Carbon nanotubes growth on expanded perlite particles via CVD method: The influence of the substrate morphology

Dense multi-walled carbon nanotubes (CNTs) have been successfully fabricated on expanded perlite particles by the pyrolysis of a camphor-ferrocene mixture at 800 °C. Scanning electron microscopy images show that the CNTs' growth is strongly affected by the specific surface area of perlite samples and it is more efficient in the case of perlite particles with a coarse surface and a high value of specific surface, likely due to the homogeneous dispersion of the catalyst. The optimum synthesized nanotubes have uniform outer diameters ranging between 25 and 50 nm, and a length of ∼40 μm. Transmission electron microscopy reveals a typical hollow nanotube structure with the majority of catalytic Fe particles located at the nanotube tips suggesting a tip-growth mechanism. HR-TEM images of individual nanotubes show that their external walls consist of about 50 carbon sheets. Finally, the synthesized CNTs were separated from the substrate, and the dielectric permittivity of a low density powder of nanotubes was measured at various temperatures and frequencies using the cavity perturbation method.