| 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. Because of their nano-size particles and porous distribution, aerogels have lots of particular application especially as superinsulation materials. The gel is called xerogel by using non-supercritical drying. In this paper, silica and silica-alumina binary xerogels were prepared through sol-gel and ambient pressure drying.In the course of sol-gel, two-step acid-base catalyzed silica gels were prepared by using of tetraethoxysiliane (TEOS) as precursor, absolute alcohol as solvent, 0.2mol/L hydrochloric acid (diluting with absolute ethanol) and ammonia as acid and base catalyzer respectively. According to actual experiment and combining theory with former experience, the parameters are confirmed: hydrolyzation and condensation temperature is 50℃, the hydrolysis time is 10min under acid solution, the aging solution is 70 vol.% TEOS/ethanol mixing solution and alcogel is dipped three times in 24h at 50℃, cyclohexane or normal heptane is chosen as exchanging solvent and drying is in atmospheric pressure. An orthogonal array (OA) design OA9(34) was applied to select the optimum conditions of additives. The results show that the most optimal molar ratio of TEOS, H2O, alcohol, hydrochloric acid and ammonia is 1: 4: 10: 7.5×10-4: 0.0375.The influence for the sol-gel course of silica xerogels between one-step hydrofluoric acid and two-step acid-base was investigated comparatively and the catalysis among Fˉ, Clˉand OHˉanion was analyzed. Silica xerogels are porous and cluster-cluster network structure consisting of nano-size particles. After heat treatment, grains of silica xerogels grow at the same time the pores reduce. The materials which are amorphous structure made up of Si?O?Si short bonds form shrink, become stiff and compact at 1200℃. The specific surface area is up to 720.83m2/g and pore distribution is relatively narrow by the two-step acid-base catalyze. The porous structure is better than that of one-step acid catalyze. The ratio of shrinkage is high which predicates specific surface area and porosity can...
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