Parameters for spray drying ZnO nanopowders as spherical granules

Abstract

Spray drying is a versatile method to perform atomization, drying, and granulation. Spray dryers enable agglomeration of particles into a spherical granule form with a nano-meter size and thus very high specific surface areas (SSA). For this, the synthesized Zn(OH)(2) precipitate should be concurrently atomized and dried under desired spray drying conditions. The drying process has many complex and critical parameters. In order to obtain ZnO nanopowders in a spherical granule form the inlet temperature and the flow rate of the hot air, the feeding rate and the solidliquid ratio of the suspension, need to be optimized for 150 degrees C <= ITHA <= 180 degrees C, 5 mL/min <= FRS <= 15 mL/min, 50 g/L <= SLRS <= 200 g/L, 0.4 m(3)/min <= FR HA <= 0.6 m(3)/min and 60 degrees C <= OTDC <= 90 degrees C, respectively. The powders synthesized by these modifications have a range of 5-200 nm (TEM) and high SSA of 21114 m(2) . g(-1) (average particle size: 9-51 nm according to the SSA analyses) depending on the drying process parameters. The ZnO nanopowders have a soft granule structure according to the SSA analyses. Therefore, there is no need to grind the powders. They can be easily processed at all of the mixing and forming steps. In addition, they do not contain any contamination coming from grinding.