Mechanism and kinetics of nanosilver formation by ultrasonic spray pyrolysis progress report after successful up-scaling (Part 2)
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In 2006 the authors presented in Metall [Vol. 60, No. 6, pp. 377-382] first results on this promising new technology for nanopowder synthesis. Since then a significant improvement and up-scaling took place at IME Aachen and this article present the first results in the unique vertical tube reactor. Spherical, non-agglomerated nanosized particles of silver were prepared by ultrasonic dispersion of solutions from silver nitrate in nitrogen atmosphere. A controlled particle size was realized through the choice of the solution concentration as well as by changing the aerosol decomposition parameters. The experimental investigations were performed by an ultrasonic source of 2.5 MHz, acting on the water solution of the silver nitrate forming aerosols with constant droplet sizes. The droplet size depends on the characteristics of the solution and the frequency of the ultrasound. Subsequent thermal decomposition of the aerosol droplets was performed in nitrogen atmosphere between 300 °C and 60...0 °C. During synthesis the particle sizes of nanosized silver are measured using SMPS. The residence time and time for nanoparticle formation was calculated using a new mathematical model proposed in this work. Silver nanoparticles were collected in an electrostatic field. The paper presents also ways to control synthesis over the choice of the reaction parameters and compares the experimental results with a model.