The Study On Synthesis And Preparation Of SiO₂ Aerogel

SiO₂ aerogel is a kind of non-crystal solid material with nano-holes network structure,low density, high porosity and great surface area,and widely used in lots of fields. It is a great significance to search the method and conditions of manufacturing SiO₂ aerogel.Tetraethyoxysilane (TEOS) as the source of silicon, hydrochloric acid as acid catalyst, ethanolamines or theirs aqueous solutions as basic catalysts, SiO₂ aerogel was prepared by sol-gel technique and dried under the conditions of negative pressure and temperature programmed in this thesis. The samples of SiO₂ aerogels obtained were investigated by the porosity, BET, FTIR, SEM, TEM and XRD. Comparing with the samples which were synthesized by the basic catalysts of ammonia, the effects of the concentrations, proportions of the ethanolamines on the performances of SiO₂ aerogels have been analyzed and discussed. The results showed that the catalytic abilities of ethanolamines catalysts were mono-ethanolamines (MET) > di-ethanolamines (DEA) > tri-ethanolamines (TEA); the appropriate rates of ethanolamines /TEOS (mol/mol) were 1.7×10-2, 1.7×10-2, 5.1×10-2 respectively, and the optimal concentrations of ethanolamines aqueous solutions were TEOS/water (v/v) = 1:20, 1:5, 1:2 respectively.In order to search the best process conditions to prepare SiO₂ aerogel, according to above steps and conditions, experiments were carried out for the effects of seven factors such as the amount of solvent, water, acid, stirred time, aging time and the dried pressure on performances of SiO₂ aerogels, respectively using MEA aqueous solution (v/v=1:20) and DEA aqueous solution (v/v=1:5) as the basic catalyst. The results demonstrated the best conditions to prepare SiO₂ aerogels were: TEOS: alcohol: water (mol/mol/mol)=1:4⁵:4⁶; basic catalyst: acid catalyst: TEOS (mmol/ mmol/mol) = 17.3:5.3:1; the stirred time 3 hours; aging time 2³ days; aging temperature 50⁷0℃and dried pressure was a degree of vaccum of 60⁸0kPa.A series experiments were conducted to decrease the cost further and kept the SiO₂ aerogel with better performance. the SiO₂ aerogel which were prepared by adding the drying control chemical additives (DCCA), aging with different aging additives and modifying surface were tested by porosity,BET and FTIR. The results demonstrated: the glycol did not take evidence effect in improveing the performance of SiO₂ aerogel; it was better to prepare SiO₂ aerogel by using H2O: TEA (v/v)=60:1 as aging additives; by surface modifying, the SiO₂ aerogels prepared possess better structure.