Carbon nanotubes-Fe-alumina nanocomposites. Part I: influence of the Fe content on the synthesis of powdersReport as inadecuate

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1 CIRIMAT - Centre interuniversitaire de recherche et d-ingenierie des matériaux

Abstract : Oxides based on a-alumina and containing various amounts of Fe 2, 5, 10, 15 and 20 cat.% were prepared by decomposition and calcination of the corresponding mixed-oxalates. Selective reduction of the oxides in a H2-CH4 atmosphere produces nanometric Fe particles which are active for the in-situ nucleation and growth of carbon nanotubes. These form bundles smaller than 100 nm in diameter and several tens of micrometers long. However, the carbon nanotubes-Fe-Al2O3 nanocomposite powders may also contain Fe carbide nanoparticles as well as undesirable thick, short carbon tubes and thick graphene layers covering the Fe-Fe carbide nanoparticles. The influence of the Fe content and the reduction temperature on the composition and micro-nanostructure of the nanocomposite powders have been investigated with the aim of improving both the quantity of nanotubes and the quality of carbon, i. e. a smaller average tube diameter and-or more carbon in tubular form. A higher quantity of carbon nanotubes is obtained using a-Al1.8Fe0.2O3 as starting compound, i. e. the maximum Fe concentration 10 cat.% allowing to retain the monophase solid solution. A further increase in Fe content provokes a phase partitioning and the formation of a Fe2O3-rich phase which upon reduction produces too large Fe particles. The best carbon quality is obtained with only 5 cat.% Fe a-Al1.9Fe0.1O3, probably because the surface Fe nanoparticles formed upon reduction are a bit smaller than those formed from a-Al1.8Fe0.2O3, thereby allowing the formation of carbon nanotubes of a smaller diameter. For a given Fe content ≤ 10 cat.%, increasing the reduction temperature favours the quantity of nanotubes because of a higher CH4 sursaturation level in the gas atmosphere, but also provokes a decrease in carbon quality.

keyword : Carbon nanotubes Al2O3 CCVD

Author: Alain Peigney - Christophe Laurent - O. Dumortier - Abel Rousset -



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