Cosolvent-assisted spray pyrolysis for the generation of metal particles
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Valeri I. Babushok Fire Research Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Thomas A. Germer Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
George W. Mulholland Fire Research Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Sheryl H. Ehrmana) Department of Chemical Engineering, University of Maryland, College Park, Maryland 20742 (Received 14 February 2003; accepted 9 April 2003)
A cosolvent-assisted spray pyrolysis process was developed for the formation of phase-pure metal particles from metal salt precursors without the direct addition of hydrogen or other reducing gas. Generation of phase-pure copper and nickel particles from aqueous solutions of copper acetate, copper nitrate, and nickel nitrate over the temperature range of 450 to 1000 °C was demonstrated. Addition of ethanol as a cosolvent plays a crucial role in producing phase-pure metal powders. Results of a modeling study of ethanol decomposition kinetics suggest that cosolvent decomposition creates a strong reducing atmosphere during spray pyrolysis via in situ production of hydrogen and carbon monoxide.
I. INTRODUCTION
Micrometer- or nanometer-size metal particles have various applications such as electrode materials for electronic products,1 electromagnetic interference shielding materials for electronic packaging,2 and catalysts for synthesizing carbon nanotubes.3 Spray pyrolysis is a useful tool for large-scale or small-scale production of particles with controlled particle size because the final product properties can be controlled through the choice of precursor and solution concentration or by changing aerosol decomposition parameters. Generally, in a spray pyrolysis process, reaction temperature and carrier gas composition are basic operating variables. In addition, solution properties such as precursor composition, concentration, or the addition of a cosolvent may be crucial to achieve the desired product composition and morphology. For example, morphological variation of magnesium oxide particles produced by the evaporative decomposition technique from three different precursors, magnesium chloride, magnesium acetate, and magnesium nitrate, was reported.4
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Preparation of metal particles by spray pyrolysis of metal salts is especially challenging. In chemical vapor deposition (CVD) of metals, the decomposition of the organic ligand may, such as in the case of the CVD of copper from bis(hexafluoroacetylacetonato)copper(II) [Cu(hfac)2], create a reducing environment at the surface resulting in the deposition of pure metal from a precursor containing metal in an oxidized form.5 In spray pyrolysis, however, both surface and solid-state chemical reactions occur during the conversion from precursor to product particle. For the metal salt precursors commonly used in spray pyrolysis processes, decomposition of the anion does not typi
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