Strengthening and aging of wet silica gels for up-scaling of aerogel preparation

In order to enhance the mechanical properties of wet gels for aerogel production, aging studies by using three different routes was performed. The wet gels were prepared from a polyethoxydisiloxane precursor by using HF as a catalyst. The three different aging routes studied were i) aging in sealed mould, ii) aging in solvent and iii) aging in simulated pore liquid, i.e. a solvent with small amounts of water and HF resembling the mother liquor. All aging processes gave stronger and stiffer wet gels however, a maximum in strength and stiffness was observed after a certain aging time. The simulated pore liquids allowed short aging time in the range of 8 h to achieve the maximum mechanical strength, however the maximum in strength was lower than for the other two aging routes. From the wet gels, monolithic and transparent aerogels were obtained by supercritical drying at small-, mid- and large-scale. The aging strengthening process was successfully transferred to larger scales giving both lower density and higher transparency compared to small-scale.