Abstract
The researchers elucidated the transformation of the state between silica / titania particles and inorganic salts during the calcination of the solid mixture of silica / potassium halide (KX) or titania / potassium halide at temperatures near 700°C. The silica sol / KX or the titania sol / KX dispersed mixture was volatized, and its dried solid was prepared for the measurement of pore size (distribution), observation of pore structure by using focused ion beam-scanning image microscope (FIB-SIM) and the determination of X-ray diffractometry (XRD). In the solid state of mixture, inorganic salt existed as a crystal was found to be transformed to the amorphous state during the heat treatment of the solid mixture. From the result of the XRD test, diffraction pattern ascribed to the inorganic salt was almost disappeared at temperatures ca. 100 ∼ 200°C lower than the melting point of it. Both silica and inorganic salt were considered to be in an amorphous state at this temperature range in the case of silica / inorganic salt system. In the titania / inorganic salt system, however, both of two components were in the crystalline state, which caused to limit of their phase separation even at temperatures near the melting point of inorganic salt. After removing of inorganic salt phase dissolved into water, porous species with having narrow pore size distribution was obtained. Through this process, during the phase separation between silica or titania and KX proceeded, the resulting porous structure was considered to form. At a calcination temperature higher than 800°C, construction of the silica or titania crystal existed as a separated domain without the formation of the porous structure.
