【作者】 周小春；

【导师】 魏坤；

【作者基本信息】 南昌大学 ， 无机化学， 2005， 硕士

【摘要】 本文以正硅酸乙酯（TEOS）为原料,乙醇和水为溶剂,分别采用一步法和类似“两步法”的溶胶一凝胶技术,通过常压干燥,制备了轻质多孔SiO₂气凝胶,同时开展了工艺条件对溶胶一凝胶化过程和产物性能的影响。 实验结果表明:对溶胶的形成来说,氢氟酸是一种有效地催化剂,其用量越大,凝胶化时间就越短;不同的用水量对凝胶化时间有一定的影响;乙醇用量的增大会引起凝胶化时间变大,乙醇原则上不参加反应,它只在网络孔道中占据一定体积;因而可以通过改变乙醇的量来控制二氧化硅气凝胶的密度。在类似“两步法”中,通过同时使用的氢氟酸和氨水,凝胶化时间更短,其最佳条件是无水乙醇和水与正硅酸四乙酯的体积比各自是4和0.6,同时加入氢氟酸和氨水的体积比为1:1时,获得的比表面积最大。 此外还研究了不同的老化条件以及表面活性剂对SiO₂气凝胶制备的影响。在研究三甲基氯硅烷（TMCS）表面化学改性SiO₂机理时发现,TMCS能有效地防止了常压干燥过程中气凝胶骨架的收缩或坍塌,使得到的SiO₂气凝胶成为憎水性的产品。最后用X射线衍射分析（XRD）、扫描电镜（SEM）、比表面与粒度分析、红外光谱分析、热重分析和差热分析等手段对合成的二氧化硅气凝胶产品结构和性能进行了表征。结果表明它们的组成基本上是无序的连续网络多孔结构非晶态SiO₂。比表面积测定仪测试表明,优化制备工艺后的气凝胶产品的BET比表面积最大为430m²/g。更多还原

【Abstract】 In this thesis, silica aerogels were prepared by sol-gel method with ambient drying technique.The alcogels were made from tetraethoxysilane（TEOS）, water and ethanol by means of one-step or similarity two-step respectively. At the same time, the effects of preparation conditions and procedures on the properties of products were investigated.The results show that the hydrofluoric acid（HF） is a effective catalyst for the gel formation, the more the HF, the shorter the gelation time. However, the gelation tune was decreased with the increase of water amount and increased with the increase of ethanol amount. At the same time, the density of silica aerogel was controlled by the amount of ethanol due to its filling in the free space. In the case of two-step method, the gelation time can be shortened greatly by increasing the amount of HF and NH₄OH; The optimal parameters for silica aerogel were determined that in the case of HF and NH₄OH（volume ratio 1:1） as catalysts, the volume ratios of ethanol and water to TEOS are 4 and 0.6 respectively.It was also found that the surface modification TMCS（trimethylchlorosilane） can effectively prevent aerogels framework from shrinkage during drying, and result in the formation of silica aerogels with hydrophobicity. The structure and some physical properties of aerogels synthesized were characterized by means of X-ray diffraction （XRD）, scanning electron microscopy（SEM）, specific surface area, transmission electron microscopy（TEM）, FTIR. The results show that the synthesized silica aerogels are disorder and coherent non-crystalline silica with nano-sized and mesoporous pore structure. The maximum BET specific surface areas of silica aerogel obtained by optimizing preparation technology is 430m²/g.更多还原