Healing Nanotubes to Achieve One Meter LengthCategory: Science & Technology
Posted: June 21, 2012 10:23AM
Modern construction techniques allow a skyscraper to be built using cranes at the top of the partially finished building. As floors are completed the cranes rise up to continue working. This is somewhat similar to how carbon nanotubes are grown. The cranes are like the catalyst, and it is at the catalyst that new material is added, making the nanotube grow longer. Just as in construction, mistakes can happen when growing nanotubes, but the speed at which nanotubes grow makes it much more difficult to correct or repair a mistake, before it can be an issue. Researchers at Rice University, Hong Kong Polytechnic, and Tsinghua University have modeled the growth of nanotubes and found a way to potentially repair these issues at the catalyst.
Single-walled carbon nanotubes, like those the researchers were working with, look like chicken wire wrapped up into a cylinder, with the carbon atoms bond in hexagons. At least that is the goal. Sometimes the atoms bind in pentagons or heptagons (seven-sided polygon) and these imperfections can comprise the nanotube. Fortunately they always occur together, so the extra atom in the heptagon can be moved over to the lacking pentagon, if there is a mechanism to enable the move. According to the researchers' model, iron works as such a mechanism and it is already a catalyst for nanotube growth.
Using an iron catalyst is not the ultimate solution though because its effects are not far reaching. From four atoms away, the iron does not enable the nanotube to repair, so if a defect escapes that far, it will not be so easily repaired. Fortunately the researchers found it should be possible to slow the growth of nanotubes, which will give the iron more time to act as a catalyst. Potentially slowing down like this could allow a meter-long nanotube to be grown.