Experimental and numerical investigation of the position-dependent growth of carbon nanotube-alumina microparticle hybrid structures in a horizontal CVD reactor

The hybrid structures of carbon nanotubes (CNTs) and alumina microparticles were produced in a horizontal chemical vapor deposition (CVD) reactor using ferrocene/xylene/acetylene mixture as the catalyst-carbon source. At a given temperature and hydrogen ratio, the CNT diameter, number density, growth rate and their hybrid structures varied greatly along the axial direction of the reactor. This non-uniform growth is attributed to the position-dependent chemical reaction kinetics inside the reactor, mainly along the gas flow direction. Mass spectrometry was used to identify and quantify the chemical species of the exhaust gas. A numerical simulation of the reacting gas flow in the reactor was conducted in parallel by taking into account the space-dependent pyrolysis kinetics of the catalyst and carbon sources, the reactor temperature gradient and the fluid dynamics. A good agreement existed between the modeling and the experimental results. A double-end-injection method was proposed based on the above results, and the uniform hybrid structures were synthesized in a larger zone inside the CVD reactor. A new kind of CNT structure containing iron crystal particles at their two extremities was obtained under certain conditions, which can be very useful for various CNT junction applications. (C) 2011 Elsevier Ltd. All rights reserved.