Mass Production and Particle Characterization of Fine Spherical Ag Powder by Gas Combustion-Type Spray Pyrolysis

Abstract

A large-scale spray pyrolysis apparatus in which the mist is pyrolyzed by a flame using a gas burner was developed for the mass production of Ag powder. Forty ultrasonic vibrators with a frequency of 1.6 MHz generated 4 dm³/h of mist. The thermal stability of the ultrasonic vibrators was improved using water-cooling. Spherical Ag powder was continuously produced, and the yield of the powders remained above 95% over 60 hours of continuous production with starting solution concentrations of up to 1.5 mol/dm³. Scanning electron microscopy (SEM) analysis showed that the particles were sub-micrometer in size with a dense microstructure, and they did not aggregate. Powder X-ray diffraction (XRD) demonstrated that the as-prepared Ag powder exhibited high crystallinity. The particle size of the Ag powder was approximately in agreement with the predicted size, calculated under the assumption that one Ag particle was formed from one droplet of mist. Moreover, 7 kg of Ag powder was produced over 12 h at 1.5 mol/dm³. This apparatus exhibited good reliability for the continuous mass production of Ag powder.