Temperature-dependent growth of carbon nanotubes by pyrolysis of ferrocene and acetylene in the range between 700 and 1000 °C

Aligned carbon nanotubes were grown by pyrolysis of ferrocene and acetylene in the temperature range 700–1000 °C. The average diameter is constantly 20 nm for all growth temperatures. As the temperature increases, the growth rate increases by 60 times. The length reaches up to 3 mm at 1000 °C. These long carbon nanotubes exhibit a cylindrical structure. The relative amount of crystalline graphitic sheets increases significantly with the growth temperature. The Arrhenius plot yields the activation energy 35±3 kcal/mol, which is close to the diffusion energy of carbon in bulk γ-Fe. We suggest that the bulk diffusion of carbons would play an important role in the growth of cylindrical structured carbon nanotubes.