PREPARATION AND PROPERTIES OF MONOLITHIC SILICA XEROGELS FROM TEOS-BASED ALCOGELS AGED IN SILANE SOLUTIONS

In previous work, tetramethoxysilane-based alcogels were strengthened and stiffened by providing new monomers to the alcogel subsequent to g elation. It is shown that also by aging tetraethoxysilane (TEOS)-based alcogels in solutions of TEOS/ethanol (EtOH) the strength and stiffne ss can favourably be increased and hence reduce the shrinkage during d rying at ambient pressure. Low-density silica xerogels (rho = 0.24 g/c m(3)) are obtained by changing aging parameters such as time and tempe rature. The water content in the pore liquid is important for the agin g process and is increased by changing the pore liquid prior to provid ing the monomers for aging. The shear modulus has been increased by 23 times and the modulus of rupture by five times, reducing the correspo nding shrinkage during drying to similar or equal to 0.5%.