Preparation of carbon nanotubes from vacuum pyrolysis of polycarbosilane

Carbon nanotubes (CNTs) were synthesized by vacuum pyrolysis of two types of polycarbosilane (PCS) with iron nano-particles between 800 and 1100 °C. Straight nanotubes were obtained from low molecular weight (990 g/mol) PCS whereas curled nanotubes were derived from medium molecular weight (1290 g/mol) PCS. Diameters of these straight and curled nanotubes were between 5 and 20 nm. The mechansim of condensed phase growth of carbon nanotubes was discussed. Electron emission capability of these carbon nanotubes increased with their pyrolyzing temperature. The electric fields required to emit a current density of 10−2 A/cm2 from the straight nanotubes being pyrolyzed at 800, 900, 1000, and 1100 °C were 1.17, 0.73, 0.67, and 0.33 V/μm, respectively.