Carbon Nanotubes

Growing kilometers long single-walled carbon nanotubes in microgravity as currently only few cm lengths can be made.

Last updated: 2018-12-10

Status

Carbon nanotubes have been made in space and synthesis by arc in water has proven to have gravitational effects, but complete theory to manufacture long strands is missing.

Applications

  • Space elevator
  • Space suits
  • Vechicles
  • ...

Why & Solution

Carbon nanotubes are the toughest material known to science - two hundred times stronger than stell and stronger even than diamonds. Carbon nanotubes are sheets of graphene rolled into long tunes. They are practically unbreakable and nearly invisible. If you built the suspension for the Brooklyn Bridge out of carbon nanotubes, the bridge would look like it was floating in midair. At the moment, it is exceedingly difficult to product large quantities of pure graphene. The slightest impurity or imperfection at the molecular level can ruin its miraculous physical properties. It is difficult to produce sheets larger than a postage stamp. Extremely difficult to manufacture beyond a centimeter or so. You might hear announcements that nanotubes many feet long have been constructed, but those materials are actually composites. They consist of tiny threads of pure carbon nanotubes compressed into a fiber and lose the wondrous properties of pure nanotubes. 1

Only very short carbon nanotubes can be currently made. 3 cm length is common and record is 55 cm. Many kilometer lengths of single-walled carbon nanotubes are required. Preferably tens of thousands of kilometers for space elevator. Short strands are very difficult to connect with the same strength. Long single strands could be then interwowen into even stronger cables.

Physicists have theorized, but not proven, that in microgravity the elimination of convection could allow for the successful production of single-walled carbon nanotubes longer than one centimeter (Alford, Mason, and Feikema 2001). Longer lengths of carbon nanotubes open up possibilities for spinning super strong fibers that can be used for a variety of purposes needing strength, lightness, and conductivity (Zhang et al. 2013). 5

The "arc-in-liquid" method is a simple and inexpensive technique for the synthesis of carbon nanotubes and related nano-materials. In this paper, we report on the synthesis of carbon nanotubes by means of the arc-in-water method under microgravity and normal gravity conditions. It was determined that the synthesis of carbon nanotubes by the arc-in-water method is strongly affected by gravity. 4

High temperatures inside the plasma of a carbon arc generate strong buoyancy driven convection which has an effect on the growth and morphology of the single-walled carbon nanotubes (SWNTs). To study the effect of buoyancy on the arc process, a miniature carbon arc apparatus was designed and developed to synthesize SWNTs in a microgravity environment substantially free from buoyant convective flows. An arc reactor was operated in the drop towers at the NASA Glenn Research Center. Principal result is that no dramatic difference in sample yield or composition was noted between normal gravity and 2.2 and 5s long microgravity runs. Much longer duration microgravity time is required for SWNT's growth such as the zero-G aircraft, but more likely will need to be performed on the international space station or an orbiting spacecraft. 3

It has been demonstrated that microgravity can eliminate the strong convective flows from the carbon arc and single-walled carbon nanotubes have been successfully produced in microgravity. Authors believe that microgravity processing will allow to better understand the nanotube formation process and eventually allow to grow nanotubes that are superior to ground-based production. 2

References