Oldest Known Human-made Nanostructures In Ancient Artifacts Discovered in Tamil Nadu

Scientists have discovered the oldest known human-made nanomaterials in the "unique black coatings" of ancient pottery shards -- dated to 600 BC -- unearthed from an archeological site in Keeladi, Tamil Nadu.

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The research, published recently in the journal Scientific Reports, revealed that these coatings are made of carbon nanotubes (CNTs) which have enabled the layer to last more than 2600 years, raising questions on the tools used during those periods to achieve high temperatures for making earthenwares.

CNTs are tubular structures of carbon atoms arranged in an ordered manner, Chandrasekaran said, adding that coatings in ancient artifacts may not usually last this long due to wear and tear caused by changing conditions.

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According to the scientists, including those from Vellore Institute of Technology (VIT) in Tamil Nadu, the coatings are "the oldest nanostructures observed till now." "Until this discovery, to our knowledge, the most ancient known nanostructures in human-made artifacts are from the eighth or ninth century AD," study co-author Vijayanand Chandrasekaran from VIT told PTI.

"But the robust mechanical properties of the CNT based coating has helped the layer sustain more than 2600 years," he added. Carbon nanotubes have superlative properties, including high thermal and electrical conductivity, and very high mechanical strength, explained nanomaterial scientist M. M. Shaijumon from IISER Thiruvananthapuram, who was unrelated to the study.

According to Chandrasekaran, the closest scientific explanation for the finding is that some "vegetal fluid or extract" might have been used in the coatings of these pots which may have led to the formation of CNTs during high-temperature processing.

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Rajavelu S, Professor of History at Alagappa University in Tamil Nadu, who was unrelated to the study said the ancient people would not have known these as CNTs, but may have just had the need to make their pots have high durability, "and may have needed a certain colour out of their products on applying high-temperature firing."

"They likely knew the technique to make these coatings practically, but may not have known this as a thesis with any kinds of formulae," Rajavelu added.

Commenting on the significance of the research, Sharada Srinivasan, an expert in archaemetallurgy associated with the National Institute of Advanced Studies (NIAS) in Bengaluru, said nanotechnology has made strides since the 90s with the advent of advanced techniques like the scanning tunnelling microscopy.

Based on their analysis, Chandrasekaran said the ancient Tamil civilization of this time were aware of, and mastered high-temperature processing, but added that the means and mechanism by which they produced these artifacts with carbon-nanotubes is not widely explored.

He said these earthenwares were likely used by the "sophisticated people of the time," adding that "a lot of the shards" have been found in Keeladi, "some dating back even as early as 900 BCE." "We have known for a long time that in iron smelting and manufacture, India was a world leader at the time. Even the Sangam ancient Tamil literature has noted about steel manufacture," Rajavelu said.