Carbon Nanotubes

Overview

Carbon nanotubes are tubular molecules made of a carbon graphite sheet. These tubes can be a few nanometers diameter up to over 100 nanometers and be a singular tube or dozens of nested tubes. This arrangement of carbon atoms results in the strongest possible material existing at room temperature. For example, in tensile strength carbon nanotubes can be roughly 30 times stronger than the strongest steel. When compared to graphene or conventional carbon fibers (stacks of graphite sheets) the internal strength is the same though the external strength can be 30 times higher because the carbon nanotubes have no edges where tensile forces can concentrate and tear the sheet.

History and Current Status of Nanotubes for Construction of the Space Elevator

This history focuses on long carbon nanotubes of interest to construction of the space elevator. Since 2010 numerous companies have produced short (<10 micron length) carbon nanotubes by the ton for industrial applications. These nanotubes are too short for use in the space elevator or composite applications for strength improvement.

• 1991:Iijima discovers carbon nanotubes. A few years later they were being grown in arrays.
• 2002:University of Cincinnati was growing arrays of carbon nanotubes 1cm in length.
• 2003:Don Rusch spun 1cm nanotubes in a thread blended with polyester.
• 2004:Yuntian Zhu at Los Alamos National Laboratory had reported growing a 4 cm long carbon nanotube.
• 2011:Rufan Zhang, et.al. had reported carbon nanotubes with a strength of 200GPa.
• 2013:Rufan Zhang, et.al. had grown an individual nanotube 55cm in length.
• 2016:Edwards et. al. production system produced pounds of nanotubes millimeters in length with measured strengths of ~150GPa in a single two hour run.
• 2020:Hisashi Sugime, et. al. reported growing “forests” of carbon naoutubes 14cm in length with the bundles exhibiting 70GPa bulk strength.

Figure 1: Array of carbon nanotubes. Image is an optical image of an array of ~2 mm long nanotubes seen from above.

Figure 2: Carbon Nanotube Production Oven. This system produces pounds of millimeter length nanotubes in two hours.

Figure 3: Forest of nanotubes grown by Hisashi Sugime, et. al.

Requirements for Construction of the Space Elevator

* Operating 100 machines, 20 hours per day would produce 1,000,000 kg in 3 years.