K. Stano, J. Jur, P.D. Bradford
NC State University,
Keywords: alumina, aerogel, carbon nanotube foam, multi-functional
Summary:Aerogel-like structures have drawn significant recent attention due to their very low densities, thermal stability, chemical stability and high specific surface area. These structures have been traditionally produced using sol-gel percursors with supercritical drying and have been used in applications such as thermal insultation, catalyst support substrates, water purification and electrochemical devices. While silica has been the most studied ceramic aerogel there has been an increasing interest in low density materials made from alumina because of its superior thermal performance. However the chemical methods used to make alumina aerogels have been limited to small sample sizes, very long processing times and relatively high densities (> 20 mg/cm3). This abstract describes a new method to produce ultralow density alumina structures (as low as 1.2 mg/cm3) through atomic layer deposition (ALD) of alumina on very low density carbon nanotube (CNT) foam templates. The CNTs can be left to make a hybrid structure or be burned out (800 oC in air) to leave behind pure alumina. The resulting structures are macroscopic in size and are made up of an interconnected network of alumina nanotubes which have an anisotropic architecture. We show that density and mechanical ridigity of the structures can easily be tuned by changing the number of deposition cycles during the ALD processing step. A 2 cm thick structure was produced to demonstrate the thermal stability and low thermal conductivity of the material in the presence of a propane flame. We demonstrate the ability to predefine the shape of the low density alumina structures by preshaping the CNT foam before ALD treatment and also the ability to make highly sensitive humidity sensors based on these materials.