NANOPARTICLE PRODUCTION BY SPRAY DRYING AND SPRAY PYROLYSIS

In spray pyrolysis technique (SP), a precursor solution that contains a solvent such as water and a solute that usually contains a metal and a non-metal element is converted to a spray of small droplets, using a spray generator. The droplets are then introduced into a hot environment where the solvent evaporates and the solute is precipitated. Provided that the process temperature is high enough a chemical decomposition takes place, forming the final particles. A schematic diagram of the spray pyrolysis process is shown in Fig. (1). Spray drying technique (SD) is similar to spray pyrolysis, except that there is no chemical decomposition and usually the process temperature is lower [2].
Particles produced via SP and SD techniques may be fully-filled or hollow, depending on the operating conditions. Hollow particles form if at the onset of solute precipitation on the droplet surface, the solute concentration at the droplet centre is smaller than the equilibrium saturation [3]. Figure (2) illustrates some of the scenarios that may occur during spray drying and pyrolysis [4].
For some precursors such as NaCl aqueous solution, which is a strong ionic solution, spherical solution droplets produce