Friday, August 25, 2017

Carbon Based: Nanotubes and Vantablack

wikipedia |  Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. Owing to the material's exceptional strength and stiffness, nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1,[1] significantly larger than for any other material.

In addition, owing to their extraordinary thermal conductivity, mechanical, and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber) baseball bats, golf clubs, car parts or damascus steel.[2][3]

Nanotubes are members of the fullerene structural family. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete ("chiral") angles, and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metal or semiconductor. Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Individual nanotubes naturally align themselves into "ropes" held together by van der Waals forces, more specifically, pi-stacking.

Applied quantum chemistry, specifically, orbital hybridization best describes chemical bonding in nanotubes. The chemical bonding of nanotubes involves entirely sp2-hybrid carbon atoms. These bonds, which are similar to those of graphite and stronger than those found in alkanes and diamond (which employ sp3-hybrid carbon atoms), provide nanotubes with their unique strength.

wikipedia |   Vantablack is a substance made of vertically aligned carbon nanotube arrays[1] and is one of the blackest artificial substances[2] known, absorbing up to 99.965% of radiation in the visible spectrum.[3][4]

Vantablack is composed of a forest of vertical tubes which are "grown" on a substrate using a modified chemical vapor deposition process (CVD). When light strikes Vantablack, instead of bouncing off, it becomes trapped and is continually deflected among the tubes, eventually becoming absorbed and dissipating into heat.[1]

Vantablack was an improvement over similar substances developed at the time. Vantablack absorbs 99.965% of visible light. It can be created at 400 °C (752 °F); NASA had previously developed a similar substance, but that can only be grown at 750 °C (1,380 °F). For this reason, Vantablack can be grown on materials that cannot withstand higher temperatures.[1]

The outgassing and particle fallout levels of Vantablack are low. The high levels in similar substances in the past had prevented their commercial usefulness. Vantablack also has greater resistance to mechanical vibration, and has greater thermal stability.[6]