扩孔剂对SiO_2气凝胶微观结构与性能的影响

Effect of the Pore-expanding Agents on the Microstructure and Performances of SiO_2 Aerogel

以正硅酸乙酯为硅源,乙醇为溶剂,在溶胶-凝胶法和CO_2超临界干燥的基础上,采用分别加入聚乙二醇(400)、六次甲基四胺和尿素作为扩孔剂的方法制备低密度SiO_2气凝胶。利用扫描电镜(SEM)、傅里叶变换红外光谱仪(FT-IR)、孔径分布及比表面积测试仪(BET)、纳米压痕仪对未加扩孔剂和加入不同扩孔剂所制备的SiO_2气凝胶的表面形貌、结构、比表面积、孔径分布、力学性能以及密度进行研究。结果发现:随着增加扩孔剂的加入量,SiO_2气凝胶的密度明显降低;与未加扩孔剂的样品相比,加入扩孔剂所制备的SiO_2气凝胶的比表面积和孔径增大;其中,六次甲基四胺具有较佳的扩孔效果,制备得到的SiO_2气凝胶的性能较佳,孔径分布主要集中在15~55nm,平均孔径为35.4nm,比表面积高达1006m^2·g^(-1),孔体积为5.3cm^3·g^(-1),孔隙率高达96.2%。

Combining with a sol-gel method and a CO2 supercritical drying technique, the silica aerogels with low density were prepared from ethyl orthosilicate as the silica source and ethyl alcohol as the solvent by adding the pore-expanding agent of polyethylene glycol （400）, hexamethylenetetramine or carbamide. The surface morphology, microstructure, specific surface area, pore size distribution, mechanical properties and density of silica aerogels without and with different pore-expanding agents were characterized by SEM, FT-IR, BET and nano indentation techniques. It was found that the density of SiO2 aerogels obviously decreased with increasing the content of the pore-expanding agent. Comparing with the SiO2 aerogel without pore-expanding agent, the specific surface area and the pore size of the SiO2 aerogels with the pore-expanding agent enlarged. Especially, hexamethylenetetramine brought out the better pore-expanding effects. And the as-prepared SiO2 aerogel had the superior properties, the pore size distribution of 15-55 nm, the average pore size of 35.4 nm, the specific surface area of 1006 m2· g^-1, the pore volume of 5.3 cm3 · g^-1 and the porosity of 96.2%.