PROPERTIES OF SILICA-GELS PREPARED FROM HIGH-ACID HYDROLYSIS OF TETRAETHOXYSILANE

The gelation behavior and properties of silica eels prepared by hydrolytic polycondensation of tetraethoxysilane (TEOS) with large amounts of nitric acid as the catalyst have been studied. The molar compositions were TEOS:H2O:HNO3 = 1 : 10:x (x = 0.1-1.0). The effects of the acid content, drying temperature and mixing rate were investigated. It was found that the gelation time decreased with increasing amount of acid and increasing gelling temperature. In the presence of a large amount of nitric acid, the gels had higher specific surface areas and higher pore volumes as the drying temperature increased from 45 degrees C to 60 degrees C. A higher drying temperature at 120 degrees C led to an increase in pore volume, whereas it led to a decrease in specific surface area and density with an increase in acid content. Increasing the drying temperature is more effective than increasing the acid content in order to increase pore size.