The microstructures, growth mechanisms and properties of carbon nanowires and nanotubes fabricated at different CVD temperatures

Polycrystalline carbon nanowires (p-CNWs) has been synthesized via the CVD strategy using C₂H₄ as carbon source and Ni particles distributed in porous Si₃N₄ ceramic as growth seeds at 700 °C. As-received p-CNWs showed the solid core and the basal planes of graphite nanosheets were perpendicular to the wire axis. Elevated growth temperatures encouraged the formation of hollow carbon nanotubes (CNTs) at 750 °C and amorphous carbon above 800 °C, which in turn altered the electrical conductivity and dielectric properties of carbon reinforced Si₃N₄ composite ceramics. The growth mechanisms and microstructures of solid wires and hollow tubes were discussed and compared detailedly. It is energetically favorable for p-CNWs, which shows high surface energy, to convert itself into crystallized CNTs during the annealing at 1000 °C. The four-state transition process was accompanied by the diffusion of carbon atoms and the rearrangement and growth of nanosheets. The present research strategies and results are not only beneficial to investigate the growth and graphitization behavior of carbon nanoscale materials, but also probably extended to investigate other nanowire-nanotube systems.