Morphology maps of ice-templated silica gels derived from silica hydrogels and hydrosols

Ice-templated silica gels with various shapes were prepared through the unidirectional freezing of silica hydrogels and silica hydrosols that were synthesized from aqueous sodium silicate solutions. The relationship between the characteristics of the precursors (hydrogels and hydrosols) and the resulting shape was investigated. The dominant factor which governs the shape of the resulting gel was found to be the mobility of silica. From hydrogels, porous monoliths with straight channels (microhoneycombs), fibers with polygonal cross-sections, and powders were obtained. On the other hand, from hydrosols, lamellas, flat fibers, and microhoneycombs were obtained. For both hydrosols and hydrogels, we attempted to establish morphology maps which allow us to easily predict the resulting shape from the adjustable parameters of the precursors. In the case of hydrogels, the map could be divided into individual regions which correspond to each type of shape according to the elapsed time between gelation and freezing, and the gelation time of the hydrogel. On the other hand, in the case of hydrosols, the map could be divided into individual regions which correspond to each type of shape according to the relaxation time of the hydrosol at the time of freezing and the gelation time of the hydrosol.