Evaluation and control of the characteristics and morphology of functional fine particles preparing by spray pyrolysis method.

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Using spray pyrolysis method, the preparation of fine metal sulfide particles such as ZnS and CdS used as phosphor or crystalline materials, and CuS used as solar cell materials, were investigated experimental and numerically. During the process, the effects of 1) droplet size, 2) initial concentraiton of starting solution, 3) heating rate and residence time of droplets or particles, on the characteristics and morphology of metal sulfide particles were investigated.The starting solutions were sprayd to micron scale droplets by an ultrasonic nebulizer and an electrospray atomizer. The droplets were introduced into a tubular furnace and the prepared particles could be collected at the outlet of the furnace. From the analysis of X-ray diffraction and SEM photographs, single phase of CuS,ZnS and CdS particles could be obtained at wide range temperatures by changing the composition ratio of the precursors.By the way, the study of spray pyrolysis is not well understood. At present, the models or theoretical studies proposed were very limited due to the mathematical complication and the difficulty to obtain the data or properties. We developed a simulation software to evaluate the preparation of fine particles during spray pyrolysis using the following steps : 1) during the droplet evaporation, the solute concentration profiles in the droplet and the vapor distribution inside the furnace could be obtained by solving numerically the related diffusion equations. 2) After determining the onset of solute nucleation in droplet, we could calculate the solute precipiration profiles formed and as the result, the particle norphology could be predicted. The model was applied to the preparation of zirconia fine particles. This system was chosen because the properties of the precursor are relatively well knwon. The numerical simulation could describe the results obtained by experiments.