| Aerogels are high dispersive solid materials which consist of colloid particles or high polymer molecule and have continuous random network structure filling with gaseous dispersive medium. According to their low densities, low refractive indices, small pore sizes, and good transparencies, Much attention have been given to the aerogels for use in several applications:catalyst supprot, thermal insulators, Cherenkov detectors, monolithic, capacitors and cosmic dust capture etc.Silica aerogels, TiO2/SiO2 aerogels and Fiber/SiO2 were synthesized by two-step sol-gel polymerization of tetraethoxysilane (TEOS) in alcohol and using ambient pressure drying with ternary azeotropes as components of pore fluid. The physical properties such as density, appearance, hydrophobicity, surface area, pore size distribution and thermal stability were measured. According to the data of absorption-desorption experimental and Small Angle X-ray Scattering, the surface fractal of silica serogels and the composites were studied.The wet gels were synthesized via acid-base catalysis using tetraethyl orthosilicate as silica precursor and alcohol as solvent. The molar rate of TEOS, alcohol and water is 1:4:6. Alcohol was exchanged by n-butanol, and the gel surface was modified by a mixture mixed by n-butanol and trimethylchlorosilane (TMCS).Then the solvent was exchanged by several steps by saturated hydrocarbon, so as to obtain the pore fluids which contain azeotropic mixtures such as water, n-butanol and hexane. Ambient pressure drying was performed in two steps, at the boiling points of the ternary azeotropes (60℃)and the hydrocarbons(80℃), respectively.The structure and physical properties of these aerogels were investigated by several experimental methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM),thermo-gravimetric and differential scanning calorimetry (TG-DSC), Fourier transform infrared spectroscopy (FTIR), specific surface area analyzer,pore size analyzer and so on. The result shows that silica aerogels are coherent, amorphous form, hydrophobic and nanosized porous solids. And its high specific surface achieves 838.6 m2/g.Titania-silica aerogels with different Titania content were prepared. Two preparation methods differing mainly in approach to precursor hydrolysis were applied. The high specific surface area is obtained by adding TiO2 powder, and the maximal one is 1107.38 m2/g while the content of it is 15wt%. While adding tetraisopropyl orthotitanate as one of precursor, the specific surface area is sharp decline and the N2 adsorption and desorption experiment shows that there are a lot of micropores (<2nm). Methyl orange photocatalytic experimental result shows that:photodegradation rate of Methyl Orange is higher by TiO2 powder mixed in SiO2 aerogels than pure TiO2 powder, and when the content of TiO2 powder accounts for 15wt%, the best photocatalytic properties appears. Compare the photocatalytic experiment using TiO2 and TiO2/SiO2 as catalyst. It's easy to know that when mixed in the SiO2 aerogels, the catalytic of TiO2 is mucher better.Fiber/SiO2 aerogels with maximal diameter 103mm were synthesized using two different methods:the first one is adding fibers in precursors while the second one is dipping fiber's preformed units in the SiO2 sol. The characteristic of SiO2 aerogels haven't changed because of the adding of the fibers. When the content of fiber was 20%, the pore volume was similar to pure SiO2. Nitrogen adsorption and desorption isotherms indicated that the composite material had a big adsorptive capacity and pore volume.The results of SAXS shows that at low q-domain, the scattering intensity of SiO2 aerogels was low, because of heat treatment, the particles of SiO2 became bigger. While the the scattering intensity of SiO2 aerogels prepared in airproof reactor was higher. It also shows that the SAXS profiles do not agree with Porod's law and have positive slopes, suggesting that the dispersive interfacial layer exists between sol particle and dispersing agent. The three kinds of silica aerogels prepared in airproof reactor,ambient pressure, and heat treated at 400℃have different surface fractal dimension Ds at high scattering intensity region, the surface fractal dimension Ds were 2.65,2.48 and 2.11 respectively. And all of the three has have different mass fractal dimension Dm at low scattering intensity region, the mass fractal dimension Dm were 2.23,2.36 and 2.43 respectively. The results of N2 adsorption and desorption shows that the surface fractal dimension Ds of pure silica aerogels and composites were between 2.4-2.9. The Ds of fiber/SiO2 and pure silica aerogels were uniform, so their structures were very similar. The silica aerogels by adding tetrabutyl titanate have complicated surface, whose fractal dimension were between 2.6 and 2.9. The results from SAXS and N2 adsorption and desorption were so uniform, it indicated that the results were believable.
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