The Preparation And Characterization Of Low-Density Silica Aerogels And Spherical Products

SiO₂ aerogels, as a kind of controllable nanoporous materials with low density, are used as target materials and supporting layer materials in ICF experiments. In this paper, we prepared SiO₂ aerogels sphere used ethylsilicate?TEOS? as silicon source, combined with sol-gel technology, followed by the ambient pressure and carbon dioxide supercritical drying for optimized process parameters. We obtained cm-level SiO₂ aerogels sphere via designing molds, injection molding by gel forming process and CO₂ supercritical drying technology. The phase, hydrophobic, shrinkage rate, microstructure, thermal stability, structure and properties of aerogels were characterized.The optimum mole ratio of H₂O/TEOS and Et OH/TEOS obtained by the ambient pressure drying method are 4 and 8. The optimum p H value is 6.6-7.5. In derivative method of surface modification, the aerogel modified by MTES/VTES has lowest density?0.203 g·cm-3?, the great hydrophobic property?152.02 °?, more loose structure, and specific surface area?889.2 m2·g-1?. In situ modification method, when the MTES/TEOS is 1.0 the aerogel has largest hydrophobic angle?153.62 °?, and the lowest density?0.186 g·cm-3?.SiO₂ aerogels were prepared by CO₂ supercritical drying, choosing the smaller surface tension solvents mixed with Et OH for exchange. We draw the conclusion that the performance of SiO₂ aerogel drying in mixing medium were obviously better than drying in ethanol medium. The aerogels obtained by the ethanol/n-hexane and ethanol/acetone as the solvent have good mechanical properties and low density. Aging temperature has an effect on the structure and mechanical properties of SiO₂ aerogel. At 5 ? of preparation, the aerogel is complete, and low density?0.180 g·cm-3?.We designed mold, and prepared wet gel ball by gelcasting. We discuss the effects of time and temperature on the volume shrinkage rate. Hydrophobic silica aerogel balls??6 cm? were prepared using MTES/TEOS co-precursor with different molar ratio?I? by sol-gel process and molding technology followed by the CO₂ supercritical drying. Hydrophobic property increased with the increase in I value, and silica aerogels at I = 0.8 have a superhydrophobic characterization with highest contact angle?152°?. When I is 0.8, the obtained aerogel sphere has better properties, which are less crack, little shrinking percentage?17 %?, low apparent density?0.103 g·cm-3?, large surface area?996.3 m2·g-1?.This paper put forward the new drying method. Centimetre-sized mesoporous SiO₂ aerogel spheres??4 cm? are synthesized via a rapid and one-step aging/solvent exchange method at 2 MPa using DMSO-CO₂ as solvent. The sphere with satisfactory performance is manufactured at 4 ?. It has a typical three-dimensional porous structure with pore diameter about 25.4 nm, minimum bulk density 0.12 g·cm-3 and specific surface area as high as 1078 m2·g-1.