| The main objective of this thesis is to investigate the effect of operating conditions on the quality and characteristics of micro- and nano-powders produced by spray drying and pyrolysis. The main tasks performed in this thesis are as follows:;A reactor capable of drying and pyrolyzing solution sprays at low pressures is designed and constructed. The effect of low pressure and temperature on the morphology, crystallinity, and decomposition behavior of powders produced by spray pyrolysis is investigated. It is found that zirconia and magnesium sulphate powders are spherical, whereas the sodium chloride powders are cubic. The experimental data and the calculations indicate that the evaporation rate, which is a function of pressure and temperature, controls the solute distribution within the droplet and as such determines the morphology of the powders. The decomposition and crystallinity of the powders is determined using XEDS and XRD analyses, respectively. The crystallinity and decomposition of the powders are weak functions of pressure and strong functions of temperature.;In a different experiment, the thermal history of a suspended evaporative droplet in reduced pressures is studied. Using suspended droplets makes it possible to measure the variation of the droplet size and temperature during the process.;A mathematical model for the evaporation of micro- and nano-sized solution droplets is developed. This model is used to predict whether the produced particles by spray drying and pyrolysis are fully filled or hollow. The model includes the non-continuum effects on the droplet evaporation. Correlations for the final particle size and its wall thickness in terms of reactor temperature and pressure and the initial solution concentration are developed. In addition, a second mathematical model is developed to predict the morphology of powders, prepared by spray pyrolysis of high velocity solution droplets. Using the solute mass fraction distribution, the model predicts whether the final particle is fully-filled or hollow with two cavities.;Effect of different droplet size and velocity and solute concentration on the morphology of spray dried magnesium sulphate particles is investigated. Spray characteristics, such as droplet number density, droplet size and velocity distribution, and accompanying atomizing air are found to have major influence on the drying and morphology of the particles. |
