| With the development of industrial technology, it is difficult for the traditional insulationmaterials to meet the requirements of social development. Silica Aerogels is a heat insulatingmaterial with the nanoporous network structure, whose density is0.003~0.5g/cm3, thermalconductivity is less than0.02W/(m.k), and a high porosity of80%~99%, so it is a newpromising super insulation material. Preparation of Silica Aerogels by ambient drying is themain means for the mass industrialized preparation, however, the unstable process and theresulting large amounts of organic waste cause a high cost, difficult to be competitive in themarket. This paper aims to find out the means of the process optimization for the preparationof Silica Aerogels in the stable state and the waste recycling for high-performance SilicaAerogels. Besides, the paper also uses a variety of analytical tools to test the microstructure ofthe Aerogels, phase structure, specific surface area and pore size distribution, hydrophobicity,and insulation.Water glass is used as silicon source for Silica Aerogels preparation. This paper choosesfive types of maturing process to carry the comparative experiments, designs different agingtime and solvent exchanging time to show the influence of Silica Aerogels preparation, anduses absolute ethyl ethanol to help aging avoid the thick network skeleton; meanwhile,absolute ethyl ethanol’s locking water effect can replace the water in the wet gel networkpores, thereby reduces the capillary forces in the drying process. The tap density of theprepared Silica Aerogels is0.073g/cm3. After the surface modification, increasing the3dsolvent exchange can further reduce the tap density to0.069g/cm3, but will cause a sharpcost increase. Using the aging process3in this paper to magnify the experiment25times canexactly-once steadily prepare the Silica Aerogels with a tap density of0.0736g/cm3. Theadsorption experiment has been conducted and proved that experimental prove SilicaAerogels’s adsorption capacity on oily substance is30times to its quality. The paper also usesthe double glass model to the relations between Silica Aerogels’s tap density and thermalconductivity coefficient, finding that when the tap density ρ＞0.1g/cm3, the coefficient willdecline sharply with the decrease of tap density; when the tap density ρ＜0.1g/cm3, its impacton the coefficient will drop.Aging waste liquid is used as silicon source to recycle and purify n-hexane for high-performance Silica Aerogels preparation. Add40%ethanol to the recycling waste, use1.5%dry chemical control agent formamide to determine the gel system, and then hydrolyze for 24h, use1mol/L ammonia to do base-catalysis and adjust PH to6; Use the recycling n-hexanepurified by the combination of phase separation and distillation to do solvent exchange withwet gel, the resulting Silica Aerogels’s tap density is0.0795g/cm3, increasing8.9%comparedwith Silica Aerogels prepared by using water glass as silicon source to do solvent exchangewith new n-hexane, of which the tap density is0.0736g/cm3, but reducing the costdramatically and avoiding the wasting of resources and environmental pollution.Analyzing and testing tools including spectroscopy, SEM, BET specific surface area areused to characterize the phase structure, morphology, specific surface area, hydrophobicity,and the insulation of Silica Aerogels typical sample, which are prepared by using aging wasteliquid and purifying waste n-hexane. The results show that: the tap density of the typicalsample is0.0759g/cm3, the porosity is94.5%, specific surface area is571m2/g, average porediameter is20.20nm, and the thermal coefficient is0.02403W/(m·K), hydrophobic contactangle is141°; the morphology shows that Silica Aerogels consists of large number ofnanoscale particles which are small and homogeneous, and the pore distribution is alsohomogeneous. |
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