(439c) Co-Solvent Assisted Spray Pyrolysis for the Preparation of Metal Microparticles

Spray pyrolysis processes offer many advantages over solution phase routes for powder production, but extension to metals on an industrial scale has been restricted to only a few oxidation resistant systems such as silver and palladium. The requirement of addition of high concentrations of reducing gas to produce metallic particles has limited extension to base metal production. In our approach, a co-solvent is added to the aqueous solution of metal salt precursors, which decomposes in the reactor to produce small amounts of hydrogen, less than the flammability limit in air, reducing inexpensive metal salt precursors to metallic powders. We have constructed a reactor system capable of producing several grams/hour of micron sized metallic copper powder using an ultrasonic droplet generator operating at a frequency of 1.65 MHz. This process operates with nitrogen as a carrier gas, and particles are quenched with additional nitrogen. We have also shown that these metal powders can be produced using ethylene glycol as the co-solvent rather than ethanol as used previously by our group. This represents an additional process safety advance, because of the higher flash point of ethylene glycol relative to ethanol, our original co-solvent choice. The oxide free copper metal particles were made from copper nitrate precursor, and different reaction conditions were investigated to optimize the process. It was found that the amount of co-solvent, carrier and quench gas flow rates, and reaction temperature play an important role in this process. We have successfully made pure copper particles with a narrow size distribution using 30 volume% ratio of ethylene glycol, 5 L/min nitrogen (N2) carrier gas and 10L/min N2 quench gas. The experiment results also indicated that the co-solvent-assisted spray pyrolysis technology is a promising method for the preparation of multi components alloy particles such as Ag/Cu/Co.