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Research On Preparation And Application Of Hydrophobic Silica Aerogels By Ambient Pressure Drying

Posted on:2014-06-30Degree:MasterType:Thesis
Country:ChinaCandidate:J X WangFull Text:PDF
GTID:2251330422964620Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
As a kind of light, porous material, silica aerogels whose structures could becontrolled are playing an irreplaceable role in the field of optics, mechanics, acoustics aswell as calorifics due to its excellent properties, such as extremely low thermalconductivity, low bulk density, large surface area and high porosity. Aerogel is regardedas one kind of super thermal insulation materials which could be large-scalely used asbuilding materials in today whose theme is “Energy Saving and EnvironmentalProtection”. But, the high production cost and poor mechanical property have been thebottleneck of its application in the construction industry.The expanded perlite (EP), a kind of light porous material, which has a high porosityup to90%, attracts more and more attention because of its low price, excellent fireresistance and high mechanical strength. However, building thermal insulation materialsmade by EP have higher thermal conductivity than polystyrene board as well aspolyurethane material. We are thinking of mixing silica aerogels into EP to develop anovel low-cost building thermal insulation material which has both low thermalconductivity and good mechanical properties.In this paper, using water glass as precursor and hexmethyldisilazane (HMDZ) as asurface modifying agent, hydrophobic silica aerogels were synthesized successfully bythe one-step sol-gel method and ambient pressure drying. By analyzing experimentalresults of the proper comparative experiments, we obtained the optimum conditions ofthe experiment. The results showed that the required aerogels can be prepared when thevolume ratio of sodium silicate and water is1:16, pH is8.5, modified for24h. On thebasis of the optimal ratio, silica was mixed into EP successfully.XRD, SEM, TEM, BET absorption, and FI-IR analysis were used to research thephase, microstructure, structure and surface group. Also the thermal conductivity ofmixed expanded perlites were tested by thermal conductivity tester. Tests revealed that silica aerogels what we made have good hydrophobic property whose contact angle is101.4°, specific surface area is625.6m2/g, mean pore diameter is10~20nm, particlediameter is about10nm; The thermal conductivity of mixed expanded perlites are only0.0331W/m.K, which reduce about10%compared to the original perlites.
Keywords/Search Tags:silica aerogels, ambient drying, hydrophobic modification, expanded perlite, mixture, building thermal insulation material
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