Nucleation as Self-assembling Step of Carbon
Deposit Formation on Metal Catalysts
V.L. Kuznetsov
1
, A.N. Usoltseva
1
, Yu.V. Butenko
1
, A.L. Chuvilin
1
,
M.Yu. Alekseev
2
, L.V. Lutsev
2
1
Boreskov Institute of Catalysis, Pr. Akademika Lavrentieva 5, 630090 Novosibirsk, Russia
2
Research Institute "Ferrite-Domen", Chernigovskaya 8, St Petersburg, 196084, Russia
Abstract. A thermodynamic analysis of the carbon nucleation on the metal surface was
performed. The master equation for the dependence of critical radius of the carbon nucleus on
the reaction parameters, such as the reaction temperature, the catalyst nature, the supersaturation
degree of catalyst particle by carbon was obtained. This equation and the phase diagram
approach were used for discussion of different scenarios of carbon deposits formation, namely,
encapsulated particles, carbon fibers and filaments, multi-wall and single-wall carbon nanotubes.
Carbon filament growth via CO disproportionation on cobalt supported catalyst was
investigated. Here we demonstrate the possibility to vary the reaction products using the same
catalyst just changing the reaction conditions and catalysts pretreatment procedure. For the first
time the formation of the carbon filament ropes on Co catalysts was observed.
INTRODUCTION
The processes of self-assembly and self-organization underlying of self-processes,
which spontaneously assemble and organize various building blocks into hierarchical
structures, have emerged as the most promising techniques for the efficient production
of nanostructured materials. In this paper we consider carbon nucleation on metal
surfaces as one of the main self-assembling factor, which is important in nanocarbons
formation.
For any type of carbon deposits their formation occurs via the common steps
including metal-carbon particles formation and carbon nucleation. Carbon deposit
nucleation from metal-carbon particles is a crucial stage for the formation of different
carbon deposits, namely, catalyst deactivation, carbon filament and nanotubes
formation. It can be explained in terms of relatively high thermal stability of
nanocarbons due to the low self diffusion of carbon in carbon materials at temperature
up to 1500-1700°C. So single wall carbon nanotubes (SWNT) double their diameter
only after thermal treatment at the temperature higher then 1500
°
C [1], while multi-
wall nanotube formation from SWNT ropes occurs only at the temperature higher than
2000
°
C [2]. The formation of stable mosaic closed graphitic nanostructures on the
annealed diamond surface at the temperature higher than 1500°C was observed [3].
Thus once formed the nanosize carbon nucleus are stable enough and nucleation step
can determine the of carbon deposit types.
© 2003 American Institute of Physics 0-7354-0154-3/03/$20.00
Electronic Properties of Novel Materials,
edited by H. Kuzmany, J. Fink, M. Mehring, and S. Roth
CP685,
Molecular Nanostructures: XVII Int'l. Winterschool/Euroconference on
82