2002 Volume 118 Issue 3,4 Pages 202-205
By using a solid mixture of silica (SiO2) with water-soluble inorganic salts as pore constructing agents, porous materials were fabricated through the coagulation / phase separation process. During the formation of the porous structure in the SiO2 / inorganic salt system, dispersibility of the mixture of silica sol with inorganic salt and the SiO2 / inorganic salt ratio are considered to strongly influence the coagulation/phase separation. In this study, we elucidated the dispersibility during the mixing of silica sol with inorganic salt, and the influence of the SiO2 / inorganic salt ratio in the solid mixture on the coagulation / phase separation. When SiO2 sol is mixed with inorganic salt in the solution, the surface electric potential is varied depending on the pH of the solution. Hence, dispersibility affected by the pH of the mixture is considered to strongly influence the resulting coagulation / phase separation in the SiO2 / inorganic salt system. In this system, the SiO2 / inorganic salt solution mixture had good dispersibility under the acidic condition of pH less than 4. On the other hand, gelation abruptly occurred after mixing SiO2 sol with inorganic salt under the conditon of pH nearly 7. Furthermore, the SiO2 / inorganic salt solution mixture had poor dispersibility under the acidic condition of pH less than 4, and the resulting porous material was found to have broad pore size distribution. To clarify the influence of the SiO2 / inorganic salt ratio on the coagulation/phase separation, solid mixtures having various ratios of SiO2 / inorganic were prepared. SiO2 / inorganic salt (KBr) with the volume fraction ratios widely ranging from 10 / 90 to 90 / 10 could form the monodispersed pore structure. Remarkably, the thickness of the framework in the porous material increased with the increase of the SiO2 volume fraction. Namely, the thickness of the framework as well as the pore size or the pore size distribution was influenced by SiO2 / inorganic salt ratios.
