中文摘要：

针对气凝胶在航空航天领域的应用需求，为了进一步拓展单一密度气凝胶的应用范围，对密度梯度SiO2气凝胶的制备进行了研究。采用自建密度梯度制备成型装置，以正硅酸乙酯为有机硅源，经溶胶共凝工艺，结合CO2超临界干燥技术，获得密度范围在60～160mg／cm^3的准连续密度梯度SiO2气凝胶。采用光学显微镜、扫描电子显微镜、X射线相衬成像等手段对制备获得的SiO2气凝胶进行测试表征。通过与逐层凝胶法制备的密度渐变SiO2气凝胶进行对比发现，溶胶共凝工艺消除了层间界面处所产生的致密层和密度突变，有利于相邻两层间的互扩散，使密度变化更趋于连续。采用该法制备的密度梯度气凝胶拓展了常规气凝胶的应用范围，在声阻抗匹配和空间粒子捕获等领域有潜在的应用前景。

英文摘要：

For the application requirement in aerospace and further expanding the application field of aerogel, the fabrication of gradient density aerogel SiO2 has been researched in this paper. By a self-built device, a continuously graded silica aerogel is fabricated via special sol-co-gelation techniques, with tetraethoxysilane （TEOS） as the organic precursor and by a supercritical drying process. Its density ranges from 60 mg/cm^3 to 160 mg/cm^3. Scan electron microscope, X-ray phase contrast method and optical microscopy are used to characterize the graded density silica aerogel prepared. Compared with the graded density silica aerogel produced by layer-by-layer gelation techniques, the sol-co-gelation techniques smooth out density mutation and increase the interdiffusion between adjacent layers, which makes density change tend to be more continuous. The gradient density aerogel fabricated by such a method expands greatly the application of conditional aerogel. It can potentially be used in many fields such as acoustic impedance matching and interstellar particles collection.