Hollow alumina microspheres from boehmite sols

Hollow alumina microspheres were obtained from emulsified boehmite sols by an ion extraction method. The viscosity and the equivalent alumina content of the sols were found to affect the characteristics of the derived microsp heres. High-viscosity sols produced broken microspheres. A temperature of a bout 400-500 degrees C for boehmite to gamma-Al2O3 transformation in the ge l microspheres was observed by differential thermal analysis and X-ray diff raction. Complete crystallization of the gel microspheres to alpha-Al2O3 oc curred at 1200 degrees C. A tentative mechanism for the formation of the ho llow microspheres is presented. (C) 1998 Kluwer Academic Publishers.