In Situ Monitoring the Thermal Dependence of the Growth of Carbon Nanotubes by Chemical Vapor Deposition Investigated by Tapered Element Oscillating Microbalance

摘要: Recently, it has been shown that the catalytic chemical vapor deposition (CCVD) synthesis at atmospheric pressure of multiwalled carbon nanotubes (MWCNTs) and nanofibers can be very well monitored with a tapered element oscillating microbalance (TEOM) (V. Svrcek et al., J. Chem. Phys. 2006, 124, 184705). In this paper, temperature dependence MWCNTs growth by thermal CCVD is investigated. Iron nanoparticle catalysts are dispersed on porous alumina powders. It scanning electron microscopy appear above 903 K. The mass increase obtained from decomposition an ethane-hydrogen gas mixture, TEOM, occurs large initial transient rate v 1 generally followed constant steady-state 2 . Activation energy around 100 kJ/mol derived for throughout range. A kinetic three-dimensional model based finite differences developed to account these results. With only two basic assumptions, calculations agree experimental first assumption supposes variable competitive adsorption/desorption kinetics surface, other one assumes transition iron catalyst solid liquidlike state 973 thus inferred controlled adsorption hydrocarbon hydrogen step process. By contrast, displays abrupt changes governed partial melting iron-based nanoparticles below 973K, diffusion surface diffusion. Above enhanced several orders magnitude corresponding "liquidlike" At high temperature, suppression accounted desorption. nucleation involving preliminary saturation as coverage precursor observed low temperatures. From simulations, proposed carbyne chain circumventing may provide precursor. or collective poisoning interferes temperatures general scheme.