Abstract
Multi-Walled Carbon Nanotubes (MWCNTs) have promising properties that make them potentially useful in a wide variety of applications. The decoration of MWCNTs by metallic or semiconducting nanoparticles aims to intensify some of their properties, in particular thermal and electrical conductivity. Fluidized Bed Chemical Vapour Deposition (FBCVD) is an efficient process to uniformly coat powders by various materials. The coating by SnO2, Fe and Si nanoparticles of MWCNTs (Graphistrength®) tangled in balls of 360 microns in mean diameter using the FBCVD process has been studied. The influence of some deposition parameters with and without oxidative pre-treatment is analysed on the nucleation and growth of nanoparticles. The various results obtained indicate that the intrinsic surface reactivity of MWCNTs is high enough for CVD precursors involving the formation of highly reactive unsaturated species such as silylene SiH2 formed from silane SiH4 pyrolysis in the case of Si deposition. But it must be enhanced for less reactive CVD precursors such as tin tetrachloride SnCl4 which needs the presence of oxygen-containing groups at the nanotube surface to allow Sn nucleation. So, provided the reactivity of the powder surface and that of the CVD precursors are well tuned, the FBCVD process can uniformly coat the outer surface of MWCNTs by metallic or semiconducting nanoparticles.
Highlights
Multi-Walled Carbon Nanotubes (MWCNTs) are nowadays a popular nanoform of graphenic carbon in which graphenes are arranged more or less parallel to the nanofilament axis
This explains that the temperatures measured by T1 and T2 are very close to each other, thanks to the good gas-solids mixing and particle-wall contact existing in the fluidized bed
Multi-walled carbon nanotubes were decorated by three kinds of nanoparticles from precursors of very different reactivity using the fluidized bed chemical vapour deposition process
Summary
Multi-Walled Carbon Nanotubes (MWCNTs) are nowadays a popular nanoform of graphenic carbon in which graphenes are arranged more or less parallel to the nanofilament axis. The gas processes yield products purer than the wet methods They are single-step methods and generally involve high coating rates (Bacsa and Serp, 2012). If the MWCNTs can be fluidized, this technology allows multi-gram-scale beds of nanotubes to be uniformly coated with a high conversion rate of the gaseous precursor into solids, high versatility, good homogeneity of products and the possibility of continuous operations (Vahlas et al, 2006) This technology is easy to use and to rescale, and requires low equipment costs (Vahlas et al, 2006). It will be shown that surface activation is not always necessary to coat MWCNTs by metallic or semiconducting particles
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