44 O 03 Gas-phase particle size distributions of (Bi,Pb)-Sr-Ca-Cu-O superconducting powders made via spray pyrolysis

J. Aerosol Sci.. Vo[. 24, Suppl. 1, pp. $567-$568, 1993 Printed in Great Britain.

(~)21-8502/93 $6.00 + 0.00 Pergamon Press Ltd

44001 GENERATION OF NANOMETER-SIZE FULLERENE PARTICLES VIA VAPOR CONDENSATION J. Joutsensaari 1, E. I. Kauppinen 1, A. S. Gurav 2 and T. T. Koclas2 1Aerosol Technology Group, Technical Research Center of Finland (VTT), Laboratory of Heating and Ventilation, P.O.Box 206, FIN-02151 Espoo, Finland 2Center for Micro-Engineered Ceramics, Chemical Engineering Department, University of New Mexico, Albuquerque, NM 87131, U.S.A.

KEYWORDS fullerenes, C60, vapor condensation, nanophase, ultrafine particles METHODS Nanometer-size (30-40 nm) particles of fullerenes (C60, C70, etc.) were generated by evaporation-condensation in a continuous flow system starting from pure C60 and mixed fullerene extract (MFE, C60/C70). The aerosol flow system consisted of a mullite tube (3.25 in. I.D., 36 in. heated length) in a three zone furnace. Nitrogen was used as a carrier gas. The system was purged thoroughly before and after the runs. Batches of 100 mg of pure C60 or MFE were loaded at the center of the tube and heated to 400-650 °C at a rate of 2 to 4 °C/min. While heating, the temperature was held at 250 °C for one hour to remove any solvent remaining in the powders. Total particle concentrations were monitored with a condensation particle counter (CPC, TSI Model 3022). Number size distributions in the size range 0.02-0.7 Bm were monitored with a differential mobility analyzer (DMA, TSI Model 3071). The DMA data were corrected for diffusion losses and inverted using TSI inversion routine. Mass size distributions in the size range 0.03-16 Bm were measured by a Berner-type low-pressure impactor (BLPI) fitted with a ejector-based dilution system (Hilamo and Kauppinen, 1991). The BLPI data were inverted by a method based on constrained regularization (Wolfenbarger and Seinfeld, 1990). Scanning and transmission electron microscopy were used to study the morphology and crystallanity of the particles produced. Particles were collected in situ at the reactor exit onto polycarbonate filters and copper TEM grids for SEM (Hitachi Model S-800) and TEM (JEOL 2000FX, 200 kV) analysis. The transmission electron microscope had a direct resolution of about 2.7 A, which is much better than that required for the lattice-imaging of C60. RESULTS Fullerenes are volatile above 400 °C and have appreciable vapor pressures above 500 °C (Abrefah et al., 1992; Pan et al., 1992). Thus, fullerenes vaporized at the reactor temperatures used (400-650 °C) and the vapors were carried through the reactor by nitrogen carrier gas. The mixture of fullerene vapors and nitrogen $567

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cooled beyond the hot-zone of the reactor, thereby increasing the saturation ratio which led to the formation of ultra-fine fullerene particles via homogeneous nucleation, condensation and coagulation.

1.2E-'.-7 - - - - m - - 5(i) c

1.0E÷7

525 C

8.0E+6 --°--

SSOC

6.0E÷6 4.0E+6 2.0E÷6

O,OE+O 0.01

0.1 Dp (l.lm)

Fig. 1. SEM micrograph of fullerene particles produced at 500 °C

Fig. 2. Gas-phase number size distribution of fullerene particles made via vapor condensation

Figure 1 shows a SEM micrograph of fuUerene particles produced at 500 °C using MFE as the starting material. The particles were spherical in shape for the range of temperature studied (400-650 °C). Energy dispersive spectroscopy (EDS) confirmed that carbon was the only element present in the particles. TEM analysis indicated that the particles were partly amorphous at 400 °C and became crystalline C60 for processing temperatures of 500 °C and above. Figure 2 shows the number size distributions in the gas-phase for the processing temperatures of 500, 525 and 550 °C. The particles had an average size of 30, 35 and 40 nm, and a total number concentration of 2.2x106, 3.5x106 and 5.0x106 #/cm 3 at 500, 525 and 550 °C, respectively. Thus, we have demonstrated the application of vapor condensation to generate nanophase (30-40 nm size), solid, spherical and unagglomerated fullerene particles. REFERENCES Abrefah, J., D.R. Olander, M. Balooch, W.I. Siekhaus (1992), Appl. Phys. Lett. Vol. 60, 1313-1315. Hilamo, R.E., and E.I. Kauppinen (1991), Aerosol Sci. Technol. Vol. 14, 33-47. Pan, C., M.S. Chandrashekharaiah, R.H, Hauge and J. L. Margrave (1992), J. Physl Chem. Vol. 96, 6752-6755. Wolfenbarger, J.K. and J.K.Seinfeld (1990), ]. Aersol Sci. Vol. 21, 227-247.