Fabrication of Boehmite Nanofiber Aerogels by a Phosphate Gelation Process for Optical Applications

A transparent wet gel was obtained in a few minutes at room temperature by adding an aqueous phosphoric acid solution of appropriate concentration to boehmite nanofiber sol. After room temperature aging and supercritical carbon dioxide drying, low bulk density aerogels with visible light transmittance of over 90 % at 10 mm thickness were obtained. These aerogels exhibited superior mechanical properties and visible light transmittance, while having the same bulk density as the samples obtained by a conventional gelation process using a base. The optical properties of the aerogel were hardly lost even at high humidity because the phosphorylation of the skeletal surface reduced the percentage of hydroxyl groups. The three-dimensional imaging inspection of the exterior and interior of the aerogel and the laser processing method were also demonstrated. The various developments reported in this paper make aerogels with ultralow bulk density and high visible light transmission even more promising for applications in the physical field.