Synthesis of Metal Nanoparticles

Nanostructured metal particles are used in a variety of applications such as catalysis, superalloys, and thin film coatings in the chemical and electronics industries. Often, the particles are required to be non-aggregated and smaller than 50 nm in diameter so that thin dense metal layers can be synthesized. Furthermore, high demands are set concerning the purity of metal nanoparticles. Traces of oxides make the nanoparticles unusable as their physical properties are changed severely.

Currently synthesis of Bi nanoparticles in hot-wall flow reactors is investigated as Bi nanoparticles find applications in manufacture of phototools. Synthesis of Al as well as Pd has been studied in the past (1,2). In this project a process is developed for production of bismuth nanoparticles with diameters below 50 nm. This process relies on rapid heat transfer by forced convection in a jet aerosol flow condenser in contrast to free convection that is dominant in conventional inert gas evaporation-condensation methods (2). The saturated hot metal vapor is condensed in a cold inert gas stream which also sweeps the newly synthesized particles out of the particle formation zone of the reactor. The aerosol particles further grow by coagulation in the carrier gas stream. Particle growth stops rapidly when the aerosol is quenched by a cooling gas which is introduced from the other side of the tubular reactor at room-temperature. High cooling rates are achieved by the mixing of the hot aerosol with the cooling gas. Thus, the residence time of the particles in the reaction zone can be altered by adjusting the flow rates of the carrier gas and the cooling gas. Including reactor and carrier gas temperature, a total of four parameters is at hand to influence particle size leading to a much better control of particle formation and –growth than hitherto possible. Here the influence of these four parameters on the characteristics of product bismuth particles is investigated experimentally and theoretically. Simulations for synthesis of Bi nanoparticles were carried out accounting for nucleation, condensation and coagulation (3). These simulations mapped out the effect of carrier gas flowrate and process temperature on Bi production rate and on primary particle size. The focus is on developing a procedure for the synthesis of pure and non-aggregated bismuth-nanoparticles with diameters below 50 nm. The results of Bi nanoparticles synthesis as determined by nitrogen adsorption indicate that particles in the range of 30 to 90 nm in diameter are produced. Information on particle morphology and composition will be presented using transmission electron microscopy (TEM) and X-ray diffraction (XRD).

1. V. Haas, R. Birringer, H. Gleiter, S.E. Pratsinis, "Synthesis of Nanostructured Powders in an Aerosol Flow Condenser", J. Aerosol Sci., 28, 1443-1453 (1997).
2. S. Panda, S.E. Pratsinis, "Modeling the Synthesis of Aluminum Particles by Evaporation- Condensation in an Aerosol Flow Reactor", Nanostructured Mater., 5, 755-68 (1995).
3. S. Tsantilis, S.E. Pratsinis, V. Haas, "Modeling of Synthesis of Pd Powders in a Jet Aerosol Flow Condenser", J. Aerosol Sci., 53, 785-803 (1999).