Preparation of Transparent, Monolithic Silica Xerogels with Low Density

A new process to make monolithic and transparent silica xerogels with similar properties as silica aerogels by drying at ambient pressure has been studied. The xerogels are produced by strengthening the gel structure by additional precipitation of silica after the initial gelation. The additional precipitation of silica is achieved by ageing the alcogels in solutions of tetraethoxysilane (TEOS) and the aging is followed by a relatively rapid drying (<48 h) at ambient pressure. Due to the increased strength of the alcogels it is shown that the shrinkage during drying can be reduced and hence low density xerogels are obtained even if new monomers are added.