Preparation And Characterization Of Organic-Inorganic Hybrid Silica Aerogel

RnSiX4-n (R is alkyl or phenyl, X is Cl or alkoxy, n=0-3) type organic silane, such as methyltrimethoxysilane (MTMS, H3C-Si-(OCH3)3), tetraethoxysilane (TEOS, Si-(OC2H5)4) were chosen as precursor or modifying agent to synthetic a series of nano porous amorphous silica aerogel, and the silica aerogel was organic hybrid processing.Methods of acid-base two-step catalytic sol-gel method, surface graft modification, solvent replacement and special drying etc were carried out to synthetic nano porous silica aerogel under ambient pressure with RnSiX4_n precursors. With acid-base two-step catalytic sol-gel method to control the hydrolysis and condensation reaction to obtain more homogeneous gel network, aging treatment to make "bridge" in the gel network more solid, modified organic surface treatment makes the gel surface hydrophobization, solvent displacement decreases gel surface gas liquid volatilization capillary pressure, special drying means weaken capillary pressure in the process of solvent evaporation, by these means, using TEOS as silicon source, transparent porous silica aerogel was prepared. By introducing MTMS as hybrid silicon source modifier, hydrophobic gel surface with methyl was obtained and this method has the same effect with surface modification. The silica gel surface grafting polyurethane can enhance strength of gel network, by this method yellow transparent monolithic silica aerogel was prepared under the condition of atmospheric drying. Microstructure of aerogel was studied by scanning electron microscopy and nitrogen adsorption/desorption tests, found its porous nanometer structure of aerogels and very large specific surface area. By thermogravimetric analysis and flame retardant test, heat resistant and flame retardant ability of the aerogel were studied, the results showed that the aerogel has good heat resistance and flame retardant performance. In addition, the paper also useed gas chromatography to study the kinetics of hydrolysis process for various types of organic silicon source. Research results showed that the higher concentration of the acid catalyst, higher hydrolysis temperature shorten the hydrolysis time. The order of hydrolysis rate is MTMS, TEOS.Monolithic silica aerogels were prepared via supercritical fluid drying of methanol gels, which were obtained using the sol-gel co-precursor method with MTMS and TEOS as precursors, methanol as solvent, oxalic acid and ammonia as catalysts. The microstructure, specific surface area, pore size distribution, bending and compressibility, and thermal stability of silica aerogels were studied by scanning electron microscopy, nitrogen adsorption/desorption tests, and thermogravimetric analysis. The properties of the silica aerogels, prepared with different mole ratios of MTMS/TEOS, varied obviously. The silica aerogel, prepared with mole ratio of MTMS/TEOS at8/1, was a flexible material with density of0.11g·cm-3, porosity of94.2%, specific surface area of693.3m2·g-1,maximal bending angle of92°, maximal compression ratio of41.2%and compression spring-back of100%.In addition, the paper also studied the impact of TEOS, surfactant and the concentration of acid and alkali, silicon alcohol ratio on the micro structure of the silica aerogel, studies showed that TEOS can effectively build silica aerogel network. The decrease of the acid concentration concentration or the rise of alkali concentration can make network of silica aerogel more uniform.