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Preparation Of High Surface Aera And Low Density Silica Aerogels By Ambient Pressure Drying

Posted on:2013-08-10Degree:MasterType:Thesis
Country:ChinaCandidate:Y N LvFull Text:PDF
GTID:2231330392457463Subject:Materials science
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Silica aerogels are light mesoporous materials with low density, high sueface aera,high porosity and low thermal conductivity whose structure could be controlled. Theseproperities make silica aerogels be widely used in themal insulation, acoustic impedancecoupling, water treatment as well as catalyst and catalyst carrier. Aerogels made bytraditional method have many water absorption groups. These groups make it easy to burstin the air which affects its performance greatly. Also it will greatly improves the cost ofsilica aerogels by supercritical drying which is bad for its large-scale production.In this paper, using tetraethylorthosilicate(TEOS) as precursor as well ashexmethyldisilazane(HMDZ) as a suface modifying agent, silica aerogels weresynthesized by the two-step sol-gel method and ambient pressure drying which solve theproblem that the silica aerogels are easy to broken in the air as well as reduce the cost ofsilica aerogels.At the same time, this paper discussed the silica aerogels’ mixing with othermaterials. In the sol-gel process, the orthogonal experiment was designed by using fourfactors and three levels to research the influence on performance by different factors, aswell as the optimal proportion was confirmed from the experiment, Viz. the molar ratio ofTEOS and H2O is1:4, the molar ratio of TEOS and EtOH is1:6. In the best condition,nano Ag and nano Au were mixed in the wet gel to enhance the strength of silicaaerogels.As well as silica was mixed in the cellular materials to keep the sameheatshielding performance and reduce the cost.The FI-IR, SEM, TEM, BET absorption, XRD and DTA-TG analysis were used toresearch the surface group, microstructure, structure and thermal stability. The resultsshow that silica aerogels made by surface modification has good hydrophobic propertywhose contact angle is139.4°, surface area is952m2/g, mean pore diameter is5~10nm,porosity is94.2%, the heat decomposed temperature is300℃and density is only0.127g/cm3. The heat decomposed temperature of silica aerogels mixing with nano Ag and nanoAu is400℃, better than unmixed silica. While mixing silica aerogel in the cellular materials improved there heat stability as well as reduced the cost.
Keywords/Search Tags:silica aerogels, ambient drying, hydrophobic modification, mixture
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