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4SYNTHESIS OF CARBON NANOSTRUCTURES WITH THE USE OF HYDRIDES OF INTERMETALLIC COMPOUNDS
B. P. Tarasov, V. N. Fokin, V. E. Mouradyan, P. V. Foursikov, A. A. Volodin, O. N. Efimov
Institute of Chemical Physics Problems, Russian Academy of Sciences Chernogolovka, Moscow Region, 142432, Russia Fax: 8-096-515-48-20, e-mail: btarasov@icp.ac.ru
Carbon nanostructures (CNS), namely, graphite nanofibres and nanotubes, attract rapt attention due to their unique physical and chemical properties. One of the most widely spread methods of their synthesis is py-rolysis of various nanocarbons on metallic catalysts, in particular, on powders of such transition metals as Fe, Co, Ni.
In this report, it is proposed to use, as catalytic systems for the CNS synthesis, powders of hydrides of in-termetallic compounds (IMC) and mixtures of metal hydrides with nickel. In order to produce highly dispersed powders, a hydride dispersion procedure has been developed based on the reversible interaction of intermet-allides with hydrogen leading to the grinding of compact materials (with the size of 1-3 cm):
Y + 3/2H
YNi„
2
xH„
=> YH
=> Y + 3/2H
LaNi5+ xH2
compact
=> YNiH => YNi -
2-5 2x 2-5
=> LaNi5H2 => LaNi-
5 2x 5 2
hydride powder metal powder
2
XH2
x H,
Particles with the same size are formed with the use of ammonia as the chemical dispersing reagent.
It has been established that the use of powders of YNi2 5Hx and YH2 3+Ni for the electric arc synthesis of single-walled carbon nanotubes (SNT) (comparison with the Co-Ni-system) (Table 1):
— simplifies the technology of preparation of homogeneous metal-graphite compositions,
— leads to the generation of a homogeneous metal-carbon vapour in the arc area,
— reduces the anode evaporation time,
— suppresses the attendant fullerene generation pro-
cess,
ucts,
■ increases the SNT content in evaporation prod-
With increasing «hydrationydehydration» cycles, the powder particle size decreases up to 1-3 microns. By means of treatment of the hydride phases with a ball mill, one can reduce the particle size up to 0.1-0.2 microns.
— increases the SNT diameters.
It has been established that the use of LaNi. ^H
2-5 x
powders for the pyrolysis synthesis of graphene nanofi-bres (comparison with a Ni-catalyst) (Fig. 1):
— simplifies the process of preparation of the catalytic system,
— allows to regulate the amount of nickel particles on the intermetallide surface,
—reduces the ethylene decomposition temperature,
Table 1
Characteristics of the metal-graphite electrode, parameters and products of the electrical arc evaporation
Characteristics being compared 3Co/Ni catalyst YNi2Hx catalyst Without a catalyst
Amount of metals in the anode, at.% mass.% 0.64 + 1.9 11.2 1.9 + 0.95 14.4 —
Interelectrode distance, mm 2.5-3 1-2 0.5
Helium pressure, Ton- 650 500 600
Current strength, A 93 98 115
Evaporation rate, g/min ~0.2 ~0.8 ~0.3
Fullerene content in the soot, mass.% ~10 <1 20
SNT content in the «flange» and «near-wall» soot (mass.%) 15-20 2-3 30-40 10-15 —
Mean SNT diameter, nm ~1.2 ~1.4 —
ISJAEE Special issue (2003)
Second International Symposium «Safety and Economy of Hydrogen Transport»
IFSSEHT-2003
400 500 600 700 800
Temperature, °C
Fig. 1. The soot mass growth at various temperatures of ethylene pyrolysis on LaNi5Hx.
— allows obtaining the hydrogen-sorbing compositions of intermetallide-graphene nanofibre-nickel.
The research has been carried out with the support by RFFR (Projects No. 02-03-32962 and No. 03-03-06565-MAC) and by ISTC (Project No.1580).
