Hierarchically structured silica via combination of salt sintering process and phase separation

Hierarchically structured, porous glass monoliths have been prepared successfully via combination of a salt sintering process and phase separation of a sodium borosilicate glass. The materials were characterized by N2-adsorption, Hg-intrusion and scanning electron microscopy. Secondary pore sizes were adjusted by the use of different grain fractions of the filler, different primary pore sizes could be obtained by a variation of the annealing conditions. Thus, both pore systems could be adjusted independently. The resulting monoliths consist of a system of secondary pores between 20 and 150 ?m and primary pores within the walls of the open-pored sintered material between 1 and 70 nm. The hierarchical porous materials exhibit surface areas up to 420 m2g-1 and total porosities up to 74%. Various shapes, e.g., rods, plates and granules were obtained by using appropriate pressing tools.