Microarchitectured and nanoscale hierarchical structures of carbon in ancient archaeological carburisation slags

The famed Wootz steels are hypothesized to contain carbon nanotubes. However, the primary context of such nanostructures in Wootz steels is not known. In this letter, we present the microarchitectured and nanoscale hierarchical carbon structures in ancient archaeological carburization slags from 400 BCE to 16th century CE. We show that carbon microrods at the micro-scale are composed of finer carbon microrods, which are arranged in a co-axial manner. Carbon microrods are composed of twisted carbon nanotubes at the nanoscale. Such carbon nanostructure formation in the crucible process provides the possible source of carbon nanostructures in crucible steels of antiquity.