Building material

As we have already seen above, carbon nanotubes with various characteristics have been designed and produced. The following characteristics are required for the proposed nano to meter scale building process:
  1. bearing strength (for bearing of loads)
  2. conductivity (for electrical power and communication installations) 
  3. chemical resistance (for coatings and pipes)
  4. color (for coatings)
  5. transparency (for lighting)
  6. self-decomposition (for decomposition of supporting structures).
Carbon nanotubes possess many of the properties one would choose in designing an ideal structural material. They have a very high strength to weight ratio, are stable and inert at a wide range of temperatures, and can have varying degrees of conductivity based on their geometric properties. However, one challenge in utilizing carbon nanotubes in meter-scale building is finding a natural configuration of nanotubes that allows for unlimited assembly in all three spatial dimensions while retaining the afore mentioned properties. One very promising family of configurations can be found in Schwarzite structures, named so in honor of the mathematician H. A. Schwarz who first explored similar triply periodic minimal surfaces.

Schwarzite structures are a class of fullerenes that exhibit negative Gaussian curvature. They are produced by the insertion of heptagonal and octagonal rings into the graphene lattice otherwise containing only hexagons. It is these lattice deformities that produce the negative curvature necessary to create a structure that has symmetries in three spatial dimensions. In contrast, spherical fullerenes such as C60 contain pentagon rings that produce a positive curvature leading to a closed structure. The spatial symmetries of Schwarzite structures fulfill the necessary requirement of unlimited assembly in three dimension. In addition Schwarzite structures are stiff and can be either conductive or insulating depending on their topology. The figure shows a possible nanotube configuration to be used as a nano-scale building block. The tube junctions are Schwarzite structures that have been connected by single wall carbon nanotubes of similar diameter.
The source of the raw material

As stressed already, carbon, the raw material for producing carbon nano tubes, should be extracted from the CO2 from the air. Our first consideration was whether it is possible to gain enough carbon from the air for the process to execute in reasonable time. Calculations confirm that this seems indeed possible (note that growing trees do this as well). The CO2 quantity in the air is 0,00076626 kg/m3 or approximately 1g/m3. The quantity of carbon is thus 0,0002088 kg/m3 or approx. 0.2 g/m3. Regarding the density of carbon nanotubes, which is approximately 1400 kg/m3, for a 1m3 of CNT 6.7*10**6 m3 of air is needed. This quantity seems enormous, however, with the air speed of just 1m/s, the quantity required for a 1m high structure can be extracted in 78 days. Speeding the air flow would of course speed the process in a linear way. 3D CNT array desity is much lower. The structure shown on Fig. 3 has a density of 182 kg/m3, which reduces the calculated values by a factor of 0.13. For 1m3 of such nanomaterial 8.7*10**5 m3 of air contains the adequate quantity of carbon. With the air flow of 1 m/s this volume of air passes 1 m2 in just 10 days. Rising a building 1m per day is close enough to reasonable expectations.

As CO2 is heavier then other gases in the air, its molecules tend to fall to the Earth's surface so the CO2 molecules will always flow towards the ground and thus neutralize the effect of CO2 reduction through its decomposition. Capturing of carbon and production of carbon nanotubes is the primary function of the bionanorobots.
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Danijel Rebolj,
Jan 5, 2017, 5:16 AM
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