硅酸钠模数对SiO_(2)气凝胶结构和表面改性机制的影响

Effect of Sodium Silicate Modulus on Structure and Surface Modification Mechanism of SiO_(2) Aerogel

以粉煤灰为原料制备五种不同浓度的硅酸钠溶液,采用溶胶-凝胶法对硅酸钠溶液进行处理,在常压干燥条件下获得了疏水性SiO_(2)气凝胶。通过测试气凝胶的密度、比表面积和接触角,研究了硅酸钠溶液模数m对气凝胶结构的影响,阐述了气凝胶表面疏水改性的亲核取代S_(N)1化学反应机制。研究结果表明,气凝胶的疏水性能与其表面连接的硅甲基—Si—(CH_(3))_(3)数目有直接关系,当硅酸钠模数m=2.50时,气凝胶的疏水性能最佳。气凝胶的密度和比表面积均随硅酸钠模数的增大而增大,当硅酸钠模数m=0.75时,气凝胶的密度和比表面积最小,其值分别为0.0739 g/cm^(3)和588.5 m^(2)/g。

Five different concentrations of sodium silicate solutions were prepared from fly ash.The sodium silicate solutions were treated by sol-gel method,and hydrophobic SiO_(2) aerogel was obtained via ambient pressure drying.The influence of sodium silicate modulus on the structure of aerogels was investigated through measurements of density,specific surface area and contact angle.The chemical reaction mechanism of nucleophilic substitution S_(N)1 for hydrophobic modification of aerogel surface was proposed.The results show that the hydrophobic performance of aerogel is directly related to the number of—Si—(CH_(3))_(3) attached to the surface.When sodium silicate modulus is equal to 2.50,the best hydrophobic performance of aerogel is achieved.The density and specific surface area of aerogel increase with the increase of sodium silicate modulus.When the sodium silicate modulus is equal to 0.75,the lowest density and specific surface area of aerogel are recorded,which are 0.0739 g/cm^(3) and 588.5 m^(2)/g,respectively.