Monolithic dried gels

Monolithic dried silica gels were formed by treating a mixture of tetraethyl orthosilicate, ethanol and water with small additions of HCl, increasing the solution density by a vacuum distillation process, casting samples at densities between 0.9 and 1.3 g/cm 3 and drying these samples slowly for one month in the laboratory. Samples which remained monolithic had 0.040 mol of 1 N HCl for a liter of solution and had been cast at a density of about 1.0 g/cm 3. They showed about 25% weight loss, were about 65 mm in diameter and had a density of about 1.60 g/cm 3 when dried. These samples were optically transparent, amorphous and undistorted. Firing to 900°C produced another 25% weight loss, which was attributed to the elimination of hydroxyls. A suggested structural unit for dried gels is adjacent chains of silicates with hydroxyls that are linked by bridging oxygens at every sixth silicon.