Modeling of the carbon nanotube chemical vapor deposition process using methane and acetylene precursor gases

Chemical vapor deposition of carbon nanotubes (CNTs) in a horizontal tube-flow reactor has been investigated with a fully coupled reactor-scale computational model. The model combined conservation of mass, momentum, and energy equations with gas-phase and surface chemical reactions to describe the evolution of a hydrogen and hydrocarbon feed-stream as it underwent heating and reactions throughout the reactor. Investigation was directed toward steady state deposition onto iron nanoparticles via methane and hydrogen as well as feed-streams consisting of acetylene and hydrogen. The model determines gas-phase velocity, temperature, and concentration profiles as well as surface concentrations of adsorbed species and CNT growth rate along the entire length of the reactor. The results of this work determine deposition limiting regimes for growth via methane and acetylene, demonstrate the need to tune reactor wall temperature to specific inlet molar ratios to achieve optimal CNT growth, and demonstrate the large effect that active site specification can have on calculated growth rate.