Synthesis of high porosity, monolithic alumina aerogels

Many non-silica aerogels are notably weak and fragile in monolithic form. In particular, few monolithic aerogels with densities less than 50 kg/m3 have any significant strength. It is especially difficult to prepare uncracked monoliths of pure alumina aerogels that are robust and moisture stable. In this paper, we discuss the synthesis of unusually strong, stable, monolithic, high porosity (>98% porous) alumina aerogels, using a two-step sol–gel process. The alumina aerogels have a polycrystalline morphology that results in enhanced physical properties. For an alumina aerogel with a density of 37 kg/m3, the specific surface area is 376 m2/g, the elastic modulus is 550 kPa, and the thermal conductivities at 30°C, 400°C and 800°C, are 29, 98 and 298 mW/mK, respectively. All of the measured physical properties of the alumina aerogels except the specific surface area are superior to those for silica aerogels for equivalent densities.