Preparation And Characterization Of Hydrophobic Silica Aerogels At Ambient Pressure

Recently, silica aerogels are the lightest solid material. The silica aerogels have many unique properties owing to their special structure, such as they have the best properties in thermal insulation, the lowest sound velocities and have the higher porosity in all solid materials and so on. So they have many extensive applied values.The influences of each factor on their different properties had been studied in this dissertation. The orthogonal experiment was designed by using four factors and three levels, selecting two methods: one-step sol-gel and two-step sol-gel to study their optimal prepared conditions. But the key of shrinkage and crack when drying at ambient pressure was the preparation of hydrophobic silica aerogels. Hydrophobic modification had been studied by two methods: co-precursor and derivatization methods.The results showed that the properties of silica aerogels which produced by two-step sol-gel method were better than those produced by one-step sol-gel method. The properties of the samples which were modified by derivatization method were better than those modified by co-precursor method, and those were more suitable to be dryed under ambient pressure.In this dissertation hydrophobic silica aerogels had been prepared by two-step sol-gel method with trimethylchlorosilane(TMCS) as the structural surface chemical modification via derivatization method. The XRD,SEM, ED, TEM,IR and DTA-TG analysis were used to observe the structure, the surface morphology and the chemical composites of the samples. The results showed that the samples were non-crystallized, porous and light nanometer materials with higher thermal stability and higher specific surface area. And their average density was 134.3 kg·cm^3-, BET specific surface area was 729 m²Â·g^-1, porosity was 99% approximately, average pore diameter was 10nm. The obtained samples had higher purity. The particles which constituted the continual net structure of aerogels were spherical with average diameter 5nm, and the particles dispersed evenly. The IR, DTA-TG spectrogram and contact angle(120°) had indicated that the hydrophobic group methyl had substituted hydrophilic group hydroxyl on the structure and surface of aerogels modified by TMCS. The preparation of bulk hydrophilic silica aerogels dried at ambient pressure had been realized.