DETERMINATION OF THE OPTIMUM PREPARATION CONDITION OF THE SOL-GEL SiO₂ USING THE RESPONSE SURFAC METHODOLOGY

Abstract

A typical sol - gel process consists of the liquid reaction, the solution gelation, and followed by the dehydration. The surface properties of silica gel such as surface area, pore volumes, and the pore diameter were affected by the manufacturing variables including pH values, gelation and dehydration temperatures. The objective of this study is to determine the optimum preparation conditions to maximize a response of surface area, or minimize its pore diameter. In addition, interactions between process variables were studied and their significance to the surface properties was also weighted. It was found that the surface area of silica gels increased with an increasing amount of NH₄OH to a maximum value and then decreased. As a drying temperature kept constant, the surface area and the pore volume increased with an increasing gelation temperature. However, the pore diameter was not influenced by this factor and the pore size was almost uniform at a low NH₄OH concentration. 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 analysis, the optimum processing condition was found to be 0.0155 mole of NH₄OH, 80,3°C for gelation temperature, and 63.2°C for the dehydration. As a result the maximum surface area corresponding to the optimum preparation conditions was 818.9 (m²/g) as expected.

Keywords:

• Sol - gel process
• Response surface methodology
• Silica gel
• Surface properties