Abstract: 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/cm³ to 160 mg/cm³. 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.

Key words: sol-co-gelation, continuous aerogel, graded density, layer-by-layer gelation, interdiffusion