Granulating fine powders into millimetric spheres with a multiscale porosity: The case of titania

A new simple process based on the controlled dispersion of powders in water to shape millimetric spheres exhibiting a micro/mesoporous structured network is described. A formulation containing latex spheres (d50 = 4 microns) and titania aggregates (d50 = 1 micron) is agglomerated by addition of hydrous alumina nanofilaments carrying a high density of positive charges. By selecting the suitable ratios for each raw material, the structure of primary agglomerates consists of core (latex)/shell (titania monolayer) type. The coalescence of such agglomerates in suspension is induced by a continuous rotational movement which forces agglomerate surfaces to interact. The control of the solid surfaces chemistry, which determines the nature and intensity of interactions between the powders, allows to produce cohesive objects with a spherical form. After calcination, the spheres obtained exhibit a hierarchical multiscale porosity. It is expected that the process described can be extended to other oxides to produce catalysts, filters.

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► Agglomeration by colloidal way of a co-dispersion of titania and latex.
► The structure of primary agglomerates consists of core (latex)/shell (titania monolayer) type.
► Elaboration of millimetric porous spheres.
► Spheres obtained exhibit a hierarchical multiscale porosity.