CERAMIC POWDER SYNTHESIS BY SPRAY-PYROLYSIS

A variety of spray pyrolysis (SP) techniques have been developed to di rectly produce ceramic powders from solutions. This paper reviews the current status of these processes in terms of the process parameters t hat enable the formation of particles with controlled morphology and c omposition. A model incorporating solute diffusion in the droplet and solvent evaporation from the droplet surface is presented to establish the critical parameters leading to solid particle formation. The mode l illustrates that solid particles can be obtained if solutes with hig h solubility and a large difference between the critical supersaturati on and equilibrium concentration are used and if the process is design ed to avoid solvent boiling. It is demonstrated that mixed metal oxide , non-oxide, and composite particles that are solid, hollow, porous, o r fibrous can be produced by modifying the precursor characteristics, solution properties, and process parameters. The physical and chemical flexibility of SP processes offers numerous opportunities for the con trolled synthesis of advanced ceramic powders and films. However, prod uction rates are limited by the need to produce <5-mum-diameter drople ts and to avoid subsequent droplet coagulation. Developments in proces s controls, atomization, and system design are required for wider comm ercialization of SP-type processes.