EFFECT OF PRECURSOR, SOLVENT, AND WATER MOLAR RATIOS ON SURFACE-AREA AND POROSITY OF TETRAETHOXYSILANE SILICA AEROGELS

For most applications, not only are monolithic and transparent silica aerogels required but they should also have low density, large surface area, and high porosity (> 90%). The aerogels have been prepared by h ydrolysis and polycondensation of tetraethoxysilane (TEOS) rising an o rganic acid (citric acid) catalyst, followed by supercritical drying i n an autoclave. The molar ratio of ethanol/TEOS (A) and H2O/TEOS (B) c ause significant structural rearrangement of citric acid catalysed TEO S silica aerogels, for example, changes in surface area, pore diameter , porosity, etc. The experimental results presented here shown the eff ect of precursor, solvent, and water molar ratios on surface area and porosity of TEOS silica aerogels. The values of A and B were varied fr om 2.5 to 20 and 1 to 10 respectively. fr has been found that as the v alue of A increases up to 5, the surface area, pore diameter, and per cent porosity increase, and then remain almost constant for A > 5. On the other hand, the lower (<6) and higher (>9) values of B resulted in lower surface area, smaller pore diameter, and lower per cent porosit y, whereas medium values of B (6 < B < 9) resulted in larger surface a rea, pore diameter, and the per cent porosity. For values of A between about 4 and 6 and values of B between about 6 and 9, monolithic and t ransparent silica aerogels with larger surface area, pore diameter, an d, per cent porosity were observed. It has been found that A and B val ues of similar to 6 resulted in narrow and uniform pore size distribut ion, which reduces the differential pressures during supercritical sol vent extraction and leads to monolithic silica aerogels.