Experiments at Rice University showed nanodiamonds and other forms of carbon were created when carbon nanotube pellets were fired at a target at hypervelocity. Credit: Illustration by Pedro Alves da Silva Autreto
Superman can famously make a diamond by crushing a chunk of coal in his hand, but Rice University scientists are employing a different tactic. They are making nanodiamonds and other forms of carbon by smashing nanotubes against a target at high speeds. The process of making them will enrich the knowledge of engineers who design structures that resist damage from high-speed impacts. The diamonds are the result of a detailed study on the ballistic fracturing of carbon nanotubes at different velocities. The results showed that such high-energy impacts caused atomic bonds in the nanotubes to break and sometimes recombine into different structures.
The work led by the labs of materials scientists Pulickel Ajayan at Rice and Douglas Galvao at the State University of Campinas, Brazil, is intended to help aerospace engineers design ultralight materials for spacecraft and satellites that can withstand impacts from high-velocity projectiles like micrometeorites. Knowing how the atomic bonds of nanotubes can be recombined will give scientists clues to develop lightweight materials by rearranging those bonds. The researchers packed multiwalled carbon nanotubes into spherical pellets and fired them at an aluminum target in a 2-stage light-gas gun at Rice, and then analyzed the results from impacts at three different speeds.
At what the researchers considered a low velocity of 3.9km/s, a large number of nanotubes were found to remain intact. Some even survived higher velocity impacts of 5.2km/s. But very few were found among samples smashed at a hypervelocity of 6.9km/s. The researchers found that many, if not all, of the nanotubes split into nanoribbons, confirming earlier experiments.
Chandra Sekhar Tiwary, a Rice postdoc researcher, noted the few nanotubes and nanoribbons that survived the impact were often welded together, as observed in transmission electron microscope images.
“In our previous report, we showed that carbon nanotubes form graphene nanoribbons at hypervelocity impact,” Tiwary said. “We were expecting to get welded carbon nanostructures, but we were surprised to observe nanodiamond as well.” The orientation of nanotubes both to each other and in relation to the target and the number of tube walls were as important to the final structures as the velocity. “The current work opens a new way to make nanosize materials using high-velocity impact,” said Leonardo Machado of the Brazil team.
http://pubs.acs.org/doi/abs/10.1021/acsami.6b07547
http://news.rice.edu/2016/09/06/nanodiamonds-in-an-instant/
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