Study Of Preparation Of Silica Aerogel Adopting Silica Sol As Precursor By Ambient Pressure Drying

Abstract:SiO2aerogel as a new type of ultra-light porous solid materials, has attracted wide attention from all walks of life in the world. Itself has unique superior properties such as lightweight, heat resistance, sound resistance, adsorption, transparent, etc. SiO2aerogel has been widely applied in the building energy conservation, aerospace, purification of waste, and it has a broad development prospect.To reduce the production cost, this paper adopted the alkaline silica sol (15%wt) as precursor, combined with the step of acid catalytic method and atmospheric drying process implemented the preparation of the hydrophobic SiO2aerogels. First of all, through the orthogonal experiment analysis, the primary and secondary relations among factors of affecting the gelation time is that pH> H2O/silicon sol volume ratio> temperature> EtOH/silica sol volume ratio. Took gelation time, gel hardness and transparency as evaluation indexes,we got the optimal parameters for preparation of gel that pH=5.5, the volume ratio of H2O/silica sol=1, temperature=45℃, the volume ratio of EtOH/silica sol=0.5.Hydrophobic silica aerogels were prepared by using different acids as catalysts and dried at ambient pressure. The samples were characterized by FT-IR,SEM,TEM,BET, respectively. The results indicate that the properties of samples prepared with four acids are superior, and the use of acid in the preparation has an effect on the gelation process, structures and performance of the samples. SiO2aerogel catalyzed by oxalic acid has better micro-structure and properties, with apparent density of0.157g·cm-3, surface area of542.1m2·g-1,pore volume of1.9cm3·g-1, average pore size of19.05nm and contact angle of153.8°.Aging process,replacement method and surface modification technology were optimized by using a single variable method. The characterized results indicate that the best aging conditions were temperature (T)=35℃, time (t)=50h, the volume ratio of EtOH/TEOS (w)=1:4; optimal replacement process conditions were the volume ratio of EtOH/n-hexane (α1)=30%, the volume ratio of n-hexane/silica sol (α2)=2, replacement temperature (T’)=50℃and replacement number (n)=3; the best mix modifier was25%(volume ratio) of TMCS/hexane solution. Under the optimum preparing conditions, the sample has better microstructure and properties,with specific surface area of540.2m2·g-1, density of0.155g·cm-3, porosity of92.05%, the total pore volume of1.94cm3·g-1, the average pore diameter of18.95nm, thermal stability of up to440℃。There are42figures,14tables and79references。...