on aluminium-carbon nanotube composites has granted her the prestigious Egyptian State Encouragement Award and AUC’s Excellence in Research and Creative Endeavors Award, both in 2009, and had Elsevier Publishers name her as a “top-cited author” in 2011.
“When you are trying to build for example an airplane or car, you want a very strong material, but it needs to be light so it can be fuel-efficient,” Esawi explained. Airplanes burn a significant amount of fuel because of the materials that are used to build them (a Boeing 747 uses almost one gallon of fuel every second). However, by applying carbon nanotubes to a metal like aluminium, airplanes can be just as strong, but also lighter.
Types of carbon nanotubes
When comparing aluminium to steel, aluminium is lighter, but not as strong. Also aluminium is three to four times more expensive to make because it needs to be strengthened with rare and costly metals through a process called alloying. Shaped like tiny, cylindrical chain-linked fences, these nano-sized rolls of interconnected carbon atoms are revolutionising the world of engineering materials.
“Carbon nanotubes are stiffer and stronger than steel while being three to five times lighter. Also these nano-sized materials are becoming cheaper year by year,” Esawi said.
After being first produced in the 1990s, the price of carbon nanotubes has decreased from $1,500 per gram in 2000 to about $35 – $50 today for the highest quality carbon nanotubes; they can be as low as $400 per kilogram for lower quality ones. In addition, techniques for making carbon nanotubes have increasingly become common knowledge over the past few years, according to Esawi.
“Last semester, a group of mechanical engineering undergraduate thesis students succeeded in producing high-quality carbon nanotubes by modifying some equipment available in the mechanical engineering workshop,” said Esawi.
It’s not just the current low cost of these materials that makes them so appealing, but also the fact that you can use less of them. “Because individual nanotubes are very strong, but still light, you can use less of them when you are adding them to aluminium,” Esawi explained. “So you are minimising the waste of materials, thereby increasing sustainability while reducing cost.”
As with other nanomaterials, which tend to agglomerate due to their tiny sizes, the uniform dispersion of carbon nanotubes in aluminium has been, by far, the most significant challenge facing researchers. Esawi looked at ways to uniformly disperse carbon nanotubes in aluminium and has found that ball milling, a mechanical technique that grinds and fractures metal particles that then weld together to create metal mixtures, has shown the most potential.“The strength and stiffness values we found through ball milling exceeded those reported by other researchers who used different techniques to combine carbon nanotubes and aluminum powders.”
Beyond studying how carbon nanotubes can be used to strengthen aluminium, Esawi has also examined the wear behaviour, or the extent of erosion, of aluminium reinforced by carbon nanotubes. In addition to mechanical applications, Esawi is also currently investigating the potential of using aluminium reinforced with carbon nanotubes as one of the conductive layers in silicon solar cells.
Esawi believes that these carbon nanotubes, although tiny, have huge potential for the future. “Before we know it, nanotechnology will be touching virtually every aspect of our lives –– to the better.”