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 microspheres. High-viscosity sols produced broken microspheres. A temperature of about 400-500 °C for boehmite to γ-Al2O3 transformation in the gel microspheres was observed by differential thermal analysis and X-ray diffraction. Complete crystallization of the gel microspheres to α-Al2O3 occurred at 1200 °C. A tentative mechanism for the formation of the hollow microspheres is presented.