The Effects Of Co-precursor、Aging Conditions And Ultrasonic On The Structures And Properties Of SiO₂Aerogels

ABSTRACT:In this dissertation, light-weight porous silica aerogels are made from TEOS and MTMS as a co-precursor and TEOS as a single precursor respectively, water and ethanol as solvent, hydrochloric acid and ammonia water as acid-base catalyst by two-step sol-gel process and ambient drying method. FTIR, SEM, BET, gelation time measurements and density measurements were used to characterize aerogels. The effect of the molar content of MTMS, the molar ratio of water/co-precursor, the molar ratio of EtOH/co-precursor and ammonia concentration on the sol-gel process and the properties of aerogels which were made from TEOS and MTMS as a co-precursor were investigated.The effect of aging condition on the properties of aerogels which were made from TEOS as a single precursor were investigated.The aging mechanism which SiO2gels were aged in TEOS as the aging solution was investigated.In the system which silica aerogels were made from TEOS and MTMS as a co-precursor by ambient drying method, the silica aerogels prepared with a molar ratio of co-precursor, H2O, EtOH, HC1, NH4OH constant at1:4:6:1.8×10-3:0.144and molar content of MTMS at60%possessed the best properties. The density, specific surface area, pore volume and average pore diameter were0.15g·cm-3,944m2·g-1,2.264cm3·g-1and9.592nm, the contact angle was143°In the system which silica aerogels were made from TEOS as a single precursor by ambient drying method, when used H2O/EtOH solution as the aging solution, the best aging condition were:aging time was24h, aging temperature was50℃, the water content of aging solution was60%,the prepared silica aerogels possessed the best properties. The density, specific surface area, pore volume and average pore diameter of SiO2aerogels were0.16g/cm3,940m2/g,2.227cm3/g,9.423nm. when used TEOS/EtOH solution as the aging solution, the best aging condition were:aging time was24h, aging temperature was50℃, the TEOS content of aging solution was60%, the prepared silica aerogels possessed the best properties. The density, specific surface area, pore volume and average pore diameter of SiO2aerogels were0.152g/cm3,950m2/g,2.264cm3/g,9.566nm.In the process of sol preparation, when ultrasonic time and ultrasonic power were5h and100w respectively, the prepared silica aerogels possessed the best properties, the specific surface area, pore volume and average pore diameter of SiO2aerogels were922m2/g,2.23cm/g,9.41nm respectively.In the process of gel, when ultrasonic time and ultrasonic power were10min and60w respectively, the prepared silica aerogels possessed the best properties.the specific surface area, pore volume and average pore diameter of SiO2aerogels were937m2/g,2.283cm3/g,9.36nm respectively.