Preparation of Millimeter-scale Alumina Hollow Spheres by Oil$lt;inf$gt;1$lt;/inf$gt;-in-water-in-oil$lt;inf$gt;2$lt;/inf$gt; Emulsions

Abstract

To prepare millimeter-scale alumina hollow spheres by oil1-in-water-in-oil2 emulsions, the influence factors of formation of precursor and curing process were studied. Composite droplets with paraffin liquid as inner core and alumina sol as outer shell were used as precursor. Results showed that the com-droplets had homogeneous and com- plete core-shell structure when emulsion generator was designed that inner oil could be injected into water phase with the size of millimeters scale. Thickness and diameter of droplets were adjusted by both controlling the injection speed of oil and water phase in the range of 30-80 μm and 800-2200 μm. In the curing process, the semisolid spheres kept hollow structure and spherical when the speed of rotation between 20 r/min to 60 r/min and the flask being put in horizontal. Finally, the prepared hollow ceramic spheres with wall thickness in micrometer-scale and diameter in mil- limeter-scale formed complete hollow structure and high sphericity after calcining at 1200 ℃ for 4 h. The surface of sphere was relatively smooth with roughness of about 22 nm. The main crystal of the prepared ceramic hollow spheres was alpha alumina.