Effect of water content on properties of one-step catalyzed silica aerogels via ambient pressure drying

• The effect of water content on physical properties of silica aerogel was studied.
• Increase in water content, decreased gelation time, porosity and surface area
• Compression strength and bulk density increased by increasing water content.
• Lower amount of water showed lower density & higher porosity but weaker 3D network.
• Samples with 1.5 or 2 molar ratio of water had the highest specific properties.

Tetraethylorthosilane was hydrolyzed and condensed in methanol as solvent, and catalytic aqueous ammonium fluoride and different amounts of water as co-solvent. The prepared gels were aged and solvent exchanged by n-hexane. The surfaces of the gels were modified using trimethylchlorosilane. Finally ambient pressure drying was performed. The surface area of the samples was determined by BET analysis and the pore size distributions were measured using the BJH method. FT-IR spectroscopy was used to confirm surface silylation. Compressive properties were investigated before drying. By increasing the amount of water, gelation time decreased significantly and compression modulus rose by increasing water content. Specific compression modulus (modulus/density) of the samples exhibited decrease with larger water content. The BET and BJH results showed that at first by adding more water, the specific surface area of silica aerogels decreased, this declination is more significant for the sample with 3 molar parts of water and after that, the surface area again increased slightly. The FE-SEM micrographs showed the pearl necklace structure for prepared samples.