Simulation and experimental study of spray pyrolysis of polydispersed droplets
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I. Wuled Lenggoro Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
Ferry Iskandar and Kikuo Okuyamaa) Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan (Received 10 January 2007; accepted 21 March 2007)
The size distribution and morphology of particles (dense or hollow) produced from polydispersed droplets in spray pyrolysis were studied both experimentally and theoretically. Zirconia, generated from a zirconyl hydroxychloride precursor, was selected as a model material. The simulation method that was previously developed by our group [J. Mater. Res., 15, 733 (2000)], in which droplets were assumed to be uniform, was improved to evaluate the effect of polydispersity in droplets on the size and morphology of the resulting particles. Simultaneous equations for heat and mass transfer of solvent evaporation and solute mass transfer inside droplets were solved numerically for a number of discrete classes of droplet size distribution. The role of the decomposition reaction was also included after the evaporation stage of polydispersed droplets in an attempt to explain the densification of particles. In hollow particle generation, this simulation was used to evaluate the thickness of a particle shell. The experimental results were in good agreement with the simulation data, suggesting that the model provides a more realistic prediction.
I. INTRODUCTION
Spray pyrolysis is widely used for particle synthesis. It provides the ability to control and maintain uniform chemical composition from droplet to particle for single and multicomponent materials and to produce submicron and micron size, high-purity, and unagglomerated particles.1 The limited industrial application of spray pyrolysis is frequently attributed to inadequacies associated with the control of particle morphology.2 It has been shown that the morphology of particles generated from droplets that are sprayed by an ultrasonic nebulizer are not uniform in a single operation.3 They can be hollow, dense, or a mixture of dense and hollow particles. Attempts have been made to control and predict particle morphology both experimentally and numerically. In particular, the modeling of droplet to particle conversion in spray pyrolysis process was attempted by a few
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0235 1888 J. Mater. Res., Vol. 22, No. 7, Jul 2007 http://journals.cambridge.org Downloaded: 20 Mar 2015
groups. Many parameters have been considered in these investigations, such as droplet size, droplet size distribution, droplet number concentration, precursor concentration, physical and chemical properties of droplets, and operation conditions.4,5 These parameters influence the rates of evaporation and solute diffusion inside a droplet, which, in turn, determines the morphology of the generated particles. Jayanthi et al. numerically solved the mass and he
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