Abstract
We produce multiwall carbon nanotubes in a large-scale fluidized bed reactor, in which catalytic chemical vapour deposition occurs. The catalyst employed is iron supported over alumina, whereas the carbon source is ethylene, which is fed together with hydrogen and nitrogen.
In order to reach a deep knowledge of the mechanism and parameters involved in the growth of carbon nanotubes, the role of different conditions and variables has been investigated: the preparation method of the catalyst, the iron percentage, ethylene and hydrogen partial pressures in the gas feed. One of the reactions that takes place during the whole process, is Fe3C (cementite) formation. The role of iron carbide has been considered by many authors, although they are not completely in agreement about it. The phase evolution of the system has been investigated via X-Ray Powder Diffraction (XRPD) at different reaction times. On the basis of our experimental data, we suggest that iron carbide is an intermediate which is formed in the early stages of the reaction and subsequently decomposes to form CNTs.
