Determination of the optimum preparation condition of the sol-gel SiO2 using the response surface methodology

A typical sol-gel process consists of the liquid reaction, the solution gel ation, and followed by the dehydration. The surface properties of silica ge l such as surface area, pore volumes, and the pore diameter were affected b y the manufacturing variables including pH values, gelation and dehydration temperatures. The objective of this study is to determine the optimum prep aration conditions to maximize a response of surface area, or minimize its pore diameter. In addition, interactions between process variables were stu died and their significance to the surface properties was also weighted. It was found that the surface area of silica gels increased with an increasin g amount of NH4OH to a maximum value and then decreased. As a drying temper ature kept constant, the surface area and the pore volume increased with an increasing gelation temperature. However, the pore diameter was not influe nced by this factor and the pore size was almost uniform at a low NH4OH con centration. For a higher NH4OH concentration, the pore: volume and the pore diameter became larger but the surface area became smaller as the gelation temperature increased. By means of the response surface methodology analys is, the optimum processing condition was found to be 0.0155 mole of NH4OH, 80.3 degreesC for gelation temperature, and 63.2 degreesC for the dehydrati on. As a result the maximum surface area corresponding to the optimum prepa ration conditions was 818.9 (m(2)/g) as expected.