2600-Year-Old Carbon Nanotubes
hubie writes:
Carbon nanotubes (CNTs) are cylindrical tubes made up of very thin walls of carbon atoms. They are what you get if you roll up a sheet of graphene. They come in single walled (SWCNT) and multi-walled (MWCNT) versions, and they have some very remarkable physical and electrical properties. Despite popping up from time-to-time as early has the late 19th Century, they exploded on the science scene in the early 1990s as an area of very active research.
However, if one looks back into antiquity at the famed swords of Damascus, they were made from Damascus steel. This steel was recognized to be superior to all others, but the art of its manufacture was lost to time for hundreds of years; however, in 2006 an analysis of an ancient sabre was found to contain CNTs in the steel.
A group of researchers from India have now pushed the appearance of CNTs back even further. They were studying black polished pottery shards from a dig site in Keeladi that could be as old as 600 BCE and they determined that the black coating consists of CNTs and graphene.
At this moment, the source of carbon for the coating remains unknown. The C1s x-ray photoelectron spectrum indicates the presence of several functional groups such as carbonyl, ether, carboxyl, and alcohol indicating vegetal source might have been used as a source of carbon during the manufacturing of potteries to form the black coating. Iron observed in the sample might have originated from the vegetal source itself or the soil. So the more scientific possibility would be the plant-based material should have been carbonized, forming different carbon allotropes at high temperature achieved during the firing process of pottery. The presence of iron in the plant source and also the soil might have catalysed the carbon to form SWCNT and MWCNT. High temperature present in the firing process of pottery making might have favoured the formation of observed nano structures.
They noted that, perhaps as a testament to the structural integrity of CNTs, despite being over 2000 years old these surfaces were still smooth and black with little degradation and did not suffer mechanical nor chemical breakdown.
Journal Reference:
Manivannan Kokarneswaran, Prakash Selvaraj, Thennarasan Ashokan, et al. Discovery of carbon nanotubes in sixth century BC potteries from Keeladi, India [open], Scientific Reports (DOI: 10.1038/s41598-020-76720-z)
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