关键词: 气凝胶, 非超临界干燥, SiO₂, 制备, 形成过程

Abstract: The preparation of monolithic silica aerogels via non-supercritical drying is realized by the following procedures:(1) formation of silica alcogels with perfect network structure by controlling two-step hydrolysis and condensation reaction rates of tetraethoxysilane； (2) improvement and reinforcement of network structure and strength of silica gels through exchanging the pore fluid with ethanol solvent thoroughly, immersing of gels in the ethanol solutions of tetraethyoxysilane and aging; (3) gradual drying under ethanol fluid whose surface tension is much lower than water under ambient pressure. The resulting aerogels were characterized by means of SEM， TEM, TG-DTA, XRD, and adsorption-desorption techniques. It is found that the aerogels, which are made up of uniform spherical nanoparticles with diameters of about 10 nm, are of coherent network structures. Furthermore, the aerogels are porous, and the porosity is as high as 91％. The diameter of the pore sizes is in the range of 10～30 nm, and the density of the aerogels is low（200～400 kg•m－3）. The specific surface area of the aerogels can be as high as 625.65 m2•g－1. The appearance， microstructure，diameters of primary particles and pore size distributions of the aerogels are in concordance with those prepared by conventional supercritical drying. It is demonstrated that the quality of the resulting aerogels is affected by the preparation conditions adopted in the preparation process. In fact, by adjusting the proportions of the reaction systems， and controlling the adding amounts of acid and base during the two-step hydrolysis and condensation process，silica aerogels with required density， definite strength and ideal morphology can be produced.

Key words: Aerogels, Non-supercritical drying, SiO₂, Preparation, Formation process