Preparation And Properties Research Of Silica Aerogel And Its Composites

When preparing SiO₂ aerogels at ambient pressure drying,the solvent exchange step is a time-consuming process that takes days or weeks and consumes a large amount of solvent,which not only significantly increases the production cost of SiO₂ aerogels,but also puts a huge strain on the environment.Therefore,the solvent-free drying method is an important problem.The high porosity and empty interior of SiO₂ aerogels cause SiO₂ aerogels to be brittle and sensitive to relatively low pressures,and have very low strength and modulus,which limit their application and damage their commercial use.But SiO₂ aerogel composites,such as foam composites,fiber composites,etc.can enhance their mechanical properties and retain their characteristics.Therefore,silica aerogel composites also have very important research significance.This article has conducted research on these two aspects,the details are as follows:?1?A phase-separation induced?PSI?method of synthesizing superhydrophobic silica aerogel powders and granules is developed by direct hydrophobilization of silica alcogels in diluted trimethylchlorosilane organic solution and followed by ambient pressure drying?APD?.Without the essential solvent-exchange step that frequently employed in the traditional APD methods.The silica aerogel powders and granules synthesized by the PSI method possess specific surface areas up to 756.0 m²/g,thermal conductivity down to 0.0164 W/m·K,and variable densities from 47.6 to 120.0 g/cm³.Besides,the appearance of the silica aerogels could be well-controlled to be highly transparent powders or granules.In sum,the PSI method provide a simple method to synthesize high quality silica aerogel powders and granules in an economic way,and the aerogels may find valuable applications in thermal insulation,environmental remediation and adsorption,etc.?2?A PI foam/SiO₂ aerogel composite material was prepared by filling PI foam with SiO₂ aerogel.A series of PI/SiO₂ composite foams with different densities were prepared by adjusting the mass concentration of SiO₂ in the solution during the sol-gel process.Composite foam possess specific surface areas up to 725.6 m²/g,superhydrophobic,contact angle value up to 152.7°,density down to 0.036 g/cm³,and very low thermal conductivity,down to 0.017 W/m·K,also has good thermal stability.The most important thing is that the PI/SiO₂ composite foam synthesized by this method has excellent flame retardant and thermal insulation properties.The 2 cm thick composite foam can be burned under an alcohol lamp for 90 minutes or longer without burning,and can Isolate a lot of heat,and keep the original shape without shrinking.Therefore,PI/SiO₂ composite foam is a safe and excellent flame-retardant insulation material,which has great application prospects and potential in building insulation materials.