Mechanical Properties of Metal Oxide Aerogels

In this study we report on mechanical properties of molded, single component Al₂O₃, Ga₂O₃, Fe₂O₃, and ZrO₂ as well as mixed aerogels, made from yttrium stabilized zirconia, yttrium aluminum garnet, and zinc aluminum spinel. Initially all aerogels were produced equally in molded bodies by a facile epoxy method and were annealed afterward at 300 °C. Then we performed uniaxial pressure tests on cylindrical aerogel monoliths to gain Young's modulus which depends on composition, density, and post-treatment. Already pure aerogels like ZrO₂ show well-promising Young's modulus of 10.7 MPa, whereas most popular SiO₂ materials display a modulus between 2 and 3 MPa at comparable densities. Moreover we focused on Al₂O₃ aerogels which exhibit high stability and interesting densification behavior depending on the annealing temperature. On the basis of this observation, we combined the toughness of the Al₂O₃ scaffold with the extraordinary hardness of ZrO₂, by adding up to 20 atom % Zr, to increase the specific Young's modulus. For the mixed material with a Zr content of 20 atom %, we reach a record value for compressible aerogels of 125 MPa mL g^-1.