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 gelation. It is shown that also by aging tetraethoxysilane (TEOS)-based alcogels in solutions of TEOS/ethanol (EtOH) the strength and stiffness can favourably be increased and hence reduce the shrinkage during drying at ambient pressure. Low-density silica xerogels (rho = 0.24 g/cm(3)) are obtained by changing aging parameters such as time and temperature. The water content in the pore liquid is important for the aging process and is increased by changing the pore liquid prior to providing the monomers for aging. The shear modulus has been increased by 23 times and the modulus of rupture by five times, reducing the corresponding shrinkage during drying to similar or equal to 0.5%.