Preparation of microencapsulated powders by an aerosol spray method and their optical properties

Microencapsulated powders were prepared by an aerosol spray method using a precursor comprised of a mixture of two types of sols as well as a sol-aqueous mixture precursor solution. Two different types of sols were used as precursors to prepare microencapsulated small-SiO(2)/largeSiO(2) and Al(2)O(3)/SiO(2) powders. A microencapsulated ZrO(2)/SiO(2) powder was also prepared from a mixture Of SiO(2) sol and an aqueous precursor solution of zirconyl nitrate dihydrate. For preparing small-SiO(2)/large-SiO(2) powders, two different sizes, i.e. 6 and 109 nm, Of SiO(2) sols were used as precursors. The results show that the larger SiO(2) particles were encapsulated with the smaller ones. A similar result was also observed in the preparation of an Al(2)O(3)/SiO(2) powder prepared from a mixture of Al(2)O(3) (18 nm) and a SiO(2) (109 nm) sol precursor. The Al(2)O(3) particles appeared on the surface of the prepared powder. In the case of the ZrO(2)/SiO(2) powder, the morphology indicates that the SiO(2) particles (109 nm) were encapsulated by a ZrO(2) shell. The effect of precursor ratios on the morphology of powders was also investigated. The light scattering characteristics of the prepared particles were also investigated using a laser particle counter coupled with-a pulse height analyzer. The effective refractive indices of the microencapsulated powders varied considerably with the content of coating material.