The effect of processing conditions on carbon nanostructures formed on an iron-based catalyst

The carbon nanostructures formed during chemical vapour deposition (CVD) of ethene and hydrogen over an iron(III) oxide catalyst precursor have been investigated. Graphitic nanofibres and carbon nanotubes were both observed during synthesis, with the structures observed depending on the temperature and gas mix (C₂H₄ and H₂) used. Mixtures ranging from 100% to 5% ethene in hydrogen were investigated at different temperatures. During the synthesis, the iron(III) oxide was transformed into iron carbide (Fe₃C). The samples were characterised using transmission electron microscopy and X-ray diffraction. Filamentous nanostructures were observed with high hydrogen content (?80%) in the gas stream, whereas no filamentous structures were observed with ?20% H₂. The temperature of synthesis was varied between 500 and 800 °C, with higher temperatures giving higher carbon deposition rates, but also affected the nanostructures observed. However, it was found that increasing the temperature during CVD did not change the type of carbon deposited but did increase the deposition rate, providing a route to increase growth yields for a desired type of carbon nanostructure.