Simulation of synthesis of palladium nanoparticles in an aerosol flow condenser

J. Aemsol SC;. Vol. 29, Suppl. I, pp. S5254526. 1998 8 1998 Published by Elsevier Science Ltd. All tights reserved Printed in Great Britain 0021s8502/98 $19.00 + 0.00

Pergamon

SIMULATION

OF SYNTHESIS OF PALLADIUM NANOPARTICLES AEROSOL FLOW CONDENSER

S. TSANTILIS, Department USA.

of Chemical

Engineering,

*Geb. 43, FB 10.3, Technische 6604 1, Saarbrucken, Germany.

S. E. PRATSINIS, University

Physik,

V. HAAS*

of Cincinnati,

Universitat

IN AN

Cincinnati

des Saarlandes,

OH 45221-0171,

Postfach

15-l l-50,

D-

KEYWORDS Palladium;

Nanoparticles;

Nucleation;

Condensation;

Coagulation;

Jets; Flow Condenser

Nanostructured Pd particles are used in a variety of applications such as catalysis, semiconductor films and hydrogen separation. The so-called inert gas condensation technique (IGC) has been employed for some time now to make these particles though it has some serious limitations with respect to process scale-up. Here a new technique is investigated and theoretically modeled in which Pd nanoparticles are continuously made in an aerosol jet flow condenser. This new technique relies on rapid heat transfer by forced convection in contrast to free convection that is dominant in the IGC technique. More specifically, a Pd rod is inductively heated while nitrogen gas is issued from four horizontally arranged nozzles carrying away the Pd vapor that rapidly condenses into Pd nanoparticles 2 - 10 nm in diameter. An outer, sheath nitrogen jet flow surrounds the inner nitrogen jet streams in order to minimize backstreaming and particle deposition on the chamber walls. Flow visualization is carried out using a commercial flow dynamics software (Fluent). As a result, temperature and velocity profiles are obtained that are in agreement with established correlations for free turbulent jets (Bejan, 1984; Koch et al., 1993). Based on these temperature and velocity profiles, the dynamics of newly formed Pd particles can be calculated by modifying a simple model for aerosol nucleation, condensation and coagulation (Panda and Pratsinis, 1995). It appears that coagulation is the dominant mechanism for growth while nucleationcondensation are important only at the very early stages of the process. Despite the complexity of the condenser, the model predictions compare well to the Pd particle sizes measured by transmission electron microscopy for a wide range of inner and sheath flowrates (250 seem IQ, I 1000 seem and 100 seem 2 Q, 2 2000 seem). The range of validity of the model is also investigated. s525

S526

Abstracts of the 5th International Aerosol Conference

1998

10

Sheath Flowrate, l

2000 seem

Data, Haas et al. (1997) Model (this study)

8 -

6 -

4;

,,

-0:\ *a

0

0

0 0

2 200

1 300

I c II 400 500 Inner Nozzle

i 600 Flowrate

, 700 Qn,

I 800 seem

I 900

1000

Fig 1 : Effect of inner nozzle flowrate (seem) on the average diameter (run) of collected particles at a distance of 25 cm from the nozzle system. Comparison of simulation results with experimental data (Haas et al., 1997) for a sheath flowrate of 2000 seem. ACKNOWLEDGEMENTS This research was supported

by the U. S. National

Science Foundation.

REFERENCES Bejan, A. (1984) Convection

Heat Transfer. Wiley, New York.

Haas, V., Birringer, R., Gleitter, H., Pratsinis, S. E. (1997) Synthesis Powders in an Aerosol Flow Condenser. J. Aerosol Sci., 28,1443.

of Nanostructured

Koch, W., Windt, H., Kafiich, N. (1993) Modeling and Experimental Evaluation of an Aerosol Generator for very High Number Currents Based on a Free Turbulent Jet. J. Aerosol Sci., 24, 909. Panda, S., Pratsinis, S. E. (1995) Modeling the Synthesis of Aluminum Particles Evaporation-Condensation in an Aerosol Flow Reactor. Nanostruct. Mat&., 5, 755.

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