Processing alumina spheres by a colloidal route using silica-polystyrene hybrid nanoparticles

Colloidal granulation of alumina is an original shaping process leading to spherical granules directly in suspension from a diluted system. It is based on a heterocoagulation mechanism where silica added in small amount acts as a binding agent. The role of a submicronic latex of polystyrene was investigated, free, or as a hybrid object covered by silica nanoparticles synthesized by a Pickering emulsion polymerization method. Latex particles were not able to form primary agglomerates despite a high negative zêta potential. An addition of latex in combination with silica improved the state and homogeneity of the final microstructure which could be attributed to a decrease of the internal strains during the processing. Hybrid nanoparticles, by combining the binding agent (silica) and the organic phase, were able to form primary agglomerates, and to finally obtain alumina spheres exhibiting both a spherical morphology and a greater homogeneous microstructure.