Processing effect on structural changes of high acid-catalysed silica gel

The structure of silica gels prepared by hydrolysis of tetraethoxysilane (TEOS) with high acid content has been investigated. The gels were obtained by varying the nitric acid contents at a constant H2O/TEOS molar ratio of 10. The molar compositions were TEOS:H2O:HNO3 =1:10: x(X=0.1-1.0). The effects of acid content and drying temperature on structural changes in the gels were examined. In addition, the surface area, pore volume, pore size distribution, and the microstructure were determined. The results showed that the pore structure changed to larger pore sizes and broader size distributions as a result of increasing the drying temperature. However, at a constant drying temperature, a higher acid content yielded a higher pore volume. The gels dried at lower temperatures had slit-shaped micropores and a narrow pore size distribution; whereas, the gels dried at higher temperatures had ink bottle-shaped pores and a relatively broad size distribution.