Carbon nanotubes (CNTs) were synthesized in large scale by pyrolyzing ferrocene at 550 degrees C in sealed autoclaves. Characterization by X-ray powder diffraction, transmission electron microscope, field emission scanning electron microscopy and high-resolution transmission electron microscopy demonstrates that the as-obtained product is CNTs with uniform outer diameters of about 40 nm, inner diameters of 20 nm or so, and lengths of several micrometers. Fe nanoparticles can be clearly found at the tips of the as-prepared CNTs. The formation of the CNTs conforms to a Fe-catalyzed mechanism similar to a typical vapor-liquid-solid (VLS) growth process for one-dimensional materials. (C) 2014 Elsevier B.V. All rights reserved.