Particle Formation from Solution and Slurry Sprays

ABSTRACT

The initial morphology of particles formed by spray drying or spray pyrolsis of solutions, sols or slurries, is determined by the relative velocity between the atomized droplet and the ambient gas in the furnace. A1 high relative velocities, the droplet can be disintegrated or flattened, whereas at low relative velocities the droplet remains spherical throughout the drying process. The time for respheroidization depends on the liquid properties and the solid content of the drying droplet. When the droplet reaches the percolation limit, the higher viscosity inhibits respheroidization, and the morphology of the deformed droplet is fixed. A new model based on the Weber number, percolation criteria, and the drying kinetics, is presented to predict particle morphology for various drying conditions. In addition, the effects of segregation during drying will be discussed in regard to its effect on particle formation during spray formulation. We will show how physical and chemical segregation processes occur in drying droplets, and how these segregation processes can be controlled to yield particles of designed morphology and internal phase distribution.