Synthesis and characterization of carbon filaments grown from Pd 3 P colloids
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Synthesis and characterization of carbon filaments grown from Pd3P colloids F. Cesar, J-O. Bovin, and L.R. Wallenberg National Center for High-Resolution Electron Microscopy, Inorganic Chemistry 2, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-221 00, Lund, Sweden
G. Karlsson The Biomicroscopy Unit, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-221 00, Sweden
L.K.L. Falk Division for Microscopy and Microanalysis, Department of Experimental Physics, Chalmers University of Technology, S-412 96, Gothenburg, Lund, Sweden
T. Oku Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan (Received 9 February 2000; accepted 6 June 2000)
Amorphous carbon filaments were synthesized by catalytic pyrolysis of propene over Pd3P colloids. The channel close to the center of the filaments usually contained particles, which were analyzed by analytical electron microscopy to be palladium. The palladium particles could be found anywhere along the filament. The carbon filaments were of two types and of different diameters, about 8–15 nm and about 40–80 nm. The thinner type of filament shows a channel diameter of about 5 nm. The type of filament produced depends on the reaction conditions. Increased reaction time results in a large number of filaments, whereas an increased propene gas flow results in more of the thicker type of filaments. Carbon nanotubes and filaments have created much interest in recent years due to their chemical, mechanical, and conducting properties, believed to be dependent on their structure, geometry, and dimensions. However, it is still difficult to produce defect-free nanotubes and filaments of different kinds, necessary for fundamental studies, so new synthesis methods are constantly sought. One such method, frequently used for its simplicity, is catalytic pyrolysis of hydrocarbons.1–4 In this study, a new type of material, consisting of palladium phosphide colloids, supported on active carbon, was used as catalyst. The reaction parameters were varied, and the resulting materials were examined by transmission electron microscopy (TEM), analytical microscopy using energy dispersive x-ray spectroscopy (EDS), and energy-filtered imaging (EFTEM). The different microscopes used were JEM-2000FX, JEM-4000EX, Philips CM 200 FEGTEM, and Philips CM 120 BioTWIN Cryo. The precursor to the Pd3P colloids was a ligandstabilized palladium boride colloid, which was formed by reaction of gaseous B2H6 with the metal complex Cl2Pd(PR3)2 (PR3 ⳱ tripropylphosphine or tributylphosphine) in toluene at room temperature.5 The resulting precursor, in this case Pd4B6Cl(PBu3), was annealed in J. Mater. Res., Vol. 15, No. 9, Sep 2000
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argon with an active carbon support (with a total amount of ≈2 wt% Pd). When the annealing temperature was increased, the original 2-nm particles coalesced and reacted with the ligand shell and the active carbon support. The re
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