Measurement of High Carbon Nanotube Growth Rate, Mass Production, Agglomeration, and Length in a Floating Catalyst Chemical Vapor Deposition Reactor

The growth kinetics of carbon nanotubes (CNTs) and precursor pyrolysis mechanisms within floating catalyst chemical vapor deposition (FCCVD) reactors have remained opaque despite significant interest in the catalytic mechanisms, CNT growth, and aerogel formation. This study utilizes in situ characterization of reactants and CNTs to determine CNT growth kinetics. By modulating precursors, we avoid the formation of a CNT aerogel within the reactor, which enables direct sampling at independent axial locations of single and agglomerated CNTs and catalyst nanoparticles. Electron microscopy of the in situ sampled aerosols enables measurement of the length of the nanotubes within them and the extent of nanotube agglomeration. Concurrent real-time individual CNT and catalyst mass measurements via a centrifugal particle mass analyzer details the evolution of individual and bundled CNT masses. The number density of CNT-containing particles increases >10-fold as flow travels through a zone of rising temperature. CNT lengths range from 0.1 to 54 μm, and CNTs of length >10 μm account for over half of the total mass produced. A conservative measure of the CNT mean growth rate of 250 μm/s is the highest growth rate observed in literature. A comparison of experimentally determined CNT growth rates reveals that the exceptionally high rates achieved in FCCVD reactors is due to the uniquely high reactor temperatures (>1500 K). The rate of CNT mass production within the reactor does not vary monotonically with temperature, which suggests that other factors, such as changing activity of catalyst, determine the overall CNT mass production rate.