Preparation And Characterization Of Silica Aerogels With SoL-Gel Method By Ambient-dried Technique

In this thesis, silica aerogels were prepared by sol-gel method with ambient drying technique.The alcogels were made from tetraethoxysilane(TEOS), water and ethanol by means of one-step or similarity two-step respectively. At the same time, the effects of preparation conditions and procedures on the properties of products were investigated.The results show that the hydrofluoric acid(HF) is a effective catalyst for the gel formation, the more the HF, the shorter the gelation time. However, the gelation tune was decreased with the increase of water amount and increased with the increase of ethanol amount. At the same time, the density of silica aerogel was controlled by the amount of ethanol due to its filling in the free space. In the case of two-step method, the gelation time can be shortened greatly by increasing the amount of HF and NH₄OH; The optimal parameters for silica aerogel were determined that in the case of HF and NH₄OH(volume ratio 1:1) as catalysts, the volume ratios of ethanol and water to TEOS are 4 and 0.6 respectively.It was also found that the surface modification TMCS(trimethylchlorosilane) can effectively prevent aerogels framework from shrinkage during drying, and result in the formation of silica aerogels with hydrophobicity. The structure and some physical properties of aerogels synthesized were characterized by means of X-ray diffraction (XRD), scanning electron microscopy(SEM), specific surface area, transmission electron microscopy(TEM), FTIR. The results show that the synthesized silica aerogels are disorder and coherent non-crystalline silica with nano-sized and mesoporous pore structure. The maximum BET specific surface areas of silica aerogel obtained by optimizing preparation technology is 430m²/g.