Preparation Of Low Density High Thermal Insulation Silica Aerogels By Ambient Drying And The Study On The Structure The Properties

SiO₂aerogel is a kind of nano light porous materials with high specific surfacearea, low density, low thermal conductivity and low velocity. As the important methodfor SiO₂aerogel, ambient drying often cracks and break during drying withunsatisfactory property. The paper researched how to avoid pore collapse and gelcracks by the research on two-step sol-gel and gel aging. The objective is obtaining akind of SiO₂aerogel with low density and low thermal conductivity.The effect of ammonia concentration, hydrolysis time, sol pH value on the geltime, aerogel density have been studied within sol-gel. The result shows that, sol pHvalue on the gel time has great influence on SiO₂aerogel, in sol-gel process, theprocess of sol-gel was at last confirmed as: adjusting pH value to1², standing for24h, adjusting pH value to5⁶. Compared with one-step, two-step sol-gel make thepore more tinier, the constitution more loser, the density decreased55.1%, theconductivity decreased28.3%. The effect of aging time, exchanging time of solvent,the arrangement of aging procedure and the proportion of flux have been studiedwithin gel aging procedure. The result shows that, a different arrangement of agingprocedure has great influence on SiO₂aerogel. The process of gel aging procedurewas at last confirmed as: aging48h-exchanging solvent24h-aging48h-exchangingsolvent48h-surface modification12h, the proportion of flux isV（TEOS）:V（EtOH）=2:8.FT-IR, XRD, SEM and BET surface area have been studied to characterize phase,specific surface area, partical size, morphology and hydrophobic, heat insulationperformance of SiO₂aerogel. The result shows that: SiO₂aerogel was a kind ofamorphous material with desenty0.0903g/cm³, porosity95.9%, pore size9.35nm,partical size9.39nm, specific surface area635m²/g, thermal conductivity0.02103W/（m·k）. It appears white with bluish fluorescence and translucent; themicro-morphology shows that the SiO₂aerogel was composited by nanometer-gradegrain with a loose structure which was homogeneous diameter, and the FT-IR shows that there was-CH₃in surface, contact angle125°and well hydrophobicity. Besides,the thermal conductivity decrease with the density decrease.